PHASE-TRANSFORMATIONS IN DICALCIUM SILICATE .3. EFFECTS OF BARIUM ON THE STABILITY OF FINE-GRAINED ALPHA-L' AND BETA PHASES

Fine-grained materials containing both alpha(L)'-Ca2SiO4 and beta-Ca2S iO4 were fabricated as an analogue to tetragonal zirconia polycrystals (TZP) with the use of barium to stabilize the high-temperature polymo rphs of Ca2SiO4. The microstructure of dense alpha(L)'-Ca2SiO4 exhibit ed none of the twinning or residual strain previously observed in fine -grained beta-Ca2SiO4 and there was no evidence of barium-rich grain b oundary phases. Materials fired in the alpha region exhibited large gr ain sizes. Stress-induced alpha(L)' --> beta transformation was observ ed on ground surfaces but not on fracture surfaces.