THERMAL-PROPERTIES AND DEVITRIFICATION BEHAVIOR OF (2-X)CAO-CENTER-DOT-X 3Y(2)O(3)CENTER-DOT-2SIO(2) GLASSES/

The thermal properties (glass transformation, T-g, softening, T-s, and exo-peak, T-p, temperatures), and the devitrification behaviour of gl asses in the system CaO-Y2O3-SiO2 are reported The T-g, T-p and E(c) r esults can be explained on the basis of the increased structural rigid ity when Ca+2 ions are substituted by Y+3 ions, with the formation of stronger bonds to the oxygen. For the molar ratio of Ca/Si = 0.7 or mo re, wollastonite is no longer formed; at the same time a new and as ye t unidentified phase appears. Surface nucleation occurs preferentially , but, in finely powdered samples, which soften and sinter before devi trifying, surface nuclei behave virtually as bulk nuclei.