Synthesis of PbTe Intermetalic Compound by Mechanical Alloying
The formation of PbTe intermetallic compound by mechanical alloying (MA) has been investigated. The elemental starting materials were 99.5% pure lead and tellurium, with a sieve size of 80 and 200 mesh, respectively. A SPEX 8000 shaker milling was used to perform the MA, using WC balls as milling media in a cylindrical hardened tool steel vial. X-ray diffraction analysis was performed with a profile-fitting program, to evaluate time evolution of the alloy formation. An exotermical reaction occurs on PbTe formation, with entalphy H= - 16.3 Kcal/mol. The *T value is confirmed by the heat exchange equation *Q = |*Hf | =* i (mici ) *T, where the summation comprises the mass and specific heat of vial, balls and powder material. For the standard milling conditions employed, the PbTe formation occurs at aproximately 90 seconds of milling, when using charge ratios between 3:1 and 7.5:1. However, for lower charge ratios (8:1 to 10:1), isolated reactions at the mixture occurs, but the amount of material is not enough to raise the temperature of adjacent regions, and the propagation of the reaction is avoided. There is therefore a minimum amount of powder (“critical mass”), and below this value the reaction will not be self-sustained.
Lucio Salgado and Francisco Ambrozio Filho
Y.A. Chen et al., "Synthesis of PbTe Intermetalic Compound by Mechanical Alloying", Materials Science Forum, Vols. 660-661, pp. 347-352, 2010