The present invention relates to materials and more particularly to particulate materials suitable for use as thermal spraying powders. There is disclosed a process for the preparation of a particulate material suitable for use as a thermal spraying powder which includes treating a mixture comprising an inorganic substance as a major component (as defined in the Specification) and a sol to gel the sol thereby to form an intermediate material comprising inorganic substance and gel and heating the intermediate material. One example of thermal spraying is plasma spraying.
The corrosion and erosion resistance of ceramic bodies, such as submerged pouring shrouds and nozzles, exposed to molten steel and slag during continuous casting, is improved by applying a layer of a ceramic material to the exposed surfaces by plasma spraying. The apparent porosity of the coating is at least 15% lower than that of the ceramic body. Corrosion and erosion resistant material suitable for such plasma sprayed coatings on alumina-graphite and zirconia-graphite bodies include one or more as mixtures or compounds of the following: zirconia; chromium oxide; alumina; silica; magnesia; zirconium silicate; and titanium oxide. A corrosion and erosion resistant coating system for fused silica, which is also resistant to thermal cracking, includes an outer coating of a plasma sprayed ceramic material, such as zirconia, and one or more intermediate layers of plasma sprayed material containing varying amounts of zirconium silicate.
