Refractory filler sands with core–shell composite structure for the taphole nozzle in slide-gate system of steel ladles

Refractory sand used for filling the taphole nozzle in slide-gate system of steel ladle needs to form a suitable sintered crust to prevent molten metal from direct contact with the gate system which, when opened, permits flow of metal from the ladle through the taphole well. Conventional filler sand consists of powdered mixtures of at least two compositions with suitable particle size and mass ratio. We herein propose a novel core–shell-structured composite particle as the refractory sand. Silicon carbide (SiC) particles with an average diameter of 50 μm were oxidized in air at 1100–1600 °C to form SiC@SiO2 core–shell structure. As the oxidation temperature increases, silica weight-ratio increases from 0.8 to 7.9 wt.%, equivalent to a calculated shell thickness of 20–157 nm, respectively. The crust thickness can be tailored by adjusting the shell thickness. X-ray photoelectron spectroscopy, X-ray diffractometry, and scanning electron microscopy were used to characterize the core–shell structure.