YTTRIUM SIALON GLASSES - NUCLEATION AND CRYSTALLIZATION OF Y35SI45AL20O83N17

The crystallization of a glass with a composition Y35Si45Al20O83N17 ex pressed in equivalent %, which corresponds to a normalized composition Y0.28Si0.27Al0.16ON0.13, has been studied using an ultrasonic techniq ue. The results were compared with those obtained by more classical te chniques such as high temperature X-ray diffraction or differential th ermal analysis. The analysis of the data was made within the frame of the general theory of transformation kinetics classically used for the interpretation of differential thermal analysis and differential scan ning calorimetry experiments. The structure was studied by transmissio n electron microscopy at different stages of the glass to glass-cerami c transformation. The devitrification was shown to develop by homogene ous nucleation in the bulk and crystal growth was controlled by diffus ion. The optimum nucleation temperature was determined to be 960 degre es C and an activation energy for crystal growth rate found equal to 1 025 +/- 20 kJ mol(-1).