DD269378A5 - Process for the production of ceramic materials and processes according to manufactured ceramic material - Google Patents

Abstract

The invention relates to a process for the preparation of a precursor, which is a polymeric material and from which a ceramic material can be produced, and to a process which can the additional step or additional steps of the production of ceramic material, for. Example, a carbide, nitride, boride or silicide of a metallic or non-metallic element. According to the present invention, there is provided a process for producing a precursor which is a polymer material containing at least one metallic or non-metallic element, oxygen and carbon and from which a ceramic material can be produced by pyrolysis, which process comprises: reacting (1) a first reactant consisting of a compound or compounds of at least one metallic or non-metallic element having two or more hydroxyl-reactive groups, and (2) a second reactant consisting of at least one organic compound having two or more hydroxyl groups.

Description

Process for the production of ceramic materials and

/ ibrgeetellter ceramic material

Field of application of the invention

This invention relates to a method of making a precursor which is a polymeric material and to which a ceramic material can be made, and to a method comprising the additional step or steps of preparing precursor ceramic material. The ceramic material may, for. Example, a carbide, nitride, boride or silicide of a metallic or non-metallic element.

Characteristic of the known state of the art

Particles of refractory carbides have been prepared in a traditional manner by the so-called carbothermic reaction in which an intimate mixture of carbon and an oxide of the metallic or non-metallic element is heated in an inert atmosphere. For example, in the production of silicon carbide, an intimate mixture of carbon and silica corresponding to the overall equation

SiO ₂ + 3C ►SiC + 2CO

react.

To produce the nitride, the reaction can be in the presence

I

^; , Π ·;

a reaction-containing nitrogen-containing gas, ζ. Nitrogen or ammonia. In the case "where the karbothermieche reaction takes place in the presence of nitrogen", the reaction can therefore according to the overall equation

3SiO ₂ + 8C + N ₂ ►Si ₃ N ₄ + 6CO

to be expressed ·

The problems associated with the carbothermic reaction are illustrated by the problems associated with the production of silicon carbide. In the production of silicon carbide, therefore, an intimate mixture of carbon and silicon dioxide in an inert atmosphere at a temperature "which can after all be 2500 ⁰ C" heated "where", in which heating is generally carried out in an electric furnace. This conventional method suffers from a problem that "although the ratio of silica to carbon required to produce silicon carbide" can be readily achieved ", it is difficult to" achieve the necessary intimate contact between the carbon and the silica. " to produce a product of homogeneous composition, which is of homogeneous composition on a molecular scale. In particular, the manufactured particles "nominal silicon carbide" may be contaminated with unreacted silica and / or carbon. This is even the fill when very small particles of silicon dioxide and carbon are used, e.g. For example, silica sol and carbon black. Furthermore, it is also difficult in this traditional process "particles of silicon carbide of very small size" z. Less than 1 micron.

-β-

It has been proposed "ceramic materials, such as e.g. Silicon carbide, by pyrolysis of organic Polymermateriölien containing the elements of the ceramic material, for. As silicon and carbon in the case of Siliziumkaroid, but do not contain oxygen. In one such process, the polymeric material is first coked to convert the organic component of the polymeric material into carbon, and then the carbon and silicon are reacted in a pyrolysis reaction. This is not the conventional carbothermic reaction in which carbon and silica are reacted. The aim of using such a polymeric material is to provide, in a coked product made from the polymeric material, a more intimate mixture of the elements of the ceramic material, such as a ceramic material. As silicon and carbon, as z. B. can be achieved with a physical mixture of silicon dioxide and carbon in the production of silicon carbide.

An early example of such a "preceramic" polymeric material has already been demonstrated in U.S. Patent 2,697,029, in which the preparation of a polymer material by copolymerization of a silyl-substituted monomer, e.g. Trimethylsilylstyrene, and another monomer, e.g. Oivinylbenzene or ethylvinylbenzene, to obtain a crosslinked resin, and by pyrolysis of the resin to obtain a carbon and silicon-containing solid is described.

Further examples of such "preceramic" materials are those produced by the pyrolysis of dodecamethylcyclohexasilane (Yajima et al., Formerly Lett. 1975, p. 931) and by heating poly (dimethylsilane) in an autoclave (Yajima 1976,

Nature, vol. 273, p. 525). These carbon silanes can be spun into fiber composites, from which thin, high temperature fireproof silicon carbide can be made. The reaction, which can be effected at high temperature, occurs between silicon and carbon and is not the aforementioned conventional carbothermic reaction "d. H. the reaction between silicon dioxide and carbon * This method has the disadvantage that the silicon carbide product is impure.

A recent example of such a "preceramic" material from which a refractory carbide can be made is provided by OP No. 57-17412, which describes a process in which a halogen compound or an alkoxide of silicon, vanadium, Zirconium, tantalum or tungsten is reacted with a carbohydrate, and the resulting reaction product is fired. The halogen compound or the alkoxide may, for. As SiCl ₄ , ZrOCl ₂ , Si (0C ₂ H ₅ ) ₄ , Si (OC ₂ Hg) ₃ -C ₂ H ₅ . Si (OC ₂ H ₅₂ ) (CH ₃ ) ₂ , Zr (OC ₄ Hg) ₄ , WCl ₂ (OC ₂ H ₅ J ₄ , and the carbohydrate may be, for example, a monosaccharide or a polysaccharide, e.g. Glucose, galactose, arabinose, starch or cellulose The reaction may be effected in the absence of a solvent, but is preferably carried out in the presence of a solvent, for example an aromatic solvent, for example benzene or toluene, of an aliphatic solvent. for example, hexane, heptane or octane, or a halogenated aromatic or aliphatic solvent The reaction product is fired in the presence of an inert gas at a temperature in the range of 700 to 1700 ^° C. Before firing at a very high temperature, a coked ReaktiotiSf.rodukt containing carbon and an oxide of Si, Zr, V, Ta or W, by heating dee

2 * 9378

React.toneproduktee be prepared at a relatively low βιΐι-. 'Ätur »and this coked product can be crushed to a very fine powder Although this publication states that the reaction between the halogenated compound or the alkoxide and the carbohydrate in a solvent can be effected and that the solvent can be used in an amount sufficient to dissolve or suspend * we note that the carbohydrates disclosed are not soluble in the solvents and can only be suspended therein in particulate form, with the result that the reaction does not lead to the production of a reaction product w) of homogeneous composition, or which is in a particularly manageable form. In fact, the reaction product must be crushed to produce a powder, and the refractory carbide prepared from the reaction product also does not have a homogeneous composition.

A current development, described in Thermochimica Acta, 81 (1984) 77-86, is the production of silicon carbide by the fysis of rice skins. The rice skins are made of silica and cellulose, and when thermally decomposed, they form a mixture of silica and carbon. Reignicles have a large surface area, and this, together with the intimate contact between the carbon and the silica in the thermally decomposed rice skins, enables the formation of silicon carbide by subsequent pyrolysis in an inert atmosphere or in a reducing atmosphere at relatively low temperatures. The production can be accomplished in a two-step process, in dsm rice skin by heating in the absence of air at a relative

2 * 9378

low temperature, ζ. * Β be coked at 700 ⁰ C * ι to zeraetzen the cellulose into amorphous Kohlenetoff # eo and the coked Reiehäutchen that Kohlonetoff and 811izlumdioxid contain "werdon to a high temperature, for example. To a temperature of more than ISOO ⁰ C, and heated in an inert or reducing atmosphere to produce silicon carbide. In the alternative, silicon nitride may be produced by heating the coked cellulosic in a nitrogen atmosphere or a reactive nitrogenous compound-containing atmosphere. The use of rice bran in the manufacture of ceramic free-flowing materials is, of course, not very adaptable, since it is only used in the production of a few ceramic materials Silicon carbide and silicon nitride can be used * carbides and nitrides of elements other than silicon can not be produced from rice *

The quality of the ceramic material produced by the previously described processes depends, at least in part, on the composition and structure of the precursor from which the ceramic material is made, and on the conditions of impoundment. For example, when silicon carbide is prepared from a precursor that is a mixture of silica and carbon, there is no difficulty in achieving the overall silica to carbon ratio required to produce silicon carbide through the carbothermic reaction, but it is impossible to achieve the silicon carbide To achieve close contact between the silicon dioxide and the carbon in the precursor, which is necessary to produce a silicon carbide product of homogeneous composition on a microscopic scale, not to mention the molecular scale, and which free

unreacted silica and / or carbon let.

When the ceramic material is produced by pyrolysis of a precursor which is a reaction product containing the elements of the ceramic material, eg, a reaction product containing silicon and carbon or a reaction product containing silica and carbon, the elements may not be in the ratio required to produce a substantially contaminant-free ceramic material, and moreover, it may be difficult to prepare the precursor reaction product in a workable and readily handleable form from which the ceramic material can be made in the desired form For example, the precursor reaction product may be formed into an unmanageable mass, from which it is difficult, if not impossible, to produce particulate ceramic material of particularly low and relatively homogeneous particle size ceramic material.

Ceramic materials have been used for many years in such applications as abrasives and in the production of tools. While in these applications the quality of the ceramic material may not have been of paramount importance, there are other applications of more recently developed ceramic materials in which the quality of the ceramic material and physical F-jrm can be of crucial importance. These more recently developed applications of ceramic materials include applications as engineering materials and use in electronic materials

2 * 9378

applications · Object of the invention

The aim of the invention is "to produce ceramic materials of the generic type in a cost-effective manner.

Explanation of the essence of the invention

The object of the invention is * to find a method for the production of ceramic materials which are characterized by a high quality and their ready-to-use physical form and to produce these ceramic materials by methods «

The present invention provides a process for preparing a precursor "which is a polymeric material and from which a ceramic material can be made" and relates to a process for producing the ceramic material from the precursor. The former method is very versatile "insofar as it can be used in the manufacture of a large number of keremic materials" z. For the preparation of precursors which can be converted into carbides, nitrides, borides and silicides of a variety of metallic or non-metallic elements, and it results in the preparation of a precursor which is a particularly desirable particulate form and which rapidly turns a particulate ceramic material can be produced.

According to the present invention there is provided a process for the preparation of a precursor which comprises a miner

249378

which is a metallic or non-metallic element, oxygen and carbon containing polymer material, and from which a ceramic material can be made by pyrolysis, which process comprises: allowing it to react

(1) a first reactant consisting of a compound or compounds of at least one metallic or non-metallic element having two or more hydroxyl-reactive groups, and

12) a second reactant consisting of at least one organic compound having two or more hydroxyl groups,

wherein said reaction is effected in a liquid medium in which the reactants are soluble and / or dispersible, and in which the polymer material produced by the reaction is insoluble or in which the polymer material is insoluble, and precipitating the polymer material in the liquid medium Particle shape and the recovery of the polymer material from the liquid medium in particulate form.

The process of the invention is essentially a dispersion polymerization process. The reactants are selected in the process so that they are miscible with each other, in which case the liquid medium may contain the reactant mixture, and / or that they are soluble in a common solvent, in which case the reactants and the solvent form a homogeneous liquid medium or that they are readily dispersible in the liquid medium. In this latter case, one of the reactants may be soluble in one solvent and the other reactant may be present in the solvent

6 9 3 7

Solvents are dispersed or both reactants may be dispersed in the solvent. The polymer material produced by the reaction is either insoluble in the liquid medium, e.g. B * in the usual Lösunoemittel so that the polymer material produced is precipitated, or the polymer material prepared by the reaction is precipitated, for. By the addition of a non-solvent to the liquid medium or by the removal of a reaction product or by the removal of some solvent, and the precipitated polymer material is recovered from the liquid medium. Since the polymeric material is a precursor for the subsequent production of a particulate ceramic material, it is important that the precipitated and recovered polymeric material be in particulate form. The shape of the polymer material which precipitates, and in particular the size of the particles of polymer material which are precipitated, can be regulated by the use of the high-speed mixture of reactants, by the variation of reactant concentrations in the liquid medium and by the use of a dispersant in the liquid medium as will be disclosed in more detail later herein.

The ability to produce the polymeric material precursor in particulate form, and in particular the ability to produce the precursor in the form of small spherical particles, is particularly important. Thus, a precursor in such a form is particularly suitable for use in the production of particulate ceramic materials by pyrolysis of the precursor, and small particles of the precursor can be converted into small particles of the ceramic material, which is a particularly desirable form for the

In addition, the process of the invention can be operated in such a way that the particle size of the precursor and thus the particle size of the ceramic material produced from the precursor are regulated.

The polymeric material precursor is pyrolyzed in a subsequent step or steps to yield a ceramic material. The precursor can be heated in a first further step to elevated temperature ι to produce a coked product »containing an extremely intimate mixture of an oxide of the metallic or non-metallic element and carbon * and in a second further step, the coked product can be further increased to an increased Temperature to be heated "to produce a ceramic material. For example, the coked product may be heated in an inert atmosphere to produce a carbide of the metallic or non-metallic element, or the coked product may be heated in an atmosphere of nitrogen or a reactive nitrogen-containing compound Produce nitride of the metallic or non-metallic element. Where, alternatively, the first reactant contains a compound of a metallic or non-metallic element and a compound of boron or silicon such that the precursor prepared in the process of the invention contains the metallic or non-metallic element, boron or silicon, oxygen and carbon, and from it If the coked product produced contains an intimate mixture of carbon, an oxide of the metallic or non-metallic element and an oxide of boron or silicon, the coked product may be heated to an elevated temperature in an inert atmosphere to form a boride or silicide of the metallic or non-metallic

to produce lischan element.

In the process of the invention, the first reactant contains a compound of a metallic or non-metallic element * containing two or more groups capable of reacting with hydroxyl groups, and the second reactant contains an organic compound having two or more hydroxyl groups.

The metallic or non-metallic element must be such that it is a ceramic material, e.g. Example, a refractory carbide or nitride can form, and examples of such elements are aluminum, silicon, titanium, tantalum, zirconium, hafnium, tungsten and boron, although the method is not limited to the use of the compounds of these specific elements. Oio compound of the metallic or non-metallic element contains at least two groups which can react with hydroxyl groups, and it may also contain groups which are less reactive. For example, the compound may have a formula MX _n V _n habcan, where M is the metallic or non-metallic element, X is a group that is reactive with hydroxyl groups, and Y is a non-reactive hydroxyl group "η is an integer of at least 2 , and m is zero or an integer. The group X can z. B. its halide, z. As chloride or bromide, amide or alkoxy, ζ. Β. a group of the formula OR, where R is an alkyl group with z. B. 1 to 8 carbon atoms, for. Methoxy, ethoxy or butoxy. The group Y, if present in the compound of the metallic or non-metallic element, e.g. B "be a Hydrokarbylgruppe, z. As alkyl, cycloalkyl, aryl or

Alkaryl. Specific examples of such groups include methyl, ethyl, propyl, cyclohexyl and benzyl. The group Y may be an oxy group, e.g. For example, the compound of the metallic or non-metallic element may be an oxyhalide.

Specific examples of compounds of metallic or non-metallic elements in which all of the groups in them are reactive for hydroxyl groups are tetramethoxyeilane, tetraethoxyeilane, tetraethoxy-zirconium, pentaethoxy-tantalum, penta-n-propoxy-tantalum, siliconotrachloride, zirconium tetrachloride, dichlorodiethoxyeilane, chlorotriethoxy Zirconium, dichloro-butoxy-tantalum, boron-chloride, boron tri-isopropoxide, aluminum triisopropoxide and aluminum trichloride.

Examples of precursors of the metallic or non-metallic element containing both reactive and nonreactive hydroxyl groups include methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, oimethyldiethoxysilane, dimethyldimethoxysilane, diphenyldiethoxyeilane, phenyltrimethoxysilane and hexachlorodisilanoxane, and equivalent compounds of other metallic or non-metallic elements.

The first reactant may contain two or more of these aforementioned compounds where it is desired to produce a ceramic material, e.g. For example, a carbide or nitride of two or more different metallic or non-metallic elements. Where it is desired to produce a boride or silicide of a metallic or non-metallic element, the first reactant may comprise a compound of boron or silicon and a compound of a metal or non-metallic element.

metallic or non-metallic element "except boron or silicon

In general, the compound of the metallic or non-metallic element contains no hydroxyl groups "since hydroxyl-containing © compounds of metallic or non-metallic elements" which can form a ceramic material "are generally unstable" or they may not even exist as hydroxides "or they readily condense themselves and form a polymer product "or they may exist as a hydrogenated oxide" and not as a hydroxide "such as * B * in the case of hydrogenated alumina.

In the process of the invention, the compound of the metallic or non-metallic element is reacted with an organic compound "having two or more hydroxyl groups" and forming a polymeric material. B * be aliphatic "aromatic or cycloaliphatic" Examples of suitable aliphatic organic compounds containing the two hydroxyl groups include glycols, eg, ethylene glycol, propylene glycol, butylene glycol and diethylene glycol. Examples of suitable aliphatic organic compounds "containing more than two hydroxyl groups" include glycerol, trihydroxybutane and trihydroxypentane. Examples of at least two hydroxyl-containing cycloaliphatic organic compounds include oxyhydroxycyclohexane and trihydroxycyclohexane. Aromatic organic compounds containing two or more hydroxyl groups are advantageous because they contain a large amount of carbon and, when incorporated into the polymer material, help to produce the desired ratio of carbon to oxide of the metal.

Examples of such aromatic compounds include cresols, oxyhydroxytoluene, and oihydroxynaphthalene. The second reactant may contain two or more of the aforementioned compounds.

In order for the ceramic material made from the coked product to have the desired composition, it is desirable that the ratio of carbon to oxide of the metallic or non-metallic element in the coked product be close to or substantially equal to that theoretically required * Z * B * In the production of a carbide from the coked product, a mixture of carbon and an oxide MO ₂ , as in the case of SiO ₂ , TiO ₂ and ZrO ₂ *, the so-called carbothermic reaction

MO ₂ + 3C ►MC + 2CO,

and the theoretically required molar ratio of the oxide to carbon is 1 to 3. In the cases of the oxides of silicon, titanium and zirconium are the theoretically required mass ratios of oxide and carbon

SiO ₂ 62.5 % Carbon: SiO ₂ 1: 1.67 Carbon 37.5 %

TiO ₂ 68.9 % Carbon: TiO ₂ 1: 2.22 Carbon 31.1 %

ZrO ₂ 77.4 % carbon-.ZrO ₂ 1: 3 * 42 carbon 22.6 %

The stoichiometry of the carbothermic reaction must be different, as in the case of the reaction between carbon and the oxide of tantalum.

Ta ₂ Og + 7C 2TaC + 5CO

In this case, the molar ratio of oxide to carbon "theoretically must be 1 to 7", which corresponds to 84 mass% Ta ₂ O ₅ and 16 Μβ88β-% carbon in the coked product prepared from the polymer product "d * h. a mass ratio of carbon s ^Ta 2 ° 5 ^{of 1} * ⁵ « ²⁵ ·

The ratio of carbon to oxide of the metallic or non-metallic element "required in the coked product" may be different "when a nitride is to be produced. For example, in the case of the elements titanium "vanadium, zirconium and hafnium" whose oxides can be represented by the formula MO and whose nitrides can be represented by the formula MN, the overall reaction may be al3

2 MO ₂ + 4C + N ₂ ► 2MN + 4CO

* The theoretically required stoichiometric ratio is a molar ratio of oxide to carbon of 1 t 2, which corresponds to the following Maseenverhältnissen

TiO ₂ 76.9 % Carbon: TiO ₂ 1: 3.33 Carbon 23.1 %

V0 _? 77.5 % carbon: VO ₂ 1: 3.44 carbon 22.5%

ZrO ₂ 83.7 % carbon ι ZrO ₂ X ι 5.13 carbon 16.3 %

HfO ₂ 89.8% carbon t HfO ₂ 1 t 8.80 carbon 10.2 %

The ratio of carbon to oxide of the metallic or non-metallic element in the product of co-product may be controlled by the choice of the first and second reactants and by the choice of the proportion of these reactants used in the preparation of the polymeric material. For example, if a relatively high proportion of carbon in the coked product is required, the second reactant may contain an organic compound containing a cyclic group. " An aromatic or cycloaliphatic group or an unsaturated group, since the loss of carbon in the conversion of a polymer product made from such a compound into a coked product is not coarse, ie, it gives a high carbon yield. Suitable such organic compounds include dihydroxynaphthalene and dihydroxycyclohexane. On the other hand, the organic »allphatieche groups when a product made from such a compound, polymer product is converted to a coked product containing compounds tend to high carbon loss, and the loss zn carbon Judges depends strongly on the chain length of the aliphatic group from. Therefore, if a coked product containing a high carbon content is desired, the use of aliphatic glycols and polyols, at least at a high level, is not preferred. The production of a polymer material and a coked product containing a high carbon content also becomes

favored by the use of an additional reactant containing an organic compound having a single hydroxyl group, e.g. An alcohol containing a cyclic moiety, e.g., cyclohexanol, or an alcohol containing an unsaturated group, which is preferably also cyclic, e.g. B. furfuryl alcohol. Such a single hydroxyl-containing reactant reacts with the first reactant to form a unit which protrudes from the chain of polymer material and not a unit within the polymeric material chain. *** If a relatively high level of the oxides of the metallic or non-metallic element is desired in the pre-coked product For example, an additional reactant can be used in the preparation of the polymeric material containing a compound of the metallic or non-metallic element having a single hydroxyl-reactive group. Such a compound reacts with the second reactant and forms a moiety that protrudes from the chain of polymer material and not a unit within the polymer material chain. Examples of such reactants include a trialkylalkoxysilane, e.g. B. trimethylethoxysilane and corresponding compounds of titanium, zirconium, vanadium, tantalum and other metallic and non-metallic elements.

The process of the invention is carried out in a liquid medium in which the reactants are soluble or dispersible, and the reactants, and their properties, as well as the solvents for the reactants, if present, are selected so that the reactants are miscible with each other or in a common solvent soluble or easily diepsrgierbar. The first reactant, that is the metallic or non-metallic compound, and the second

Reactant which is said to be "miscible or soluble or dispersible in a common solvent." When the reaction is effected between miscible reactants or when the reaction is effected in a solvent for the reactants and the resulting polymer material is precipitated "It is possible to produce the polymer material in the form of small and uniform particles" having a homogeneous composition. "A polymer material of such a shape can also be prepared" when a dispersion of the reactants is polymerized in a liquid medium "especially" if a colloidal Dispersion of the reactants is polymerized ·

Reactants which are miscible with each other and which are intended to dissolve or disperse reactants may be selected by simple experimentation, particularly the following examples of such reactants and solvents.

Examples of compounds of metallic or non-metallic elements and organic hydroxyl-containing compounds "which are miscible with each other" are u. s-tetraethoxysilane and glycerol "which may optionally also contain furfuryl alcohol" tetraethoxyeilane and diethylene glycol "which may optionally also contain furfuryl alcohol" and triethoxyboron and glycerol "when heated to a slightly elevated temperature.

Solvents that can be used include high-boiling hydrocarbons. B * the petroleum ether and liquid boiling at a temperature above 200 ^° C

Paraffins. Ethanol may be a suitable solvent for use with a variety of different compounds of metallic or non-metallic elements and organic compounds containing the hydroxyl groups such as titanium tetrachloride and glycerol, tantanetetraethoxide and glycerol, titanium tetraethoxide and glycerol optionally mixed with furfuryl alcohol, aluronium trichloride and glycerol "Aluminum triisopropoxide and glycerol" optionally mixed with furfuryl alcohol "zirconium tetrachloride" glycerol and furfuryl alcohol "tetraethoxysilane and cyclo-1" 4-diol, resorcinol • nol or 1 "3" 5-trihydroxybenzene and hafniocarbon tetrachloride and glycerol "

Although the reactants are miscible with each other, "they can be reacted in the presence of a solvent" in which they are soluble or dispersible. In fact, the use of such a solvent is preferred for reasons to be explained later herein.

When the reactants are neither miscible nor soluble in a common solvent, they must be allowed to react with each other in the form of a dispersion in a liquid medium, preferably in the form of a highly colloidal dispersion.

Since the reaction between the metallic or non-metallic compound and the hydroxyl-containing organic compound is by nature a condensation polymerization, the proportions of the reactants are chosen so that the desired condensation is achieved, and there may be only a small range for varying the proportions of reactants , The shares of the selected

Actinons depend on the number of ¹ hydroxyl-reactive groups in the metallic or non-metallic compound and on the ZaIO of the hydroxyl groups in the organic compound. The relative proportions of the reactants can be chosen such that in the reaction mixture ee there is an approximately equimolar ratio of hydroxyl groups to the groups reacting with hydroxyl groups. For example, when tetraethoxyeilane containing four reactive groups reacts with glycerol containing three reactive groups, the reaction is a tranesterification in which ethanol is split off, and for a sufficiently high molecular weight polymer material, the molar ratio of Tetraethoxysilane to glycerol, which is selected to be in the range of 3: 4. However, an excess of one reactant over the other can be chosen to drive the reaction to completion.

In the process of the invention, the reaction is effected in a medium in which the reactants are soluble or dispersible and in which the produced polymer material is precipitated in particulate form. The polymer material formed must therefore be insoluble in the medium. The formation of the polymer material in particulate form can be assisted by carrying out the reaction in the presence of a common solvent for the reactants, rather than merely a homogeneous mixture of the reactants, and by choice of reactant concentrations in the solvent. Although the optimum concentration of reactants in the common solvent to form particulate polymer material may to some extent depend on the nature of the reactants, the concentration of the first and second reactants and any other reactants may be

generally, generally in the range of 5% to 60% by weight of the total mass of reactants and liquid medium. The formation of the polymer material in particulate form is also assisted by thorough and vigorous stirring of the reactants and the use of a dispersant "which helps to keep the polymer material in the well-dispersed state in the reaction medium." The concentration of the dispersant which is suitably selected depends on the Concentration of the reactants in the reaction medium, but suitably, the concentration is in the range of 0.5 to 10% by mass of the total mass of the first and second reactants and any additional reactants. Suitable dispersants include materials which have an affinity for Polymer material "formed in the reaction" and to the liquid medium. Examples of suitable dispersants include derivatives of polyhydroxystearic acid "z * B. a polyhydroxystearic acid derivative of glycidyl methacrylate or polymethylmethacrylate" which is reacted with polyhydroxystearic acid and contains residual acid groups. The use of a dispersant is also recommended "when one or more of the reactants are in the form of a dispersion in a liquid medium, especially when a dispersion is desired which is substantially colloidal.

The particle size of the polymer produced can be regulated by the choice of reactant concentration in the reaction medium "by the use of a dispersing agent and the choice of its concentration" by controlling the extent of reaction of the reactants and by using vigorous stirring. In general

the lower the concentration of reactants in the reaction medium and the greater the concentration of dispersant, the more thoroughly the reaction medium is agitated and the lower the conversion of the reactants into the polymer material ", even though the above-mentioned criteria are intended for general orientation only.

The particle size of the ceramic material that is ultimately produced depends on the particle size of the polymer material from which the ceramic material is produced. A particle size for the polymer material in the range of 1 to 500 micrometers is generally suitable. The preferred particle size is less than 100 microns.

It may be advisable or even necessary to run the reaction under a dry inert atmosphere, especially if the compound of the metallic or non-metallic element is readily hydrolyzable, e.g. When the compound is an alkoxide of silicon or titanium. Some halides of metallic or non-metallic elements, e.g. As SiCl ₄ and TiCl ₄ , are also easily hydrolyzed.

The temperature at which the reaction is effected depends on the particular reactants. So you can reactants, such. As silicon tetrahalides or glycols or polyols, for. Ethylene glycol or glycerol, allowing the reaction to proceed at or about ambient temperature, although with other reactants and in the case of reaction in a solvent, it may be necessary to carry out the reaction at elevated temperature. The reaction temperature

is generally not above the boiling point of solvents, although a temperature above the boiling point can be used. The reaction can be carried out at elevated temperature to remove a reaction product and assist in the formation of the polymeric material. For example, if the reaction is a transesterification reaction in which an alcohol is split off, such as, for example, For example, in the case of the reaction of a silicon alkoxide with a hydroxy compound, the reaction temperature is preferably split above the boiling point of the alcohol during the reaction.

The reaction can be enhanced by the presence of suitable catalysts in the reaction mixture. Acidic catalysts "if the reaction is a transesterification. Suitable catalysts for such transesterifications are known in the art.

The polymer material "which is produced" from the liquid medium "z. B. from the. Solvent "takes place in the reaction" to be precipitated without special measures being taken "to achieve this precipitation. On the other hand, it may be necessary to precipitate the polymer material or at least to intervene in the precipitation. This can z. B. be achieved by adding an inactive solvent to the reaction mixture or by removing a portion of the solvent from the reaction mixture or by removing a reaction product from the reaction mixture «z. By removing the alcohol caused by the reaction of an ester of a metallic or non-metallic element and an organic compound having two or more

The removal of such a reaction product or a part of such a solvent can be achieved by distillation *

The polymer material produced can be separated by any conventional means, e.g. By filtration of the reaction medium, and it can be washed to remove solvent and unreacted reactants, and dried.

The process of the present invention can be carried out in a continuous manner. Thus, the first and second reactants, and optionally a dispersant and a solvent for the reactants, can be continuously fed to a reaction vessel. The contents of the reaction vessel can be continuously withdrawn from the reaction vessel and the reaction mixture removed Polymer material can be separated from the contents of the reaction vessel from which it was removed. After separation of the polymer material, the unreacted reactants and, if present, solvents and dispersants can be returned to the reaction vessel using additional reactants and solvents and dispersants, if used , also be fed into the reaction vessel according to the need,

In a subsequent step or steps, the particulate polymer produced in the process of the invention may be pyrolyzed to give a particulate ceramic material. The polymer material may be pyrolyzed in two steps consisting of a step of heating the material to an elevated temperature to produce a coked product containing a

highly intimate mixture of an oxide of the metallic or non-metallic element and carbon, and a second step of heating to an elevated temperature to produce a ceramic material in an inert atmosphere to produce a carbide of a metallic or non-metallic element , in an atmosphere containing nitrogen or a reactive nitrogen-containing compound to produce a nitride of a metallic or non-metallic element. This further processing of the polymer material is described using the name of a two-step process.

The temperature at which the heating takes place in the coking step depends on the nature of the organic component of the polymer material, but generally a temperature of up to 600 ^° C will suffice, although a higher temperature may be used, e.g. B * a temperature up to about 800 ⁰ C. The heating should be carried out over a period of time sufficient for complete coking of the organic component of the polymer material, for. B * sufficient time until no further weight loss of the cokote product occurs at the selected temperature.

In the second step of the pyrolysis, the coked product is heated beyond the temperature used in the coking step to cause carbothermal reaction between the carbon and the oxide of the metallic or non-metallic element in the coked product. In general, a temperature up to about 1600 ⁰ C, possibly slightly higher, z. B * up to 1800 ⁰ C, and the brhitzung should take place in an inert atmosphere, eg. B. in one

Atmosphere of an inert gas, "eg helium" if a carbide of the metallic or non-metallic element is to be produced by the carbothermal reaction "or the heating should be in an atmosphere of a reactive nitrogen compound, eg nitrogen itself or ammonia" a nitride of the metallic or non-metallic element is to be produced «

Out of leadership examples

The solution according to the invention will be explained in more detail in several examples below *

example 1

The following reaction mixture was fed under nitrogen to a reaction vessel equipped with a high speed stirrer, a reflux condenser, and an inlet and outlet for nitrogen.

Tetraothoxysilane 92 , 7 G furfuryl 22 G glycerol 30 G Tetraisobutane 90 250 ml ρ Dispersant 1 .5 G

Mainly C16 isoparaffins with a share of C12 l8oparaffinen. Boiling point 225 to 255 ⁰ C.

50% by mass solution in polyhydroxystearic acid

derivatives of glycidyl in white spirit The content of the reaction vessel in the form of a solution was

heated to the reflux temperature for 3 hours under a nitrogen atmosphere and stirred vigorously. Thereafter, vigorous agitation was dae continued and a flüeelge phase which consisted mainly of ethanol and some unreacted Tetreethoxyeilan "has been distilled from the reaction vessel, initially at a temperature of 80 ⁰ C * With the Fortechreiten the distillation a polymeric material in the form of fine was brown particles precipitated »and the distillation was continued ι bie reached a temperature of 190 ⁰ C, at which no further liquid could be distilled *. The contents of the reaction vessel were allowed to cool. An equal volume of petroleum ether was added 40-6Oer, the contents were filtered to separate the teilohenförmige polymeric material and the particulate material was washed with petroleum ether, dried in vacuo at 60 ⁰ C. The yield of the fine particles of the particulate polymer material was 54.2 g.

The particulate polymer material containing 15.3% by mole of silicon and 39.3% by mole of carbon and oxygen was heated to a temperature of 800 ^° C. in a nitrogen atmosphere at a rate of 7 K per minute to produce a coked product composed of silica and carbon (62.5% by mass of silica and 37.5% by mass of carbon) and the coked product was heated in a helium atmosphere with the temperature rising from ambient temperature to 450 at a rate of 7K per minute ⁰ C and then at a rate of 5 K per minute to 1600 ⁰ C was increased.

Examination of the particulate product with X-ray diffraction and Raman spectroscopy showed that it was β-SiC

contained as well as some residual carbon. The product consisted of fine particles »

Example 2

The procedure of Example 1 was repeated »except that the reaction mixture consisted of

Aluminum triisopropoxide 46.6 g Furfuryl alcohol IO g

Glycerol 12.3 g

Tetraieobutane 90 150 ml Dispersant 2 g

duration.

Polymethyliaethacrylat «containing polyhydroxystearic acid groups.

The liquid phase distilled off mainly consisted of isopropanol, the maximum temperature reached was 150 ^° C., and the particulate polymer material produced consisted of fine particles of pale yellow material. The polymer material was 13.62% by mass carbon, 4.6% by mass hydrogen, 19% , 6 M% aluminum and oxygen, and the particle size analysis showed that 100% of the particles have a size of less than 100 microns and that the median particle size is 10 microns. The light yellow material was pyrolyzed to a coked product, and the product coked was further pyrolyzed by heating according to the procedure described in Example 1, except that the pyrolysis of the coked product in an embroidered product was pyrolyzed.

fabric atmosphere was carried out

Oils Examination of the fine particles of the resulting product by X-ray diffraction and Raman spectroscopy revealed that it consists of AlN with some residual carbon.

Beiopiel 3

The polymerization procedure of Example 1 was repeated except that the reaction mixture consisted of

Titanium tetraethoxide 11.4 g Triethyl boron 14.6 g

Glycerol 18.4 g

Tetraisobutane 90 50 ml Dispersant (as used in Example 2) 1.0 g

and the maximum temperature reached was 150 ^° C. The particulate polymer material was prepared in the form of a white particulate material and in a yield of 20.5 g. The particles of the polymer material had an average size of 11 microns, and 100 % of the particles had a size of less than 113 microns.

The polymer material served as a precursor for the production of titanium boride.

Example 4

The polymerization process of Example 1 was repeated, except that the reaction mixture

Tetraethoxysilane 43.5 g Furfuryl alcohol 13.7 g

Olyzerol 20 g

liquid paraffin 200 ml dispersant (like

used in Example 2) 1.2 g

The product of the polymerization was a brown polymerisation material in the form of fine brown particles. The yield of polymer material was 30 g *

Example 5

The polymerization procedure of Example 2 was repeated, except that the reaction mixture consisted of

Aluminum triisopropoxide 51 g Furfuryl alcohol 14.7 g

Glycerol 13.8 g

Tetraisobutane 90 100 ml Dispersant (as

used in Example 1) 5.0 g

The product of the polymerization was a pale yellow polyisomer in the form of fine particles. The yield was 42 g.

Example 6

The polymerization process of Example 2 was used, except that the reaction mixture consisted of

Aluminum tri-8-propoxide 25 * 5 kg Furfuryl alcohol 5.4 kg

Glycerol 6.7 kg

liquid paraffin 65 1 dispersant (as used in example 3) 1.0 kg

The product of the polymerization was a light yellow polymer material in the form of fine particles. The yield of polymer material was 16.5 kg.

Example 7

The polymerization process of Example 1 was repeated, except that the reaction mixture of

Aluminum triisopropoxide 46.6 g Furfuryl alcohol 11 g

Glycine-ol 12.4 g

Tctreisobutane 90 75 ml Dispersant (as

used in Example 2) 2.0 g

oestand. The contents of the reaction vessel were heated at 150 ^° C. for 1 hour, and isopropanol was distilled off from the reaction vessel. The polymer material formed in the reaction, which was obtained in the form of light yellow fine particles, was filtered, washed with a low-boiling paraffin and dried in vacuo at 70 ^° C. for 1 hour. The yield of polymer material was 36.7 g, the average size of the particles of the polymer material was 10 microns, and the particles had a size of less than 65 micrograms.

The polymer material consisted of 35 # 10 M% carbon, 5.09 M% hydrogen, 14.2 % aluminum and Sauoretoff.

Example 8

Ee, the procedure of Example 7 was repeated except that the reaction mixture contained 150 ml of tetraeuobutane and 0.5 g of dispersant. 41 g of polymer material was produced in the form of fine particles, the particles had a mean size of 4 microns, and 100 % of the particles had a size of less than 65 microns, and the polymer material consisted of 46.02 M% carbon, 7, 45 M% hydrogen, 13.1 M% aluminum and oxygen *

Example 9

Ee, the procedure of Example 7 was repeated, except that the reaction mixture

Aluminum triisopropoxide 23.3 g Furfuryl alcohol 5.5 g

Glycerol 62 g

Diothylenglykoldimethyl-

ether 75 ml

Dispersants (such as

used in Example 2) 1 g

There were prepared 17 g of polymer material in the form of fine particles, 100 % of the particles had a size of less than 100 microns, and 50 % had a size of less than 11 microns, and the polymer material was

of 36.12 M% carbon, 5.70 M% hydrogen, 13.90 Μ ··% aluminum and oxygen.

Example 10

Ee, the procedure of Example 9 was repeated except that the diethylene glycol dimethyl ether was replaced by 75 ml of N-methylpyrrolidone.

Ee, 18 g of polymer material were prepared in the form of fine particles, the average size of the particles was 10 microns, and the polymer material consisted of 35.50 M% carbon, 5.54 M% hydrogen, 14.1 M% aluminum and Oxygen.

Example 11

The procedure of Example 7 was repeated, except that the reaction mixture

Titanium tetraethoxide 22.9 g Furfuryl alcohol 9.8 g

Glycerol 9.2 g

Tetraisobutane 90 80 ml Dispersant (as used in Example 2) 1 g

duration. The contents of the reaction vessel were heated at 160 ^° C. for 1 hour, and ethanol was distilled off from the reaction vessel.

21.4 g of polymer material were in the form of fine particles

100 % of the particles were less than 100 microns in size and 50 % of the particles were less than 25 microns in size and the polymer material was 40.60 M% carbon, 4.97 M% hydrogen, 20 , 4 M-SK titanium and oxygen.

Example 12

The procedure of Example 11 was repeated, except that the reaction mixture

Titanium tetraethoxide 29.2 g

Furfuryl alcohol 11 g glycerol 9.2 g

Tetraisobutane 90 50 ml Dispersant (as used in Example 2) 1 g

24 g of polymer material was produced in fineness of fine particles, 100 % of the particles had a size of less than 160 microns, and 50 % of the particles had a size of less than 20 microns, and the polymer material berry of 41.27 M-jg carbon, 4.95 M% hydrogen, 20,?. M-% titanium and oxygen.

Example 13

The procedure of Example 7 was repeated except that the Rer. tion mixture

Titanium tetraethoxide 22.9 g Boron trimethoxide 11.6 g Furfuryl alcohol 19.8 g

Glycerol 11 g

Tetraisobutane 90 100 ml Dispersant (as

used in Example 2) 2 g

was "The contents of the reaction vessel was heated for 1 hour at 160 ⁰ C, and distilled Methanoi action vessel.

160 ^° C., and methanol and ethanol were removed from the

Thirty grams of polymer material was produced in the form of fine particles, 100 % of the particles were less than 280 microns in size, and 50 % of the particles were less than 105 microns in size, and the polymeric material was 40.15 M% carbon , 4.54 M% hydrogen, 12.6 M% titanium, 4.43 M% boron and oxygen.

Titanium boride was produced by pyrolysis of the polymer material.

Claims (29)

claims (1) a first reactant "consisting of a compound or compounds of at least one metallic or non-metallic element having two or more groups" which react with hydroxyl groups, and A process for the preparation of a precursor "which is a polymer material" which consists of at least one metallic or non-metallic element "oxygen and carbon and from which a ceramic material can be prepared by pyrolysis" characterized by reacting 2 A 93 78 the second reactant contains a glycol and / or glycerol. 2. The method according to claim 1, characterized in that the reactants are soluble in a conventional solvent. (2) a second reactant consisting of at least one organic compound having two or more hydroxyl groups. « wherein said reaction is effected in a liquid medium in which the reactants are soluble and / or dispersible and in which the polymer material produced by the reaction is insoluble or achievable in that the polymer material is insoluble and precipitates the polymeric material in the liquid medium in particulate form, and recovering the polymer from the liquid medium in particulate form. 3. The method of claim 2 «characterized« that the polymer material in the usual solvent insoluble let. 4. The method of claim 1 or 2 »characterized» that the Folymermaterial is brought by the removal of reaction product from the liquid medium to precipitate » 5. The method according to claim 1 to 4, characterized in that «the first reactant contains a compound of aluminum« silicon, titanium, tantalum, zirconium, hafnium, tungsten or boron · A process according to claims 1 to 5, characterized in that the first reactant has the formula MX Y _m , where M is a metallic or non-metallic element, X is a hydroxyl reactive group and Y is a non-hydroxyl reactive group; η is an integer of at least 2, and m is zero or an integer. 7. The method according to claim 6, characterized in that X is a HaJogenidgruppe, an amide group or an alkoxy group. 8. The method according to claim 1 to 7, characterized in that the first reactant contains a compound of boron or silicon and a compound of a metallic or non-metallic element (except boron or silicon). 9. The method according to claim 1 to Θ, characterized 10. The method according to claim 1 to 9, characterized in that «the second reactant contains an organic compound having a cyclic group. 11. The method according to claim 1 to 10, characterized in that »the second reactant contains an organic compound having an unsaturated group. The process of claims 1 to 11 characterized in that it comprises reacting an additional reactant containing an organic compound having a single hydroxy group. 13. The method according to claim 12, characterized in that the additional reactant contains a cyclic group. 14. The method according to claim 12 or 13, characterized in that the additional reactant contains an unsaturated group. A process according to claims 1 to 11, characterized in that it comprises reacting an additional reactant containing a compound of a metallic or non-metallic element with a single group reactive with hydroxyl groups. 16. The method according to claim 1 to 15, characterized in that the liquid medium contains a hydrocarbon. 17. The method according to claim 16 «characterized» that the hydrocarbon has a boiling point of more than 200 ⁰ C. 18. The method of claim 1 to 17, characterized in that the concentration of the first reactant and the second reactant and the additional reactant, if present, in the range of 5 Maese-% to 60 Maeee-% of the total mass of the reactants and the liquid medium lies. 19. The method according to claim 1 to 18, characterized in that the reactants are stirred vigorously. 20. The method according to claim 1 to 19, characterized marked that a dispersant is used. 21. The method according to claim 20, characterized in that the concentration of the dispersant in the range of 0.5 to 10 mass% of the total mass of the first and second reactants and the additional reactant, if present. Process according to claims 1 to 21, characterized in that the polymer material produced has a particle size in the range of 1 to 500 microns. 27i. Process according to claims 1 to 22, characterized in that the reaction is effected in a dry inert atmosphere » 24. Polymer material in particulate form, characterized that it was made by a process according to Arjpruch 1 to 23 « 25. The method of claim 1 to 24 «characterized« that the polymer material is pyrolyzed in an additional step or additional steps «to obtain a ceramic material * 26. The method of claim 24, characterized in that the polymeric material is heated in a first additional step to an elevated temperature to obtain a coked product containing an intimate mixture of an oxide of the metallic or non-metallic element and in a second step The coked product is heated to an elevated temperature to obtain a ceramic material. 27. A method according to claim 26, characterized in that the coked product is heated in an inert atmosphere to produce a carbide of the metallic or non-metallic element. 28. A method according to claim 26, characterized in that the coked product is heated in a nitrogen atmosphere or in the atmosphere of a reactive nitrogen-containing compound to produce a nitride of the metallic or non-metallic element. 29. Ceramic material «characterized in that it was prepared by a method according to claim 25 to 28.