Monolith silicon carbide

Leventis N, Sadekar A, Chandrasekaran N, Sotiriou-Leventis C (2010) Click synthesis of monolithic silicon carbide aerogels from poly acrylonitrile-coated 3D silica networks. Chem Mater 22 2790-2803 Boday D J, DeFriend K A, Wilson K V Jr, Coder D, Loy D A (2(X)8) Formation of polycyanoacrylate-sUica nanocomposites by chemical vapor deposition of cyanoacrylates on aerogels. Chem Mater 20 2845-2847 Boday D J, Stover R J, Muriithi B, Keller M W, Wertz J T, DeFriend Obrey K A, Loy D A (2009) Strong, low density nanocomposites by chemical vapor depositim and polymerization of cyanoacrylates on aminated siUca aerogels. ACS Appl Mater Interfaces 1 1364—1369... 

Figure 3.5. Schematic representation of the ROTACAT concept a homogeneous complex, immobilised on monoliths, and the implementation of these monoliths in the blades of a mechanical stirrer. Inset a picture of the stirrer with a silicon-carbide monolith...

Brown, D. M., et al., High Temperature Silicon Carbide Planar IC Technology and First Monolithic SiC Operational Amplifier IC, Trans, of 2nd Inti. High-Temp. Elec. Conf. (HiTEC), 1994, pp. XI-17-XI-22. 

As observed by D. Johnson and J. Stiegler, "Polymer-precursor routes lor fabricating ceramics offer one potential means or producing reliable, cost-effective ceramics. Pyrolysis of polymeric metalloorganic compounds can be used to produce a wide variety of ceramic materials." Silicon carbide and silicon oxycarbide fibers have been produced and sol gel methods have been used In prepare line oxide ceramic powders, such as spherical alumina, as well as porous and fully dense monolithic forms. 

In one application (production or aluminum beverage can lids), a monolithic silicon nitride punch has demonstrated a useful life greater than ten times that of a cemented carbide tool. 

Although few applications have so far been found for ceramic matrix composites, they have shown considerable promise for certain military applications, especially in the manufacture of armor for personnel protection and military vehicles. Historically, monolithic ("pure") ceramics such as aluminum oxide (Al203), boron carbide (B4C), silicon carbide (SiC), tungsten carbide (WC), and titanium diboride (TiB2) have been used as basic components of armor systems. Research has now shown that embedding some type of reinforcement, such as silicon boride (SiBg) or silicon carbide (SiC), can improve the mechanical properties of any of these ceramics. 

Baskaran, S., and Halloran, J.W. (1993), Fibrous monolithic ceramics II, Flexural strength and fracture behavior of the silicon carbide/graphite system , J. Am. Ceram. Soc., 76(9) 2217-2224. 

There is the possibility to make substrates in various materials Alumina is an obvious possibility, but monoliths formed from alumina are particularly susceptible to thermal shock problems, and they readily crack during rapid temperature excursions. Silicon carbide and boron nitride are other possible materials having good properties, but they are expensive. 

Materials such as aluminum titanate and silicon carbide appear to be promising for high-temperature catalytic combustion. However, problems such as extrudability, the application of washcoats, and reaction with deposited washcoats are not solved yet. For instance, when hexa-aluminate, presented in the introduction to this section, was applied to silicon carbide monoliths, solid-state reactions occurred at 1200-1400 C [76], causing exfoliation of the coating and the formation of new phases. The application of an intermediate mullite layer was suggested as an approach to hinder these solid-state reactions. 

Silicon carbide has attracted considerable interest because of its good mechanical and physical properties and chemical inertness. One of the most important applications of SiC is to produce a matrix reinforced by fibres, forming ceramic-matrix composites. These composite materials exhibit much better fracture toughness than monolithic ceramics. Compared with carbon/carbon composites, fibre-reinforced SiC matrix composites possess superior oxidation resistance and mechanical properties. The Si-C-H-Cl system (e.g. methyltrichlorosilane, CH3SiCl3) has been used for SiC deposition because it is easy to produce stoichiometric SiC deposits. 

An exploratory study was carried out with respect to the performance of a copper fuel additive in combination with monolithic wall flow filters for the removal of soot firom diesel exhaust gas. Cordierite filters, copper coated cordierite filters, and silicon carbide filters were studied. Model experiments have been performed to investigate the influence of contact between soot and catalyst on the oxidation rate. 

Metal based fuel additives, such as Ce [3], Cu [4, 5], Fe [6], and Mn [7, 8, 9] have been studied for use in combination with a particulate filter. In general, a wall flow monolith is applied as a particulate filter in this kind of operations. In this study the performance of a copper fuel additive in combination with a cordierite wall flow monolithic filter is compared with that of copper coated wall flow monolithic filters. Furthermore, the performance of a silicon carbide wall flow monolithic filter was compared with that of a cordierite one. 

The copolymer (PhMeSi) (Mc2Si) is also used as a silicon carbide precursor, especially for monolithic formed objects. 

Zeolite monoliths have been found to be useful for such applications as rotatory adsorbers for use as dehumidifiers and desiccant cooling processes [360] or in VOC treatment systems [379]. Alumina-coated silicon carbide monoliths have also been employed as supports for B-ZSM-5 membranes [380] providing a larger surface area per unit volume, compared to traditional membrane supports. With these membranes, the same authors have reported n/t-butane and Hj/t-butane separation selectivities of 35 and 77, respectively [119]. Also, SIL-1 membranes supported on stainless steel grids (Figure 11.30) have shown a good performance in the separation of /t-butane mixtures, with separation factors as high as 53 at 63°C [362]. 

The importance of hot-pressed silicon carbide has decreased considerably since the introduction of pressureless sintering, although it is currently still the most suitable method of obtaining the best mechanical properties for pure, monolithic SiC. 

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