DD159320A1 - METHOD FOR PRODUCING HIGH-POROUS FIRE-RESISTANT COOLINGS AND FORMKOERPER - Google Patents

Abstract

The invention relates to a process for producing hochporoeser refractory materials, which are used in high-temperature processes, in particular in the ceramic, metallurgical, chemical and refractory and glass industry. The aim of the invention is to reduce the specific energy costs of high-temperature processes while at the same time extending the life of refractory materials. The object of the invention is to provide an environmentally friendly, controllable process for producing hochporoeser refractory Koernungen and Formkoerper. According to the invention, the object is achieved by adding metallic aluminum in powdery and / or spherical form as well as phosphoric acid in quantified proportions to known refractory substances and their mixtures and thus controlling the process of pore formation in the refractory mixtures. The highly porous refractory materials produced according to the invention have a homogeneous and reproducible pore size distribution, are free from cracks and are furthermore distinguished by an extremely low thermal conductivity at elevated strength.

Description

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, Title of the invention

Process for producing highly porous refractory grains and shaped bodies

Field of application of the invention

The invention relates to a process for producing highly porous refractory materials, which are used as a shaped body or as a grain in the ceramic, refractory and glass industry and, in the metallurgy and the chemical industry.

Characteristic of the known technical solutions

In particular, there is known, among other methods, a process for producing high porosity refractory materials, in which pore formation is effected from the reaction of phosphoric acid with highly active calcined clay (Al 0 ).

/: "\ (Roberts, AL et al." Improvements in or relating to processes for ^k .J

The disadvantage of this method is that the use of highly active alumina, a considerable reduction in the reproducibility of the pore formation processes and thus a reduction in the controllability of the technology occurs, since such substances their properties already during storage and also change during the reaction in an uncontrollable way.

Another method uses the reaction ZAvischen aluminum powder and sodium hydroxide (NaOH) for pore formation. (Magder, Jo "Foamable Ceramic Materials" BRD-OS 2 "5o3 _e 271) The disadvantage of this process is particularly due to the fact that sodium compounds are formed in the refractory mixture after pore formation.

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which are known to greatly reduce the strength and space resistance of porous materials at high temperatures.

Object of the invention

The object of the invention is to reduce the specific energy expenditure in high-temperature processes while at the same time prolonging the life of refractory materials.

Explanation of the essence of the invention

The invention has for its object to provide a method for producing hochpöröser refractory grains and moldings, after the refractory materials can be produced by an environmentally friendly technologically controllable process, which are distinguished over known solutions by lower average pore size, lower thermal conductivity and higher strength in the high temperature range ,

According to the invention, this object is achieved in that refractory materials, such as kaolin, clay, Al "0, Al (OH), ZrSiO ^ or mixtures of these are made to a slurry of suitable consistency, added to the metallic aluminum and phosphoric acid and after Homogenizing is given in arbitrarily shaped forms. The reaction between the additives leads to gas evolution, associated with pore formation, after the completion of the molding is dried and sintered in a known manner. The production

highly porous grits from this sintered product is carried out in a known manner by crushing and classifying in the desired grain classes. The timing of pore formation and the volume fraction of the pores, their average size and size distribution are controlled by the amount of additives, by particle shape and particle size distribution of the aluminum and by the consistency of the mixture.

The inventive solution of producing highly porous refractory molded body with controllable change in volume during the drying and firing process is that the inventively produced, highly porous sintered grain again with a mixture of

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refractory materials, aluminum and phosphoric acid is made as a bond, the shaping of this mixture by pouring, shaking, stamping or pressing takes place and the subsequent drying and firing process is performed in a known manner. For the production of moldings with special properties it is possible to dispense with one or more of the listed components, and a partial or complete replacement of these by high-temperature cements is also possible.

An inventive feature of the production of highly porous grain is characterized in that the addition of metallic aluminum is preferably in a grain size * <"5 mm to Io to 1 weight percent and phosphoric acid to 15 to 1 weight percent based on the dry mixture of refractory materials.

An inventive feature of the production of highly porous refractory moldings _s is that the highly porous sintered refractory grit O constitutes up to 95 percent by weight of the dry mixture of components, accordingly, the binding 5 to loo by weight.

An inventive feature of the binding is characterized in that it can be constituted in the same way as the mixture for producing highly porous grains, wherein the ratio of aluminum and phosphoric acid is chosen such that on the one hand after completion of pore formation of metallic aluminum remains in the bond which causes a reduction in the shrinkage of the molding during the firing process due to oxidation, but that KJ can also be worked with an excess of phosphoric acid, so that the free phosphoric acid during the drying and firing process contributes to the increase in strength of the molding.

An inventive feature is characterized in that the highly porous refractory grain produced according to the invention is given an aqueous slurry of alumina cement, which can be mixed with phosphoric acid and then followed by a molding and drying process of the mixture.

The highly porous granulations and shaped bodies produced according to the described, controllable technological processes have a homogeneous and reproducible pore size distribution and are free of cracks,

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embodiment

The invention will be explained in more detail below using an exemplary embodiment.

The mixture for the realization of the process for producing highly porous, refractory grains is composed of the following constituents:

45% by weight refractory slurry kaolin and / or clay with an Al ₂ O content of> 38%

55 weight percent AIp (L

3 weight percent aluminum powder 2 weight percent aluminum semolina

Additions:

2% by weight 80% technical grade phosphoric acid

44% by weight of water

7 weight percent dextrin solution

The preparation of the mixture is carried out such that the solid components are mixed dry and then mixed with water and dextrin solution to a pulp. After sufficient homogenization, the phosphoric acid is added, homogenized again and the mixture poured into suitable forms »After a few minutes, the reaction between aluminum and phosphoric acid in motion. The pore formation is associated with a simultaneous stiffening of the slurry. After drying the shaped bodies at 135o are - I600 ⁰ C blown · The fired shaped body can be calibrated and then used as conglomerates, or they are used for the production of refractory grains which are used as insulating bulk or as temper in insulating bricks using.

A comparison of the technical material parameters of a refractory material produced according to the invention to a refractory material known from the specialist literature will be given below.

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new material known product of type JIvI 3ooo (USA) upper application limit temperature ( ⁰ C) I65o l65o Bulk density ^ g (g / cnT) o, 9o 1, o4 A (kcal / ra grd. H) at 2o ° C o, 28 o, 38 at looo ⁰ C o, 34 o, 43

Claims (4)

1 _# Process for the preparation of highly porous refractory grains and moldings from known refractory materials, such as kaolin, clay, Al ₂ O, Al (OH), ZrO ₃ , ZrSiO ₄ , SiO ₂ , Mulii *, Sillimanit and mixtures thereof, which are to a Slush or mash, which is poured, dried and sintered in suitable molds, characterized in that added to the mixture of refractory materials, aluminum in powdery and / or granular form and phosphoric acid in quantified proportions and thus the process of pore formation in these refractory mixtures becomes controllable, 2, method according to point 1, characterized in that the mixed with refractory substances 1 to 10% by weight of aluminum in powdered and / or granular form and 1 to 15% by weight of phosphoric acid, either the aluminum powder or the phosphoric acid being added as last component to the mixture, 2 05 76 9 : '- β -.--. · · · ·. - · invention claims 3, method according to points 1 and 2, characterized in that the mixture of refractory materials produced according to the invention highly porous refractory grain in proportions of ο to 95 weight percent is added, 4, method according to the points 1 and 2, characterized in that the highly porous refractory grain is added to an aqueous slurry of alumina cement, which can be mixed with phosphoric acid and the mixture is formed and dried.