DE2842176C2 - Chemically setting mass with a high alumina content based on bauxite without the addition of clays and its use as shaped bodies, in particular stones, for lining aluminum melting units - Google Patents

Description

The invention relates to a chemically setting composition with a high alumina content based on bauxite without the addition of clays and their use as shaped bodies, in particular stones, for aluminum melting units.

Chemically setting compounds with a high alumina content based on bauxite without the addition of clays are already known, they will inter alia. for the production of ;; refractory moldings and in particular refractory bricks used.

Such masses contain bauxite as main constituents, for example in the order of magnitude of 80 to 95 wt%. In addition, a small amount of caicinated clay, usually in a Amount of 5 to 12% by weight, can be added.

The grain size of the bauxite is the same as that usually used in the manufacture of refractory masses or their further processing into stones applied area, d. H. the maximum grain size is usually between 3 and 8 mm. and the grain size distribution is such that the closest possible packing is achieved.

The coarse-grained portion of the bauxite with a grain size above 1 mm usually makes 35 to 70 wt .- 'ϊί of the total mass. Of course it is also possible to produce a mass with a grain gap, i.e. H. a mass at which has a certain mean grain size range, usually between 0.2 to 0.5 mm. is missing.

A conventional, optionally processed bauxite can be used as the bauxite starting material, the content of Fe ₂ O, however, if possible not exceeding 5 ^{r /} r and in particular 2.5%. The SiO ₂ content of the bauxite is usually below \ 2 ^{r /} r, more advantageously below K) ^r i. So-called latent bauxites are preferably used, which have a high alumina, low silica * and low iron content.

Such masses are chemically bound, ie with the addition of usually phosphoric acid or an acidic aluminum phosphate, eg. B, monoaluminum phosphate. The phosphoric acid is usually used as an 80% solution, ie with a P ₂ Oy content of 58%. The monoaluminium phosphate can be added either in dissolved form or as a finely divided powder.

Such masses are adjusted to a ϊ moisture content between 3 and 6% for processing, in Thoroughly mixed in a compulsory mixer and then shaped under pressure into moldings or stones. Then either just drying at temperatures of up to 120 ° C or firing up to temperatures of 700 ° C.

Such masses or shaped bodies produced therefrom and in particular stones are mainly used in aluminum smelting units, d. H. in aluminum melting troughs, aluminum melting pots

ij or aluminum smelting furnaces that operate at temperatures can be operated up to 1000 ° C. At higher operating temperatures and also at a content in the Mass or moldings of clay as a binder, the infiltration and corrosion is significantly increased, so

in that the materials listed are no longer suitable for these conditions. A major disadvantage of such ^{known masses used up to 1000 J} C is, however, that the liquid aluminum or the slag floating on it to the

r> crawls up vertical walls to a large extent and steps over horizontally lying parts.

The object of the invention are chemically setting compositions or molded articles produced therefrom which this undesirable trait of creeping up

«Ι do not have aluminum or slag.

Surprisingly, it has now been found that the addition of finely divided barium sulfate to such Masses has the effect that stones made from such masses in aluminum smelting aggregates

There was a creeping up of aluminum metal or slag floating on it on the vertical ones Walls of the aluminum smelting aggregates made from such masses are not occurs more.

The chemically setting masses with a high alumina content based on bauxite without the addition of clays according to the invention are therefore distinguished by this. that they have 3 to 30 percent by weight of finely divided barium sulfate contain.

■ r. Preferably such compositions comprise from 10 to 25 wt ^r i barium sulfate.

In the case of using the composition according to the invention in The shape of molded bodies produced therefrom, and in particular stones, should be at most

in 1000 'C corresponding to those in Aluf ;; rnium melting units be fired at the prevailing temperatures. The firing is preferably at 650-750 ° C performed.

Among finely divided barium sulfate is one material

v. to understand the maximum com limit of 0.2 mm. advantageously 0.1 mm and preferably 0.04 mm. The grain size distribution of barium sulfate within the range up to the upper grain size is not critical, usually it is

(, ο being a material that either goes up to this top Grain size has been completely broken or made from a broken material by sieving up to the one in question, upper one! Grain size was obtained. A commercially available material can be used as the barium sulfate, as is also the case, for example, as a pigment Is used. It can be a finely ground, natural barite, of course However, it is also possible to cut a

To use barium sulfate, which is then already in a very finely divided state, d. H. no longer ground must be, since its grain size is below 0.1 mm.

The use of barium compounds in refractory materials is already known, see Harders-Kienow, Feuerfestkunde (1960), p. 490, according to which barium carbonate has already been added to fire bricks for the glass industry in order to produce bricks containing barium oxide that are resistant to boi vapors and lead oxide vapors . According to this prior art, however, the barium oxide should expediently be introduced in the form of barium carbonate and not as barium sulfate. Furthermore, US Pat. No. 2,474,544 discloses a melt-cast Al ₂ O ₃ brick which can contain 4 to 9% of aggregates, one of which is BaCO ₃ . These additives serve to introduce about 1.5% glass phase into the stone. According to the information in this US patent, the maximum BaO content is 0.4% each. In addition, the Al ₂ O ₃ is at such a stone -Gehait over 90%, while produced in the from the compositions of this invention, the chemically bonded stones AljOj content in addition to the inevitable impurities in the bauxite 88 wt .-% Al ₂ O ₃ does not exceed the final fired product.

The invention is illustrated in more detail by means of the following examples.

example 1

The following starting mixture was made from a lateritic bauxite, barium sulfate and calcined Alumina produced:

40% Iateritic bauxite, grain size, 1-4 mm
15% Iateritic bauxite, grain size 0.5-1 mm
18% Iateritic bauxite, grain size 0-0.5 mm
21% by weight barium sulphate flour, grain size 0-0.1 mm, 6% calcined clay.

After thoroughly mixing these ingredients, 6% phosphoric acid was added as an 80% solution Mass added in a running compulsory mixer and the moisture content by further addition adjusted to 5% of water.

After thorough mixing in the compulsory mixer, this mass was made into a hydraulic press Stones with the dimensions 15 X 20 X 10 cm produced and fired at a temperature of 650 ° C.

Small crucibles in which aluminum was then made from the stones were then bored out Temperatures of 800 ° C for several hours ge-Hi was kept melted. There was a layer of slag on top of the aluminum.

It was found that neither the aluminum the slag still creeps up vertically on the walls of the crucible and also not on the horizontal chi) tan edge of it transgresses.

In the case of crucibles made for comparison purposes that were made from a starting material, in which the barium sulfate flour is replaced by an equal weight of bauxite flour M grain size had been replaced, the aluminum and the slag crept up the vertical crucible wall and stepped over to the horizontal sections of the top of the crucible.

,, Example2

A second starting mixture was prepared with the following composition:
55% Iateritic baaxite, grain size 1-4 mm
15% Iateritic bauxite, grain size 0-1 mm
so 20% lateritic bauxite, grain size 0-0.5 mm
5% by weight barium sulfate flour, grain size

Grain size 0-0.04 mm

5% calcined clay (flour)

The further processing of the mass was carried out according to the instructions in Example 1, but instead of 6 parts by weight of 80% phosphoric acid, only 4 parts by weight of phosphoric acid and 2 parts by weight of monoaluminum phosphate powder were added as an agent for chemical setting became.
Even with crucibles made from this mass, there was no creeping up of aluminum or melt.

Claims (4)

Patent claims: 1. Chemically setting compound with a high alumina content based on bauxite without the addition of Clays for lining aluminum smelting units, thereby characterized in that it contains 3 to 30% by weight of finely divided barium sulfate. 2. Composition according to claim 1, characterized in that it contains 10 to 25% by weight of barium sulfate contains 3. Use of the composition according to claim 1 or 2 in the form of molded articles produced therefrom, in particular stones, for lining aluminum melting units. 4. Use of the composition according to claim 3, characterized in that the shaped body in particular Stones are burned at a maximum of 1000 ° C, preferably between 650 and 750 ° C.