Hot-press sintering method for boron nitride products

Currently, there are two methods for producing boron nitride products: cold pressing sintering and hot pressing sintering. Today, our editor will introduce the hot pressing sintering method for boron nitride products. Let's take a look together.

The hot-press sintering method for manufacturing boron nitride products involves mixing fine boron nitride powder (particle size less than 0.05 mm) with a small amount of additives until they are evenly mixed. The mixture is then pre-pressed once in an isostatic press with a pressure ranging from 100 to 150 MPa, and subsequently crushed to a particle size of less than 0.5 mm. The crushed material is placed into a graphite mold and heated and pressed in a hot-press furnace heated by carbon tubes. The temperature is maintained at 600-900°C, with a pressure ranging from 20 to 25 MPa, and the material is kept at this temperature for several minutes to one hour.

Cooling and processing. It should be noted here that the presence or absence of B2O3 has a significant impact on the performance of the product. In the absence of B2O3, it is difficult to obtain high density, but the water resistance is good. However, in the presence of B2O3, the product is easy to densify, but its stability to water deteriorates. Therefore, for pure boron nitride without B2O3 (which is difficult to sinter by hot pressing), an appropriate amount of binder, such as B2O3, boron phosphate, or CaO-B2O3-Al2O3, should be added to promote sintering without affecting the stability of the product. For boron nitride powder with high B2O3 content, an appropriate amount of stabilizer should be added, or for boron nitride products with high B2O3 content, high-temperature treatment should be performed in a vacuum or argon and nitrogen atmosphere after hot pressing to volatilize B2O3.

Products prepared by hot pressing can be used in N2 or argon gas at 2800, with no apparent melting point, and sublimate in nitrogen at 3000 and 0.1 MPa. However, they have poor stability in oxidizing atmospheres and can only be used at temperatures below 900 degrees.

The product boasts a low expansion coefficient, high thermal conductivity, excellent thermal shock stability, and serves as an excellent insulator. Boron nitride possesses numerous unique properties, making it exclusively suitable for use as a protective tube for high-temperature thermocouples, a container for melting metals, and a thermal insulation material for space travel. In summary, boron nitride products exhibit vast prospects in the future development of high-tech products.