Papers by Keyword: Polymer Derived Ceramics

Abstract: Polymer Matrix Composites (PMC) are often used in lightweight applications due to their excellent mechanical properties combined with a low density. The manufacturing technologies are fully developed and raw materials are cheap. The limiting factor of these reinforced polymers is the maximum service temperature. Ceramic Matrix Composites (CMC) are suitable for service temperatures up to 1500 °C and more. These composites are composed of ceramic matrices combined with ceramic fibers based on alumina or silicon carbide. This class of composites is handicapped by the high cost of processing and raw materials and therefore only attractive for applications in astronautics and military aviation. Composite materials, bridging the gap between PMC and CMC, are manufactured by the use of polysiloxanes, carbon-and basalt fibers. Such competitive free formable Hybrid-composites are capable for service temperatures up to 800 °C in oxidative atmosphere. In order to make the material attractive also for series applications, manufacturing technologies like filament wet winding, Resin Transfer Moulding (RTM) or pressing techniques are employed. Beside the improved thermal resistivity in comparison to reinforced polymers and light metals, a major benefit of SiOC composites is investigated in the field of friction materials. The excellent properties in wear resistance and an adjustable coefficient of friction make it an interesting alternative for CFC and CMC.

Abstract: Precursors for nitride-based ceramic composites have been prepared from two types of building blocks, cage-type poly(iminoalane) with Al-N backbones and cyclic poly(silazane) with Si-N backbones. Two combinations of poly(iminoalane) and cyclic poly(silazane) were utilized to prepare precursors. For the combination of poly(isopropyliminoalane) and [MeSi(H)NH]n, two building blocks were connected via dehydrocoupling, while Pt-catalyzed hydrosilylation was utilized for the combination of poly(allyliminoalane-co-ethyliminoalane) and [Me(H)SiNH]n. The ceramic yields of poly(iminoalane)s increased upon reactions with [MeSi(H)NH]n.

Abstract: The present contribution reports two different approaches to achieve a good dispersion of single-walled carbon nanotubes (SWCNTs) in a precursor-derived Si-C-N matrix, which represents an important prerequisite for attaining a high-performance material. The first approach involves the use of SWCNTs covalently functionalized by disilazane groups, aiming at enhanced interfacial interaction between the nanotube surface and the matrix. Within the second approach, the effect of an electrical field applied in the cross-linking step during the nanocomposite synthesis was studied toward the task of dispersing and simultaneously aligning the SWCNTs in the Si-C-N matrix.

Abstract: This work reports the synthesis and thermal characterization of poly(borosiloxanes) (PBS) derived from methyltrietoxysilane (MTES) and vinyltriethoxysilane (VTES), aiming to use these polymers as precursors of ceramic matrices for the protection of carbon fibers in ceramic matrix composites (CMCs). The resulting materials exhibited better thermal stability than the carbon fiber, especially the Cfiber/SiBCO composite derived of the methyltriethoxysilane (MTES) system prepared with a B/Si ratio of 0.5. This study showed that poly(borosiloxanes) are promising materials for the oxidation protection of carbon fibers, and consequently for thermal protection systems.

Abstract: Metal particles were embedded in a silicon carbonitride (SiCN) matrix, derived from the commercially available polysilazane Ceraset®. Metal powders, such as Fe, Mn, Co, Ni, were mixed and milled with pre-cross-linked polysilazane and subsequent pyrolysis. The metals act as active fillers to increase the density of composite. The phases and microstructures of metal/ceramic composites were studied using XRD, SEM and EDS. The magnetic property was measured with Magnetic Property Measurement System at –196oC and 27oC. The results show that there were two main domains in composites, one was metal-rich domain and another was metal-poor domain. The reaction compound between metal and matrix had great effect on the magnetic properties of composites, filled with different metals.

Abstract: The metal elements, such as Fe, Mn, Co, Ni, Ni-Mn, Co-Mn and Fe-Mn, were mixed and milled with pre-cross-linked polysilazane Ceraset® and subsequent pyrolysis. The metals act as active fillers to increase the density of composite. The phases and microstructures of metal/ceramic composites were studied using XRD, SEM and EDS, and the magnetic property was measured with Magnetic Property Measurement System at –196oC. The results show that there are two main domains in composites, one is metal-rich domain and another is metal-poor domain. The density of composite is larger than that of polymer-derived SiCN ceramic, but the hardness varies little. The compound generated by the reaction between metal and matrix has great effect on the magnetic properties of composites, which are filled with different metals.

Abstract: Microflaws were detected on the cross-section of polymer-derived silicon carbide fibers and their formation mechanism was studied by varying the curing degree and the firing rate. The results show that microflaws decrease in size with increase of the curing degree due to an increased ceramic residue. The results also show that microflaws decrease in size with decrease of the firing rate. No microflaws are detectable when the firing rate is as low as 10K/h. This indicates that the microflaws are the main channels of evolution gases and the pressure of these gases leads to their formation and propagation. So a high curing degree and a low firing rate are both preferred in the preparation of dense silicon carbide fibers.

Abstract: Polymer derived ceramic composites have been developed for SOFC seals. The formation and properties of the ceramic composite derived from a mixture with polysiloxane and filler were investigated. In the presence of filler materials such as ZrO2 and AlCo, the thermal properties of the ceramic composite could be controlled. The mixtures with polymethylsiloxane and fillers were prepared and their conversions to ceramic composites by annealing in N2 atmosphere were studied. The microcrystalline composites with filler embedded in a silicon-boron-oxycarbide glass matrix were formed. The thermal expansion behaviors were measured and discussed.

Abstract: Processing techniques for producing microcellular silicon carbide, mullite, and cordierite ceramics with cell densities greater than 108 cells/cm3 and cells smaller than 30 μm have been developed by a reaction method that incorporates a polysiloxane and reactive fillers. The techniques developed in this study offer substantial flexibility for producing microcellular ceramics whereby cell size, cell density, degree of interconnectivity, composition, and porosity can all be effectively controlled. It is demonstrated that the adjustment of filler composition enables the possibility of tailoring the composition and properties of the microcellular ceramics. The present results suggest that the proposed novel processing techniques are suitable for the manufacture of microcellular ceramics with high morphological uniformity.