Polymer-derived ceramics oxidation

Fiber reinforced ceramic matrix composites (CMCs) are under active consideration for large, complex high temperature structural components in aerospace and automotive applications. The Blackglas resin system (a low cost polymer-derived ceramic [PDC] technology) was combined with the Nextel 312 ceramic fiber (with a boron nitride interface layer) to produce a sihcon oxycarbide CMC system that was extensively characterized for mechanical, thermal, and electronic properties and oxidation, creep mpture, and fatigue. A gas turbine tailcone was fabricated and showed excellent performance in a 1500-hour engine test. 

Although polymer precursors to non-oxide ceramics offer considerable potential for processing a wide variety of novel shapes, at quite low temperatures with respect to standard ceramics processing methods, very few commercial products based on this approach have been forthcoming [1-5]. Furthermore, very few polymer derived non-oxide ceramics exhibit properties commensurate with those found for the same ceramics produced by high temperature methods. 

Polymer-derived ceramics (PDCs) represent a rather novel class of ceramics which can be synthesized via cross-linking and pyrolysis of suitable polymeric precursors. In the last decades, PDCs have been attaining increased attention due to their outstanding ultrahigh-temperature properties, such as stability with respect to decomposition and crystallization processes as well as resistance in oxidative and corrosive environments. Moreover, their creep resistance is excellent at temperatures far beyond 1000 °C. The properties of PDCs were shown to be strongly related to their microstructure (network topology) and phase composition, which are determined by the chemistry and molecular structure of the polymeric precursor used and by the conditions of the polymer-to-ceramic transformation. 

Polymer-derived ceramics have been investigated in the last two decades concerning their high temperature oxidation behavior (i.e., usually temperatures exceeding 1000 °C and oxidizing environments such as air or combustion atmosphere). Mainly ternary and multinary systems based on the Si-M-O-C and Si-M-C-N-O systems (M = B, Al, Zr) were tested and showed passive oxidation behavior. (Chollon, 2010) Within this context, they can be considered as behaving to some extent like silica formers (e.g., silicon, metal silicides, SiC or SijN ). 

Polymer derived ceramics have been known for the last four decades and are prepared via solid-state thermolysis of preceramic polymers. They exhibit a unique combination of remarkable properties due to their covalent bonding and amorphous nature. Thus, silicon oxycarbide (SiOC) and silicon carbonitride (SiCN) based ternary PDCs have been shown to possess outstanding high-temperature properties such as stability with respect to crystallization and decomposition, oxidation and corrosion resistance as well as excellent thermomechanical properties (e.g., near zero steady state creep resistance up to temperatures far beyond 1000 °C). Their properties are directly influenced by the chemistry and the architecture of the preceramic precursors, thus there is an enormous potential in tuning the microstructure and properties of the PDCs by using tailored polymers. Furthermore, suitable chemical modification of the preceramic precursors leads to quaternary and multinary ceramics, as it has been shown for instance for silicon boron carbonitride ceramics in the last 25 years, which in some cases exhibit improved properties as compared to those of the ternary materials. 

Chollon, G. (2010). Oxidation behavior of polymer-derived ceramics. In Colombo, P., Riedel, R., Kleebe, H.-J., Soraru, G. D. (Eds.), Polymer-Derived Ceramics From Nanostructure to Applications (pp. 292-307). Lancaster, PA DesTech Pnb-lications, Inc.. 

The following discussion covers the chemical synthesis of ceramics derived from organometallic polymers BN, AIN, TiN, TiC, and TiBa. It should be emphasized here that some of the syntheses involve starting materials, monomers, and intermediates, as well as polymers, that are oxidatively unstable and/or susceptible to hydrolysis. These syntheses therefore generally require inert atmospheres and the extensive use of vacuum (Schlenk type) line or dry-box techniques. This makes it obvious that collaborations between synthetic chemists and materials and ceramic scientists and engineers is important. Here we outline a selected number of synthetic routes to preceramic polymers. 

Carbon fibers, as well as ceramic oxide and carbide fibers, which have a combined sales volume well below that of glass fibers, are derived from solid precursor or green fibers. These precursor fibers are in turn derived from a liquid phase, e.g., from a viscous solution or from a viscous polymer by dry or melt spinning, respectively. By virtue of its organization, this book is uniquely able to pay equal attention to the formation, structures and properties of the... 

Electrical conductivity measurements have been reported on a wide range of polymers including carbon nanofibre reinforced HOPE [52], carbon black filled LDPE-ethylene methyl acrylate composites [28], carbon black filled HDPE [53], carbon black reinforced PP [27], talc filled PP [54], copper particle modified epoxy resins [55], epoxy and epoxy-haematite nanorod composites [56], polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) blends [57], polyacrylonitrile based carbon fibre/PC composites [58], PC/MnCli composite films [59], titanocene polyester derivatives of terephthalic acid [60], lithium trifluoromethane sulfonamide doped PS-block-polyethylene oxide (PEO) copolymers [61], boron containing PVA derived ceramic organic semiconductors [62], sodium lanthanum tetrafluoride complexed with PEO [63], PC, acrylonitrile butadiene [64], blends of polyethylene dioxythiophene/ polystyrene sulfonate, PVC and PEO [65], EVA copolymer/carbon fibre conductive composites [66], carbon nanofibre modified thermotropic liquid crystalline polymers [67], PPY [68], PPY/PP/montmorillonite composites [69], carbon fibre reinforced PDMS-PPY composites [29], PANI [70], epoxy resin/PANI dodecylbenzene sulfonic acid blends [71], PANI/PA 6,6 composites [72], carbon fibre EVA composites [66], HDPE carbon fibre nanocomposites [52] and PPS [73]. 

Borazine is isoelectronic and isostructural with benzene. Poly(borazylene), a polymer of borazine and its derivatives, is reported extensively as a precursor of BN-coated ceramic libers.86 Polymeric borazine oxide derivative is claimed to be flame resistant (Figure 9.10).87... 

In earlier investigations by the author [3,4] high-temperature oxidatively stable easterners containing 1,7-dodecacarboranyl (carborane), (III), or borate-terminated derivatives, (IV), respectively, were prepared that could be thermally crosshnked to a cured polymer or pyrolyzed to a ceramic surface. 

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