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Surface modification of titanium

Views: 0     Author: Site Editor     Publish Time: 2022-09-02      Origin: Site

The later surface treatment of the casting 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 micro ecology, but also increase the aesthetic feeling of the denture; More importantly, through these surface treatment and modification processes, the surface properties and suitability of the casting can be improved, and the physical and chemical properties such as wear resistance, corrosion resistance and stress fatigue resistance of the denture can be improved.

Titanium: removal of surface reaction layer

The surface reaction layer is the main factor affecting the physical and chemical properties of titanium castings. Before grinding and polishing of titanium castings, the surface contamination layer must be completely removed to achieve a satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by sand blasting and pickling.

1. Sandblasting: white corundum is generally used for the sandblasting treatment of titanium castings. The sandblasting pressure is lower than that of non precious metals, and is generally controlled below 0.45MPa. This is because when the injection pressure is too high, the sand particles will impact the titanium surface to produce intense sparks, and the temperature rise can react with the titanium surface to form secondary pollution and affect the surface quality. The time is 15 ~ 30s, and only the sand, surface sintering layer and part of oxide layer on the casting surface can be removed. The rest of the surface reaction layer structure should 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-hcl and hf-hno3 acid washing solutions can be used for titanium pickling. However, hf-hcl acid washing solution has a large hydrogen absorption capacity, while hf-hno3 acid washing solution has a small hydrogen absorption capacity. The concentration of HNO3 can be controlled to reduce hydrogen absorption, and the surface can be polished. Generally, the concentration of HF is about 3% ~ 5%, and the concentration of HNO3 is about 15% ~ 30%.

Treatment of casting defects

Internal air holes and internal defects of shrinkage holes: they can be removed by hot isostatic pressing, but they will affect the accuracy of dentures. It is better to remove the exposed air holes on the surface after X-ray flaw detection and repair welding with laser. The surface porosity defect can be directly repaired by laser local welding.

Grinding and polishingtitanium bar manufacturer - TIRONG TECH

1. Mechanical grinding: titanium has high chemical reactivity, low thermal conductivity, high viscosity, low mechanical grinding ratio, and is easy to react with abrasives. Ordinary abrasives are not suitable for titanium grinding and polishing. It is better to use super hard abrasives with good thermal conductivity, such as diamond and cubic boron nitride. The polishing line speed is generally 900 ~ 1800m / min Otherwise, the titanium surface is prone to grinding burns and microcracks.

2. Ultrasonic grinding: through the action of ultrasonic vibration, the abrasive particles between the grinding head and the surface to be polished and the surface to be polished move relatively to achieve the purpose of grinding and polishing. It has the advantage that it is easy to grind the grooves, pits and narrow parts that cannot be reached by conventional rotary tools, but the grinding effect of large castings is not satisfactory.

3. Electro mechanical composite grinding: conductive grinding tool is used to apply electrolyte and voltage between the grinding tool and the grinding surface. Under the joint 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 support is still in the research stage.

4. Barrel grinding: use the centrifugal force generated by the revolution and rotation of the grinding barrel to make the denture in the barrel move relative to the abrasive 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. The grinding accuracy is poor. It can be used for deburring and rough grinding before the precision polishing of dentures.

5. Chemical polishing: chemical polishing is to achieve the purpose of leveling and polishing through the oxidation-reduction reaction of metal in the 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 polishing liquid are polished without special and complex equipment. It is easy to operate and is more suitable for polishing titanium denture brackets with complex structures. However, the process parameters of chemical polishing are difficult to control, and it is required to have a good polishing effect on the denture without affecting the accuracy of the denture. A good titanium chemical polishing solution is prepared by HF and HNO3 in a certain proportion. HF is a reducing agent, which can dissolve titanium metal and play a leveling role. The concentration is less than 10%. HNO3 plays an oxidizing role to prevent excessive dissolution and hydrogen absorption of titanium, and can produce a bright effect. Titanium polishing solution requires high concentration, low temperature and short polishing time (1 ~ 2min.).

6. Electrolytic polishing: it is also called electrochemical polishing or anodic dissolution polishing. Due to the low conductivity and strong oxidation performance of titanium, it is almost impossible to polish titanium with aqueous acidic electrolyte such as hf-h3po4 and hf-h2so system electrolyte. After the external voltage is applied, the titanium anode immediately oxidizes, which makes the anodic dissolution impossible. However, the anhydrous chloride electrolyte has a good polishing effect on titanium under low voltage, and small-scale specimens can be mirror polished, but for complex restorations, the purpose of complete polishing cannot be achieved. Perhaps the method of changing the cathode shape and adding a cathode can solve this problem, which needs further research.

Surface modification of titanium

1. Nitriding: chemical heat treatment technologies such as plasma nitriding, multi arc ion plating, ion implantation and laser nitriding are used to form golden tin nitrided layer on the surface of titanium denture, so as to improve the wear resistance, corrosion resistance and fatigue resistance of titanium. However, the technology is complex and the equipment is expensive, so it is difficult to achieve clinical application for 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, so as to improve its corrosion resistance, wear resistance and weather resistance. The electrolyte for anodic oxidation generally adopts H2SO4, H3PO4 and organic acid aqueous solution.

3. Atmospheric oxidation: titanium can form a thick and solid anhydrous oxide film in high temperature atmosphere, which is effective for comprehensive corrosion and interstitial corrosion of titanium. The method is relatively simple.

Coloring

In order to increase the aesthetic feeling of the titanium denture and prevent the discoloration of the titanium denture due to continuous oxidation under natural conditions, surface nitriding treatment, atmospheric oxidation and anodic oxidation method can be used for surface coloring treatment to form light yellow or golden yellow on the surface and improve the aesthetic feeling of the titanium denture. The anodic oxidation method makes use of the interference of titanium oxide film with light to naturally color, and can form colorful colors on the titanium surface by changing the cell voltage.

Other surface treatments

1: Surface roughening: in order to improve the bonding performance of titanium and facing resin, the surface of titanium must be roughened to improve its bonding area. Sand blasting is often used for roughening in clinic, but sand blasting will cause pollution of alumina on the titanium surface. We use oxalic acid etching method to obtain good roughening effect, and the surface roughness (RA) can reach 1.50 ± 0.30 after etching for 1H μ m. After etching for 2h, RA was 2.99 ± 0.57 μ m. Compared with RA (1.42 ± 0.14 μ m) The bonding strength was increased by 30%.

2: High temperature oxidation resistant surface treatment: in order to prevent the rapid oxidation of titanium at high temperature, titanium silicon compound and titanium aluminum compound are formed on the surface of titanium, which can prevent the oxidation of titanium at temperatures above 700 ℃. This kind of surface treatment is very effective for the high-temperature oxidation of titanium. Perhaps coating this kind of compound on the surface of titanium is beneficial to the bonding of titanium and porcelain, and further research is still needed.

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