Solid state metathesis preparations of hard refractory ceramics.

摘要

This thesis presents the synthesis of binary and ternary transition metal borides, carbides, nitrides and silicides the solid state metathetical processes. The reactions were initiated both in bulk and in the propagation modes. Rapid solid state metathetical reactions of Group 3-5, 13 and rare earth metal halides with nitriding agents such as Li3N, Mg3N2, Ca3N2 and NaN3 lead to formation of crystalline nitrides and co-product salts of Group 1 or 2 metals. Similarly, crystalline transition metal borides, carbides and silicides of Groups 4-8 have been synthesised using the halides and A1B2, CaC2, SrC2, AI4C3, Li2Si, Mg2Si or CaSi2. The rates of these reactions and their final product crystallinity were related to the reagents used and the mode of reaction initiation. Thermally unstable transition metal nitrides of Group 6 transition metals, manganese, iron and cobalt have been synthesised using their halides and magnesium nitride with the aid of magnesium chloride as an inert heat sink. This work also reports the SSM (Solid State Metathesis) synthesis of highly crystalline transition metal carbides and silicides from the transition metal oxides and CaC2, SrC2, Li2Si, Mg2Si, CaSi2. All the co-products from the various reactions were removed using solvents such as THF, methanol, water or dilute acids. The final products were analysed using X-ray powder diffraction, FT-IR and SEM/EDXA. A selected group of carbides and nitrides were analysed using TEM and PEELS/ELNES (photoelectron energy loss spectroscopy/energy loss near-edge structure). Besides the identification of the final products, the main objectives in these analyses were to determine the elemental composition (and oxygen contamination) of these interstitial compounds. The compounds formed by SSM processes were shown to be useful in standardising ELNES measurements.