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AssigneeMinnesota Mining and Manufacturing Company
InventorsThomas E. Wood, David M. Wilson, Harold G. Sowman
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Microcrystalline alpha-alumina based ceramic articles comprising at least 60% alumina by weight, and 0.1-7.0 percent by weight iron equivalence in which substantially all the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites with an average crystallite size less than 0.5 micrometer and a density greater than 90% theoretical are disclosed. Ceramic articles particularly useful as high modulus refractory fibers, among other shaped bodies such as beads, flakes, coatings, and shaped or randomly-shaped abrasive particles, are produced from a unique sol-gel process wherein hydroxy iron polymers are utilized to nucleate the alpha alumina transformation. An inherent advantage of the unique process disclosed is the resulting fine grained microstructure, and a surface roughness height of less than 100.0 nm, which is essential if a ceramic article such as an alpha alumina fiber is to have reasonable strength.
A solid, fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and no grains are larger than 0.5 micrometer in diameter, the density of the article is greater than 90% of theoretical density, and the surface roughness height of said article is less than 100 nm.
A solid, shaped and fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60 percent alumina by weight in which at least 99 percent of the alumina is in the alpha phase comprising alpha alumina crystallites wherein at least 99 percent of the alpha alumina crystallites are less than 0.2 micrometer in diameter and all are less than 0.7 micrometer in diameter, and the specific surface area of the article is greater than 15 m.sup.2 /g.
A ceramic fiber comprising in the range of 0.1 to 7.0 percent iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 99 percent are less than 0.7 micrometer in diameter, said fiber having a density of at least 90% of theoretical density, and the surface roughness height of said fiber is less than 100.0 nm.
A solid, fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is in the range of 0.3-0.4 micrometer, and no grains are larger than 0.4 micrometer, the density of the article is greater than 90% of theoretical density.
Dependencies are inferred from the claim text.