Titanium is easy to react with O, H, N, and other elements in the air and Si, Al, Mg, and other elements in the embedding material at high temperature, forming a surface contamination layer on the surface of the casting, making its excellent physical and chemical properties worse, hardness Increase, plasticity, elasticity decreases, brittleness increases.
The density of titanium is small, so the inertia of the titanium liquid is small when flowing, and the poor fluidity of molten titanium results in a low casting flow rate, a large temperature difference between the casting temperature and the mold temperature (300 ° C), and the cooling is fast. The casting is carried out in a protective atmosphere, and the surface of the titanium casting is And internal defects such as pores are inevitable, which has a great impact on the quality of castings.
Therefore, the surface treatment of titanium castings is more important than other dental alloys. Due to the unique physical and chemical properties of titanium, such as low thermal conductivity, surface hardness, low elastic modulus, high viscosity, low electrical conductivity, easy oxidation, etc., which brings great difficulty to the surface treatment of titanium, it is difficult to achieve the desired effect by using conventional surface treatment methods. Special processing methods and operating means must be used.
The later surface treatment of castings is not only to obtain a smooth and bright surface, reduce the accumulation and adhesion of food and plaque, maintain the balance of the patient's normal oral microecology, but also increase the aesthetics of the denture; more importantly, through These surface treatment and modification processes improve the surface properties and suitability of castings, and improve the physical and chemical properties of dentures such as wear resistance, corrosion resistance, and stress fatigue resistance. 1. Removal of the surface reaction layer
The surface reaction layer is the main factor affecting the physical and chemical properties of titanium castings. Before the grinding and polishing of titanium castings, the surface contamination layer must be completely removed to achieve a satisfactory polishing effect. The surface reaction of titanium can be completely removed by pickling after sandblasting. Floor. 1. Sandblasting: The sandblasting treatment of titanium castings is generally better to use white corundum for rough blasting. The blasting pressure is smaller than that of non-precious metals and is generally controlled below 0.45Mpa because when the blasting pressure is too large, the sand particles will impact. Intense sparks are generated on the titanium surface, and the temperature rise can react with the titanium surface to form secondary pollution and affect the surface quality. The time is 15 to 30 seconds. Only remove the sticky sand, surface sintered layer, and part of the oxide layer on the surface of the casting. . The rest of the surface reaction layer structure can be quickly removed by chemical pickling. 2. Pickling: Pickling can quickly and completely remove the surface reaction layer, and the surface will not be polluted by other elements. Both HF-HCI series and HF-HNO3 series pickling liquids can be used for titanium pickling, but HF-HCI series pickling liquids absorb more hydrogen, while HF-HNO3 series pickling liquids have small hydrogen absorption, which can control HNO3 The concentration of HF can reduce the absorption of hydrogen, and the surface can be brightly treated. Generally, the concentration of HF is about 3%~5%, and the concentration of HNO3 is about 15%~30%. Second, the treatment of casting defects. Internal pores and shrinkage Defects inside the hole: It can be removed by hot isostatic pressing, but it will affect the accuracy of the denture. It is best to use X-ray inspection to remove the exposed pores on the surface and use laser repair welding. Surface porosity defects can be directly repaired by laser local welding. 3. Grinding and polishing 1. Mechanical grinding: Titanium has high chemical reactivity, low thermal conductivity, high viscosity, low mechanical grinding, and grinding ratio, and is easy to react with abrasives. Ordinary abrasives are not suitable for grinding and polishing titanium. It is best to use super hard abrasives with good thermal conductivity, such as diamond, cubic boron nitride, etc., and the polishing line speed is generally 900~1800m/min. Straight, otherwise, grinding burns and micro-cracks are prone to occur on the titanium surface. 2. Ultrasonic grinding: Through the action of ultrasonic vibration, the abrasive particles between the grinding head and the ground to be ground are moved relative to the ground to achieve the purpose of grinding and polishing. The advantage is that grooves, dimples, and narrow areas that conventional rotary tools cannot grind become easier, but the grinding effect of larger castings is still unsatisfactory. 3. Electrolytic-mechanical composite grinding: using conductive abrasive tools, applying electrolyte and voltage between the abrasive tool and the grinding surface, through the combined action of mechanical and electrochemical polishing, the surface roughness is reduced and the surface gloss is improved. The electrolyte is 0 . 9NaCl, the voltage is 5v, the rotation speed is 3000rpm/min., this method can only grind the plane, and the grinding of complex denture brackets is still in the research stage. 4. Barrel grinding: Using the quotient force generated by the revolution and rotation of the grinding barrel, the denture and the abrasive in the barrel are relatively rubbed to reduce the surface roughness. The grinding is automatic and efficient, but it can only reduce the surface roughness but not improve the surface gloss, and the grinding precision is poor. It can be used for deburring and rough grinding before fine polishing of dentures.
5. Chemical polishing: Chemical polishing is the purpose of leveling and polishing through the redox reaction of metal in the chemical medium. The advantage is that chemical polishing has nothing to do with the hardness of the metal, the polishing area, and the structural shape, and all the parts in contact with the polishing liquid are polished, no special complex equipment is required, the operation is simple, and it is more suitable for the polishing of titanium denture brackets with complex structures. However, the process parameters of chemical polishing are difficult to control. It is required to have a good polishing effect on the denture without affecting the accuracy of the denture. A better titanium chemical polishing solution is HF and HNO3 prepared in a certain proportion. Dissolves titanium metal, plays a role in leveling, the concentration is less than 10%, HNO3 plays an oxidation role, prevents excessive dissolution of titanium and hydrogen absorption, and can produce a bright effect at the same time, titanium polishing liquid requires high concentration, low temperature, and short polishing time (1 ~2min.).6. Electrolytic polishing: also known as electrochemical polishing or anodic dissolution polishing. Due to the low conductivity of titanium and its strong oxidation performance, an aqueous acidic electrolyte such as HF-H3PO4 and HF-H2SO is used for electrolysis. The liquid can hardly polish the titanium. After the external voltage is applied, the titanium anode is immediately oxidized, so that the anode dissolution cannot be carried out. However, the use of anhydrous chloride electrolyte at low voltage has a good polishing effect on titanium, and small specimens can be mirror polished, but for complex restorations, the purpose of complete polishing can still not be achieved. Maybe change the shape of the cathode and add an additional cathode The method can solve this problem, and further research is needed. 4. Surface modification of titanium 1. Nitriding: Using chemical heat treatment technologies such as plasma nitriding, multi-arc ion plating, ion implantation, and laser nitriding, a golden TiN infiltration coating is formed on the surface of titanium dentures, thereby improving the titanium denture. Wear resistance, corrosion resistance, and fatigue resistance. However, the technology is complex and the equipment is expensive, and it is difficult to achieve clinical practicality for the surface modification of titanium dentures. 2. Anodizing: The anodizing technology of titanium is relatively easy. In some oxidizing media, under the action of applied voltage, the titanium anode can form a thick oxide film, thereby improving its corrosion resistance, wear resistance, and weather resistance. The electrolyte for anodic oxidation generally adopts H2S04, H3PO4, and organic acid aqueous solution. 3. Atmospheric oxidation: Titanium can form a thick and strong anhydrous oxide film in a high-temperature atmosphere, which is effective for overall corrosion and crevice corrosion of titanium, and the method is relatively simple. 5. Coloring In order to increase the beauty of titanium dentures and prevent the discoloration of titanium dentures from continued oxidation under natural conditions, surface nitriding treatment, atmospheric oxidation and anodizing surface coloring treatment can be used to make the surface light yellow or golden yellow, improve The beauty of titanium dentures. The anodic oxidation method utilizes the interference effect of the titanium oxide film on light to naturally develop color and can form colorful colors on the titanium surface by changing the cell voltage. 6. Other surface treatment 1: Surface roughening: In order to improve the bonding performance between titanium and veneer resin, the surface of titanium must be roughened to increase its bonding area. In clinical practice, sandblasting is often used for roughening treatment, but sandblasting will cause the pollution of aluminum oxide on the surface of the titanium. We use the oxalic acid etching method to obtain a good roughening effect, and the surface roughness (Ra) of etching 1h can reach 1. 50±0.30μm, 2h of etching Ra is 2.99±0.57μm, more than double the Ra (1.42±0.14μm) of sandblasting alone, and its bond strength is improved by 30%.2: Surface treatment for high-temperature oxidation resistance: In order to prevent the rapid oxidation of titanium at high temperatures, titanium silicon compounds, and titanium aluminum compounds are formed on the surface of titanium, which can prevent the oxidation of titanium at temperatures above 700 °C. This kind of surface treatment is very effective for the high-temperature oxidation of titanium. Maybe the surface of titanium should be coated with such compounds, which is beneficial to the combination of titanium and ceramics, and further research is needed.
