The main factor influencing the physical and chemical properties of titanium workpieces is the surface reaction layer of titanium plate and titanium rod. The surface contaminated layer and defect layer must be completely removed prior to processing. Surface polishing of titanium plates and titanium rods by physical mechanical polishing:
Sand blasting:
Titanium sandblasting treatment is generally superior to white corundum, and the sandblasting pressure is lower than that of non-precious metals, which is generally controlled below 0.45MPa. Because if the injection pressure is too high, the sand impact on the titanium surface generates fierce sparks, and the temperature rise can react with the titanium surface, forming secondary pollution and affecting surface quality. The time is between 15 and 30 seconds. Only the sticky sand, sintered layer, and a portion of the oxidized layer on the casting's surface can be removed. Chemical pickling should be used to quickly remove the remaining surface reactive layer structure.
2. Pickling
Pickling can quickly and completely remove the reactive layer without contaminating the surface with other elements. Both the HF-HCl system and the HF-HNO3 system can be used for pickling titanium, but the HF-HNO3 system has a larger hydrogen absorption capacity, whereas the HF-HCl system has a smaller hydrogen absorption capacity, which can be controlled to reduce hydrogen absorption and carry out surface polishing treatment. In general, the concentration of HF is between 3% and 5%. The appropriate HNO3 concentration is between 15% and 30%.
Pickling after sandblasting can completely remove the surface reaction layer of titanium plate and rod.
In addition to physical and mechanical polishing, there are two kinds of reaction layers on the surface of titanium plate and titanium rod: 1. Chemical polishing; 2. Electrolytic polishing.
1. Chemical polishing:
Chemical polishing achieves the purpose of polishing through the REDOX reaction of the metal in the chemical medium. Its advantages are that chemical polishing has nothing to do with the hardness of the metal, polishing area and structure shape, and all the parts in contact with the polishing liquid are polished, no special complex equipment is required, simple operation, more suitable for the polishing of complex structure titanium denture support. But the process parameters of chemical polishing are difficult to control, so it is required to have a good polishing effect without affecting the accuracy of the denture. The better titanium chemical polishing liquid is prepared by HF and HNO3 in a certain proportion. HF is a reducing agent, which can dissolve titanium metal and play a leveling role. The concentration is < 10%, HNO3 plays an oxidation role to prevent the excessive dissolution of titanium and hydrogen absorption, and at the same time can produce a bright effect. Titanium polishing solution requires high concentration, low temperature and short polishing time (1 ~ 2min).
2. Electrolytic polishing:
Also known as electrochemical polishing or anodic dissolution polishing, due to the low conductivity of titanium alloy tube, oxidation performance is very strong, the use of water acidic electrolyte such as HF-H3PO4, HF-H2SO4 system electrolyte to titanium almost can not be polished, after the application of external voltage, titanium anode immediately oxidation, and the anodic dissolution can not be carried out. However, the application of anhydrous chloride electrolyte at 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 still cannot be achieved. Perhaps the method of changing the shape of cathode and adding cathode can solve this problem, which needs to be further studied.
