Thermal Synthesis of Nanocrystalline (CoxNi1-x)yFe1-y KOVAR Alloy through Gaseous Reduction of Mixed Oxides

Abstract

KOVAR is a very interesting and widely applied Fe-Ni-Co alloy. Nanocrystalline KOVAR alloy is successfully synthesized in the present investigation. The effect of hydrogen reduction on composition, microstructure and magnetic properties of produced Fe-Ni-Co alloy is investigated. A molar ratio of (99.9%) nickel oxide, cobalt oxide and ferric oxide for synthesis of 29% Ni-17% Co-Fe (KOVAR) alloy were thoroughly mixed and compressed into compacts. The dried compacts were reduced partially and completely at 500, 600, 700 and 800C in a constant flowing hydrogen gas atmosphere (100% H-2). The course of reduction was followed up using the thermogavimetric technique to study the reduction behavior and kinetics reaction mechanism. The initial dried powder and the various reduction products were characterized by XRD, VSM, FE-SEM, EDX and reflected light microscope. At the higher reaction temperature (700-800C) complete reduction was achieved with synthesis of nanocrystalline (13.9 nm) Fe-Ni-Co alloy. The activation energy values were calculated from the Arrhenius equation, and the approved mathematical formulations for the gas solid reaction were applied. It was found that the initial and final reduction stages are controlled by the combined gaseous diffusion and interfacial chemical reaction mechanisms.