Ceramic char

Pyrolysis of poly(organoborosilazane) (entry 6) under argon at 1,050 °C gives an amorphous ceramics, which resist crystallization up to 1,700 °C and thermally degradation up to 2,200 °C [210]. It should be noticed that the ratio of ceramic elements (B Si N) in the ceramic chars is about the same as that in the polymer precursors, illustrating the importance to control the ratio of ceramic elements in the preceramic polymers. Ceramic fibers can be obtained from this type of polymer for high temperature application... 

The procedures that we developed to evaluate preceramic polymers as binders are summarized in the following five steps. (1) pyrolyze a sample of bulk polymer to -1800 °C to obtain a stable ceramic char. As is shown in Figure 1 all of the polymers, if sufficient levels of carbon are present, afford stable chars by 1800 °C under an inert atmosphere. 

Upon pyrolysis to 1800 °C under an Ar atmosphere Polycarbosilane (PCS)23 affords a ceramic char that is composed of 37.3 weight % C and 62.0 weight % Si in a 55.8 % char yield. Employing the equations described earlier one gram of polymer gives 0.494 g of SiC and 0.064 g of C. 

With the screening results obtained with the polycarbosilane it had become obvious that a polymer or a series of polymers that had bodi controllable carbon levels in their ceramic chars and respectable char yields (ca. greater than 40 %) was needed. By combining portions of two previous studies (vida infra) we began to investigate the use of silazanes as silicon carbide precursors and their use as binders for SiC powders. 

Earlier Bums, et. al. examined the utility of using alkyl and arylsilsesquaizanes as precursors to Si, C, N ceramic materials upon pyrolysis to 1200 °C.25 Of particular importance to this discussion it was found that (1) saturated alkyl groups contribute approximately the same amount of carbon to the ceramic char independent of the structure of the alkyl group, (2) unsaturated groups (alkyl or aryl) increase the carbon content of a ceramic char as the number of the carbons in the unsaturated group increases. Also in this previous work the synthesis of 1200 °C (Si, C, N) ceramic materials from a series of... 

Alkly- and Arylsilsesquizanes The effecy of the R Group on Polymer Degradation and Ceramic Char Composition, J. Mater. Sci., 22, 2609-14. 

High temperature thermosets and ceramics have been synthesized by heat treatment of various blends of poly (siloxane-acetylene) and poly (carborane-siloxane-acetylene). The polymeric blends give high char yields on pyrolysis, and the resultant chars show excellent oxidative stability to at least 1500 °C. The thermosets and ceramic chars show similar oxidative stability to previously studied copolymers containing varying amounts of siloxane, carborane, and acetylene units within the backbone. It has been determined that only a small percentage of carborane is necessary to provide this oxidation protection. Thus, these precursor linear hybrid polymers are more cost-effective than previous polymers which contained carborane in each repeating unit. 

Conversion to Ceramic 5. Various mixtures of 1 and 3a or 4 were weighed into a TGA pan and heated to either 1000 °C or 1500 C under inert conditions. Upon cooling the ceramic chars were reheated to 1500 °C under a flow of air to determine the oxidative stability. 

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). 

Furthermore, 60—100 L (14—24 gal) oil, having sulfur content below 0.4 wt %, could be recovered per metric ton coal from pyrolysis at 427—517°C. The recovered oil was suitable as low sulfur fuel. Figure 15 is a flow sheet of the Rocky Flats pilot plant. Coal is fed from hoppers to a dilute-phase, fluid-bed preheater and transported to a pyrolysis dmm, where it is contacted by hot ceramic balls. Pyrolysis dmm effluent is passed over a trommel screen that permits char product to fall through. Product char is thereafter cooled and sent to storage. The ceramic balls are recycled and pyrolysis vapors are condensed and fractionated. 

Solvent extraction of the total lipid extracts from ceramic sherds and charred surface residues Isolation of DAGs and TAGs on silica solid phase cartridges Formation of lithiated adducts from the TAG fraction by addition of 2% lithium chloride in methanol... 

Bitumen traces in ceramic vessels from Neolithic Iran, 137-151 pottery sherds, sampling and characterization, 141-142 Black willow, charred, infrared spectra, 63,64/... 

One process that was developed but not commercialized was the TOSCOAL process, in which crushed coal is fed to a horizontal rotating kiln. There it is heated by hot ceramic balls to between 425 and 540°C. The hydrocarbons, water vapor, and gases are drawn off, and the char is separated from the ceramic balls in a revolving drum with holes in it. The ceramic balls are reheated in a separate furnace by burning some of the product gas. 

Reinforcement of the char through partial ceramization, enhancement of the thermal stability... 

REIN FORCED-CHAR-FORMING CERAMIZER INTERLAYER... 

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