Active filler-controlled pyrolysis

P.Greil, Active-filler-controlled pyrolysis of preceramic polymers, J. Am. Ceram. Soc., 78,835-48(1995)... 

C(/SiC-BN composites and C(/SiC-ZrC composites were fabricated to improve the oxidation resistance and high temperature performance of C /SiC composites through the modification of matrix. SiC-BN matrix was formed through an in-situ reaction of active filler boron and protective gas N2 in the active-filler-controlled polymer pyrolysis (AFCOP). The oxidation performance of C(/SiC-BN composites was greatly improved when oxidized at 1000°C compared to that of C /SiC composite. Meanwhile, SiC-ZrC matrix was fabricated using the ZrC particles as inert filler. Both C(/SiC-BN composites and Ci/SiC-ZrC composites show non-catastrophie ftaeture behavior. The microstructures were also characterized by SEM and EDS. It was shown that the fiber reinforcement hindered the impregnation of solid particles into the fiber bundles so that most of the fillers remained in the inter-bundle matrix and most of the intra-bundle matrices were composed of Sic that resulted from the decomposition of polycarbosilane (PCS). 

Dong et al proposed a facile route to fabricate carbon fiber reinforced ceramic matrix composites (Cf/SiC-BN) by an active-filler-controlled polymer pyrolysis (AFCOP) process. In the proposed process, boron was introduced into the carbon fibers as active filler to form some boron-bearing species by in-situ reactions during the subsequent heat-treatment process. The composites were prepared by PIP using PCS as the polymer precursor. XRD patterns of the obtained composites confirmed the presence of H-BN. With the presence of BN, the oxidation of the composites was greatly improved. The weight losses of Cf/SiC and Cf/SiC-BN after being oxidized at 800°C for lOh were 36% and -16% respectively and most of the carbon fibers in... 

AFCOP) In this technique for making multiphase ceramic matrix composites, an active filler material (a transition metal or compound thereof which will yield a carbide or other ceramic) is mixed with an organometallic polymer and pyrolysed. The kind, content and structure of the filler control the kinetics of the polymer pyrolysis and the resulting microstructure, which may contain disordered or glassy areas. (M. Seibold and P. Greil, 1st European Conf on Adv. Mater Processes.)... 

Other techniques include oxidative, steam atmosphere (33), and molten salt (34) pyrolyses. In a partial-air atmosphere, mbber pyrolysis is an exothermic reaction. The reaction rate and ratio of pyrolytic filler to ok products are controlled by the oxygen flow rate. Pyrolysis in a steam atmosphere gives a cleaner char with a greater surface area than char pyroly2ed in an inert atmosphere however, the physical properties of the cured compounded mbber are inferior. Because of the greater surface area, this pyrolytic filler could be used as activated carbon, but production costs are prohibitive. Molten salt baths produce pyroly2ed char and ok products from tine chips. The product characteristics and quantities depend on the salt used. Recovery of char from the molten salt is difficult. 

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