Boron nitride is known as white graphite. It got its name because it is white and has some characteristics in common with graphite. Boron nitride has two forms, one is the hexagonal structure, the other is the cubic structure. A hexagonal structure can be transformed into a cubic structure in a high temperature and high pressure environment. There are two major production methods of boron nitride ceramics, namely the cold-pressing sintering and hot-pressing sintering.
1. In order to produce boron nitride ceramics, it is necessary to mix boron nitride fine powder with a certain amount of additives. The size of the boron nitride fine powder particles is strictly required and needs to be within 5 microns. Then predict the pressure of the hydraulic press, the test pressure is between 100-150 MPa, and then the raw material is crushed to less than 0.5mm, and then the raw material is put into a graphite abrasive tool, and the high temperature and high pressure treatment is carried out in a hot press furnace. There are carbon tubes in the hot pressing furnace, and the carbon tubes are mainly used for heating. The heating temperature can be increased to 1600 to 1900 degrees, the pressure can be controlled between 20 and 25 MPa, and the heat preservation can be about one hour. It can be heated after cooling.
2. Diboron trioxide plays a vital role in the production of boron nitride ceramics, directly affecting the quality of boron nitride ceramics. If there is no diboron trioxide in the boron nitride product, the density of the boron nitride product will be Greatly reduced, but better waterproof performance. If boron trioxide is added, the density of the product will increase, but the water resistance will be greatly reduced. Therefore, the boron nitride raw materials that do not contain diboron trioxide should be appropriately added with a binder to increase the difficulty of thermal sintering and promote sintering without affecting the stability of the product.
If the boron nitride ceramic contains a high content of boron trioxide in the production process, it is necessary to appropriately add stabilizers during the production process. For hot-pressed boron nitride ceramics, it is necessary to perform high-temperature treatment in a vacuum or nitrogen environment to volatilize B2O3, thereby improving the quality of the ceramic product and maintaining its stable performance.
