How will titanium alloy materials react in air?
The reaction of titanium alloy materials in the air, such as titanium rods, titanium tubes, etc., is usually related to three non-metallic elements: oxygen, nitrogen, and hydrogen. Their reaction process is closely related to temperature.
Titanium reacts very slowly with oxygen in the air below 100 degrees, and only the surface is oxidized at 500 degrees. As the temperature increases, the surface oxide film begins to dissolve in the titanium and oxygen begins to diffuse into the metal. However, at 700°C, oxygen does not enter the metal's internal lattice. When the temperature exceeds 700°C, the diffusion of oxygen into the metal accelerates, and the surface oxide film loses its protective effect at high temperatures.
The reaction of titanium with oxygen depends on the shape and temperature of the titanium. Titanium powder will burn or explode violently under the action of static electricity, sparks and friction in the air at room temperature. However, dense titanium is stable in air at room temperature. When dense titanium is heated in air, it begins to react with oxygen. First, oxygen enters the crystal lattice on the titanium surface to form a dense oxide film. The oxide film on the surface can prevent oxygen from diffusing into the interior and play a protective role. Therefore, titanium is stable in air below 500°C. The color of the surface oxide film is related to the formation temperature. Below 200 degrees, it is silvery white, 300 degrees is light yellow, 400 degrees is golden yellow, 500 degrees is blue, 600 degrees is purple, 700-800 degrees is red gray, and 800-900 degrees is gray. In pure oxygen, the initial temperature ratio of titanium to oxygen is lower than in air. At around 500-600°C, titanium burns in oxygen.
Titanium does not react with nitrogen at room temperature, but at high temperatures, titanium is one of the few metallic elements that can burn in nitrogen. When the combustion temperature of titanium in nitrogen is higher than 800°C, the reaction between titanium and nitrogen is very violent. The reaction between titanium and nitrogen can not only generate titanium nitride (Ti3n, TiN, etc.), but also form a Ti-N solid solution. When the temperature is 500-550°C, titanium begins to absorb nitrogen and form an interstitial solid solution; when the temperature exceeds 600°C, the nitrogen absorption rate of titanium increases. In the Ti-N solid solution, nitrogen enters the titanium lattice in the form of titanium nitride, and the phase transition temperature of titanium increases. Nitrogen is also a stabilizer for titanium. The solubility (mass fraction) of nitrogen in air is 7% at 1050°C and 2% at 2020°C. However, titanium absorbs nitrogen much more slowly than it absorbs oxygen. Therefore, titanium mainly absorbs oxygen from the air, while the absorption of nitrogen is secondary.
