GB2173179A

GB2173179A - Preparation of fibres and/or transparent gels

Info

Publication number: GB2173179A
Application number: GB08508583A
Authority: GB
Inventors: Jonathan Mark Boulton; Harold Garton Emblem; Kenneth Jones
Original assignee: Clinotherm Ltd
Current assignee: Clinotherm Ltd
Priority date: 1985-04-02
Filing date: 1985-04-02
Publication date: 1986-10-08
Also published as: JPS6297922A; GB8508583D0; GB2173179B

Abstract

A solution from which fibres can be drawn or a transparent gel obtained is prepared by reacting water, a lower alkyl silicate and an aluminium hydroxyhalide of the general formula Al2(OH)nX6-n or a polymer, hydrate, hydroxy complex or zirconium complex thereof, where X is Cl, Br or I and n is less than 6 in a water-miscible alcohol solvent.

Description

SPECIFICATION Preparation of fibres and/or transparent gels This invention relates to the preparation of fibres and/or transparent coherent gels. The preparation of solutions containing silicon and aluminium which are suitable for binding refractory grains are described in British Patent 1,356,248 and in U.S. Patent 3,979,215. The preparation of a solution containing silicon and aluminium in the oxide stoichiometry required for mullite and the use of this solution to bind refractory grains is described in British Patent 2,004,263.

According to the invention, a solution containing aluminium and silicon, optionally present in the oxide stoichiometry required for mullite, from which fibres and/or transparent coherent gels can be obtained is prepared by reacting water, a lower alkyl silicate and an aluminium hydroxyhalide of the general formula Al2(OH)nX6n or a polymer, hydrate, hydroxy complex or zirconium complex thereof, where X is Cl, Br or I and n is less than 6 in a water-miscible alcohol solvent, optionally at a temperature of 60"C or higher.

The desired gell derived from the above solution is homogeneous and it is from this characteristic that transparency and the ability to form fibres stems.

When the aluminium compound is an aluminium hydroxyhalide of the general formula Al2(OH)nX5n or a polymer or hydrate thereof, the reaction should be carried out at a temperature of 60"C or higher. Irrespective of the nature of the aluminium compound, it is preferred to carry out the reaction at a temperature of 60"C or higher.

The preferred lower alkyl silicate is ethyl silicate and the preferred aluminium hydroxyhalide is a hydroxychloride (or chlorhydrate) in which n is 5. The invention will be described in detail with reference to these preferred materials.

The traditional method of preparing ethyl silicate is by treating tetrachlorosilane with ethanol. When anhydrous ethanol is used, the product is tetraethoxysilane (ethyl orthosilicate) Si(OEt)4 with hydrogen chloride as by-product. In the industrial preparation, the ethanol used invariably contains some water (industrial spirit), hence the product obtained consists of a mixture of tetraethoxysilane and ethoxypolysiloxanes (ethyl polysilicates) which are formed by condensation -polymerisation reactions resultant on water being present and being catalysed by the hydrogen chloride by-product. Reaction conditions are chosen to yield a product which will give on ignition SiO2 equivalent to 40% w/w, which corresponds to a mixture of ethoxysiloxane oligomers with an average of 5 silicon atoms. This material is known as technical ethyl silicate 40, or ethyl silicate 40.It is the preferred ethyl silicate in the present invention because it contains polymeric material which enhances fibre-forming. Other methods for the production of mixtures of tetraethoxysilane and ethoxypolysiloxanes are given in British Patent 2,017,129, European Patent 0,004,730; Canadian Patent 1,172,649 and U.S. Patent 4,211,717.

Methods of making the aluminium hydroxychlorides include: treating aluminium metal with dilute hydrochloric acid solution, treating aluminium hydroxide with hydrochloric acid under pressure, electrolytically from aluminium metal and dilute hydrochloric acid solution as described in British Patent 1,006,384.

Suitable aluminium hydroxychlorides are available under the Trade Marks of CHLORHYDROL and MI CRO-DRY. In these materials, n is 5 in the formula Al2(OH)nCI6n. They have aluminium as Awl203 = 47% and Cl = 16.3%. Aluminium hydroxychlorides of the formula Al2(OH)5ClmH2O where m is a number less than 4 are available and may be used. Hydroxy complexes of aluminium hydroxychlorides include the lactate complexes described in British Patent 845,670, also the aluminium hydroxychloride-propylene glycol complexes available under the Trade Mark of REHYDROL as REHYDROL II.These complexes have Aluminium as Awl203 - 36% min Chlorine - 12.5% min Propylene glycol - 25.0% max Suitable complexes with zirconium include the aluminium zirconium pentachlorohydrate sold under the Trade Mark REZAL as REZAL 67P. This has Al = 20% Zr = 10% Other complexes which may be used include the aluminium zirconium tetrachlorohydrex-glycine complex sold under the Trade Mark REZAL as REZAL 36GP. This has Al = 15% Zr = 14% Glycine = 12% Usually it is convenient to dissolve the aluminium hydroxychloride material in the water required and incorporate a mutual solvent for the solution and the lower alkyl (e.g. ethyl) silicate. Examples of suitable solvents include the water-miscible alcohols, such as ethanol. propanol, isopropanol and ethanediol.

Other aluminium hydroxyhalide materials may be treated similarly.

For aluminium hydroxyhalide-glycol complexes, such as the aluminium hydroxychloride-propylene glycol complexes, it is convenient to dissolve the complex in a solution of the lower alkyl (e.g. ethyl) silicate and an alcohol such as ethanol. Any excess solvent alcohol may be removed by distillation. Solvents such as ethanol usually contain ca 1% water; this water can be used as the water required in the reaction.

To obtain fibres and/or transparent coherent gels the reaction temperature is preferably 60"C or higher.

Depending on the reaction temperature and the reaction time, the resulting solution sets to a transparent coherent gel and fibres may be obtained from the resulting solution before it sets to a transparent coherent gel. For fibre preparation, the use of hydroxy complexes of aluminium hydroxy halides is preferred. It is imDortant to note that the formation of fibres and transparent coherent gels according to the present invention does not need the gelation inducing agent or accelerator necessary for binding refractory grains using the solutions containing silicon and aluminium whose preparation is described in British Patents 1,356,248 and 2,004,263, also U.S. Patent 3,979,215.

To be able to form fibres and to obtain transparent coherent gels, the solution must be homogeneous.

The amount of water and the amount of solvent are therefore important. The order of addition of reagents is also important. Preferably the solution contains silicon and aluminium in the oxide stoichiometry required for mullite, an aluminium silicate of the approximate formula 3A12O3. 2SiO2. The fibres and the transparent coherent gels obtained may be dried and fired to remove any remaining organic material.

Fibres made according to the present invention may be used in optical equipment and procedures in which fibres are required (fibre optics). They may also be used as thermal insulating materials, also in the construction of thermal insulating units based on fibrous materials. For use in thermal insulation applications the fibres may be used as prepared, or they may first be dried and fired to remove any remaining organic material. Fibres made according to the present invention may be used to manufacture a lining element for the hot-face surface of a furnace following the procedures set out in British Patents 1,466,241 and 1,481,571. They may also be used in the construction of the thermal insulating units and in the procedures described in U.S. Patents 4,194,036 and 4,324,602, also in British Patents 1,548,866 and 1,548,867.They may also be used in the manufacture of the two-layer heat insulating liner for furnace construction which is described in British Patent No. 1,555,459. and in U.S. Patent 4,344,753. Transparent coherent gels made according to the present invention may be used as sight-glasses for furnaces and in the manufacture of lenses for cameras required to be used at high temperatures.

The invention is illustrated by the following examples.

Example 1 16.49 of aluminium chlorhydrate Al2(OH)5CI (CHLORHYDROL or MICRO-DRY material) was dissolved in 16.4 cm3 of distilled water. To this solution was added, with vigorous stirring, a solution of 10g technical ethyl silicate (SiO2 equivalent to 40% by weight) in ethanol. The mixture was brought to reflux temperature and refluxed. Table I gives the volume of ethanol used; the time to reach reflux temperature; the reflux time and the gelation characteristics. Gelation occurred about 5 minutes after the time of refluxing.

TABLE I - Effect of ethanol solvent Vol.of ethanol Time to reach Reflux time Gel Charac added (cm3) reflux (min) min. teristics 25. 22 6 Slightly Cloudy 35 16 13 -ditto 45 34 16 -ditto 55 18 26 Clear (i.e.

homogenous) 65 12 43 Cloudy 85 25 67 Cloudy 105 10 95 Cloudy 125 15 140 Cloudy All gels were coherent gels. Coherency does not necessarily equate with homogeneity and hence transparency.

Example 2 16.49 of aluminium chlorhydrate Al2(OH)5CI (CHLORHYDROL or MICRO-DRY material) was dissolved in varying amounts of water. This solution was vigorously stirred and then a solution of 109 technical ethyl silicate (SlO2 equivalent to 40% by weight) in 55 cm3 of ethanol was added. The resulting mixture was brought to reflux temperature. Table II gives the volume of water used; the reflux conditions and the gelation characteristics.

TABLE II - Effect of water Vol.of water Time to reach Reflux time Gel Charac added (cm3) reflux (min) (min) teristics 37.4 2 45 Very Cloudy 34.4 4 38 Cloudy 31.4 5 33 Very Cloudy 28.4 10 23 Cloudy 25.4 20 22 Cloudy 22.4 2 26 Cloudy 19.4 3 27 Cloudy 13.4 4 26 Slightly cloudy (almost trans parent) Gelation occurred about 5 minutes after refluxing ceased. All gels were coherent gels.

Example 3 16.49 of aluminium chlorhydrate Al2(OH)5CI (CHLORHYDROL or MICRO-DRY material) was dissolved in 16.4 cm3 of water. To this was added a solution of 10g technical ethyl silicate (SiO2 equivalent to 40% by weight) in 55 cm3 of ethanol. Table III gives the reaction temperature; the time required for gel formation, being the total of time of heating plus gelation time, also the gel characteristics.

TABLE III - Effect of temperature Reaction Temperature Time required to Gel character "C form gel (min) istics 75 45 Clear 70 56 Clear 65 64 Clear 60 75 Clear 55 92 Slightly cloudy 50 125 Slightly cloudy All gels were coherent gels.

Example 4 13.449 of aluminium chlorhydrate propylene glycol complex sold under the Trade Mark REHYDROL as REHYDROL II were dissolved in a solution of 27 cm3 ethanol and 5.0 of technical ethyl silicate (SiO2 equivalent to 40% by weight). Then varying amounts of water were added and the resulting solutions refluxed to give gels having molar ratio At203: SlO2 as 2.88 : 2. Gelation occurred about 5 minutes after refluxing ceased. Table IV gives the amount of water added; the heating times and the gel characteris tics.

TABLE IV - Gels formed from aluminium chlorhydrate propylene glycol complex Vol. of water Time to reach Reflux Time Gel character added (cm3) reflux (min) (min) is tics 2.5 10 83 Slightly cloudy 3.5 12 89 Clear 4.5 5 67 Slightly cloudy 5.0 33 82 Very clear 5.5 8 83 Very clear 6.5 11 102 Slightly cloudy 7.5 13 52 Slightly cloudy All gels were coherent gels. A molar ratio A12O3:SiO2 = 2.88:2 is in the mullite range of the alumina-silica system.

Example 5 In the following series, 13.44 g of the aluminium chlorhydrate propylene glycol complex sold under the trade mark of REHYDROL as REHYDROL II was dissolved in a solution of 5.0g technical ethyl silicate (SiO2 equivalent to 40% by weight) and varying amounts of ethanol; then varying amounts of water were added to the resulting solution. These solutions were refluxed giving very viscous liquids (in some cases temperatures were kept below reflux). Fibres were formed by inserting into and pulling out of the solution a glass rod 10 mm in diameter. Table V gives the condition under which the fibres were formed, also the properties of the resulting fibres.

TABLE V - Formation of fibres from aluminium chlorhydrte propylene glycol complex Vol. of ethanol (cm ) Vol. of water (cm ) Time to reach Reflux Time (min) Length of fibre Reflux (min) (inches) 15 2.5 8 31 ca 2 20 2.5 10 63 ca 15 2.5 6 33 ca 17.5 2.5 7 43 ca 17.5 1.55 9 75 -1 22 5.5 2 30 -1 17.5 5.5 5 30 17.5 1.75 17.5 1.25 70-79 C for 70 min 3 17.5 0.75 70-79 C for 55 min 4 - 5 17.5 0.55 70-79 C for 77 min 4 17.5 0 70-79 C for 112 min 4 (Water obtained) (from solvent) 4 90 Solution left to (ethanol) stand for 4 days gave fibres 3" long.

Example 6 13.44 g of the aluminium chlorohydrate-propylene glycol complex sold under the Trade Mark REHY DROL as REHYDROL II was dissolved in a solution of 5.0g technical ethyl silicate (SiO2 equivalent to 40% by weight) in varying amounts of ethanol. In some cases varying amounts of water were added to the resulting solution. Varying amounts of ethanol were removed by distillation under reduced pressure and the residue poured into a sample tube and periodically tested for fibre formation by inserting into and pulling out from the residue a glass rod 10mm in diameter. The results are given in Table VI. All gels were coherent gels.

TABLE VI - Preparation of fibres Vol. of EtOH Vol. of H2O Boiling point Time to Time at Vol. of Comments Initially Initially (B.P.) of reach B.P. Ethanol (cm ) (cm ) solution ( C) B.P.(mins) (mins) removed (cm ) 27 0 68 28 22 13 -1" fibre formation immediately. After ca 24 hours fibre up to ca 20" formed.

The solution gelled to a clear gel (yellow tinge) after another period of 4.5 hrs.

27 0 59 15 16 15.5 3" fibre formation immediately. After 1 hr. 6" fibre formed. After another 1.75 hrs fibres up to 20" could be formed. After a further period of ca 21.5 hrs fibres of 3-4" formed. Gelles to a clear gel (yellow tinge) overnight.

27 0 63 20 15 18 20" fibres immediately; ca 24 hrs later - 12" fibres.

The solution gelled to a clear gel (yellow tinge) after another period of 3.5 huors.

27 0 63 12 42 20.5 Soln. almost gelles in flask but fibres up to 20" could be pulled immediately. After ca 6.5 hrs 6" fibres could be formed. Soln. nearly completely gelles after another period of 19.5 hrs to a pale yellow clear gel.

TABLE VI - Preparation of fibres (continued) Vol. of EtOH Vol. of H2O Boiling point Time to Time at Vol. of Comments Initially Initially (B.P.) of reach B.P. Ethanol (cm ) (cm ) solution ( C) (mins) removed (cm ) 17.5 0 63 20 17 8 2 fibres immediately.

After ca 3/4 hrs-6" fibre.

After further period of ca 1 1/4 hrs - 8" fibres.After further period of ca 19 3/4 hrs 14" fibres- After further period of ca 22 hrs - 6" fibres. Gelled in further period of 6 hrs to pale yellow clear gel.

27 0.75 39 6 17 16 Very viscous/cloudy after removing 16cm of solvent 4" fibres pulled immediately After ca 1 hr-10" fibres.

Gelled overnight to a slightly cloudy gel.

27 3.3 62 5 18 20 Very pale yellow viscous soln obtained.2" fibre formed immediately.After ca hr 12" fibres could be pulled.

Gelled overnight to clear gel.

27 5.5 46 2 20 20 2"fibres immediately. After ca 2 hrs 8" fibres could be formed.Gelled overnight to a clear gel.

Example 7 In the following series 13.449 of the aluminium chlorhydrate-propylene glycol complex sold under the Trade Mark of REHYDROL as REHYDROL II was dissolved in a solution of 5.09 technical ethyl silicate (SiO2 equivalent to 40% by weight) in varying amounts of ethanol. In some cases varying amounts of water were added. The resulting solutions were allowed to stand at ambient temperature or at 40"C and periodically tested for fibre formation by inserting into and pulling out of the solution a glass rod 10mm diameter. The results are given in Table VII.

TABLE VII - Effect of water and temperature on fibre formation [A.T. = ambient temperature] Vol. of Vol. of Temp. Results Ethanol Water fDCJ (cm2) (cm3) 27 0 A.T. Clear solution : after 41 hrs a pale yellow solution was ob tained. No indication of fibre formation after a further period of 25 hours.

22.5 0 A.T. Clear solution : after 42 hrs gave a very pale yellow soln.

After further period of 24 hrs crust formation and 3"-4" fibres formed. After further period of 4 hrs. 4"-5" fibres could be formed 17.5 0 A.T. Slightly cloudy soin, which gave a very pale yellow viscous soln.

on standing (with slight crust formation).1-2" fibre could be pulled ca 43 hrs later. After further period of 6.5 hrs 4" fibres could be pulled.

further period of 17.5 hrs 12" fibres could be pulled. After further period of 4 hrs. 12" fibre could still be pulled.

27 0 40 Clear solution; after 21 3/4 hours gave a very pale yellow viscous soln. After 24 hrs. 1" fibres could be pulled. After further period of 4 hrs 1" fibres could be pulled.

22.5 0 40 Clear solution; after 22 hrs gave a very pale yellow vis cous soln. from which 1-2" fibres could be pulled. After further period of 24 hrs a thick crust was formed and 5" fibres could be pulled. After further period of 4 hrs. 6" fibres could be pulled.

17.5 0 40 Slightly cloudy soln. after 21 3/4 hrs. a very pale yellow viscous soln. a crust was formed and 5" fibres could be pulled. After a further period of 24 hrs - thick crust, 3-4" fibres; after fur ther period of 4 hrs a very vis cous clear soln. resulted from which 1/4" fibres could be pulled.

TABLE VII - Effect of water and temperature on fibre formation [A.T. = ambient temperature] (continued) Vol. of Vol. of Temp. Results Ethanol Water pC) (cm2) (cm2) 17.5 0.75 A.T. Slightly cloudy soln. after 20.5 hrs gave a very pale yellow viscous soln. After fur ther period of 24 hrs-slight crust formation, 2" fibres; after further period of 4 hrs 6 - 7" fibres could be pulled.

17.5 3.3 A.T. Clear soln. after 20 hours no detectable change. After fur ther period of 24 hrs slight crust formation no change over a further 4 hour period.

17.5 5.5 A.T. Clear solution, after a period of 48.25 hours no detectable change occurred.

17.5 0.75 40 Cloudy solution, after 20 hrs gave a very pale yellow vis cous soln. from which 4" fibres could be pulled. After a further period of 24 hrs thick crust formation, - fibres. After further period of 4 hrs. gellation was almost complete 17.5 5.5 40 Cioudy soln. after ca 19.5 hr gave a clear soln. with a slight crust. After a further period of 24 hrs - thin crust, 21 fibres. After a further period of 4 hrs - 1 to 2 " fibres.

17.5 3.3 40 Cloudy soln. after ca 19.25 hrs gave a clear solution with a slight crust. After a further period of 24 hrs.-thin crust, 2" fibres. After a further period of 4 hrs.- 1 to 2" fibres.

Example 8 Fibres having the molar ratio A12O3:SiO2 of 2.88 : 2 were obtained by the following preferred method.

209 of technical ethyl silicate (SiO2 equivalent to 40% by weight) was added to 70 cm3 ethanol; this solution was vigorously stirred while 53.769 of the aluminium chlorhydrate polyethylene glycol complex sold under the Trade Mark of REHYDROL or REHYDROL II was slowly added. To the solution 3cm3 of water were added, then the mixture was brought to reflux temperature and kept at this temperature for 1 to 19 hours. Fibres up to 9 inches in length could be drawn for a period of 2 to 2- hours by inserting into and pulling out from the solution a glass rod 10mm in diameter.

Example 9 A transparent, coherent gel was obtained by the following method. A solution of 109 technical ethyl silicate (SiO2 equivalent to 40% by weight) in 55 cm3 ethanol was added to a vigorously stirred solution in aluminium chlorhydrate Al2(0H)5CI (CHLORHYDROL or MICRO-DRY material) in 16.4 cm3 water. This gave a slightly cloudy solution which became clear on heating to 65 - 70"C. The solution was heated to ca 77"C in a period of about 10 minutes becoming very viscous on holding at this temperature for about 30 minutes. Gelation occurred about 5 minutes after heating ceased.

Example 10 Fibres having the molar ratio of A12O3:SlO2 as 2.88:2 were obtained by the following preferred method.

80.649 of the aluminium chlorohydrate-polyethylene glycol complex sold under the Trade Mark of RE HYDROL as REHYDROL II was dissolved in a solution of 30g technical ethyl silicate (SiO2 equivalent to 40% by weight) in 162 cm3 ethanol. Then 108 cm3 ethanol was removed under reduced pressure at a temperature between 80"C and 90"C in a period of about 20 minutes, using a rotary evaporator, giving a highly viscous solution. Fibre formation was tested by inserting into and pulling out from the solution a glass rod 10mm in diameter Fibres could be pulled from the solution immediately; fibres up to ca 36" long were formed. Fibres could be pulled from the solution for a period > 24 hours.

After firing to 1000"C for one hour, the fibres obtained remained transparent.

Claims

1. A method of preparing a gel, optionally in the form of a fibre, such method being based on a precursor solution containing aluminium and silicon, optionally present in the oxide stoichiometry required for mullite, from which fibres and/or transparent coherent gels can be obtained and prepared by reacting water, a lower alkyl silicate and an aluminium hydroxy haiide of the general formula A12(OH),X6., or a polymer, hydrate, hydroxy complex or zirconium complex thereof, where X is CI, Br or I and n is less than 6, in a water-miscible alcohol solvent, optionally at a temperature of 60"C or higher.

2. A method as claimed in Claim 1 in which the gel is in the form of a fibre and the precursor solution containing aluminium and silicon is prepared from ethyl silicate and a hydroxy complex of an aluminium hydroxy chloride of the general formula Al2(OH)Cl6., where n is 5 or less.

3. A solution containing aluminium and silicon, optionally present in the oxide stoichiometry required for mullite, from which a homogeneous coherent gel, optionally in the form of a fibre, can be obtained, prepared by reacting water, a lower alkyl silicate and an aluminium hydroxyhalide of the general formula Al2(OH),X or a polymer, hydrate, hydroxy complex or zirconium complex thereof, where X is Cl, Br, or I and n is less than 6, in a water-miscible alcohol solvent.

4. A solution as claimed in Claim 3 from which a gel in the form of a fibre can be obtained, prepared by reacting water, ethyl silicate and a hydroxy complex of an aluminium hydroxy chloride of the general formula A12(OH),C16., where n is 5 or less.