INVESTIGATION OF MICROWAVE ALLOYING USING ELECTRON MICROSCOPY: SEGREGATION BETWEEN MANGANESE AND BISMUTH BY PERITECTIC REACTION
A microwave furnace combining the power of 2,000-2,500 W from 4 commercial magnetrons is demonstrated as an apparatus for melting alloys. Under an argon atmosphere, the microwave heating was transferred to pieces of broken bismuth (Bi) ingots and manganese (Mn) flakes via a silicon carbide plate for 1 h. Field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS) revealed inhomogeneous composition and morphology, similar to MnBi alloyed in arc-melting and induction furnaces. Due to the peritectic reaction, the product contained mixed phases of Mn, Bi, Bi2O3, and MnBi with particle size ranging from 100 nm to over 1 mm. Bulky cubic-like particles were unreacted Mn clusters, whereas fine particles were Bi and Bi2O3. Homogeneous regions among Mn-rich and Bi-rich particles were characterized as the MnBi phase. Areas with a balanced composition between Mn and Bi were increasingly observed after annealing at 280°C under the pressure of 60 psi for 12 h.