Macrocrystalline .alpha.-alumina hexagonal platelets

A process for the preparation of .alpha.-alumina macrocrystals comprising monocrystalline hexagonal platelets having a diameter ranging from 2 to 20 .mu.m, a thickness ranging from 0.1 to 2 .mu.m and a diameter/thickness aspect ratio ranging from 5 to 40, comprising calcining admixture of transition or hydrated alumina and a fluorocompound flux, said fluorocompound flux having a melting point of up to 800.degree. C. and, in the molten state, serving to dissolve said transition/hydrated alumina, the fluorocompound flux being present in an amount sufficient to dissolve the transition/hydrated alumina during said calcining.

A process for the preparation of .alpha.-alumina macrocrystals comprising monocrystalline hexagonal platelets having a diameter ranging from 2 to 20 .mu.m, a thickness ranging from 0.1 to 2 .mu.m and a diameter/thickness aspect ratio ranging from 5 to 40, comprising calcining admixture of transition or hydrated alumina and a fluorocompound flux, said fluorocompound flux having a melting point of up to 800.degree. C. and, in the molten state, serving to dissolve said transition/hydrated alumina, the fluorocompound flux consisting essentially of a B-free fluorocompound flux.

A process for the preparation of .alpha.-alumina macrocrystals comprising monocrystalline hexagonal platelets having a diameter ranging from 2 to 20 .mu.m, a thickness ranging from 0.1 to 2 .mu.m and a diameter/thickness aspect ratio ranging from 5 to 40, comprising calcining admixture of transition or hydrated alumina and a fluorocompound flux, said fluorocompound flux having a melting point of up to 800.degree. C. and, in the molten state, serving to dissolve said transition/hydrated alumina, said fluorocompound flux comprising Li.sub.3 Na.sub.3 (AlF.sub.6).sub.2.