Rigid mullite=whisker felt and method of preparation

摘要

A process in which (1) AlF3 and SiO2 or AlF3, SiO2, and Al2O3 powders are formed into a green body of a desired shape and size; (2) the green body is heated at 700 DEG C. to 950 DEG C. in an anhydrous SiF4 atmosphere to form barlike topaz crystals; and then (3) heated in an anhydrous SiF4 atmosphere at about 1150 DEG C. to 1700 DEG C. to convert the barlike topaz crystals to needlelike single crystal mullite whiskers which form a porous, rigid felt structure. The felt has the same shape as the green body with about 1.5 or less percent change in linear dimensions. The felt can be used as preforms for ceramic-matrix or metal-matrix composites or by itself as thermal insulation.