CS219959B1 - Fine-grained raw material for special aluminum oxide ceramics - Google Patents

Abstract

The invention addresses the preparation of a fine-grained raw material for special ceramics based on alumina. It achieves a fine-grained raw material for special ceramics based on alumina, which can be prepared by thermal decomposition of oxygenated aluminum salts with the addition of substances with a disintegrating effect, which decompose into gaseous products at the calcination temperature.

Description

The invention provides a fine-grained raw material for special ceramics based on alumina.

The development of the component base for electronics and the production of progressive lighting, the development of new materials for machining and a number of other applications have significantly increased the demands on the quality of finely powdered raw materials based on aluminum oxide. In addition to the requirement for greater purity, emphasis is also placed on the size, or possibly the size distribution, of fine particles.

The starting material for obtaining fine-grained raw materials for special ceramics based on alumina is ammonium aluminum sulfate, aluminum sulfate, aluminum hydroxide and possibly other oxygen-containing aluminum compounds, which decompose into aluminum oxide upon heating. Gaseous products formed during thermal decomposition (hereinafter referred to as calcination) affect the size of aluminum oxide particles. However, the disintegration effect of gaseous products is not enough to prevent the formation of a large proportion of particle clusters above 50 μΐη, which can only be broken up with difficulty during sorting. The cohesion of these clusters is determined, among other things, by the temperature during calcination and the calcination time. The powder obtained in this way must therefore not only be sorted, but in many cases also ground. The disadvantage of grinding is the possibility of introducing impurities into the final product and complicating the production process.

The mentioned disadvantages, i.e. the formation of difficult-to-disintegrate aggregates, are not present in the fine-grained raw material for special ceramics based on alumina according to the invention, which can be prepared in the presence of substances with a disintegrating effect, decomposing at the calcination temperature exclusively into gaseous products, in a molar ratio of oxygenated aluminum compound: disintegrating agent 1:0.01 to 3, preferably with the addition of substances affecting the optical and other physical properties of ceramics, one-stage or two-stage calcination of oxygenated aluminum compounds.

This disintegrating admixture must not introduce impurities into the final product. Some ammonium salts, such as ammonium carbonate, ammonium bicarbonate, ammonium amidocarbonate, urea, urotropine, ammonium acetate and others, and organic acids, such as oxalic acid, citric acid, etc., can be used with advantage. In addition to the above advantage, this disintegrating admixture also shortens the calcination time; intensive boiling of the product significantly facilitates the escape of gaseous products from the oxide formed.

For some applications, additives such as MgO, TiO2, CaO, Y2O3, SC2O2, S1O2, NiO, CoO and others and their mixtures are added after the product, with the aim of positively influencing the properties of ceramics produced from this material. When introducing additives and their mixtures, it is possible to proceed in such a way that they are added before calcination or the calcination process is divided into two stages; in the first, powdered /-AlgOs is obtained at a temperature of 850' to 1150 “C, and after introducing the desired additives, it is calcined again at a temperature of 1200 to 1450 °'C to (X-Al2O3, while the disintegrating additive can be introduced into the product in both stages.

Example 1

Ammonium aluminum sulfate hydrate with the addition of 0.01 to 3 moles of urea was heated to a temperature of 1050 °C for 1 hour. The fine-grained raw material for special ceramics based on aluminum oxide prepared in this way was sorted on a 100 DIN sieve, with the residue on the sieve being negligible. The obtained product contained up to 50% less undecomposed sulfate residues. As shown in the attached table, the proportion of fine-grained particles increases with increasing addition of disintegrant.

Effect of the addition of a disintegrant on the particle size distribution of fine-grained raw material for special alumina-based ceramics:

Particle diameter d in μη

Particle fraction in weight percent Addition of disintegrant in moles

0 0.01 0.05 0.1 0.2 0.5 1 3 to 1.5 3 7 11 14 15 17 22 23 to 5 12 21 40 63 62 63 65 68 to 10 38 58 75 80 78 78; aoi 82 to 15 81 77 86 85 88 88 90. 91 to 30 80 90 91 93 95 94 95 96 50% by weight size particles into 13 9 8.2 4.7 4.5 4.4 3.6 3,

(average d in μΐη)

Example 2

Aluminum sulfate with the addition of 1 mole of oxalic acid was calcined for 1 hour at a temperature of 980 °C. An admixture of 0.2 wt. % magnesium nitrate, 0.001 wt. % T1O2 as titanyl sulfate and 0.0005 wt. % CaO as calcium nitrate was incorporated into the obtained product. After calcination at 1250 °C for 2 hours, the product was screened on a 100 DIN sieve. The fine-grained raw material for special ceramics based on aluminum oxide contained 96 wt. % particles smaller than 30 µm,

Example 3 was calcined at 1300 °C for

2.5 hours. Sorted raw material for special

The additives according to Example 2 were added to an alumina-based ceramic containing 2 moles of aluminum hydroxide, with an addition of 77% by weight of particles smaller than 15 μm.

ammonium carbonate and the mixture thus obtained

Claims (1)

SUBJECT Fine-grained raw material for special alumina-based ceramics, obtainable in the presence of disintegrating agents, decomposing solely to gaseous products at the calcination temperature, in a molar ratio of oxygen-containing aluminum compound: desinvynAlez 1: 0.01 to 3, preferably with addition substances affecting the optical and other physical properties of ceramics, by one-step or two-step calcination of oxygen-containing aluminum compounds.