Pyrolyzate, composition

Slip infiltrated, HlPed carbon fiber reinforced material, slip infiltrated SiC fiber reinforced nitrided SisN4, and polysilazane solution infiltrated pyrolyzed composites with SiC fibers have been fabricated [159]. All materials exhibited non-brittle fracture. 

In this article we present further observations on the pyrolytic phenomena of polysilazanes. Special emphasis is given to the relationship between the polymer substituents and the ceramics products and to the development of pyrolyzed compositions in an ammonia environment. 

Researchers [8-9] used a facile method to obtain carbon nanofibers with a nanoporous structure using selective pyrolyzate composite formation. A blend of polyacrylonitrile and a copolymer of acrylonitrile and methyl methacrylate in dimethylformamide was electrospun into nano fibers with a microphase-separated structure. With pyrolyzing the copol5uner domains in oxidation process, nanoporous structure was obtained, and preserved after carbonization. 

Nonpowder Synthesis. Many ceramic composites (qv) under iavestigation utilize reinforcing ceramic whiskers or fibers to achieve toughening (19). Whiskers (17,19,20) are produced by vapor-synthesis techniques. SiC whiskers can be produced by the rice hull or vapor—soHd (VS) method whereby rice hulls are pyrolyzed to produce a mixture of carbon, C, and Si02, and whiskers are produced by directional growth by vapor... 

Table II. Ceramic Products from Metal Powder-Polysilazane Composites Pyrolyzed to 1500 °C under a Flow of Argon.

The polysilazanes were also melt spun, cured, and pyrolyzed to give silicon carbonitride fibers (Eq. 7). The carbon content of these fibers depends on the molecular composition of the polysilazane and the pyrolysis gas. When ammonia is used as reactive gas pure silicon nitride fibers will be obtained (Eq. 8) [14]. 

Polymers have served roles in PEM fuel cell cathodes such as modifiers to macrocycle-based electrodes to improve conductivity and stability,165 composite materials with heteropolyacids,166 and as precursors to pyrolyzed catalysts.38,112,132,133 However, as discussed in the previous section, the activity of nitrogen-containing carbon raises the possibility of non-metal electrodes functioning in a cathode environment. Likewise, researchers have noted ORR activity for various conducting polymers containing nitrogen, and recently studies on their potential use in PEM fuel cell cathodes have been reported. 

Gasteiger et al. reviewed the best performing Fe-based catalysts in the literature up to 2004 1. Even the best of these catalysts (Fe on pyrolyzed peryle-netetracarboxylic dianhydride) showed a corrected turnover frequency of 7% and a volume activity density of 0.2% of Ft. More recent work has focused on optimizing the metal, nitrogen, and carbon composition of the materials. 

The polymer sample (35 mg) was pyrolyzed in a quartz cell which was directly attached to the inlet flange of a quadrupole mass spectrometer. Gases evolved from the pol3raier compound were dynamically sampled via a 1.0-mm diameter orifice, formed into a modulated molecular beam, and mass analyzed. Information was obtained on the total yield of volatile products, product composition, and individual product yields as a function of temperature. 

Polymer Infiltration. Polymer infiltration is similar to sol infiltration. The polymer is introduced in liqnid form nnder vacuum and coats the fibers. The polymer is then dried and pyrolyzed to yield the desired composition. Multiple infiltration cycles... 

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