Oxidation of titanium materials and method for improving oxidation resistance

The rapid oxidation of titanium at high temperature forms titanium-silicon compound and titanium-aluminum compound on the surface of titanium, which can prevent the oxidation of titanium at a temperature above 700 °C. This surface treatment is very effective for high-temperature oxidation of titanium. Perhaps the coating of such compounds on the surface of titanium is beneficial to the bonding of titanium and ceramics, and further research is still needed. From the perspective of oxidation resistance, the service temperature of titanium alloy should not exceed 500°C. Generally, the difference between the shrinkage of area of the sample with oxide film and the sample without oxide film is measured as the index of oxidation degree. Oxidation is the limit of high temperature of titanium materials. One of the main reasons to use it. The process of titanium material and oxidation synthesis oxide. Titanium materials are stable in air at room temperature, but are easily oxidized when heated in air or in an oxidizing atmosphere. The degree of oxidation depends on the characteristics of the titanium material itself and the concentration of oxygen in the environment, heating time and heating temperature, etc. At high temperatures, titanium materials oxidize rapidly, resulting in brittle alloys and deterioration of mechanical properties.
When studying the phase composition of titanium anode films, it was determined that the oxide films are generally Roentgen (X-ray) amorphous films, which when formed have a low potential breakdown level. According to some authors, under certain voltage conditions The anodic film breakdown found during film formation is always accompanied by crystal formation. Titanium on the surface of the anodized film has a high degree of oxidation resistance. Low-molecular-weight titanium oxides are found under titanium dioxide (TiO2), and the thickness increases when the oxide formation potential is raised, and the low-molecular-weight titanium oxides in the film partially decrease. In the potential region of titanium oxide formation, titanium oxides of composition Ti50B to titanium oxide are found on the surface of titanium. This range of titanium oxides is transformed into titanium dioxide Ti02 (octoside stone) as the anode potential increases. Since then, according to the anode As the potential increases, the composition of the oxide film of titanium changes, and the degree of oxidation changes from zero to very high.
Because the spark temperature is sufficient for the polymorphic transformation of fausidendite to rutile, it has not been elucidated why the quasi-stable variant (variant) of the oxide is observed in the coating. Even as a result of plasma spraying alumina, although the temperature of the sprayed oxide is very high, a low temperature modification is still obtained. This is the case where plasma spraying and micro-arc oxidation are used, the same can be found in the process of forming the coating. It seems that one of the main reasons may be that a small part of the oxide layer melts during the micro-arc oxidation, and the melt in this region cools violently when the micro-arc moves. Short-term discharges help to form the amorphous phase in the coating. As a result of the rapid cooling rate in the electrolyte of the anode micro-segments responsible for the breakdown, quenching of the thin film material occurs without reaching thermodynamic equilibrium and without the formation of a fully crystalline phase. The study of Roentgen’s amorphous form of this film found that there is a polycrystalline structure of deformation (octahedral stone) in the amorphous matrix, and the film formed in sulfuric acid or phosphoric acid is composed of crystalline phase TiO2. This phase is a phase that crystallizes under the voltage increasing condition. Using the crystallography method, it is clarified how brookite forms crystalline products under low-density current conditions. It has been determined that the anode thin film TiO2 is in the modified state of anatase (octahite). Under the condition of forming voltage, the inclusion rutile of modified titanium oxide was found by thin film spark voltage asymptotic method. When the film voltage is further increased, it is completely transformed into rutile.
Improving the oxidation resistance of titanium materials can be achieved by coating and developing more oxidation-resistant alloys. The coating can use surface processing technology to coat a protective metal layer (such as aluminum, platinum, gold, etc.) or a metal-oxide mixture layer (such as Al+SiO2) on the surface of the titanium material to improve the oxidation resistance of the titanium material performance. Using platinum ion plating, Ti-6Al-2Sn-4Zr-2Mo does not oxidize for a long time at 590°C. Using tungsten and platinum as the bottom layer of the coating respectively, the anti-oxidation temperature can be increased to 700°C. Adjusting the composition of titanium alloy can also improve the oxidation resistance of titanium materials. The Pilling-Bedworth ratio of selected alloying elements should be greater than 1, and the Gideon free energy is lower than that of titanium, which is in line with Hauffe’s law. Alloying elements that improve oxidation resistance include: niobium, aluminum, molybdenum, tungsten, tin, silicon, etc. Add these alloying elements to obtain titanium alloys with good oxidation resistance, such as Ti-5A1, Ti-5Al-2.5, Ti-4Al-3Mo-1V, Ti-5.8Al-4Sn-3.5Zr-O.5Mo-O.7Nb -O.35Si-0.06C etc. Ti3A1, Ti-Al, Ti-Al-Nb and other intermetallic compounds have higher anti-oxidation ability. The anti-oxidation temperature of Ti3A1 can reach above 750°C, and that of TiAl can reach above 900°C. The anti-oxidation ability of Ti-A1-Nb is higher than that of TiAl is higher.
When the temperature is higher than 800°C, the oxide film will decompose, and oxygen atoms will enter the metal lattice through the oxide film, resulting in embrittlement. In general, the oxidation kinetics of titanium follows a parabolic law at low temperatures and a linear law at high temperatures. The molecular volume of the oxide film formed by titanium is larger than the volume of metal atoms consumed to form the oxide film, so the formed oxide film can cover the entire surface of the metal. At 500°C, the oxide film formed on the surface of the titanium material has a protective effect, can prevent the penetration of oxygen, and prevent the titanium material from continuing to oxidize. As the temperature continues to rise, the oxide film loses its protective effect, and intense oxidation occurs. Oxygen diffuses through the oxide film to the inside of the metal, forming an obvious gas permeation layer.

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Longbai titanium sponge will reach 80,000-100,000 tons/year

At the 2022 China Panxi Vanadium and Titanium Forum, Li Jianjun of Longmang Sponge Titanium made a detailed report on the theme of “Building a World-Class Titanium Chemical Group Leading by ‘Double Carbon'”. He described it from four aspects: “International carbon progress, domestic carbon progress, Longbai empowerment, innovation leadership, and all employees working together to reduce carbon”. He said that around the titanium element, Longbai Group is focusing on creating products such as titanium dioxide, titanium sponge and titanium alloys, and lithium-ion battery materials, giving full play to its industrial advantages, realizing multi-industry coupling, and building an ecological circle with “Longbai characteristics”. A number of technological breakthroughs have been achieved in the comprehensive utilization of vanadium, iron, scandium, chromium, cobalt, nickel and other resources and industrialization has been achieved. Through technological innovation, the efficient recycling of various metal elements in raw material ores has been achieved, effectively promoting the green and low-carbon development of enterprises. , Circular development. The Honggebei mining area of ​​Longbai Panzhihua Company has become the largest production base of titanium raw materials in the country, which has proved the comprehensive strength of the enterprise in the integration of mineral resources, technological innovation, green industry development and efficient development and utilization of mineral products. Under the guidance of the “Double Carbon” strategy, Longbai Group adheres to the “big chemical industry” route, builds a high-quality, low-cost production process for the entire industrial chain, greatly improves the level of comprehensive resource utilization, and realizes circular economy to help reduce carbon. Focusing on mineral products, titanium and zirconium products, new energy products and rare and scattered metal products, Chen Jianjian introduced the industrial advantages of the group in detail. At present, the company’s titanium dioxide and sponge titanium production capacity has reached an annual output of 1.5 million tons and 50,000 tons respectively, both ranking first in the world; in terms of new energy products, it has formed an annual output of 100,000 tons of iron phosphate and 50,000 tons of iron phosphate Lithium + 100,000 tons of graphite anode material integrated new energy product industrial system; in terms of rare and scattered metal products, the company now has the world’s largest production base of scandium oxide and metal scandium, with an annual production capacity of 50 tons, ranking first in the world First, and form a production scale of 600 tons/year of vanadium series products, and plan to form a production line of 30,000 tons/year of vanadium series products in the future. He said that Longbai Group actively responded to the call of the national “double carbon” policy, paid attention to environmental and ecological protection, proposed and gradually implemented green electricity consumption, hydropower consumption, solar energy utilization, fossil fuel reduction and substitution, terminal energy electrification, industrial Taking measures such as utilization of surplus energy and improvement of equipment energy efficiency, we have continuously cultivated the titanium chemical industry, joined hands with all employees to reduce carbon, realized multi-industry coupling, and achieved remarkable results.

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