Yellow Tungsten Oxide
Yellow Tungsten Oxide (YTO) is a kind of tungsten trioxide, because the early purification of WO3 color is mostly yellow, so the early tungsten trioxide compounds are known as yellow tungsten oxide.
Yellow tungsten oxide two different sizes of different particles, showing different color. When the yellow tungsten oxide crystal size is about 1.5um, it appears to be yellow. When the yellow tungsten crystal size is about 15um, it appears to be green. Although the appearance of different, the characteristics are similar.
Before 1970s, yellow tungsten oxide was widely used, and a large amount of tungsten oxide was used in the production of metal tungsten powder and tungsten carbide powder, and a large number of applications and production of tungsten alloy products, such as tungsten copper, tungsten nickel, tungsten nickel iron, tungsten silver, tungsten rhenium, thorium tungsten and so on. Another part is used in the manufacture of paints, coatings and catalysts for the petroleum industry.
There are many ways to prepare yellow tungsten oxide, the general method is the use of ammonium paratungstate (APT) calcination reduction, usually has four stages:
1. During the heating process, the material is dried and four crystal water is lost at 100 degrees centigrade.
2. Between 100 °C-220 °C, NH3 evaporated, and formed into amorphous ammonium metatungstate.
3. Between 220 °C - 450 °C, both NH3 and H2O are volatilized to form tungsten bronze.
4. When the temperature is above 450 °C, only WO3 remains in APT.
In the process of converting APT 4H2O to WO3, color changes are very prominent. When the material is calcined at 240 °C shows white or gray, 270 °C from yellowish-white turn into yellow, with the decomposition degree yellow becomes darker, and starts to turn orange at 330 °C, and finally changed to brown, after cooling at room temperature changes into yellow.
The purity of APT determines the purity of yellow tungsten oxide. The crystal shape of APT has heredity to the crystalline form of yellow tungsten. The calcination temperature and the rate of thermal decomposition have obvious influence on the physicochemical properties of yellow tungsten.
Before the 1970s, domestic and foreign tungsten powder production mostly used tungsten trioxide as raw material. But after the 1970s, the industry developed a more stable nature, more easily doped blue tungsten oxide, yellow tungsten oxide finally retired after winning merit.
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