CS220143B1 - Process for preparing alpha-AhO; - Google Patents

Abstract

The aim of the invention was to prepare the alpha modification of alumina in a single continuous operation. The aim was achieved by the process according to the invention in that the thermal decomposition of the oxygenated aluminium compounds takes place in the presence of inorganic fluorides.

Description

The invention relates to a process for the preparation of powdered high-temperature alpha alumina modification, which is used in particular for the production of alumina-based ceramics (corundum ceramics) with technical and special applications.

To prepare this alpha-AUCU there are presently used aluminum salts, in particular oxygen, which are thermally decomposed (hereinafter only calcined in the first stage to form low temperature modifications of Al 2 O 3). It is calcined at a temperature of about 1050 ° C for one hour to form low-temperature γ-AhOj. The resulting powder of low-temperature forms ΑΙ2Ό3 is screened and after the addition of technological additives affecting in particular the physical properties of The resulting α-AhOs containing MgO as a sintering additive, possibly containing other admixtures affecting the physical properties of the final corundum ceramic, are sorted again and further processed into corundum ceramic products by sintering technology. Preparation of alpha-Al2O3 by a single continuous calcination process of alum and / or other aluminum salts together with technological and sintering additives at temperatures above 1200 ° C is not possible. since low-temperature forms of AI2O3 are formed first, which gradually convert to alpha-AbCU as a result of polymorphic alumina conversion, accompanied by a contraction of ΑΙ2Ό3 powder volume and an overall change in its physical and chemical properties, resulting in hard lumps of sintered alpha-AkOj. a product suitable for corundum ceramic sintering technology can only be converted by other demanding operations, such as grinding and other alpha-AlzOs grain size adjustments, which increases laboriousness and the possibility of undesirable contamination of the highly pure product. admixtures.

These deficiencies are largely eliminated by the process of preparing the alpha modification-oxide. Minic acid curing of the aluminum salts according to the invention in that the calcination is carried out in the presence of inorganic fluorides or mixtures thereof in an amount of 0.1 to 10% by weight, based on the aluminum salts, at a temperature of 500 to 1400 ° C.

The advantages of the process according to the invention are lower energy consumption (up to 50%), lower time consumption (up to 50 ° / oJ), less preparation effort consisting of a single continuous: curing of aluminum salts, single grain size adjustment step and elimination of the possibility of undesirable contamination.

Example 1

The alum was calcined in the presence of 0.025% MgO and 1% aluminum fluoride. at 10 ^° C for C. 4 hours, the alpha-AhO 3 formed having a specific surface area of 18 m ² . ^_1 g and was workable technology for sintering corundum ceramics.

Example 2

The aluminum nitrate was calcined in the presence of 1% magnesium fluoride at 1200 ° C for 2 hours. The resulting alpha-Al2O3 did not contain low-temperature alumina modifications.

Example 3

The aluminum sulphate was calcined from 0.25% by weight of BN * nostix by weight of magnesium-araonic hexahydrate and 0.1% by weight of NH3HF3 on sulfur; The reaction time was 3 hours at 105 ^{° C.} afMα-Al2O3 had a specific surface area of 20 m ² . g ” ¹ and was workable after sorting into corundum ceramics.

Claims (1)

Subject Process for the preparation of alpha-AkCl by caicination of aluminum salts, characterized in that the calcination is carried out in the presence of inorganic fluorides OF THE INVENTION or mixtures thereof in an amount of 0.1 to 10% by weight of these substances, based on aluminum salts, at a temperature of 500 to 1400 ° C.