On 2018-08-08 14:48:54
Silicon carbide - new energy vehicle and new favorite in nuclear power field
Silicon carbide is a rare mineral in nature, which is called morsonite. It is a compound with strong covalent bond composed of carbon atom and silicon atom, so it has very strong stability. According to the introduction of the application of silicon carbide materials in nuclear fuel elements, there are more than 200 varieties of silicon carbide according to the different stacking sequence. Among them, the SiC with face centered cubic structure is β - SiC, which is the main crystalline phase of SiC. Under 2100 ℃, β - SiC has high stability.
β - SiC is widely used in material processing, electronics, aerospace and chemical industry because of its stable chemical properties, high thermal conductivity, small thermal expansion coefficient and high hardness. According to the application of silicon carbide materials in nuclear fuel elements, silicon carbide also has the characteristics of small neutron absorption cross section, good irradiation stability, low intrinsic activity and decay heat, making it suitable for nuclear reactor field.
In the field of nuclear power, at present, the whole ceramic spherical fuel element is used in domestic high temperature gas cooled reactor. The diameter of fuel element is less than 1mm and dispersed in graphite matrix. It is composed of spherical ceramic nuclear fuel core, loose pyrolytic carbon layer, inner dense pyrolytic carbon layer, SiC layer and outer dense pyrolytic carbon layer.
The high stability of SiC is one of the guarantees for the inherent safety of HTGR. According to the application of silicon carbide materials in nuclear fuel elements, the most important part of the four layer cladding structure is silicon carbide layer. A complete silicon carbide layer can block most of the gas and solid fission products, and can withstand the internal pressure of the gas products in the cladding fuel, which is an important guarantee for the safety of high temperature gas cooled reactor. In addition, silicon carbide maintains a strong stability below 2100 ℃, and the temperature of high temperature gas cooled reactor core will not exceed its safety limit of 1620 ℃, so the fuel particles will not be burned in any case, fundamentally avoiding radioactive leakage. In addition, it has wide application prospects in molten salt reactor and gas cooled reactor silicon carbide.
In the field of new energy vehicles, silicon carbide can be compounded with graphite, carbon nanotubes, nano titanium nitride to make negative materials for lithium batteries. Silicon carbide materials have large specific surface area, many naked leakage atoms, and can embed more lithium ions, with a specific capacity of more than 800 MAH / g, while the current mature graphite anode has a specific capacity of about 350 MAH / g. the use of silicon carbide can increase the capacity of rechargeable lithium-ion batteries by more than three times, and can also increase the number of charge and discharge cycles. With the rapid promotion of new energy vehicles, the endurance mileage becomes more and more important for user experience, and the energy density of battery gradually becomes the main bottleneck. Now some battery manufacturers begin to try to use silicon carbide to improve battery performance. Tesla, the global benchmark of new energy vehicles, is also reportedly trying to adopt silicon carbide technology.