Growth kinetics of solid-liquid Ga interfaces: Part I. Experimental
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INTRODUCTION
THE development of realistic
solid-liquid (S/L) interfacial kinetics laws, in addition to its theoretical significance, is of great interest for the solution of a series of technical problems during solidification and crystal growth. Despite the numerous experimental studies reported, little conclusive information is available regarding the kinetics of crystal growth from a melt.t2] Among the intrinsic experimental difficulties in studying metallic systems are their opacity, which precludes direct determination of the interface morphology and migration rate, high melting temperatures, impurity effects, and the establishment of satisfactory heat-transfer conditions at the interface. Another inherent difficulty in monitoring all S/L transformation processes is the measurement of the actual interface temperature. Without the precise determination of the interfacial temperature and growth rate (and the interracial composition in case of multicomponent systems), a reliable determination of the kinetics cannot be made. Several methods of direct or indirect measurement of the S/L interface temperature have been attempted in the past. t31 The most commonly used direct technique consists of embedding a thermocouple probe into the crystal or melt. This technique, however, has limited accuracy, since it gives the average temperature of the thermocouple bead rather than the actual interface temperature. The presence of the bead also disturbs the thermal and solutal fields and obviously introduces imperfections at S.D. PETEVES, formerly Research Assistant with the Department of Materials Science and Engineering, University of Florida, is Research Scientist with the Institute of Advanced Materials, CEC, JRC Petten, 1755 ZG Petten, The Netherlands. R. ABBASCHIAN, Chairman and Professor, is with the Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611. This paper is based on a presentation made in the symposium "The Role of Ledges in Phase Transformations" presented as part of the 1989 Fall Meeting of TMS-MSD, October 1-5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations Committee of the Materials Science Division, ASM INTERNATIONAL. METALLURGICAL TRANSACTIONS A
the growth front, t2cj In order to circumvent these effects, the thermal wave t4] and Peltiert51 techniques were proposed to evaluate the growth rate and interface supercooling based on an analysis of the response of the interface to a periodic heat input. The former has been subjected to wide criticism, t6,71 and the reported kinetics tS,9j are conflicting; on the other hand, the Peltier effect has been widely used for crystal growth-related experimentsfwl but not for kinetics studies. The thermoelectric probe technique, tm which has been used to determine the growth rate of Sn, Bi, and Sn-Pb, also disturbs the actual growth process and is applicable only under constrained growth conditions. An indirect method for obtaining the interface temperature relies upon mathematical analysis of heat
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