Sintering and Crystallization Processes of the Glass Powder Having Cordierite Composition

Abstract

Sintering and crystallization processes of the glass powder of various particle sizes with cordierite composition have been investigated by means of thermal shrinkage measurement, D. T. A., X-ray diffraction and polarized microscopic observation.The results obtained are summarized as follows:1) Viscous flow mechanism was applicable for the sintering of the glass powder that initiated at 820°-920°C, whereas plastic flow mechanism became to be available in the final stage of sintering where μ-cordierite began to crystallize from the glass phase at 900°-980°C. Sintering measured by thermal shrinkage of the compact body ceased at 950°-1000°C owing to the almost complete crystallization at the periphery of individual particles. Thereafter, μ-cordierite transformed to α-form at 970°-1070°C, and the microstructure of sintered bodies was unchanged up to 1300°C.2) As shown above, there existed ranges for the temperatures where sintering, crystallization and phase transformation started, since the initiation of the phenomena was affected by the particle size and the heating rate. The smaller particle size and the faster heating rate resulted in the larger thermal shrinkage and the denser sintered body. Accordingly, physical properties of the sintered body can be controlled to a considerable wide range.Activation energies for the sintering of glass powder by viscous flow, the crystallization of μ-cordierite and the transformation to α-form obtained by the Arrhenius plot were 36-115 (920°-855°C), 86, and 60kcal/mole respectively, and enthalpy changes estimated for the crystallization of μ-cordierite and the transformation were found to be 16 and 18kcal/mole respectively.