Abstract: An apparatus for forming a refractory mass on a surface of a substrate by spraying against the surface a mixture of particles including oxidizable particles and refractory particles in a carrier gas, which carrier gas may contain oxygen but is not substantially all oxygen, and combusting the oxidizable particles to generate sufficient heat to soften or melt at least the surfaces of the refractory particles and form the refractory mass, which apparatus includes means for mixing the mixture of particles with a stream of the carrier gas; a lance having an outlet; a feed line for conveying the carrier gas and entrained mixture of particles to the lance outlet for spraying and having defined therein at least one orifice located downstream of the mixing means and at least 1 m from the lance outlet; and means for introducing oxygen gas into the carrier gas and entrained mixture of particles connected to the at least one orifice defined in the feed line.

Abstract: When forming a refractory mass on a surface a mixture of oxidizable particles and refractory particles in a comburent carrier gas is sprayed against that surface from an outlet of a lance. Thus on combustion of the oxidizable particles, sufficient heat is generated to soften or melt at least the surfaces of the refractory particles to bring about the formation of the refractory mass. The mixture of particles is itself mixed with a carrier gas stream, for example, by using venturi, and is fed along a line towards a lance outlet. Oxygen is introduced into such feed line at at least one location along the feed line and is mixed with the carrier gas/particle mixture during its flow towards the lance outlet before reaching that outlet, and preferably at least 1 meter from the outlet of the lance.