Monolithic ceramics silica

Ceramic Ablators, Several types of subliming or melting ceramic ablators have been used or considered tor use in dielectric applications particulady with quartz or boron nitride [10043-11-5] fiber reinforcements to form a nonconductive char. Fused silica is available in both nonporous (optically transparent) and porous (slip cast) forms. Ford Aerospace manufactures a 3D silica- fiber-reinfo reed composite densified with colloidal silica (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see Composite materials, ceramic matrix). 

Very recently, hierarchically arranged aerogel monoliths [209], silica-based monoliths from swollen liquid crystals [210] or heptane/water/ethanol/sodium dodecylsulfate microemulsion [211], monolith-based hybrid components such as the PMOs [212], and silicon oxycarbide monoliths with better thermal properties than the pure (organo) silica monoliths [213] have been reported. These approaches have been extended also to alumina or aluminumsilicates [214, 215], titania [216, 217], zirconia [218], or ceramic-based [219] systems. 

Ceramic matrix composites (CMCs), in which carbon or ceramic fibers are embedded in a ceramic matrix, have been designed to overcome the intrinsic brittleness of monolithic ceramics with a view toward structural uses at extremely high service temperatures. The most commonly used are carbon (C/C) and SiC matrix composites (C/SiC and SiC/SiC). Ceramic matrix composites with a silica based glass or glass-ceramic matrices have also been studied [12] [53-56]. 

A ceramic monolith catalyst support, cordierite, consisting of silica, alumina and magnesium oxide. The purpose of this is to provide support, strength and stability over a wide temperature range. 

Zeolite BEA(75) coatings can be deposited on a ceramic cordierite (2AI2O3 5Si02 2MgO) monolithic substrate. The coating is performed with a suspension of zeolite, with silica as the binder, and a surfactant in water. The mixture is well stirred the cordierite monolith is dipped into the mixture and dried at 200°C, and finally is calcined at 400°C for 4 h. ... 

The preparation and use of active catalysts coated on a structure packing was further studied as an attractive replacement for conventional catalysfs in randomly packed beds or slurry reactions. A method was developed in which catalytically active and selective BEA coatings could be prepared onto ceramic monoliths constituted either of pure silica or cordierite (Figure 4.7a) and mefallic wire gauze packings (Figure 4.7b). ... 

The bare monolithic structures used were made of cordierite (a ceramic material consisting of magnesia, silica and alumina in the ratio of 2 5 2). The main characteristics are shown in Table 1. 

The physical form of the support has to be chosen with a view to the type of reactor in which its use is intended. Silica and alumina are available as coarse granules or fine powders, and may be formed into various shapes with the aid of a binder (stearic acid, graphite) they can then be used in fixed bed reactors. For fluidised beds, or for use in liquid media, fine powders are required. Ceramic monoliths having structures resembling a honeycomb are used where (as in vehicle exhaust treatment) very high space velocities have to be used, but they are made of a non-porous material (a-alumina, muUite) and have to have a thin wash-coat of high area alumina applied, so that the metal can be firmly affixed. 

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Wei, T, Chang, T, Lu, S, Chang, Y (2007) Preparation of monolithic silica aerogel of low thermal conductivity by ambient pressure drying. J Am Ceram Soc 90(7) 2003-2007. 

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Morrow A.B., Gay I.D. Infrared and NMR characterization of the silica surface. In Adsorption on Silica Surfaces. Papirer E. Marcel, ed. New York Dekker, 2000, p. 26 Nikolic L. J., et al. Effect of drying control chemical additives in sol-gel-glass monolith processing. Ceram. Int. 1994 20(5) 309... 

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