Ceramic welding composition and process

In a ceramic welding process for the repair of a hot oven wall having an initial temperature of not higher than about 3500.degree. F. wherein a finely divided welding composition containing a refractory material intimately admixed with an exothermically oxidizable metal is transported and sprayed onto the wall by an oxygen-containing gas to ignite the composition and fuse it to said wall, the improvement which comprises:

• transporting and applying to said wall a welding composition containing in intimate admixture--(A) a substantially noncombustible refractory material in a major proportion with reference to the total weight of the composition,--(B) exothermically oxidizable metal components consisting essentially of (1) a granular aluminum powder having a size range of about 70 to 150 microns in a proportion of about 8 to 12% by weight with reference to the total composition and (2) a finely grained aluminum powder or aluminum flake in which the powder has a size range of less than 5 microns and the flake has an equivalent size by volume, in a proportion of about 2 to 6% by weight with reference to the total composition, and--(C) a group of control components consisting essentially of (1) iron oxide of the formula Fe.sub.2 O.sub.3 with a particle size of about 80 microns or less in a proportion of about 2 to 10% by weight with reference to the total composition, (2) a dross obtained as the byproduct of aluminum smelting, containing about 15-25% Al, 60-70% Al.sub.2 O.sub.3 and 10-15% NaCl or KCl, said dross having a particle size of about 70 microns or less and being used in a proportion of about 1 to 7% by weight of the total composition, and (3) a fluorspar having a fluoride content of at least about 70%, said fluorspar having a particle size of about 150 microns or less and being used in a proportion of about 2-7% by weight with reference to the total composition.