Effects of silicon addition on optical properties of mould flux with iron oxide and estimation of apparent thermal conductivity of flux

Mould flux with high absorptivity had been obtained in the reduction process of mould flux by silicon. For further utilisation of the mould flux with high absorptivity, the effect of silicon addition on the optical property has been investigated. The synthesised mould flux powder with iron oxide was melted with the addition of silicon powder at 1703 K followed by quenching, thus forming a glassy sample. After 5–30-min reduction, the samples exhibited black opaque colour. Meanwhile, the samples that were reduced for 45–60 min had a bluish grey colour. Many iron-based particles dispersed in the samples were micrometre order in diameter. To determine the effect of iron particles on the optical properties of the sample, extinction, scattering and absorption efficiencies were calculated according to Mie theory. Result showed that both scattering on the iron particle and absorption by iron effectively increase the extinction efficiency in the mould flux. Moreover, the silicon particle in the flux has large scattering efficiency. The black opaque colour is contributed by the existence of silicon and iron particles. The apparent thermal conductivity was calculated for the solid flux. Results also indicated that the entire glassy mould flux would effectively work for mild cooling in a continuous casting process owing to high absorptivity and small thermal conductivity.