The surface morphology and crystal structure change of dental zirconia after hydrofluoric acid (HF) etching were evaluated. Four groups of sintered zirconia specimens were 1) control group, 2) immersion in 9.5%HF at 25oC for 1, 2, 3, or 24 h, 3) immersion in 9.5%HF at 80oC for 1, 3, 5, or 30 min and 4) immersion in 48%HF at 25oC for 30 or 60 min. The specimens were evaluated under SEM and XRD. The SEM analysis revealed changes in surface topography for all the HF-etched zirconia specimens. The irregularities surface increased with increasingly longer immersion times and higher etching solution temperatures. 

The XRD analysis of the hydrofluoric acid etched zirconia specimens revealed the presence of a crystalline monoclinic phase along with a tetragonal form. It was concluded HF can etch dental zirconia ceramic, creating micro-morphological changes. Tetragonal-to-monoclinic phase transformation was induced on the etched zirconia surface.

Discussion of hydrofluoric acid - nitric acid system, the amount of hydrogen absorption rate of corrosion and corrosion in the process of TCA titanium and titanium alloys. The corrosion behavior of TCA in such a system using electrochemical methods. The results show that the corrosion rate increases with increasing temperature and concentration of hydrofluoric acid, and then increased with the decrease of the concentration of nitric acid. TCA titanium alloy in hydrofluoric acid. Nitrate system hydrogen storage capacity is small, the amount of hydrogen absorption decreased with the increasing concentrations of nitrate. In the etching solution containing only hydrofluoric acid.