Synthesis of Ternary Nitrides From Intermetallic Precursors: Modes of Nitridation in Model Cr3Pt Alloys to Form Cr3PtN Perovskite and Applications to Other Systems

The use of intermetallic alloy precursors is explored as a new means to synthesize complex transition and refractory metal nitrides, carbides, and related phases. The conditions under which model single-phase Cr{sub 3}Pt and two-phase Cr{sub 3}Pt-dispersed Cr alloys form Cr{sub 3}PtN antiperovskite when thermally nitrided were studied. Phenomenological experiments suggest that the key variable to achieving single-phase Cr{sub 3}PtN surface layers is the Cr{sub 3}Pt phase composition. In two-phase {beta}-Cr-Cr{sub 3}Pt alloys, the formation of single-phase Cr{sub 3}PtN at Cr{sub 3}Pt precipitates by in-place internal nitridation was found to be a strong function of the size of the Cr{sub 3}Pt dispersion in the microstructure. Nanoscale Cr{sub 3}Pt dispersions were readily converted to near single-phase Cr{sub 3}PtN, whereas nitridation of coarse Cr{sub 3}Pt particles resulted in a cellular or discontinuous-type reaction to form a lath mixture of Cr{sub 3}PtN and a more Cr-rich Cr{sub 3}Pt or {beta}-Cr. The potential for using such external/internal oxidation phenomena as a synthesis approach to layered or composite surfaces of ternary ceramic phases (nitrides, carbides, borides, etc.) of technological interest such as the Ti{sub 3}AlC{sub 2} phase, bimetallic nitride, and carbide catalysts (Co{sub 3}Mo{sub 3}N and Co{sub 3}Mo{sub 3}C and related phases), and magnetic rare earth nitrides (Fe{sub 17}Sm{sub 2}N{sub x} or Fe{sub 17}Nd{sub 2}N{sub x}) is discussed.