REFRACTORY OXIDES CONTAINING BARIUM AND ALUMINUM

The preparation and uses of refractory oxides containing barium and al uminium and, optionally, chromium are described. A gel precursor of an oxide having the formula BaO.n(Al-2k Cr-2y O-3) where 1 less than or equal to n less than or equal to 6.6, x + y = 1 and 0 less than or equ al to y less than or equal to 0.5 was prepared by mixing a solution of a barium salt with a solution of an aluminium salt or a solution of a n aluminium salt and a chromium (III) salt, then forming a gel which w as fired to obtain the desired oxide. The gel was formed by heat or by adding a separate gelling agent such as ammonium acetate. Alternative ly, gelation can be induced by a salt already present, such as barium acetate. Filaments, which convert to ceramic fibres when fired, may be drawn as the gel is forming, or extruded from a semi-rigid gel. Refra ctory components can be made from a suitably graded grain mix bonded w ith the gel. A powder mixture suitable for firing to an oxide of the f ormula BaO.m(Al-2x Cr-2y O-3) where 4.6 less than or equal to m less t han or equal to 6.6, x + y = 1 and 0 less than or equal to y less than or equal to 0.5 was prepared from source materials barium oxide, bari um carbonate or barium monoaluminate, alumina and/or a hydrated alumin a 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 for mula BaO.6 Al2O3 (m = 6 and y = 0). The oxides can be used in the prep aration of ceramic shapes or in grouting mixes. When n or m = 6 and y = 0, barium monoaluminate is formed as a low temperature intermediate phase during slow firing of the gel or powder mixture to a high temper ature.