Among the characteristics of titanium, the most praised […]
Among the characteristics of titanium, the most praised is its excellent corrosion resistance-its corrosion resistance is almost as good as platinum. Titanium is not corroded by dilute sulfuric acid, dilute hydrochloric acid, chlorine gas, chlorine solution and most organic acids. But it can still be dissolved by concentrated acid. Although the following potential-pH diagram indicates that titanium is a highly active metal thermodynamically, its reaction with water and air is very slow.
When titanium is exposed to high-temperature air, a protective film of passive oxide is formed to prevent the oxidation from continuing. When initially formed, the protective layer is only one to two nanometers thick, but it will slowly continue to thicken; it can reach 25 nanometers in four years. But when titanium is placed in high-temperature air, it easily reacts with oxygen.
This reaction occurs when the air temperature reaches 1200 degrees Celsius, and in pure oxygen, it only needs 610 degrees Celsius to produce titanium dioxide. Therefore, titanium cannot be melted in the air, because titanium will burn before reaching the melting point, so it can only be melted in an inert gas or vacuum. At 550 degrees Celsius, titanium will combine with chlorine. Titanium also combines with other halogens and absorbs hydrogen.
Titanium is also one of the few elements that will burn in pure nitrogen, and it will burn up to 800 degrees Celsius, forming titanium nitride, leading to embrittlement.
Experiments pointed out that natural titanium will be radioactive after being bombarded by deuterons, which mainly releases positrons and hard gamma rays.