Velocity and absorption coefficient of ultrasonic waves in molten and glassy silicates and borates
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I.
INTRODUCTION
S O N I C waves are propagated by the fluctuation of density in materials. Thus, the velocity and absorption coefficient of ultrasonic waves would give such mechanical and thermodynamic properties of materials as adiabatic compressibility and volume (compressional) viscosity. Verma I in 1950 classified the absorption coefficients of organic liquids in terms of four absorption mechanisms. The absorption of sonic waves is caused by one or two changes in the heat content of the medium, viscosity, the vibration and rotation of molecules, and chemical reactions. Then, the absorption mechanisms of sonic waves in the molten oxide can be estimated from the dependency of absorption coefficient on temperature and viscosity. Sonic waves propagate in materials as phonons. The mean free path of phonons can be estimated from thermal conductivity, specific heat capacity, and velocity of sound by means of the Debye's equation which has been derived by analogy with the kinetic theory of gases. 2 Kittel 3 interpreted the distinguishing characteristics of the thermal conductivity of glasses from that of crystalline materials in terms of an approximately constant mean free path of phonons in glasses. Nagata, Susa, and Goto 4 measured the thermal conductivity of silicates in the wide temperature range of 300 to 1773 K. They found that the thermal conductivity becomes maximum near 1000 to 1200 K and above that temperature it decreases with increasing temperature. The mean free path of phonons in molten and glassy oxides may be the reason for the behavior of thermal conductivity at high temperatures. It is conceivable that ultrasonic waves are used for refining processes. For example, the size and distribution of nonmetallic inclusions in molten steel and the thickness of refractory walls of blast furnaces can be estimated. There are, however, a few available acoustic data of metallurgical materials at high temperatures. 5-8 In the present study, the acoustic properties of the velocity and absorption coefficient of longitudinal ultrasonic waves in glassy and molten oxides have been measured. KAZUHIRO NAGATA, Associate Professor, and KAZUHIRO S. GOTO, Professor, are with the Department of Metallurgy, Tokyo Institute of Technology, Tokyo, Japan. KATSUMI OHIRA is with Toppan Insatsu Co., Ltd., Tokyo, Japan. HISAO YAMADA is Research Associate, Industrial Research Institute of Kanagawa Prefecture, Yokohama-shi, Japan. Manuscript submitted December 16, 1986. METALLURGICALTRANSACTIONS B
II.
EXPERIMENTAL
The velocity and absorption coefficient of longitudinal ultrasonic waves (with 5 and 10 MHz) in glasses and melts were measured by means of a pulse-echo method. As shown in Figure 1, ultrasonic pulse is generated from a piezoelectric transducer of BaTiO3 crystal and transfers through a recrystallized alumina rod to the sample in a platinum crucible. The pulse is reflected first at the interface between the alumina rod and sample and second on the surface of the flat bottom of the platinum crucible. Then, the pulse is reflect
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