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Corros Sci , 88 : 49— Ceram Int , 41 : — J Alloys Compd , : — Appl Surf Sci , : — Gleiter H. Nanostructured materials: State of the art and perspectives. Nanostruct Mater , 6 : 3— Mechanical and electrical properties of silicon nitride-silicon carbide nanocomposite material.

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J Am Ceram Soc , 74 : — Chem Soc Rev , 41 : — Reactive hot pressing of ZrC—SiC ceramics at low temperature. J Am Ceram Soc , 96 : 32— J Am Ceram Soc , 89 : — Google Scholar.

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J Mater Sci , 39 : — J Eur Ceram Soc , 30 : — Inorg Chem , 53 : — Nanoscale , 6 : — Polymer precursor-derived HfC—SiC ultrahigh-temperature ceramic nanocomposites. J Am Ceram Soc , : 20— Preparation and high-temperature behaviour of HfC—SiC nanocomposites derived from a non-oxygen single-source-precursor.

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J Am Ceram Soc , : — Dalton Trans , 42 : — Polymer precursor synthesis of TaC—SiC ultrahigh temperature ceramic nanocomposites. RSC Adv , 6 : — Mater Lett , 68 : — However, the corrosion rates of the SiOC ceramic materials were found to be remarkably lower than those of silicon carbide and were comparable to values reported for silicon nitride. Thus, a corrosion rate of 0. Thus, a rate of 0. Figure 4. Obviously, the corrosion resistance the surface of SiHfOC does not seem to be damaged; whereas the surface of SiOC clearly indicates that corrosion occurred.

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This feature makes the PDCs quite unique with respect to other ceramic materials. The creep behavior of silicon oxycarbides was shown to rely on viscous flow, as it is also the case for silica glasses Renlund, ; Soraru, ; Rouxel, ; ; ; Ionescu, d. The main interest within this context was to assess the glass transition temperatures and viscosities of SiOC-based materials. Since silicon oxycarbides can be considered as silica-based glasses in which carbon is present within the glass network, it was expected that their mechanical properties and refractoriness will be improved if compared to silica Soraru, ; Rouxel, ; Ionescu, d.

This effect was expected as a consequence of formally replacing bivalent oxygen atoms within the glassy network with tetravalent carbon atoms, as it was for instance observed in SiAlON glasses in which bivalent oxygen atoms are partially substituted by trivalent nitrogen atoms Hampshire, Studies on the high-temperature apparent shear viscosity of SiOC materials derived from bending or compression creep experiments indicate that at a specific temperature the viscosity of SiOC glasses is several orders of magnitude higher than that of amorphous silica.

This consequently indicates that the glass transition temperatures for SiOC glasses are significantly higher than that of vitreous silica. Ionescu, d The lower border of the grayish area represents the viscosity of vitreous silica; whereas the upper border indicates the viscosity of other reported silicon oxycarbides with the permission of Wiley-Blackwell. A recent study considers SiOC materials consisting of two continuous and interpenetrating phases, i.

This microstruc- ture consideration was shown to be able to rationalize not only the creep rates of SiOC-based materials, but also the activation energies of creep, which were shown to be strongly affected by the nanodomain size of silica i. It was shown that the modification of SiOC with additional elements such as Al, Zr, Hf induces an increase of the creep rates i.

This was explained as a consequence of the strong decrease of the content of the segregated carbon phase Ionescu, d. Silicon carbonitride ceramics were also studied with respect to their creep behavior at high temperatures An, ; Shah, ; Zimmerman, Si-C-N samples show similar creep behavior and shear viscosity values with those determined for Si-O-C materials. Also in the case of SiCN, a creep hardening behavior was observed and was claimed to rely not necessarily on crystallization processes as SiCN exhibits an improved crystallization resistance at high temperatures if compared to SiOC , but to a nanoscale densification creep mechanism Shah, Some case stud- ies revealed that a thermal annealing of SiBCN at high temperatures, e.

As presented in this chapter, the variation of processing parameters allows for a controlled synthesis and design of multifunctional PDC materials with tailored properties. In the recent years, it was shown that SiOC and SiCN ceramics are suitable candidates for electrical energy storage and mobile applications ranging from cell phones to electric cars Riedel, ; Colombo, a.

Moreover, PDCs are promising ceramics for use under extreme conditions, as they exhibit high strength, creep and thermal shock resistance, as well as stability in oxidative and corrosive requirements Ionescu, a; Linck, Some of these structural properties and some related prospective applications will be briefly addressed here.

PDCs Coatings for TBC and EBC Applications Due to the possibility to deposite the preceramic polymers on substrates of vari- ous kinds using different deposition techniques based either on a liquid melt or solution or a vapor phase, PDCs found a lot of interest as ceramic coatings. PDCs were reported to be low temperature, cost effective suitable materials for protecting metal surfaces against oxidation, wear and corrosion Torrey, ; a; b; Gunthner, a; b; ; Wang, a. Different techniques have been used in order to prepare PDC-based coatings.

Precursor-Derived Ceramics: Synthesis, Structure and High-Temperature Mechanical Properties

Within this context several properties of the preceramic polymers have been identified as strongly affecting the quality of the ceramic coatings, such as polymer composition, viscosity, environmental stability, wetting of the substrate. It was observed that there is a critical thickness beyond which the coatings crack and delaminate during the polymer-to-ceramic conversion.

Thus, in order to prepare thick coatings, different solutions have been applied: multiple layer deposition with or without intermediary thermal treatment , or the use of fillers. Different ceramic systems have been used to prepare PDC coatings for thermal and environmental protection purposes.

Silicon oxycarbide-based coatings have been prepared from silicones such as polyhydridomethylsiloxane Torrey, a , polyhydroxymethylsiloxane, or polymethylsilsesquioxane Goerke, ; Manocha, Usually active fillers are added such as TiSi2 Torrey, a in order to prepare thick coatings.

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Polysilazanes were used to prepare non-oxidic SiCN-based coatings. Also in this case filler systems such as alumina Konetschny, , zirconia Gunthner, a , or boron nitride Kraus, were used in order to provide thick ceramic coatings. Microcomponents for MEMS to be used at UHT and in Harsh Environments The use of preceramic polymers, processed by various lithographic methods, of- fers the possibility to realize microcomponents miniaturized ceramic components with features below one micron in size Colombo, a; Ionescu, b; Mar- tinez-Crespiera, ; Martinez-Crespiera, They already found application such in photonics and fluidic devices, and as components for electrical heating micro igniters or glow plugs , micro-parts and actuators Lee, ; Yang, ; Liew, ; ; Liu, Within this context, the preparation and pyrolysis of preceramic microcompo- nents, which can be shaped via different micromachining techniques, has become an interesting alternative method which offers a more facile route to synthesize three-dimensional ceramic microparts.

The preparation of microstructured ceramic parts can be achieved either by using direct microstructuring techniques such as lithography methods UV, X-ray, E-beam or laser lithography techniques or soft- lithographic approaches, which use elastic or thermosetted masters for molding or printing processes. In both cases UV photo-crosslinking provided an effective cross-linking process, being a rapid and crack-free procedure to obtain infusible polymers.

Whereas the photolithographic approach allows for producing microstructures on substrates, the soft lithography technique used was shown to be an excellent and reliable approach to produce free standing and complex-shaped micro components Figure 6 Martinez-Crespiera, PDC-based sensors developed for monitoring the environment in extremely harsh environments in jet engine turbines and energy generation turbines are commercial- ized by Sporian Microsystems Inc. Membranes for UHT Gas Separation Purposes The gas evolution during thermal decomposition of preceramic polymers can eas- ily create micro- and meso-porosity in the ceramic structure, properties important for the application of these materials as membranes for ultrahigh temperature gas separation purposes.

Hauser, , Iwamoto, , Prasad, SiBCN ceramic thin films prepared by dip coating are suitable micro- and mesoporous membrane materials for high-temperature gas separation. Thus, it was recently shown that the pore size in SiCN PDCs is strongly dependent on the organization of carbon-phase. These materials might be useful for separation processes at ultrahigh temperatures.

Under uniaxial compressive loading conditions, SiCN ceramics display a piezoresistive coefficient from to , the highest values known so far for any existing ce- ramic. Wang, ; Zhang, This outstanding behavior was claimed to rely on a tunneling-percolation mechanism, which is however difficult to assess and understand for these PDC samples with complex compositions and microstructures.

This indicates that the different degree of organization of the carbon phase strongly affects the piezoresistive behavior of the PDCs. Riedel, b, Toma, This fact was found to rely on the processing procedure chosen for the preparation of the ceramics. In order to demonstrate the viability of polymer-derived ceramics as suitable ultrahigh-temperature sensors, the piezoresistivity of a silicon oxycarbonitride polymer-derived ceramic PDC material Si0.

The piezoresistive gage factor was found to be in the range of — at an applied stress of 1MPa, depending on both stress and temperature, exceeding the performance of any other known material in this temperature range. Terauds, The combination of unique structural properties of PDCs SiCN, SiOC and SiCNO such as stability at high temperatures, chemical durability, with the large gage factors promotes these materials as ideal candidates for sensor materials in extreme environments at ultrahigh-temperatures.

They exhibit a unique combina- tion 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. Their properties are directly influenced by the chemistry and the architecture of the preceramic precur- sors, thus there is an enormous potential in tuning the microstructure and properties of the PDCs by using tailored polymers.

Furthermore, suitable chemical modifica- tion 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.

One of the main advantages of the PDCs if compared to other ceramic materials is that they can be processed through techniques similar to those used for polymer processing. Well developed shaping techniques such as pressing, melt spinning, spin or spray coating as well as lithography methods can be used in order to obtain green bodies with complex geometries which are subsequently transformed into ceramic parts via pyrolysis process.

The use of preceramic polymers thus allows the production of dense ceramic monoliths, fibers, coatings as well as foams. Additionally, selected struc- tural properties of the PDCs, such as their high-temperature behavior with respect to decomposition and crystallization, their oxidation and corrosion behavior as well their high-temperature creep resistance are highlighted.

Also some prospec- tive high-temperature applications, such as environmental protection PDC-based coatings , high-temperature gas separation PDC-based ceramic membranes , ultrahigh-temperature sensing microstructured ceramic parts, force and pressure sensors are briefly introduced. This allows for a knowledge-based design of ceramic materials with tailored high-temperature properties. However, despite intensive research on the effect of the precursors on the microstructure and properties of the resulting ceramics, a reliable fundamental knowledge on this aspect is rather scarce.

Also other aspects related to the microstructural evolution of the PDCs at elevated temperatures and to the effect of the microstructure on their properties e. This requires synergistic and interdisciplinary ap- proaches to materials design, processing optimization as well as device engineering. Newtonian viscosity of amorphous silicon carbonitride at high temperature. Journal of the Ameri- can Ceramic Society, 81 5 , — An, L. Silicoaluminum carbonitride with anomalously high resistance to oxidation and hot corrosion.

Advanced Engineering Materials, 6 5 , — Babonneau, F. Chemical characterization of Si-Al-C-O precursor and its pyrolysis. Journal of the American Ceramic Society, 74 7 , — Chemistry of Materials, 1 5 , — Belot, V. Thermal re- activity of hydrogenosilsesquioxane gels. Chemistry of Materials, 3 1 , — Blum, Y. Synthesis and character- ization of carbon-enriched silicon oxycarbides. Journal of the European Ceramic Society, 25 , — Brequel, H.

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Systematic structural characterization of the high-temperature behavior of nearly stoichiometric silicon oxycarbide glasses. Chemistry of Materials, 16 13 , — Radial distribution function of amorphous silicon oxycarbide compounds. Burns, G. High- temperature chemistry of the conversion of siloxanes to silicon carbide.

Chemistry of Materials, 4 6 , — Butchereit, E. Oxidation behaviour of precursor derived Si- B -C-N ceramics. Oxidation behaviour of precursor derived ceramics in the system Si- B -C-N. Cancado, L. General equation for the determination of the crystallite size L-a of nanograph- ite by Raman spectroscopy.