Silicon carbide Pure silicon carbide is one of the most corrosion-resistant materials. Only strong bases, oxygen above about , and molten metals react with it to form carbides and silicides. The reaction with oxygen forms and , whereby a surface layer of slows down subsequent oxidation (passive oxidation). Temperatures above about and a low partial pressure of oxygen result in so-called active oxidation, in which CO, and gaseous SiO are formed causing rapid loss of SiC. If the SiC matrix is produced other than by CVI, corrosion-resistance is not as good. This is a consequence of porosity in the amorphous LPI, and residual silicon in the LSI-matrix. Silicon carbide fibers Silicon carbide fibers are produced via pyrolysis of organic polymers, and therefore their corrosion properties are similar to those of the silicon carbide found in LPI-matrices. These fibers are thus more sensitive to bases and oxidizing media than pure silicon carbide. Applications CMC materials overcome the major disadvantages of conventional technical ceramics, namely brittle failure and low fracture toughness, and limited thermal shock resistance. Therefore, their applications are in fields requiring reliability at high-temperatures (beyond the capability of metals) and resistance to corrosion and wear. These include: Heat shield systems for space vehicles, which are needed during the re-entry phase, where high temperatures, thermal shock conditions and heavy vibration loads take place. Components for high-temperature gas turbines such as combustion chambers, stator vanes, exhaust mixers and turbine blades. Components for burners, flame holders, and hot gas ducts, where the use of oxide CMCs has found its way. Brake disks and brake system components, which experience extreme thermal shock (greater than throwing a glowing part of any material into water). Components for slide bearings under heavy loads requiring high corrosion and wear resistance. In addition to the foregoing, CMCs can be used in applications which employ conventional ceramics or in which metal components have limited lifetimes due to corrosion or high temperatures. Developments for applications in space During the re-entry phase of space vehicles, the heat shield system is exposed to temperatures above for a few minutes. Only ceramic materials can survive such conditions without significant damage, and among ceramics, only CMCs can adequately handle thermal shocks. The development of CMC-based heat shield systems promises the following advantages: Reduced weight Higher load-carrying capacity of the system Reusability for several re-entries Better steering during the re-entry phase with CMC flap systems In