Chementator: A new Mg2Si-production process promises to advance thermoelectric devices    

The Seebeck effect — the direct conversion of a temperature difference to electricity — is responsible for the operation of thermocouples. But taking advantage of this phenomenon to make electricity from waste heat in so-called thermoelectric (TE) devices has been hindered by the high cost or toxicity of common TE materials, such as lead-tellurium or cobalt-antimony. And up to now, production of the non-toxic alternative material, magnesium silicide (Mg2Si), has been hindered by difficulties in growing Mg2Si crystals. This situation may change, thanks to a new process developed by Tsutomu Iida, associate professor at the Dept. of Materials Science & Technology, Tokyo University of Science (Japan; edlinks.chemengonline.com/7370-564). To make the Mg2Si, a stoichiometric mixture of granular Mg (99.95%) and powdered Si (99.99999%) is first ground into a powder in a controlled environment. A dopant, such as bismuth (for n-type TE electrodes) or silver (for p-type), is added to the powder, which is then sintered under a mixture of argon and hydrogen at 0.08 MPa pressure and a temperature 20K above the melting point of Mg2Si. Ingots are then sliced and polished to make 1 – 2-mm thick wafers, which are then made into…