Flux‐Mediated Wetting of Alumina by Liquid Fe–Ti–Csat

Abstract

Metals do not wet oxides as a general rule. Exceptions to this occur in the presence of dissolved species or chemical reactions. Fe–Csat–Ti is seen to wet alumina crucibles but not crucibles of graphite or MgO. This is determined to be macroscopically due to reactive wetting of the ternary alloy on Al2O3; microscopically, the reaction formed a nanoscale layer of TiC on Al2O3, with the hot metal wetting the TiC substrate. Molten fluxes offer a way to mitigate the wetting of the alumina crucible by preventing the reaction. The liquid‐state Al2O3–CaF2 flux wets the Al2O3 crucible, coating both the crucible walls and bottom. This is effective in preventing wetting despite alumina activity being unity in the initial components. The volatilization of fluorine results in a calcium aluminate coating on the original crucible. Using the molten flux is more effective than sintering CA particles onto the crucible bottom because the liquid flux coated the crucible walls. Though wetting is a problem in industry, this offers practical mitigation of wetting using a flux coating.