The surface reaction layer of titanium plates and rods is a major factor affecting the physical and chemical properties of titanium workpieces. Before processing, it is necessary to remove the surface contamination layer and defect layer. Physical and mechanical polishing process for the surface polishing of titanium plates and rods:

Sandblasting

The sandblasting treatment for titanium wire castings generally uses white corundum, as it is more effective. The sandblasting pressure should be lower than that of non-precious metals, typically below 0.45 MPa. This is because excessive jet pressure can cause intense sparks upon impacting the titanium surface, raising temperatures that may react with the titanium, leading to secondary contamination and affecting surface quality. The process takes 15-30 seconds, removing only the adhered sand on the casting surface, the sintered layer, and part of the oxidation layer. The remaining surface reaction layers should be rapidly removed using chemical acid washing.

2. Pickling:

Pickling can rapidly and completely remove the surface reaction layer without contaminating the surface with other elements. Both HF-HCL and HF-HNO3 acid pickling solutions are suitable for titanium pickling. However, the HF-HCL system absorbs more hydrogen, while the HF-HNO3 system absorbs less hydrogen, allowing for controlled HNO3 concentration to reduce hydrogen absorption and to provide a brightened surface finish. Generally, the concentration of HF is around 3%-5%, and the concentration of HNO3 is around 15%-30%.

The surface reaction layer of titanium plates and bars can be completely removed by sandblasting followed by acid washing.

Titanium plate and rod surface reaction layers, in addition to physical and mechanical polishing, include two other types: 1. Chemical polishing, 2. Electrolytic polishing.

Chemical Polishing

Chemical polishing achieves flattening and polishing by means of oxidation-reduction reactions of metal in a chemical medium. Its advantages include being independent of the hardness of the metal, the polishing area, and the structural shape. All parts in contact with the polishing fluid are polished, requiring no special complex equipment, and is easy to operate, making it particularly suitable for polishing complex structures of titanium dental frameworks. However, the process parameters of chemical polishing are difficult to control, necessitating a good polishing effect on the dental frameworks without affecting their accuracy. A good titanium chemical polishing fluid is made by mixing HF and HNO3 in a certain proportion, where HF acts as a reducer, dissolving titanium metal and providing leveling, with a concentration less than 10%. HNO3 serves as an oxidizer, preventing excessive titanium dissolution and hydrogen absorption, while also providing a brightening effect. Titanium polishing fluid requires a high concentration, low temperature, and short polishing time (1-2 minutes).

2. Electrolytic Polishing:

Also known as electrochemical polishing or anodic dissolution polishing, due to the low electrical conductivity and strong oxidizing properties of titanium alloy tubes, they are nearly unpolishable using aqueous acidic electrolytes such as HF-H3PO4 or HF-H2SO4 systems. When an external voltage is applied, the titanium anode immediately oxidizes, preventing the anodic dissolution process from occurring. However, using anhydrous chloride electrolytes at low voltages, titanium can be effectively polished, allowing for mirror-like finishes on small specimens. Nevertheless, complete polishing of complex restorations remains unattainable. Perhaps altering the shape of the cathode and adding a supplementary cathode could resolve this issue, although further research is needed.