| 1. |
- Dahl, P., et al.
(författare)
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Densification and properties of zirconia prepared by three different sintering techniques
- 2007
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 33:8, s. 1603-1610
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Tidskriftsartikel (refereegranskat)abstract
- Densification of nanocrystalline yttria stabilized zirconia (YSZ) powder with 8 mol% Y2O3, prepared by a glycine/nitrate smoldering combustion method, was investigated by spark plasma sintering, hot pressing and conventional sintering. The spark plasma sintering technique was shown to be superior to the other methods giving dense materials (>= 96%) with uniform morphology at lower temperatures and shorter sintering time. The grain size of the materials was 0.21, 0.37 and 12 mu m after spark plasma sintering, hot pressing and conventional sintering, respectively. Total electrical conductivity of the materials showed no clear correlation with the grain size, but the activation energy for spark plasma sintered materials was slightly higher than for materials prepared by the two other densification methods. The hardness, measured by the Vickers indentation method, was found to be independent on grain size while fracture toughness, derived by the indentation method, was slightly decreasing with increasing grain size.
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| 2. |
- Gustafsson, Stefan, 1976, et al.
(författare)
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Alumina/silicon carbide composites fabricated via in situ synthesis of nano-sized SiC particles
- 2009
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 35:3, s. 1293-1296
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Kese, K. O., et al.
(författare)
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Effect of ageing on the electrical resistivities of (Ba0.69Pb0.31)Ti-3 PTCR ceramic thermistors
- 2005
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 31:3, s. 375-378
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of (Ba0.69Pb0.31)TiO3 PTCR ceramic thermistors aged at temperatures of 175, 200, 250 and 300 degrees C, respectively, were measured. When the samples were aged at temperatures of 175 and 200 degrees C, room-temperature resistivity decreased at the initial ageing stage, and then increased with the ageing time. The samples displayed a monotonous rise of the room-temperature resistivity when the ageing treatments were performed at 250 and 300 degrees C. PTCR effects showed different characteristics after different ageing treatments. These ageing characteristics were analyzed by considering interior oxidation and reduction reactions.
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| 4. |
- Li, Z. C., et al.
(författare)
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Synthesis and characterization of nanostructured Bi2O3-doped cerium oxides fabricated by PVA polymerization process
- 2008
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 34:8, s. 1949-1953
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Tidskriftsartikel (refereegranskat)abstract
- Bi2O3-doped ceria oxygen-ion conductors were prepared by a wet chemical synthesis method, which is per-formed by polymerization of polyvinyl-alcohol (PVA). The experiments showed that Bi2O3-CeO2 solid solution with 9.2 nm grains and pure fluorite type phase can be synthesized at a calcination temperature of 500 degrees C by PVA polymerization process. X-ray analysis revealed that high density narrostructured bulks could be prepared at a sintering temperature of 900 degrees C, and these bulk samples with an average grain size less than 70 nm could effectively be obtained at various heating rates during sintering. Oxygen-ion conductivity increased with the increase of dopant concentrations between 5 mol% and 15 mol% in present study.
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| 5. |
- Goel, Ashutosh, et al.
(författare)
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Structure and crystallization behaviour of some MgSiO3-based glasses
- 2009
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842. ; 35:4, s. 1529-1538
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Tidskriftsartikel (refereegranskat)abstract
- We report on the structure and crystallization behaviour of four enstatite based glasses. Two glasses with nominal compositions of Y0.125Mg0.875Si0.875B0.125O3 and Y0.125Mg0.725Ba0.15Si0.875B0.125O3 were prepared as parent glasses while the other two glasses were derived by the addition of 8 wt.% Al2O3 to the parent glass compositions, respectively. Structural features of the glasses were accessed by Fourier transform infrared spectroscopy (FTIR). Non-isothermal crystallization kinetics and thermal stability of Al2O3-free glasses were studied using differential scanning calorimetry (DSC). It has been shown that these glasses exhibit higher activation energy of viscous flow and are prone to surface crystallization. Activation energy of crystallization decreases with the addition of BaO in the glasses. Crystallization behaviour of all the experimental glasses in the temperature range of 800–1000 °C was followed by X-ray diffraction (XRD) and FTIR. Clinoenstatite and orthoenstatite were the major crystalline phases in the BaO-free glass-ceramics while BaO-containing compositions featured the early formation and stabilization of protoenstatite.
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| 6. |
- Gustafsson, Stefan, 1976, et al.
(författare)
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Pressureless Sintered Al2O3-SiC Nanocomposites
- 2008
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842. ; 34:7, s. 1609-1615
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Tidskriftsartikel (refereegranskat)abstract
- Al2O3 + 5 vol% SiC composite ceramics were prepared via a conventional powder processing route followed by pressureless sintering. Commercially available Al2O3 and SiC powders were milled together in an aqueous suspension. The slurry was freeze granulated, and green bodies were obtained by cold isostatic pressing of the granules. Pressureless sintering was carried out in a nitrogen atmosphere at 1750 and 1780 °C. Near full density (>99%) was achieved at 1780 °C. Densification at the lower sintering temperature was promoted by smaller additions of MgO. Vickers hardness and indentation fracture toughness varied around 18 GPa and 2.3 MPa m1/2 after sintering at 1780 °C. Transmission electron microscopy revealed that the SiC particles were located predominantly to the interior of the matrix grains and well distributed throughout the composite microstructures. The intragranular particles had sizes in the range 50-200 nm while the intergranular particles were larger, typically 200-500 nm in diameter.
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| 7. |
- Hylander, Kristoffer, et al.
(författare)
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The conservation ecology of cryptogams - editoral
- 2007
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Ingår i: Biological Conservation. - : Elsevier BV. - 0006-3207 .- 1873-2917. ; 135:3, s. 311-314
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A conference entitled 'Conservation Ecology of Cryptogams' was held in Bispgården, Sweden in November, 2005 to increase awareness about the amount of ecological research on cryptogams and the inclusion of these organisms in practical conservation. The conference brought together researchers in the field and helped in collecting findings on the ecology of cryptogams. The topics discussed at the event covered theoretical developments in ecology and the links between these areas of research and their application in applied conservation. It was also helpful in reducing the gap between leading researchers and conservation professionals and covered a wide range of topics on significant ecological research on cryptogams. Participants at the conference also revealed that many general ecological theories can be applied to cryptogams and specific theories, models, and applications need to be developed for conservation of cryptogams.
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