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Journal Title
Journal of the American Ceramic Society
ISSN
0002-7820
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Item-typ:Veröffentlichung, High surface area SiC(O)‐based ceramic by pyrolysis of poly (ethylene glycol) methacrylate‐modified polycarbosilane(The American Ceramic Society, 2019-06-18); ; ; ; In the present work, a high surface area SiC(O)-based ceramic powder was synthesized upon thermal transformation of a polymer-derived macromolecular precursor, which was obtained by the chemical modification of a allylhyldrido polycarbosilane with poly(ethylene glycol) methaacrylate under argon environment. The pyrolysis of developed precursor led to the formation of amorphous and high surface area SiC(O)-based ceramic powder with in situ generated micro/meso-porosity. The specific surface area of the obtained powders depends on the processing temperature. It decreases from 363 to 122 m2/g as the pyrolysis temperature increases from 600 to 1200°C, respectively. Furthermore the promising samples were fabricated using pressing technique, which led to crack-free SiC(O) monoliths on subsquent heat treatment. The present study also emphasizes the potential of produced SiC(O) ceramic powder to support NiO catalyst. The impregnation method were used to produce high surface area NiO@SiC(O) ceramic powder (NiO as a catalyst; SiC(O) as a catalyst support) for further catalytic applications. Interestingly, the distribution of the NiO was shown to strongly depend on the oxygen content present in the SiC(O) matrix. Thus, larger oxygen contents induce homogeneously distributed flower-like NiO catalyst onto SiC(O).Wissenschaftlicher ArtikelBand:102Heft:12159 104 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Obtaining complex‐shaped oxide ceramic composites via ionotropic gelation(Wiley, 2018-08-23); ; ; In this communication, we present a new processing method for obtaining oxide ceramic composites based on the ionotropic gelation technique. Nextel 610 fiber fabrics were infiltrated by an alumina-zirconia suspension with a total solid content of 50 vol.% and alginate as the binder. Subsequently, the suspension was slowly cross-linked by adding Al3+ cations and transferred to a gel state. The gelled fabric layers could be easily cut, stacked and shaped, as well as joined to other ceramic materials and composites. Furthermore, the fiber content could be adjusted by pressing the layers together. In summary, the composites produced with this technique presented a very good fiber bundle infiltration, matrix with fine porosity and excellent mechanical properties. Nextel 610/alumina-zirconia composites sintered at 1200°C for 1 h showed bending strength of 306 MPa, interlaminar shear strength of 9.8 MPa and nominal fracture toughness of 13.6 MPa m0.5.Wissenschaftlicher ArtikelBand:102Heft:1122 112 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Thermal exposure effects on the long‐term behavior of a mullite fiber at high temperatureThe behavior of an oxide fiber at elevated temperatures was analyzed before and after thermal exposures. The material studied was a mullite fiber developed for high-temperature applications, CeraFib 75. Heat treatments were performed at temperatures ranging from 1200°C to 1400°C for 25 hours. Quantitative high-temperature X-ray analysis and creep tests at 1200°C were carried out to analyze the effect of previous heat treatment on the thermal stability of the fibers. The as-received fibers presented a metastable microstructure of mullite grains with traces of alumina. Starting at 1200°C, grain growth and phase transformations occurred, including the initial formation of mullite, followed by the dissociation of the previous alumina-rich mullite phase. The observed transformations are continuous and occur until the mullite phase reaches a state near the stoichiometric 3/2 mullite. Only the fibers previously heat treated at 1400°C did not show further changes when exposed again to 1200°C. Overall, the heat treatments increased the fiber stability and creep resistance but reduced the tensile strength. Changes observed in the creep strain vs. time curves of the fibers were related to the observed microstructural transformations. Based on these results, the chemical composition of the stable mullite fiber is suggested.Wissenschaftlicher ArtikelBand:100Heft:9110 108 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Thermal behavior of mullite between 4 K and 1320 KThe evolution of metric parameters of 2:1 and 3:2 mullites have been measured between 4 K and 1320 K using neutron and X‐ray powder diffraction. Negative thermal expansion was observed at low temperature for the a‐cell parameter and consequently for the cell‐volume, which is more pronounced for 2:1 mullite than those for 3:2 mullite. Each parameter is simulated using Grüneisen first‐order approximation for the zero pressure equation of state at 0 K, where the vibrational energy was calculated using microscopic approach. While the b‐ and c‐cell parameters require only one Debye term, a second Debye spectrum with negative Grüneisen parameter was required to fit the a‐cell parameter as well as the cell volume. At 4 K, 300 K and 1320 K the model, respectively, calculates the volume thermal expansion coefficients of 0.09x10−6 K−1, 9x10−6 K−1, and 17.3x10−6 K−1 for 2:1 mullite, and 0.09x10−6 K−1, 8.7x10−6 K−1, and 17.3x10−6 K−1 for 3:2 mullite. Temperature‐dependent Raman spectra and phonon density of states hint for the possible microscopic sources of the cell contraction at low temperature. A simple polynomial approach is presented to calculate the elastic stiffness coefficients of the 3:2 mullite, which are not available from experiments.Wissenschaftlicher Artikel292 544 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Strong and super tough: Layered ceramic-polymer composites with bio-inspired morphology(Wiley, 2018); ; ; ; Bio-inspired layered ceramic-polymer composites with high strength and toughness were prepared from sintered aluminum oxide ceramic sheets and cationically curing epoxy resins toughened with poly(ε-caprolactone) (PCL). The architecture of the composite is inspired by nacre but is arranged on a larger scale. Ceramic sheets with a nominal thickness of 250 μm were assembled into composite plates by adhesive layers with a nominal thickness of 20 μm. Before the manufacturing of the composites, the stress-strain properties of the polymer component were tailored by the variation in the PCL content between 0 and 39 wt%. For composites with 4 and 15 ceramic layers, the bending strengths achieved 327 MPa and 376 MPa, which are higher than that of pure ceramic sheets. Moreover, composites with 15 ceramic layers show a 16 times higher toughness compared to that of the pure ceramic sheets. The results indicate that the toughness of the layered composites increases significantly with the number of layers. Inspired by the geometrical ratio of the natural sheet composite nacre, we have achieved a similar strength but a 2 times higher toughness than nacre by only adding up to 6 vol% of the polymer.Wissenschaftlicher Artikel194 267