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  • Articles  (243,984)
  • 2005-2009  (124,826)
  • 1980-1984  (80,969)
  • 1925-1929
  • Natural Sciences in General  (243,984)
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  • 1
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    Springer
    Naturwissenschaften 13 (1925), S. 619-622 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
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  • 2
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    Naturwissenschaften 13 (1925), S. 623-624 
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  • 3
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    Naturwissenschaften 13 (1925), S. 188-193 
    ISSN: 1432-1904
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    Naturwissenschaften 13 (1925), S. 198-201 
    ISSN: 1432-1904
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    Naturwissenschaften 13 (1925), S. 203-204 
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    Naturwissenschaften 13 (1925), S. 624-627 
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    Naturwissenschaften 13 (1925), S. 213-218 
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  • 8
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    Naturwissenschaften 13 (1925), S. 223-226 
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    Naturwissenschaften 13 (1925), S. 627-628 
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    Naturwissenschaften 13 (1925), S. 13-16 
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    Naturwissenschaften 13 (1925), S. 627-627 
    ISSN: 1432-1904
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  • 12
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    Naturwissenschaften 13 (1925), S. 5-10 
    ISSN: 1432-1904
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  • 13
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    Naturwissenschaften 13 (1925), S. 1-5 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Notes: Zusammenfassung Wenn wir das Gesamte überblicken, sehen wir, daß wir heute eine befriedigende theoretische Vorstellung des Kaltreckungsvorganges geben können, die in sich Elemente sowohl der älteren Gleitungstheorie, als auch der Verlagerungstheorie enthält. Damit ist nicht gesagt, daß die Probleme, die mit der Kaltreckung zusammenhängen, erledigt sind. Im Gegenteil, jetzt, nach einer vorläufig gewonnenen Übersicht, treten neue Probleme mit einer Deutlichkeit und Präzision auf, die ihre Bearbeitung aussichtsvoll erscheinen lassen. Einige sollen hier genannt werden. Das Rätsel der Zerreißfestigkeit in ihrem Widerspruch zu den Bornschen Kohäsions-kräften und in ihrer Abhängigkeit von der Kalt-reckung wird bereits bearbeitet. Der Vorgang der krystallographischen Gleitung, mit dem wir die Kaltreckung erklärt haben, tritt uns in seiner vollen Rätselhaftigkeit entgegen. Wir haben heute kaum die oberflächlichste Vorstellung, wie dieser Vorgang zustande kommt. Die Verteilung und die Beschaffenheit der mikroskopischen verborgenen Spannungen in ihren Beziehungen zu den bei der Kaltreckung nachweislich auftretenden makroskopischen Eigenspannungen ist aufzuklären. An das Problem der Verfestigung fügt sich das der Entfestigung, sei es durch Spannungsausgleich, sei es durch Neubildung des Gefüges, und damit das der Rekrystallisation. Auf Grund der gewonnenen präziseren Bilder der Kaltreckung müssen die Fragen der hierbei auftretenden Änderung der elektrischen Leitfähigkeit und ihres Temperaturkoeffizienten, der Thermokraft und der magnetischen Eigenschaften untersucht werden.
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  • 14
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    Naturwissenschaften 13 (1925), S. 196-197 
    ISSN: 1432-1904
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    Naturwissenschaften 13 (1925), S. 613-619 
    ISSN: 1432-1904
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    Naturwissenschaften 13 (1925), S. 10-11 
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    Naturwissenschaften 13 (1925), S. 181-188 
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    Naturwissenschaften 13 (1925), S. 193-196 
    ISSN: 1432-1904
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  • 19
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    Naturwissenschaften 13 (1925), S. 197-197 
    ISSN: 1432-1904
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  • 20
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    Naturwissenschaften 13 (1925), S. 205-212 
    ISSN: 1432-1904
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  • 21
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    Naturwissenschaften 13 (1925), S. 12-12 
    ISSN: 1432-1904
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  • 22
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    Naturwissenschaften 13 (1925), S. 201-203 
    ISSN: 1432-1904
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  • 23
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    Naturwissenschaften 13 (1925), S. 222-223 
    ISSN: 1432-1904
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  • 24
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1103-1108 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Ceramic laminates with different architecture have been produced and characterized inthis work. Thickness of single layers, composition and stacking sequence have been changed inorder to modify the corresponding stable growth range of surface defects and final strength.Laminates composed of alumina/zirconia and alumina/mullite have been considered. Themechanical behaviour of the materials is discussed in terms of the residual stress profile and theapparent fracture toughness curve
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1124-1133 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Functionally graded materials (FGM) were fabricated for bio-medical applications,(1) implants, (2) dental core and post, (3) guided tissue regeneration (GTR) membranes.(1) FGM implants of Ti/HAP and TiN/HAP with the concentration changing gradually in thelongitudinal direction of cylinder were fabricated to optimize both mechanical properties andbiocompatibility in each region. Concentration gradient was formed by packing of dry powders intomold. Spark plasma sintering was effective for sintering of non-uniform composition in FGM. Brinelhardness decreased gradually from Ti part to HAP part, which contributes to stress relaxation in theimplanted region of bone. In vivo tests showed that osteogenesis and maturation is more advanced inthe HAP rich region.(2) FGM dental core and post made of composite resin was fabricated by laser lithography, oneof the photo-curing type CAD/CAM systems. The elastic modulus changed gradually from 10.6GPain core part to 2.9GPa at the apex of post by decreasing the filler content of ceramic powders from64% to 0% in polymer matrix. Stress analysis using finite element method showed the stressrelaxation by further 30 % in FGM, compared with the uniform composite resin.(3) Biodegradable GTR membrane composed of nano HAP/collagen reinforced with PLGA wasprepared. The membrane has the three layer structure with the thickness of about 100μm for eachwhere the composition of HAP/collagen is increased from pure PLGA. The graded membranestructure could give the different functions of the high degradation speed and Ca ion release toenhance osteoconductivity for bone remodeling in the high HAP/collagen side and the relatively lowdegradability to prevent the ingrowth of fibroblasts in the pure PLGA side
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1145-1154 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: The paper will present the methodology used to design optimized die coatings employed inmaterial forming processes in an effort to extend the life and effect efficient operation of the dies. Anoptimized die coating 'architecture' requires that the coating system be essentially non-wetting withthe material (metal, glass, polymer) being formed in the die, coupled with good wear and oxidationresistance Other factors, such as delaying the onset of thermal fatigue cracking (heat checking), andan acceptably low coefficient of friction. And, possibly, self-lubricating, also need to be consideredbased on the processing and forming conditions that include both liquid and solid materials. Manydifferent die coatings have and are being used with different levels of success. This paper presents thecurrent understanding that has been gained in laboratory testing, in-plant trials, and modeling in aneffort to generate a fundamental understanding of how such optimized die coating systems may bedesigned for specific forming operations and conditions, with examples based on dies used inaluminum pressure die casting, glass molding, and metal forming operations
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  • 27
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: TiN/ZrN multilayers coatings have been deposited using a reactive R. F. magnetronsputtering process. Nitride layers with different sputtering conditions have been stacked in order toobtain superlattices having different preferred orientations. The deposition rate has beenconsidered as independent parameter which changes the energy and the momentum transfer of thebackscattered particles, influencing films structure evolution
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1246-1251 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: The coating of polymer surfaces with ceramics up to now is basically only accomplishableby vacuum-based technologies such as sputtering, because the thermal load is low compared toother methods such as sol-gel processing. Since the investment costs for the equipment required areconsiderably high and the coating is limited to line-of sight deposition, simple and cost-effectiveprocessing routes are sought.In all higher organisms inorganic materials are synthesized at ambient temperatures under physiologicalconditions. Therefore the study of biomineralization processes has gained considerable academicattention in the last decades. One of the key features of inorganic material deposition in vitois the interaction between supersaturated solutions and specifically modified surfaces.Following this paradigm so-called bio-inspired approaches can be developed which go beyond thecurrent limitations of synthetic techniques. One example is the mineralization of planar polymersurfaces with TiO2 at 50oC. Using polystyrene latex particles as templates, all four stagescommonly found in natural biomineralization can be emulated in a completely artificial system
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1134-1138 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: The electrodes for solar thermoelectric modules require high thermal conductivity in thethickness direction and high electrical conductivity in the plane direction; but the whole electrodemust be electrically insulated in the thickness direction. To meet such requirements, two materialsystems of TiB2/AlN/Cu and Cu/AlN/Cu with AlN as a middle layer were designed and studied,because AlN has high thermal conductivity and electrical resistance. The TiB2/AlN/Cu FGMs werefabricated via spark plasma sintering (SPS) method, in which a temperature gradient was achievedby using a specially designed mold. The Cu/AlN/Cu symmetrical FGMs were fabricated by aninfiltration-like process using a symmetrical porosity-graded AlN plate as a preform
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1163-1172 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1178-1183 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: We discuss simulations of grain boundary motion utilizing a grain-continuum approach torepresenting polycrystalline films; i.e., as a system of distinct but interacting continua. Fieldvariables are computed as functions of position in each grain; e.g., internal stresses andconcentrations. Grain boundaries are represented and tracked using multiple level sets, providing amethod to evolve the grain structure in time. We demonstrate the approach using stress-driven grainboundary migration in polycrystalline copper films, assuming that migration is due to vacancymigration. The anisotropic elastic constants of single crystal copper are used for each grain, underspecified rotations (grain orientations). Stresses and stress gradients are thermally induced in a filmwith 〈111〉 texture, with the exception of a single 〈100〉 grain on a silicon dioxide film on a siliconsubstrate. Grain boundary velocities are calculated from the fluxes of vacancies to grain boundaries.The computed velocities are then used to update the level sets that represent the grain boundaries
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 17-24 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: This paper shows how phase equilibria and thermodynamic properties of variousmulticomponent oxide systems can be represented with the use of model equations for the Gibbsenergies of all phases as functions of temperature and composition. Starting from the stoichiometricphases and random solutions, the complexity of the models increases tremendously when orderingtendencies or certain defects in the lattice of ionic crystals, such as vacancies and/or variableoxidation states have to be taken into account
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1029-1034 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Combustion synthesis techniques have been applied to an equiatomic mixture ofAluminium, Nickel, Titanium and Carbon powders in order to obtain NiAl/TiC composites. Bothcombustion modes have been used: the Self-propagating High-temperature mode (SHS), in whichthe reaction propagates through the sample under the form of a heat wave and the ThermalExplosion mode (TES), in which the reaction occurs simultaneously in the complete sample. Thereactions have been followed in-situ by time-resolved diffraction, using synchrotron X-rays for theSHS mode and neutrons for the TES mode. Scanning Electron Micrographs and X-ray diffractionpatterns of the final product have shown that the same final products were obtained when themixture was synthesised under both combustion modes: a composite made of small and round TiCparticles (~1 micron) embedded into a matrix of larger NiAl grains (5 microns). However, theTime-Resolved Diffraction studies have shown that, even with the same final products, the twocombustion modes follow two completely different routes. Thus, for the SHS mode, the reaction istriggered by the formation of Nickel Aluminide and 3 intermediate phases are observed, and for theTES mode, the self-sustained reaction starts with the formation of Titanium Carbide and nointermediate phases have been seen
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1377-1384 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Directionally solidified oxide eutectic ceramics were prepared from Al2O3, Ln2O3 and ZrO2 basedbinary or ternary systems. Their microstructures consist of continuous networks of single-crystalAl2O3 and oxide compounds (LnAlO3, Ln3Al5O12) which interpenetrate without grain boundaries.The outstanding stability of these microstructures gives rise to a high strength and creep resistanceat high temperature. Influence of growth conditions on the morphology of the as-obtainedmicrostructures was studied. Preferred growth directions, orientation relationships between phasesand single-crystal homogeneity of specimen were revealed. Low residual stresses were measured inthe binary eutectics and fracture toughness at room temperature was improved by the addition ofzirconia at a eutectic composition in ternary systems
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1399-1404 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Nanocomposites made of linear low-density polyethylene (LLDPE) and two differenttypes of clays were obtained and studied by using zinc neutralized carboxylate ionomer as acompatibilizer. Two different clays, natural montmorillonite (Closite Na+) and a chemicallymodified clay Closite 20A has been used. Nanocomposites were prepared by melt blending in atwin-screw extruder using two mixing methods: two-step mixing and one-step mixing. The relativeinfluence of each compatibilizer was observed from structural analysis by WAXD, and mechanicalproperties. Experimental results confirms that the film samples with ionomer showed goodmechanical performance and that the two step mixing conditions resulted in a better dispersion andintercalation for the nanofillers than one step mixing
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1411-1416 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Spark Plasma Sintering (SPS) represents a very attractive technique for the obtainment ofdense materials including nanostructured ones. SPS basically consists in the simultaneousapplication of a pulsed DC current and an uniaxial mechanical load through a powder compact.Other than providing rapid Joule heating and likely enhancing mass transport throughelectromigration, the imposed pulsed high current is also reported to generate a plasma within thevoids surrounding the powder particles, thus facilitating the removal of oxides surface layers thatmay hinder the sintering process. Selected results obtained through SPS in our laboratory for thepreparation of a wide variety of materials, i.e. TiC-TiB2, MgB2, and NbAl3, will be presented in thiswork. Specifically, all the chosen examples are related to the use of the SPS technique for obtainingthe desired material by simultaneously performing synthesis and consolidation stages in one-step
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1316-1321 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Stability under normal environmental conditions over a long period of time is crucial forsustainable thin-film device performance. Pure ZnO films with thicknesses in the 140 - 450 nmrange were deposited on amorphous glass microscope slides and (100)-oriented single crystalsilicon wafers by radio frequency magnetron sputtering. The depositions were performed at astarting temperature of 200 oC. ZnO films had a columnar microstructure strongly textured alongthe 〈0002〉 direction. XRD peak-shift analysis revealed that the films were under residual,compressive, in-plane stress of -5.46 GPa for the glass substrate and -6.69 GPa for the Si substrate.These residual stresses could be completely relaxed by thermal annealing in air.When left under normal environmental condition over an extended period of time the filmsfailed under buckling leading to extensive cracking of the films. The XRD and SEM resultsindicated different mechanisms of stress relaxation that were favored in the ZnO thin filmsdepending on the energy provided. Although thermal annealing eliminated residual stresses, seriousmicro-structural damage upon annealing was observed. Thermal annealing also led to preferentialgrowth of some ZnO crystals in the films. This kind of behavior is believed to be indicative ofstress-induced directional diffusion of ZnO. It appears that for the extended stability of the films,the stresses have to be eliminated during deposition
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1450-1455 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Although structural kaolin based ceramics are attractive and useful materials, havinggood mechanical characteristics, low density, good corrosion and high temperature resistance, theiruse is restricted by their brittle behaviour. In order to improve their properties and mainly strength,toughness and high temperature performance, fibre composite ceramics have been developed. In thepresent work a series of kaolin-short random dispersed Grafil carbon fibre composites wereproduced and sintered in an inert atmosphere of Argon at 1000oC and 1300oC and characterisedusing various techniques. XRD analysis of the kaolin matrix at 1000oC showed that the crystallinephases were decomposed without the formation of mullite a fact which also reconfirmed by SEMexamination. However at 1300oC mullite formation was well evidenced. XRD analysis of the fibresin “as received” showed that they have graphite structure which was also retained, as SEMexamination revealed, after sintering. Examination of the Grafil fibres showed that they were quiteuniform in length and diameter and retained their integrity after sintering at the examinedtemperatures. Examination the fractured composite surfaces showed only a weak bond betweenfibres and matrix and at the pull out areas the fibres were replicated in the matrix
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1469-1474 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Multi-wall carbon nanotubes (MWCNTs) with a diameter of 20-30 nm were dispersed asa conductive phase into yttria stabilized tetragonal zirconia polycrystalline (3Y-TZP) to addelectrical conductivity. The 3Y-TZP/MWCNT nanocomposites were fabricated by pressurelesssintering under inert atmosphere. Electrical conductive function was successfully introduced bysmall amount of CNT addition. Critical volume fraction of the conductive phase for the percolationwas analyzed and was found to be 0.390 vol% of CNT, which was much smaller than that fornano-sized carbon black dispersed 3Y-TZP (2.55 vol%). Microstructural investigation revealed thatdispersed CNTs formed continuous 3-dimensional nano-network within the 3Y-TZP matrix, thatcontributed to the excellent conductive properties. Fracture strength was not improved much, whilefracture toughness was increased by the CNT addition, due mainly to its crack bridging and/orpull-out mechanisms. It was considered that the use of anisotropic nano-sized conductive phase isadvantageous to obtain electrically functionalized nanocomposite ceramics
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1483-1488 
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    Topics: Natural Sciences in General , Technology
    Notes: The degradation of electrical conductivity in porous nickel-yttria stabilized zirconiacomposite cermets in a H2/H2O atmosphere under high temperature treatments has beeninvestigated. The parameters varied were: temperature, water partial pressure, and electrical currentload. The microstructure was analyzed before and after the treatment by optical microscopy andfield emission scanning electron microscopy (FE-SEM). From the optical images the particle sizeand total amount of Ni, as area fraction, in the sample were measured. By the use of charge contrast(CC) in the FE-SEM particle size and area fraction of percolated Ni was measured. Temperatureproved to have the largest effect on the degradation. Samples tested at 1000°C, in contrast to 750°C,showed a severe decrease of conductivity and growth of Ni particles. Higher water partial pressureaccelerated Ni particle growth at both temperatures, but the loss of percolation and conductivity at1000°C was less severe under high water partial pressure. A possible explanation for this behavioris discussed
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  • 41
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1505-1514 
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    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Next generation of reusable launch vehicles and new hypersonic space vehicle conceptsare currently under development, moving from traditional aerodynamic configuration towardsslender profiles. Main expected benefits are reduction of drag, enhancement in lift-to-drag ratio andreduction of interferences with radio frequency transmissions during the re-entry. Flexibility indesigning sharp profiles is strictly conditioned to the availability of suitable materials andprocessing technologies, required to fabricate components and surfaces able to withstand higherheat fluxes induced by the new profiles. Advances in the field of CMC's for high temperaturestructures and TPS are the basis for innovative approaches to the design of future RLV's. Besidebaseline solutions, already available and well characterized, as for C/SiC CMC's, ultra hightemperature ceramics seem to offer the right chance to fabricate hot structures having the requiredheat-resistant and load carrying capabilities. This paper deals with technologies based on the use ofdiboride based CMC's which can be considered promising candidate materials for the fabrication ofhot structures of slender bodies, such as nose cap and wing leading edges. Recent experimentalresults will be presented and discussed
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1532-1536 
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    Notes: The wettability of calcium fluoride by liquid Ga and Ge was studied. The initial contactangles indicate that pure liquid Ge and Ga do not wet CaF2. Different spreading kinetics during theexperiments was observed. The contact angle in CaF2/Ge system increases with time, while thecontact angle in CaF2/Ga system decreases. The same differences were also observed fortemperature dependences of the contact angle. It was suggested that these wetting/dewettingtendencies are related to the ratio of the vapor pressure values for the melt and for the substrate.The experimental observations were confirmed by a thermodynamic analysis
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1543-1550 
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    Notes: The framework of this study is the thermo-mechanical analysis of the brazingprocess of ceramic metal assemblies. The thermal expansion gradient between ceramic andmetallic materials leads to the development of residual stresses during the cooling phase ofthe brazing process which induce consequently an important reduction of the strength of thesecomposite structures. In the present work, numerical simulations are performed in order firstto predict the residual stresses distribution after the brazing process and in a second step, tostudy their influence on the tensile strength of metallized ceramic seals. Results obtained arecompared with experimental tests
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1558-1567 
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    Notes: The state of knowledge of anodic bonding is reviewed, paying particular attention to thecreation of intimate contact and to the microstructure of anodic bonds formed between silicon andPyrex. Equivalent electrical circuit models of differing degrees of sophistication which have beenproposed in the literature to predict the current-time characteristics observed experimentally for arange of conditions of applied voltage and temperature in anodic bonding are critically analysed. Itis shown that relatively simple equivalent circuit models comprising capacitors and resistors can beused to account for the main features of the observed current-time characteristics, but that theserequire the assumption of large relative permittivities for the capacitative components in the models
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  • 45
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1252-1259 
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    Topics: Natural Sciences in General , Technology
    Notes: Nanostructured ceramic thin films and membranes are used for protective or functionalpurposes and prepared on dense or porous substrate materials. Wet chemical methods enablecheap, low-temperature, mass-scale manufacturing routes. They produce fine-grained porous anddense micro-structures that cannot be realized otherwise. In wet-chemical processing, cleannanoparticle dispersions are deposited on the substrate at, primarily, ambient conditions. Thedeposition is followed by a (rapid) thermal processing treatment to remove liquids and organicadditives, to convert precursors to the target composition, and to establish the final porous anddense micro-structure. In the synthesis of precursor dispersions it is very important to obtainnanoparticles with a near-isometric shape and a fairly narrow particle size distribution, without theformation of secondary (agglomerate) structures. In particular the latter requires careful control ofsolution and interfacial chemistry to achieve proper colloidal stability, during and after thesynthesis process. Characterization of coating integrity, defect morphology and defect populationis done by decoration methods, microscopy, ellipsometry and statistical methods that employmembrane transport properties
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1260-1267 
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    Notes: Zeolites find various applications in heterogeneous catalysis, microreactor techniques,sorption techniques, ion exchange and more recently in heat pump applications. In commonprocesses zeolites are used as shaped bodies with a size in the millimeter range. Novel processesmade it necessary to apply zeolites as coating on inert or reactive bulk or porous substrate materials.In the past fifteen years various methods for zeolite coatings have been developed and adapted tothe specific requirements with respect to the process they are to be used and to the specific physicaland chemical properties of the support material
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1293-1298 
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    Topics: Natural Sciences in General , Technology
    Notes: We describe a novel surface micromachining process for the fabrication of ceramic-typeMEMS devices, such as free-standing cantilevers, that is based on the use of high-aspect ratiomicromolds of SU8 and aluminum as sacrificial layer. 250μm-high and 100-1000μm-wide moldswere used to confine a liquid precursor of SiC/Si3N4 based ceramics on the sacrificial layer thatenables the detachment of the green body before the pyrolysis step at 1000°C. The final ceramiccantilever has dimensions ranging from 100-500μm x 1-2mm x 50μm and a smooth surface. Detailsof the processing, structural and material characterization such as Dynamic Rheological andThermogravimetric Analysis under UV will be presented and compared to those found in theliterature
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1281-1286 
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    Notes: The preparation of mullite coatings for the oxidation protection of carbon fibre reinforcedcomposites using a combination of sol-gel synthesis and electrophoretic deposition (EPD) has beeninvestigated.Mullite precursor sols were synthesised by controlled hydrolysis and condensation reactions of themetal alkoxides TEOS (tetraethoxysilane) and Al(OBus)3 (aluminiumtri-sec-butylate).The structure and properties of the mullite precursor were strongly influenced by the synthesisparameters, especially by the water to TEOS ratio (rw/Si) and the pH value of the water. A variety ofsynthesis conditions was tested for optimising the mullite precursor sols regarding their suitabilityfor the electrophoretic deposition. The electrokinetic behaviour of the sols and the charging of thesol particles which is necessary for a successful EPD were investigated by measurements of theElectrokinetic Sonic Amplitude (ESA signal).29Si CP/MAS NMR measurements were used to get information about the coordination of thesilicon and the homogeneity of the Al/Si distribution in the precursors. Heat-treated samples werecharacterised by X-ray diffraction for investigating the mullite formation.Coatings prepared by EPD and sintering at 1300 °C in Ar enabled an effective oxidation protectionin the temperature range 1200 °C ≤ T ≤ 1550 °C
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    Notes: High temperature creep and superplastic flow in high-purity oxide ceramics such asalumina and tetragonal zirconia polycrystals is very sensitive to a small amount of doping by variousoxides. High-resolution transmission electron microscopy and an energy-dispersive X-rayspectroscopy analysis revealed that grain boundaries in high-purity oxide ceramics are free fromamorphous phase, and that the doped cations tend to segregate along the grain boundaries. Since thehigh temperature plastic flow in oxide ceramics takes place mainly by grain boundary mattertransport by atomic diffusion, the grain boundary nano-structure control must be a useful way todevelop new high-performance functional ceramics in the near future
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1632-1639 
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    Notes: Intra-type nanocomposites, in which nanosized second-phase particles are embeddedwithin matrix grains, generate dislocations around the dispersed nanoparticles. The intra-typenanostructure induces a thermal expansion mismatch between the matrix and the dispersed particles,which will yield nanoscale stress distribution around the particles and generate lattice defects, suchas dislocations. The dislocations of ceramics can be generated at elevated temperatures, becomesessile dislocations at room temperature, and serve as nanocrack nuclei in highly stresses fields, e.g.at a main crack tip. The frontal process zone size ahead of a crack tip is expanded due to creation ofnanocracks and hence the fracture toughness is improved. Annealing after sintered nanocompositesis important in controlling the dislocation activities. Appropriate annealing will dispersedislocations into the matrix grains. However, dislocations are sensitive to temperature, and highertemperature or longer annealing time result in dislocation disappearance and cause the reduction ofthe strength and fracture toughness of nanocomposites. In this study, commercially availableγ-alumina agglomerated powder with high porosity was used to create the intra-type nanostructure.Nickel nitrate solution was infiltrated into nanopores of the γ-alumina agglomerates in vacuum. Thealumina/nickel composite powder following reduction in hydrogen atmosphere was sintered using apulse electric current sintering method. The volume fraction of nickel was about 3 vol %. Afterappropriate annealing, the highest fracture toughness was obtained to be 7.6 MPam1/2, which is twotimes higher than that of monolithic alumina
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1658-1663 
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    Notes: Electro-stimulated piezo-spectroscopy (PS) can be quantitatively used for obtaininginformation about applied and residual stress fields piled up in ceramic materials and devices. PSexperiments can be conducted in a field-emission-gun scanning electron microscope (FEG-SEM)equipped with a high spectral resolution cathodoluminescence (CL) spectrometer. Micromechanicalinformation can be thus added to the microscopic crystallographic and chemical information alreadyavailable in conventional SEM devices. Independent of the physical mechanisms behind CLemission, the spectral position of selected bands in ceramics is shown to possess high stresssensitivity. In addition, given the high scanning flexibility and spatial resolution of the electronbeam, residual stress assessments can be performed on relatively large areas with significantlyimproved spatial resolution as compared with the more popular photo-stimulated PS approach (i.e.,using a laser beam as the excitation source). In this paper, we first quantitatively characterize thestress dependence of the spectroscopic bands observed in ruby. Then, based on this knowledge, anapplication is shown of bi-dimensional residual stress mapping around an indentation print
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1674-1679 
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    Notes: The fracture strength σf of ZrO2-based ceramics tends to increase with decreasing grainsize d. As compared with the data for submicrometer-grain-sized material with d ≈ 350 nm,nano-crystallization of ZrO2 ceramics less than d ≈ 90 nm can improve σf by a factor of 2.0-2.5. Themaximum strength reaches σf ≈ 2500 MPa, which is classed as the highest σf of oxide ceramicmaterials. The high σf can be associated with an increase in the critical t →m transformation stress anda decrease in the flaw size due to nano-crystallization
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1690-1695 
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    Notes: The mechanical properties of ceramic injection molded (CIM) components are largelyinfluenced by microstructural inhomogeneities that result from the interaction of rheologicalproperties of the thermoplastic feedstock with machine parameters and the design of mold andinjection gate. These inhomogeneities (e. g. texture, turbulences, joints, and density gradients) canform weak spots in the material or lead to anisotropy of the material properties. Additionally, theycan influence the local sinter shrinkage behavior and thereby lead to the formation of residualstresses in the component. For this reason, it is of great importance to analyze theseinhomogeneities in order to improve CIM processes and CIM components.A method has been developed for the investigation of preferred crystal orientation andmicrostructural defects, applying polarization microscopy of ceramic thin sections and colorimetry.Polarization microscopy is used in order to visualize the crystal orientation of the single grains.Different orientations of the optical axes will result in different colors of interference for opticallyuniaxial materials. The polarization micrographs themselves are already suitable for the analysis ofthe microstructure of CIM components regarding texture, separation planes, etc. Colorimetry isused in order to measure and describe the colors in a standardized color system. By means ofcolor/orientation calibration curves that are measured with single crystal references, a quantitativedescription of the orientation of single grains as well as texturized areas can be obtained
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1385-1393 
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    Notes: Co-extrusion processing is a powder-based forming method that uses thesimultaneous ram extrusion of two or more materials to form multi-phase systemswith functionally designed architectures. A functionally designed material hasfunctional properties that are specifically tailored for an application by changing themacrostructure (100’s of microns) with little or no change in overall composition.Thus, co-extrusion can be used to improve the functional properties of compositematerials, with or without a concurrent boost of its intrinsic properties. An exampleof a functionally designed material with a coaxially co-extruded architecture, knownin the ceramic field as a “fibrous monolith”, has elongated cells of a major (70-90vol.%) phase surrounded by cell boundaries of a minor (10-30 vol.%) phase. Avariety of strong-phase/weaker-phase combinations have been demonstrated,including Si3N4/BN, SiC/graphite, SiC/BN. Several wear resistant-phase/ductilephasecombinations have also been studied, including Diamond(Co)/WC(Co) for usein the petroleum drilling industry. The presentation will cover co-extrusionprocessing as a technology, applications that are being considered or are in productionfor most of the latter materials combinations, and a discussion of the functionalproperties that can be achieved using co-extrusion as a means to create functionallydesigned materials
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1405-1410 
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    Notes: The purpose of the study was to increase the thermal conductivity of multilayered andself-sealing ceramic matrix composites via the silicon melt infiltration process.The first step of the process consisted in filling porosity using various organic xerogels by thesol-gel route. Carbon xerogels obtained by subsequent pyrolysis may reduce and homogenize theporous network within the composite. Cracking of the xerogels due to volumic shrinkageoccurring during air drying may be decreased by controlling the initial parameters as concernsthe gel solution and/or by operating a second impregnation/pyrolysis step.Filling of such composites by liquid silicon revealed that a specific route and particularconditions are necessary to eliminate porosity by controlling gas production species from poresurface at high temperature. This may be achieved through a directional flow and using highlyviscous silicon (thanks to a localized wick), and by keeping the sides of the materials permeableto gas.This led to composite materials with a thermal conductivity which was four times as high as thatof those materials densified via CVI. An increase in mechanical properties was also observed
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1423-1428 
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    Notes: The effect of magnetic powders and powders loading on magnetic properties andmechanical properties of magnetic rubbers were studied. The natural rubber with magnetic powders,Barium ferrite, Neodymium iron boron, were used as starting materials to prepare magnetic rubbers.Barium ferrite (BaO.6F2O3) powders had been sintered at 1285 oC for 30 hours to improve itscrystal structure. The physical properties of magnetic rubbers, residual flux density (Br), coerciveforce (Hc), maximum energy product (BHmax), hardness and density, had a trend to increase asenhancing magnetic powders loading. However, some properties such as, intrinsic coercive force(Hci), tensile strength and elongation at break, had a trend to decrease when the magnetic powderloading was increased. Magnetic properties of the anisotropic type, sintered powders, were higherthan isotropic type, non-sintered powders, except the Hci because anisotropic magnetic rubberindicated crystal orientation in the same direction
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1444-1449 
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    Notes: This study presents the results of mechanical tests of commercial 2D SiCf/SiC ceramicmatrix composite for fusion reactors applications.The creep behaviour was investigated by means of flexural constant load stress-rupture tests, incontrolled atmosphere at 600 and 1000°C. The creep strain and time to failure vary with applied loadaccording to a power law. Cyclical tests at room temperature and at high temperature showed thatthe material has a good fatigue behaviour at room temperature, as no evident fatigue damage wasdetected after 80.000 cycles at a peak load up to 98 % of MOR. Conversely at high temperature(1000°C) the specimens showed a progressive compliance increase and limited cycles to failure evenat peak load as low as 40 % of MOR. Creep phenomena seem to influence the fatigue behaviour.Creep strain analysis, crack growth and fracture surface observations allowed to investigate themechanisms that affect the crack propagation, the fracture process and the rupture life under cyclicloading and under constant stress loading at different temperatures
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1462-1468 
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    Notes: This study presents an investigation about the damage characteristics and mechanicalproperties of Al2O3/ZrO2 laminate composites under low velocity biaxial and transient loading (BLTL).These multilayer laminates have different layer thickness therefore residual stresses and arecompared to a 13-layer alumina specimen. Impact tests were conducted using a drop-weight testfacility with impact energies ranging from 0.033-0.160 kgm. Optical microscopy was used toobserve the damage characteristics of the impacted specimens. The load-time and energy-timehistories produced by the impact tests in conjunction with the observation of the opticalphotographs give a good view of the behaviour that characterize the multilayers of Al2O3 (A) andAl2O3/ZrO2 (AZ) ceramics under the selected experimental conditions
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1489-1494 
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    Notes: The fracture toughness increases but the long-term oxidation resistance of carbon short fiberreinforced C/SiC composites decreases if the volume fraction of carbon fibers is high. Tounderstand the oxidation kinetic and their dependence from the C/SiC microstructure thecomposites and also the used carbon short fiber bundles were investigated by a thermo balance andby scanning electron microscopy. Additionally the oxidation of single carbon short fibers wasmeasured in situ by a hot stage light microscope. To simulate oxidation kinetics a software programusing Finite Element methods was developed. Below 800 °C oxidation resistance can be improvedby increasing the degree of graphitization of the carbon material within the short fiber bundles.Above 800 °C the number of junctions between the short fiber bundles has to be reduced
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1515-1519 
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    Notes: The paper presents results of investigations on the application of glass-ceramic tobonding the CBN grains into abrasive composite. The application of the glass with specificchemical composition makes it possible to generate the designed crystalline phase in it. A type ofcrystalline phase has a significant influence on the elastic modulus E
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1931-1940 
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    Notes: Burning or transmutation of minor actinides (MA: Np, Am, Cm) as well as plutonium is anoption for the future nuclear fuel cycle. For the transmutation of MA, research and development ofMA-bearing fuels that are quite different from the current UO2 and (U,Pu)O2 fuels have to be made.Among various fuel types, nitride is one of the attractive fuels to the MA-bearing fuel. Thethermochemical and thermophysical properties of nitride fuels available in literature, such as thethermal expansion, specific heat capacity, thermal conductivity, thermal creep, vaporization behavior,etc., are briefly reviewed and the new data obtained on actinide nitrides are presented. The thermalexpansion was measured by high-temperature X-ray diffraction, the thermal diffusivity by laser-flashmethod, the thermal creep by compression method, Young’s modulus by pulse echo method, and thehardness by indentation method
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1537-1542 
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    Notes: The paper presents the results concerning the formation of a ‘barrier’ layer on AlNceramic during its joining with copper by the Copper Direct Bonding (CDB) technique. Prior to thejoining, the AlN surface was modified by isothermal oxidation or by titanium ion implantation. Theeffects of the oxidation process temperature were examined within the temperature range from 673to 1473K. The surface of the ceramic was modified by titanium ion implantation at various iondoses and various accelerating voltages. The modified ceramic was joined with oxidized copper in anitrogen atmosphere with about 1.5ppm of oxygen, using a belt-type furnace at a temperature of1323K. The microstructure and phase changes induced on the surfaces of the joints were examined.The modification yielded a ‘barrier’ layer (TiN), which ensured a continuous pore-less contactbetween the materials being joined. The results obtained under all the experimental conditionsindicate that the implantation gives better effects than thermal oxidation. Ion implantation seems tobe ideally suited for these purposes. The preferential dose appears to be 5*E16ions/cm2 and thepreferential accelerating voltage – 15kV
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 218-222 
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    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: The thermal expansion of a ceramic material in general leads to a positive thermalexpansion coefficient (α). In the last decennium, several families of materials which exhibitnegative thermal expansion, arising from a specific geometrical effect in their so-called openframework structures, have been discovered. Usually, this negative thermal expansion coefficient issmall, anisotropic and the phenomena occur in a very small temperature interval. ZrW2O8 is anexception because of its large and isotropic negative thermal expansion coefficient (NTE) in atemperature range from 0.5K to 1050K. A cubic symmetry is found over the entire stability rangewith a phase transition from α-ZrW2O8 to β-ZrW2O8 near 430K. This phase transition is noticed bya change in α. The aqueous citrate-gel method is a suitable synthesis route for negative thermalexpansion ceramics and will give a fine, pure and homogenous oxide mixture, well suitable for thepreparation of ZrW2O8. The expansion coefficient of α–ZrW2O8 is -11 μm/m K whereas for the β-ZrW2O8 a value of -3 is obtained
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 223-230 
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    Topics: Natural Sciences in General , Technology
    Notes: Synthesis by freeze-drying basically consists in rapidly freezing an aqueous salt solutioncontaining the desired cation and the further sublimation of ice under vacuum conditions. After aconventional thermal treatment, the oxide nanoparticles are obtained. The influence of theparameters involved in the synthesis of γ-Al2O3 nanoparticles by a freeze-drying method have beenstudied: type of precursor salt (chloride and sulphate), salt solution concentrations (0.76-1.40 M),freezing rate and thermal treatment.Amorphous aluminium sulphate spherical granules with diameters ranging from 1 to 100 μmhave been obtained. This compound decomposes at 825ºC, leading to the formation of γ-Al2O3.These porous granules are constituted by soft agglomerates of nanoparticles with primary particlesize lower than 20 nm and values of the specific surface area of 120-180 m2/g. By optimizing thedispersing conditions a minimum particle size 〈 30 nm is measured, thus confirming that granulescan be easily dispersed into nanoparticles. The thermal treatment determines the crystalline degreeof the γ-Al2O3 and the surface area. A multimodal porosity is always obtained. The mesoporositywith mean size of 10 nm, attributed to the interparticulate porosity is practically constant, and theinteragglomerate porosity (100-600 nm) strongly depends on the salt concentration, freezing rateand thermal treatment of the powders
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 231-236 
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    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Two techniques were applied to prepare single phase YAG powder: i) citrate processbased on complexing properties of citric acid with isopropyl alcohol additive as esterification agentand ii) co-precipitation from relative nitrates solution with ammonia. At low temperature heattreatment both techniques lead to the X-ray amorphous bodies. Their calcination at elevatedtemperatures results in single-phase YAG powder. Differences in the behaviour of the amorphousprecursors during heat treatment will be shown
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 237-241 
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    Topics: Natural Sciences in General , Technology
    Notes: During the past few years, a pilot-scale spray pyrolysis set-up able to produce largequantities of submicronic powders (1kg/day) has been assembled in our laboratory. Duringthe process, droplets of a precursor solution are dried and decomposed to the requiredcompound.The presence of an additional soluble flux in the precursor solution permits to obtainagglomerate - free nanoparticles after washing the product. Therefore, pure zinc oxidenanoparticles have been successfully synthesized by adding lithium or sodium nitrates to theinitial zinc nitrate solution. The nanoparticles have been characterized by X-ray diffraction,field-emission scanning electron microscopy, laser scattering size analyzer. The influence ofthe precursor solution composition and of the operating parameters on the morphology andthe average size of ZnO nanoparticles is discussed
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 242-247 
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    Topics: Natural Sciences in General , Technology
    Notes: Nanocrystalline cordierite powders were prepared by the polymerized complex method.The synthesized precursor was calcined in air at 600-1200 oC for 1h, and the calcined powders werefully characterized by TG/DTA, BET, XRD, SEM, and TEM. The XRD and selected-area electrondiffraction (SAED) analysis confirmed the development of the phase composition of cordieritepowders showing amorphous phase after calcination at temperature below 800oC, mixed phases ofspinel and μ-cordierite phase after calcination at 800oC and 900oC, and mixed phases of spinel, μ-cordierite and α-cordierite phases after calcination at above 900oC. The BET specific surface areasof the calcined powders varied from 3 to 107 m2/g, depending on calcination temperature. Thehighest specific surface area of 107 m2/g was found in the powders calcined at 800oC. The averageparticle sizes evaluated by BET were less than 60 nm, depending on calcination temperature. Thepowders calcined at 800oC and 1000oC were uniaxially pressed and pressureless-sintered in air at1250-1350oC for 2h. Densities of the sintered samples evaluated by Archimedes’s method were 87-91 % of theoretical value. The crystal structure of all the sintered samples, determined by XRD, wasmainly α-cordierite, having a small amount of spinel as second phase
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 248-253 
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    Topics: Natural Sciences in General , Technology
    Notes: Indium oxide, a wide band gap transparent conductor, is of great interest for manydevice applications due to its unusual combination of high transparency in the visible regionand high electrical conductivity. Several methods, comprising all three phases, namely, thesolid phase, the solution phase, as well as the vapor phase, have been used for the preparationof In2O3 powders and thin films. In this work, indium oxide nanoparticles were synthesizedby homogeneous precipitation using hexamethylenetetramine as ligand and indium nitrate orindium chloride as precursor materials. Thermogravimetry and differential thermal analysisresults evidenced the relatively low temperature for crystallization of indium oxide. Sphericalclusters consisting of about 8 nm of diameter indium oxide nanoparticles were obtained afterthermal decomposition at 400 ºC for 2 h, as revealed by X-ray diffraction experiments andnitrogen adsorption measurements. Transmission electron microscopy observations confirmthe single-crystalline nature of the prepared nanoparticles. This material exhibitsphotoluminescence emission at room temperature with peak onset at 315 nm as aconsequence of the small size of the particles
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 254-259 
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    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: We have investigated a novel synthesis for highly spherical and ultrafine barium titanate(BaTiO3) powders using a peptized titania (TiO2) nano-sol as a precursor. The obtained TiO2nano-sol had the size less than 10 nm, which could be easily converted to BaTiO3 under 100 ℃. Thesize of the resulting BaTiO3 powder could be controlled from 42 to 167 nm by lowering the solutionconcentration from 1.00 M to 0.15 M. BET analysis indicated that the as-prepared BaTiO3 powdershad some porosity which was increased with the particle size. It was also found that the as-preparedBaTiO3 with smaller size had higher tetragonality and less intra-granular pores after annealing
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 260-265 
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    Topics: Natural Sciences in General , Technology
    Notes: A pseudoboehmite was obtained by sol-gel synthesis using aluminum nitrateas precursor. It was used a 2n full factorial design for studying the effect of thetemperature of synthesis, the concentration of ammonium hydroxide, and the radiationdose in the product of sol-gel synthesis. The product of the synthesis was analyzed byscanning electron microscopy, x-ray diffraction of the product (after firing thepseudoboehmite at different temperatures), and it was also analyzed the temperature ofendothermic and exothermic transformations using the thermo gravimetric analysis(TG) and differential scanning calorimetry (DSC). The X-ray diffraction data show thatα-alumina was obtained at 1100o C
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 272-275 
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    Notes: Ceramic pigments with Cr-doped sphene structure (CaSn1-xCrxSiO5, CaTi1-xCrxSiO5)were synthesized by both spray drying an aqueous solution of precursor salts plus further calciningthe resulting powders and conventional ceramic method. The thermal evolution of products wasstudied by X-Ray Powder Diffraction (XRPD). The powder morphology and chemical compositionwere analyzed by SEM-EDX. The color efficiency of pigments was evaluated by colorimetricanalysis (CIELab system). Results showed that the spray drying process decreased the maximumfiring temperature and increased the color efficiency of Cr-doped sphene pigments thereforeenhancing a higher reactivity of powders compared with the solid state process
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1759-1764 
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    Notes: Advanced structural ceramics such as Hot Pressed Silicon Nitride (HPSN) and ReactionBonded Silicon Carbide (RBSC), thanks to their low density (3.1 ÷ 3.4 gr/cm3) and to their thermostructuralproperties, are interesting candidates for aerospace applications. This research investigatesthe feasibility of employing such monolithic advanced ceramics for the production of turbine vanesfor aerospace applications, by means of a finite element analysis. A parametric study is performedto analyse the influence of the coefficient of thermal expansion, the specific heat, the thermalconductivity, and the Weibull modulus on structural stability, heat transfer properties and thermomechanicalstresses under take-off and flying conditions. A nodal point that is evidenced is the highintensity of thermal stresses on the vane, both on steady state and in transient conditions. In order toreduce such stresses various simulations have been carried out varying geometrical parameters suchas the wall thickness. Several open questions are evidenced and guidelines are drawn for the designand production of ceramic vanes for gas turbines
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 1786-1791 
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    Notes: CeramTec AG is a well-known manufacturer of cutting tool materials, especially for inserts basedon silicon nitride. Some years ago it started the production of alpha/beta-SiAlONs because of theirsuperior properties. Due to strong competition in the cutting tool business there is a constant needfor further development of the cutting tool materials. One possibility to increase wear resistance andlife time of cutting tools is to increase the hardness and maintaining the good toughness at the sametime. This can be done by adding hard particles like e.g. SiC to an alpha/beta-SiAlON. In 2003 animproved grade had been presented: a SiC-reinforced alpha/beta-SiAlON. This composite materialshows a significantly reduced wear during machining of cast iron. The effect of SiC-addition onmechanical and thermal properties is discussed
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 281-284 
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    Notes: Fe- and Eu-doped TiO2 nanocrystals were synthesized via Ar/O2 thermal plasma oxidationof liquid precursor mists. The use of mists ensures atomic level mixing of the elements and highsupersaturation of the evaporated species upon plasma oxidation, which favors nanocrystal formationupon condensation. Iron-doped TiO2 nanopowders with controlled iron to titanium atomic ratios(RFe/Ti) ranging from 0 to 20%, were synthesized by oxidative pyrolysis of liquid-feed metallorganicprecursors containing titanium tetra-n-butoxide (TTBO) and ferrocene. Europium doped TiO2luminescent nanocrystals were also synthesized via RF thermal plasma oxidation of liquid precursormists containing TTBO and europium nitrate
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 285-290 
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    Notes: This investigation was aimed at preparing nanocrystalline TiO2 powder byself-propagating-high-temperature synthesis. Titanium (IV) n-butoxide was hydrolyzed toobtain titanl hydroxide [TiO(OH)2], and titanyl nitrate [TiO(NO3)2] was obtained by reactionof TiO(OH)2 with nitric acid. Finally, the aqueous solution containing titanyl nitrate[TiO(NO3)2] and a fuel, urea, were mixed and combusted to obtain the nano-sized titania. Theanatase TiO2 nanocrystalline ( ~56nm) with high BET surface area( 280 m2g-1) and narrowband gap energy( 2.7 eV) were thus obtained
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 291-296 
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    Notes: Oxide nanopowders Y2O3, ZrO2, YSZ (Y2O3-stabilized ZrO2), Ce0.8Gd0.2O2 and Y2O3-Al2O3 compounds were prepared with the help of laser evaporation and subsequent vaporcondensation in the flow of buffer gas. An efficient technology and setup to produce high purityweakly agglomerated nanopowders are demonstrated. The output rate, alteration of elementalcomposition, size distribution and crystalline structure of the nanopowders depending onparameters of laser radiation and buffer gas flow are reported
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 297-302 
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    Notes: The activation of silicon carbide by boron and carbon is required to obtain dense monophasesintered body from SiC powder. The presence of carbon renders casting from aqueoussuspension impossible. The SiC powders with boron and extra carbon were prepared by combustionmethod (SHS), where carbon was bound to SiC particles in a stable way. The experiments showedthat this powder could be used for processing by casting of aqueous suspension. Finally nearlydense polycrystals were obtained by pressureless sintering
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 309-314 
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2362-2370 
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    Notes: A series of PTC thermistors, based on BaTiO3, doped with Ca, Mn and Y, were prepared withadditions of SiO2 at levels of 0, 1, 2 and 3 at. %. The effect of the SiO2 additions and cooling rateon microstructural development and bulk performance were characterised using a combination ofSEM, EBSD, and R-T experiments. It was found that the addition of SiO2 increased grain sizemarginally, and decreased sample density by reducing the amount of grain-grain contact. Theaddition of SiO2 also modified the distribution of grain boundary types by systematically decreasingthe proportion of low-Σ grain boundaries within the microstructure. Electrical behaviour wasmodified by adding SiO2 or increasing the sample cooling rates; in both cases there was an increasein ρ25 and a decrease in ρmax, with ρmax also being displaced to higher temperatures
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2392-2399 
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    Notes: Ferroelectrics are among the most advanced materials for non-volatile storageapplications. Their two thermodynamically equivalent groundstates of spontaneous polarization canbe toggled between by an external electric field. We present recent progress in the fabrication,registration, manipulation and characterization of nanoscale ferroelectrics. Chemical solutiondeposition is adapted to a pre-registration process by e-beam lithography to fabricate registeredferroelectric nanostructures below 100 nm width. A post-processing by chemical mechanicalpolishing either for embedded or free grains modifies the aspect ratio thus controlling the coercivefield distribution of nanoferroelectrics. We also discuss some very recent findings of the complexinteraction of field and piezoelectric tensor in a real piezoresponse force microscope. This methodrequires a comprehensive treatment of all contributions to tell apart extrinsic from intrinsic effects
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2422-2431 
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    Notes: Piezoelectric microelectromechanical systems (MEMS) employing ferrroelectric thinfilms have been extensively studied. In this paper, materials issues of the piezoeletric films arepresented. Temperature dependence of the electrical and electromechanical properties ofPb(ZrxTi1-x)O3 (PZT, x= 0.3, 0.52, and 0.7) thin films were measured using scanning probemicroscopy in the temperature range from -100°C to 150°C. The field-induced displacementincreased with increase of the temperature; however, their temperature dependence was relativelysmall, compared with that reported on bulk PZT ceramics. Thus far, the use of PZT film has beenmost widely studied for MEMS applications. However, the lead toxicity associated with PZT andother lead oxide-based ferroelectrics is problematic. Therefore, properties of the lead-free thin filmpiezoelectrics are also described in this paper. As candidate for the lead-free piezoelectrics,Bi4-xNdxTi3O12 (BNT) and Ba(Zr0.2Ti0.8)O3 (BZT) thin films are chosen. BNT and BZT filmsprepared by chemical solution deposition exhibit field-induced strain corresponding to 38 pm/V and35 pm/V, respectively
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2459-2463 
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    Notes: Lead zirconate titanate (PZT) fibres with diameters between 70 and 300 μm have beenextruded and sintered at 1200°C in a PbO-enriched atmosphere. Subsequently, the influence of fibrediameter on the microstructure (porosity and grain size) was investigated. The measurementsrevealed that with decreasing fibre diameter, the porosity decreases whereas the grain sizeincreases. The influence of these microstructural differences on the piezoelectric properties wasevaluated using a novel characterisation procedure for single PZT fibres. Fibres with an as-extrudeddiameter of 100 μm developed an average maximum strain of 3800 ppm at an applied electricalfield of 3 kV/mm and exhibited the best performance for all fibres processed with the chosensintering parameters
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2464-2471 
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    Notes: Motivated by predicting the performance and reliability of piezoelectric devices,considerable research efforts have been made in recent years to mathematically describe the largesignalnonlinear behaviour of ferroelectric piezoceramics. The success of such modelling approachdepends strongly on our knowledge of the loading history dependence of the material properties. Inthis experimental work, the nonlinear ferroelastic behaviour was investigated in detail for acommercially available soft lead zirconate titanate (PZT) material under low-frequencycompressive stress loading. It was found that the strain response was significantly loading ratedependent. The evolution of the elastic moduli was determined using fast small-stress partialunloading method, which was specially designed to minimize the time-dependent effect as much aspossible. The results were used to separate the reversible elastic deformation from the irreversibleplastic strain due to domain switching
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2224-2228 
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    Notes: The slag from steel plants or incinerators was tried to be recycled and be reused as foammaterials through plasma arc melting. The study was intended to investigate the making of foam slagwith laboratory plasma melting facilities. The investigated materials consisted of different mixturesof Al2O3、SiO2 、FetO、CaO and Na2O, with the fluxes that were necessary to examine thecapability of pore-formation in the solidified ingots. It has been found that the foam slag could beobtained with the proper compositions and conditions of arc heating. The dimensions anddistributions of pores were studied and correlated with the temperatures and compositions of slag.The results showed that the sizes of pores inside the solidified ingots were in the range of 1~5 mm,and the thickness of slag was around 20 mm. As to the distributions of the pores in the ingots of slag,further improvement would be needed in the future
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2656-2663 
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    Notes: Experiments on combustion synthesis for the Ti-2B and Ti-C systems diluted with aninert metal are presented. The paper shows the influence of geometry, composition, density andparticle size of diluent on the combustion front velocity. A Ti-2B reactant mixture diluted with Aland Cu and a Ti-C reactant mixture diluted with Al are studied. The metallic diluent and itsconcentration are varied. Besides, each experiment is based on a stack of cylinders with decreasingdiameter in order to vary the heat losses. In some experiments the eventual quenching of thecombustion reaction has been observed. Furthermore these experimental results are compared withtheoretical calculations based on analytical expressions derived for such systems
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2566-2571 
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 337-346 
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    Notes: In this work the rheological behaviour of aqueous alumina suspensions with solidsloadings ranging from 37 to 59 vol% is studied. A complete rheological characterisation isperformed by measuring under both controlled rate and controlled stress conditions to obtainexpanded flow curves, and by oscillatory tests to determine the elastic moduli. A commercialpolyelectrolyte was used as dispersant. The interparticle potentials are calculated considering theelectrostatic and the steric contributions. The electrostatic pair potential is estimated through thedetermination of the elastic modulus, G’, the double layer thickness and the surface potential byusing a spatial particle distribution model. The consideration of the steric potential, by using a softspheres model, produces significant changes in the shape and values of the potential energy curvesand allows predicting the stability of suspensions that should coagulate according to the DLVOequation. The colloidal stability and the rheological behaviour are correlated with the green andsintered densities of Al2O3 bodies produced by slip casting
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 347-355 
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    Notes: Use of environmentally friendly processing additives for nanometricpowders has tremendous technological implications. In this study, the rheology ofaqueous nanometric alumina powdersuspensions and variation of viscosity withsolids content and with fructose concentration were studied by rheometry. Themechanism of dramatic viscosity reduction by fructose addition is studied bydifferential scanning calorimetry (DSC) and thermogravimetry (TGA). Theinterparticle forces between the particles were investigated by colloidal probe-atomicforce microscopy (CP-AFM). DSC indicates that the significant fraction of water isbound on the surface hence does not contribute to flow of the particles. It alsoindicates that the fructose displaces water from the particle surface and reducing theinterparticle forces. The interactions between the nanometric alumina particles inwater can be explained by the DLVO theory. The interaction forces (amplitude andrange) between nanometric alumina particles decrease with increasing fructoseconcentration
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 363-367 
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    Notes: An apparatus which presents a mechanical milling with electric discharge is introduced.As a model experiment, an anatase TiO2 nanopowder was processed by the methodusing NH3(10%)/N2 gas. The influences of specific surface area, crystal structure, andoptical property were investigated. Relatively high specific surface areas exceeding250m2/g were observed for all processed powders. The crystal structure and crystallinityof TiO2 did not change by the milling with electric discharge. On the other hand,noticeable absorption in Vis light range was observed, suggesting nitrogen doping intothe powder
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 356-362 
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    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Processing of colloidal gels with electrified interfaces to form ceramic bulk and composite materialsas well as coatings of complex shapes with well definded structures in the nanoscale requires theunderstanding of fundamental role of the coupling between hydrodynamic and electric interactionsin colloidal deposition and colloidal arrangement.In this article, fundamental equations of electrohydrodynamics of membrane supported electrophoreticdeposition (EPD) as well as exemplary numerical FEM-simulations of electrophoreticallydeposited colloidal gels are presented. Based on microfluidic physics a model is then used to studyelectrohydrodynamic EPD phenomena, especially electroosmotic flow incorporated with modulatedsurface potentials, particle interactions and electrostatic potentials. Some practical applications ofEPD as well as visions of general purpose of the computational modelling results were given
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  • 91
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2382-2391 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: A recently-developed Pt/SrBi2Ta2O9/(HfO2)x(Al2O3)1-x /Si FET (x=0.75) shows outstanding dataretention characteristics. The drain current ratio between the on- and off-states is more than 2 x 106after 12 days, and the decreasing rate of this ratio is so small that the extrapolated ratio after 10 yearsis larger than 1 ×105. Among various materials researched for this decade, the combination ofSrBi2Ta2O9 and (HfO2)x(Al2O3)1-x or Hf-Al-O is regarded as the best choice presently. Deviceperformance by changing the Hf and Al composition ratio is investigated, and an Hf-rich-side regionaround x = 0.75 is found most suitable. Pure HfO2 (x=1) is also a good candidate, but the gate leakagecurrent increase due to HfO2 crystallization is observed. Very recently, we fabricated a self-alignedgate Pt/SrBi2Ta2O9/Hf-Al-O/Si FET, and measured the retention characteristics for 33.5 day that isthe longest period measured so far. This also shows a sufficiently large ratio of 2.4 × 105 after 33.5day which will be 6.5 × 104 after 10 years by extrapolation. The development of a self-aligned gateFeFET is an inevitable step of FeFET miniaturization according to the LSI scaling rule
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  • 92
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2440-2447 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Micro electromechanical systems (MEMS) are finding uses in an increasing number ofdiverse applications. Currently the fabrication techniques used to produce such MEMS devices areprimarily based on 2-D processing of thin films. The challenges faced by producing more complexstructures (e.g. high aspect ratio, spans, and multi-material structures) require the development ofnew processing techniques.Potential solutions to these challenges based on low temperature processing of functional ceramics,selective chemical patterning, and micro-moulding are presented to show that it is possible to createcomplex functional ceramic structures which incorporate non-ceramic conducting and supportstructures. The capabilities of both techniques are compared and the relative advantages of eachexplored
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  • 93
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    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: PbBi4Ti4O15 belongs to the bismuth oxide layers family discovered byAurivillius more than 50 years ago. In the last few years, there has been considerableinterest in layered oxides exhibiting ferroelectric, piezoelectric and other relatedproperties due to their wide range of application in technical devices. In the presentwork the PbBi4Ti4O15 solid solution formed with Eu3+ was synthesized bycoprecipitation method and solubility limit was found. All compounds werecharacterized by scanning electron microscopy, density measurements and X-raydiffraction. The variation of lattice parameter with the Eu3+ concentration was obtained.Raman spectroscopy was carried out in order to determine the Eu3+ site in the lattice.Thermal analysis (thermogravimetry and differencial scanning calorimetry) results arealso presented
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  • 94
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2503-2513 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Pyroelectric infra-red detector arrays provide an attractive solution to the problem ofcollecting spatial information on the IR distribution in a scene. They have theproperty that they are only sensitive to changes in the IR flux. This means that theyare particularly-well suited to the monitoring of movements of people in applicationssuch as retail outlets and in safety and healthcare applications. The applications oflow cost arrays with limited (few hundred elements) for people sensing and imagingradiometry will be illustrated. The performances and costs of uncooled pyroelectricarrays are ultimately driven by the materials used. For this reason, continuousimprovements in materials technology are important. In the area of bulk ceramics, itis possible to obtain significant improvements in both production costs andperformance though the use of tape-cast, functionally-gradient materials. The use ofdirectly-deposited ferroelectric thin films on silicon ASIC’s is offering considerablepotential for low cost high performance pyroelectric arrays. The challenges involvedin developing such materials will be discussed
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  • 95
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 2534-2538 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: The magnetic anisotropy of Co/Ti-doped Ba ferrite particles for application in recordingmedia is studied. A method which deduces the anisotropy from the measurement of the reducedperpendicular magnetization and allows to find also the distribution of anisotropy fields isemployed. The effect of the doping ions content, of the alignment degree of the particles and of thevariation of the temperature on the anisotropy is analysed and discussed, taking account of thecontemporary presence of magnetocrystalline and shape anisotropy, with different easymagnetization axes, in the Ba ferrite particles
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  • 96
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 413-420 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
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  • 97
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 407-412 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Aqueous freeze casting is an alternative wet shaping technique where water-basedceramic suspensions containing a cryoprotectant are cast in molds, frozen and dried. The methodcan be applied to various ceramic systems depending mainly on the ability to produce high solidloading in aqueous ceramic slurries. Against this background, aqueous aluminum nitride (AlN)suspensions were developed for the application in freeze casting.The results show that the applied process additives are most effective not only in chemicallyprotecting AlN against hydrolysis but also in obtaining colloidally stable slurries with solid loadingsin excess of 50 vol.-%. After optimization of the viscosity, the freeze cast green samples exhibithomogeneous microstructures without cracks and warpage. Besides, the systematic control of thefreezing step and the solid loading allow the preparation of sintered samples with defined density
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  • 98
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 397-406 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Miniaturisation and multi-functionality are the driving forces in the field of manytechnical market segments. Ceramic multilayer technology via tape casting and lamination isone of the key technologies to generate complex, highly integrated devices for future applications.The technique offers a tremendous potential for the integration of different materialscombined with the possibility to form complex 3-D structures by layered object manufacturing.The ceramic multilayer technology is based on shaping, screen-printing and stacking of individualceramic green tapes, which are laminated and co-fired. The tapes can offer ferroelectric,piezoelectric and magnetic behaviour, insulating and semi-conducting properties, voltage-,temperature- and atmosphere-dependent resistances, high thermal conductivity, corrosionresistance, or bio inert behaviour. For the integration of additional features like reactors or sensors,the described layered manufacturing method allows to introduce simultaneously microchannelsand other cavities. - New developments in processing and in materials concepts areaddressed to overcome limitations and to take maximum advantage of this technique. Thetechnique is illustrated considering e.g. microwave circulators for communication, sensors forautomotive applications, and piezoelectric actuators as examples, which demonstrate thepotential of the technology for the manufacture of highly integrated multifunctional systems
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  • 99
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    Advances in science and technology Vol. 47 (Oct. 2006), p. 104-107 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Superconductive ceramics with nominal composition Bi3.2Pb0.8Sr4Ca5Cu7Ox wereprepared by solid state synthesis with 10 wt% of nanopowdered silver and were compared withthose prepared by sol-gel method. The "in situ" polymerization route with citric acid and ethyleneglycol was used to enhance homogeneity of the reaction mixture. The quality of samples wascharacterized by X-ray analysis, scanning electronic microscopy and the measurement of porosity.The superconducting properties were investigated by the measurement of the temperaturedependence of magnetic susceptibility and by current voltage characteristic. All samples havecritical temperatures in the range from 109 to112 K. Addition of silver always increases the volumeof Bi-2223 phase and critical current density of the samples. Sol-gel samples reveal lower porosity,higher bulk density and better connectivity of the grains, resulting in the further enhancement ofcritical current density
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  • 100
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    Advances in science and technology Vol. 45 (Oct. 2006), p. 436-441 
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: A mathematical model has been derived to describe the pressure drop along theconveying and reverse sections of a partly full, fully intermeshing co-rotating twin-screw extruder.The model extends previous work on single screw extrusion, whereby the Benbow-Bridgwatermodel of paste rheology is combined with a force balance on a plug of paste.Experiments to verify the model have been carried out using a laboratory scale twin-screwextruder fitted with a hydraulic feeder and a modified barrel section allowing the collection ofpressure data at numerous points along the extruder. Initial results suggested that the model wasable to correctly predict the trends observed but underestimated the absolute values of the pressure.This was attributed to a change in the rheology of the paste due to viscous heating effects. Furtherexperimental work was carried out to determine the relationship between the rheological parametersand temperature; this allowed a temperature correction to be made to the initial data after which theagreement with the predictions was greatly improved
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