Abstract
Bi-Co-Sb is an important material system. To provide fundamental understanding, the phase equilibria isothermal sections of the Bi-Co-Sb system and the interfacial reactions of the (Bi,Sb)/Co couples at 500 degrees C and 600 degrees C were experimentally determined. A CALPHAD-type thermodynamic modeling was carried out. Besides the isothermal sections at 500 degrees C and 600 degrees C, the liquid projection and isothermal sections at 200 degrees C and 300 degrees C of the Bi-Co-Sb were calculated. At 500oC and 600oC, there are no ternary compounds and they have four tietriangles, (Co + CoSb + Liquid), (CoSb + CoSb2 +Liquid), (CoSb3 + CoSb2 + Liquid) and (CoSb3 + CoSb2 + Liquid). In the (Bi,Sb)/Co couples reacted at 500oC and 600oC, only CoSb is found initially, followed by the formation of CoSb2 and then CoSb3. The reaction layers grow thicker with longer reaction time. A peculiar phenomenon, that the reaction rates in the Co/(Bi,Sb) couples are faster at 500 degrees C than at 600 degrees C, is observed and illustrated. The dominating diffusion species is Sb and the reaction path of the (Bi,Sb)/Co couple is Co/CoSb/ CoSb2/CoSb3/Liquid (Sb-deplted)/(Bi,Sb) with longer reaction time.