Titanium alloy is a very active material. Titanium has good corrosion resistance in many corrosive media. As long as there is sufficient oxygen, even if the film is mechanically damaged, the film itself can immediately heal or regenerate at its own expense.
(1) The corrosion resistance of titanium is affected by the surface oxide film, so this material is more suitable for use in an oxidizing environment, or where oxygen is easily obtained. In a reducing solution, titanium will react with the solution to generate hydrogen.
(2) Like all metals, galvanic couples are formed when titanium is in direct contact with dissimilar metals in an electrolyte. After the galvanic couple is formed, one or both metals corrode much faster than before the galvanic couple is formed. In almost all cases, titanium is the more inert pole of the galvanic couple, thus causing corrosion of the other metal. Increase. The degree of corrosion depends on the relative area ratio and the actual electrolyte used, so the formation of galvanic couples should be avoided when designing equipment.
(3) Generally, titanium alloys are only used in some occasions where the corrosion rate is very slow, so it is not necessary to provide a corrosion tolerance margin when designing equipment. In this way, it is possible to use relatively thin titanium plates as carbon-titanium containers, heat exchanger tail boxes and bushings for tube sheets, pumps, valves, etc. - also use thin titanium tubes for tube heat exchangers and thin titanium plates for plate heat exchangers heat exchangers to reduce equipment costs and improve heat exchange performance. Since the passivation of titanium depends on the presence of an oxide film, the corrosion resistance in an oxidizing solution is much more significant than that in a non-oxidizing solution. Titanium can corrode at a higher rate in a non-oxidizing medium. Therefore, titanium can be used in various concentrations of aqueous nitric acid below the boiling point. Likewise, it does not corrode in wet chlorine gas. In chloride solutions, such as sodium chloride and hypochlorite solutions, it does not corrode . The oxide protective film on the titanium surface is usually formed in contact with water, and the protective film can be formed even if only a small amount of water or water vapor exists. Therefore, if titanium is exposed to a highly oxidizing environment that is completely devoid of water, rapid oxidation will occur and often cause combustion. Such phenomena occur in the reactions between titanium and dry nitric acid and titanium and dry chlorine. However, in this case, as long as there is very little water content (even as long as 50ppm), this corrosion can be avoided. There is no evidence of pitting and stress corrosion of titanium in inorganic metal chloride aqueous solutions. In seawater, even under the high-speed erosion of seawater, titanium has good corrosion resistance. Although it is reasonable to say that titanium alloys will undergo significant corrosion in media such as sulfuric acid and hydrochloric acid, and thus react to generate hydrogen, as long as there is a small amount of oxidant in the acid, a passivation film can be formed on the titanium surface. Therefore, in the mixed solution of strong sulfuric acid and nitric acid, in the mixed solution of hydrochloric acid and nitric acid, even in the mixed solution containing free
In the strong hydrochloric acid of chlorine gas, titanium has corrosion resistance. The presence of copper ions or iron ions in the solution can also reduce the corrosion rate of titanium, which is equivalent to alloying with precious metals or using anodic passivation techniques.