CS242296B1 - Process for preparing a raw material for an alumina-based mixed ceramic with admixtures - Google Patents

Abstract

A method for preparing alumina containing admixtures of metal oxides forming alkoxides, the essence of which consists in decomposing a homogeneous liquid mixture of at most four-carbon alkoxides to form a mixture of hydrated metal oxides and/or metal oxides, which is subjected to one- to two-stage calcination at a temperature of 400 to 1,400 °C.

Description

aluminum with admixtures

2

A process for the preparation of alumina comprising an additive of metal oxides forming alkoxides, the process comprising decomposing a homogeneous liquid mixture of at most four-carbon alkoxides to form a mixture of hydrated metal oxides and / or metal oxides which is subjected to one-stage to two-stage calcination 1400 ° C.

BACKGROUND OF THE INVENTION The present invention relates to a process for preparing a feedstock for mixed alumina-based ceramics with admixtures.

Polycrystalline ceramic materials based on very pure alumina have limited use in some applications due to low thermal conductivity and some unfavorable mechanical properties. These undesirable properties are eliminated, for example, in ceramic cutting tools by the fact that the base material, alumina powder, is doped with an admixture of metal oxides, for example T1O2, ZrO2, MgO in the amount of tenths to tens of percent by weight. However, this mixed feedstock cannot be prepared simply by mixing the metal oxides in powder form and homogenizing the mixture. The mixing of the oxides must take place at a microcrystalline to molecular level, which is aided by the process of preparation of the mixture by thermal decomposition of the homogenized mixture of the salts of the respective metals, most often the sulphate crystals. During their thermal decomposition, crystalline microaggregates with a chemical composition corresponding approximately to the ratio of the starting salts are formed.

The disadvantage of this process is in some cases a limited degree of homogeneity of the mixture (e.g. Al2O3 i-ZrCte), high calcination temperature of the sulphates (more than 1000 ° C), the necessity of subsequent conversion of low temperature oxides modifications to high temperature further calcination at temperatures up to 1,400 ° C. release of SO2 and SO3 emissions and relatively high demands on the chemical purity of the starting components, i.e. the corresponding metal salts.

The process for preparing a homogeneous mixture of Al 2 O 3 with metal oxide admixtures according to the invention removes these disadvantages completely by preparing the mixed ceramic raw material from a homogeneous liquid mixture of at most quadruplicate alkoxides of the respective metals which undergo hydrolytic decomposition to form a hydrated metal oxide mixture and / metal oxides homogenized at the molecular level.

As metal alkoxides, compounds of the type M ⁿ (OR] ⁿ where M is the corresponding metal (Al, Ti, Zr, Mg and the like), n its valency and R the corresponding organic radical such as ethyl, propyl and butyl and the like can be used. alkoxides can be prepared, for example, by treating the corresponding metal (Al, Mg) with the appropriate alcohol ROH or by alcoholysis of the corresponding metal chlorides or dialkylamines (Ti, Zr) either separately or together. such as benzene, xylene, or the corresponding alcohol R-OH to form a mixture of metal alkoxides corresponding to the desired ratio of metals in the final powdered feedstock.

This homogeneous liquid mixture can be subjected to several types of decomposition such as hydrolysis, pyrolysis or combustion, the most preferred of which is hydrolysis.

Hydrolysis produces mostly hydrated oxides in Al and Mg, predominantly oxides in M ^IV (Ti, Zr) metals, and the hydrolysed mixture of hydrated oxides and metal oxides is converted by thermal decomposition from the reaction mixture to a homogeneous powder mixture of oxides mixed ceramics.

In the process of hydrolysis of the metal alkoxides, it is advantageous to control the grain size of the powdered feedstock, for example by stirring, by hydrolysis at the water-solvent interface, by the presence of surfactants, by ultrasound or other disintegration methods. Another advantage of hydrolytic decomposition of alkoxides is the possibility of regeneration of all solvents.

The advantages of the process of preparing the mixed feedstock according to the invention are the complete homogeneity of the metal oxide mixture, the minimum requirements for the purity of the starting materials, the low calcination temperature of the mixture of hydrated oxides and metal oxides up to 600 ° C. The first low-temperature calcination resulting from the low-temperature modification of the metal oxides can be converted to high-temperature calcination at a temperature of up to 1400 ° C.

Example 1

Liquid mixture of aluminum and titanium (isobutanolate) containing an excess of isobutanol and an equal volume of xylene with an Al:

The Ti water (1: 0.02 molar) was hydrolyzed with water under ultrasound, the resulting organic suspension was distilled to remove organic solvents and the aqueous slurry of the mixture of hydrolysed oxides and oxides Al and Ti was dried in a spray drier. at 550 DEG C. for 1 hour The resulting powdered feedstock had a mean grain size of 13.5 µm and contained 3% TiO 2.

Example 2

A liquid mixture of isopropanolates of aluminum, magnesium, titanium and zirconium containing said metals in molar ratios of 1: 0.01: 0.02: 0.1 was subjected to hydrolysis in the presence of xylene of the same volume as the mixture of alcoholates. The hydrolysis medium consisted of a 1% aqueous hydrogen peroxide solution placed in an ultrasonic bath heated to 50 ° C. A 25 ° C warm liquid mixture of alcoholates was metered into this medium with vigorous stirring at a rate of 10 ml per minute. After complete hydrolysis, xylene and isopropanol were separated by distillation and the aqueous suspension of hydrated oxides and metal oxides was filtered, the solids washed and vacuum dried. Then the powder mixture was calcined at 800 ° C for 1 hour. The mean grain size of the powdered feedstock was 15.2 gm and the mixture contained 0.6% MgO, 2.45% TiO2 and 18.8% ZrO2.

Example 3

The liquid metal alkoxide mixture of Example 2 in the absence of additional additional solvents was thermally decomposed in a distillation apparatus at atmospheric pressure at 150-300 ° C. The decomposition products were a mixture of metal oxides Al2O3, MgO, T1O2 and ZrO2, isopropanol and olefins. X-ray diffraction showed an amorphous structure of the powder raw material, whose mean grain size was 20.8 µm.

Claims (1)

Fri E D MĚT Process for preparing an alumina-based mixed ceramic raw material with metal oxide-forming admixtures in an amount of 0.1 to 30% by weight, characterized in that the homogeneous liquid mixture of at most four-carbon alkoxides of the respective metals is decomposed to form mixtures of hydrated metal oxides and / or metal oxides homogenized at a microcrystalline to molecular level which is subjected to one-stage to two-stage calcination at a temperature of 400 to 1400 ° C.