Ultrasonic Properties of Calcium Phosphate Glasses and Glass-Ceramics

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[Objective] The purpose of the present research is to measure ultrasonic properties of calcium phosphate glasses and glass-ceramics and to elucidate the elastic properties of these bioceramics.[Experimental] Calcium phosphate glasses, xCaO・ (1-x) P_2O_5, were made in the composition range x=0.25-0.50. First, required amounts of H_3PO_4 and CaCO_3 were made to react in an aqueous solution in a beaker made of poly (tetrafluoroethylene) and after evaporation of the water a chemically reacted powder was obtained. The powder was fused in an alumina crucible at a temperature of 1300ﾟC for 2h. Then the liquid was poured into a graphite mold which had been preheated at 300ﾟC and cooled at a rate of 1K/min to room temperature to form a cylindrical bulk glass. The glass transition temperature and the crystallization temperature for the glass of each composition were determined by differential thermal analysis. After each bulk glass had been annealed at the glass transition temperature, the ultrasonic properties were measured. Moreover, each bulk glass was crystallized at the crystallization temperature and the ultrasonic properties of the glass-ceramics were also measured. In order to measure the ultrasonic velocity with high accuracy, the ultrasonic pulseecho overlap method was refined during the present research. It was ascertained that ultrasonic velocity can be measured within an error of 0.02% by use of a silica glass as the standard specimen.[Results and Discussion] For these glasses and glass-ceramics, the following physical properties were measured : ultrasonic velocity, ultrasonic absorption coefficient, temperature coefficient of ultrasonic travel time, density, and thermal expansion. Especially, from the density and the ultrasonic velocity, elastic constants such as Young's modulus, rigidity modulus, bulk modulus, Poisson's ratio, and acoustic impedance were evaluated, from which the elastic properties of these bioceramics were elucidated.