Abstract: A process for cleaning a surface of a refractory structure which is at an elevated temperature, including projecting against the surface a comburent gas stream which is a powder stream including fuel particles carried in an oxygen-containing carrier gas the comburent gas stream impinging upon the surface at an impingement zone, whereby the fuel particles are caused or allowed to burn in a reaction zone defined generally around the impingement zone and the heat generated by the combustion of the fuel particles causes the surface or material adhered thereto to melt and provide a melted material, and projecting a scouring stream including oxygen simultaneously or alternately at the surface to scour the surface in the vicinity of the reaction zone and thereby clean the surface due to the scouring stream blowing away the melted material.

Abstract: In ceramic welding processes, oxidizing gas and a mixture of refractory and fuel powders are projected against a surface and the fuel is burnt to generate sufficient heat that the refractory powder becomes at least partially melted or softened and a cohesive refractory weld mass is progressively built up against that surface. In order to reduce any tendency for the weld mass to include a low-grade refractory phase and thus promote the refractoriness of that weld mass, the fuel powder is present in a proportion of not more than 15% by weight of the total mixture and includes at least two metals selected from aluminum, magnesium, chromium and zirconium, in that at least the major part by weight of the refractory powder consists of one or more of magnesia, alumina and chromic oxide, and in that the molar proportions of silica and calcium oxide present in the refractory powder (if any) satisfy the following expression:molar concentration of SiO.sub.2 in %.ltoreq.0.2+molar concentration of CaO in %.