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  • 2005-2009  (8)
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Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Rare-earth-doped Ca-α-SiAlON phosphors, with the compositions of (Ca1−3/2xREx)m/2Si12−m−nAlm+nOnN16−n (RE=Ce, Sm, and Dy, 0.5≤m=2n≤3.0), were prepared by sintering at 1700°C for 2 h under 10 atm N2. The concentration of rare earths varied from 3 to 30 at.% with respect to Ca. The photoluminescence (PL) properties were investigated as functions of the composition of the host matrix (i.e., m) and the concentration of rare earths (i.e., x). The results show that the emission properties can be optimized by tailoring m and x. The Ce3+ luminescence originating from the 4f–5d interconfigurational transitions is greatly affected by the environment surrounding the Ce3+ ions, which differs from the Sm3+ or Dy3+ luminescence arising from the 4f–4f intraconfigurational transitions. X-ray diffraction and scanning electron microscopy were used to explain the composition and concentration dependence of PL properties.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We report the preparation of nanosized silicon nitride (Si3N4) ceramics via high-energy mechanical milling and subsequent spark plasma sintering. A starting powder mixture consisting of ultrafine β-Si3N4 and sintering additives of 5-mol% Y2O3 and 2-mol% Al2O3 was prepared by high-energy mechanical milling. After milling, the powder mixture was mostly transformed into a non-equilibrium amorphous phase containing a large quantity of well-dispersed nanocrystalline β-Si3N4 particles. This powder precursor was then consolidated by spark plasma sintering at a temperature as low as 1600°C for 5 min at a heating rate of 300°C/min. The fully densified sample consisted of homogeneous nano-Si3N4 grains with an average diameter of about 70 nm, which led to noticeable high-temperature ductility and elevated hardness.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 287 (June 2005), p. 166-170 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The fabrication of dense Si3N4 nano-ceramics via a high-energy mechanical millingprocess and subsequent spark plasma sintering (SPS) was reported in this paper. A thermodynamically stable β-Si3N4 powder mixed with 5-mol% Y2O3 and 2-mol% Al2O3 was used as starting powders for high-energy mechanical milling. Milling resulted in the significant decrease of crystalline size and the amorphization of the starting powders. Based on XRD measurements, the amount of the amorphous phase and the grain sizes of the remaining crystalline silicon nitridedepended on the charge ratio. Milled powders could be SPSed at relatively low temperature. A homogenous dense silicon nitride ceramics with grain diameter of about 70 nm could be fabricated through SPS at a low temperature of 1600oC for 5 min. The significant decrease of grain size greatly increased the hardness of obtained ceramics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 352 (Aug. 2007), p. 189-192 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A commercial silicon nitride powder with sintering additives was ground by high-energymilling to reduce particle size. Nanometer sized powder was obtained. The powder was densified forshort time by spark plasma sintering to prevent grain growth. Nanometer-grained Si3N4 ceramicswere obtained. Plastic deformation of the Si3N4 nano-ceramics has been studied in compression overa wide range of strain rates and temperatures. The experimental results revealed that a transition instress exponent, n, at each temperature. The n value decreased from ~ 2 to ~ 1 with increasing appliedstress. Activation energy was also different for the two regions, decreasing from 858.2 kJ/mol in then ~ 2 region to 571.8 kJ/mol in the n ~ 1 region. Effect of sintering additives on plastic deformationwas also discussed
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 403 (Dec. 2008), p. 83-86 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: -sialon and related compounds have been long known as structural ceramics due to their excellent thermomechanical properties. In this paper, we will present the luminescence of rare earth ions (i.e., Ce3+, Eu2+, Tb3+, Yb2+) in -sialons. The emission of Eu2+ in -sialon related compounds is also summarized. The interesting luminescent properties -sialon and related compounds enable them for use as promising down-conversion phosphors in white light-emitting diodes (LEDs)
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 317-318 (Aug. 2006), p. 797-802 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Rare-earth doped Ca-α-SiAlON phosphors, with the compositions of(Ca1-3/2xREx)m/2Si12-m-nAlm+nOnN16-n (RE = Ce, Sm, Eu, Tb, Yb and Dy, 0.5 ≤ m = 2n ≤ 3.0), wereprepared by reaction at 1700oC for 2h under 10 atm N2. The concentration of rare earths varied from 3to 30 at% with respect to Ca. The photoluminescence properties of the powders were investigated atroom temperature. The results show that (i) strong visible emissions are observed in rare-earth dopedCa-α-SiAlONs; (ii) the emission properties can be optimized by tailoring the activator concentrationand the composition of the α-SiAlON host crystal; and (iii) the yellow Eu2+-doped Ca-α-SiAlONphosphors can be used in warm white LEDs
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 336-338 (Apr. 2007), p. 1001-1004 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In previous report, we succeeded in preparing dense nano-sized ceramics with the compositionof Y- α-sialon (m=1.35, n=0.675) by high-energy mechanical milling followed by spark plasma sintering.The superplastic deformation of the obtained nano-ceramics was studied in this report. A good ductility ofthe nano-sized ceramics has been confirmed, which arised from the nano-sized grains and large amount oftransient liquid phase. The effects of deformation on the phase and microstructural evolution were alsostudied. The nano-sized grains promoted the formation of elongated α-sialon grains during post-annealingat 1850oC for 3 h, which would strengthen and toughen the deformed ceramics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 317-318 (Aug. 2006), p. 629-632 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Y- α-sialon (m=1.35, n=0.675) ceramics were prepared by high-energy mechanicalmilling followed by spark plasma sintering. The milling promoted not only liquid-phase sintering,but also phase transformation from β-Si3N4 to α-sialon. Under the same holding time of 5 min,milled powder could be completely densified at 1500oC, which is about 250oC lower than thatrequired for as-received powder. The temperature where the phase transformation finished was1600oC and 1750oC for milled and as-received powder, respectively. The grain size of obtaineddense ceramics from milled powder was significantly decreased. Nano-sized dense ceramics havebeen obtained by sintering the milled powder at 1500oC for 5 min. Although 100 % α-sialon has notbeen achieved, the nano-sized ceramics can be used for superplastic deformation, taking advantageof small grain size and large amount of transient liquid phase
    Type of Medium: Electronic Resource
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