Densification and phase transformation of Si3N4 in the presence of mechanically activated BaCO3-Al2O3-SiO2 mixture

Densification as well as the alpha --> beta phase transformation of Si3N4 w ere monitored as a function of activation time of the BaCO3-Al2O3-SiO2 addi tive mixture. The composition of the ternary mixture corresponded to celsia n (BaAl2Si2O8-BAS). Previously, mechanically activated powder mixtures for various lengths of time were added to Si3N4 in the amount of 10-30%. Sinter ing was performed at 1650-1700 degreesC in nitrogen atmosphere up to 8 h. T he changes in densification degree, as well as phase composition, were foll owed as a function of heating time and the time of mechanical activation of the additive mixture. The results obtained showed that mechanical activati on retarded densification in samples heated up to 1700 degreesC. On the oth er hand, for the constant sintering time, alpha --> beta transformation of Si3N4, was enhanced with increasing activation time, and the amount of addi tives. (C) 2001 Elsevier Science B.V. All rights reserved.