Glass, Ceramics & Metallurgy

A deflocculant gives clay particles a like electrical charge so they repel each other, which lets a slip flow at much lower water content. Tile and sanitaryware plants use sodium silicate, STPP, SHMP or TSPP to reach a high specific gravity at workable viscosity, cutting drying and spray-drying energy and lowering shrinkage. Dose by trial: past the optimum, viscosity rises again and the slip settles hard or casts poorly.

Fluorspar, mainly calcium fluoride, lowers the melting point and viscosity of lime-rich slag, so a basic slag stays fluid enough to take up sulphur and other impurities from the steel quickly, especially in ladle refining. The trade-off is refractory wear: very fluid, fluoride-bearing slag penetrates and attacks magnesia linings at the slag line, so additions are kept to what the process needs. Specify CaF₂ content, silica and size when you enquire.

It keeps pickled steel clean until it meets the zinc. After degreasing, pickling and rinsing, work is dipped in a zinc ammonium chloride pre-flux and dried; the salt film stops re-oxidation, and in the kettle the ammonium chloride etches away residual oxide so molten zinc wets the steel evenly. Too little ammonium chloride leaves bare spots and too much fumes heavily, so flux ratio and bath strength are controlled.

Small additions of transition-metal compounds give most fired colours: cobalt gives strong blues, chromium oxide greens, copper greens and turquoise in oxidising firing and reds in reduction, manganese browns and purples, and iron ambers and browns. Zirconium compounds and fluorides opacify rather than colour, giving whites. Final shade depends on the base glaze or glass, firing temperature and kiln atmosphere, so trial a new source before switching.