CN109867290B - Silica sol for chemical mechanical polishing solution and preparation method thereof - Google Patents
Silica sol for chemical mechanical polishing solution and preparation method thereof Download PDFInfo
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Abstract
The invention provides silica sol for a chemical mechanical polishing solution, which is prepared by purifying kaolin, obtaining magnetic separation materials by pulping and grading, removing iron and titanium by gradient magnetic separation, roasting and whitening, and performing high-temperature calcification to finally obtain silica for the silica sol raw material, effectively improve the application range of the kaolin in the polishing field, facilitate the expansion of the kaolin to the high-precision chemical mechanical polishing field, and prepare the silica nanoparticles with uniform size and good dispersibility, so the silica nanoparticles are suitable for being used as the raw material of silicon element in the sapphire polishing solution.
Description
Technical Field
The invention belongs to the technical field of CMP (chemical mechanical polishing), and relates to a method for preparing uniform nano silicon oxide particles by using kaolinite as a silicon source and application of the method in the field of sapphire polishing.
Technical Field
China kaolin mineral resources rank the front of the world, a mineral producing area at 267 has been proved, and the reserve is proved to be 29.10 hundred million tons, wherein: the method is characterized in that kaolin is built in non-coal in China, the resource reserves occupy the fifth place in the world, the ascertained reserves are 14.68 hundred million tons and mainly and intensively distributed in the Guangdong, Shaanxi, Fujian, Jiangxi, Hunan and Jiangsu provinces, and account for 84.55 percent of the total reserves in China; the reserve of kaolin (kaolinite rock) containing coal for construction accounts for the first place in the world, the proven reserve is 14.42 hundred million tons, and the reserve is mainly distributed in great identity in Shanxi, Huanyu, inner Mongolian Junger, Wuda, Anhui Huai Bei, Shanxi Hancheng and the like, wherein the resources of the inner Mongolian Junger coal field are the most.
Kaolin is an industrial mineral with excellent performance and is widely applied to the fields of ceramics, papermaking, rubber, plastics, petroleum, chemical industry and the like. The kaolin is mainly composed of kaolinite group minerals, and the main component of the kaolin is Al2O3And Si02Part of Fe 203, Ti02Small amounts of CaO, MgO, K20, Na2O, etc. The kaolin mineral belongs to 1:1 type layered silicate, the crystal mainly comprises silicon-oxygen tetrahedron and aluminum-oxygen octahedron, wherein the silicon-oxygen tetrahedron is connected along two-dimensional direction in a mode of sharing apex angle to form a grid layer in hexagonal arrangement, and the tip oxygen not shared by each silicon-oxygen tetrahedron faces to one side; the 1:1 type unit layer is composed of the pinnate oxygen of the common siloxy tetrahedral layer of the siloxy tetrahedral layer and the aluminoxy octahedral layer.
At present, the development and research direction of kaolin is mainly focused on the development of high whiteness, ultra-fine refinement and organic composite modification directions, for example, CN103086390A of China geological university (Wuhan) discloses a high-efficiency iron removal process of kaolin, a 325-mesh sieving and high-gradient superconducting magnetic separation process is adopted to effectively remove different magnetic iron-containing and iron-containing titanium-containing minerals in high-iron kaolin minerals, the iron removal efficiency is high and can reach 69 percent at most, the whiteness of the kaolin is remarkably improved, the sintering whiteness can be improved to 91.3-93.69 from 74.7 percent before the magnetic separation, and the method has the advantages of high iron removal efficiency, low cost, no environmental pollution, novelty and practicability, and has general applicability and guiding significance for 'dead ore' high-iron kaolin resources in China living in inventory. In addition, publication No. CN1613818A discloses a process for preparing superfine kaolin, which comprises, subjecting kaolin to slurry-making, three-stage cyclone classification, horizontal spiral classification, high gradient magnetic separation, chemical bleaching, surface activation treatment, centrifugal dehydration, filter-pressing dehydration, superfine grinding and drying, wherein the superfine grinding comprises adding dispersant and water into filter cake, mechanically stirring and breaking into slurry with solid content of 55-60%, adjusting pH value of the slurry to 5.5-6.0, and subjecting to superfine grinding by stripping machine to obtain kaolin with size of 0.37 μm.
In addition, kaolin is directly ground to prepare polishing powder, the preparation process difficulty is mainly focused on particle size distribution, roasting process and product whiteness, but the preparation process is rough, the components of the polishing powder are not complex and varied, the cutting force is unstable, and the use dimension and the use direction of the product are finally influenced.
In addition, there is a rare case where silica abundant in kaolinite is purified by a purification process and used for a raw material of a sapphire polishing liquid, and a sapphire crystal (α -a 1)2O3) It is a high-quality optical functional material with high-temp. resistance, wear resistance, corrosion resistance and wide light-transmitting wave band, and it has the hexagonal close-packed type identical to that of group III nitride, and is a good material formed from three unique combinations of physical, mechanical and chemical properties. In the field of optical communications, sapphire crystals are used not only as short-wavelength active devices but also as passive devices for polarized light in the field of microelectronics, and sapphire can be used as a substrate for a new generation of semiconductor substrate SOI (on insulator), and due to the excellent blocking effect of sapphire, the capacitance effect of a transistor can be reduced, and the operation speed thereof can be made faster and the power consumption thereof can be made lower. In the field of optoelectronicsSapphire crystals are the preferred substrate material for fabricating GaN Light Emitting Diodes (LEDs). Before growing a thin film on a sapphire substrate, scratches, pits, stress regions, and the like generated during slicing are first removed, and then surface roughness is reduced. The greater the roughness of the surface, the more dangling bonds of the surface, the easier it is to adsorb other impurities, and there is a poor lattice match with the overlying film. In the traditional pure mechanical polishing, polishing powder is used for continuously grinding the surface of a polished material, so that deep scratches are easily generated. In CMP (chemical mechanical polishing), chemical reactants are removed by mechanical action under the environment of chemical action, so that the removal rate of materials is improved, and good surface morphology is obtained.
The CMP process currently used is silica-silica sol, a hard and brittle ceramic material with very low surface chemical activity. SiO 22The hydrosol is a colloid SiO prepared by a condensation method, and has a double-electron-layer structure, and electrons on the outer layer show negative charges2The surface of the particle is rich in silicon hydroxyl, and researches also find that the silica sol prepared by adopting the condensation method is also rich in silicon hydroxyl, which is the characteristic that SiO prepared by adopting the condensation method is enabled to be2The colloid has low viscosity, moderate hardness, no edge angle and no scratch during CMP.
Disclosure of Invention
Aiming at one or more problems in the prior art, the invention firstly proposes the purification process of the kaolin for purifying the silicon oxide enriched in the kaolin, the purification process of the kaolin has simple treatment process, easy operation, low requirement on equipment and small corrosivity, magnetic separation materials are obtained by utilizing pulping classification, gradient magnetic separation for removing iron and titanium, roasting for whitening and high-temperature calcification are obtained, finally, the silicon oxide is respectively purified, the use range of the kaolin in the polishing field is effectively improved, the preparation method is convenient to expand to the high-precision chemical mechanical polishing field, and the prepared silicon oxide nano particles have uniform size and good dispersibility and are suitable to be used as raw materials of silicon elements in sapphire polishing solution.
Silica sol for chemical mechanical polishing solution, wherein the silicon element in the silica sol is derived from CaO purified from kaolin.SiO2Powder of CaO.SiO2SiO in powder2The content is more than 97wt.%, and the size of the silicon oxide nano-particles prepared from the silica sol is intensively distributed in 50-60nm, D98≤75nm。
A method for preparing silica sol for chemical mechanical polishing solution comprises the following steps:
(1) pulping and grading to obtain magnetic separation materials: carrying out coarse grinding, slurry preparation and sand removal and particle size classification treatment on kaolinite in a swirler, wherein the mass ratio of slurry preparation is kaolin subjected to coarse grinding: dispersing agent: water = (0.05-0.15): (0.001-0.01): 1, mixing and stirring speed is 500-;
(2) gradient magnetic separation for removing iron and titanium: background magnetic field strength 1.5 x 104Oe, the flow rate is 1-2 cm/s; magnetization period 3-8min, such that titanium content is below 0.3wt.% and iron content is below 0.2wt.%;
(3) baking whitening and simple phase transition: dehydration, drying, roasting at 800-oC, rate of temperature rise 10oC/min, keeping the temperature for 2-3h after the roasting temperature is reached, and roasting the oxygen-nitrogen mixed gas O in the atmosphere2/N2= 5-8 wt.%, and Al with whiteness of more than 90% is obtained2O3 .xSiO2Materials, 0<X≤1。
(4) High-temperature calcification: to the above Al2O3 .xSiO2Adding CaO powder into the materials, uniformly stirring, and heating to 1200-1300 DEG CoC, reacting for 1-2h to obtain CaO.SiO2With CaO.Al2O3Cooling the mixture to 80-90 deg.CoC。
(5) Separating silicon oxide: adding 30-40wt.% Na to the above mixture2CO3Stirring the aqueous solution for reaction for 2-4h, filtering for many times, and collecting the solid
(6) Preparing sodium silicate: adding aqueous solution of sodium hydroxide into the solid collected in the step (5) at 70-85 deg.CoHeating and stirring for 4-4.5h under the condition of C, carrying out suction filtration, washing with deionized water to obtain sodium silicate aqueous solution
(7) Preparing silica sol: 10-20ml of the silicon obtained above are chargedRespectively adding ethanol and ammonia water into sodium acid water solution, stirring for reaction for 1 hr, adding polyethylene glycol/ethanol mixed solution, and reacting at 40 deg.CoAnd C, continuously reacting for 24-36h to obtain the white nano silicon oxide dispersion.
Further, in the white nano silicon oxide dispersion, the purity of silicon oxide is higher than 99%.
Further, in the step (6), the concentration of sodium hydroxide is 10-30 wt.%, and the concentration of the obtained sodium silicate aqueous solution is 5-15 wt.%.
Further, the volume ratio of the ethanol to the ammonia water in the step (7) is 70 (1-3), and the concentration of the polyethylene glycol/ethanol mixed solution is 3-15 wt%.
Further, the dispersing agent is a mixture of sodium hexametaphosphate, sodium polyacrylat and sodium oxalate, and the mass ratio is 0.2-0.5: 1: 1.
Furthermore, the pH value of the prepared slurry is adjusted by using ethylamine, and the pH value is more than or equal to 9.0 and less than or equal to 10.0.
Further, SiO in the kaolin240-50 wt.% of Al2O3Content of 27-39 wt.%, Fe2O3Content 2-3 wt.%, TiO2Content 3-4.5 wt.%, K2O+Na2O + CaO + MgO < 1wt.%, and the remainder is loss on ignition.
Furthermore, the recovery rate of the silicon oxide in the kaolin crude ore reaches more than 90 percent.
Furthermore, the application of the silica sol to the chemical mechanical polishing solution is characterized by being applied to the field of polishing of alumina sapphire mixed with a small amount of titanium and iron impurities.
The beneficial technical effects are as follows:
(1) the mixture of sodium hexametaphosphate, sodium polyacrylat and sodium oxalate is used as the dispersing agent, the dispersing effect is good, and impurities cannot be introduced into the prepared pulp by using the ethylamine regulator.
(2) The gradient magnetic separation parameters are reasonable, titanium and iron in kaolin can be effectively removed, the content of titanium is lower than 0.3 wt%, the content of iron is lower than 0.2 wt%, the whiteness of the kaolin is improved, and finally, almost no ferrotitanium is contained in the obtained aluminum oxide or silicon oxide.
(3) In the presence of oxygenMixed nitrogen gas O2/N2Roasting kaolin at a high temperature to obtain Al with whiteness of more than 90%2O3 .xSiO2And (3) feeding.
(4) The silicon oxide raw material is effectively extracted by a chemical purification method, and the silicon oxide polishing solution has high purity, small particle size and good polishing stability.
(5) The preparation process is simple, the raw material source is wide, the product has high cost performance, can be widely used in various industries and fields, and can meet the CMP polishing requirement.
Drawings
FIG. 1 is a particle size distribution diagram of silica separated in step (5) of example 2;
FIG. 2 TEM image of silica nanoparticles prepared in example 2;
FIG. 3 is a size distribution diagram of silica nanoparticles prepared in example 2;
FIG. 4 is a flow chart of a silica sol process for chemical mechanical polishing solution.
Detailed Description
Usually, the source for preparing the silica sol is mainly silicon or ethyl orthosilicate, the price is high, and the kaolin with low price and wide source is explored and adopted as the raw material for preparing the Si02The particles or the organic silica sol have important application value.
The preparation flow chart of the silicon oxide nano-particles is shown in the attached figure 4 and concretely explained as follows: firstly, the dispersant used in the slurry preparation process is a mixture of sodium hexametaphosphate, sodium polyacrylat and sodium oxalate, the compound dispersant has obvious improvement on the dispersion stability of the prepared slurry, and the sodium hexametaphosphate and the sodium polyacrylate can effectively improve the dispersion stability of the slurry. The sodium hexametaphosphate is attached to the surface of the mineral after being dissociated, so that the negative charge of the surface of the mineral is increased, mineral particles are separated due to static electricity, meanwhile, the ultra-large molecular group of the sodium hexametaphosphate is attached to the surface of the mineral to generate a strong steric hindrance effect so as to enhance the dispersion effect, sodium oxalate is introduced to enhance the adsorption and the negative ion of the surface characteristic of the mineral, so that the surface potential is changed to be negative, the isoelectric point is reduced, and the addition of the sodium polyacrylate is beneficial to the dispersion and the separation of compound minerals, namely the use of the dispersing agent is beneficial to subsequent sand removal, particle size classification, gradient magnetic separation and whitening, so that the purity of kaolin purification is effectively improved, and the kaolin purification is more uniform and thorough.
The main impurity minerals in the ore sample are iron-containing titanium minerals, wherein the titanium-containing minerals are mainly anatase and rutile, a small amount of brookite, ferrotitanium rutile and ilmenite, the iron-containing minerals are mainly limonite, hematite, tourmaline and the like, in addition, Fe and Ti are dyeing elements which need to be removed in the CMP polishing process so as to avoid pollution to a polishing substrate, coloring elements such as iron and titanium and organic carbon in kaolin are main factors influencing the whiteness of a polishing material, and the current method for removing the ferrotitanium mainly comprises the following steps: (A) flotation: the method is to separate the coloring matter such as anatase, tourmaline and the like from the kaolin suspension dispersed in water by utilizing the characteristic that the oleophylic energy of the coloring matter enters organic liquid such as fatty acid, benzene, carbon tetrachloride and the like, and the industrial application of the method is mainly limited by the cost at present. The main defects of iron and titanium removal by a flotation method are that the amount of residual medicament adsorbed on the surface of kaolin particles is large, dehydration is difficult, and the whole process is complex; (b) chemical reduction: the iron is removed by direct acid leaching or reduction bleaching, the factors influencing the bleaching effect by chemical reduction are many, such as the characteristics, temperature, pH value, medicament dosage, ore pulp concentration, bleaching time, stirring strength and the like of the ore, and if the ore contains high organic substances and impurities, the bleaching effect is poor, and the whiteness is not greatly improved. (c) The microbiological method comprises the following steps: the microorganism method is to use some microorganisms (malt, azotobacter and aspergillus niger) to oxidize or reduce impurity iron (pyrite, iron oxide ore and the like) into soluble iron to achieve the aim of removing iron impurities in kaolin, but the microorganism oxidation method has large floor area and long treatment period, has different fungus treatment efficiencies for different types of clay, and is subject to further research and optimization. Through high-gradient magnetic separation on kaolin, the content of titanium is reduced from 4-5.5 wt.% to 0.3wt.%, and the content of iron is reduced from 3-4 wt.% to 0.2wt.%, so that the effect is obvious.
In addition, factors influencing whiteness include organic carbon, and organic matters are easy to burn at high temperature, so that calcination is the most economical and effective method for removing organic carbon in kaolin powder, the calcination atmosphere has great influence on carbon removal in the calcination process, the oxidation atmosphere is favorable for burning removal of carbon, and the reduction atmosphere is unfavorable for carbon removal. Under the reducing or weak oxidizing atmosphere, the organic carbon in the kaolin powder can be converted into CO, and when the ventilation is poor and the temperature is low, the CO is decomposed into CO2And dispersed carbon, which is the function of low-temperature carbon deposition. For this reason, when the calcination temperature is low and the oxidizing atmosphere is weak, the surface of the product is gray. The oxygen-nitrogen mixed gas O of the roasting atmosphere of the invention2/N2= 5-8 wt.%, and Al with whiteness of more than 90% is obtained2O3 .xSiO2The material can also have simple phase change in the roasting process to generate Al2O3 .xSiO2And (3) feeding.
High temperature calcification is used to form CaO which can react with an aqueous solution of sodium carbonate.Al2O3Generating sodium tetrahydroxy chlorate and CaO which does not react with the sodium carbonate aqueous solution.SiO2And further realize CaO.Al2O3And CaO.SiO2To obtain CaO.SiO2The grain diameter of the powder is less than 1mm, CaO.SiO2SiO in powder2The content is more than 97 wt.%.
To obtain a silica source which has large size of silica particles and has a particle size distribution and dispersion thereof, as shown in FIG. 1, and cannot be directly used for polishing solution, the prepared disordered silica is firstly dissolved in sodium hydroxide solution to form colloid, and then ethanol and ammonia water mixed solution is added to the colloid, so that intermediate Si (OH) is formed4Upon condensation to ≡ Si-O-Si ≡, an increase in the proportion of aqueous ammonia leads to an increase in pH, while in an environment of high pH aqueous ammonia can enhance electrostatic repulsion between primary particles, reducing condensation polymerization between them and thus forming a colloid having a smaller particle size. On the contrary, if increasedThe proportion of ethanol, the amount of ammonia water is reduced, the pH of the solution is lower, the electrostatic repulsion effect among colloidal particles is weakened by the ethanol, primary particles are more easily aggregated, the volume ratio of the mixed solution is 70 (1-3), the mixed solution of polyethylene glycol and ethanol is added later, hydrogen bonds formed on the surface layers of the polyethylene glycol and silicon hydroxyl are beneficial to the stability of silica sol, the viscosity of a sol system is increased, and Si (OH) is reduced4The diffusion of (a) contributes to the formation of a silica dispersion of smaller particles, and in addition, the temperature is an important factor affecting the stability of the silica sol, the higher the temperature, the shorter the time for the silica sol to form a gel, and the higher the temperature, the higher the average kinetic energy of the sodium silicate molecules increases, thereby accelerating the hydrolysis reaction of the sodium silicate. Meanwhile, when the silica colloidal particles are polymerized to form gel, silicon-oxygen bonds can be formed among the colloidal particles, and the higher the temperature is, the more easily the silicon-oxygen bonds are formed, so that the temperature is increased, the rate of forming the gel is also increased, and further the particle size is influenced, namely the particle size of the nano silica can be adjusted through the temperature, the proportion of ethanol and ammonia water and the proportion of ethylene glycol and ethanol, and based on the subsequent polishing effect, the size of silica sol prepared from silica purified from kaolin is intensively distributed at 50-60nm, and D is distributed at 50-60nm through adjusting the parameters98≤75nm。
Example 1
A method for preparing silica sol for chemical mechanical polishing solution comprises the following steps:
(1) pulping and grading to obtain magnetic separation materials: carrying out coarse grinding, slurry preparation and sand removal and particle size classification treatment on kaolinite in a swirler, wherein the mass ratio of slurry preparation is kaolin subjected to coarse grinding: dispersing agent: water =0.05:0.001:1, stirring speed of slurry preparation is 500r/min, stirring time is 1h, and the content of the kaolin with the granularity smaller than 3mm is larger than 90%, so that the magnetic separation raw material is obtained.
(2) Gradient magnetic separation for removing iron and titanium: background magnetic field strength 1.5 x 104Oe, the flow rate is 1 cm/s; magnetization period 3min, resulting in titanium content below 0.3wt.% and iron content below 0.2 wt.%.
(3) Baking whitening and simple phase transition: dehydrating, drying, roasting at 800 deg.CoC, rate of temperature rise 10oC/min, keeping the temperature for 2-3h after the roasting temperature is reached, and roasting the oxygen-nitrogen mixed gas O in the atmosphere2/N2=5wt.%, Al with a whiteness of more than 90% is obtained2O3 .xSiO2Materials, 0<X≤1。
(4) High-temperature calcification: to the above Al2O3 .xSiO2Adding CaO powder into the materials, stirring uniformly, and heating to 1200 DEGoC, reacting for 1h to obtain CaO.SiO2With CaO.Al2O3Cooling the mixture to 80 deg.CoC。
(5) Separating silicon oxide: to the above mixture was added 30wt.% Na2CO3Stirring the aqueous solution for reaction for 2-4h, filtering for many times, and collecting the solid.
(6) Preparing sodium silicate: adding aqueous sodium hydroxide solution to the solid collected in step (5) at 70 deg.CoAnd C, heating and stirring for 4 hours, carrying out suction filtration, and washing with deionized water to obtain a sodium silicate aqueous solution.
(7) Preparing silica sol: adding ethanol and ammonia water into 10ml of the obtained sodium silicate aqueous solution respectively, stirring and reacting for 1h, adding polyethylene glycol/ethanol mixed solution, and reacting at 40 DEGoAnd C, continuously reacting for 24 hours to obtain a white nano silicon oxide dispersion.
Further, in the white nano silicon oxide dispersion, the purity of silicon oxide is higher than 99%.
Further, the concentration of sodium hydroxide in step (6) was 10wt.%, and the concentration of the obtained sodium silicate aqueous solution was 5 wt.%.
Further, in the step (7), the volume ratio of the ethanol to the ammonia water is 70:1, and the concentration of the polyethylene glycol/ethanol mixed solution is 3 wt%.
Further, the dispersing agent is a mixture of sodium hexametaphosphate, sodium polyacrylat and sodium oxalate, and the mass ratio is 0.2:1: 1.
Example 2
A method for preparing silica sol for chemical mechanical polishing solution comprises the following steps:
(1) pulping and grading to obtain magnetic separation materials: carrying out coarse grinding, slurry preparation and sand removal and particle size classification treatment on kaolinite in a swirler, wherein the mass ratio of slurry preparation is kaolin subjected to coarse grinding: dispersing agent: water =0.1:0.005:1, stirring speed of slurry preparation is 750r/min, stirring time is 2h, and the content of the kaolin with the granularity smaller than 3mm is larger than 90%, so that the magnetic separation raw material is obtained.
(2) Gradient magnetic separation for removing iron and titanium: background magnetic field strength 1.5 x 104Oe, flow rate 1.5 cm/s; magnetization period 6min, resulting in titanium content below 0.3wt.% and iron content below 0.2 wt.%.
(3) Baking whitening and simple phase transition: dehydrating, drying, and roasting at 1000 deg.CoC, rate of temperature rise 10oC/min, keeping the temperature for 2.5h after the roasting temperature is reached, and roasting the oxygen-nitrogen mixed gas O in the atmosphere2/N2=6.5wt.%, Al having a whiteness of more than 90% is obtained2O3 .xSiO2Materials, 0<X≤1。
(4) High-temperature calcification: to the above Al2O3 .xSiO2Adding CaO powder into the materials, stirring uniformly, heating to 1250oC, reacting for 1.5h to obtain CaO.SiO2With CaO.Al2O3Cooling the mixture to 85 deg.CoC。
(5) Separating silicon oxide: to the above mixture was added 35wt.% Na2CO3The aqueous solution is stirred and reacted for 3 hours, and the solid is collected after multiple times of filtration.
(6) Preparing sodium silicate: adding aqueous solution of sodium hydroxide into the solid collected in the step (5) at 70-85 deg.CoAnd C, heating and stirring for 4.2 hours, carrying out suction filtration, and washing with deionized water to obtain a sodium silicate aqueous solution.
(7) Preparing silica sol: adding ethanol and ammonia water into 10-20ml of the obtained sodium silicate aqueous solution respectively, stirring for reaction for 1h, adding polyethylene glycol/ethanol mixed solution, and reacting at 40%oAnd C, continuously reacting for 30 hours to obtain a white nano silicon oxide dispersion.
Further, in the white nano silicon oxide dispersion, the purity of silicon oxide is higher than 99%.
Further, the concentration of sodium hydroxide in step (6) is 20wt.%, and the concentration of the obtained sodium silicate aqueous solution is 5-15 wt.%.
Further, in the step (7), the volume ratio of the ethanol to the ammonia water is 70:2, and the concentration of the polyethylene glycol/ethanol mixed solution is 10 wt%.
Further, the dispersing agent is a mixture of sodium hexametaphosphate, sodium polyacrylat and sodium oxalate, and the mass ratio is 0.3:1: 1.
Example 3
A method for preparing silica sol for chemical mechanical polishing solution comprises the following steps:
(1) pulping and grading to obtain magnetic separation materials: carrying out coarse grinding, slurry preparation and sand removal and particle size classification treatment on kaolinite in a swirler, wherein the mass ratio of slurry preparation is kaolin subjected to coarse grinding: dispersing agent: water =0.15:0.01:1, stirring speed of slurry preparation is 800r/min, stirring time is 3h, and the content of the kaolin with the granularity smaller than 3mm is larger than 90%, so that the magnetic separation raw material is obtained.
(2) Gradient magnetic separation for removing iron and titanium: background magnetic field strength 1.5 x 104Oe, the flow rate is 2 cm/s; magnetization period 8min, resulting in titanium content below 0.3wt.% and iron content below 0.2 wt.%.
(3) Baking whitening and simple phase transition: dehydrating, drying, and calcining at 1100 deg.CoC, rate of temperature rise 10oC/min, keeping the temperature for 3 hours after the roasting temperature is reached, and roasting the oxygen-nitrogen mixed gas O in the atmosphere2/N2= 5-8 wt.%, and Al with whiteness of more than 90% is obtained2O3 .xSiO2Materials, 0<X≤1。
(4) High-temperature calcification: to the above Al2O3 .xSiO2Adding CaO powder into the materials, stirring uniformly, and heating to 1300 DEG CoC, reacting for 2 hours to obtain CaO.SiO2With CaO.Al2O3Mixing, cooling to 90 deg.CoC。
(5) Separating silicon oxide: to the above mixture was added 40wt.% Na2CO3Stirring the aqueous solution for reaction for 4 hours, filtering and collecting solids for multiple times, wherein the purity of the separated silicon oxide is high, but the nano-particle size is largeThe distribution is chaotic as shown in fig. 1.
(6) Preparing sodium silicate: adding aqueous sodium hydroxide solution to the solid collected in step (5) at 85 deg.CoHeating and stirring for 4.5h under the condition of C, carrying out suction filtration, and washing with deionized water to obtain a sodium silicate aqueous solution.
(7) Preparing silica sol: adding ethanol and ammonia water into 10-20ml of the obtained sodium silicate aqueous solution respectively, stirring for reaction for 1h, adding polyethylene glycol/ethanol mixed solution, and reacting at 40%oAnd C, continuously reacting for 36h to obtain a white nano silicon oxide dispersion.
Further, in the white nano silicon oxide dispersion, the purity of silicon oxide is higher than 99%.
Further, in the step (6), the concentration of sodium hydroxide was 30wt.%, and the concentration of the obtained sodium silicate aqueous solution was 15 wt.%.
Further, in the step (7), the volume ratio of the ethanol to the ammonia water is 70:3, and the concentration of the polyethylene glycol/ethanol mixed solution is 15 wt%.
Further, the dispersing agent is a mixture of sodium hexametaphosphate, sodium polyacrylat and sodium oxalate, and the mass ratio is 0.5:1: 1.
As can be seen from FIGS. 2 to 3, the silica nanoparticles prepared from the silica sol have a size distribution of 50 to 60nm, D98≤75nm。
The embodiments of the present invention have been described in detail, but the embodiments are merely examples, and the present invention is not limited to the embodiments described above. Any equivalent modifications and substitutions to those skilled in the art are also within the scope of the present invention. Accordingly, equivalent changes and modifications made without departing from the spirit and scope of the present invention should be covered by the present invention.
Claims (8)
1. A method for preparing silica sol for chemical mechanical polishing solution is characterized by comprising the following steps:
(1) pulping and grading to obtain magnetic separation materials: carrying out coarse grinding, slurry preparation and sand removal and particle size classification treatment on kaolinite in a swirler, wherein the mass ratio of slurry preparation is kaolin subjected to coarse grinding: dispersing agent: water = (0.05-0.15): (0.001-0.01): 1, mixing and stirring speed is 500-;
(2) gradient magnetic separation for removing iron and titanium: background magnetic field strength 1.5 x 104Oe, the flow rate is 1-2 cm/s; magnetization period 3-8min, such that titanium content is below 0.3wt.% and iron content is below 0.2wt.%;
(3) baking whitening and simple phase transition: dehydration, drying, roasting at 800-oC, rate of temperature rise 10oC/min, keeping the temperature for 2-3h after the roasting temperature is reached, and roasting the oxygen-nitrogen mixed gas O in the atmosphere2/N2= 5-8 wt.%, and Al with whiteness of more than 90% is obtained2O3 .xSiO2Materials, 0<x≤1；
(4) High-temperature calcification: to the above Al2O3 .xSiO2Adding CaO powder into the materials, uniformly stirring, and heating to 1200-1300 DEG CoC, reacting for 1-2h to obtain CaO.SiO2With CaO.Al2O3Cooling the mixture to 80-90 deg.CoC；
(5) Separating silicon oxide: adding 30-40wt.% Na to the above mixture2CO3Stirring the aqueous solution for reaction for 2-4h, filtering for many times, and collecting solids;
(6) preparing sodium silicate: adding aqueous solution of sodium hydroxide into the solid collected in the step (5) at 70-85 deg.CoHeating and stirring for 4-4.5h under the condition of C, carrying out suction filtration, and washing with deionized water to obtain a sodium silicate aqueous solution;
(7) preparing silica sol: respectively adding ethanol and ammonia water into 10-20mL of the obtained sodium silicate aqueous solution, stirring for reaction for 1h, adding polyethylene glycol/ethanol mixed solution, and reacting at 40%oContinuously reacting for 24-36h under the condition of C to obtain white nano silicon oxide dispersion silica sol, wherein the size of silicon oxide nano particles in the silica sol is intensively distributed at 50-60nm, and D98≤75nm。
2. The method of claim 1, wherein the silica sol has a purity of greater than 99% in the white nano silica dispersion silica sol.
3. The method of claim 1, wherein the concentration of the aqueous sodium hydroxide solution in the step (6) is 10 to 30wt.%, and the concentration of the aqueous sodium silicate solution obtained is 5 to 15 wt.%.
4. The method according to claim 1, wherein the volume ratio of ethanol to ammonia in step (7) is 70 (1-3), and the concentration of the mixture of polyethylene glycol and ethanol is 3-15 wt%.
5. The method of claim 1, wherein the dispersant is a mixture of sodium hexametaphosphate, sodium polyacrylat and sodium oxalate in a mass ratio of 0.2-0.5: 1: 1.
6. The method of claim 1, wherein ethylamine is used to adjust the pH of the slurry to 9.0-10.0.
7. The method of claim 1, wherein the kaolin comprises SiO240-50 wt.% of Al2O3Content of 27-39 wt.%, Fe2O3Content 2-3 wt.%, TiO2Content 3-4.5 wt.%, K2O+Na2The content of O + CaO + MgO is less than 1wt.%, and the rest is loss of ignition.
8. The method according to claim 1, wherein the recovery rate of silica in kaolin is more than 90%.
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