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  • 1
    Electronic Resource
    Electronic Resource
    Electrical Properties of Mn-Co-Ni Oxides Prepared at Low Temperatures (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Advanced materials research Vol. 29-30 (Nov. 2007), p. 359-362 
    Details
    ISSN: 1662-8985
    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: Changes in crystal phase and electrical properties of oxides composed of Mn, Co, and Niwith the molar ratios of 5:2:1 and 3:3:1 were investigated. Starting oxides were fired from 250°C to800°C, then maintained at prescribed temperatures for 3 h in air. In the 5:2:1 specimen, a monophaseconsisting of a cubic spinel oxide that is important to electrical conductivity was obtained at firingtemperature of 800°C. In the 3:3:1 specimen, the monophase was obtained at temperatures rangingfrom 600°C to 800°C. Electrical resistance decreased exponentially with increasing temperature forall specimens fired at temperatures ranging from 250°C to 800°C, indicating that the oxides haveintrinsic thermistor characteristics with negative temperature coefficient (NTC). The temperaturedependence of the thermistor constant (B value) necessary for practical application was considered tobe related to the existence ratio of cubic spinel-type and ilmenite-type structures and the latticeconstant of the cubic spinel-type structure. The electrical conduction was stabilized by annealing atprescribed temperatures for more than 720 minutes
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/40/transtech_doi~10.4028%252Fwww.scientific.net%252FAMR.29-30.359.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Electrical Properties of AlN-SiC Ceramics (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 317-318 (Aug. 2006), p. 641-644 
    Details
    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: AlN-SiC ceramics with 0 to 75 mol% of AlN were fabricated through pressurelesssintering of very fine AlN and SiC. Powder compacts with different amounts of AlN were fired at2000°C for 1 h in Argon gas flow using an induction-heating furnace. The microstructure andphases present in the products were evaluated using SEM and XRD. The AlN-SiC ceramics had aporous structure with 30% porosity, and the grain size was increased with the addition of AlN. XRDanalysis showed that 2H was a main phase in all samples, though 3C and 6H phases were found in25 mol%AlN-75 mol%SiC ceramic. The electrical properties of the AlN-SiC ceramics wereevaluated at various temperatures ranging from room temperature to 300°C. The electricalconductivity of the AlN-SiC ceramics depended on the amount of AlN and on the temperature. The75 mol%AlN-SiC ceramic had higher electrical resistance, though the other samples were electricalconductors. The highest electrical conductivity was obtained with the 25 mol% AlN composition,which was 7 S/m at room temperature and 30 S/m at 300°C. The Seebeck coefficient for theAlN-SiC ceramics increased with rising temperatures. The AlN-SiC ceramics with 50 mol%AlNhad the highest Seebeck coefficient of 220 2V/K at 300°C
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/51/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.317-318.641.pdf
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  • 3
    Electronic Resource
    Electronic Resource
    Electrically Conductive CNT-Dispersed Silicon Nitride Ceramics (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    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: Carbon nanotube (CNT)-dispersed Si3N4 ceramics with electrical conductivity were developed based on the lower temperature densification technique, in which the key point is the addition of both TiO2 and AlN as well as Y2O3 and Al2O3 as sintering aids. This new ceramic with a small amount of CNTs exhibits very high electrical conductivity in addition to high strength and toughness. Since Si3N4 ceramics with Y2O3–Al2O3–TiO2–AlN were originally used as a wear material, electrically conductive Si3N4 ceramics are expected to be applied for high-performance static-electricity-free bearings for aerospace and other high-performance components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00539.x
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  • 4
    Electronic Resource
    Electronic Resource
    Formation Mechanism of Nano AlN Powder by Gas-Reduction-Nitridation (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 317-318 (Aug. 2006), p. 215-218 
    Details
    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: AlN powders were synthesized by gas-reduction- nitridation of γ-Al2O3 powders usingNH3 and C3H8 as reactant gases. AlN was identified from the products that synthesized at1100-1400 oC for 120 min in the NH3-C3H8 gas flow, and it was confirmed that AlN can be easilyfabricated by the gas-reduction-nitridation of γ-Al2O3. The products synthesized at 1100oC for120min contained unreacted γ-Al2O3. By the 27A1 MAS NMR spectra, Al-N bonding in the productincreased with an increase in the nitridation ratio of the tetrahedral AlO4 shoulder which decreasedprior to that of the octahedral AlO6 shoulder. It seems that γ-Al2O3 was preferentially nitrided fromAlO4 rather than AlO6. AlN nano particles were easily converted directly from γ -Al2O3 at a lowtemperature because the AlO4 within γ-Al2O3was preferentially nitrided
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/51/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.317-318.215.pdf
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  • 5
    Electronic Resource
    Electronic Resource
    Control of Shrinkage during Sintering of Alumina Ceramics Based on Master Sintering Curve Theory (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 317-318 (Aug. 2006), p. 11-14 
    Details
    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 Master Sintering Curve (MSC) is quite useful for analyzing the shrinkage behavior ofceramics. It is possible to compare shrinkage behavior using MSCs that are obtained from different firingprofiles. In this study, shrinkage behavior during sintering of green bodies of several kinds of Al2O3based ceramics were evaluated, using an electric furnace equipped with a dilatometer to be controlledbased on the MSC theory. Although all of the samples shrank monotonically, shrinkage behaviordepended on the additive and heating rate. The MSC theory was applied to analyze shrinkage behavior.As a result, a different MSC could be obtained in Al2O3 with and without the addition of MgO. In thepure Al2O3, a single MSC could be obtained from shrinkage curves by firing at a heating rate of7.5-20oC/min, though the shrinkage curve at a heating rate of 3-5oC/min did not correspond with theMSC. In contrast, shrinkage curves at heating rate of 5-20oC/min were converged in the case of the MgOdoped Al2O3 to obtain a unique MSC independent of firing profile. Apparent activation energy forsintering was estimated as 555 kJ/mol in the pure Al2O3 and 880 kJ/mol in the MgO doped Al2O3. Thefiring profile to obtain a requested sintering shrinkage curve was predicted from the resultant MSC. Acomparison between the predicted and the experimental shrinkage curves, showed good consistency,thus confirming that it is possible to control shrinkage behavior using the MSC
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/51/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.317-318.11.pdf
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  • 6
    Electronic Resource
    Electronic Resource
    Improving the Microstructure of Si〈sub〉3〈/sub〉N〈sub〉4〈/sub〉-TiN Composites Using Ammonium Citrate to Disperse Raw TiO〈sub〉2〈/sub〉 Powders (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 352 (Aug. 2007), p. 115-118 
    Details
    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: Dense and homogenous Si3N4-TiN composites (5 vol% TiN) were prepared by using in situsynthesis method from Si3N4, AlN and TiO2 mixtures, containing Y2O3 and Al2O3 as sintering aids. Inthe prepared Si3N4-TiN composites, TiN grains were formed from TiO2 and AlN powders during thesintering process, in which ammonium citrate was used as a dispersant for raw TiO2 powders. Themicrostructures of the Si3N4-TiN composites with the increase of ammonium citrate wereinvestigated by scanning electron microscopy (SEM). Citrate ions modified on the surface of TiO2particles and protected the TiO2 particles in the mixed slurry to reduce the aggregations of TiO2powders, and homogenous Si3N4-TiO2-AlN composite powder was prepared for sintering. Themicrostuctures of Si3N4-TiN were developed after sintering with the uniform distribution of TiNgrains in the Si3N4 ceramics. It was found that the microstructure of Si3N4-TiN composite wasimproved significantly with 0.20 g ammonium citrate in the system, TiN grains with 0.2-0.3 μm indiameter distributed throughout Si3N4 matrix. It was a practical and useful way to improve themicrostructure of Si3N4-TiN composite without the alteration of the preparation procedure
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/55/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.352.115.pdf
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  • 7
    Electronic Resource
    Electronic Resource
    Fabrication of Electrically Conductive Si〈sub〉3〈/sub〉N〈sub〉4〈/sub〉 Ceramics by Dispersion of Carbon Nanotubes (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 403 (Dec. 2008), p. 19-22 
    Details
    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: Electrically conductive Si3N4 ceramics were fabricated by dispersion of different characteristics of carbon nanotubes (CNTs). When the sintering aid of Y2O3-Al2O3-TiO2-AlN was used for lower temperature densification, it was confirmed that CNTs existed in Si3N4 ceramics from SEM observation and SiC was not identified in XRD analysis, which means that CNTs did not react with Si3N4. Relative density and electrical conductivity of the CNT dispersed Si3N4 ceramics depended on the characteristics of CNTs. Aggregation of CNTs, which is outstanding in much thinner CNTs, should limit densification of Si3N4. CNTs were well-dispersed by beads milling in ethanol. As a result, beads milling process was confirmed to be effective in unraveling and dispersing CNTs. It was shown that better dispersion of CNTs with higher aspect ratio resulted in higher density and electrical conductivity
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/58/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.403.19.pdf
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  • 8
    Electronic Resource
    Electronic Resource
    Sintering Shrinkage Behavior of Si〈sub〉3〈/sub〉N〈sub〉4〈/sub〉 Ceramics Prepared by a Post-Reaction Sintering Technique (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 403 (Dec. 2008), p. 31-34 
    Details
    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: Post-reaction sintering is one of the fabrication processes of Si3N4 ceramics, which has received considerable attention as a cost-effective process due to the use inexpensive Si powder as a raw material. So far, many researches on the development of this method have been performed in order to improve their properties; however, the sintering shrinkage behavior, which is valuable for the optimization of the firing conditions, has not been well clarified. In this study, we focus on the post-reaction sintering of the Si-Y2O3-Al2O3 system, and investigate its sintering shrinkage behavior by dilatometery. It was found that there is no shrinkage from 1400 to 1600 °C due to grain rearrangements in the green body of the reaction-bonded Si3N4. Furthermore, the shrinkage of the reaction-bonded Si3N4 commenced at approximately 1750 °C, which is higher than the shrinkage temperature of the green body of conventional Si3N4 powder. The restriction of the shrinkage appears to result from the neck growth and strong aggregation among the reacted Si3N4 particles
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/58/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.403.31.pdf
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  • 9
    Electronic Resource
    Electronic Resource
    Sintering Shrinkage Behavior and Mechanical Properties of HfO〈sub〉2〈/sub〉-Added Si〈sub〉3〈/sub〉N〈sub〉4〈/sub〉 Ceramics (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 403 (Dec. 2008), p. 35-38 
    Details
    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: HfO2-added Si3N4 ceramics are known to exhibit excellent high-temperature strength and excellent damage characteristics because HfO2 assists the crystallization of the grain boundary phase. However, the sintering shrinkage behavior and mechanical properties of HfO2-added Si3N4 have not been well clarified so far, although it has been reported that TiO2, in which Ti is from the same group as Hf in the periodic table, enhances the densification of the Si3N4-Y2O3-Al2O3-AlN system and wear resistance due to TiN formed from TiO2 and AlN in the grain boundary. In the present study, we focus on HfO2 as the sintering aid to investigate the sintering shrinkage behavior and mechanical properties of HfO2-added Si3N4. The powder mixtures are prepared by the addition of HfO2 to the Si3N4-Y2O3-Al2O3 or Si3N4-Y2O3-Al2O3-AlN system. The sintering shrinkage curves of HfO2-added Si3N4 ceramics show rapid shrinkage at 1600°C as compared with those of the Si3N4 ceramics without HfO2.The shrinkage can be explained by the formation of SiO2-Y2O3-HfO2 derived liquid phases. Furthermore, the mechanical properties of HfO2-added Si3N4 were as excellent as those of the Si3N4 ceramics without HfO2
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/58/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.403.35.pdf
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  • 10
    Electronic Resource
    Electronic Resource
    Fabrication and Evaluation of AlN–SiC Solid Solutions with p-Type Electrical Conduction (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 403 (Dec. 2008), p. 39-42 
    Details
    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: AlN–SiC solid solutions with p-type electrical conduction were fabricated with the addition of small amounts of Al and C. Powder mixtures of AlN and SiC with small amounts of Al and C (below 10 mol%) were consolidated by spark plasma sintering (SPS) at 2000°C for 10 min under 1 atm Ar, and then heat-treated at 2200°C for 3 h in an Ar flow to afford 2H AlN–SiC solid solutions. The relative densities of the 50AlN-50SiC-Al4C3 (A50-1AC) and 50AlN-50SiC-3Al4C3 (A50-3AC) samples were about 95%, whereas that of the 75AlN-25SiC-Al4C3 (A75-1AC) sample was about 86%. X-ray diffractometry (XRD) analysis showed that the samples comprised only the 2H phase, and except in the case of the A50-3AC sample, no diffraction peaks of Al and C were observed. Although the samples without the additives (Al and C) were electrical insulators, addition of Al and C introduced p-type semiconduction. The electrical conductivities at 300°C of the A50-1AC and A50-3AC samples were about 30 and 100 S/m, respectively, whereas that of the A75-1AC sample was about 10–1 S/m. It was found that addition of Al and C brought about electrical conduction in AlN–SiC solid solutions
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/58/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.403.39.pdf
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