In recent years, titanium pots made of pure titanium have become popular in everyone’s kitchens due to their corrosion resistance, light weight, high temperature resistance and no precipitation of heavy metals. After the titanium pot was used for a long time, many people found that it would change color. For example, when cooking, it was yellow; when the pot was cooled, it turned back to silvery white. Why does the titanium pot change color? This has a lot to do with the titanium material it used.
Titanium is very stable in air at room temperature, and color changes only occur when heated for a period of time. This is mainly because when titanium is heated in the air, it oxidizes with oxygen to form a dense oxide film. This oxide film not only protects the surface of titanium, but also is the fundamental source of titanium color change.
The reaction equation for titanium oxidation is Ti+O2==TiO2, and the reaction conditions are high temperature heating. When the heating temperature is low, the oxide film on the surface of the titanium is almost transparent, which is difficult to detect with the naked eye, but when the temperature rises, the oxide film in the pot will gradually thicken and interfere with the light. In the eyes of people, they will also show different colors. Therefore, the thickness of the oxide film determines the color of the titanium surface.
According to related research, after heating in air for half an hour, the surface of titanium heated at 200 ° C is silver white, 300 ° C is light yellow, 400 ° C is golden yellow, 500 ° C is blue, 600 ° C is purple, 700 °C (to) – 800 ° C for gray red, 900 ° C for gray, the entire color change can be described as colorful. The ignition temperature of natural gas is 270-540 °C, the ignition temperature of liquefied petroleum gas is 365-460 °C, and the ignition temperature of city gas is 270-605 °C, which can reach the temperature of oxidative discoloration of titanium. If your titanium pot can change color, it means that you have bought a pure titanium pot.
The oxide film of titanium not only changes the color of titanium, but also greatly improves the corrosion resistance of titanium. However, the thicker the oxide film of titanium, the better the corrosion resistance. When the heating temperature is below 500 °C, oxygen and titanium will form a dense oxide film of TiO2, which has a certain protective effect on the surface of titanium; When the heating temperature reaches 600 °C-700 °C, the oxide film on the surface of titanium will become thicker; After the temperature exceeds 700 ° C, although the thickness of the oxide film increases, it becomes loose, easily broken, and loses its protective effect. Therefore, titanium generally has good corrosion resistance at normal temperature.
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