In the production process of titanium and titanium alloy processed material, the removal of oxidized skin is a crucial step, and pickling is the main means to achieve this goal. Before pickling, it is usually necessary to pre-treat the titanium material, such as molten alkali washing, mechanical scale breaking or sand blasting, etc., in order to remove most of the dirt on the surface and the thicker oxidized layer, so as to create favorable conditions for the subsequent pickling.
For the slight titanium oxide film formed below 600°C, pickling is a very effective removal method. During pickling, titanium reacts chemically with the acid to form metal ions, which results in the removal of the oxide skin. However, pickling of titanium is more than a simple chemical reaction; it also involves electrochemical phenomena.
When pickling in a mixed acid solution containing hydrofluoric acid or fluoride, special attention needs to be paid to the reduction reaction of hydrogen ions. These hydrogen ions have the potential to be reduced to either atomic or molecular hydrogen. Among these, molecular hydrogen has a tendency to diffuse into the metal, and once inside the metal, it may lead to hydrogen embrittlement of the metal, which can seriously affect the performance and service life of titanium.
Therefore, when pickling titanium, the composition and ratio of the acid solution must be strictly controlled to prevent the occurrence of hydrogen absorption. In particular, the ratio of nitric acid to hydrofluoric acid needs to be maintained at all times at a level greater than 5. The control of this ratio is essential to prevent hydrogen embrittlement. However, care needs to be taken that the nitric acid content is not too high, as too high a content of nitric acid will lead to a reduction in reaction speed and productivity, as well as generating a large amount of fumes, which will make operation difficult.
In addition, the pickling process also needs to pay attention to the control of temperature, time and other process parameters. Too high a temperature or too long a time may lead to excessive corrosion of titanium, affecting the surface quality. Therefore, in actual operation, according to the material of titanium, thickness and severity of the oxide skin and other factors, reasonable adjustment of the pickling process parameters to ensure the optimization of the pickling effect.
In short, the pickling process of titanium and titanium alloy processing material is a complex and delicate work. Only strict control of the acid composition, proportion and process parameters to ensure the pickling effect at the same time, to avoid unnecessary damage to the titanium material. Interested friends can continue to pay attention to our sharing to learn more about the knowledge and technology of titanium metal in production.
