Boron nitride is a heat-resistant chemical refractory compound of boron and nitrogen, and its chemical formula is BN. Boron nitride materials exist in various crystal forms such as carbon lattices of similar structure and other electrons.
Boron nitride is a crystal composed of nitrogen atoms and boron atoms. The crystal structure is divided into hexagonal boron nitride and cubic boron nitride.
Among them, the crystal structure of hexagonal boron nitride has a layered structure similar to that of graphite, and it is a white powder with loose, lubricated, easy to absorb moisture, and light weight, so it is also called "white graphite". In addition, it is similar to graphite in terms of thermal conductivity, high temperature resistance, and chemical stability. However, its properties are not the same as graphite. For example, boron nitride is an excellent insulating material, while graphite has good conductivity.
Cubic boron nitride has excellent physical and chemical properties, its hardness is second only to diamond, in addition to its high strength, it has great application and development prospects in many fields. In addition, cubic boron nitride is currently the highest temperature semiconductor material with high thermal conductivity and good semiconductor properties. However, the existing preparation methods have many inherent shortcomings that are difficult to overcome, so that it is not easy to make them widely used.
In recent years, the research on the synthesis of boron nitride has been mainly developed in the direction of low temperature, low pressure and nanometerization. Therefore, many new synthetic methods with great development potential have been developed on the basis of traditional synthetic methods.
1. Hydrothermal synthesis: The hydrothermal method is to use water as the reaction medium in the high temperature and high pressure reaction environment in the autoclave to dissolve the normally insoluble or insoluble substances. This hydrothermal synthesis reaction can also be recrystallized . The hydrothermal synthesis method has two characteristics, one is its relatively low temperature, and the other is that it is carried out in a closed container. This reaction environment avoids the volatilization of components. As a low-temperature and low-pressure synthesis method, hydrothermal synthesis is used to synthesize cubic boron nitride at low temperature.
2. Self-propagating technology: the use of external energy to induce high-exothermic chemical reactions, local reaction occurs in the system to form the front of the chemical reaction (combustion wave), the chemical reaction proceeds quickly with the support of its own heat release, and the combustion wave spreads throughout the system. Although this method is a traditional inorganic synthesis method, it has only been reported for the synthesis of boron nitride in recent years.
3. Carbothermal synthesis technology: On the surface of silicon carbide, boric acid is used as the raw material, carbon is used as the reducing agent, and boron nitride is obtained through the reaction mode of ammonia nitriding. The resulting product has very high purity. Preparation has great application value.
In summary, there are many methods for preparing boron nitride. With the continuous development of research methods of functional ceramic materials, more new synthetic methods of boron nitride will be discovered. These new methods have provided new opportunities for the application research of boron nitride ceramics.
Boron nitride has good thermal conductivity and can be used as high-frequency electrical insulation materials, heat sinks for integrated circuits, and nozzles for accessory parts of ion rockets. These objects have complex shapes and high processing accuracy requirements, so that boron nitride with excellent processing performance can fully meet its requirements. In addition, boron nitride has high pressure resistance, high resistance and good dielectric properties, and can be used to make ultra-high voltage wire insulation materials.
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