Brief Introduction on the Origin of Color of CBN
The use of different catalysts will produce different impurities during the formation of CBN single crystals, resulting in differences in the color and performance of the final synthesized CBN crystals. The color of CBN crystals is related to the type and quantity of impurities. In addition to the main source of impurities, it may also come from HBN raw materials. The shape and color of CBN crystals are diverse, and the development direction is controllable and adjustable. As the color of CBN crystal deepens, the more complete the crystal shape, the larger the crystal grain size. In the HBN+Mg system, adding an appropriate amount of MgO can cause the color of the synthesized CBN crystal to change from black to yellow.
There are many different opinions on the formation mechanism of CBN crystal color. Some people think that the change of crystal color is mainly caused by the increase of oxygen content in the crystal. Others think that the blackening of crystal color is related to the temperature during crystal growth. The color of crystals in the system becomes darker with the increase of temperature.
It is now generally believed that the darkening of the crystal color is due to the imbalance of the ratio of B and N atoms in the CBN crystal. In the process of synthesizing CBN, metal, nitride, and nitrogen boride are used as catalysts. Under different temperature and pressure conditions, black, yellow, amber and colorless CBN crystals can be synthesized.