The Experts below are selected from a list of 72 Experts worldwide ranked by ideXlab platform
Ralf Riedel - One of the best experts on this subject based on the ideXlab platform.
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nano structured metal containing polymer precursors for high temperature non oxide Ceramics and ceramic fibers syntheses pyrolyses and properties
Journal of The European Ceramic Society, 2002Co-Authors: A M Tsirlin, Ralf Riedel, G I Shcherbakova, E K Florina, N A Popova, S P Gubin, E M Moroz, Edwin Kroke, M SteenAbstract:Nano-structured metal-containing ceramic polymer precursors have a potential for progress in the field of polymer-derived Ceramics. In this paper the synthesis and characterization of nano-metallopolycarbosilanes (nMPCS) and their transformation into ceramic materials are reported. The formation of metal nano-particles via fast thermolysis of metal- containing compounds in polymer solution or melt previously developed by the authors was applied to preceramic polymers. Tetrabenzyltitanium, tetrabenzylzirconium, bis(cyclopentadienil)dichloride-titanium and zirconium as well as tetrachlorides of these metals and tetrakis(diethylamino)zirconium were used for the introduction of metal nano-particles. The products were characterized by thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), differential-thermal analysis (DTA), gel-penetration (GP)-chromatography, X-ray diffraction (XRD), scanning electron microscopy (SEM) and other special analyses. The results of these studies may be useful for the fabrication of Non-Oxide ceramic fibers, interphase coatings and high temperature ceramic matrix composite (HT-CMC) matrices. Cp2ZrCl2 and Zr[N(C2H5)2]4 provided nano-particles with diameters of 2–4 nm and turned out to be the most suitable compounds for the preparation of ceramic matrices. Besides, they open a new way of oxygen-free curing. Coreless fibers were obtained from nZrPCS with up to 3 mass% of metal. Future investigations will be focused on optimization of the oligocarbosilanes used as starting materials and the development of less reactive polycarbosilane (PCS)–metal-containing compound (MCC) systems.
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progress in silicon based non oxide structural Ceramics
International Journal of Refractory Metals & Hard Materials, 1997Co-Authors: Wolfgang Dressler, Ralf RiedelAbstract:Abstract The progress in monolithic Si3N4 and SiC as well as in Si3N4/SiC-composites for structural applications is reviewed. The conventional processing including the powder synthesis, densification and microstructural design is discussed. The mechanical properties of the resulting silicon based Non-Oxide Ceramics and their industrial applications as structural components are summarized. As an alternative route to fabricate Si3N4/SiC composites the hybrid processing utilizing the thermal conversion or organosilicon precursors to amorphous and polycrystalline multicomponent materials is described. The hybrid processed Ceramics exhibit ultra-high temperature stability with respect to crystallization, oxidation and decomposition.
Jian Luo - One of the best experts on this subject based on the ideXlab platform.
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high entropy metal diborides a new class of high entropy materials and a new type of ultrahigh temperature Ceramics
Scientific Reports, 2016Co-Authors: Joshua Gild, Yuanyao Zhang, Tyler Harrington, Sicong Jiang, Matthew C Quinn, William M Mellor, Naixie Zhou, Kenneth S Vecchio, Jian LuoAbstract:Seven equimolar, five-component, metal diborides were fabricated via high-energy ball milling and spark plasma sintering. Six of them, including (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Mo0.2Nb0.2Ti0.2)B2, (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2, (Mo0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2, and (Hf0.2Zr0.2Ta0.2Cr0.2Ti0.2)B2, possess virtually one solid-solution boride phase of the hexagonal AlB2 structure. Revised Hume-Rothery size-difference factors are used to rationalize the formation of high-entropy solid solutions in these metal diborides. Greater than 92% of the theoretical densities have been generally achieved with largely uniform compositions from nanoscale to microscale. Aberration-corrected scanning transmission electron microscopy (AC STEM), with high-angle annular dark-field and annular bright-field (HAADF and ABF) imaging and nanoscale compositional mapping, has been conducted to confirm the formation of 2-D high-entropy metal layers, separated by rigid 2-D boron nets, without any detectable layered segregation along the c-axis. These materials represent a new type of ultra-high temperature Ceramics (UHTCs) as well as a new class of high-entropy materials, which not only exemplify the first high-entropy Non-Oxide Ceramics (borides) fabricated but also possess a unique non-cubic (hexagonal) and layered (quasi-2D) high-entropy crystal structure that markedly differs from all those reported in prior studies. Initial property assessments show that both the hardness and the oxidation resistance of these high-entropy metal diborides are generally higher/better than the average performances of five individual metal diborides made by identical fabrication processing.
Luis Guerra Rosa - One of the best experts on this subject based on the ideXlab platform.
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solar sintering of cordierite based Ceramics at low temperatures
Solar Energy, 2005Co-Authors: Fernando Costa A Oliveira, Nobumitsu Shohoji, Jorge Cruz Fernandes, Luis Guerra RosaAbstract:Abstract Solar furnaces allow materials processing at much higher heating and/or cooling rates compared with those in the conventional industrial and laboratory processes using electric furnaces. During the course of our recent works using solar furnace, we demonstrated usability of solar furnace for sintering-consolidation of oxide Ceramics (alumina) and Non-Oxide Ceramics (WC with Co additive) as well as for producing raw material powders including carbide and carbonitride of transition metals and silicon. Being encouraged by these earlier solar-consolidation experiment results obtained for Ceramics with relatively simple composition, we decided to continue this line of solar-sintering experiments for other industrial Ceramics with more complicated composition. In this work, two types of commercial ceramic powder mixtures, BL7 and RP7, supplied by Rauschert Portuguesa Lda, were subjected to sintering under concentrated solar beam at 950 °C for 20 min. No evidence of formation of cordierite (2MgO · 2Al 2 O 3 · 5SiO 2 ) phase was detected for the present solar sintered specimens whereas evidence of cordierite phase formation was detected for the RP7 powders heated to 950 °C in a laboratory electric furnace. As such, the present results implied that, for the preparation of consolidated cordierite using solar furnace, control over the heating rate is of critical importance as well as selection of the starting materials and setting of the processing temperature.
M Steen - One of the best experts on this subject based on the ideXlab platform.
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nano structured metal containing polymer precursors for high temperature non oxide Ceramics and ceramic fibers syntheses pyrolyses and properties
Journal of The European Ceramic Society, 2002Co-Authors: A M Tsirlin, Ralf Riedel, G I Shcherbakova, E K Florina, N A Popova, S P Gubin, E M Moroz, Edwin Kroke, M SteenAbstract:Nano-structured metal-containing ceramic polymer precursors have a potential for progress in the field of polymer-derived Ceramics. In this paper the synthesis and characterization of nano-metallopolycarbosilanes (nMPCS) and their transformation into ceramic materials are reported. The formation of metal nano-particles via fast thermolysis of metal- containing compounds in polymer solution or melt previously developed by the authors was applied to preceramic polymers. Tetrabenzyltitanium, tetrabenzylzirconium, bis(cyclopentadienil)dichloride-titanium and zirconium as well as tetrachlorides of these metals and tetrakis(diethylamino)zirconium were used for the introduction of metal nano-particles. The products were characterized by thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), differential-thermal analysis (DTA), gel-penetration (GP)-chromatography, X-ray diffraction (XRD), scanning electron microscopy (SEM) and other special analyses. The results of these studies may be useful for the fabrication of Non-Oxide ceramic fibers, interphase coatings and high temperature ceramic matrix composite (HT-CMC) matrices. Cp2ZrCl2 and Zr[N(C2H5)2]4 provided nano-particles with diameters of 2–4 nm and turned out to be the most suitable compounds for the preparation of ceramic matrices. Besides, they open a new way of oxygen-free curing. Coreless fibers were obtained from nZrPCS with up to 3 mass% of metal. Future investigations will be focused on optimization of the oligocarbosilanes used as starting materials and the development of less reactive polycarbosilane (PCS)–metal-containing compound (MCC) systems.
Juan Carlos Fariñas - One of the best experts on this subject based on the ideXlab platform.
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Microwave-assisted acid dissolution of sintered advanced Ceramics for inductively coupled plasma atomic emission spectrometry
Journal of Analytical Atomic Spectrometry, 1997Co-Authors: M. T. Larrea, I Gómez-Pinilla, Juan Carlos FariñasAbstract:The microwave-assisted acid dissolution of sintered bodies of 28 structural and electronic advanced ceramic materials was systematically evaluated. These materials included zirconia-based Ceramics, such as m-ZrO2 (a non-stabilized monoclinic zirconia), Ca-PSZ and Mg-PSZ (two partially stabilized zirconias), Y-FSZ (a fully stabilized zirconia) and Ce-TZP, Yb-TZP and Y-TZP/Ce (three tetragonal polycrystalline zirconias); alumina-based Ceramics, such as Al2O3, mullite and spinel; ceria-based Ceramics, such as CeO2-Gd2O3 (cubic ceria gadolinia); titania-based Ceramics, such as TiO2; titanate-based Ceramics, such as Al2TiO5, BaTiO3 and BIT (bismuth titanate); lead titanate-based Ceramics, such as Ca-PT, La-PT, Nd-PT, Sm-PT and Gd-PT; lead zirconate titanate-based Ceramics, such as PZT and PLZT; niobate-based Ceramics, such as PMN (lead magnesium niobate); Non-Oxide-based Ceramics, such as AlN, BN, Si3N4 and SiC; and oxide and Non-Oxide-based Ceramics, such as ? + ?-sialon (silicon aluminium oxynitride). Fifteen acids or mixtures of acids were tried, including HCl, HNO3, H2SO4, aqua regia, H2SO4-(NH4)2SO4 and mixtures of these acids with HF and with H2O2. A commercially available laboratory medium pressure microwave oven was used. Eleven optimized microwave methods were developed. These methods are simple (three stages maximum), fast (15-35 min digestion time) and mild (20-60% of the microwave oven power). By applying these microwave methods, it was possible to dissolve completely all the sintered advanced Ceramics, except SiC and ? + ?-sialon. These two Non-Oxide Ceramics were the only samples that could not be dissolved by any of the acids or mixtures of acids tested. The microwave-assisted acid dissolution was compared for ICP-AES with conventional dissolution procedures, i.e., alkali fusion in a platinum crucible and in a graphite crucible and acid decomposition by conductive heating at elevated pressure (in a PTFE bomb). It was demonstrated that microwave-assisted dissolution presents many advantages over the other procedures. When compared with acid decomposition by conductive heating in a PTFE bomb, one of the most important advantages is the drastic shortening of the digestion time from hours to minutes. When compared with alkali fusions, one of the most important advantages is the use of smaller amounts of high-purity acids, which contain less impurities than the fluxes; because of this, matrix effects and contamination from the attack reagents are lower, and consequently there is an improvement in the analytical figures of merit of ICP-AES.