Silicon nitride and carbide

The preparation and structure of Si3N4 were discussed at the end of Section 13.12. Its uses as a refractory material are widespread, as are its applications in the microelectronics 

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The spectrum of silicon based polymers is enriched by high tech ceramics like silicon nitride and carbide, respectively. These materials are produced by pyrolysis of appropriate polymeric precursors such as polysilanes, polycarbosilanes and polysilazanes (preceramics). These synthetic ceramics display a certain analogy to silicates, having SiC, SiN, or Si(C,N) as structural subunits instead ofSiO. 

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. 

Si MAS NMR is a very useful technique to study the crystal-phase composition and transition in silicon nitride and carbide [27,28]. The a phase of... 

We will not consider here the large domain of silicon-based microdevices (including silicon nitrides and carbides), which would hardly be considered for fuel processing at the industrial level due to the cost of the substrate material. A general literature review and detailed information on silicon technology-based microreactor... 

TABLE 9.1.1 Silicon Nitride and Carbide as High-Temperature High-Strength Ceramics... 

Silicon nitride powder can be produced by sol-gel by using volatile silazanes as precursors. These materials are converted to silicon nitride and carbide. By the introduction of oxygen during the conversion process, the silicon carbide is reduced and the nitride is left. Other precursors of interest are as follows ... 

Phenylimino >N-C H3 6 b (100) 525 UHV face species leading to silicon nitride and carbide [225]... 

Malghan SG, Pei PT, Wang PS. Analysis of surface chemistry of silicon nitride and carbide powders. In Cima MJ, ed. Ceramic Transactions, Vol. 26. Eorming Science and Technology for Ceramics. Westerville, OH The American Ceramic Society,... 

The covalently-bonded silicon carbide, silicon nitride, and sialons (alloys of Si3N4 and AI2O3) seem to be the best bet for high-temperature structural use. Their creep resistance... 

More reasonable choices include silicon carbide and alumina. In addition, our intuition tells us that similar materials like silicon nitride and tungsten carbide may fit into this category, even though they are not specifically listed in the chart. 

Considerable recent activity in the area of ceramic processing is aimed toward the formulation of materials with high strengths, comparable to the room temperature strength of metal alloys, at high temperatures (of the order of 2000 K). The impetus comes from the significant gains made in the last 20 years with materials formed from submicron powders of silicon nitride and silicon carbide and the promise of similar improvements in the near future. 

NISTCERAM National Institute of Standards and Techology Gas Research Institute, Ceramics Division mechanical, physical, electrical, thermal, corrosive, and oxidation properties for alumina nitride, beryllia, boron nitride, silicon carbide, silicon nitride, and zirconia... 

Japan Heatproof turbine rotors made of silicon nitride and silicon carbide. 

Silicon nitride and silicon carbide-based ceramics 537... 

The bulk densities of all the materials were determined using Archimedes method (AS 1774.5, 1979). The Vickers indentation technique was used to measure the hardness in each case. The applied load in the Vickers hardness tests was 10 kg for silicon nitrides and sialons. However, using the same load produced severe lateral cracking in silicon carbides around indents, which prevented the accurate measurement of the diagonals of indents. Therefore the load was reduced to 0.3 kg for silicon carbide samples. 

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