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Boron nitride and some of its preparation methods



Boron nitride


The first application of hexagonalboron Nitride (or h-BN) was in high-temperature lubricants. Its invention occurred more than 100 years ago. H-BN is a graphite substitute. Its structure and performance are similar, making it also known as white graphite.
There are many types of boron nutride. The most popular is the hexagonal crystal form. Other than the hexagonal crystal, there are several crystal forms of Boron Nitride, such as rhombohedral, cubic, and wurtzite types. Even two-dimensional graphene boron nitride has been discovered (similar to MoS, two-dimensional crystals).

Wentorf first synthesized cubicBN in 1957. If the temperature exceeds 1700degC, and the minimum pressure is between 11-12 GPa, then pure hexagonal boron nitride can be transformed to cubic boron nitride. The use of catalysts can reduce both the temperature and the pressure. Alkali and other alkaline minerals, alkali & alkaline soil nitrides (alkali and kaline), alkali & alkaline mineral fluoronitrides (alkaline earth fluoronitrides), ammonium borate, and inorganic Fluorides are all common catalysts. Ammonium borate is one of the most common catalysts. It requires the least temperature and pressure. When the pressure is 6GPa, the minimum pressure required is 5.GPa. The temperature range for ammonium borate is 600700. The addition of catalysts can reduce both the temperature and the pressure but they still have a significant impact on the temperature and pressure. The equipment required to make it is expensive and complicated, making its industrial applications difficult.


You can prepare boron nutride in many different ways



1.Chemical vapor synthesis


Sokolowski was able to use pulsed plasma technology in 1979 to make cubic boron Nitride (CBN) films under low pressure and temperature. Because the equipment is straightforward and simple, it is also easy to do. This is how this technology was quickly developed. Many vapor deposition options have been developed. Conventionally, this term refers to thermal chemical vapour deposition. A heat-resistant quartz tube is used as the heating element. A heating furnace (hot wall CVD), or high frequency induction heating (cold–wall CVD), can heat the substrate. A reaction gas forms on the top of high-temperature substrates and simultaneously a chemical reaction is initiated to create a layer. A mixture of BCl3/B2H4 or NH3 is the reaction gas.


2.Hydrothermal synthesizing


In order to dissolve insoluble or non-soluble compounds, this method employs water as the reaction media in an autoclave. The temperature and pressure of the environment can be high and it is possible for the reaction to also be refractorized. Two characteristics of hydrothermal technology are their low temperature and enclosed container. This prevents the component volatilization. This synthesis process is low-temperature, low-pressure and can produce cubic boron nutride at very low temperatures.


Thermal synthesis of 3.Benzene


Low-temperature method of creating nanomaterials, benzene thermosynthesis, has been gaining a lot attention in recent years. Because it has a stable conjugated structure, the solvent is excellent for solvothermal production. Recent developments in benzene thermal synthesy technology have led to its successful development, as shown by the reaction formula.

BCl3+Li3N-BN+3LiCl

BBr3+Li3N-BN+3LiBr

Reaction temperature at 450°C is achieved by the benzene thermosynthesis technology. Metastable phases can be formed under very low pressure under extreme conditions. This technique allows the formation of cubic-boron nitride with low temperature at low pressure. Although this is still an experimental method, it has great applications potential.


4. Self-propagating technology


In order to induce high exothermic chemical processes, energy is supplied from the exterior. The system then reacts locally to produce a “combustion wave” (chemical reaction front). It is possible to accelerate the chemical reaction by using heat from the outside. The combustion wave then spreads through the whole system. It is an old method of inorganic synthesizing, however it has not been extensively used for the recent synthesis of Boron Nitride.

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