Self-propagating metathesis preparations of inorganic materials.

摘要

The potential of self-propagating reactions, with reagents such as lithium nitride, calcium nitride, sodium arsenide and magnesium silicide, in the production of inorganic materials has been investigated. Reactions were performed with anhydrous d-block and rare earth metal chlorides and can be described by the following generic equation where M is a Group 3-12 metal, Alk is a Group 1 or 2 element and E is Si, N, P, As, Sb, Bi or O. MClm + xAlknE → yMalphaE + xAlkClbeta + zEgamma Crude products were obtained normally as fused masses of material consisting of the products coated in the alkali chloride co-products. Grinding followed by washing with an appropriate solvent yielded the pure products with low levels of contamination from the other elements present in the reaction flux. The phases produced include rare earth and transition metal nitrides, metals and alloys, d-block phosphides, arsenides and antimonides, metal silicides and d-block oxides. The products were variously characterised by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray analysis, magnetic susceptability, X-ray photoelectron spectroscopy, microanalysisand solid state (magic angle spinning) nuclear magnetic resonance spectroscopy. Thermocouple experiments, differential scanning calorimetry, photography and constant pressure calculations were used to examine the thermal aspects and timescales of reactions. Dilution with inert solids was used to reduce voracity of reactions and to control crystallinity of products. Liquid chlorides (TiCl4 and VCl4) were successfully employed to make high quality ternary phases such as Ti0.5V0.5E (E= N, P, As). Such reactions can progress via ionic or elemental mechanisms and evidence for either of these was gathered. Examples were found for both mechanisms which supported that the process was occurring. These conclusions were based on end- product analysis since the reaction conditions and timescales precluded the use of other techniques.