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- Ali, Sharafat, 1976-, et al.
(författare)
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A cubic calcium oxynitrido-silicate, Ca2.89Si2N1.76O4.24
- 2011
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Ingår i: Acta Crystallographica Section E. - 1600-5368. ; 67
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Tidskriftsartikel (refereegranskat)abstract
- The title compound, tricalcium oxynitride silicate, withcomposition Ca3-xSi2N2-2xO4+2x (x ’ 0.12), is a perovskiterelatedcalcium oxynitrido silicate containing isolated oxynitridosilicate 12-rings. The N atoms are statistically disorderedwith O atoms (occupancy ratio N:O = 0.88:0.12) and occupythe bridging positions in the 12 ring oxynitrido silicate anion,while the remaining O atoms are located at the terminalpositions of the Si(O,N)4 tetrahedra. The majority of the Ca2+cations fill the channels along [100] in the packing of the 12-ring anions. The rest of these cations are located at severalpositions, with partial occupancy, in channels along the bodydiagonals.
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- Cai, Yanbing, et al.
(författare)
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Sialon Ceramics Prepared by Using CaH2 as a Sintering Additive
- 2008
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Ingår i: Journal of the American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 91:9, s. 2997-3004
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Tidskriftsartikel (refereegranskat)abstract
- In developing elongated a-sialon grains, a nitrogen-rich liquidphase sintering method was introduced by using CaH2 as asintering aid, so as to vary the N/O ratio of the liquid phaseformed in the sintering process while keeping the Si/Al ratiosconstant. With increasing addition the phase contents changedfrom single b-sialon to dual b/a-sialons and to single Ca-a-sialon.At low N/O ratios the microstructures contained mainlyequiaxed b-sialon grains, and at high N/O ratios well facetedelongated Ca-a-sialon grains. The improved toughness(KIC57.8 MPa .m1/2) and hardness (HV10517.5 GPa) propertiescan be attributed to the formation of interlocked microstructures.High-temperature compressive deformation testsindicated that the deformation onset temperature is determinedmainly by the Si/Al and N/O ratios, whereas the deformationrate is affected by the microstructure, i.e., the morphology andamounts of elongated a-sialon grains and residual glass phase,especially for the sialons with low N/O ratios.
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- Cai, Yanbing, 1972-
(författare)
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Synthesis and Characterization of Nitrogen-rich Calcium α-Sialon Ceramics
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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