Surface treatment technology of titanium

_ _ _ _ titanium at elevated temperature easily and air in the O, H, N and other elements and embedding material in Si, Al, Mg element reacts in the casting surface, forming surface contamination layer, make its excellent physical and chemical properties of variation, and increased hardness, plasticity, and decreased elasticity, brittle increase. Titanium density is small, so the titanium liquid flow inertia is small, melting titanium liquidity difference to cause low castability. Casting temperature and mold temperature (300 degrees C ) large, fast cooling, casting in protective atmosphere, titanium casting surface and internal defects such as pores will appear, largely influence the quality of castings. Therefore, titanium castings, surface treatment and other dental alloys are more important than titanium, due to unique physical and chemical properties, such as small thermal conductivity, surface hardness, and a low modulus of elasticity, viscosity, low conductivity, easy oxidation on titanium surface treatment, this brought very great difficulty, using conventional surface treatment method is very difficult to achieve the desired results. Must use special processing method and operation method. Casting post-surface treatment is not only to get the smooth and bright surface, reducing food and plaque, accumulation and adhesion, maintained in patients with normal oral microecology balance, but also increase the denture aesthetics; more important is to pass the surface treatment and modification process, improve casting surface characters and fit sex, improve denture abrasion resistant, resistant to corrosion and stress fatigue and other physicochemical properties. One, the surface reaction layer by removal of the surface reaction layer is the effect of titanium castings physicochemical properties of main factors in titanium casting, polishing, must achieve complete removal of surface contamination layer, to achieve a satisfactory polishing effect. Through sand blasting pickling method can completely remove the surface reaction layer of titanium. 1: titanium castings blasting sandblasting processing usually use white corundum coarse spray is better, blasting stress than in non precious metal is smaller, generally below 0.45Mpa. Because, injection pressure, sand blast titanium surface produces intense spark, temperature and titanium surface reaction, forming two pollution, affect the surface quality. Time is 15 ~ 30 seconds, only to remove the casting surface adhering sand, sintered on the surface layer and part and the oxide layer can be. The rest of the surface reaction layer structure should adopt the chemical pickling method for rapid removal. 2: to quickly complete removal of acid pickling surface reaction layer, and the surface will not produce other elements pollution. HF - HCl and HF - HNO3 acid lotion can be used for titanium acid, but the HF - HCl acid solution hydrogen absorption capacity is large, and the HF - HNO3 acid solution hydrogen absorption capacity is small, can control the HNO3 reduced concentrations of hydrogen, and the surface bright treatment, general HF concentration in the 3% ~ 5%, HNO3 at the concentration of 15% ~ 30% or so is proper. In two, casting defect treatment internal porosity and shrinkage cavity internal defects: heat static pressure technology ( hot isostatic pressing ) removal, but on the denture precision will influence, preferably with X-ray inspection, surface grinding of exposed holes, using laser welding. Surface porosity defects can be directly localized by laser welding repair. Three, grinding and polishing machinery grinding 1: titanium chemical reactivity of high, low thermal conductivity, viscosity, mechanical grinding grinding ratio is low, and is easy to occur in response to conventional abrasives abrasives, should not be used in grinding and polishing of titanium, preferably with good thermal conductivity of superhard abrasive, such as diamond, cubic boron nitride, polishing line speed is generally 900 ~ 1800m / min. Is appropriate, otherwise, the titanium surface easy grinding burn and crack. 2: ultrasonic grinding by ultrasonic vibration, the grinding head and grinding surface between the abrasive and abrasive surface produce relative movement to achieve the purpose of grinding, polishing. The utility model has the advantages of conventional rotary tools grinding to ditch, fossa and the stenosis becomes easier, but larger castings finishing effect is not satisfactory. 3 electrolytic mechanical compound polishing: using conductive abrasive, abrasive and abrasive surface in applied between electrolyte and voltage, through mechanical and electrochemical polishing common function, reduce the surface roughness increases the surface gloss. Electrolyte for 0.9NaCl, Voltage 5V, speed is 3000rpm / min, this method can only be grinding plane, to complex denture grinding is still in the research stage. 4 drum grinding grinding barrel: use of the revolution and rotation of the centrifugal force generated, so that the barrel of denture and abrasive relative friction movement to reduce the surface roughness of abrasive purposes. Grinding automation, high efficiency, but it can only reduce the surface roughness and can improve the surface gloss, grinding has poor precision, can be used with the denture precision polishing deburring and coarse grinding before. 5 chemical polishing chemical polishing is: through the metal in the chemical medium in the oxidation reduction reaction to achieve the purpose of leveling polishing. The utility model has the advantages of chemical polishing and the hardness of the metal, polishing area and structural shapes unrelated, where the polishing liquid contact part is polished, does not need special complex equipment, convenient operation, is suitable for the complex structure of the polishing of titanium denture. But chemical polishing process parameters are difficult to control, the effect of denture precision requirements in cases of denture has good polishing effect. Good titanium chemical polishing solution is prepared by a certain percentage of HF and HNO3, HF is a reducing agent, capable of dissolving the titanium metal, to leveling action, concentration < 10%, HNO3 oxidation, preventing excessive titanium dissolution and hydrogen absorption, which can produce light effect. Titanium polishing fluid requirements of high concentration, low temperature, polishing time is short ( 1 ~ 2min. ). 6 electrolytic polishing: also called electrochemical polishing or polishing titanium anodic dissolution, because of low conductivity, oxidation performance of strong acidic electrolyte, using water such as HF - H3PO4, HF - H2SO system electrolyte on titanium can hardly polishing, the applied voltage, titanium anode oxidation that occurs immediately, and the anodic dissolution cannot. But the anhydrous chloride electrolyte at low voltage, the titanium has good polishing effect, small specimen can be polished, but for the repair of complex body still can not reach complete purpose of polishing, perhaps by changing the shape of the cathode and additional cathode method can solve this one difficult problem, still remain at further research. In four, the surface modification of titanium nitride by plasma nitriding, 1: multi arc ion plating, ion implantation and laser nitriding chemical heat treatment technology in titanium denture, formed on the surface of Staphylococcus TiN infiltration layer, thereby improving titanium wear resistance, corrosion resistance and fatigue resistance of. But the technology is complex, expensive equipment, used for the surface modification of titanium denture is difficult to achieve the clinical practicability. 2: anodic oxidation of titanium anode oxidation technology more easily, in some oxidizing medium, a function of the applied voltage, the titanium anode can be formed thicker oxidation film, thereby improving the corrosion resistance and wear resistance and weatherability of. Anodic oxidation electrolyte generally use the H2SO4, H3PO4 and organic acids in aqueous solution. 3: the atmospheric oxidation of titanium in high temperature atmosphere can be formed thicker solid anhydrous oxide film on titanium, general corrosion, crevice corrosion are effective, method is simple. Five, in order to increase the aesthetic coloring of titanium denture, prevent the titanium denture under natural conditions to oxidation discoloration, can adopt surface nitriding, atmospheric oxidation and anodic oxidation surface coloring treatment, so that the surface form a pale yellow or golden yellow, to improve titanium denture aesthetics. Anodic oxidation method using titanium oxide film on optical interference effects, natural hair color, can be obtained by changing the voltage on the titanium surface form a colorful colors. In six, the other surface processing 1: surface roughening: in order to improve titanium and veneering resin bonding property, must be on titanium surface roughening treatment, improve the bonding area. Clinical go up to often use sandblasting roughening treatment, but the blast will cause titanium alumina pollution, we used oxalic acid etching method, get good coarsing, etching 1H surface roughness ( Ra ) can reach 1.50 + 0.30 u m, etching of 2H Ra 2.99 + 0.57 m, than the separate blasting Ra ( 1.42 + 0.14 M) more than doubled, the bond strength was increased by 30%. 2: resistance to high temperature oxidation surface treatment: in order to prevent the titanium under high temperature rapid oxidation, formed on the surface of titanium in titanium silicon compound and titanium aluminum compound, can prevent the titanium at temperatures above 700 DEG C temperature oxidation. The surface treatment on the high temperature oxidation of titanium is very effective, perhaps titanium coating on the surface of this class of compounds, the bond of porcelain fused to titanium favorable, still need further research.