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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 30 (1990), S. 211-214 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Determination of adduction contant ; Enthalpies and entropies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The adduction constants for the following eight binary systems were measured by gas liquid chromatography, at different temperatures: tetrachloromethane/p-xylene, tetrachloromethane/pseudocumene, chloroform/p-xylene, chloroform/pseudocumene, chloroform/aniline, m-methylphenol/aniline, o-methylphenol/aniline, and o-chlorophenol/aniline. The relationships between the adduction constant and temperature were used to fit the enthalpies and entropies of adduct formation.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 449-452 (Mar. 2004), p. 1017-1020 
    ISSN: 1662-9752
    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: Hydrogenated amorphous silicon (a-Si:H) has attracted much attention in various electronicsapplications such as thin films transistors, color sensors, and solar cells[1]. However, many devicesmade from a-S:H are observed to degrade with time, which is commonly associated with hydrogenrelated defects [1]. It has been observed that, by increasing the hydrogen dilution in the precursorgas used in the plasma, one can obtain hydrogenated nanocrystalline silicon (nc-Si:H), whichcontains crystalline grains embedded in an amorphous silicon matrix. These materials can bedeposited by plasma enhanced chemical vapor deposition (PECVD) techniques. The presence of nc-Si in a-Si:H changes the optical and electronic properties of the material [2]. Nc-Si:H thin filmshave exhibited unique and useful characteristics. In particular, nc-Si:H thin films exhibitphotoluminescence (PL) and electroluminescence (EL) behavior at room temperature [3].The dilution of SiH4 with hydrogen has been recognized as an effective method for thetransition from the amorphous to the nanocrystalline phase in the nc-Si:H thin films. The presenceof hydrogen on the growing surface gives termination of dangling bonds and also an extraction ofSiH3 radicals [4]. The supply balance between the hydrogen and SiH3 radicals is a key factor indetermining the film structure [4]. The presence of excess hydrogen or hydrogen-bonded Si radicals(SiHn = 1, 2, 3) in the gas mixture passivates the dangling bonds on the growing surface and etchesthe growing surface. Etching eliminates part of the disordered structure and enhances the crystallinephase because the crystalline structure is the lowest energy configuration.In this paper, we report the study of the effects of the hydrogen species on the nanostructuresand optical properties of nc-Si:H thin films prepared by PECVD techniques
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  • 3
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The microstructure variation ofβ-Al2O3 with different compositions during hot-pressing and its effect on ionic conductivity were studied. It is found that, besides the phase composition, the conductivity of hot-pressedβ-Al2O3 materials of the same composition is also related to the measurement direction, microstructure and density. The resistivity in the direction parallel to hot-pressing is about three times higher than that perpendicular to the hot pressing. The pores in the material are particularly detrimental to the ionic conduction. It was observed that the shape of complex impedance plane spectrum changed with measurement temperature and such change was affected by chemical composition and sample preparation condition. This phenomenon is explained successfully with the help of the ideal equivalent circuit of polycrystalline fast ionic conductor and the results of the conductivity measurement of hot-pressedβ-Al2O3.
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  • 4
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Ultrafine zirconia powders were prepared by a coprecipitation and spray-drying method. Agglomerates may be fragmented or present in green bodies after compaction. The effect of agglomerates on sintering and microstructural development was studied and it was found that the agglomerate content in compacts was a major factor affecting the microstructure development and the sintered densities. The interaction between agglomerates themselves, and between agglomerates and the primary particle matrix is discussed. It is argued that the hard agglomerates in the powder from the water-washed coprecipitates are formed by oxobridging between non-bridging hydroxyl groups present in the zirconium hydroxide structures due to the effect of hydrogen bonding in the aqueous system. The substitution of organic -OR groups for the non-bridging hydroxyl groups removes this hydrogen-bonding effect between the zirconium hydroxide units and thus eliminates the cause of agglomeration.
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  • 5
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The stability of closed pores in two and three dimensions has been discussed and it is found that the stability of pores in two dimension can be determined mathematically from their particle coordination number and dihedral angle; while those in three dimension can be approximately determined by a spherical pore model. This model is set up by first excluding the effect of interface tension, so the pore was supposed to be spherical, and then the tensile stress arising from the interface tension was allowed to act on this hypothesized spherical pore. On the basis of the spherical pore model, pore microstructure models for real powder compacts were set up and the densification equations for the intermediate and final stages of sintering were derived. The criterion for pore shrinkage, and the effect of pore size distribution and green density were discussed according to the derived equations. The densification equations for pressureless solid state sintering can be easily extended to describe the densification behaviour during hot-pressing or hot-isostatic-pressing. Densification characteristics in liquid state sintering were also considered from the result of solid state sintering.
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  • 6
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Dense Al2O3 particle-Y-TZP matrix (Al2O3〈40 vol%) composite was prepared by pressureless sintering at 1550°C. Composites with 10–30 vol% Al2O3 particles showed enhanced fracture toughness, bending strength and Vicker's hardness as compared to single-phase Y-TZP. The highest strength (1150 MPa) and highest toughness (12.4 MPa m1/2) were obtained for the composite containing 10 vol% Al2O3. It was found that, in addition to the contribution by the crack-deflection effect, the enhanced phase transformation from tetragonal to monoclinic during fracture was the main toughening mechanism in operation in the composites.
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  • 7
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Spherical basic zirconium sulphate particles were prepared by homogeneous precipitation in mixed solutions of zirconium sulphate and urea. Values of [SO 4 2− ]/[Zr4+] and [urea]/[Zr4+] in starting mixed solutions and cooling rate may affect the formation of spherical particles. Complexes such as [Zr(OH)n]4−n could prevent the formation and thus lead to gel precipitation. In addition, spherical particles could only be obtained in the presence of SO 4 2− ; for NO3− and Cl−, only gel precipitation occurred.
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  • 8
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Superfine Y-TZP powders of high purity were prepared by using clean-room facilities. The effects of several kinds of minute or small amounts of additives on the densification and microstructural development of the Y-TZP powder were investigated. It was found that ≤1 wt% ferric or calcium oxides did not affect the densification of the Y-TZP powder compacts, while the addition of sodium oxides retarded the densification and that of copper oxide accelerated it, and these effects are most obvious at an additive level of 1 wt%. The retardation of the densification by sodium oxide was found to result from the agglomeration effect of the powder, and the formation of the eutectic liquid phase between zirconia and copper oxides promoted the densification and grain growth during sintering of copper oxide-doped powder. In addition, sodium and copper oxides both destabilize the tetragonal Y-TZP and lead to the formation of monoclinic phase.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 15 (1996), S. 928-930 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An experimental method is proposed for measuring the refractive indices of anisotropic crystals. The results of the first measurements are in good agreement with those of other methods.
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