Silīcija karbīda struktūra un lietojumi

Silicon carbide is an extremely hard synthetically produced crystalline compound of carbon and silicon. It is commonly used in refractory and wear-resistant applications as well as solid state devices like light emitting diodes.

American inventor Edward G. Acheson made this discovery while searching for ways to produce artificial diamonds; he named this new material carborundum.

Fizikālās īpašības

Silicon carbide’s unique combination of high thermal conductivity, low thermal expansion, hardness and resistance to chemical attack makes it a versatile material with many applications ranging from abrasive tools and structural material (bulletproof vests and ceramic brake plates for automobile brake discs), lightning arresters and telescope mirrors to lightning arresters and lightning arresters. Furthermore, SiC is also used as an integral part of electric vehicle driving range, including inverters which help conserve energy more efficiently while enabling smaller and lighter battery management systems.

Manufacturers produce cubic silicon carbide by either using carbon-based synthesis or chemical vapor deposition methods, both requiring significant energy, equipment, and expertise for success.

Silicon carbide contains two covalent bonds between its carbon atoms that form by the lateral overlap of their p-orbitals, giving silicon carbide its characteristic lustre and leading to its common name of “moissanite”, although natural crystals of moissanite are relatively scarce; most commercially available moissanite today is synthetically created.

Ķīmiskās īpašības

Silicon carbide (commonly referred to as carborundum) is a hard, durable industrial ceramic used in numerous processes for production. It has played an invaluable role in driving industry and technology forward over many years.

SiC crystals offer a diverse array of chemical properties due to its distinctive covalent structure in which silicon and carbon atoms form strong coordination tetrahedra through covalent bonds sharing electron pairs in sp3 hybrid orbitals. These tetrahedra can then be organised in various patterns within a crystal lattice, yielding multiple polytypes.

The arrangement of silicon and carbon layers within each polytype determines its electronic properties. As such, each has different bandgap energies; those found in a-SiC range from 2.2eV to 3.3eV depending on its structure.

Silicon carbide in its purest form acts like an electrical insulator; however, impurities such as aluminium and nitrogen can be added to change its properties into semiconductor-like behaviour, which allows devices such as IGBTs and MOSFETs to reach high breakdown voltages with low turn-on resistance.

Elektriskās īpašības

Silicon carbide possesses several unique physical and chemical properties that make it an excellent material for power electronics applications. In comparison to silicon, its wider bandgap allows electronic devices to operate at higher temperatures, voltages, and frequencies than its silicon equivalent.

Mohs scale rating 9 ceramic with superior properties such as thermal conductivity and resistance to chemical reaction and corrosion is used extensively for automotive brakes, bulletproof vests, power tools and many other uses. It features low coefficient of expansion, excellent thermal conductivity and resistance to abrasion/wear. With high thermal conductivity and resistance to chemical corrosion it provides ideal thermal management properties and makes an excellent replacement material in applications involving automotive brakes, bulletproof vests or power tools.

Produced using silica sand mixed with carbon (typically petroleum coke) at high temperatures in an Acheson furnace, Green and Black SiC are produced as ingots differentiated by purity grades such as A-SiC with hexagonal crystal structure similar to Wurtzite while lower grade metallurgical grades have zinc blende crystal structures similar to diamond.

Mehāniskās īpašības

Modern silicon carbide production for use in abrasives, metallurgical, and refractories industries involves mixing finely ground silica sand with carbon in coke form. This mixture is then placed in an electrical resistance-type furnace heated with an electric current to produce silicon carbide from silicon and carbon; its sintering process is enhanced through non-oxide biners; after which extrusion or cold isostatic pressing can form tubes from it.

One-dimensional disordered (ODD) SiC structures have been shown to have significant impacts on mechanical properties, such as tensile strength and elastic strain. Through in situ tensile tests of single SiC NWs with different ODD occupation ratios, researchers found that their strength approaches their ideal theoretical limit when the ratio exceeds a critical value; this phenomenon likely stems from micro twin formation allowing shear localization with micro plasticity occurring at twin boundaries and hence shear localization and micro plasticity at twin boundaries.