Crystallisation kinetics of a 2 center dot 3Li(2)O(center dot)1 center dot1ZrO(2 center dot)6 center dot 6SiO(2) glass

The nucleation and growth of zircon (ZrSiO4) crystals on the free surface o f a 2.3Li(2)0.1.1ZrO(2).6.6 SiO2 glass was investigated through differentia l thermal analysis (DTA), x-ray diffraction (XRD) and scanning electron mic roscopy (SEM). The crystallisation completed at about 860 degrees C with an activation energy value corresponding to 740 kJmol(-1). Samples with polis hed free surfaces were nucleated at selected temperatures in the range 640- 690 degrees C and then heated at 750 degrees C for 30 min for crystal growt h. A dominant effect of surface nucleation was observed and the number of Z rSiO4 crystals per unit area and the mechanism of crystallisation were dete rmined. It was concluded that the nucleation starts from a fixed number of surface nuclei which reach a maximum at 670 degrees C corresponding to a zi rcon crystal number density, of 133x10(11) m(-2) and that at 880 degrees C a uniform surface crystalline layer was formed with a rate of growth of 1.9 3 mu m min(-1).