Growth and Properties of Pyrolytic Boron Nitride Crucible Materials
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Growth principle of pyrolytic boron nitride crucible
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.
Process of pyrolytic boron nitride crucible
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.
Major Properties of Pyrolytic Boron Nitride Crucible
Physical properties of PBN
Pyrolytic boron nitride crucible (PBN crucible) has good machinability.
The density of PBN crucible is between 2.15 and 2.22 g/cm3.
The PBN crucible wall has a helium permeability of <1×10-10cm/s.
PBN crucible is immersed in water for 10 days without moisture absorption, hydrolysis, and no change in size and weight.
PBN crucible has good vacuum performance and does not emit any harmful gases at high temperatures.
Chemical properties of PBN
PBN crucible is non-toxic
PBN crucible does not react with acids, alkalis, salts, and organic reagents at room temperature slightly corrode in molten salt and alkali, but resists corrosion of various acids at high temperatures.
PBN crucible does not react with most molten metals, semiconductors, and their compounds.
The oxidation resistance is good at temperatures below 1000 °C.
The purity of PBN material by spark source ion mass spectrometry is close to 99.99% BN.
Thermal properties of PBN
PBN crucible has good thermal shock resistance, and no cracks are found in the water at 2000 °C.
The specific heat of the PBN is measured by the drop method of the copper card meter. The enthalpy value △H is measured first, and then the average specific heat is calculated.
The thermal conductivity of PBN is measured by the laser pulse method. The diffusion rate α of the sample is first measured, and then the thermal conductivity λ is calculated from the specific heat c and density ρ of the sample.
The thermal expansion of PBN is measured using a quartz differential thermal expansion meter.
Electrical properties of PBN
The dielectric strength of PBN was measured to be 56000 V/mm at room temperature and oil immersion (oil temperature 22 ° C).
The volume resistivity is 3.11×1018 Ω•cm (normal).