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Common inorganic binder for refractory materials

Date:2019-09-21 16:39 | From:Zhengzhou Sunrise Refractory | Author:admin
As is known, refractory materials are mainly composed of refractory aggregates, refractory powders, binders, admixtures and other raw materials. Commonly used binders can be divided into four major categories, and their binding mechanisms are different.
1. Calcium aluminate cement
Calcium aluminate cement is a cement containing calcium aluminate or calcium aluminate as the main mineral component. It is made by mixing natural alumina or industrial alumina with calcium carbonate in a certain proportion, by calcination or electrofusion, and also by melting and mixing with bauxite and limestone. Mainly used as a binder for refractory castables and shots. The low-grade refractory castables are made of ordinary calcium aluminate cement, and the high-grade refractory materials (corundum, mullite, chrome corundum, corundum spinel) are made of pure calcium aluminate cement.
Second, phosphoric acid and phosphate
Phosphate binding is a thermosetting bond. Under normal circumstances, if no hardening agent such as cement is added, it is necessary to react with refractory materials to form a chemical bond under elevated temperature conditions.
After heating, the phosphate binding phase undergoes very complex chemical changes, depending on the temperature, the original composition of the binder, and the composition and activity of the refractory. For example, after mixing phosphoric acid and industrial alumina, heat treatment at 1200 ° C to form aluminite AIPO4.2H2O; after 200 ° C heat treatment, the combined phase is still aluminophosphate; after 350 ° C heat treatment, the formation of aluminophosphate AIPO4; After heat treatment at 500 ° C or higher, the formation of AIPO4 in the phosphorus quartz and cristobalite phases began.
In general, the aluminum phosphate binding phase needs to be heat treated at 500 ° C or higher to maintain stability in the atmosphere for a long time. Because the anhydrous aluminum phosphate AIPO4 has a variety of crystal forms, in addition to phosphorus quartz type, cristobalite type, aluminosilicate type, there are also metastable crystals such as A, B, C, D, E. Among them, A, B, C, D, E and other metastable aluminum phosphate will absorb moisture and soften. If the heat treatment temperature is insufficient and there is not enough coagulant, the performance and life of the phosphate bonded refractory will be affected.
Phosphoric acid is used in phosphate-bonded refractory bricks, castables, fire mud; aluminum phosphate is used for acidic and neutral refractory materials; sodium hexametaphosphate can be used as alkaline refractory binder.

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