The mechanical strength (structural strength) of refractory products, especially unfired refractory products and unshaped refractory materials, is mainly provided by binders. However, there are many kinds of binders used for refractory materials, and their bonding principles are also different. Therefore, in actual production and use, appropriate binders should be selected according to the refractory material, molding or construction methods, service conditions and other factors. The selection principles are as follows.
① The properties of the binder must be compatible with the properties of the bonded refractory. Acidic, neutral or weakly alkaline binders can be selected for acidic and neutral refractories. For alkaline refractories, acid binders cannot be used directly, and only neutral or alkaline binders can be used. If used under reducing conditions, organic binders with high carbon residue can also be selected.
② The selected binder shall be compatible with the molding method or operation performance (construction performance) of the material.
Fired refractory products generally use temporary binders (such as lignosulfonic acid, etc.), while unfired refractory products generally use chemical binders (such as aluminum dihydrogen phosphate, sodium silicate, etc.);
The casting refractory shall be made of binders that can produce condensation and hardening at room temperature, such as hydration bonding or chemical bonding (adding hardening agent), or coagulation bonding (adding coagulant).
The ramming material and plastic can be adhesive bonded, chemical bonded or ceramic bonded binders;
The binder similar to the casting refractory can be selected for spraying refractory.
③ The selected binder must be compatible with the high-temperature performance of the material. The use of binder shall not reduce the high temperature structural strength, corrosion resistance and slag penetration resistance of materials. For example, high alumina or clay castables can use ordinary calcium aluminate cement or combined clay as the binder, while corundum or corundum spinel castables should use pure calcium aluminate cement or reactive aluminum oxide as the binder.