| 1. |
- Mangalaraja, Ramalinga Viswanathan, et al.
(författare)
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Synthesis of nanocrystalline yttria through in-situ sulphated-combustion technique
- 2009
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Ingår i: Ceramic Society of Japan. Journal. - : Ceramic Society of Japan. - 1882-0743 .- 1348-6535. ; 117:1370, s. 1065-1068
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Tidskriftsartikel (refereegranskat)abstract
- An in-situ sulphated-combustion reaction was conducted on the precursor mixture consisting of yttrium nitrate, organic fuels (urea, citric acid and glycine) and 10 mol% ammonium sulphate [(NH4)(2)SO4] at 500 degrees C. Effect of sulphate addition on yttria particles morphology has been analyzed with respect to the types of fuels. In un-sulphated combustion, the calcined yttria powders showed rectangular particle morphology and low specific surface area. Whereas in sulphated-combustion spherical shaped yttria particles were achieved for glycine fuel. In the case of citric acid fuel, yttria powders with high specific surface area [26 m(2)/g] were obtained. For all the fuels, the sulphated-combustion reaction produced nanocrystalline yttria powders and they also had primary crystallite size below 4 nm in the as prepared conditions. Upon calcination at 1100 degrees C, these powders attained mean particle size of 50 nm which was confirmed by TEM.
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| 2. |
- Jiang, Zhiwu, et al.
(författare)
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Combustion synthesis and mechanical properties of MoSi2-ZrB2-SiC ceramics
- 2018
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Ingår i: Journal of the Ceramic Society of Japan. - : Ceramic Society of Japan. - 1882-0743 .- 1348-6535. ; 126:7, s. 504-509
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Tidskriftsartikel (refereegranskat)abstract
- MoSi2ZrB2SiC ceramics were synthesized using Mo, Zr, Si and B4C powders by self-propagating high-temperature synthesis and densifying by spark plasma sintering. The effects of MoSi2 content on the combustion synthesis process, microstructure, and mechanical properties of the ceramics were investigated. The results showed that combustion synthesis is an unstable mode, spiral combustion. The Gibbs calculations and combustion temperature curves indicate there are two reactions occurring at the same time. The volume fraction of the four different phases and their relative densities were also measured and calculated. Compared to pure MoSi2, the 1.0MoSi20.2ZrB20.1SiC (M10) ceramic exhibits excellent mechanical properties with its maximum Vickers hardness and fracture toughness being 14.0 GPa and of 5.5 MPa m1/2, respectively. The hardness is in agreement with the rule of mixture. The morphology of indentation cracks reveals that the fracture toughness improves as a result of toughening mechanisms such as crack bridge, crack deflection, and microcracks.
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| 3. |
- Li, Jinfu, et al.
(författare)
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Oxidation kinetics of magnesium aluminum oxynitride-boron nitride (MgAlON-BN) composites
- 2014
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Ingår i: Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/Journal of the Ceramic Society of Japan. - : Ceramic Society of Japan. - 1882-0743. ; 122:1429, s. 829-834
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation behaviour of MgAlON-BN composite was investigated under the air atmosphere using thermogravimetry (TG), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques in the present articles. Non-isothermal experimental results indicated that the rate of oxidation can be neglected at low temperature and, with further increasing temperatures, an increase of the oxidation was observed. While BN addition promoted the oxidation above 1100 K, and the weight gain was observed to decrease due to the fast evaporation of boron oxide as the temperature was beyond 1580 K. Isothermal studies also clearly indicated the decrease of weight gain due to evaporation after a certain oxidation time. The oxidation mechanism was investigated, and the results showed the oxidation products were gamma-Al2O3 at low temperature and transformed to alpha-Al2O3 as the temperature was above 1100 degrees C. BN addition promoted the transformation from gamma-Al2O3 to alpha-Al2O3. From the isothermal oxidations, the kinetics of oxidation and evaporation were evaluated, and the overall kinetics of oxidation and evaporation were studied, and the activation energy for evaporation of B2O3 and for the oxidation of MgAlON-15 vol% BN at the later stage are 115.4 and 196.1 kJ/mol, respectively. The present paper provides a way to deal with oxidation of composites containing evaporating component.
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| 4. |
- Mangalaraja, Ramalinga Viswanathan, et al.
(författare)
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Sintering, microstructural and mechanical characterization of combustion synthesized Y2O3 and Yb3+-Y2O3
- 2009
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Ingår i: Journal of the Ceramic Society of Japan. - : Ceramic Soc of Japan. - 1882-0743 .- 1348-6535. ; 117:1371, s. 1258-1262
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Tidskriftsartikel (refereegranskat)abstract
- The present work highlights the microstructural features and mechanical properties of Y2O3 prepared with and without Yb3+ doping that processed through combustion synthesis involving various organic fuels such as urea, citric acid and glycine. Properties such as powder-now, particle packing, green density, % of shrinkage, sintered density, grain size, Vicker's microhardness (H-v) and fracture toughness (K-IC) were analyzed and compared with respect to the fuel sources. The as combusted precursors were calcined at 1100 degrees C for 4 h under oxygen atmosphere to obtain fully crystalline Y2O3 powders. Cylindrical pellets were fabricated as test specimens and sintered at 1600 degrees C for 3 h. The SEM images of the sintered yttria samples show an average grain size of < 3 mu m irrespective of the fuels. However, the mechanical properties show significant dependence on the fuels used. A maximum hardness of 6.8 +/- 0.1 and 7.0 +/- 0.1 GPa was obtained for Y2O3 and Yb3+ doped Y2O3 derived from glycine fuel. Whereas the maximum fracture toughness of 2.6 +/- 0.3 MPa m(1/2) was obtained for the samples derived from urea. The Yb3+ doping found to increase the bulk hardness of yttria from 0.2 to 0.6 GPa. The study contributes to appropriately select the fuels for obtaining high dense, mechanically stable yttria ceramics through combustion process.
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