The reactions of Titanium materials such as titanium rods and Titanium Tubing in the air generally react with oxygen, nitrogen, and hydrogen, which are non-metallic elements. Their reaction processes are closely related to temperature.
Titanium reacts with oxygen in the air, slowly at less than 100 degrees, and at 500 degrees only the surface is oxidized. With the increase of temperature, the surface oxide film began to dissolve in titanium, and the oxygen began to diffuse to the internal surface of the metal, but the oxygen did not enter the internal lattice of the metal in large quantities when the temperature was 700 degrees. When the temperature exceeds 700 degrees, the diffusion of oxygen to the interior of the metal accelerates, and the surface oxide film loses its protective effect at elevated temperature.
The reaction of titanium with oxygen depends on the form of titanium present and the temperature. Powder titanium in the air at room temperature, due to static electricity, spark, friction and other effects of intense combustion or explosion. But dense titanium is stable in air at room temperature. When compact titanium is heated in the air, it begins to react with oxygen. Initially, oxygen enters the lattice of titanium surface and forms a dense oxide film. This layer of surface oxide film can prevent oxygen from spreading to the interior and has a protective effect. The color of the oxide film on its surface is related to the formation temperature, which is silver white below 200 degrees, light yellow at 300 degrees, golden yellow at 400 degrees, blue at 500 degrees, purple at 600 degrees, reddish-gray at 700 to 800 degrees, and gray at 800 to 900 degrees. In pure oxygen, the initial temperature of the violent reaction between titanium and oxygen is lower than that in air, about 500 ~ 600 degrees titanium will be burned in oxygen.
At normal temperature, titanium does not react with nitrogen, but at elevated temperature, titanium is one of the few metal elements that can be burned in nitrogen, and the combustion temperature of titanium in nitrogen is higher than 800 degrees. The reaction between molten titanium and nitrogen is extremely intense. In addition to the nitrides (Ti3N, TiN, etc.) that can produce titanium, the reaction of titanium with nitrogen also forms Ti-N solid solution. When the temperature is 500-550 degrees, titanium begins to absorb nitrogen obviously, forming an interstitial solid solution. When the temperature reaches more than 600 degrees, the nitrogen absorption rate of titanium increases. In the Ti-N solid solution, the phase transition temperature of titanium increases because nitrogen enters the titanium lattice in the form of titanium nitride, and nitrogen is also the stabilizer of titanium. At 1050 degrees, the maximum solubility (mass fraction) of nitrogen in titanium is 7%, and at 2020 degrees, the maximum solubility (mass fraction) of nitrogen in titanium is 2%. However, the nitrogen absorption rate of titanium is considerably slower than its oxygen absorption rate, so titanium is mainly oxygen absorption in air, nitrogen absorption is secondary.
Titanium reacts with hydrogen to form TiH, TiH2 compounds and Ti-H solid solutions. Hydrogen is extremely nicely dissolved in titanium, and one mole of titanium absorbs nearly two moles of hydrogen. The hydrogen absorption rate and amount of titanium are related to the temperature and hydrogen pressure. The hydrogen absorption capacity of titanium is less than 0.002% at room temperature. When the temperature reaches 300 degrees, the hydrogen absorption rate of titanium increases. It reaches its maximum value at 500 ~ 600 degrees. Then, with the increase of temperature, the hydrogen absorption of titanium decreases, and most of the hydrogen absorbed by titanium is decomposed when it reaches 1000 degrees Celsius. The increase of hydrogen pressure can accelerate the absorption rate of hydrogen and increase the amount of hydrogen absorption. On the contrary, the reduction of pressure condition can make the titanium dehydrogenation. So the reaction between titanium and hydrogen is reversible. The reaction between titanium and hydrogen does not form a film on the surface, because the hydrogen atom is tiny in volume and can quickly spread to the depth of the titanium lattice to form a gap solid solution. The dissolution of hydrogen in titanium can reduce the phase transition temperature of titanium. Hydrogen is the stabilizer of Ti.