1. Corrosion resistance of titanium
Titanium is a metal with a strong passivation tendency, which can quickly generate a stable oxidizing protective film in air and oxidation or neutral aqueous solution, even if the film is damaged for some reasons, it can quickly and automatically recover. Therefore, titanium has excellent corrosion resistance in oxidizing and neutral media.
Due to the huge passivation properties of titanium, in many cases, when in contact with dissimilar metals, corrosion is not accelerated, but may accelerate the corrosion of dissimilar metals. For example, in low-concentration non-oxidizing acids, if Pb, Sn, Cu or Monel alloy is contacted with titanium to form a couple, the corrosion of these materials is accelerated, and titanium is not affected. In hydrochloric acid, when titanium is in contact with low carbon steel, new hydrogen is generated on the surface of titanium, destroying the oxide film of titanium, which not only causes the hydrogen embrittleness of titanium, but also accelerates the corrosion of titanium, which may be due to the high activity of titanium to hydrogen.
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The iron content in titanium has an impact on the corrosion resistance of some media, the reason for the increase of iron in addition to the reasons of raw materials, often contaminated iron infiltration into the weld bead during welding, so that the local iron content in the weld bead increases, then the corrosion has an uneven nature. When using iron parts to support titanium equipment, iron contamination on iron-titanium contact surfaces is almost inevitable and corrosion acceleration in iron-contaminated areas, especially in the presence of hydrogen. When the titanium oxide film on the stained surface is mechanically damaged, hydrogen penetrates into the metal, and according to temperature, pressure and other conditions, hydrogen is diffused correspondingly, which makes titanium produce different degrees of hydrogen embrittlement. Therefore, titanium is used in medium temperature and medium pressure and hydrogen-containing systems to avoid surface iron contamination.
Under normal circumstances, titanium will not be pitted. Titanium also has anti-corrosion fatigue stability.
Titanium has good crevice corrosion resistance, especially Ti-0.3Mo-0.8Ni and Ti-0.2Pd alloys, so Ti-0.3Mo-0.8Ni and Ti-0.2Pd alloys are widely used in sealing surface materials of container equipment to solve the problem of gap corrosion of equipment sealing surface.
2. Application of titanium materials
Due to its excellent corrosion resistance, titanium is widely used in petroleum, chemical industry, salt making, pharmaceutical, metallurgy, electronics, aviation, aerospace, ocean and other related fields.
Titanium has excellent corrosion resistance to most salt solutions, such as titanium in chloride solution than high chrome-nickel steel corrosion resistance, and no corrosion phenomenon. However, the corrosion rate in aluminum trichloride is higher, which is related to the concentrated hydrochloric acid produced by the hydrolysis of aluminum trichloride. Titanium also has good stability to hot sodium chlorite and various concentrations of hypochlorite. Therefore, titanium is widely used in vacuum salt making and bleaching powder industry.
Titanium has good corrosion resistance to most alkali solutions. Titanium is relatively stable in sodium hydroxide and potassium hydroxide solutions with concentrations less than 50%. If the alkali solution contains chloride ions or chlorides, its corrosion resistance even exceeds that of nickel and zirconium. However, in the case of increasing temperature and concentration, corrosion will increase. Now the chlor-alkali industry is a large field of domestic civil titanium applications.
Titanium in the dry chlorine is not resistant to corrosion, while there is a risk of fire, but in the wet chlorine has a high stability, more than zirconium, Hastelloy C and Monel, and even in the saturated chlorine of sulfuric acid, hydrochloric acid and chloride and other media is also stable, so titanium is the sulfuric acid process of titanium dioxide production of key equipment materials.
Because titanium has good corrosion resistance in hydrocarbons, it is also good even when containing acids and chloride-like impurities. Therefore, titanium is also widely used in organic chemicals, such as PTA (refined terephthalic acid), PVA (Vinylon) and so on.
Titanium has excellent corrosion resistance in seawater, so titanium is also widely used in Marine fields such as offshore oil drilling platforms and seawater desalination.
