Abstract: Ceramic preforms comprising monocrystalline hexagonal platelets of .alpha.-alumina, well adopted for conversion into refractory bricks or ceramic composites, are prepared by crystallizing a settled fine powder of amorphous alumina, transition alumina or alumina hydrate, advantageously in the presence of a fluoro-compound flux, into a coherent mass of such hexagonal platelets of .alpha.-alumina.

Abstract: Ceramic preforms comprising monocrystalline hexagonal platelets of .alpha.-alumina, well adopted for conversion into refractory bricks or ceramic composites, are prepared by crystallizing a settled fine powder of amorphous alumina, transition alumina or alumina hydrate, advantageously in the presence of a fluoro-compound flux, into a coherent mass of such hexagonal platelets of .alpha.-alumina.

Abstract: Macrocrystalline .alpha.-alumina hexagonal platelets, well adapted as reinforcing materials and polishing agents, are prepared by calcining admixture of transition or hydrated alumina and a fluorocompound flux, such fluorocompound flux having a melting point of up to 800.degree. C. and, in the molten state, serving to dissolve the transition/hydrated alumina.

Abstract: Hydrocarbons are oxychlorinated by reaction with gaseous HCl and an oxygen-containing gas, in the presence of a catalytically effective amount of a ternary copper/molybdenum chalcogenide having the formula:Cu.sub.x Mo.sub.6 Ch.sub.8wherein x is a number ranging up to 4 and Ch is sulfur, selenium or tellurium, advantageously, in the added presence of a known oxychlorination catalyst and, optionally, a proportion of inert particulate solids; the ternary molybdenum chalcogenides of the formula M.sub.x Mo.sub.6 S.sub.8 are also prepared, wherein M is a metal, advantageously by the hydrogen gas reduction of intimate admixture of MoS.sub.2 and metal M, or precursors thereof.