The surface reaction layer of titanium plate and titanium rod is the main factor affecting the physical and chemical properties of titanium workpiece. Before processing, the surface pollution layer and defect layer must be completely removed.

1. Sand blasting:

  white corundum is generally used for sand blasting of titanium wire castings, and the pressure of sand blasting is smaller than that of non precious metals, which is generally controlled below 0.45MPa. Because when the spray pressure is too high, the sand particles impact the titanium surface to produce intense sparks, and the temperature rise can react with the titanium surface, resulting in secondary pollution and affecting the surface quality. The time is 15-30 seconds, and only the bonded sand, surface sintered layer and partial oxide layer on the casting surface can be removed. The rest of the surface reaction layer structure should be quickly removed by chemical pickling.

2. Pickling:

 Pickling can quickly and completely remove the surface reaction layer, and the surface will not be polluted by other elements. Both HF-HCL series and HF-HNO3 series pickling liquids can be used for titanium pickling, but hf-hcl pickling solution has a large hydrogen absorption capacity, while hf-hno3 pickling solution has a small hydrogen absorption capacity, which can control the concentration of HNO3, reduce hydrogen absorption, and brighten the surface. Generally, the concentration of HF is about 3%-5%, and the concentration of HNO3 is about 15%-30%.

3. Chemical polishing:

 During chemical polishing, the purpose of leveling and polishing is achieved through the oxidation-reduction reaction of metal in chemical medium. The advantage is that chemical polishing has nothing to do with the hardness of the metal, the polishing area and the structural shape, and all the parts in contact with the polishing liquid are polished, no special complicated equipment is required, the operation is simple, and it is more suitable for the polishing of titanium denture brackets with complex structures. However, the process parameters of chemical polishing are difficult to control, so it is required to have a good polishing effect on denture without affecting the accuracy of denture. The better titanium chemical polishing solution is HF and HNO3, which are prepared in a certain proportion. HF is a reducing agent, which can dissolve titanium metal and play a leveling role. The concentration is less than 10%. HNO3 plays an oxidizing role, prevents excessive dissolution and hydrogen absorption of titanium, and can produce a bright effect at the same time. Titanium polishing fluid requires high concentration, low temperature and short polishing time (1 ~ 2min).

4. Electro polishing:

 Electro polishing is also known as electrochemical polishing or anodic dissolution polishing, due to the low conductivity and strong oxidation performance of titanium alloy tubes, it is almost impossible to polish titanium with aqueous acidic electrolytes such as hf-h3po4 and hf-h2so4. After the external voltage, the titanium anode is oxidized immediately, so that anodic dissolution cannot be carried out. However, using anhydrous chloride electrolyte under low voltage has a good polishing effect on titanium, and small specimens can get mirror polishing, but for complex restorations, the purpose of complete polishing cannot be achieved. Maybe changing the shape of cathode and adding cathode can solve this problem, which needs further research.