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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.
The European Commission funded a research project, C 3 HARME, under the NMP-19-2015 call of Framework Programmes for Research and Technological Development in 2016-2020 for the design, manufacturing and testing of a new class of ultra-refractory ceramic matrix composites reinforced with silicon carbide fibers and Carbon fibers suitable for applications in severe aerospace environments.
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.
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 ...
For pure metals, k 0 is large, so the thermal conductivity is high. At higher temperatures the mean free path is limited by the phonons, so the thermal conductivity tends to decrease with temperature. In alloys the density of the impurities is very high, so l and, consequently k, are small. Therefore, alloys, such as stainless steel, can be ...
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.
TiB 2 does not occur naturally in the earth. Titanium diboride powder can be prepared by a variety of high-temperature methods, such as the direct reactions of titanium or its oxides/hydrides, with elemental boron over 1000 °C, carbothermal reduction by thermite reaction of titanium oxide and boron oxide, or hydrogen reduction of boron halides in the presence of the metal or its halides.
Copper-silver alloy matrix containing 55% by volume diamond particles, known as Dymalloy, is used as a substrate for high-power, high-density multi-chip modules in electronics for its very high thermal conductivity. AlSiC is an aluminium-silicon carbide composite for similar applications.