Contrary to other materials, boron nitride is known for its synthetic technical ceramic quality. The chemical formula is BN. This is available in powder form and also in solid and liquid forms respectively. When it is the solid form, it can be machined easily using the ordinary metalworking tools. Studying in details about the ceramic it has been proved to have thermal characteristics. This power enables it to have higher thermal conductivity and thus it has become an excellent shock resistant for thermal currents.
There are three grades of boron nitride in the solid form, but each of them has different characteristics. The grades are calcium borate binder system, boric oxide binder system and pure diffusion bonded grade. The calcium borate binder is resistant to moisture. The boric oxide binder is the one that causes property degradation by swelling due to the absorption of moisture content. And the last one pure diffusion bonded grade. This has no binders but they are used for their extreme temperature conditions. As they are pure, so, they can be used in places where the pure substance is needed. The most common grade of the ceramic is produced by hot pressing.
A naturally occurring Boron nitride was found in 2009, in Tibet. This was then called gingsongite. In the chromium rocks, they appeared in dispersed micron sized inclusions. Finally, in 2013, the International Mineralogical Association confirmed the mineral and gave it the name.
Properties of the Substance
The crystals are generally hexagonal in structure. The uniaxial densification method creates the anisotropy of HPBN platelet. So, due to that several physical properties occur parallel and perpendicularly to the direction of pressing. Thus, for having such a quality it is called as the “White Graphite”. As HPBN is non-toxic, so, it can be machined easily. They do not corrode away easily and are stronger for UV emission. The substance remains stable at 1000°C in air, 1400°C in vacuum and 2800°C in an inert environment.
There are several applications or rather uses of Boron nitride ceramic substances. Let us discuss them one by one.
• They are used in the thermocouple tubes because of their high electrical resistivity.
• Because the compound is chemically stable they are used as crucibles and nozzles for the molten metals.
• Their excellence in thermal shock behaviour makes them good electrical insulators for the high-temperature uses.
• In the glass manufacturing industries, they are used as rolls and support elements because of their thermocycling properties.