GB2170189A

GB2170189A - Materials

Info

Publication number: GB2170189A
Application number: GB08601503A
Authority: GB
Inventors: Dr Edward Sydney Lane
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1985-01-25
Filing date: 1986-01-22
Publication date: 1986-07-30
Also published as: GB2170189B; GB8501882D0; GB8601503D0

Abstract

The present invention relates to the preparation of materials, and finds application in the preparation of particles of materials. The invention provides a method for the preparation of an inorganic material in a selected physical configuration which includes the step of hydrolysing, in the presence of a protective colloid, an organic compound containing an element, or elements, appropriate to the inorganic material to be prepared in the presence of a protective colloid. The organic compound may be in a physical configuration during hydrolysis appropriate to a physical configuration to be prepared. The invention also provides a method for the preparation of an inorganic material by hydrolysing an organic compound under heterogeneous conditions. High pore volume silica may be prepared.

Description

SPECIFICATION Materials The present invention relates to the preparation of materials, and finds application in the preparation of particles of materials.

According to one aspect of the present invention a method for the preparation of an inorganic material in a selected physical configuration includes the step of hydrolysing, in the presence of a protective colloid, an organic compound containing an element, or elements, appropriate to the inorganic material to be prepared, the organic compound being, during hydrolysis, in a physical configuration appropriate to the physical configuration to be prepared.

According to a further aspect the present invention provides a method for the preparation of an inorganic material which includes the step of hydrolysing, under heterogenous conditions, an organic compound containing an element, or elements appropriate to the inorganic material to be prepared.

By "under heterogenous conditions" we mean that the hydrolysis is carried out in a system having more than one phase, the organic compound being present throughout hydrolysis in one of these phases. Preferably the hydrolysis is carried out in a two phase liquid system.

In one embodiment the inorganic material is prepared in particulate form the organic compound being in dispersed form during the hydrolysis.

The organic compound may be dispersed during hydrolysis by dispersing it in a liquid with which it is substantially immiscible.

The particulate form may be for example microspheres, in which case the organic compound may be dispersed in droplet form during hydrolysis thereby to produce the inorganic material in the form of microspheres.

By "protective colloid" it is meant a substance capable of inhibiting aggregation of selected physical configurations (e.g. microspheres) produced by hydrolysis. Generally such protective colloids are water soluble compounds having groups capable of sorption onto the surface of the inorganic material. Examples of protective colloids that may be used in accordance with the present invention are polyvinyl alcohols, water soluble cellulose ethers, dextran and hydroxy alkylated natural gums such as hydroxyalkylated guar gum. Monomeric compounds such as glucose, glycerol and triethanolamine may also be used as protective colloids.

By "element, or elements, appropriate to the inorganic material to be prepared" it will be understood that the organic compound is chosen on the basis of the element, or elements, it is required to obtain in the inorganic material. For example, if it is desired to produce silica the organic compound chosen for hydrolysis can be an organic silicon compound (e.g. an alkyl silicate).

It will be appreciated that the inorganic material as formed by the hydrolysis step will generally contain organic material (e.g. from the organic compound and/or the protective colloid) and that this inorganic material will generally be treated to remove the organic material, (e.g. by boiling in water or heating in air). By incorporation of organic material in the inorganic material produced upon hydrolysis, porosity may be introduced into the inorganic material. Thus, for example, sufficient protective colloid of organic nature may be used such that on heating, carbon from the organic protective colloid acts as a fugitive additive thereby to give porosity.

In the preparation of silica in accordance with the present invention, of the organic silicon compounds available we prefer to use alkyl silicates.

In one particular embodiment of the invention there is provided a method for the preparation of silica microspheres which method includes the step of hydrolysing an alkyl silicate, in the presence of a protective colloid, the alkyl silicate being dispersed in droplet form during hydrolysis.

Of the alkyl silicates that may be used in accordance with the present invention it is preferred to use ethyl silicate (i.e. tetraethoxysilane) (e.g. as obtainable from BDH Ltd.) or mixtures of this compound with ethyl polysilicate (e.g. those commercially available from Monsanto Chemicals Ltd. such as the mixture sold under the Trade Name Silester OS or the alcoholic solution of a hydrolysed ethyl silicate sold under the Trade Name Silester AR).

Examples of other organic compounds suitable for use in accordance with the present invention are alkyl titanates (e.g. tetrabutyl titanate as available from BDH Ltd.) and aluminium alkoxides (e.g. aluminium isopropoxide).

By using two or more organic compounds it is possible, in accordance with the present invention, to prepare inorganic materials containing a variety of elements. Thus, for example, by using a mixture of an alkyl silicate and an alkyl titanate it is possible to produce a siliceous material containing titania. Similarly by using a mixture of an alkyl silicate and an aluminium alkoxide it is possible to produce a siliceous material containing alumina.

In one embodiment of the present invention the organic compound is dispersed in a liquid containing a protective colloid and a hydrolysing agent to achieve the hydrolysis.

In accordance with the immediately preceding embodiment the liquid is preferably an aqueous solution of the protective colloid and hydrolysing agent.

In another embodiment the organic compound is dispersed in a liquid containing a protective colloid, and a hydrolysing agent is added subsequently.

In a further embodiment the organic compound and the hydrolysing agent are mixed together and subsequently dispersed in the protective colloid.

In both of the immediately preceding embodiments of the invention the liquid is preferably an aqueous solution of the protective colloid.

Where the protective colloid is an aqueous solution it is preferred that the organic compound is dissolved in a diluent prior to dispersion therein, said diluent being immiscible with water, so as to assist in dispersion into droplet form. Thus, for example, the organic compound and diluent can be stirred into an aqueous solution of a protective colloid and a hydrolysing agent to disperse the organic compound and diluent as droplets in the aqueous solution.

Alternatively, for example, the organic compound and diluent may be stirred into an aqueous solution of a protective colloid to disperse the organic compound and diluent as droplets in the aqueous solution and the hydrolysing agent added subsequently.

Preferred diluents for the preparation of microspheres of silica with high pore volume are halogenated hydrocarbons with boiling points below 100"C. One example is methylchloroform. Such diluents enable the silica microspheres containing the diluent to be removed from a hydrolysing system by settling and removal of the diluent by heating the silica microspheres in water. As an alternative the obtained microspheres containing diluent can be filtered and the diluent allowed to evaporate in a current of air (which air may, optionally, be heated).

If desired the alkyl silicate may be mixed with other alcoholates prior to hydrolysis so as to give a final product comprising mixtures of oxides. Examples of such suitable alcoholates are alkyl titantes (e.g. tetrabutyl titanate or aluminium isopropoxide). Silica having a high pore volume may find appiication as a catalyst support for use in a number of catalysis processes (e.g. polymerisation).

In accordance with the present invention the hydrolysing agent can be a base such as ammonium hydroxide solution. A wide range of concentrations of this solution can be used, but in general we have found that it is not usually necessary to employ solutions having > 30% ammonia by weight.

As alternatives to ammonium hydroxide, basic amines may be used as the hydrolysing agent (e.g.

morpholine, cyclohexylamine, dicyclohexylamine, benzyl-dimethylamine, and related compounds, and triethanolamine, monoethanolamine and hydrazine.

As a further alternative, given by way of example, the organic compound, diluent and hydrolysing agent may be mixed together and subsequently dispersed in a solution of the protective colloid.

The diluent may be, for example, an alcohol such as n-hexanol, 2-ethyl hexanol, isopropanol) or a glycol such as a polypropylene glycol (e.g. polypropylene glycol 400 or 1035 available from BDH Ltd.). Further examples of diluents that may be used are esters (e.g. ethyl acetate), hydrocarbons (such as toluene, benzene, hexane or heptane and mixtures thereof) and halogenated hydrocarbons (e.g. chlorinated hydrocarbons such as chloroform, methylchloroform, 1, 1, 1-trichloroethane and carbon tetra chloride).

The amount of diluent that may be used to assist in dispersion into droplet form varies with the nature of the diluent and the protective colloid chosen. However, in general no improvement in dispersion is achieved if more than an equal volume of diluent to the volume of the organic compound is used. The size and density of the microspheres produced can be influenced by the choice and quantity of diluent used.

For example it has been found that, using a method in accordance with the present invention, it is possible to obtain microspheres of silica with high pore volumes in excess of 2 to 3 ml per gram. This may be achieved by using an amount of a substantially water-insoluble diluent up to 3 times the volume of alkyl silicate. Microspheres of silica produced in this way are of sufficient rigidity to allow separation from hydrolysing mixture and subsequent removal of the diluent by volatilisation, solvent extraction or any other suitable processes.

It will be appreciated that where a base is used as hydrolysing agent the process is operating under alkaline conditions.

Where water is present in the reactants used in carrying out the present invention (e.g. where the protective colloid is used in an aqueous solution) it will be appreciated that an inorganic material as obtained after the hydrolysis step will generally be in the form of an hydrous gel which may also contain some protective colloid or some hydrolysing agent.

In accordance with another embodiment of the invention, it is possible to introduce further elements (e.g. metal species) during the hydrolysis, by carrying out the hydrolysis step in the presence of an element capable of forming an ammine. The element can be present as an amine complex in excess of the complexing amine. Suitable elements for introduction into the inorganic material in this way are, for example, copper, zinc, silver, chromium and nickel. The inorganic material prepared in this way then includes some ammine groups (e.g. metal ammine groups).

In some preparations we have found it advantageous to use a hydrolysis promoting agent (e.g. to aid preparation of dense microspheres in relatively short reaction times (e.g. - 1 hour). Examples of hydrolysis promoting agents are: Ammonium salts (e.g. ammonium halides, carbonate, acetate chloracetate and quaternary ammonium salts) and betaines. It has been found that quaternary ammonium salts of the kind disclosed in the Complete Specification of B.P. No. 1, 303, 353 can be used as hydrolysis promoting agents.The quaternary ammonium salts dislosed therein may be represented by the formula:

where X- is a halide ion and R1, R2, R3 and R4 each are aliphatic, aryl, alkoxy ether radicals or heterocyclic radicals, with at least two of the foregoing groups being lower alkyl (i.e. containing < 12 C atoms) and at least one of the foregoing groups being an aliphatic radical containing at least 12 C atoms, an aryl, a heterocyclic or an alkyl ether radical. In B.P. Specification No. 1, 303, 353 "aryl" is used broadly to refer to a hydrocarbon residue containing an aromatic ring.

The quaternary ammonium salts of the above general formula disclosed in B.P. 1, 303, 353 are (cationic) surface active agents. It has been found that, however, quaternary ammonium salts containing small alkyl groups (e.g. tetramethyl-ammonium halides) which normally are devoid of surface active properties are effective in promoting hydrolysis of, for example, alkyl silicates in aqueous amine solutions to form dense microspheres.

The use of a hydrolysis promoting agent may be omitted, it has been found that this generally means that the reaction time is longer or that more vigorous reaction conditions or a more reactive hydrolysing agent is required.

The choice of reagents used, and particularly the choice of hydrolysing agent and hydrolysis promoting agent (if used), may be used to influence the nature of the microspheres produced in accordance with the present invention.

The hydrolysing agent should be sufficiently basic to hydrolyse the compound within practically convenient periods of time.

Generally combinations of reagents (i.e. the compound, organic liquid, protective colloid, hydrolysing agent and hydrolysis promoting agent (if used), are chosen in accordance with the present invention such that during hydrolysis there is the minimum formation of water soluble substances (e.g. water soluble polysilicic acids), which would pass into any aqueous media present.

Preferred hydrolysing agents are cyclohexylamine, dicyclohexylamine, benzyl dimethylamine, morpholine and ammonia, and preferred hydrolysis promoting agents are the quaternary ammonium salts Hyamine 2389 (ex BDH Ltd.), tetramethyl ammonium bromide and tetraethyl ammonium bromide. (Hyamine 2389 is an approximately 50% by weight solution of methyldodecyl benzyl trimethyl ammonium chloride and methyl dodecylxylene bistrimethylammonium chloride. "Hyamine" is a Trade Name of Rohm and Haas).

For large (up to - 1000 > m) microsphere production it has been found that it is convenient to use cyclohexylamine as the hydrolysing agent in combination with a lower alkyl ammonium halide (i.e. alkyl = methyl or ethyl) as the hydrolysis promoting agent. For small 0.1 - 201lm diameter) microsphere production it has been found that it is convenient to use cyclohexylamine in combination with longer chain quaternary ammonium salts (e.g. having at least one chain of about 12 C atoms, e.g. Hyamine 2389).

It will be appreciated that the behaviour of various combinations of reagents differ. However, satisfactory combinations of reagents can be easily confirmed by simple experimentation.

The size of microspheres which may be produced in accordance with the present invention can be, for example, in the size range of < wm to 1000 > m. In addition to the influence of the choice of reagents on the size of microspheres (as hereinbefore mentioned) the size can be influenced, where agitation is employed to disperse the inorganic compound in droplet form, by the degree of agitation used. Also the presence of surface active agents may be used to influence interfacial surface tension and hence the size of droplets. The usual effect of the addition of a surfactant is to reduce the size of microspheres produced. Both ionic and non-ionic surfactant may be used.Examples of cationic surfactant are the quaternary ammonium salts hereinbefore disclosed and an example of an anionic surfactant is Sarkosyl 0 (ex Geigy Chemical Co. Ltd., England). An example of a non-ionic surfactant is Tergitol NPX (alkyl phenyl ether of polyethylene glycol, ex BDH Ltd., England). Since certain hydrolysis promoting agents may have surface active properties, (e.g. quaternary ammonium salts as hereinbefore disclosed) it will be appreciated that in some circumstances the hydrolysis promoting agent can have a dual function (e.g. in promoting hydrolysis or influencing size or acting as a protective colloid).

It is also possible for either or both the hydrolysing agent (e.g. amine) and the hydrolysis promoting agent to perform the function of diluent for the organic compound in addition to performing hydrolysing or hydrolysis promoting functions.

As herein before disclosed where water is present in the reactants used in accordance with the present invention (e.g. where the protective colloid is used in an aqueous solution) it will be appreciated that an inorganic material as obtained after the hydrolysis step will generally be in the form of an hydrous gel which may also contain some protective colloid, some hydrolysing agent or some diluent.

Also, by use of water insoluble hydrolysing agents (e.g. amines) or hydrolysis promoting agents (e.g.

quaternary ammonium salts) such as benzyl dimethylamine, Primene JM and Aliquat 336, these agents can be retained in the inorganic microspheres of hydrous gel and thereby modify the gel structure thereof.

The hydrolysis can be terminated before completion (at any time sufficient mechanical strength and rigidity has been obtained) to enable microspheres having unreacted centres to be obtained. If desired, unreacted reactants can be leached therefrom (e.g. by ethanol or acetone) to give hollow or very porous microspheres.

Termination of the hydrolysis can be effected, for example, by using the hydrolysis promoting agent in an aqueous phase and the other reactants (hydrolysing agent, organic compound and diluent) in an immiscible phase such that microspheres can be filtered off as soon as the hydrolysis has proceeded as far as is required.

Hydrous gel microspheres produced in accordance with the present invention are preferably at least partially dried before use. They may be further heated to, say - 600"C in air to burn off residual organic substance and subsequently at higher temperature (e.g. - 1000"C) to produce ceramic microspheres.

Microspheres prepared in accordance with the present invention may be applicable as chromatographic sorbents, catalytic supports (e.g. for use in fluidised systems), fillers and in a variety of ceramic applications.

The invention further provides in another aspect an inorganic material in the form of microspheres, produced by a method in accordance with the invention.

The invention will now be further described, by way of example only, with reference to Examples 1 to 14 and with reference to the single Figure 1 of the accompanying drawing which shows pore volume and pore size distribution for the product of Example 14.

Example 1 An aqueous ammoniacal solution of polyvinyl alcohol was prepared by adding 50 mls of a 5% by weight solution of polyvinyl alcohol (Moviol N 85-88 ex Hoechst UK Ltd., Brentford, England) to 200 mls of 0.880 SG ammonia with stirring. A mixture of 40 mls of ethyl silicate (ex BDG Ltd.) and 20 mls of nhexanol was added in a thin stream to the stirred ammoniacal solution and the resulting dispersion (of organic droplets in the aqueous ammoniacal solution) allowed to stir for half an hour. The resulting mixture was poured into one litre of distilled water and allowed to settle overnight. The supernatant liquor was decanted from the residue, which was reslurried in 500 mls of distilled water.Steam at one atmosphere pressure was passed into the suspension for a further hour. The suspension was then filtered and the filter cake washed with distilled water and dried in air at 80"C. The product was found to consist essentially of microspheroidal silica passing a 90pm sieve.

Example 2 An aqueous ammoniacal solution was prepared by adding 50 mls of a 5% by weight solution of polyvinyl alcohol (Moviol N 85-88) to 200 mls 0.880 SG ammonia containing 10 mls Hyamine 2389 (approx 50% by weight solution of a mixture of methyldodecyl benzyl trimethylammonium chloride and methyl dodecylxylenebistrimethylammonium chloride, ex BDH Ltd.). (Hyamine is a Rohm and Haas Company Trade Name). A mixture of 20 mls ethyl silicate and lOmls n-hexanol was added to the stirred ammoniacal solution in a thin stream and the resulting dispersion (of organic droplets in the aqueous ammoniacal solution) allowed to stir for half an hour. The resulting mixture was centrifuged and the residue reslurried with distilled water and recentrifuged.This operation was repeated three times after which the solid residue was dried in air at room temperature. It comprised microspheroidal silica in the size range 1-50im the bulk being 20 m diameter.

Example 3 An aqueous ammoniacal solution was prepared by adding 50 mls of a 2.5% by weight aqueous solution of hydroxypropylmethyl cellulose (Methocel 90 HG 40 ex Dow Chemical Co. Ltd.) to 200 mls of a 0.880 SG ammonia solution containing 0.5 gm of Sarkosyl O (Geigy Chemical Co. Ltd.). A mixture of 40mls of ethyl silicate and 20mls n-hexanol was added in a thin stream to the stirred aqueous ammoniacal solution and the resulting dispersion (of organic droplets in the aqueous ammoniacal solution) allowed to stir for one hour. It was diluted with 500 mls of distilled water and centrifuged. The solid residue was slurried in water and steam at one atmosphere pressure passed through the resulting suspension for one hour.The suspension was then centrifuged, and the cake of solid residue washed with five 200 mls portions of methylated spirits and dried in air at room temperature. The resulting silica gel was in the form of microspheres, the majority being less than 2 Am diameter in size.

Example 4 An aqueous solution was prepared by adding 100 mls of 2.5% by weight aqueous solution of Methocel 90 HG to 450 mls of water containing 50 mls of monoethanolamine and 10 mls of Hyamine 2389. To this solution a mixture of 40 mls of ethyl silicate, 20 mls tetrabutyl titanate (ex BDH Ltd.) and 20 mls n-hexanol was added in a thin stream with stirring and the resulting dispersion (of organic droplets in the aqueous solution) stirred for one hour at room temperature. The resulting mixture was centrifuged and the solid residue repeatedly slurried with water and recentrifuged.The solid residues were finally dried with five 100 ml portions of methylated spirits followed by exposure to air at room temperature. The residue comprised siliceous titania microspheres, the majority being less than 10 > m in diameter.

Example 5 50 gm of hydrated copper sulphate were dissolved in 150 mls of distilled water and 150 mls of SG 0.880 ammonia added to form a deep blue cuprammonium solution. 50 mls of 5% by weight aqueous polyvinyl alcohol (Moviol N 85-88 was added to the cuprammonium solution and stirred in. A mixture of 40 mls ethyl silicate and 20 mls n-hexanol was added to the cuprammonium-polyvinyl alcohol solution in a fine stream of drops with continued stirring. After one hour the dispersion was centrifuged and the residue repeatedly washed with distilled water. It was then dried by exposure to air at room temperature.

Blue microspheres were obtained comprising siliceous material carrying cuprammonium species, the majority being below 20iim diameter in size.

Example 6 An aqueous solution was formed by adding 30 mls of a 5% by weight aqueous solution of polyvinyl alcohol (Moviol N 85-88) to 200 mls of SG 0.880 ammonia solution. To this stirred aqueous solution was added a mixture of 10 mls of ethyl silicate with 5 mls of 2-ethylhexanol in the form of a thin liquid stream. The resulting suspension was agitated for a further one hour and then filtered. The residue was reslurried in distilled water (500 mls) and steam at one atmosphere passed through for one hour. Filtration of the resulting suspension after washing and air-drying yielded gel siliceous spheres 50pm to 100 > m diameter.

Example 7 50 mls of glycerol was added to 200 mls of concentrated ammonia solution. This mixture was stirred and a mixture of 10 mls of ethyl silicate with 10 mls of n-hexanol added dropwise. The resulting suspension (dispersion of organic droplets in aqueous solution) was stirred for 30 minutes centrifuged and the solid residue repeatedly washed with distilled water. After drying in methylated spirits microspheroidal siliceous material was obtained.

Example 8 A mixture of Silester OS (35 mis)* and cyclohexylamine (5 mls) was added in a thin stream to a stirred solution of 300 mls of water containing 0.15 g of Methocel 90 HG 40. Tetraethylammonium bromide (3 gm) was added to the stirred dispersion (of organic droplets in aqueous solution) and the reaction continued for two hours. When stirring was stopped a granular layer of spheres settled out on the bottom of the reaction vessel and the supernate was decanted. The spheres were washed three times with their own volume of water and then with three volumes of industrial methylated spirits. The colourless spheres were filtered, dried by exposure to warm air and heated to 800 C in air.The product comprised colourless, transparent silica spheres with a size distribution between 5 - 350 Wm diameter.

(*Silester OS (Registered Trademark) is a mixture of tetraethyl orthosilicate and ethyl polysilicates produced by Monsanto Ltd. It has a SG of 1.07 at 15.5 C and contains approximately 41% by weight of silica).

Example 9 100 parts of Silester OS (see Example 8) were stirred with a mixture of 4 parts Hyamine 2389 (See Example 2). 10 parts of industrial methylated spirits and 5 parts of cyclohexylamine until an homogeneous solution was formed. Over the course of one minute this solution was added to a stirred mixture of 400 mls water containing 1 g polyvinylalcohol and 2 gms of tetraethylammonium bromide to form a dispersion. After 15 minutes stirring at room temperature the resulting microspheres were decanted and filtered off in a glass sinter, and washed with water. The water wash was followed by washing with three bed volumes of industrial methylated spirits which extracted ungelled material from within the microspheres. The microspheres were allowed to soak in aqueous 2 M hydrochloric acid, drained and dried in air.The residue remained in microspheroidal form even on firing in air to 8000C.

Example 10 100 parts of Silester OS (see Example 8) were stirred with a mixture of 4 parts of Hyamine 2389 (see Example 2), 10 parts of industrial methylated spirits and 5 parts of cyclohexylamine until an homogeneous mixture was formed. During one minute this mixture was added to a stirred mixture of 400 parts of water containing 10 gm of a low molecular weight, fully hydrolysed polyvinyl alcohol and 2 parts of tetraethylammonium bromide, to form a dispersion of organic droplets in aqueous solution. After one hour's stirring at room temperature the supernate was decanted and replaced by 5% aqueous ammonium chloride solution and stirring proceeded for a further 3 hours. The resulting microspheres were decanted, filtered, washed with dilute (2 M) hydrochloric acid, dried in air at room temperature, then raised to 8000C in air during a period of 4 hours.The product was spherical silica in the size range 50 1000 Fm diameter. The yield was 33 g. The tap density of the -75 + 150 > m diameter fraction was 0.40 gms/ml.

Example 17 A mixture of 100 mls of Silester OS (see Example 8), 3 mls of cyclohexylamine, 1 ml of Span 85, 1 ml of Nonidet P40 and 20 mls of industrial methylated spirits was poured in a thin stream into a solution of 10 mls of polypropylene glycol 400 in 190 mls of water which was agitated by a high speed paddle stirrer. 2gms of tetraethyiammonium bromide was added and the mixture stirred for 15 minutes. The mixture was poured into 2 litres of water, allowed to settle and the supernate decanted. The solid residue was filtered on a glass sinter, washed with water and then with industrial methylated spirits, dried in air at 40"C and then heated to 500"C in air.The product comprised fawn coloured spheres in the 1 - 10m diameter range. The densities obtained were as follows: Mercury : 0.21 gms/ml CCI4 : 2.09 gms/ml (Span 85 is sorbitan trioleate supplied by Koch Light Ltd. Span is a registered trade mark of Atlas Chemical Industries Inc., U.S.A.).

[Nonidet P 40 is a non ionic surfactant supplied by BDH Ltd.] Example 12 A mixture of Silester AR (50 mls) and a n-hexanol (7 mls) was poured into a mixture of 1% low viscosity polyvinyl alcohol solution (100 mls) and 10% (by weight) of aqueous ammonium carbonate soln. (10 ml).

The resulting mixture was stirred for 15 minutes at room temperature and the resulting gel particles subsequently removed by filtration, washed (with dilute aq. ammonium hydroxide) and dried at room temperature in air. The particles were then calcined to 7000C in air (50"C rise/hour) to give a product comprising microspheroidal, non-cracked silica.

Example 13 To a mixture of 10% by weight aq. solution of ammonium carbonate (50 ml) and 0.880 SG ammonium hydroxide (25 mls) Silester OS (25 mls) was added. A 20% by weight low viscosity polyvinyl alcohol aqueous solution (1 ml) was added to the mixture and the mixture stirred to disperse the Silester OS as droplets.

After 30 minutes stirring at room temperature, the droplets has solidified and were then filtered off. On drying in air spheroidal silica gel particles were obtained as a product.

Example 14 A mixture of cyclohexylamine (20 ml) and methylchloroform (stabilised "Genklene" (Trade Mark) marketed by ICI Ltd.) (200 ml) was formed and Silester OS (180 ml) added thereto.

This resulting mixture was added in a thin stream to water (1250 ml) containing Hyamine 2389 (2 gm) and tetraethylammonium bromide (5 gm) stirred with a paddle stirrer.

After 20 minutes stirring (at room temperature) the mixture was allowed to settle. The settled volume of gelled spheres was approximately 500 ml. The settled layer of spheres was added to 2 I hot water containing Triton X 100 (a proprietary wetting agent supplied by BDG Ltd.) (1 gm) and the resulting mixture was heated to remove the methylchlorofrom by co-distillation (The wetting agent was used to reduce foaming during this operation).

The residue of spheres was filtered off washed with water, dried in warm air and heated to 500"C in an air oven. The resulting product was comprised of cream microspheres of < 150 > m diameter.

The nitrogen B.E.T. surface area was decided to be 169 m2/g. The pore volume and pore size distribution is as shown in the single figure 1 of the accompanying drawing. The yield of microspheres was 679.

The volume of specimen used for pore volume and pore size distribution studies was 0.83 ml. Its weight was 0.189 g. The bulk density was 0.23 g.ml-3, the apparent solid density was 0.99 g.ml-3. The specific open porosity was 3.34 ml/g,, the open pore volume 0.63 ml and percentage open porosity 76.67.

Claims

1. A method for the preparation of an inorganic material in a selected physical configuration which includes the step of hydrolysing, in the presence of a protective colloid, an organic compound containing an element, or elements, appropriate to the inorganic material to be prepared, the organic compound being, during hydrolysis, in a physical configuration appropriate to the physical configuration to be prepared.

2. A method as claimed in claim 1 wherein the organic compound is in dispersed form during the hydrolysis and the inorganic material is prepared in particulate form.

3. A method as claimed in claim 1 or claim 2 wherein the organic compound is dispersed during hydrolysis by dispersing it in a liquid with which it is substantially immiscible.

4. A method as claimed in any one of the preceding claims wherein the organic compound is dis persed in droplet form during hydrolysis thereby to produce the inorganic material in the form of microspheres.

5. A method as claimed in any one of the preceding claims wherein the protective colloid is a polyvinyl alcohol, a water soluble cellulose ether, dextran, a hydroxy alkylated natural gum, glucose, glycerol or triethanolamine.

6. A process as claimed in any one of the preceding claims wherein sufficient protective colloid of organic nature is used such that organic material is incorporated in the inorganic material produced upon hydrolysis such that on heating, carbon from the protective colloid acts as a fugitive additive thereby to give porosity.

7. A method as claimed in any one of the preceding claims wherein organic compound, protective colloid and a hydrolysing agent are brought together to achieve hydrolysis.

8. A method as claimed in any one of the preceding claims wherein the organic compound is dispersed in a liquid containing a protective colloid and a hydrolysing agent to achieve the hydrolysis.

9. A method as claimed in claim 8 wherein the liquid is an aqueous solution of the protective colloid and hydrolysing agent.

10. A method as claimed in any one of claims 1 to 7 wherein the organic compound is dispersed in a liquid containing a protective colloid, and a hydrolysing agent is added subsequently.

11. A method as claimed in any one of claims 1 to 7 wherein the organic compound and the hydrolysing agent are mixed together and subsequently dispersed in the protective colloid.

12. A method as claimed in claim 10 or 11 wherein the liquid is an aqueous solution of the protective colloid.

13. A method as claimed in any one of claims 1 to 7 wherein the protective colloid is in an aqueous solution and the organic compound is dissolved in a diluent prior to dispersion therein, said diluent being immiscible with water, so as to assist in dispersion into droplet form.

14. A method as claimed in claim 13 wherein the organic compound and diluent are stirred into an aqueous solution of a protective colloid and a hydrolysing agent to disperse the organic compound and diluent as droplets in the aqueous solution.

15. A method as claimed in claim 13 wherein the organic compound and diluent are stirred into an aqueous solution of a protective colloid to disperse the organic compound and diluent as droplets in the aqueous solution and the hydrolysing agent added subsequently.

16. A method as claimed in any one of the preceding claims wherein a diluent is used said diluent being an alcohol, a glycol, an ester, a hydrocarbon or a halogenated hydrocarbon.

17. A method as claimed in any one of claims 13 to 16 wherein the diluent is a halogenated hydrocarbon with a boiling point below 100"C.

18. A method as claimed in claim 13 to 16 wherein the diluent is n-hexanol, 2-ethyl hexanol, isopropanol, polypropylene glycol, ethyl acetate, toluene, benzene, hexane, heptane, chloroform, methylcholoform, 1,1,1-triochloroethane or carbon tetrachloride.

19. A method as claimed in any one of the preceding claims wherein ammonium hydroxide solution is used as a hydrolysing agent.

20. A method as claimed in any one of claims 1 to 19 wherein a basic amine is used as a hydrolysing agent.

21. A method as claimed in claim 20 wherein the basic amine is morpholine, cyclohexylamine, dicyclohexylamine, benzyl-dimethylamine, triethonalamine, monoethonalamine or hydrazine.

22. A method as claimed in any one of the preceding claims wherein the hydrolysis step is carried out in the presence of an element capable of forming an ammine thereby to introduce a further element.

23. A method as claimed in any one of the preceding claims wherein a hydrolysis promoting agent is used.

24. A method as claimed in claim 23 wherein the hydrolysis promoting agent is an ammonium salt or a betaine.

25. A method as claimed in claim 23 wherein the hydrolysis promoting agent is a quaternary ammonium salt.

26. A method as claimed in any one of the preceding claims wherein a surface active agent is used.

27. A method as claimed in any one of the preceding claims wherein the organic compound is an alkyl silicate, an alkyl titanate or an aluminium alkoxide.

28. A method as claimed in any one of the preceding claims wherein the organic compound is ethyl silicate.

29. A method as claimed in claim 27 wherein the organic compound is tetrabutyl titanate.

30. A method as claimed in claim 27 wherein the organic compound is aluminium isopropoxide.

31. A method as claimed in claim 27 wherein a mixture of organic compounds containing elements is used.

32. A method as claimed in claim 27 for the preparation of silica microspheres which method includes the step of hydrolysing an alkyl silicate in the presence of a protective colloid, the alkyl silicate being dispersed in droplet form during hydrolysis.

33. A method as claimed in any one of the preceding claims wherein the inorganic material is in the form of microspheres having a size in the range of < 1lim to 100cm.

34. A method for the preparation of an inorganic material which includes the step of hydrolysing, under heterogenous conditions, an organic compound containing an element, or elements appropriate to the inorganic material to be prepared.

35. A method for the preparation of an inorganic material substantially as hereinbefore described with reference to any one of Examples 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14.

36. An inorganic material substantially as hereinbefore described with reference to any one of Exam ples 1,2,3,4,5,6,7,8,9,10, 11,12,13, or 14.