Dissolution Kinetics of Crystalline and Amorphous Silica in Hydrofluoric‐Hydrochloric Acid Mixtures

The dissolution kinetics of crystalline and amorphous silica were studied as a function of time, temperature, concentration of HF, concentration of HC1, and crystallographic orientation. The results indicate that dissolution is a surface reaction‐controlled process. The dissolution rate depends strongly on HF concentration and weakly on HC1 concentration. The dissolution rates depend on crystallographic direction in α‐quartz and are slower than for fused silica. The rate‐controlling step is thought to be a ligand exchange process at the surface.