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Ultra-high-temperature ceramics (UHTCs) are a type of refractory ceramics that can withstand extremely high temperatures without degrading, often above 2,000 °C. [1] They also often have high thermal conductivities and are highly resistant to thermal shock, meaning they can withstand sudden and extreme changes in temperature without cracking or breaking.
SiC–SiC composites have a relatively high thermal conductivity and can operate at very high temperatures due to their inherently high creep and oxidation resistance. Residual porosity and stoichiometry of the material can vary its thermal conductivity, with increasing porosity leading to lower thermal conductivity and presence of Si–O–C ...
Very high thermal conductivity measurements up to 22,600 w m −1 K −1 were reported by Fenton, E.W., Rogers, J.S. and Woods, S.D. in reference 570 on page 1458, 41, 2026–33, 1963. The data is listed on pages 6 through 8 and graphed on page 1 where Fenton and company are on curves 63 and 64.
Conventional ceramics are very sensitive to thermal stress because of their high Young's modulus and low elongation capability. Temperature differences and low thermal conductivity create locally different elongations, which together with the high Young's modulus generate high stress. This results in cracks, rupture, and brittle failure.
On the other side bulk ceramics made of ultra-high temperature ceramics (e.g. ZrB 2, HfB 2, or their composites) are hard materials which show low erosion even above 2000 °C but are heavy and suffer of catastrophic fracture and low thermal shock resistance compared to CMCs. Failure is easily under mechanical or thermo-mechanical loads because ...
It is an unusual ceramic, having relatively high thermal and electrical conductivities, properties it shares with isostructural titanium diboride and hafnium diboride. ZrB 2 parts are usually hot pressed (pressure applied to the heated powder) and then machined to shape.
Titanium diboride (TiB 2) is an extremely hard ceramic which has excellent heat conductivity, oxidation stability and wear resistance. TiB 2 is also a reasonable electrical conductor, [ 1 ] so it can be used as a cathode material in aluminium smelting and can be shaped by electrical discharge machining .
General properties such as high melting temperature, high hardness, poor conductivity, high moduli of elasticity, chemical resistance, and low ductility are the norm, [8] with known exceptions to each of these rules (piezoelectric ceramics, low glass transition temperature ceramics, superconductive ceramics).