Refractory oxides containing aluminium and barium

Abstract

Oxides containing aluminium and barium, optionally with chromium, are refractory with several possible industrial uses. A gel precursor of an oxide having the formula BaO.n(Al2xCr2yO3), where 1<n<6.6, (x+y)=1 and 0<y<0.5 was prepared by mixing a solution of a barium salt with a solution of an aluminium salt or a solution of an aluminium salt and a chromium III salt, then forming a gel which was fired to obtain the desired oxide. Filaments may be drawn as the gel is forming or extruded from a semi-rigid gel. FT-lR, XRD and 27Al NMR studies showed that barium is not incorporated directly into the gel structure. Barium aluminium oxides were obtained only after liquefaction of barium species. A powder mixture suitable for firing to an oxide of the formula BaO.m [Al2xCr2y O3] where 4.6<m<6.6, (x+y)=1 and 0<y<0.5 was prepared from source materials barium hydroxide, barium oxide, barium carbonate and barium mono-aluminate, alumina and/or a hydrated alumina and chromium III oxide, the relative amounts being varied to give the desired values of m and y on firing. A preferred oxide has the formula BaO.6Al2O3 (m=6 and y=0). Strong ceramic shapes have been prepared from this. XRD studies of oxide compositions (n or m=6 and y=0) sintered at high temperature showed that barium mono-aluminate is a low-temperature intermediate phase. Chromium III reduces the temperature required to form a barium aluminium oxide. Previously published work is summarised.