Ceramic joining through reactive wetting of alumina with calcium aluminate refractory cements

Compositions in CaO-Al₂O₃ system have been prepared by gel-to-crystallite conversion method. Reactive powders of 1 : 2, 1 : 1, 2 : 1 and 3 : 1 of CaO and₂O₃ compositions were obtained by calcining the product at 800–1200°C. Fine grained powders were used as refractory cement for joining alumina ceramics. An optimum temperature of 1450°C for 4 h produced joints of satisfactory strength. The microstructure and X-ray phase analysis of the fractured joint surface clearly indicate reactive wetting of the alumina ceramics. This wetting enhances the joining of alumina substrates and can be attributed to the formation of Ca₁₂Al₁₄O₃₃ liquid phase. The results are explained by using CaO-Al₂O₃ phase diagram.