Thermal conductivity intermetallic compound

The problems associated with direct reaction calorimetry are mainly associated with (1) the temperature at which reaction can occur (2) reaction of the sample with its surroundings and (3) the rate of reaction which usually takes place in an uncontrolled matmer. For low melting elements such as Zn, Pb, etc., reaction may take place quite readily below S00°C. Therefore, the materials used to construct the calorimeter are not subjected to particularly high temperatures and it is easy to select a suitably non-reactive metal to encase the sample. However, for materials such as carbides, borides and many intermetallic compounds these temperatures are insufficient to instigate reaction between the components of the compound and the materials of construction must be able to withstand high temperatures. It seems simple to construct the calorimeter from some refractory material. However, problems may arise if its thermal conductivity is very low. It is then difficult to control the heat flow within the calorimeter if some form of adiabatic or isothermal condition needs to be maintained, which is further exacerbated if the reaction rates are fast. 

On the other hand, the use of rare earth metals for the fixing of os gen and sulfur in light metals for production of conductive copper and conductive aluminum has remained insignificant. Hcwever, the use of rare earth elements as magnesium hardeners remains important, tfere the rare earth metals serve precipitation of intermetallic compounds of high thermal stability. 

E. Gratz and M.J. Zuckermann, Transport properties (electrical resitivity, thermoelectric power thermal conductivity) of rare earth intermetallic compounds 117... 

Most of the known chemical elements are metals, and many of these combine with each other to form a large number of intermetallic compounds. The special properties of metals - their bright, lustrous appearance, their high electrical and thermal conductivities, and their malleability - suggest that these substances are bound together in a very special way. 

Some elemental metals and many intermetallic compounds are brittle, not malleable or ductile. Borderline substances, showing metallic properties to a decreased extent, are called metalloids or semiconductors. Probably the best criterion for distinguishing a meted and a metalloid or semiconductor is the temperature coefficient of thermal and electrical conductivity. With increase in temperature, the thermal and electrical conductivity of a metal decreases, whereas that of a metalloid or semiconductor increases. 

Aluminum nitride is most commonly used for its high thermal conductivity. Recently, a poreless composite material, TiAl-TiB2-AlN, was obtained by reacting a Ti-F(0.7-0.95)A1+(0.05-0.50)8 mixture at 30- to 100-atm nitrogen pressure (Yamada, 1994). The use of high-pressure nitrogen gas was found to be effective for simultaneous synthesis and consolidation of nitride ceramics with dispersed intermetallic compounds (e.g., TiAl). Dense, crack-free products with uniform grains (approximately 10 mm in size) were obtained. 

TRANSPORT PROPERTIES (ELECTRICAL RESISTIVITY, THERMOELECTRIC POWER AND THERMAL CONDUCTIVITY) OF RARE EARTH INTERMETALLIC COMPOUNDS... 

Rare earth intermetallic (RI) compounds have been the subject of many recent experimental investigations because of the nature and variety of their physical properties (Buschow, 1977, 1979 Kirchmayr and Poldy, 1979). In this review article we concentrate on one aspect of such investigations, namely the transport properties of these interesting compounds. We describe in particular experimental data for the resistivity, thermopower and the thermal conductivity. 

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