In the production process of titanium and titanium alloys, the removal of oxide scales is a crucial step, with pickling being the primary method to achieve this objective. Prior to pickling, titanium materials typically undergo pre-treatment such as molten alkali washing, mechanical descaling, or sandblasting to eliminate most surface impurities and thick oxide layers, creating favorable conditions for subsequent pickling.
Pickling is a highly effective method for removing slight titanium oxide films formed below 600°C. During pickling, titanium reacts chemically with the acidic solution, forming metal ions to facilitate the removal of oxide scales. However, titanium pickling involves not only simple chemical reactions but also electrochemical phenomena. When pickling in mixed acid solutions containing hydrofluoric acid or fluorides, special attention must be paid to the reduction reaction of hydrogen ions to prevent hydrogen absorption. The control of the ratio of nitric acid to hydrofluoric acid, with the former exceeding 5, is crucial to prevent hydrogen embrittlement.
Furthermore, parameters such as temperature and time must be carefully controlled during the pickling process. Excessive temperature or prolonged exposure can lead to excessive corrosion of titanium, affecting surface quality. Therefore, it is essential to adjust pickling process parameters based on factors such as material composition, thickness, and severity of oxide scales to ensure optimal pickling effects.
In conclusion, the pickling process for titanium and titanium alloy materials is a complex and meticulous task. Strict control of acid solution composition, ratios, and process parameters is necessary to ensure effective pickling while avoiding unnecessary damage to the materials.
