Improvements in Process for Growing alpha-Alumina Whiskers of the Long Wool Type

摘要

1,190,283. α-Alumina whiskers. GENERAL ELECTRIC CO. 28 June, 1967 [29 Sept., 1966], No. 29846/67. Heading C1A. [Also in Division F4] Long-wool (i.e. averaging 1-10 Á diameter and 5-25 mm. in length) whiskers of α-alumina are made by heating aluminium to 1290- 1400‹ C. in hydrogen in a reaction-chamber, at least the upper portion of which is made of a refractory containing the silica required for reaction with the aluminium, the resulting whiskers then being cooled. The reaction chamber is partially closed at least at one end, and may take the form of a semi-cylindrical alumina boat topped by a slip-cast semicylindrical refractory lid open at one flat. Specified refractories are kyanite, mullite, andalusite and a mixture of alumina, silica and trace oxides. The reaction may be effected in presence of sulphur, added as powder, or derived from hydrogen sulphide. Reaction may be carried out by enclosing the loaded reaction chamber in a furnace tube and heating it in flowing or static hydrogen for about 4 hours. The reaction chamber may be purged with N 2 before the reaction and after cooling the reaction product.