Refractory cement can provide sufficient demoulding strength for castables within 24 hours. Refractory cement can be divided into CA-50, CA-70, CA-80, etc. depending on the content of AL2O3. It is a commonly used hydration bond in cast refractory materials. The hydration behavior of refractory cement after encountering water will affect the fluidity, working time and demoulding time of the castable, and then affect the normal construction of the castable.
The hydration process of refractory cement is essentially a reaction process between a low-solubility solid and water to produce a lower-solubility solid product. It can be divided into three stages: dissolution, nucleation and precipitation. When refractory cement is in contact with water, the surface of refractory cement particles is hydroxylated first, releasing Ca2+ and AL(OH)4-ions (tetrahydroxyaluminate) until the ion concentration in the solution reaches saturation; then hydration products are formed in the saturated solution The crystal nucleus grows up and the number of crystal nuclei increases, but the deposition process has not started, which is called the nucleation period or induction period; when the crystal nucleus of the hydration product grows to a critical size, the refractory cement hydration product deposits and is accompanied by The release of heat.
In addition, the hydration process of refractory cement has another feature, that is, the refractory cement can form Ca2+ and AL(OH)4-ions during the hydration process, and AL(OH)4-ions can continue to ionize in the solution. As a result, AL3+ and OH- ions are formed. Therefore, the solution after refractory cement hydration is usually alkaline. The specific reaction is shown in the formula:
Ca(AlO2)2+ 4H2O «Ca2++ 2AL(OH)4-
AL(OH)-4 «AL3++ 4OH-
After refractory cement is in contact with water, the mineral phases CA and CA2 contained in it will react with water and form hydration products during the hydration reaction. The types of hydration products will vary with the curing temperature of the refractory cement. It's different.
