Process for producing alumina fiber or alumina-silica fiber

Claim 1

A process for producing alumina fiber or alumina-silica fiber, which consists essentially of (i) spinning a solution of at least one polyaluminoxane or of a mixture of at least one polyaluminoxane and one or more kinds of silicon-containing compounds in an organic solvent to give a precursor fiber, (ii) hydrolyzing the resulting precursor fiber, and then (iii) calcining the hydrolyzed fiber, said polyaluminoxane being one or more kinds of polymers or copolymers which mainly consist of the structural units of the formula: ##STR11## wherein the pendant members Y are one or more kinds of groups selected from the group consisting of alkyl having 1 to 18 carbon atoms, alkoxy having 1 to 18 carbon atoms, acyloxy having 1 to 18 carbon atoms phenyl and phenoxy, and may be partially a halogen or hydroxy, and which may also contain cross-linkages of the formula: ##STR12## the amount of which in the polymer molecule is within the range that the polymer is soluble in the organic solvent, and said pendant groups Y of the polyaluminoxane satisfying the conditions: f(HCOO) + f(CH.sub.3 COO) + f(F) + f(Cl) + f(Br) + f(I) + f(OH) ≦ 0.2 wherein f(R) means the mole fraction for a particular group: R as defined for the pendant group Y, or ##EQU3## being in the range of from 0.0 to 1.0, and .sub.n=1 (n-1)f(C.sub.n H.sub.2n+1) + .sub.n=1 nf(C.sub.n H.sub.2n+1 O) + .sub.n=3 (n+1)f(C.sub.n-1 H.sub.2n-1 COO) + 4.5 f(phenyl) + 5.5f(phenoxy)≦8 wherein n is an integer, and further the average degree of polymerization of the polyaluminoxanes being in the range of 5 to 1,000, and the amount of the silicon-containing compounds to be mixed into the solution being not greater than an amount such that the silica content in the alumina-silica fiber obtained after the calcination is not greater than 60% by weight.