Metal that changes color - titanium
In recent years, titanium pots made of pure titanium have become popular in everyone's kitchens because of their corrosion resistance, light weight, high temperature resistance, and no heavy metal precipitation. After using the titanium pot for a long time, many people find that it will change color. For example, it is yellow when cooking, but it turns back to silvery white after the pot is cooled. Why do titanium pots change color? This has a lot to do with the material used - titanium.
Titanium metal is very stable in air at room temperature. Only when it is heated to high temperature for a period of time will it produce "colorful" changes. This is mainly because when titanium metal is heated in the air, it will undergo an oxidation reaction with oxygen to form a dense oxide film. This oxide film not only protects the surface of titanium metal, but is also the fundamental source of the color change of titanium.
Titanium oxide film thickness at different temperatures:
|
temperature °C |
320-540 |
650 |
700 |
760 |
|
Thickness㎜ |
extremely thin |
0.005 |
0.008 |
0.25 |
The color of titanium oxide film at different temperatures:
|
temperature °C |
200 |
300 |
400 |
500 |
700-800 |
900 |
|
color |
silver white |
light yellow |
Golden |
blue |
red gray |
grey |
The reaction equation of titanium oxidation is Ti+O2==TiO2, and the reaction condition is high-temperature heating. When the heating temperature is low, the oxide film on the titanium surface is almost transparent, which is difficult for people 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. Different colors will also appear in human eyes. Therefore, the thickness of the oxide film determines the color of the titanium surface.
According to relevant research, after heating in the air for half an hour, the surface of titanium heated at 200°C is silvery white, light yellow at 300°C, golden yellow at 400°C, blue at 500°C, purple at 600°C, and purple at 700°C. ℃ (to) - 800 ℃ is gray-red, 900 ℃ is 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, all of which can reach the temperature of titanium oxidation and discoloration. If your titanium pot can change color, It means that you are buying a pure high-quality titanium pot.
