Monolithic ceramic

Cera.micA.bla.tors, Several types of subliming or melting ceramic ablators have been used or considered for use in dielectric appHcations particularly with quartz or boron nitride [10043-11 -5] fiber reinforcements to form a nonconductive char. Fused siHca is available in both nonporous (optically transparent) and porous (sHp cast) forms. Ford Aerospace manufactures a 3D siHca-fiber-reinforced composite densified with coUoidal siHca (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). 

Though these materials are thermally very stable and mechanically inert they do only poorly resist mechanical stresses. This drawback can be overcome by reinforcing the monolithic ceramics with fibers. Today SiC-, Si3N4- and siliconcarbonitride fibers are commercially available, which are used in worldwide research activities to develop bulk component parts with composites. 

The gases move down the monolith ceramic cells of the ACC in plug flow with the noble metal catalyst deposited on the walls. This reactor is therefore a PFTR with catalyst... 

Weiland et al observed that a small amount of Pt metal present in the Rh-based catalyst could significantly improve the catalyst activity for ATR of gasoline range fuels. They claimed that the role of Pt is to enhance oxidation activity, whereas Rh provides high SR activity. The Rh-Pt/alumina catalyst used in the study was supported on monolithic honeycombs and had a Rh to Pt ratio of 3-10 by weight. The geometry (metal monolith, ceramic monolith, or ceramic foam) of the support did not affect the product composition. ... 

Finally a graph in which the tensile stress is plotted against the relative change in length of a so-called monolithic ceramic material (i.e. it only consists of matrix) and a fibre-reinforced ceramic material. 

Figure 7.15 Monolithic ceramic microfilter. The feed solution passes down the bores of the channels formed in a porous ceramic block. The channel walls are coated with a finely porous ceramic layer...

L. (1998) Preparation and characterization of extruded monolithic ceramic catalysts. Catal. Today, 41, 87. 

Schematics illustrating (a) laminated composite, consisting of the strong layer and the weak layer, and (b) fibrous monolithic ceramic, consisting of the strong cell and the weak cell boundary. 

In this section, we discuss three prevalent processing methods for producing fibrous monolithic ceramics, i.e. coextrusion [1, 23], microfabrication by coextrusion [24], and hybrid extrusion and dip-coating [25],... 

Fibrous monolithic ceramics consist of dense cells separated by a continuous cell boundary, in which the cells provide most of the strength of the FM and... 

Since fibrous monolithic ceramics are intended for use in applications where stresses are primarily generated due to bending, strength and work-of-fracture in flexure are measured to evaluate their basic mechanical properties. In addition, factors determining the manner of crack propagation should be... 

In the last 10 years, significant advances in fibrous monolithic ceramics have been achieved. A variety of materials in the form of either oxide or nonoxide ceramic for cell and cell boundary have been investigated [1], As a result of these efforts, FMs are now commercially available from the ACR company [28], These FMs are fabricated by a coextrusion process. In addition, the green fiber composite can then be wound, woven, or braided into the shape of the desired component. The applications of these FMs involve solid hot gas containment tubes, rocket nozzles, body armor plates, and so forth. Such commercialization of FMs itself proves that these ceramic composites are the most promising structural components at elevated temperatures. 

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. 

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