Non-frangible alumina-silica fibers

Transparent, smooth, discrete, continuous, refractory, ceramic oxide fibers of homogeneous chemical composition comprising 99 to 99.5 weight percent of a mixture or chemical combination of 70 to 75 parts by weight alumina and 25 to 30 parts by weight silica, 0.5 to 1 weight percent of boria or phosphorus pentoxide, or both, and less than 0.1 weight percent carbon, said fibers being free of alpha alumina and having a polycrystalline phase of predominantly transitional alumina in admixture with silica which admixture is transformable upon firing said fibers at 1200.degree. to 1400.degree. C to mullite crystallites, said fibers having a friability index of at least 0.5 and a surface area less than 1 m.sup.2 /g, said fibers being straight and uniformly round with a uniform diameter of 7 to 15 micrometers.

Transparent, smooth, fracture resistant, discrete, refractory oxide fibers uniformly round in cross-section and of homogeneous chemical composition comprising 96 to 100 weight percent of a mixture or chemical combination of 67 to 77 parts by weight alumina and 23 to 33 parts by weight silica, said fibers having a predominant polycrystalline phase of mullite, transitional alumina, or a mixture of both, a friability index of at least 0.2 and a surface area of less than 1 m.sup.2 /g.