A silicoboron carbonitride ceramic stable to 2,000 degree C

Article Abstract:

A polymer-to-ceramic transformation from a lone polymeric polyborosilazane parent results in a silicoboron carbonitride ceramic that is stable even at temperatures up to 2,000 degree Celsius. The product retains its stability in nitrogen-free environments as well. The ceramic Si.0B1.0C4.3N2.0 forms at 1,000 degree Celsius and starts transforming into a polycrystalline composite of silicon nitride and carbide at 1,700 degree Celsius. The significance of boron in enhancing the thermal stability of the product is suggested. Technological applications are mentioned.

Polymers, Observations, Boron, Boron (Chemical element), Silicon compounds

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A covalent micro/nano-composite resistant to high-temperature oxidation

Article Abstract:

The covalent ceramic composites and coatings withstand high-temperature oxidation up to 1,600 degrees centigrade due to the development of a few micrometers-thick, passivating surface layer of SiO2. An amorphous silicon carbonitride on crystallization at high temperature generates a composite of alpha-Si3N4 microcrystals and alpha-SiC nanocrystals. The ceramic materials are applicable for gas turbines, combustion systems, structural parts for motor engines, catalytic heat exchangers, spacecrafts and aircrafts.

Innovations, Oxidation-reduction reaction, Oxidation-reduction reactions, Ceramic materials, Ceramic coatings, Ceramic coating

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Synthesis of cubic silicon nitride

Article Abstract:

Silicon nitride is used in many technological applications due to its high fracture toughness, hardness and wear resistance. Two polymorphs of silicon nitride are known, and a third polymorph with a cubic spinel structure is now reported. The new phase is formed at pressures higher than 15 GPa and temperatures above 2,000 K, although it is metastably persistent in air at ambient pressure up to 700 K. Its hardness may be comparable to that of stishovite, the hardest known oxide.

Silicon nitride, Silicon nitrides, Spinel group

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