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| 2. |
- Cai, Yanbing, 1972-
(author)
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Synthesis and Characterization of Nitrogen-rich Calcium α-Sialon Ceramics
- 2009
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Doctoral thesis (other academic/artistic)abstract
- In this thesis, a synthesis concept has been developed, which uses nitrogen-rich liquid phases for sintering of Ca-α-sialon ceramics. First, keeping the Si/Al ratios constant, the effects of N/O ratio on the properties and microstructure were investigated through a liquid phase sintering process. Second, nitrogen-rich Ca-α-sialon ceramics, with nominal compositions: CaxSi12-2xAl2xN16, x < 2.0, was synthesized and characterized. Third, mechanical and thermal properties of nitrogen-rich Ca-α-sialons were investigated in terms of high temperature deformation resistance,reaction mechanism, phase stability and oxidation resistance, and further correlated to their phase assemblage and microstructure observation.It has been found that increasing the N/O and Ca/Al ratio simultaneously in the materials could result in development of a microstructure with well shaped, high-aspect-ratio Ca-α-sialon grains, and an improvement in both toughness and hardness.For the nitrogen-rich Ca-α-sialon, mono-phasic α-sialon ceramics were obtained for 0.51 ≤ x ≤ 1.32. The obtained Ca-α-sialon ceramics with elongated-grain microstructures show a combination of high hardness and high fracture toughness. Compared with the oxygen-rich Ca-α-sialons, the nitrogen-rich Ca-α-sialons exhibited approximately 150 oC higher deformation onset temperatures and decent properties even after the deformation.The α-sialon phase was first observed at 1400 oC, however the phase pure Ca-α-sialon ceramics couldn’t be obtained until 1800 oC. The nitrogen-rich Ca-α-sialons were thermal stable, no phase transformation observed in the temperatures range1400-1600 oC. In general, mixed α/β-sialon showed better oxidation resistance than pure α-sialon in the low temperature range (1250-1325 oC), while α-sialons with compositions located at α/β-sialon border-line showed significant weight gains over the entire temperature range (1250-1400 oC).
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| 3. |
- Fahnestock, Jesse, 1974-, et al.
(author)
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RISEnergy: Roadmaps for energy innovation in Sweden through 2030
- 2016
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Reports (other academic/artistic)abstract
- RISE Research Institutes of Sweden is a group of research and technology organisations. RISE is a leading innovation partner working global cooperation with academia, enterprise and society to create value, growth and competitiveness through research excellence and innovation.In the area of Energy, RISE has developed innovation Roadmaps covering:Energy Efficient TransportElectric Power SystemEnergy Efficient and Smart BuildingsSustainable Thermal ProcessesEfficient Energy Use in IndustryDecarbonisation of Basic IndustriesThese Roadmaps describe development pathways for technologies, non-technical elements (market design, user behaviours, policies, etc.) and key actors that deliver on a plausible, desirable vision for each respective innovation area in 2030. These Roadmaps are intended to support RISE’s strategic planning and development, but should be relevant reading for anyone interested in energy innovation in Sweden.
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| 4. |
- Gustafsson, Stefan, 1976, et al.
(author)
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Alumina/silicon carbide composites fabricated via in situ synthesis of nano-sized SiC particles
- 2009
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 35:3, s. 1293-1296
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Journal article (peer-reviewed)abstract
- Alumina/silicon carbide composites have been fabricated by a new technique involving the in situ synthesis of nano-sized SiC particles. A mixture of alumina powder and silicon carbide precursors was prepared in an aqueous suspension. Green bodies were formed by cold isostatic pressing of granules obtained by freeze granulation, and pressureless sintered at 1750 °C for 4 h in an argon atmosphere. Mullite (10-20 vol%) formed in addition to SiC during sintering. The SiC particles were located predominantly to the interior of the mullite and alumina matrix grains. © 2008 Elsevier Ltd and Techna Group S.r.l.
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| 5. |
- Gustafsson, Stefan, 1976, et al.
(author)
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Development of microstructure during creep of polycrystalline mullite and a nanocomposite mullite/5 vol.% SiC
- 2009
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In: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 29:4, s. 539-550
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Journal article (peer-reviewed)abstract
- The microstructures of as-sintered and creep tested polycrystalline mullite and mullite reinforced with 5 vol.% nano-sized SiC particles have been characterized by scanning and transmission electron microscopy. The dislocation densities after tensile creep testing at 1300 and 1400 °C were virtually unchanged as compared to the as-sintered materials which indicates diffusion-controlled deformation. Mullite matrix grain boundaries bending around intergranular SiC particles suggest that grain boundary pinning, in addition to a reduced mullite grain size, contributed to the increased creep resistance of the mullite/5 vol.% SiC nanocomposite. Both materials showed pronounced cavitation at multi-grain junctions after creep testing at 1400 °C which suggests that unaccommodated grain boundary sliding, facilitated by softening of the intergranular glass, occurred at this temperature. This is consistent with the higher stress exponents at 1400 °C. © 2008 Elsevier Ltd. All rights reserved.
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| 6. |
- Lyckfeldt, Ola, et al.
(author)
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Stabilization of alumina with polyelectrolyte and comb copolymer in solvent mixtures of water and alcohols
- 2009
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In: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 29:6, s. 1069-1076
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Journal article (peer-reviewed)abstract
- Solvent mixtures of water and ethanol and water and isopropanol have been evaluated for processing of concentrated alumina suspensions. The addition of alcohols may increase the long-term stability of suspensions with soluble ceramic species such as magnesia, which is added as a sintering aid. A poly(acrylic acid) and a hydrophilic comb copolymer were used as dispersants for the different solvent mixtures. The aim was to compare the stabilization efficiency at normal processing conditions, pH 9-10, through rheological measurements and to develop a robust system including magnesia with long-term stability. The electrostatic stabilization of the dispersants in the different solvent mixtures was studied by zeta potential measurements. Highly negative zeta potentials were observed for the poly(acrylic acid) at pH 9-10 in the solvent mixtures. A charge contribution was also seen from the adsorbed comb copolymer, however smaller than for the poly(acrylic acid). Low viscosity was obtained for suspensions stabilized with poly(acrylic acid) in solvent mixtures with either 25 vol% ethanol or isopropanol. Higher alcohol to water ratio led to flocculation of the suspension when poly(acrylic acid) was used as dispersant. Alumina suspensions with added magnesia in isopropanol:water 25:75 and poly(acrylic acid) as dispersant showed long-term stability. The viscosity remained almost constant during 4 days of aging. Suspensions stabilized with the comb copolymer dispersant gave stable systems with ethanol and isopropanol concentrations between 25 and 75 vol%. The superior dispersing efficiency of the comb copolymer at alcohol contents above 25 vol% was believed to originate from steric stabilization in combination with low effective particle size, giving low viscosity through lower apparent solid contents of the suspension. © 2008 Elsevier Ltd. All rights reserved.
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| 7. |
- Lööf, Jesper, 1977-
(author)
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Calcium-Aluminate as Biomaterial : Synthesis, Design and Evaluation
- 2008
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Doctoral thesis (other academic/artistic)abstract
- In this thesis different aspects of calcium-aluminate (CA) as biomaterial are presented. Calcium aluminate is a chemically bonded ceramic with inherent properties making it suitable for use as biomaterial in some applications. In this thesis the emphasis is put on the basic chemical, physical and mechanical properties that may be achieved using the CA system as well as synthesis of the CA raw material. The basis for using CA in any application is the synthesis of the raw material. Different synthesis routes for producing CA are presented with focus on high temperature routes and the micro-structural and phase development during synthesis. As a base for further understanding of the CA properties a thorough outline of the reaction chemistry for CA is presented also including a description of how the reactions may be controlled and how formulations can be designed. The surface reactions of CA when subjected to simulated body fluid showed that CA is in vitro bioactive. An in vivo study in teeth also indicates that CA produces apatite at the tooth material interface. Dental materials are subjected to a harsh environment in the mouth with high mechanical forces, erosion and thermal changes. Also the demands on precise handling characteristics are high. For these reasons the in vitro evaluation of physical and mechanical properties are important. In this work several mechanical and physical properties of Ca-based formulations for dental applications has been tested using different methods. Some attention is also put on the specific characteristics of CA and the difficulties that arise when new material classes needs to be tested according to consensus standard methods. Finally studies on a CA-based formulation intended for Vertebroplasty is presented. The studies include basic mechanical properties as well as testing the material in an in vitro model utilising synthetic cancellous bone.
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| 9. |
- Stiernstedt, Johanna, 1974, et al.
(author)
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Co-sintering of Solid Oxide Fuel Cells made by Aqueous Tape Casting
- 2012
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In: Proceedings of the 10th European SOFC Forum 2012.
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Conference paper (peer-reviewed)abstract
- Solid Oxide Fuel Cells (SOFC) are typically produced using organic solvent tape casting of one layer (electrolyte, anode or cathode) followed by deposition of the other layers by complex methods such as physical vapour deposition. Our aim is instead to use aqueous tape casting, followed by co-sintering. These are less costly processes, which causes less CO2-emissions, but co-sintering is a critical step. Both shrinkage and thermal expansion must be matched, and of course also the sintering temperature.Using water-based tape casting we have demonstrated co-sintering of NiO/YSZ-anode with 30% porosity and dense YSZ-electrolyte, in planar and tubular shapes. We have also shown that tape casting is a suitable prototype method for tubes. On-going work aims at increasing the porosity and decreasing the working temperature of the cell.
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| 10. |
- Stiernstedt, Johanna, 1974, et al.
(author)
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Environmental and Quality Analysis of Aqueous Tape Casting
- 2011
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Book (other academic/artistic)abstract
- Ceramic tapes are traditionally produced by tape casting using organic solvents. The use of organic solvents has been questioned due to health, environmental and fire hazard risks. The use of water-based tape casting can reduce these problems. This study contains an environmental assessment of ceramic tapes in a life cycle perspective. Two tape casting techniques, using different solvents during the tape casting, are analyzed from cradle to grave, ie, from raw material production, manufacturing, application and recycling. The functional unit was defined as tape with 1000 gram of alumina content. Tape casting with water based solvent was compared to tape casting with hydrocarbon based solvent. In principal, only differing processes were examined. There are also quality issues associated with water based tape casting: the drying is slower and can cause cracking, air bubbles can be entrapped, and in some cases there can be problems with wetting. These problems can be handled by controlling the colloidal and rheological properties and using a system with high solids loading. In conclusion the results show that water based tape casting gives tapes of high quality and that a lower environmental impact is possible compared to solvent based tape casting. It is further shown that the sintering of the green tape, which follows the tape casting, is probably the process with most climate impact in the life cycle of a ceramic tape.
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