How to deal with the surface defect reaction layer of titanium sheet and bar
The surface reaction layer of titanium plate and titanium rod is the main factor affecting the physical and chemical properties of titanium workpiece, and the contaminated layer and defective layer must be completely removed before processing. Physical mechanical polishing of titanium plate and titanium rod surface polishing process:
1, Sand blasting:
The sandblasting treatment of titanium wire castings is generally better with white corundum spraying, and the sandblasting pressure is smaller than that of non-precious metals, generally controlled below 0.45mpa. Because, when the injection pressure is too large, the sand impact on the surface of titanium sparks, temperature rise can react with the surface of titanium, the formation of secondary pollution, affect the surface quality. The time is 15-30 seconds, only remove the sticky sand on the surface of the casting, the surface sintered layer and part of the oxide layer can be removed. The rest of the surface reaction layer should be quickly removed by chemical pickling.
2, Pickling:
Pickling can quickly and completely remove the surface reaction layer without contaminating the surface with other elements. Hf-hcl series and HF-HNO3 series acid washing solution can be used for titanium pickling, but hF-HCl series acid washing solution has a large amount of hydrogen absorption, while HF-HNO3 series acid washing solution has a small amount of hydrogen absorption, which can control the concentration of HNO3 to reduce hydrogen absorption, and can carry out bright treatment on the surface. Generally, the concentration of HF is about 3%-5%. The appropriate concentration of HNO3 is about 15%-30%.
The surface reaction layer of titanium plate and titanium rod can be completely removed by pickling after sandblasting.
In addition to physical mechanical polishing, there are two kinds of reaction layer on the surface of titanium plate and titanium rod: 1. Chemical polishing, 2. Electrolytic polishing.
1, Chemical polishing:
Chemical polishing is achieved by REDOX reaction of metal in chemical medium. Its advantage is that chemical polishing has nothing to do with the hardness of metal, polishing area and structure shape, all parts in contact with the polishing fluid are polished, no special complex equipment, simple operation, more suitable for the complex structure of titanium denture bracket polishing. However, it is difficult to control the process parameters of chemical polishing, which requires a good polishing effect without affecting the accuracy of the denture. The better titanium chemical polishing liquid is made up of HF and HNO3 in a certain proportion. HF is a reducing agent, which can dissolve titanium metal and play a leveling role. When the concentration is less than 10%, HNO3 plays an oxidation role to prevent excessive dissolution and hydrogen absorption of titanium, and can produce shining effect at the same time. Titanium polishing liquid requires high concentration, low temperature, 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 electrolyte on titanium can hardly be polished, after the application of external voltage, titanium anode oxidation immediately occurs, and the anodic dissolution can not be carried out. However, the anhydrous chloride electrolyte has good polishing effect on titanium at low voltage, and the mirror polishing can be achieved for small specimens, but it still cannot achieve the purpose of complete polishing for complex restorations. Perhaps the method of changing the shape of cathode and adding cathode can solve this problem, which needs further research
