CN113993827A - Process for preparing coal ash based polymeric foam containing silica fume - Google Patents
Process for preparing coal ash based polymeric foam containing silica fume Download PDFInfo
- Publication number
- CN113993827A CN113993827A CN202180003803.0A CN202180003803A CN113993827A CN 113993827 A CN113993827 A CN 113993827A CN 202180003803 A CN202180003803 A CN 202180003803A CN 113993827 A CN113993827 A CN 113993827A
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- sample
- geopolymer
- ash
- ratio
- coal
- Prior art date
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- 239000006260 foam Substances 0.000 title claims abstract description 112
- 239000010883 coal ash Substances 0.000 title claims description 36
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 229910021487 silica fume Inorganic materials 0.000 title description 21
- 229920000876 geopolymer Polymers 0.000 claims abstract description 123
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims abstract description 69
- 239000010881 fly ash Substances 0.000 claims abstract description 69
- 239000012190 activator Substances 0.000 claims abstract description 48
- 239000010882 bottom ash Substances 0.000 claims abstract description 47
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 32
- 239000003245 coal Substances 0.000 claims abstract description 30
- 239000011863 silicon-based powder Substances 0.000 claims abstract description 23
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims description 53
- 235000019353 potassium silicate Nutrition 0.000 claims description 52
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 34
- 238000012360 testing method Methods 0.000 claims description 29
- 238000000034 method Methods 0.000 claims description 26
- 239000000203 mixture Substances 0.000 claims description 25
- 238000002156 mixing Methods 0.000 claims description 20
- 239000000377 silicon dioxide Substances 0.000 claims description 15
- 239000000843 powder Substances 0.000 claims description 12
- 230000008569 process Effects 0.000 claims description 10
- 239000007787 solid Substances 0.000 claims description 8
- 238000007873 sieving Methods 0.000 claims description 5
- 238000011049 filling Methods 0.000 claims description 4
- 238000003756 stirring Methods 0.000 claims description 4
- 238000007789 sealing Methods 0.000 claims description 3
- 239000002994 raw material Substances 0.000 abstract description 18
- 239000004568 cement Substances 0.000 abstract description 9
- 239000011259 mixed solution Substances 0.000 abstract description 5
- 238000009413 insulation Methods 0.000 abstract description 4
- 238000002360 preparation method Methods 0.000 abstract description 3
- 239000011148 porous material Substances 0.000 description 41
- 230000008859 change Effects 0.000 description 31
- 230000001965 increasing effect Effects 0.000 description 27
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 27
- 239000002245 particle Substances 0.000 description 25
- 230000000704 physical effect Effects 0.000 description 25
- 238000006243 chemical reaction Methods 0.000 description 24
- 230000007423 decrease Effects 0.000 description 22
- 229920000642 polymer Polymers 0.000 description 22
- 239000000126 substance Substances 0.000 description 21
- 238000004458 analytical method Methods 0.000 description 18
- 230000003247 decreasing effect Effects 0.000 description 15
- 125000005372 silanol group Chemical group 0.000 description 15
- 239000013078 crystal Substances 0.000 description 12
- 230000000694 effects Effects 0.000 description 12
- 238000001704 evaporation Methods 0.000 description 12
- 230000008961 swelling Effects 0.000 description 12
- 230000008020 evaporation Effects 0.000 description 11
- 238000006116 polymerization reaction Methods 0.000 description 11
- 238000010298 pulverizing process Methods 0.000 description 11
- 230000002829 reductive effect Effects 0.000 description 11
- 229910052710 silicon Inorganic materials 0.000 description 11
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 10
- 238000002474 experimental method Methods 0.000 description 10
- 238000001878 scanning electron micrograph Methods 0.000 description 10
- 238000005906 dihydroxylation reaction Methods 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 9
- 229910052500 inorganic mineral Inorganic materials 0.000 description 9
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- 239000010703 silicon Substances 0.000 description 9
- 239000011734 sodium Substances 0.000 description 9
- 230000015572 biosynthetic process Effects 0.000 description 8
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- 238000004483 ATR-FTIR spectroscopy Methods 0.000 description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 6
- 230000007246 mechanism Effects 0.000 description 6
- 239000010453 quartz Substances 0.000 description 6
- 229910020489 SiO3 Inorganic materials 0.000 description 5
- 238000002441 X-ray diffraction Methods 0.000 description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 5
- 239000001569 carbon dioxide Substances 0.000 description 5
- 229910002092 carbon dioxide Inorganic materials 0.000 description 5
- 238000004626 scanning electron microscopy Methods 0.000 description 5
- 238000007711 solidification Methods 0.000 description 5
- 230000008023 solidification Effects 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 4
- 229910008051 Si-OH Inorganic materials 0.000 description 4
- 229910006358 Si—OH Inorganic materials 0.000 description 4
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 4
- 239000012298 atmosphere Substances 0.000 description 4
- 239000011230 binding agent Substances 0.000 description 4
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical group O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 4
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 4
- SCPYDCQAZCOKTP-UHFFFAOYSA-N silanol Chemical compound [SiH3]O SCPYDCQAZCOKTP-UHFFFAOYSA-N 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- 239000011398 Portland cement Substances 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 238000004581 coalescence Methods 0.000 description 3
- 230000006378 damage Effects 0.000 description 3
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000001035 drying Methods 0.000 description 3
- 230000006870 function Effects 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 3
- 230000001788 irregular Effects 0.000 description 3
- 239000004570 mortar (masonry) Substances 0.000 description 3
- 229910052863 mullite Inorganic materials 0.000 description 3
- 238000010248 power generation Methods 0.000 description 3
- 239000004094 surface-active agent Substances 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- 239000002699 waste material Substances 0.000 description 3
- 239000004604 Blowing Agent Substances 0.000 description 2
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 2
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- 239000004809 Teflon Substances 0.000 description 2
- 229920006362 Teflon® Polymers 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 229910052661 anorthite Inorganic materials 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- 239000013626 chemical specie Substances 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 230000018044 dehydration Effects 0.000 description 2
- 238000006297 dehydration reaction Methods 0.000 description 2
- GWWPLLOVYSCJIO-UHFFFAOYSA-N dialuminum;calcium;disilicate Chemical compound [Al+3].[Al+3].[Ca+2].[O-][Si]([O-])([O-])[O-].[O-][Si]([O-])([O-])[O-] GWWPLLOVYSCJIO-UHFFFAOYSA-N 0.000 description 2
- 239000010432 diamond Substances 0.000 description 2
- 229910003460 diamond Inorganic materials 0.000 description 2
- KPUWHANPEXNPJT-UHFFFAOYSA-N disiloxane Chemical class [SiH3]O[SiH3] KPUWHANPEXNPJT-UHFFFAOYSA-N 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 229910052595 hematite Inorganic materials 0.000 description 2
- 239000011019 hematite Substances 0.000 description 2
- 230000002401 inhibitory effect Effects 0.000 description 2
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 description 2
- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 description 2
- 229910001462 kalsilite Inorganic materials 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- 238000006068 polycondensation reaction Methods 0.000 description 2
- 239000000376 reactant Substances 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Inorganic materials [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 238000001308 synthesis method Methods 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 238000004876 x-ray fluorescence Methods 0.000 description 2
- GZPBVLUEICLBOA-UHFFFAOYSA-N 4-(dimethylamino)-3,5-dimethylphenol Chemical compound CN(C)C1=C(C)C=C(O)C=C1C GZPBVLUEICLBOA-UHFFFAOYSA-N 0.000 description 1
- 229910018516 Al—O Inorganic materials 0.000 description 1
- 229910018512 Al—OH Inorganic materials 0.000 description 1
- KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 1
- 229910018557 Si O Inorganic materials 0.000 description 1
- 229910000676 Si alloy Inorganic materials 0.000 description 1
- 229910007156 Si(OH)4 Inorganic materials 0.000 description 1
- 239000004115 Sodium Silicate Substances 0.000 description 1
- YKTSYUJCYHOUJP-UHFFFAOYSA-N [O--].[Al+3].[Al+3].[O-][Si]([O-])([O-])[O-] Chemical compound [O--].[Al+3].[Al+3].[O-][Si]([O-])([O-])[O-] YKTSYUJCYHOUJP-UHFFFAOYSA-N 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 239000002551 biofuel Substances 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
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- 239000000470 constituent Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
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- 238000007571 dilatometry Methods 0.000 description 1
- 238000010828 elution Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 239000003517 fume Substances 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 239000002440 industrial waste Substances 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- NLYAJNPCOHFWQQ-UHFFFAOYSA-N kaolin Chemical compound O.O.O=[Al]O[Si](=O)O[Si](=O)O[Al]=O NLYAJNPCOHFWQQ-UHFFFAOYSA-N 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 239000013307 optical fiber Substances 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 238000012643 polycondensation polymerization Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 238000004451 qualitative analysis Methods 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000000790 scattering method Methods 0.000 description 1
- 150000004760 silicates Chemical class 0.000 description 1
- -1 siloxanes Chemical class 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Substances [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 229910052911 sodium silicate Inorganic materials 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
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- 238000009210 therapy by ultrasound Methods 0.000 description 1
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- 238000012546 transfer Methods 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- 238000003911 water pollution Methods 0.000 description 1
- 229910052844 willemite Inorganic materials 0.000 description 1
- 229910001845 yogo sapphire Inorganic materials 0.000 description 1
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- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
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- C04B12/005—Geopolymer cements, e.g. reaction products of aluminosilicates with alkali metal hydroxides or silicates
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/006—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing mineral polymers, e.g. geopolymers of the Davidovits type
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
- B02C23/08—Separating or sorting of material, associated with crushing or disintegrating
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- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B18/04—Waste materials; Refuse
- C04B18/06—Combustion residues, e.g. purification products of smoke, fumes or exhaust gases
- C04B18/08—Flue dust, i.e. fly ash
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- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B18/04—Waste materials; Refuse
- C04B18/14—Waste materials; Refuse from metallurgical processes
- C04B18/141—Slags
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
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- C04B20/00—Use of materials as fillers for mortars, concrete or artificial stone according to more than one of groups C04B14/00 - C04B18/00 and characterised by shape or grain distribution; Treatment of materials according to more than one of the groups C04B14/00 - C04B18/00 specially adapted to enhance their filling properties in mortars, concrete or artificial stone; Expanding or defibrillating materials
- C04B20/02—Treatment
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- C04B22/064—Oxides, Hydroxides of the alkali or alkaline-earth metals of the alkaline-earth metals
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- C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators, shrinkage compensating agents
- C04B22/08—Acids or salts thereof
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- C04B38/02—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by adding chemical blowing agents
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- C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
- C04B38/10—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by using foaming agents or by using mechanical means, e.g. adding preformed foam
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- C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
- C04B41/0072—Heat treatment
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- C04B7/00—Hydraulic cements
- C04B7/24—Cements from oil shales, residues or waste other than slag
- C04B7/243—Mixtures thereof with activators or composition-correcting additives, e.g. mixtures of fly ash and alkali activators
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- C04B7/28—Cements from oil shales, residues or waste other than slag from combustion residues, e.g. ashes or slags from waste incineration
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- C04B2103/00—Function or property of ingredients for mortars, concrete or artificial stone
- C04B2103/10—Accelerators; Activators
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- C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
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- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
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Abstract
The invention relates to geopolymer foam which is low in thermal conductivity and light and is prepared by using coal bottom ash and fly ash as raw materials of the geopolymer foam and adding silicon powder into a mixed solution of an alkaline activator and sodium hydroxide, and a preparation method of the geopolymer foam. The geopolymer foam of the present invention can be used to improve the thermal insulation performance and safety of buildings using eco-friendly cement.
Description
Technical Field
The present invention relates to a method for preparing a coal ash-based geopolymer (coal ash-based geopolymer) foam containing silica fume.
Background
Cement (cement) is a generic term for inorganic binders that set themselves or other substances together by reacting with various substances such as water. Typically, the Cement is referred to as Portland Cement (OPC) because Portland Cement accounts for more than 95% of the total concrete usage. Portland cement is suitable for mass production due to abundant raw materials and uncomplicated production mode, but the production process has the problems of large energy consumption and large discharge of carbon dioxide. According to a study by Davidovits, it was found that approximately 1 ton of carbon dioxide was expelled when 1 ton of cement was produced. In the cement industry, various efforts have been made to reduce the discharge amount of carbon dioxide by using bio-fuel or introducing a new cement clinker (clinker) with low energy consumption, and developing an environmentally friendly concrete structure, etc., but the global carbon dioxide discharge amount has increased from 5% in 2000 to 8% in 2014 due to the increased demand for cement in rapidly developing countries such as china and india.
Geopolymers (geopolymers) are of interest as environmentally friendly alternatives to OPC. The geopolymer is an inorganic binder having a three-dimensional structure of aluminum silicate (alumina silicate) obtained by adding Silica (SiO) to the mixture2) And alumina (Al)2O3) The substance (2) is synthesized by alkaline activation (alkali activation). The geopolymer can be produced from industrial wastes such as fly ash produced in a coal-fired power plant, mine tailing (mine tailing) produced in the mining industry, and red mud produced in the aluminum purification process, and therefore has an advantage in waste treatment.
The coal ash is fly ash (CFA) and Coal Bottom Ash (CBA). Fly ash has a spherical particle shape and its particle size is low, so the reactivity of geopolymer is high. Therefore, many studies using fly ash have been made, and most of the generated amount is also utilized in practice. On the other hand, although the composition of the bottom ash is similar to that of fly ash, it is difficult to use it as a raw material for geopolymers because of its irregular particle shape, sharp edges and large particle size. The studies on the use of the bottom ash are not many, and most of the amount of the produced coal is buried. According to the current situation that coal ash is actually generated in south korea cave power generation, 79.07% of coal ash is recycled and 17.55% of coal ash is buried in coal ash generated in 2018 in 1 year, but 76.59% of coal bottom ash is buried in coal ash. Since coal ash landfill has various difficulties such as soil and water pollution, landfill cost, insufficient landfill, and the like, there is a need for a research on utilization of coal ash, especially bottom ash.
On the one hand, the thermal insulation properties of modern buildings become an important design criterion. Organic heat insulating materials widely used as heat insulating materials for modern buildings have weak high temperature resistance, and thus have a problem in that toxic gas is discharged when a fire occurs, thereby causing damage to the human body. Accordingly, attention has been paid to inorganic heat insulating materials having excellent heat insulating properties and high heat resistance. In modern industry and academia, it is common to use the synthesis of concrete and geopolymer foams by the reaction of additives using chemicals to generate gases within the structure. In the studies of j.l.bell and w.m.kriven, a geopolymer of a foam structure was formed by using hydrogen peroxide and aluminum powder. Aguilar et al also studied synthetic polymer foams using various additives (using silicon powder). Although the prior studies as described above mainly use metakaolin and fly ash as raw materials, in the present invention, geopolymer foams using coal bottom ash as a raw material are prepared by using the above-described foam synthesis method.
Aluminum powder consumes a large amount of energy during the production process, and thus it is preferable to minimize the amount in terms of environment, and since the surfactant is an organic substance, it is decomposed at high temperature to generate toxic substances. Silicon powder (silicon fume) is an industrial by-product generated in the production of silicon or silicon alloys, and it is known that the reaction of silicon present as an impurity generates hydrogen gas. By this reaction a more stable polymer foam structure can be formed. Therefore, attempts have been made to synthesize polymer foams by adding only silicon powder as a blowing agent without using aluminum powder and a surfactant.
Korean granted patent No. 10-1901684 discloses a method for preparing a geopolymer having high strength properties using bottom ash of coal; korean laid-open patent No. 10-2013-0057024 relates to a geopolymer binder using waste disks and a refractory mortar composition using the same, and discloses a refractory mortar composition comprising waste coal ash bottom ash (bottom ash) as an aggregate.
However, the coal ash-based polymer foam containing silica powder, which is an environmentally friendly inorganic heat insulating material for improving heat insulating performance and building safety according to the present invention, has not been disclosed.
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made to solve the above problems by using bottom ash together with fly ash as a raw material of geopolymer and confirming the characteristics of having lower thermal conductivity and lighter geopolymer foam by adding silica fume to a mixed solution of an alkaline activator and sodium hydroxide.
Means for solving the problems
In order to solve the above problems, the present invention provides a method for preparing a geopolymer foam using coal ash, comprising: step (1): by mixing water glass (Na)2SiO3) A step of mixing with sodium hydroxide (NaOH) to prepare an alkaline activator; step (2): a step of stirring silicon powder in the alkaline activator; and (3): crushing the coal bottom ash; and (4): preparing coal ash by mixing the coal bottom ash and the fly ash; and (5): adding a mixture of the silica powder and an alkaline activator to the coal ash, and then further adding an alkaline activator to adjust the ratio of the alkaline activator to the solid matter and mixing the mixture; and (6): step of preparing test sample by filling and sealing in moldA step of; and step (7): and curing the test sample in an oven.
As an example of the present invention, water glass (Na)2SiO3) And sodium hydroxide (NaOH) in a 5:1 ratio by mass of alkaline activator, and may contain 15 wt% silica fume.
As another example of the present invention, the step of pulverizing the bottom ash is a step of removing a sieving process by performing a primary pulverization using a jaw crusher (jaw crusher) and then performing a pulverization 4 times using a hammer mill (hammer mill), and the fly ash may be contained in an amount of 10 to 50% by weight in the total amount of the bottom ash and the fly ash.
As another example of the present invention, the ratio of the basic activator/solid matter may be 0.38 to 0.50.
As another example of the present invention, it may further comprise a step of exposing the cured test sample at an elevated temperature of 200 ℃ to 600 ℃ for 2 hours.
In addition, the present invention provides a geopolymer foam using coal ash prepared by the above preparation method.
Effects of the invention
The invention relates to geopolymer foam which is prepared by using coal bottom ash and fly ash as raw materials of geopolymer foam and adding silicon powder into a mixed solution of an alkaline activator and sodium hydroxide, and has lower thermal conductivity and lighter weight. The geopolymer foam can be used to improve the thermal insulation performance and safety of buildings using eco-friendly cement.
Drawings
Fig. 1 is a graph showing the particle size distribution of coal bottom ash (CBA, red) and fly ash (CFA, black) according to the present invention.
Fig. 2 is a graph showing a particle size distribution of silicon powder (SF) according to the present invention.
Fig. 3 is a graph showing XRD spectra and crystallinity (crystallinity) of Coal Bottom Ash (CBA), fly ash (CFA), and Silica Fume (SF).
FIG. 4 is a vertical sectional view showing geopolymer foams having various L/S ratios according to the present invention. (a) FA10, (b) FA30, and (c) FA 50.
FIG. 5 is a graph showing the results of bulk density of geopolymer foam according to the present invention increasing with L/S ratio.
FIG. 6 is a graph showing the porosity results of geopolymer foams according to the present invention increasing with L/S ratio.
Fig. 7 is a graph showing the results of thermal conductivity of the geopolymer foam according to the present invention.
FIG. 8 is a graph showing the results of compressive strength of geopolymer foams having various L/S ratios according to the present invention.
Fig. 9 is a graph showing compressive strength results for bulk density according to the present invention.
FIG. 10 is an SEM image (5.0kV, 50) showing polymer foams of FA30 with various L/S ratios according to the present invention. (a)0.38, (b)0.42, (c)0.46, and (d) 0.50.
FIG. 11 is a SEM photograph showing (a)46FA10, (b)46FA30 and (c)46FA50 according to the present invention, and a plot (20.0Kv,. times.50) of EDS analysis points.
FIG. 12 is a graph showing TG/DTG results for the 46FA30 sample according to the present invention.
Fig. 13 is a graph showing DIL results and associated differential curves for the 46FA30 sample according to the present invention.
FIG. 14 is a graph showing DIL results for the 46FA10, 46FA30, and 46FA50 samples according to the present invention.
Fig. 15 is a graph showing differential curves of DIL results for the 46FA10, 46FA30, and 46FA50 samples according to the present invention.
FIG. 16 is an upper end and vertical cross-sectional view showing a sample of 46FA30 exposed to a high temperature column according to the present invention. (a)200 ℃, (b)300 ℃, (c)400 ℃, (d)500 ℃, (e)600 ℃.
Fig. 17 is a graph showing ATR-FTIR spectra of 46FA30 samples exposed to high temperatures according to the present invention.
FIG. 18 is a graph showing XRD results for samples of 46FA30 that were not exposed and were exposed at 200 deg.C, 300 deg.C, 400 deg.C, 500 deg.C, and 600 deg.C according to the present invention.
Fig. 19 is a graph showing the bulk density results for 46FA30 samples exposed to various temperatures according to the present invention.
Fig. 20 is a graph showing the porosity results for a 46FA30 sample exposed to high temperatures according to the present invention.
Fig. 21 is a graph showing the thermal conductivity results for the 46FA30 sample exposed to high temperatures according to the present invention.
FIG. 22 is a graph showing the compressive strength results for the 46FA30 sample exposed to high temperature in accordance with the present invention.
FIG. 23 is an SEM image (5kv,. times.50) showing 46FA30 samples exposed to (a) atmosphere, (b)200 ℃, (c)300 ℃, (d)400 ℃, (e)500 ℃ and (f)600 ℃ according to the present invention.
FIG. 24 is a top and vertical cross-sectional view showing FA30 samples fabricated through columns of various L/S ratios after exposure to 400 ℃ according to the present invention. (a)0.38, (b)0.40, (c)0.42, (d)0.44, (e)0.46, (f)0.48, and (g) 0.50.
FIG. 25 is a graph showing the bulk density results of FA30 samples according to L/S ratio after high temperature heating according to the present invention.
FIG. 26 is a graph showing the porosity results of FA30 samples according to L/S ratio after high temperature heating according to the present invention.
FIG. 27 is a graph showing the thermal conductivity results for FA30 samples at various L/S ratios after high temperature heating according to the present invention.
FIG. 28 is a graph showing compressive strength results for FA30 samples at various L/S ratios after high temperature heating according to the present invention.
FIG. 29 is an SEM image (5kV,. times.50) showing FA30 samples exposed to an L/S ratio and 400 ℃ according to the present invention. (a)0.38, (b)0.42, (c)0.46, and (d) 0.50.
FIG. 30 is a top and vertical sectional view showing columns (a)46FA10, (b)46FA30 and (c)46FA50 according to the present invention.
FIG. 31 is a graph showing the bulk density results of FA10, FA30, and FA50 with L/S ratio after exposure to 400 ℃ according to the present invention.
FIG. 32 is a graph showing the results of the porosities with L/S ratio of FA10, FA30, and FA50 after exposure to 400 ℃ according to the present invention.
FIG. 33 is a graph showing the results of thermal conductivity with L/S ratio for FA10, FA30, and FA50 after exposure to 400 ℃ according to the present invention.
FIG. 34 is a graph showing the results of compressive strength of FA10, FA30 and FA50 with L/S ratio after exposure to 400 ℃ according to the present invention.
FIG. 35 is an SEM photograph showing 50 magnification of geopolymer foams of (a)46FA10, (b)46FA30 and (c)46FA50 and 200 magnification of geopolymer foams of (d)46FA10, (e)46FA30 and (f)46FA50 according to the present invention.
Detailed Description
Hereinafter, specific examples of the present invention will be described in detail. In the following description, a large number of specific details such as specific structural elements are described, but such specific details are provided only for the purpose of facilitating a comprehensive understanding of the present invention, and it is obvious to those skilled in the art that the present invention can be carried out without such specific details. In describing the present invention, if it is considered that specific description of related known functions or configurations do not contribute to the gist of the present invention, detailed description thereof will be omitted.
In order to achieve the object of the present invention, the present invention provides a method for preparing a geopolymer foam using coal ash, comprising: step (1) is carried out by dissolving water glass (Na)2SiO3) A step of mixing with sodium hydroxide (NaOH) to prepare an alkaline activator; step (2), placing silicon powder in the alkaline activator for stirring; step (3), crushing the coal bottom ash; step (4), preparing coal ash by mixing the coal bottom ash and the fly ash; a step (5) of adding the mixture of the silica powder and the alkaline activator to the coal ash, and then further adding an alkaline activator to adjust the ratio of the alkaline activator to the solid matter and mixing the mixture; a step (6) of preparing a test sample by filling and sealing in a mold; and (7) curing the test sample in an oven.
The present invention is characterized in that coal bottom ash and fly ash are used together as a geopolymer raw material, and water glass (Na) is used2SiO3Solutions of) And sodium hydroxide (NaOH) as an alkaline activator, and synthesizing a geopolymer foam by adding silicon powder.
Korean patent laid-open No. 10-1901684 relates to a method for preparing a polymer using the high strength property of coal bottom ash, and an alkaline activator is adjusted so that the mixture of the coal bottom ash and the alkaline activator does not form gel, in contrast to the present invention which basically uses a sufficient alkaline activator to make the mixture in a fluid state. Thus, the mixture is simply poured into the mold and cured in an oven together with the mold without a process of filling and pressurizing the mixture in the mold. The amount of alkaline activator is adjusted so that the Geopolymer slurry (geopolymerization paste) has a flow regime. The ratio of the alkaline activator/solid matter (L/S ratio) is preferably adjusted to be in the range of 0.38 to 0.50, and a geopolymer foam can be formed outside this range, and the L/S ratio may be different depending on the particle size of the coal ash and the silica fume used, the concentration of the alkaline activator, and the like, but is not limited thereto.
In the present invention, the mixture is sufficiently expanded when it is in a fluid state, and when the amount of the alkaline activator added is reduced, a polymer foam having a high density and high thermal conductivity and compressive strength is formed. The present invention aims to synthesize a geopolymer foam which is low in thermal conductivity and light, and therefore experiments were conducted with increasing the amount of the alkaline activator added, and the mixture in a flowing state has an advantage of being easily cast according to the shape and size of the mold.
In addition, korean patent No. 10-1901684 issued regulates the compressive strength and thermal conductivity of geopolymer by regulating the pressure at the time of pressure molding, but the present invention provides a geopolymer foam that can regulate physical properties including compressive strength, bulk density and thermal conductivity by regulating the amounts of fly ash and alkaline activator, high temperature exposure temperature.
In particular, another technical feature is that the step of pulverizing the bottom ash of coal is performed by performing a pulverization with a jaw crusher (jaw crusher) and then a pulverization with a hammer mill (hammer mill) for 4 times to exclude the sieving process.
The invention of korean granted patent No. 10-1901684 aims to improve the compressive strength of geopolymer, but the invention aims to improve the thermal insulation performance. In this regard, the mixture is pressure-molded in korean patent laid-open publication No. 10-1901684, and then oven curing and microwave irradiation are performed to manufacture a geopolymer having a dense structure and high compressive strength and thermal conductivity and bulk density, but in the present invention, the mixture is poured into a mold and expanded by oven curing to manufacture a lightweight geopolymer foam, thereby manufacturing a geopolymer foam having low bulk density, thermal conductivity and compressive strength.
In addition, the present invention is characterized by having a process of greatly reducing thermal conductivity and bulk density by heating in an electric furnace without further using microwaves after oven curing. In this process, the water glass curing agent remaining in the foam structure expands together with the removal of the residual moisture while forming secondary foam, and it may also be a necessary step to add water glass in the mixture mixing step in order to form stable foam together with the oven curing step while such secondary foam is formed.
Water glass (Na) of the invention2SiO3) And sodium hydroxide (NaOH) as the alkaline activator, in a preferred mass ratio of 5:1, but not limited thereto.
Silica fume is an industrial byproduct, is produced as nanometer-sized particles with very small particle size, is small in volume, generates scattering, and therefore generates much transportation and storage cost. To solve this problem, silicon powder particles are generally physically agglomerated into high-density (densified) silicon powder for use. Since high-density silica fume is also used in the present invention, a process of dispersing particles by mixing with an alkaline activator to form a regular foam structure before mixing with coal ash is included as an essential element. The particle size can be reduced by pulverizing or sieving the silica powder, but it is found that the morphology of the produced geopolymer foam cannot be kept constant depending on the pulverization and sieving efficiency, and therefore the method of mixing with the alkaline activator is selected. Preferably, the silicon powder used at this time may account for 15 wt%, but is not limited thereto.
In the present invention, geopolymer foam can be formed even using only coal bottom ash as a raw material, but it was confirmed that somewhat unstable foam was formed. Therefore, it is preferable that the fly ash is contained as an essential structural element, and 10 to 50 wt% of the fly ash is contained with respect to the total amount of the preferable bottom ash and fly ash, but not limited thereto.
Further, the present invention has excellent heat insulating properties and may further include a step of exposing the cured test sample to high temperature in order to prevent a decrease in strength due to cracks or the like when a simple drying method is used for the purpose of removing residual moisture in the test sample, in order to manufacture a high temperature resistant inorganic heat insulating material. Preferably, it has moisture resistance at 200 ℃ or more, and more preferably, it may further include a step of exposing at a high temperature of 200 ℃ to 600 ℃ for 2 hours, but is not limited thereto.
In addition, the present invention provides a geopolymer foam using coal ash prepared by the above preparation method.
The advantages and features of the present invention and methods of accomplishing the same will become more apparent when reference is made to the following detailed description of the embodiments. However, the present invention is not limited to the embodiments disclosed below and can be constructed in various forms, and the embodiments are provided only for complete disclosure of the present invention and to enable those skilled in the art to fully understand and come within the spirit of the present invention and to define the present invention according to the scope of the claims.
< example 1> raw Material and Experimental method
Coal bottom ash is provided by lingxing thermal power generation, fly ash is provided by schukuan thermal power generation, and silica fume (undensified microsilica) is provided by Silkroad C & T co. In order to reduce the particle size of the bottom ash, a jaw crusher (jaw crucher) was used for primary pulverization and then a hammer mill (hammer mill) was used for four pulverization. The particle size distributions of the bottom ash, fly ash and silica fume were measured by laser scattering method (japanese horiba LA960), and the results are shown in fig. 1 and 2. The average particle size of the bottom ash is 191.7 μm, and 90% of the particles are below 99.34 μm. The average particle size of the silica powder was 497.0 μm, and it was found that 90% of the particles were high density (densed) particles of 893.5 μm or less.
For the chemical combination, X-ray fluorescence analysis (X-ray fluorescence, ZSK Primus II, Japan) was used, and Loss On Ignition (LOI) was measured according to ASTM D7348. Since the chemical combination contained the LOI values, it was recalculated so that the sum reached 100%, and the results thereof are shown in table 1 below.
TABLE 1
SiO in chemical Composition of Fly Ash (CFA)2、Al2O3And Fe2O3The proportion of the fly ash is more than 70 percent, and the fly ash is classified as F type fly ash according to ASTM C618. Coal Bottom Ash (CBA) has a chemical composition similar to fly ash, and silica fume is mostly composed of silica.
In order to confirm the crystalline phase/amorphous structure, qualitative analysis by X-ray diffraction (XRD, japan science DMAX 2500) and quantitative analysis by X-ray diffraction were carried out. The analysis was performed with Cu ka rays at a scanning width of 0.02 ° and a scanning speed of 2 °/min, and the results are shown in fig. 3. Collectively, a broad ramp-like spectrum is observed in the range of 15-40 ° 2 θ, which means that an amorphous phase (amophorus phase) is present. The crystallinity (crystallinity) of the coal bottom ash was 37.19%, the crystallinity of the fly ash was 69.18%, and the crystallinity of the silica fume was 6.83%, so that a relatively large amount of crystal phase was present in the fly ash, and it was known that the silica fume was mostly composed of amorphous phase. Peaks due to a quartz (quartz) crystal phase, a mullite (mullite) crystal phase, an anorthite (anorthite) crystal phase, and a magnetite (magnetite) crystal phase were observed in the XRD results of the bottom ash, peaks of a quartz crystal phase and a mullite crystal phase and a hematite (hematite) crystal phase were observed in the fly ash, and peaks of a quartz crystal phase, a kalsilite (kalsilite) crystal phase, and a willemite (liebermanite) crystal phase were observed in the silicon powder.
The alkaline activator for synthetic geopolymer foams uses sodium silicate solution (Na)2 O 9～10％，SiO228-30%, Daejung chemical and metal, korea) and NaOH (sodium hydroxide beads, not less than 98% pure, Samchun, korea). The heat of solution was generated during mixing, and therefore, the mixture was mixed in advance before the experiment and used after cooling to room temperature. The mass ratio of water glass/NaOH was set to 5 by preliminary experiments at an appropriate alkaline activator mixing ratio for the following reasons. When the mass ratio of water glass/NaOH is less than 5 in the experiment, the mixed solution becomes cloudy and hard at the same time, and thus is not suitable. On the contrary, when the mass ratio of water glass/NaOH is 5 or more, the free silicon contained in the silicon powder does not sufficiently react, and the Geopolymer slurry (Geopolymer paste) does not swell well. Since silicon reacts with water in an alkaline environment of the following formula to generate hydrogen gas, the alkaline environment required for the reaction of silicon cannot be sufficiently formed when the amount of NaOH is reduced.
Sio+4H2O→Si(OH)4+2H2(g)
Therefore, it was determined that the mass ratio at which the silicon powder can be reacted to the maximum extent while the mixed solution of water glass and NaOH does not solidify was 5, which is an appropriate composition.
As shown in FIG. 2, since the silicon powder has a high density (densified) form, the particles are large, and if it is used directly in the synthesis of geopolymers, the particles are not sufficiently dispersed, thereby forming an irregular foam structure. If such a high-density particle form is subjected to ultrasonic treatment, it can be effectively dispersed, and the particle size can also be reduced by physical pulverization, but this method requires additional equipment and treatment processes, and is therefore inefficient. Therefore, the present invention was prepared by placing the silicon powder in an alkaline activator and stirring with an overhead stirrer at 300rpm for 1 hour before the experiment. The amount of silicon powder added was determined as 15 wt.% of solid matter by preliminary experiments.
In the present invention, the foam can be formed using only the coal bottom ash as a raw material, but a somewhat unstable foam is formed. To solve this instability, the above-mentioned bottom ash is used as a raw material together with fly ash. In the total amount of the bottom ash and the fly ash used, the mass ratio of the fly ash was set to 10%, 30% and 50%, and samples of the geopolymer foam synthesized according to such ratio were designated as FA10 group, FA30 group and FA50 group. The ratio of basic activator/solid substance (L/S ratio) was adjusted from 0.38 to 0.50 at 0.02 intervals. The names of the samples according to such variables are named as follows.
○○FA□□
O ≈ L/S ratio × 100.
□□＝CFA/(CBA+CFA)×100。
For example, a sample manufactured so that the L/S ratio is 0.42 and CFA/(CBA + CFA) is 0.30 is named 42FA 30. The mixing ratios of the raw material substances and the sample group names according thereto are summarized and shown in the following table 2.
TABLE 2
The synthesis of geopolymer foams was carried out according to the following procedure. An alkaline activator was prepared by mixing a water glass solution and NaOH in a mass ratio of 5:1 before the experiment. Silica powder was added to the alkaline activator cooled to normal temperature, and mixing was performed with an overhead stirrer at 300rpm for 1 hour. In order to mix uniformly, the coal bottom ash and the fly ash are first mixed in a dry state, and a mixture of an alkaline activator and silica fume is added, and the L/S ratio is adjusted by further adding the alkaline activator. The mixture was mixed with a Hobart mixer (Hobart mixer) at 60rpm for 5 minutes and then poured into 50X 50mm3In the three-way plastic die, useThe plastic bags were sealed and then cured in an oven at 75 ℃ for 72 hours. At this time, a Teflon Tape (Teflon Tape) was attached in the mold to prevent the sample from sticking. After curing, the mold was removed, and a 5cm square sample was prepared by cutting the swollen portion with a diamond saw. The analysis of physical properties was performed in the following manner.
Bulk density (bulk density) was calculated by measuring the mass of the sample that was sufficiently cooled in ambient temperature, after which the thermal conductivity was measured (TPS500S, Hot disk inc. in sweden). The compressive strength of each sample was measured according to ASTM C109 by using a compressive strength tester (PL-9700H, Woojin Precision Co., Korea). A part of the inside of the test sample destroyed by the compressive strength measurement was screened and pulverized and ground using a pestle and a mortar, and then the sample powder sieved with a 100-mesh standard sieve (sieve 150 μ 5) was used in the following analysis. Using a Gas pycnometer (AccuPyc II 1340, Mimmerrel, USA) and H2The gas is used to measure the powder density (porosity) which is calculated from the measured powder density and the bulk density of the sample and using the following formula.
The average value of the results of the three test samples was used as the bulk density and the compressive strength, and the thermal conductivity and the powder density were measured 6 times and 5 times, respectively, and the average value thereof was used as the above thermal conductivity and the powder density. In order to observe the pores (holes) of the geopolymer foam, a cross section of an unnecessary sample cut in a vertical direction was photographed with a digital camera (EOS 750D, canon, japan). In addition, SEM analysis (scanning electron microscope, nova nano SEM 200, FEI usa) was performed in order to observe the foam structure and microstructure of the sample, and the sample was prepared by grinding a part of the inner fragments of the above test sample, which was destroyed after measuring the compressive strength, with 120-mesh sandpaper, and SEM/EDS analysis (field emission scanning electron microscope, hitachi SU8010, japan) was further performed with respect to a part of the test sample so as to observe the change in the proportion of the constituent elements of the microstructure. To analyze the physical properties of the geopolymer foam that change when exposed to high temperatures, the following analysis and additional experiments were performed. To confirm the mass loss phenomenon upon high temperature exposure, TG analysis (SDT-Q600, US TA instruments) was performed on representative samples that had completed oven curing. The DTG curve was obtained by heating the sample from room temperature to 1000 ℃ at a rate of 10 ℃ per minute in an air atmosphere and measuring the change in mass of the sample shown. In addition, to measure the dimensional change of the sample occurring upon high-temperature exposure, DIL analysis (dilatometry, german relaxation-resistant DIL 402C) was performed on the sample 46FA10, the sample 46FA30, and the sample 46FA 50. A part of a sample of a regular hexahedron of 5cm was cut, and the length change of the sample occurred when the sample was heated from normal temperature to 800 ℃ at a speed of 5 ℃ per minute in an air environment was measured.
Further, the test specimen after the curing was heated in an electric furnace (electric furnace, hattech, korea S-1700) to observe changes in pore structure and physical properties when the test specimen was exposed to high temperature, and first, a representative test specimen was selected to study the influence of the exposure temperature. The test sample was heated at a rate of 5c per minute from room temperature to 200 c, 300 c, 400c, 500 c and 600 c, respectively, and after reaching the target temperature, the exposure was continued for 2 hours at that temperature. The heated sample was naturally cooled to normal temperature, and then the physical properties were measured. The FA30 test samples were then exposed to 200-500 ℃ in the same manner to examine the effect of the L/S ratio, and the FA10 and FA50 groups were exposed to 400 ℃ to further investigate the effect of fly ash content. The above analysis except TG and DIL was performed on the test sample exposed to high temperature in the same manner, and the following analysis was further performed on a representative test sample exposed to 200 to 600 ℃. ATR-FTIR analysis (Fourier transform attenuated Total reflectance Infrared Spectroscopy, U.S. Perkin Elmer Fourier FT-IR Spectroscopy) was performed to analyze the chemical structural changes of the geopolymer foam upon exposure to high temperatures and at 4cm-1The resolution of the optical fiber is 4000-380 cm-1Measured with respect to the transmittance (transmission) in the range of (1). To observe exposure to highXRD (X-ray diffraction, Japan science D/max-2500/PC) analysis was performed for the change of crystal phase at a temperature, and measurement was performed in a 2. theta. range of 10 to 90 ℃ in 0.02 ℃ step size at a scanning speed of 2 °/min.
< test example 1> physical Properties of soot-based Polymer foam to which silica fume was added
1. Observing macrostructures
A vertical cross-section of the geopolymer foam sample is shown in fig. 4. The sample in fig. 4 (a) is relatively irregular and has a large pore structure, and the size of the pores in fig. 4 (b) and fig. 4 (c) is gradually reduced. In addition, the higher the L/S ratio in each sample group, the tendency of the pores to gradually increase was shown. Hereinafter, the mechanism of pore structure change will be described. In the present invention, a Geopolymer slurry (Geopolymer paste) is cured at 75 ℃ in the process of which there are two competing mechanisms, namely (1) solidification of the slurry (paste) by mineral polymerisation and (2) swelling by reaction of silicon. When more fly ash is added, mineral polymerization (geopolymerization reaction) occurs mainly due to the higher reactivity of the fly ash. Therefore, the solidification proceeds faster, thereby forming a strong pore wall (wall), and the bubbles formed by the hydrogen gas cannot be merged with each other (coalescence) to form a smaller pore structure. However, when the mineral polymerization reaction is too fast, it may solidify before a sufficient pore structure is formed, thereby inhibiting swelling. In contrast, when a small amount of fly ash is added, a larger pore structure is formed due to the coalescence of bubbles. The L/S ratio also has a large influence on the formation of pores. When the L/S ratio is relatively low, a relatively small amount of moisture rapidly evaporates while accelerating the mineral polymerization reaction, thereby allowing the curing to proceed more rapidly. On the contrary, when the L/S is relatively large, not only does the solidification proceed late, but also the amount of hydrogen gas generated by the sufficient reaction of silicon increases, so that coalescence among bubbles occurs, and as a result, a large pore structure is formed.
On the one hand, in all samples, a somewhat dense structure consisting of small pores was formed on the bottom surface and the side surface as compared with the center portion of the sample. This phenomenon is considered to be a result of uneven heat transfer to the volume of the geopolymer slurry in the oven at the initial stage of curing. At the initial stage of curing, the geopolymer slurry contained in the mold is in a state where the upper surface is exposed to the atmosphere and the side surfaces and the bottom surface are in contact with the mold. It is considered that heat is rapidly transferred to a portion in contact with the mold while curing is performed in an oven at 75 c, and heat is gradually transferred to the center portion of the slurry. At this time, the rapid temperature rise of the contact portion promotes the mineral polymerization reaction, and mainly solidification occurs, resulting in a seemingly dense structure. In particular, many oval pore structures were observed in the FA10 group of samples, which contained a small amount of fly ash and had low reactivity, and therefore, the formation of bubbles mainly occurred due to the generation of hydrogen. Although pores are formed therein, the pores collapse or have an oval shape as if being pressed by the weight of the slurry due to a slow curing speed. It should be noted that the values of the physical properties suggested later do not reflect all physical properties of the entire sample due to the heterogeneity of the pore structure.
2. Bulk density and porosity
Bulk density and porosity for each set of geopolymer foam samples as a function of L/S ratio are shown in fig. 5 and 6, respectively. The bulk density decreases with increasing L/S ratio and then again tends to increase after the lowest point. In contrast to the trend of the bulk density, the porosity shows a trend of decreasing with increasing L/S ratio. The reduction in bulk density with increasing L/S ratio is due to the higher level of expansion that occurs due to slower curing and sufficient bubble generation as described above. However, when the L/S ratio is not less than a certain value, the bulk density increases again, which is considered to be a result of residual moisture inside the structure. This was further examined in the following thermal conductivity results. Particularly in the FA10 group, the bulk density increased at a large level at L/S ratios of 0.46 or more, as a result of collapse of a part of the pores due to residual moisture and formation of unstable foam.
When fly ash was further added to the FA30 group from the FA10 group to the FA10 group for each geopolymer foam sample group, a lower bulk density was achieved overall, but in the FA50 group, a similar bulk density or, conversely, a higher bulk density was shown. In particular, the samples having an L/S ratio of 0.40 or less in the FA50 group had higher bulk densities because more fly ash with higher reactivity was present and the L/S ratio was lower, causing solidification to occur quickly, thereby inhibiting swelling. In contrast, in the FA10 group, the formed foam structure cured slowly, so that a high density geopolymer foam was produced while the pores collapsed. In summary, from the results of such bulk density and porosity, it can be seen that the pore structure of the geopolymer foam can be adjusted by adjusting the content of fly ash and the amount of alkaline activator.
3. Thermal conductivity
The sample was cut in a vertical direction to measure the thermal conductivity of the central portion, and the result is shown in fig. 7. Polymers with lower bulk densities generally have lower thermal conductivities, but show somewhat different trends in the present invention. The bulk densities of the FA10 and FA30 groups in fig. 5 decreased to an L/S ratio of 0.46, and then showed a tendency to increase again, and gradually decreased to 0.48 in the FA50 group, and then showed an increasing tendency. However, in terms of thermal conductivity, the FA10 group exhibited a similar level of thermal conductivity before the L/S ratio was 0.46, and showed a greatly increased tendency at the L/S ratio of 0.46 or more. In addition, the FA30 group and the FA50 group showed increasing trends after decreasing to an L/S ratio of 0.42 and an L/S ratio of 0.44, respectively. This is related to the characteristics of the water glass solution contained in the added alkaline activator. The water glass elutes silica and alumina from the raw material materials, so that Si chemical species present in the water glass participate in the reaction at the initial stage of the geopolymer reaction, thereby forming a geopolymer structure. In addition to this, the water glass does not participate in the reaction of the geopolymer and is self-cured to serve as a binder, and various structures including silanol (Si-OH) and siloxane (Si-O-Si) bonds are formed while being cured. In particular, silanol groups (silanol) present on the surface are generated as a result of condensation and polymerization of silicates, and OH groups of such silanol groups have the effect of binding water molecules (physically binding water). In addition, silanol (internal silanol) groups are also present inside the structure and are also structurally bound water. This physicochemical presence of water is responsible for the high thermal conductivity. Also, since OH groups present on the surface are hydrated and dissolved when they come into contact with water, the structure may be weakened if exposed to a humid environment or brought into contact with water. Therefore, in order to provide the geopolymer foam of the present study with excellent heat insulating properties and water resistance, it is important to remove such moisture and to remove OH groups from the surface.
In the FA10 group with less fly ash, although the bulk density decreased due to the formation of foam, there were many water glasses that did not participate in the geopolymer reaction due to the less reactive bottom ash particles, and therefore the thermal conductivity remained at a certain level while not decreasing. In the FA30 group and the FA50 group, water glass may participate relatively more in the geopolymer reaction while fly ash is added, and therefore the thermal conductivity decreases with the tendency of the bulk density to decrease. However, as the L/S ratio increased, residual moisture also remained in the structure of the sample set, thereby showing an increase in thermal conductivity. Such residual moisture is not easily removed even when left at normal temperature, and thus can be removed by drying or exposure to high temperature. However, since the drying method removes moisture required in the structure of the geopolymer to weaken the structure and cracks are generated while the moisture is evaporated, the strength thereof may be lowered at a large level.
4. Compressive strength
FIG. 8 is a graph showing compressive strength results for geopolymer foam samples. The compressive strength did not show a large change according to the content of fly ash, and showed a tendency to decrease as the L/S ratio increased. In fig. 9 the bulk density is substantially reduced and therefore the compressive strength is also reduced. Also, the increase in bulk density at higher L/S ratios is a result of residual moisture, and therefore samples at higher L/S ratios may form foams with lower bulk densities when such moisture is removed. In addition, residual moisture may weaken the polymer structure, and thus exhibit lower compressive strength due to these factors. Physical properties such as bulk density or porosity greatly affect the compressive strength of a substance composed of a pore structure inside such as a geopolymer foam, and thus the results of the compressive strength according to the bulk density are shown in fig. 9. Overall, as the bulk density decreases, a lower level of compressive strength is exhibited.
5.SEM/EDS
SEM images of the L/S ratio of samples according to the FA30 group are shown in FIG. 10. Fig. 10 (a) in which the L/S ratio is low has a skewed pore structure, and shows a tendency of a structure having larger pores as the L/S ratio increases. As described above, this is because as the L/S ratio increases, curing is delayed and the silica reacts sufficiently to achieve a greater level of expansion.
The polymer foams of each group exhibit different pore structures. FIG. 11 is SEM images showing EDS measurement areas and SEM images showing sample 46FA10, sample 46FA30 and sample 46FA50, and Si/Al ratio and Si/Na ratio calculated based on the element content results of the EDS measurement areas of the respective samples are shown in Table 3. A matte structure was observed inside the pores in the figures for all samples, because there were unreacted coal bottom ash particles within the structure. On the SEM images, the structural change of pores of different groups was not clearly observed, but the EDS elements of the structure were analyzed, and as a result, the change of the Si/Al ratio inside the pores was observed. In general, the Si/Al ratio represents the scale of the mineral polymerization reaction, but in the present invention, since a large amount of solidified water glass exists in addition to the structure of the geopolymer, the degree of participation of water glass in the geopolymer reaction can be estimated. The geopolymer structure is an aluminosilicate structure and the Si/Al ratio has a value of 1 to 4, compared to that of water glass made of SiO2And Na2O, if the water glass does not participate in the reaction, a large amount of Si and Na and a small amount of Al can be detected. As can be seen from the results of table 3, Si/Al inside the Matrix (Matrix) of all samples have similar values, but the pore surface portions show large differences. In particular, the Si/Al ratio of the pore surface of sample 46FA10 was very high, reaching 16.55, and the Si/Al ratios of sample 46FA30 and sample 46FA50 gradually decreased. Such a high Si/Al ratio means that the pore surfaces and the interior near the surfaces are mostly composed of solidified water glass, and this is caused by the lower reactivity of the coal bottom ashThe result of (1). Although the Si/Al ratio decreased with increasing fly ash content, it was confirmed that more solidified water glass was still present at a higher level than the value of the matrix.
TABLE 3
TG/DTG and DIL
The TG/DTG and DIL analyses provide the mass and length change activities of the sample exposed to high temperature, respectively, and when the two analysis results are interpreted together, the physicochemical structure change of the subject sample can be analyzed efficiently. FIG. 12 is the TG/DTG results on sample 46FA 30. According to the mass loss phenomenon, the following three regions can be classified. The region I (normal temperature-200 ℃) shows a steep and large mass loss, the region II (200 ℃ -350 ℃) shows a slow mass loss, and the region III (350 ℃ -1000 ℃) shows a small and continuous mass loss tendency. These regions are each due to other factors. Zone I results from the evaporation of physically present moisture (physically bound water) from the geopolymer foam structure. This moisture is present as moisture present on the outside of the geopolymer structure or as moisture physically bound to the geopolymer and OH structures of the silanol-based surface and represents the majority of the mass loss as a whole. In the relatively low temperature range of 100 ℃ to 150 ℃, moisture present in the geopolymer structure evaporates together with free water, which causes a sharp decrease in mass. In the temperature range of 150 ℃ to 200 ℃, the physical moisture present in the silicate evaporates and shows a relatively slow mass reduction. Thus, the moisture physically present can be completely removed when 200 ℃. The region II (200 ℃ C. -350 ℃ C.) shows a slower mass loss due to the evaporation of the water (chemically bound water) chemically bound in the geopolymer structure and the dehydroxylation of the silanol groups. It is known that chemically bound moisture actually evaporates in a lower temperature range (100 ℃ to 300 ℃), but since evaporation of physically present moisture occurs to a large extent in a temperature range of 100 ℃ to 150 ℃, normal observation on the DTG peak is not possible, and a weak peak is observed after 200 ℃ at which evaporation of physical moisture is completed. When the temperature is above 300 ℃, a reaction of forming siloxane bonds and water due to dehydroxylation of silanol groups occurs, so that the mass gradually decreases. In zone III, as the dehydroxylation of silanol groups continues, dehydroxylation of T-OH of the polymer also occurs, thereby exhibiting a smaller level of mass loss.
This phenomenon at high temperatures is related to the length-changing activity of geopolymer foams. Fig. 13 is a graph showing the DIL result of 45FA30 together with a differential curve drawn based on the result. When the temperature is above 700 ℃, a large level of shrinkage occurs, so that it cannot be measured with the limit of the analyzer, thereby showing only the result below 700 ℃. The cross-sectional views of the above samples all showed the result of expansion except the sample exposed to 600 ℃, but in the DIL analysis, although the sample showed the activity of expansion at 200 ℃ to 400 ℃, the sample showed the result of contraction compared to the original length. This is because the expansion is limited because the expansion cannot be freely performed due to a small force of 30cN applied at the time of DIL measurement, or because the expansion is performed by heating in the frame of the measuring instrument. Nevertheless, the length-varying activity according to the exposure temperature provides useful information as follows.
The length-change activity of the sample can be divided into 3 regions corresponding to the TG/DTG results and an additional region. In zone I (normal temperature-200 ℃), shrinkage of the sample was observed; shows expansion in region II (200 ℃ C. to 350 ℃ C.); after passing through the unchanged region III (350 ℃ C. -500 ℃ C.), a sharp contraction was observed in the final region IV (500 ℃ C. -). As shown in the above TG/DTG analysis results, when a geopolymer foam sample is exposed to high temperature, since dehydration and dehydroxylation (dehydroxylation) of the geopolymer structure and the solidified water glass occur in different temperature ranges from each other, respectively, the peak of the results is shown as a result of superposition of various reactions. As described above, the region I is a region where moisture existing physically evaporates, and it is reported that the evaporation of moisture and free water of the geopolymer structure occurring up to a temperature of 150 ℃ causes shrinkage of the geopolymer. Which is consistent with the shrinkage of the sample observed at 150 ℃. DIL results at 150 ℃ to 200 ℃ show a tendency to shrink, but samples exposed to 200 ℃ actually expand. As mentioned above, this difference is due to the fact that the sample does not freely expand during DIL measurement, and in fact, it is likely that evaporation of physically bound water and chemically bound water in the solidified water glass causes expansion of the sample. This swelling action of the sample is contrary to the findings that shrinkage of the chemical moisture removed from the geopolymer structure occurs, which is believed to occur as a result of the chemically bound moisture within the water glass solidified body within the sample evaporating while being trapped by the foam structure. This means that even a foam structure consisting of geopolymer and cured water glass does not have a complete brittleness after the curing process. The expansion phenomenon of zone III is consistent with that of a sample exposed to an actually corresponding temperature, in which the water molecules generated as a result of the dehydroxylation reaction of silanol groups are removed from the sample in the form of water vapor at a high temperature while causing the expansion of the structure. In region IV, dehydroxylation of T-OH continues, but a sharp shrinkage occurs due to softening (softening) and sintering (sintering) of the 2-fold structure of the solidified water glass.
DIL analysis was performed on the sample 46FA10, the sample 46FA30, and the sample 46FA50 in order to confirm the length variation activity of the samples according to the content of fly ash, and the results are shown in fig. 14. Likewise, when the temperature is above 700 ℃, a large level of shrinkage occurs, so that it cannot be measured with the limit of the analyzer, thereby showing only the result below 700 ℃. In addition, unlike the expansion of the above samples when exposed to temperatures of 200 ℃ to 400 ℃ for 2 hours, the samples other than 46FA10 showed a tendency to shrink compared to the original length in the results of fig. 14. As mentioned above, this is due to the limited expansion of the sample within the analyzer. A differential curve plotted based on the analysis result is shown in fig. 15. Although the above-examined contraction and expansion mechanisms showed similar length change activity, differences were observed in the degree of length change and the temperature at which expansion and contraction started for each group of samples. The less fly ash sample (46FA10) shrunk less during the initial period of heating, then expanded at a greater level, and then showed a tendency to expand dramatically. In addition, sample 46FA10 began to expand at 125 ℃ and contract at 375 ℃ and, conversely, 46FA30 and 46FA50 began to expand at the same temperature of 191 ℃ and contract at 435 ℃ and 510 ℃ respectively. This difference is due to the amount of residual water glass.
When no more geopolymer structures are formed, the chemical moisture is present in a weakly bonded manner and therefore can also evaporate at lower temperatures. In fact, when referring to the results of the expansion of the polymer from a relatively low temperature of 80 ℃ in the prior studies, it is presumed that the contraction phenomenon caused by the evaporation of physical moisture and the expansion phenomenon caused by the evaporation of chemical moisture are overlapped in the initial stage of heating. Thus, the 46FA10 sample showed less tendency to shrink due to less geopolymer structure and rapid evaporation of chemical moisture. In addition, the amount of Si determines the softening temperature, and it is reported that polymers with higher Si content undergo expansion and contraction faster than polymers with higher Al content. Considering that sample 46FA10 has a very high Si/Al ratio of 16.55 in the EDS results above, this is very consistent with the rapid expansion and contraction tendency of 46FA 10. In addition, higher Si means that a polymer structure is not well formed, and thus more solidified water glass remains, so that a large amount of water vapor generated by dehydroxylation of silanol groups in water glass causes a large swelling of 46FA 10. The lower the fly ash content (46FA10) at 600 ℃ to 700 ℃, the faster and sharper the shrinkage. Similarly, sample 46FA10 consisted of a large amount of solidified water glass and 2-fold structure of water glass, so its structure softened and sintered to allow it to undergo faster shrinkage.
< test example 2> change of physical Properties of silica fume-added fly ash-based Polymer foam at high temperature (change of physical Properties according to exposure temperature)
1. Observing macrostructures
The exposure to high temperatures was studied in order to remove the water present in the geopolymer foam. First, in order to investigate a temperature region for high temperature exposure of the sample, the sample 46FA30 was exposed at 200 ℃, 300 ℃, 400 ℃, 500 ℃ and 600 ℃, and changes in physical properties according thereto were investigated. FIG. 16 is a plot of the Top-face (Top) and Vertical cross-section (Vertical cross-section) of sample 46FA30 as a function of high temperature exposure temperature. When the sample is exposed to high temperature, expansion of the sample is caused, and the degree of expansion increases while the exposure temperature is raised to 200 ℃ to 400 ℃. However, when exposed to 500 ℃, the sample began to shrink, and when exposed to 600 ℃, the shrinkage further proceeded, thereby shrinking to a height of 5cm or less. Therefore, for the sample exposed to 600 ℃, other physical properties than thermal conductivity cannot be confirmed.
In addition, as the exposure temperature increases, the lower end of the sample expands and contracts less, whereas the upper end of the sample expands and contracts at a greater level. Such uneven shrinkage is a result of the inherent heterogeneity of the pore structure within the sample. It is known that this swelling phenomenon is caused by the water glass solidified body. Since the lower end of the sample formed a dense geopolymer and thus had less dimensional change even when exposed to high temperature, the upper end of the sample consisted of a geopolymer structure and a water glass solidified body, and thus dimensional change due to the water glass solidified body occurred when exposed to high temperature.
2.ATR-FTIR
ATR-FTIR analysis was performed in order to observe the change in physicochemical structure according to the high temperature exposure temperature of the geopolymer foam, and the result thereof is shown in fig. 17. Observed in all spectra of 800 ~ 1250cm-1Broad and strong peaks appear in the range. Considering that the polymer foam of the present invention is formed of a geopolymer structure and a reactant of silicate and silicate, it is considered that there are two reasons why the peak occurs. The first is a peak caused by asymmetric stretching vibration (asymmetric stretching vibration) of T-O (T: Si or Al) of a geopolymer structure. The mineral polymerization is carried out by hydrolyzing (hydroly) Si-OH and Al-OH chemical species eluted from raw materialsis) and condensation polymerization (polycondensation) to form an aluminosilicate structure. The Al-O bond has a lower bond energy than the Si-O bond and is unstable, and therefore, the Al-containing component is rapidly eluted from the raw material at the initial stage of the reaction, thereby forming an Al-rich geopolymer structure. It is known that, in the course of the reaction proceeding, elution of the Si component is achieved and a large amount of the Si component is incorporated into the structure of the geopolymer, whereby the corresponding peak shifts to a higher wavelength. In FIG. 17 the main peak after exposure at 200 ℃ is from 988cm-1Move to 998cm-1This is caused by the fact that the removal of moisture as a reactant promotes the mineral polymerization reaction, and thus more Si is incorporated into the geopolymer structure. However, the wavelength of the sample greatly decreased to 979cm when exposed at 300 deg.C-1Which means that Al is incorporated into the aluminosilicate structure or depolymerization occurs. Due to the high temperature exposure, Al may be further eluted from the remaining unreacted raw materials and incorporated into the geopolymer structure, or depolymerized (depolymerization) due to the destruction of bonds between the aluminosilicate structures of the geopolymer by the expansion of the sample. At temperatures above 300 ℃, the main peak again shifts to higher wavelengths with increasing temperature, a phenomenon related to the change in chemical structure of silanol groups. The silanol group forms a siloxane (Si-O-Si) bond by depolymerization, whereby the degree of polymerization of the Si-O-Si bond increases, and the main peak shifts to a higher wavelength as the degree of polymerization increases.
870cm with increasing exposure temperature-1The weaker the transmission in the vicinity, 780cm-1The stronger the peak, the clearer the pattern. 870cm-1The nearby pattern is represented by stretching vibration and bending (bending) of Si-OH, 780cm-1The nearby peaks are the result of symmetric stretching vibration of Si-O-Si bonds. This change in peak intensity means an increase in the number of Si-O-Si bonds formed by the polycondensation reaction of silanol groups (Si-OH). In addition, 3400cm was observed in the spectrum of the sample not exposed to high temperature-1Broad peaks nearby and 1650cm-1Is a peak due to moisture, and can be confirmed to be exposed to 200 fThe corresponding peak disappears at high temperatures above deg.C, indicating that water is removed. Finally, 1450cm-1The peak is composed of Na2CO3The peak appeared, and the Na component was generated by reaction with carbon dioxide in the atmosphere, and it was observed that the corresponding peak disappeared when exposed to high temperature.
3.XRD
Fig. 18 is a result showing XRD spectra at respective temperatures of sample 46FA30 exposed to high temperatures. The kind of crystalline phase does not change at each exposure temperature, but the intensity of the peak is different. The crystalline phase peak of quartz (quartz) becomes stronger upon exposure at 200 ℃, but shows less strength as the exposure temperature increases. Since 200 ℃ is a relatively low temperature, insufficient for crystallization to occur, it is believed that the bonds such as silanol groups or siloxanes are deformed with a stronger corresponding peak occurring, not due to the formation of a crystalline phase. Upon exposure to high temperatures above 300 ℃ the intensity of the corresponding peak is again observed to decrease and form an amorphous morphology. This is related to the trend of increasing and decreasing wavelength of the main peak at 200 ℃ to 300 ℃ in the FTIR analysis results.
4. Bulk density and porosity
Since the test samples exposed to 200 to 500 ℃ all expanded, the expanded portions were cut into a regular hexahedron of 5cm with a diamond saw to prepare samples and measure physical properties. In fig. 19, as the exposure temperature increases, the sample expands so that the bulk density first decreases, and then shows a tendency to increase at 500 ℃ where shrinkage begins. The porosity results of fig. 20 show a trend opposite to bulk density and are in good agreement with the shrinkage trend of the samples.
5. Thermal conductivity
FIG. 21 is a graph showing the thermal conductivity results for sample 45FA30 exposed to 200 deg.C to 600 deg.C. The moisture physically present on exposure at 200 ℃ evaporates and as the sample expands, the thermal conductivity decreases greatly from 0.243W/mK to 0.133W/mK. After exposure to 300 ℃ to 400 ℃, the thermal conductivity is further reduced as a result of the expansion of the sample due to the depolymerization of the silanol groups as described above. However, the thermal conductivity was 0.109W/mK when exposed to 400 ℃ and showed a smaller decrease in the amount of change in thermal conductivity than that decreased in the range of normal temperature to 200 ℃. This means that the removal of physically present moisture contributes significantly to the reduction of the thermal conductivity, followed by less contribution of chemically present moisture removal and expansion of the sample due to depolymerization.
6. Compressive strength
The compressive strength results for 46FA30 exposed to 200 ℃ to 500 ℃ are shown in FIG. 22. As the exposure temperature rises to 400 ℃, a structure with very large porosity is formed due to expansion, whereby the compressive strength shows a tendency to decrease. But the compressive strength increases again while the sample undergoes shrinkage at 500 c.
7.SEM
FIG. 23 is an SEM image of sample 46FA30 and a sample exposed to elevated temperatures of 200 ℃ to 600 ℃. A protruded massive bubble structure is observed inside the pores in the sample of fig. 23 (b), which is a structure formed by generating water vapor as a result of evaporation of chemically bound moisture and depolymerization (dehydration) of silanol groups, as described above. This reaction also proceeds in the matrix portion to form micropores, and such bubbles and micropore structure lead to an increase in thermal conductivity and a decrease in compressive strength. The above protruded bubble structure shows a destroyed shape after 400c and micropores are formed at the location where the bubbles are destroyed. The above-mentioned micropores were greatly reduced in the sample exposed to 600 c, so that it could be confirmed that the shrinkage of the sample was proceeding. Therefore, based on such results, it can be presumed that the shrinkage of the sample exposed to high temperature is performed by the destruction of bubbles and the reduction of micropores.
In the following experiments, the change in thermophysical properties of the samples was investigated in a temperature range of 200 ℃ to 500 ℃ except for 600 ℃ where severe shrinkage occurred.
< test example 3> change of physical Properties of silica fume-added fly ash-based Polymer foam at high temperature (change of physical Properties according to L/S ratio)
1. Observing macrostructures
All samples of the FA30 group were exposed to 200-500 ℃ in order to observe the change in thermophysical properties according to the L/S ratio, and a representative top-face and vertical-section view of the sample exposed to 400 ℃ is shown in fig. 24. All samples showed swelling and the swelling proceeded to a greater extent as more residual water was present as the L/S ratio increased. After swelling, the upper face of the sample shows a more swollen morphology, and this morphology is more prominent for samples with higher L/S ratios. The expansion described above is due to the heterogeneity of geopolymer foams.
2. Bulk density and porosity
The bulk density and porosity results for the FA30 group of samples exposed to temperatures between 200 ℃ and 500 ℃ are shown in fig. 25 and 26 in terms of L/S ratios. Likewise, more residual waterglass was present in the high L/S ratio samples, and thus the density was reduced to a greater extent due to swelling, and 50FA30 reached 0.417g/cm when exposed to 400 deg.C3The lowest bulk density of (c). The porosity results of fig. 26 show a trend opposite to bulk density.
3. Thermal conductivity
The results of the thermal conductivity of the FA30 group samples measured after exposure at high temperatures of 200 ℃ to 500 ℃ for the L/S ratio are shown in fig. 27. The thermal conductivity in all samples showed a large decrease after exposure to 200 c and further decreased with exposure to 300 c and 400c, and showed a tendency to increase again after exposure to 500 c. In particular, there is a large reduction in thermal conductivity in samples having an L/S ratio of 0.44 or greater after exposure to 200 ℃ as a result of the evaporation of the greater amount of residual moisture present in the geopolymer foam after exposure to high temperatures due to the higher L/S ratio. Thereafter, the thermal conductivity of the higher L/S ratio sample decreased more as the exposure temperature increased to 400 ℃, thereby reaching a minimum thermal conductivity of 0.0996W/mK in sample 50FA 30. However, when exposed to 500 ℃, the thermal conductivity of the higher L/S ratio sample instead rises at a relatively large level, and thus is similar to that of the lower L/S ratio sample. This result suggests that as the L/S ratio increases, the degree of expansion of the sample also increases, but the degree of contraction may also increase simultaneously.
4. Compressive strength
The compressive strength results for samples of the FA30 group exposed to high temperatures of 200 ℃ to 500 ℃ are shown in fig. 28. The compressive strength of the sample exposed to 200 ℃ showed a tendency to decrease with increasing L/S ratio, but no particular tendency appeared after exposure to temperatures above 300 ℃. It can be seen that this is due to the difference in temperature and extent to which each sample begins to expand and contract.
5.SEM
FIG. 29 is an SEM image of samples of FA30 groups exposed at 400 ℃ with L/S ratios of 0.38, 0.42, 0.46 and 0.50. A smoother pore surface was observed in the samples with lower L/S ratios. On the contrary, it was confirmed that as the L/S ratio was increased, the residual water glass was more present and non-dense geopolymer was formed, and thus micro-bubbles and pores were increased. The micro-bubbles and pores are factors that decrease the thermal conductivity, and thus are very consistent with the result that the thermal conductivity decreases as the L/S ratio increases in the above-described thermal conductivity results.
< test example 4> change of physical Properties of fly ash-based Polymer foam with silica fume added thereto at high temperature (change of physical Properties depending on fly ash content)
1. Observing macrostructures
Samples of the FA10, FA30, and FA50 groups were exposed to high temperatures in order to observe changes in the structure and physical properties of the foams when exposed to high temperatures, depending on the fly ash content. It was exposed to 400 deg.C (temperature condition capable of achieving the lowest bulk density in the above experimental results), and all L/S ratios of each group were investigated. First, representative samples of each group were decided as 46FA10, 46FA30 and 46FA50 in order to observe the change in the foam structure, and the results thereof were shown in fig. 30 by taking the upper side view and the vertical cross-sectional view of the respective samples. All samples expanded after high temperature exposure, the degree of expansion increasing as the fly ash content decreased (46FA 10)). This difference occurs even at the same L/S ratio, i.e., 0.46, because of the lower reactivity of the bottom ash particles. Since the geopolymer reaction proceeds relatively poorly, unreacted residual water glass is present in large amounts and causes swelling. Fig. 30 (c) is a sample to which much fly ash is added, in which the structure is not largely changed even after high-temperature exposure, and thus has high thermal stability.
2. Bulk density and porosity
The bulk density and porosity results for the FA10, FA30, and FA50 groups exposed to 400 ℃ are shown in fig. 31 and 32, respectively. Likewise, the lower the fly ash content (FA10) and the higher the L/S ratio, the more residual water glass is present, thus reducing the bulk density to a greater extent. The lowest bulk density achieved by each set of samples at an L/S ratio of 0.50 was FA100.336g/cm3、FA30 0.417g/cm3And FA500.487g/cm3. The porosity results of fig. 32 show a trend opposite to bulk density.
3. Thermal conductivity
The results of thermal conductivity measurements of FA10, FA30, and FA50 groups exposed to 400 ℃ are shown in fig. 33. The thermal conductivity of each group showed a tendency to decrease as the L/S ratio increased. For the lowest thermal conductivity of each group, FA10 reached 0.0895W/mK, FA30 reached 0.0996W/mK, and FA50 reached 0.125W/mK. The FA50 group is thermally stable, but expands less when exposed to high temperatures and therefore has a higher thermal conductivity. In contrast, the FA10 group underwent less mineral polymerization, but retained a large amount of residual water glass, and therefore expanded to a greater extent when exposed to high temperatures, and thus had lower thermal conductivity. This result means that the thermal conductivity that can be obtained when exposed to high temperatures can be adjusted by changing the amount of moisture and residual water glass inside the foam structure by adjusting the amount of fly ash/coal bottom ash and the amount of alkaline activator.
4. Compressive strength
The results of the compressive strength measurements of the FA10, FA30 and FA50 groups exposed to 400 ℃ are shown in fig. 34. The sample set described above, which was not exposed to high temperature, had similar compressive strength regardless of the amount of fly ash, but showed a tendency to decrease in compressive strength with decreasing fly ash after exposure to 400 ℃. Again, this is due to the residual water glass, which has a large level of swelling.
5.SEM
Fig. 35 shows SEM images of sample 46FA10, sample 46FA30, and sample 46FA50 taken at magnifications of 50 times (fig. 35 (a) to (c)) and 200 times (fig. 35 (d) to (f)), respectively. In sample 46FA10 (fig. 35 (a)), innumerable many microbubbles were observed inside the pores, and it was confirmed that the pore wall thickness was thickened due to the expansion. This microbubble reduction in the remaining samples 46FA30 and 46FA50 observed that the pore interior was relatively smooth and relatively thin pore walls were observed due to the smaller level of swelling. This difference in structure of each sample set leads to the trends in bulk density and thermal conductivity identified above.
< conclusion >
In the present invention, a coal ash based polymer foam is synthesized with silicon powder added as a blowing agent. The foam forming mechanism according to the raw material ratio is discussed while observing the vertical section, and the volume density, the porosity, the thermal conductivity, the compressive strength and the SEM/EDS analysis result are examined on the basis of the discussion. However, the geopolymer foam synthesized in this manner shows high thermal conductivity due to residual moisture and water glass structure in spite of having low bulk density, and thus studies on exposure of the geopolymer foam to high temperature have been conducted. First, reference samples were exposed to 200 ℃, 300 ℃, 400 ℃, 500 ℃ and 600 ℃, and volume density, porosity, thermal conductivity, compressive strength and microstructure changes according to the above temperature conditions were investigated. TG/DTG, DIL, ATR-FTIR, XRD and SEM analyses were performed and the mechanism thereof was grasped in order to analyze physicochemical changes upon exposure to high temperature, and the results of physical property changes in high temperature were discussed based on the above mechanism. The effects of the high temperature exposure temperature, the L/S ratio, and the content of fly ash on the change in physical properties of the geopolymer foam exposed to high temperatures were examined, and the results were as follows:
(1) as the content of fly ash decreases and the L/S ratio increases, a geopolymer foam of a porous structure consisting of larger pores is formed. Thus, following L/SThe increase in the ratio, the bulk density and the compressive strength showed a tendency to decrease, but the thermal conductivity increased at a certain L/S ratio or more due to the residual moisture and the water glass solidified body. From the results of SEM/EDS analysis, it was found that there was a considerable amount of residual water glass-cured structure in the vicinity of the surface of the pore structure, and the less the content of fly ash due to the low reactivity of the bottom ash, the larger the amount of residual water glass-cured body. The results show that the bulk density is 0.608 to 0.837g/cm3The thermal conductivity is 0.189-0.269W/mK, and the compressive strength is 3.50-6.39 MPa.
(2) Geopolymer foam test samples expanded upon exposure to 200 deg.C to 400 deg.C, and the maximum expansion was at 400 deg.C. But shrinks when exposed to 500 c to 600 c. The geopolymer foam expands mainly by water vapor (reaction products of silanol groups present in the residual water glass solidified body), which together with the removal of residual moisture leads to a lower thermal conductivity. However, as the water glass solidified body is softened and sintered at high temperature, the foam is shrunk, and thus the thermal conductivity is increased again.
(3) The test samples with high L/S ratio and low fly ash content will start to expand at lower temperatures and to a greater extent. This is due to the presence of a large amount of residual water glass solidified body, with a consequent reduction in bulk density, thermal conductivity, compressive strength. In this study, a minimum bulk density of 0.335g/cm was achieved in test sample 50FA10 exposed to a temperature of 400 deg.C3And a minimum thermal conductivity of 0.0895W/mK, and a compressive strength of 0.739 MPa. However, shrinkage also starts at relatively low temperatures and shows a tendency to shrink sharply. In summary, the geopolymer foam exposed to a high temperature of 400 ℃ exhibits a bulk density of 0.335 to 0.672g/cm3The thermal conductivity is 0.0895-0.165W/mK, and the compressive strength is 0.789-3.55 MPa.
In summary, for the coal ash based polymer foam to which the silicon powder is added, the foam is formed by hydrogen gas generated by the reaction of silicon, and various physical properties are exhibited according to the ratio of the bottom ash and the fly ash and the amount of the alkaline activator. The residual moisture and the water glass solidified body are present in the geopolymer foam subjected to only the oven curing, and thus become a cause for improving the thermal conductivity, but the thermal conductivity can be greatly reduced by removing the residual moisture and inducing the reaction of the water glass solidified body by exposure to high temperature. Specifically, the geopolymer foam expanded due to the silicon powder is further expanded by physical moisture, chemical moisture when exposed to high temperature, and simultaneously, a very low thermal conductivity of 0.0895W/mK can be achieved. This result shows that geopolymer foams of various physical properties can be synthesized by adjusting the compounding ratio of raw materials and the high temperature exposure temperature. In addition, since a surfactant required in the conventional foam synthesis method using aluminum powder is not used, it is expected to be used as an inorganic heat insulating material which does not release harmful substances at high temperatures.
The results of the present invention show that coal ash based polymer foams having excellent physical properties can be synthesized by using silica fume. In addition, the foam structure and physical properties can be adjusted by adjusting the amounts of the bottom ash, the fly ash and the alkaline activator and adjusting the high-temperature exposure temperature, and the range of use of the bottom ash can be expanded by using a large amount of bottom ash, which has not been widely used so far, for preparing the functional inorganic heat-insulating material.
The above description is merely illustrative of the present invention, and various modifications can be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present specification are not intended to limit the present invention but to illustrate the present invention, and the scope of the technical idea of the present invention is not limited by such embodiments. Also, the scope of the invention is to be construed in accordance with the following claims, and all technical equivalents thereto are intended to be included in the scope of the invention.
Claims (8)
1. A method for preparing a geopolymer foam using coal ash, comprising:
a step (1) of preparing an alkaline activator by mixing water glass with sodium hydroxide;
step (2), placing silicon powder in the alkaline activator for stirring;
step (3), crushing the coal bottom ash;
a step (4) of preparing coal ash by mixing the coal bottom ash and the fly ash;
a step (5) of adding the mixture of the silica powder and the alkaline activator to the coal ash, and then further adding the alkaline activator to adjust the ratio of the alkaline activator to the solid matter and mixing the mixture;
a step (6) of preparing a test sample by filling and sealing in a mold; and
and (7) curing the test sample in an oven.
2. The method for preparing geopolymer foam using coal ash according to claim 1,
and mixing the water glass and the sodium hydroxide into an alkaline activator in a mass ratio of 5: 1.
3. The method for preparing geopolymer foam using coal ash as claimed in claim 1, wherein said silicon powder is contained in an amount of 15% by weight.
4. The method for preparing geopolymer foam using coal ash according to claim 1,
and in the step of crushing the coal bottom ash, crushing for 1 time by using a jaw crusher and then crushing for 4 times by using a hammer crusher so as to eliminate the step of sieving process.
5. The method for preparing geopolymer foam using coal ash according to claim 1,
the fly ash accounts for 10 to 50 wt% of the total amount of the bottom ash and the fly ash.
6. The method for preparing geopolymer foam using coal ash as claimed in claim 1, wherein said alkaline activator/solid matter ratio is 0.38 to 0.50.
7. The method for preparing geopolymer foam using coal ash according to claim 1, further comprising:
the cured test sample is subjected to a step of exposing at a high temperature of 200 to 600 ℃ for 2 hours.
8. The coal ash-utilizing geopolymer foam produced by the production method according to any one of claims 1 to 7.
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| PCT/KR2021/003741 WO2022181871A1 (en) | 2021-02-24 | 2021-03-25 | Method for manufacturing coal ash-based geopolymer foam containing silica fume |
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| CA2185943A1 (en) * | 1995-09-21 | 1997-03-22 | Donald Stephen Hopkins | Cement containing bottom ash |
| CN104098282A (en) * | 2013-04-03 | 2014-10-15 | 神华集团有限责任公司 | Geopolymer composition, geopolymer material and preparation method of geopolymer material |
| CN105683120A (en) * | 2013-10-31 | 2016-06-15 | 建筑研究和技术有限公司 | Geopolymer foam preparation for noncombustible, sound-absorbing and heat-insulated geopolymer foam component |
| CN109311752A (en) * | 2016-04-07 | 2019-02-05 | 建筑研究和技术有限公司 | Geo-polymer foam formulations |
| CN110372239A (en) * | 2018-04-12 | 2019-10-25 | 兴局产业株式会社 | Utilize the preparation method of the geo-polymer of the high compressive strength of coal bottom ash |
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| KR101364149B1 (en) | 2012-08-02 | 2014-02-17 | 한국건설기술연구원 | Composition of alkali activated mortar for partial-depth repair of road and airport pavement |
| KR101535275B1 (en) | 2015-02-10 | 2015-07-09 | 한국지질자원연구원 | Composition for the preparation of geopolymer using waste coal ash and the preparation method of the same |
| KR101641536B1 (en) | 2015-11-02 | 2016-07-22 | 노재호 | Hybrid polymer binder composition including inorganic and organic polymer, conctrete composition and structure using the same |
| JP2017132658A (en) | 2016-01-28 | 2017-08-03 | 三菱ケミカル株式会社 | Method for producing geopolymer composition |
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| KR101865877B1 (en) * | 2017-12-12 | 2018-06-08 | 이계영 | Lightweight foam materials by using fly ash, bottom ash and waste glass powder and method for the manufacturing the same |
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| CA2185943A1 (en) * | 1995-09-21 | 1997-03-22 | Donald Stephen Hopkins | Cement containing bottom ash |
| CN104098282A (en) * | 2013-04-03 | 2014-10-15 | 神华集团有限责任公司 | Geopolymer composition, geopolymer material and preparation method of geopolymer material |
| CN105683120A (en) * | 2013-10-31 | 2016-06-15 | 建筑研究和技术有限公司 | Geopolymer foam preparation for noncombustible, sound-absorbing and heat-insulated geopolymer foam component |
| CN109311752A (en) * | 2016-04-07 | 2019-02-05 | 建筑研究和技术有限公司 | Geo-polymer foam formulations |
| CN110372239A (en) * | 2018-04-12 | 2019-10-25 | 兴局产业株式会社 | Utilize the preparation method of the geo-polymer of the high compressive strength of coal bottom ash |
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