Titanium is a very active metal with low equilibrium potential and high thermodynamic corrosion tendency in the medium. This is because titanium and oxygen have a great affinity, in the air or oxygen-containing medium, titanium surface generated a layer of dense, strong adhesion, large inert oxide film, to protect the titanium matrix from corrosion. It will heal or regenerate quickly even due to mechanical wear and tear. This indicates that titanium is a metal with a strong passivation tendency.
The titanium oxide film with the medium temperature below 315℃ always maintains this characteristic.In order to improve the corrosion resistance of titanium, the surface treatment technologies, such as oxidation, electroplating, plasma spraying, ion nitriding, ion implantation and laser treatment, have been developed to enhance the protective effect of titanium oxide film and obtain the desired corrosion resistance effect. A series of corrosion resistant titanium alloys, such as titanium-molybdenum, titanium-palladium, titanium-molybdenum and nickel, were developed to meet the requirements of metal materials in the production of sulfuric acid, hydrochloric acid, methylamine solution, high temperature wet chlorine gas and high temperature chloride..
Ti-32 molybdenum alloy is used in titanium castings, Ti-0.3molybdenum - 0.8nickel alloy is used in the environment where crevice corrosion or pitting often occurs, or Ti-0.2palladium alloy is used locally in titanium equipment, and good results are obtained.This property explains the high yield strength ratio (tensile strength/yield strength) and indicates the poor plastic deformation of titanium metal during forming. The ratio of yield limit to elastic modulus of titanium is large, so that the resilience of titanium forming is large.Although the thermal conductivity of titanium is lower than that of carbon steel and copper, but because of the excellent corrosion resistance of titanium, the wall thickness can be greatly reduced, and the heat transfer method of the surface and steam is drip condensation, which reduces the heat group, and the surface does not scale can also reduce the thermal resistance, so that the heat transfer performance of titanium is significantly improved.
