SU69187A1 - Method of making high alumina refractories - Google Patents

Description

Methods for the manufacture of high-alumina refractories based on alumina hydrate prepared chemically are known.

A method is proposed for the manufacture of high-alumina refractories from freshly precipitated aluminum oxide hydrate mixed with liquid glass, with or without refractory clay or kaolin, and the same mixture in compacted and calcined form as a filler.

The main raw material for the production of the proposed refractories is freshly precipitated alumina hydrate.

In order to improve the sintering properties of high-alumina hydrate masses, sodium silicate is introduced into their composition, mainly in the form of aqueous solutions.

Freshly precipitated alumina hydrate can be obtained from clays or kaolins by acid or alkaline methods known in practice.

With the acid method of lump clay, after dehydration in the temperature range of 600-800 ° C, it undergoes

extraction with acids (sulfuric, hydrochloric, nitric, etc.).

Alumina hydrate is obtained by precipitating solutions of aluminum salts obtained by extracting dehydrated clays with acids with ammonia. The resulting high silica sediment can be used to produce lightweight refractories. After precipitation of aluminum salts with ammonia, valuable by-products are obtained, in the form of ammonium salts of the corresponding acids.

In the alkaline method, a mixture of clay (kaolin) and sodium sulfate or mirabilite is briquetted and sintered at temperatures of 1350-1450 ° C. After sintering, the briquettes are leached with water and converted into sodium aluminate solution in the form of sodium aluminate. Water-insoluble calcium silicates remain in the sediment. The sodium aluminate solution is treated with carbon dioxide to produce alumina hydrate and an aqueous solution of soda. Aluminum hydroxide is separated by filtration and used to produce high 453

low-earth refractories. The soda solution is evaporated and the soda can be used to melt glass. Thus, in the alkaline process, sodium sulphate or mirabilite is processed at the same time into soda.

The alumina hydrate obtained by such methods is characterized by high plasticity and consists of crystals with a size of less than one micron. Therefore, it does not require grinding and is introduced into the masses in the process of mixing them using commonly used equipment — belt presses, runners, etc.

Hydrate masses are sintered at temperatures of about 1,400 ° C, i.e., 200 ° C lower than masses with alumina, which opens up the possibility of producing high-alumina refractories using conventional chamotte production furnaces.

Introduction smoothly in the form of sodium silicate guarantees obtaining dense products from hydrated masses after firing them at a temperature not higher than 1450 ° C.

The properties of hydrated masses are different from those of clay masses and therefore require the use of new methods for the preparation of fillers or chamottes, which can be carried out in two ways:

a) The high-alumina plastic mass, composed of freshly precipitated alumina and sodium silicate hydrates with or without clay or kaolin, is processed in belt presses, followed by cutting into small pieces. Without additional compaction, such a mass is almost unsuitable for obtaining high-alumina products or fillers, since the latter have greater porosity after roasting. Therefore, the pieces of plastic mass are subjected to additional compaction during their drying by pressing on hand or mechanical presses. Such compaction of the lumps of mass during the drying process is performed at least two times.

In this case, a dense briquette will be obtained, which provides, after calcination, the production of low porous fillers.

b) The weight after processing on belt presses is subjected to drying, grinding and moistening, followed by briquetting. This briquette after firing has a lower porosity than the pieces of mass after processing on belt presses, i.e., without further compaction.

In order to maximize the compaction of the filler, the briquettes made by the above methods can also be heated to 600-1200 ° C and then subjected to mechanical compaction by stamping or pressing in the hot state. Hot pressing completely replaces the burning of briquettes and reduces their porosity.

Subject invention

A method of manufacturing high-alumina refractories based on alumina hydrate obtained chemically, characterized in that the binder used is a mass consisting of a mixture of freshly precipitated alumina hydrate and liquid glass with refractory clay or kaolin, or without it, and the quality of the filler is the specified mixture, subjected to drying, compaction and roasting.