Thermal Conductivity of Alloys as a Function

Thermal Conductivity of Alloys as a Function of Temperature, 12-205 Thermal Conductivity of Ceramics and Other Insulating Materials,... 

Figure 4.23 Thermal conductivity of some liquid alloys as a function of temperature. Reprinted, by permission, from T. lida, and R. I. L. Guthrie, The Physical Properties of Liquid Metals, p. 241. Copyright 1988 by Oxford University Press.

Figure 4 shows the room temperature thermal conductivity of the SiGe sintered alloys as a function of the treatment time. The thermal conductivity is reduced by the plasma treatment monotonously with increasing the treatment time. The reduction of the thermal conductivity may be attributed to presence of Ge-rich layers around grain... 

Adiabatic calorimeters have also been used for direct-reaction calorimetry. Kubaschewski and Walter (1939) designed a calorimeter to study intermetallic compoimds up to 700°C. The procedure involved dropping compressed powders of two metals into the calorimeter and maintaining an equal temperature between the main calorimetric block and a surrounding jacket of refractory alloy. Any rise in temperature due to the reaction of the metal powders in the calorimeter was compensated by electrically heating the surrounding jacket so that its temperature remained the same as the calorimeter. The heat of reaction was then directly a function of the electrical energy needed to maintain the jacket at the same temperature as the calorimeter. One of the main problems with this calorimeter was the low thermal conductivity of the refractory alloy which meant that it was very difficult to maintain true adiabatic conditions. 

The lead-base babbitts are based upon the lead—antimony—tin system, and, like the tin-base, have a structure of hard crystals in a relatively soft matrix. The lead-base alloys are, however, more prone to segregation, have a lower thermal conductivity than the tin-base babbitts, and are employed generally as an inexpensive substitute for the tin-base alloys. Properly lined, however, they function satisfactorily as bearings under moderate conditions of load and speed. 

To examine the validity of the WFL relation, values of the ratio of the experimental to theoretical values for the Lorenz function (Z/Lo), for temperatures close to the melting point, were compared and L/Lq was found to be close to unity for most metals and the small deviations may be due to measurement uncertainties [68]. At lower temperatures, and for some metals, significant deviations from the theoretical Lorenz munber were found and attempts to modify the WFL relation were made [69, 70]. Even larger discrepancies occurred when using the WFL relation for alloys, because electron-electron interactions, electron-phonon interactions, as well as lattice contributions, need to be considered [71]. These limiting effects vanish at melting because the crystal structure is destroyed and the WFL relation becomes a reasonable tool for determining thermal conductivities for liquid metals and alloys. 

One condition for the functioning of a nozzle is that it be thermally insulated from the mould. The best insulation is provided by an air gap. In nozzles with an in-monld gate, this gap may be filled with melt for design reasons (to prevent contact between the nozzle tip and the mould), and is then known as an insulation chamber. Another solution is to seal off and insulate the nozzle tip using a titanimn alloy ring of low thermal conductivity. The nozzle flange may be insulated by a ceramic washer, but above all the contact area with the mould is kept to the minimum dictated by strength considerations. 

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