resistance therefore decreases with increasing temperature. Compared to (poly)crystalline SiC, the amorphous SiC fibers are relatively poor conductors of heat and electricity. Comments for the table: (p) and (v) refer to data parallel and vertical to fiber orientation of the 2D-fiber structure, respectively. LSI material has the highest thermal conductivity because of its low porosity – an advantage when using it for brake discs. These data are subject to scatter depending on details of the manufacturing processes. 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. In CMCs, the fibers bridge the cracks, and the components show no macroscopic damage, even if the matrix has cracked locally. The application of CMCs in brake disks demonstrates the effectiveness of ceramic composite materials under extreme thermal shock conditions. Corrosion properties Data on the corrosion behaviour of CMCs are scarce except for oxidation at temperatures above 1000 °C. These properties are determined by the constituents, namely the fibers and matrix. Ceramic materials, in general, are very stable to corrosion. The broad spectrum of manufacturing techniques with different sintering additives, mixtures, glass phases, and porosities are crucial for the results of corrosion tests. Less impurities and exact stoichiometry lead to less corrosion. Amorphous structures and non-ceramic chemicals frequently used as sintering aids are starting points of corrosive attack. Alumina Pure alumina shows excellent corrosion resistance against most chemicals. Amorphous glass and silica phases at the grain boundaries determine the speed of corrosion in concentrated acids and bases and result in creep at high temperatures. These characteristics limit the use of alumina. For molten metals, alumina is used only with gold and platinum. Alumina fibers These fibers demonstrate corrosion properties similar to alumina, but commercially available fibers are not very pure and therefore less resistant. Because of creep at temperatures above 1000 °C, there are only a few applications for oxide CMCs. Carbon The most significant corrosion of carbon occurs in the presence of oxygen above about . It burns to form carbon dioxide and/or carbon monoxide. It also oxidizes in strong oxidizing agents like concentrated nitric acid. In molten metals, it dissolves and forms metal carbides. Carbon fibers do not differ from carbon in their corrosion behavior.