Silicon carbide general properties

Most structural PMCs consist of a relatively soft matrix, such as a thermosetting plastic of polyester, phenolic, or epoxy, sometimes referred to as resin-matrix composites. Some typical polymers used as matrices in PMCs are listed in Table 1.28. The list of metals used in MMCs is much shorter. Aluminum, magnesium, titanium, and iron- and nickel-based alloys are the most common (see Table 1.29). These metals are typically utilized due to their combination of low density and good mechanical properties. Matrix materials for CMCs generally fall into fonr categories glass ceramics like lithium aluminosilicate oxide ceramics like aluminnm oxide (alnmina) and mullite nitride ceramics such as silicon nitride and carbide ceramics such as silicon carbide. 

Various electrical and optical properties that have been measured for the wet thermal oxide on silicon carbide are summarised in TABLE 3. In general, no systematic variation of any of the oxide properties has been reported with oxide growth temperature in the range of 1000 to 1250°C. However, oxide grown with a wet process has been shown to have lower oxide charges than oxide grown in dry oxygen. Variations in the measured electrical properties... 

Dense parts made by hot-pressing are generally considered to have a very fine microstructure (see Fig. 12g) and the best mechanical properties. Completely pure silicon carbide does not exhibit any noticeable plastic behavior up to its decomposition temperature and can therefore be densified only under diamond synthesis conditions... 

As mentioned in Ch. 2, the refractory carbides include two structurally different types (a) the interstitial carbides of the transition metals of Group IV, V, and VI (reviewed in Ch. 3, 4, 5, and 6), and (b) two covalent carbides boron carbide and silicon carbide. The structural characteristics of these two carbides are reviewed in this chapter and their properties and general characteristics in the following chapter. 

The TCON material is known for its impressive mechanical properties compared to its pure metallic and ceramic parts ". The TCON process allows the modifications of the ceramic precursor and molten metal to optimize the final properties of the composites for specific applications. The TCON foams studied here had a general composition based on aluminum, silicon carbide (SiC), aluminum oxide and silicon (Si). Two samples labeled TCON A and TCON B were created using pure aluminum or aluminum alloy baths. TCON A had a precursor material consisted of Si02, SIC, and hollow AI2O3 spheres. In contrast, TCON B s precursor consisted of a fiber material, which is a proprietary reinforcement developed by Fireline, Inc., and hollow AI2O3 spheres. Here, the hollow sphoical particles were added in an attempt lower the density of the foam system. 

---