Titanium is easy to react with elements such as O, H, N in the air and Si, Al and Mg in the air at high temperature, and the surface pollution layer is formed on the surface of the casting to make its excellent physical and chemical properties worse Increased, plasticity, reduced elasticity, increased brittleness.
Titanium density is small, so when the inertia of titanium liquid flow is insignificant, poor flow of titanium melt flow rate is low. Casting temperature and casting temperature difference (300 ℃) larger, fast cooling, casting in a protective atmosphere, titanium casting surface and the internal inevitably have defects such as porosity, the impact of the quality of the castings.
Therefore, the surface treatment of titanium castings is more critical than other dental alloys. Due to the unique physical and chemical properties of titanium, such as low thermal conductivity, low surface hardness, low elastic modulus, high viscosity, low conductivity, easy oxidation And so on, which on the surface treatment of titanium has brought great difficulty, the use of conventional surface treatment method is difficult to achieve the desired results. Must adopt special processing methods and means of operation.
The post-surface treatment of the casting is not only to obtain a smooth and bright surface, to reduce the accumulation and adhesion of food and plaque, to maintain the patient's normal oral micro-ecological balance, but also increase the beauty of denture; more importantly, These surface treatment and modification processes improve the surface properties and suitability of the castings, improve the physical and chemical properties of denture wear, corrosion resistance and stress resistance fatigue.
First, the removal of surface reaction layer
The surface reaction layer is the main factor influencing the physical and chemical properties of titanium castings. Before the grinding and polishing of titanium castings, it is necessary in order to completely remove the surface pollution layer in order to achieve satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by pickling after blasting.
1. Sandblasting: titanium casting sandblasting the usual selection of white corundum coarse spray is better, the pressure of sandblasting than non-precious metals are smaller, generally controlled below 0.45Mpa. Because the jet pressure is too large, the sand influence on the titanium surface of the spark, the temperature rise with the titanium surface reaction, the formation of secondary pollution, affecting the surface quality. Time for 15 to 30 seconds, only to remove the surface of the sticky sand, the surface sintered layer and the oxide layer can be. The rest of the surface reaction layer structure should be quickly removed by chemical pickling method.
2. Pickling: Pickling can be quickly and completely remove the surface reaction layer, and the surface will not produce other elements of pollution. HF-HCl series and HF-HNO3 acid pickling solution can be used for pickling of titanium, but HF-HCl acid pickling solution hydrogen absorption is large, and HF-HNO3 acid pickling liquid hydrogen absorption is small, can control HNO3 Of the concentration of hydrogen absorption, and the surface of the bright treatment, the general concentration of HF in the 3% to 5%, HNO3 concentration of 15% to 30% is appropriate