The pyrolytic boron nitride crucible is grown by chemical meteorological deposition. The high-purity raw material gases BCl3 and NH3 are mixed in a certain ratio and passed into a high-temperature reaction chamber. The temperature of the reaction chamber is as high as 2000 ° C, and the chemical reaction equation of the mixed gas therein is as follows:
BCl3 + NH3 = BN + 3HCl
During the growth of the PBN material, the hexagonal BN piece continuously falls on the heated graphite substrate (core mold). As time goes on, the accumulation layer is thickened, forming a PBN shell, leaving it The top is the PBN coating. Theoretically, the formation of PBN is not a simple combination of B and N atoms, but a general rule of crystal material growth, and also a process of nucleation and growth. In the process of nucleation and growth, the polymerization process with dehydrogenation and dechlorination is constantly occurring. Therefore, the growth of tantalum materials is gradually becoming more beautiful and perfect at high temperatures.
The chemical vapor deposition of PBN materials is both simple and complex. The equipment is simple, the principle is simple, and the operation is simple; however, the influencing factors of the process are complex, such as the air intake mode of the raw material, the furnace loading mode, the size of the furnace, the geometric shape, the placement position and manner of the core mold, and etc.
The main influencing parameters of vapor deposition are the temperature of the substrate, the pressure in the furnace, and the flow ratio of the gas. Generally, the temperature is 1800~1900°C, and the pressure in the furnace is 1~2mmHg. The flow rate of the gas depends on the size of the furnace space and the requirements of the sediment. For PBN coatings, low temperatures are generally used; for growing PBN defects, high temperatures are usually used.
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