There are two main methods for synthesizing boron nitride

High temperature and high pressure synthesis method
In 1957, Wentorf first artificially synthesized cubic BN. When the temperature is close to or above 1700 ℃ and the minimum pressure is 11-12GPa, pure hexagonal boron nitride (HBN) directly transforms into cubic boron nitride (CBN). Subsequently, it was discovered that the use of catalysts can significantly reduce the transition temperature and pressure. The commonly used catalysts include alkali and alkaline earth metals, alkali and alkaline earth nitrides, alkaline earth fluoronitrides, ammonium borate salts, and inorganic fluorides. The temperature and pressure required for using ammonium borate as a catalyst are the lowest, with a pressure of 5GPa at 1500 ℃ and a temperature range of 600-700 ℃ at a pressure of 6GPa. It can be seen from this that although adding catalysts can greatly reduce the transformation temperature and pressure, the required temperature and pressure are still relatively high. Therefore, its preparation equipment is complex and costly, and its industrial application is limited.
Chemical vapor synthesis method
In 1979, Sokolowski successfully prepared cubic boron nitride (CBN) films using pulsed plasma technology at low temperature and low pressure. The equipment used is simple and the process is easy to implement, so it has developed rapidly. Multiple methods of vapor deposition have emerged. Traditionally, it mainly refers to thermochemical vapor deposition. The experimental setup generally consists of heat-resistant quartz tubes and a heating device. The substrate can be heated either by a heating furnace (hot wall CVD) or by high-frequency induction heating (cold wall CVD). The reaction gas decomposes on the high-temperature substrate surface and undergoes a chemical reaction to deposit a film. The reaction gas includes a mixture of BCl3 or B2H4 and NH3.
Hydrothermal synthesis method
This method uses water as the reaction medium in a high temperature and high pressure reaction environment in a high-pressure reactor to dissolve usually insoluble or insoluble substances, and the reaction can also undergo recrystallization. Hydrothermal technology has two characteristics: firstly, its relatively low temperature, and secondly, it is carried out in a closed container to avoid component volatilization. As a low-temperature and low-pressure synthesis method, it is used to synthesize cubic boron nitride at low temperatures.
Benzene thermal synthesis method
As a recently emerging method for synthesizing low-temperature nanomaterials, benzene thermal synthesis has received widespread attention. Benzene, due to its stable conjugated structure, is an excellent solvent for solvothermal synthesis. Recently, it has successfully developed into a benzene thermal synthesis technology, such as the reaction formula:
BCl3+Li3N → BN+3LiCl
Or BBr3+Li3N → BN+3LiBr
The reaction temperature is only 450 ℃, and benzene thermal synthesis technology can prepare metastable phases that can only be obtained under extreme conditions and exist under ultra-high pressure at relatively low temperatures and pressures. This method achieves the preparation of cubic boron nitride at low temperature and low pressure. However, this method is still in the experimental research stage and has great potential for application in synthesis.
Self propagating technology
By utilizing the necessary external energy to induce high exothermic chemical reactions, local reactions occur in the system, forming a chemical reaction front (combustion wave). The chemical reaction proceeds rapidly with the support of its own heat release, and the combustion wave spreads throughout the entire system. Although this method is a traditional inorganic synthesis method, it has only been reported in recent years for the synthesis of boron nitride.
Carbon thermal synthesis technology
This method is based on the surface of silicon carbide, using boric acid as the raw material, carbon as the reducing agent, and ammonia nitriding to obtain boron nitride. The resulting product has high purity and great application value for the preparation of composite materials.
Ion beam sputtering technology
Using particle beam sputtering deposition technology, a mixture of cubic boron nitride and hexagonal boron nitride was obtained. Although this method has fewer impurities, due to the difficulty in controlling reaction conditions, the morphology of the product is difficult to control, and there is still great potential for development in the research of this method.
Laser induced reduction method
Using laser as an external energy source to induce oxidation-reduction reactions between reaction precursors and combine B and N to generate boron nitride, but this method also produces a mixed phase.