Basis for the alkaline removal process design of the alumina-based ceramic core

The basic physico-chemical behaviors and laws of etching an alumina-based ceramic core out of investment castings still puzzle the process designer. To investigate the basis, ceramic removal experiments were performed at normal pressure by varying several main factors. The de-coring rate increased as the etching temperature increased. A higher alkali concentration was beneficial to the removal efficiency but had an upper limit because of the metal alkaline corrosion. The de-coring rate underwent a convex-curve variation as the etching time increased since the deposition of a validated insoluble product gradually hinders the etching reaction. The solute additive KCl and solvent additive ethanol have the positive effects of improving the reactivity of the base solution and increasing the permeability of the etching liquid, respectively. The de-coring rate was up to 10.46wt%·h^-1 in a steady process with etching in a 70wt% KOH solution supplemented with 10wt% KCl and ethanol.