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Abstract-80mol% TeO2-20mol% LiF glass composition with 0.005 mole Gd2O3 and TbF3 was prepared by conventional casting technique. DTA analyses were carried out on the glass at different heating rates and an activation energy value of 129 kJ/mol for surface crystallization was determined graphically from a Kissinger-type plot and using the method of Ozawa and Augis-Bennett the activation energy values were 142 kJ/mol and 136 kJ/mol respectively.

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Apatite/wollastonite (A/W)—phlogopite (Ph) glass‐ceramics of various compositions were prepared by means of pressureless sintering of two frit mixtures. Sintering conditions were studied by differential thermal analysis (DTA) and hot‐stage microscopy. The sintered samples were characterized by X‐ray diffraction. The results showed that by addition of a frit of phlogopite composition to a frit of A/W composition, the crystallization temperature decreases which results in suppressing the sintering process. The 50–50 frits mixture could be sintered to 0.90 relative density after 1 h heating at 1100°C. The type and sequence of formation of crystalline phases were also modified. Whereas the A/W glass–ceramic crystallized to apatite and wollastonite, the crystallization products of 50–50 frits mixture were fluoro‐apatite, wollastonite, diopside, and mellilite.

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