High temperature coating on ceramic substrate and non-firing process for

Abstract

A process for producing a low porosity, high temperature coating on a porous substrate based on ceramic fibers of refractory compounds. The coating comprises from 30.8 to 41.9 weight % of silica (SiO.sub.2) from a silica sol, from 30.2 to 49.4 weight % of alumina (Al.sub.2 O.sub.3), from 4.0 to 16.3 weight % of silicon carbide (SiC), and from 11.6 to 16.6 weight % of molybdenum disilicide (MoSi.sub.2). The coating has an emissivity of not less than 0.8 and an operating temperature of up to 1500.degree. C. The process is carried out without a firing step and includes the steps of preparing a slurry comprising from 65 to 75 weight % of a silica sol having a content of 20 to 50 weight % of SiO.sub.2 and from 25 to 35 weight % of a mixture of particles of the refractory compounds Al.sub.2 O.sub.3, SiC, and MoSi.sub.2 ; applying the slurry to the ceramic fiber based porous substrate to form a layer of the slurry on the substrate; and drying the layer in several steps, first at ambient temperature, then at a temperature of 90.degree. to 100.degree. C., and then at a temperature of 200.degree. to 220.degree. C. until a constant weight of the coated substrate is obtained. The mixture contains from 52 to 71 weight % of Al.sub.2 O.sub.3, from 6 to 28 weight % of SiC, and from 20 to 25 weight % of MoSi.sub.2.