DE2119303A1 - Process for the manufacture of refractory bricks - Google Patents

Description

PATENT ADVOCATE DR. HANS-GUNTHER EGGERT, DIPLOMA CHEMIST

5 KOLN-UNDENTHAL PETER-KINTGEN-STRASSE 2 '2119303

Cologne, the 2o. April 1971 Eg / Ax / pz / 94

FOSECO TRADING AG, Langenjohnstrasse 9, 7ooo Chur / Switzerland

Process for the manufacture of refractory bricks

According to a known method, refractory bricks are produced by mixing a finely divided refractory material, for example alumina or bauxite, with phosphoric acid (usually in the form of an 85% aqueous solution) in such an amount that a slightly moist powder is formed that then is sometimes formed into bricks without pressing, which are then kilned at a temperature of at least 600 ^° C. In general, an amount of the phosphoric acid solution of about 4% by weight will suffice. In certain cases, clay can be added to the brick mix to improve the malleability of the mix and to increase the green strength of the undried bricks. The proportion of any added clay is preferably about 4 wt .- ^. If dense bricks are to be made, the wet powder must be pressed into the brick shape.

The liquid additives in this process reduce the density of the mixture and thus reduce it the weight of the mixture that can be filled into a mold. This is undesirable because it reduces the compression ratio of the powder (i.e. the ratio of

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linear dimensions or volume dimensions before and after pressing) is increased. When the mix to bricks is pressed, this can result in deformations, even with a sophisticated molding technique difficult to avoid. The problem is special serious when the bricks are formed by pressing under high pressure such as isostatic pressing.

It has now been found that the addition of liquid W can be avoided if, instead of the liquid phosphoric acid, a finely divided solid material is used which, when heated, forms phosphoric acid and / or phosphorus oxides.

The invention accordingly provides a method for the production of refractory bricks, which is characterized in that is ^ that one is an intimate mixture of finely divided refractory material and a solid material which, when heated, forms phosphoric acid and / or phosphorus oxides, pressed into bricks and the shaped bricks heated to a temperature at which phosphoric acid and / or ^ Oxides of phosphorus are released.

Preferably, the phosphoric acid or Phosphoroxyde forming material is used in such an amount that the finished tile has a calculated phosphorus as phosphate content of o, from 5 to 2, ο wt.%.

Preferably, phosphoric acid or phosphorus oxides-forming materials are used which contain phosphoric acid or -oxyde - release when at a temperature

ο
be heated in the range from 180 to 400 C. Suitable materials are, for example, ammonium phosphates, e.g.

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Diammonium hydrogen orthophosphate (NHh) ₂ HPOj !, ammonium polyphosphate (NH ₂ IPOp) _n , hydrazine phosphate and hydroxylamine phosphate, various salts that are formed between phosphoric acid and amines, in particular fatty amines and phosphoric acid esters of wax alcohols, polyalkylene glycols and other organic hydroxy compounds.

It is preferred to use organic phosphates which are also effective as lubricants and act on them Way to improve the compressibility of the mixture to be pressed into bricks.

The bricks can be formed in a conventional brick press, but it is preferred that the bricks be formed by isostatic pressing. The bricks are preferably pressed at a pressure of at least 2,000 kg / cm. Here it is to be noted that the improved properties of bricks produced according to the invention in higher Dimensions can be achieved when the bricks are pressed at higher pressure. Pressing at high pressure does not produce any Improvement in the properties of bricks obtained from a mixture of refractory material and liquid Phosphoric acid can be produced. In particular, in an isostatically pressed mixture of this type, the compression which the mixture experiences, so great that the finished brick is deformed and cracked after drying.

Any common refractory materials can be used for Making the bricks to be used. Alumina, for example, in the form of crushed calcined Bauxite is the preferred refractory material, but other alumina-containing materials, e.g. calci-

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how magnesium oxide, calcined dolomite, beryllium oxide, titanium oxide> or zirconium used ned alumina, lamellenfö'rmiges alumina, fused alumina, fireclay clay-based ground fireclay and mullite, and other refractory materials,

The intimate mixture of finely divided refractory material and phosphorus oxide or phosphoric acid-forming material can be prepared by simply dry grinding the constituents W or by introducing the phosphorus oxide or phosphoric acid-forming material in a suitable solvent, preferably an organic solvent, which is then used before the mixture is pressed into bricks is evaporated.

The bricks mixture according to the invention may contain in addition to the above ingredients, other ingredients such as up to 5 wt <* (which gives the bricks green strength immediately after pressing) ■% of a clay, or up to 2 wt -..% Of an internal lubricant, eg wax, to improve the press properties of the. Mixture.

The invention encompasses both the above-described method for producing the bricks and that here manufactured bricks.

example 1

A mixture was made from the following ingredients:

95 * 5 % calcined bauxite (graded from 6 mm to dust size)

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4.5% by weight of ammonium hydrogen orthophosphate (on passage ground through a sieve with a mesh size of 53 M).

Parts of this mixture were isostatically pressed into bricks under a pressure of 2,000 kg / cm, which then Were kept at 8oo ° C for 12 hours. The compression ratio during pressing was 1.04: 1. The finished Bricks had the following properties

Apparent porosity 27 %

Volume weight 2.5 g / cnr

Apparent specific gravity 3 * 5 g / cm Rupture modulus at 160 ° C 77 kg / cm

Volume change on renewed - _{V (} - &

_o + ° * (D 7 °

heat to 1600 C

Example 2

91.5 wt .- ^ calcined bauxite (as above) 4, ο wt .- ^ binding clay (dry)
4.5 wt -.% Diammonium

The clay and phosphate were ground in a vibrating mill to a particle size of 53 1 * and smaller mixed. The bauxite was then mixed in, whereupon parts of the mixture obtained changed to that described in Example 1 Way were isostatically pressed and fired. The finished bricks had the following properties:

Apparent porosity 22 %

Volume weight 2.9 g / cmr

Apparent specific gravity 3.4 g / cm

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Rupture modulus at 160 ° C 88 kg / cm

Volume change on renewed heating to 160 ° C + 0.4 %

Example 3

95.5 wt -..>% Calcined bauxite (as in Example 1) 5.5 wt "% AmmoniumpoIypho sphat '

l, o wt -.% organic salt prepared by the reaction of equal molar amounts of phosphoric acid and handeis- "usual .Alkylpropyldiamin.

The bauxite and ammonium polyphosphate were first mixed in a vibrating mill. Then the organic one Salt added to the mixture as a dispersion in acetone. The acetone was then allowed to evaporate, whereupon parts of the mixture bricks were formed and heated in the manner described in Example 1.

Example 4

A lubricant, e.g. paraffin wax or polyethylene glycol wax, was added to the mixtures of Examples 1 and 2. either in finely ground form or added as a solution, whereupon the solvent was allowed to evaporate. The amount of wax added was 0.2 wt .- ^.

In all of the experiments described in the preceding examples, refractory bricks with high dimensional accuracy were obtained and very little tendency to crack.

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Claims (7)

Patent claims 1.) Process for the production of refractory bricks, characterized in that an intimate mixture, of finely divided refractory material and a solid material which, by heating, phosphoric acid and / or Forms phosphorus oxides, presses them into bricks and the bricks thus formed are heated to a temperature in which phosphoric acid and / or phosphorus oxides are released. 2. Verfanren according to claim 1, characterized in that the mixture is isostatically pressed to form bricks. j5. Method according to claim 1 or 2, characterized in that that the phosphorus-containing material is used in such an amount that one in the final brick as phosphorus calculated phosphate content of 0.5 to 2.0 wt .- # is obtained. 4. The method according to claim 1 to 3, characterized in that that a mixture is used which contains diammonium hydrogen orthophosphate. 5. The method according to claim 1 to 4, characterized in that a consisting essentially of alumina finely divided refractory material is used. 6. The method of claim 1 to 5, characterized in that the mixture up to 5 wt -.% Of a clay are added. 109845/1709 A 8 - 7. The method according to claim 1 to 6, characterized in that up to 5 wt. % Of an internal lubricant are added to the mixture to improve the pressing properties of the mixture. 109845/1709