Wet chemical etching of silicate glasses in hydrofluoric acid based solutions

The etching of silicate glasses in aqueous hydrofluoric acid solutions is applied in many technological fields. In this review most of the aspects of the wet chemical etching process of silicate glasses are discussed. The mechanism of the dissolution reaction is governed by the adsorption of the two reactive species: HF and HF 2 - and the catalytic action of H+ ions, resulting in the breakage of the siloxane bonds in the silicate network. The etch rate is determined by the composition of the etchant as well as by the glass, although the mechanism of dissolution is not influenced. In the second part of this review, diverse applications of etching glass objects in technology are described. Etching of SiO2 and doped SiO2 thin films, studied extensively for integrated circuit technology, is discussed separately.

The formation mechanism of titania nanotube arrays in hydrofluoric acid electrolyte

Self-organized and highly ordered titania nanotube arrays (TNAs) were prepared through electrochemical anodic oxidization on a titanium foil in 0.5 wt.% hydrofluoric acid (HF) electrolyte. The current density and morphology images during the formation process of TNAs were studied. Results show that the formation of TNAs includes the following processes. Initially, dense oxide of titania was rapidly formed on the titanium surface, followed by small pore formation. The adjacent small pores were then integrated and become larger pores. At the same time, small tubes were transformed. These small tubes were further integrated into larger tubes until the primary tube formation. Finally, the tubular structure was gradually optimized and eventually developed into the highly ordered TNAs. A model was proposed to explain the formation mechanism of TNAs fabricated on a titanium foil in HF acid electrolyte.