PHASE-FORMATION OF CA-ALPHA-SIALON BY REACTION SINTERING

In this study the reaction sintering route for the formation of Ca-alp ha-sialon with a composition on the line Si3N4/CaO . 3 AlN (Ca-0.8 Si- 9.6 Al-2.4 O-0.8 N-15.2, m = 1.6, n = 0.8) has been investigated. This is compared with the hot-pressing of Ca-alpha-sialon and the reaction sintering of Y- or lanthanide-alpha-sialons. The reaction follows the same sequence: first, the formation of a Ca-rich alpha-sialon phase ( m = 1.9) which is gradually transformed to a Ca-alpha-sialon with a lo wer Ca concentration (m = 1.2). The gehlenite phase (Ca2Al2SiO7, melil ite group) is observed as an intermediate product. A potential advanta ge of Ca-alpha-sialon over Ln-alpha-sialon (Si3N4/1/3 Ln(2)O(3) . 3 Al N, where Ln = Y, lanthanide) is liquid phase formation ata lower tenzp eratuue, which has a positive influence on the processing temperature. Moreover, Ca is cheaper than the lanthanides. The solubility of Ca in the alpha-sialon is in agreement with values found in the literature. (C) 1996 Elsevier Science Limited.