In metallurgy , any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag .
iron ores. Other materials used as fluxes are silica, dolomite, lime, borax, and fluorite. In soldering , the flux removes oxide films, promotes wetting, and prevents reoxidation of the surfaces during heating. Rosin is widely used as a noncorrosive flux when electronic equipment is soldered; in other applications, a water solution of zinc chloride and ammonium chloride may be used.