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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Advanced performance materials 6 (1999), S. 57-69 
    ISSN: 1572-8765
    Schlagwort(e): coprecipitation technique ; photostriction ; photovoltaic effect ; PLZT ceramic ; sol-gel technique ; tungsten
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Lanthanum-modified lead zirconate titanate (PLZT) ceramics (3/52/48) doped with 0.5 at.% WO3 were prepared by three different processing methods, coprecipitation, sol-gel and conventional oxide mixing techniques, to investigate the effect of processing route on photovoltaic and photostrictive properties. The piezoelectric constant (d33) was observed to be independent of processing technique. Photovoltaic and photo-induced strain were found to get enhanced with decreasing grain size and increasing relative density. PLZT ceramics prepared by the coprecipitation route possess unique combination of favorable properties namely: high purity, higher degree of homogeneity, uniform distribution of doping, stoichiometric compositions, finer grain size and highest density. This resulted into enhanced photostrictive properties in coprecipitated PLZT ceramics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Materials research innovations 1 (1997), S. 44-52 
    ISSN: 1433-075X
    Schlagwort(e): Key words Microwave ; Synthesis ; Processing ; WC ; BaTiO3 ; Hydrothermal
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract  The innovations in microwave processing of ceramics have been dominated to date by serendipitous discovery, because the interaction between such radiation as delivered via available tools and the materials of widely varying properties, sizes, and shapes is so complex that it has defied quantitative analysis. For over 10 years a wide variety of inorganic ceramic and semiconducting materials have been synthesized, sintered, and reacted in our own labs, including microwave hydrothermal synthesis of metals, ferrites, and electroceramic phases. These local results are summarized and used as the reference point for reporting on two different new advances: sintering of WC-Co composite tool bits and other similar objects in under 15 min, while retaining extremely fine microstructures, without any grain growth inhibitors; using reduced TiO2 or Ta2O5 for the synthesis of phases such as BaTiO3, Ba3MgTa2O9, and Pb(Zr.Ti)O3 in a few minutes in a 2.45 GHz field at the astonishing temperatures of 300–700 ºC.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of sol gel science and technology 12 (1998), S. 15-20 
    ISSN: 1573-4846
    Schlagwort(e): sodium silicate ; silica xerogel ; washing solvent ; ethanol ; water
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract This study deals with the use of ethanol as washing solvent in the preparation of the silica gels from sodium silicate in order to enhance the textural properties, especially surface area. We here examined the effect of ethanol-washing on surface area, micro- and mesopore volume, and average pore size. The silica xerogels prepared from sodium silicate solution exhibited an extremely high surface area of 1139 m2/g by washing their hydrogels with ethanol. Compared to water-washed xerogels, ethanol-washed xerogels showed higher surface areas, total pore volumes, and larger average pore sizes. Unlike the surface area of water-washed xerogel, that of the ethanol-washed xerogel was not affected by the silica concentration of initial solution. This study indicates that the textural properties of sodium silicate-derived xerogels are further enhanced by using ethanol as washing solvent.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Journal of sol gel science and technology 11 (1998), S. 7-16 
    ISSN: 1573-4846
    Schlagwort(e): silica gel ; xerogel ; high acid gel synthesis ; low pH ; high surface area ; high density ; hydrophobic ; hydrophilic ; polymeric gels ; particulate gels
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The synthesis of hydrophilic and hydrophobic high surface area (up to 1087 m2/cc) silica xerogels at pHs below 2 is demonstrated in this work. High surface area xerogels exhibit extremely fine microstructural features and fast gelation times (less than one hour). Contrary to conventional generalization that xerogels synthesized at low pH are polymeric, it is demonstrated that particulate xerogels can also be synthesized at pHs below 2. These xerogels are synthesized by the addition of large amounts of NH4OH and have relatively lower surface areas. The particulate nature of these xerogels is indicated by their opacity and from their coarse microstructural features as observed by TEM.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 30 (1995), S. 2358-2363 
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Pure and Mn-doped willemite, Zn2SiO4 of different morphologies and particle sizes were prepared with and without NH4OH under different hydrothermal conditions. Pure willemite was synthesized at a temperature as low as 165 °C using autogeneous pressure. The nature of the anion, silica source and the NH4OH∶Zn2+ ratio played an important role in the size and morphology of the willemite phase. The presence of SO 4 2− anions resulted in mainly equiaxed grains. Such powders are expected to be good for consolidation and in the processing of phosphors.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 33 (1998), S. 3817-3821 
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A series of organically modified silica gels (ORMOSILs) with different alkyl groups such as methyl, ethyl, propyl, phenyl and octyl groups was investigated to determine the effect of substituted alkyl groups on the textural properties such as surface area, total pore volume, microporosity and hydrophobicity. Gelation time increased with increasing volume of alkyl groups. As-synthesized xerogels showed a systematic decrease in surface areas and total pore volumes and increase in microporosities with an increase in the volume of alkyl groups. All the ORMOSILs exhibited similar surface areas and total pore volumes after calcination at 500°C for 1 d. Increase in microporosities was observed in all the calcined xerogels. This study suggests that the primary particle sizes of pure silica cores are not affected by the size of the alkyl group, while their connectivity decreases with increasing volume of alkyl groups in the acid–base catalysed system of alkyltrimethoxysilane–tetramethylorthosilicate.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 15 (1996), S. 613-615 
    ISSN: 1573-4811
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 14 (1995), S. 1770-1772 
    ISSN: 1573-4811
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 15 (1996), S. 861-863 
    ISSN: 1573-4811
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of electroceramics 1 (1997), S. 105-111 
    ISSN: 1573-8663
    Schlagwort(e): photostriction ; photovoltaic effect ; sol–gel ; PLZT, doping effect ; tungsten, niobium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Notizen: Abstract Lanthanum-modified lead zirconate titanate (PLZT) ceramic materials have gained considerable attention due to their photostriction, which is the superposition of photovoltaic and piezoelectric effects. However, the photovoltaic effect and the induced strain response are also influenced by the fabrication and processing conditions. The PLZT ceramics produced by conventional oxide mixing process exhibit moderate photostrictive properties due to the inhomogeneous distribution of impurities. In this study, ceramics of PLZT (3/52/48) doped with WO3 and Nb2O5 were prepared by sol–gel technique using lead(II) acetate trihydrate, lanthanum(III) acetylacetonate hydrate, Zr, Ti, Nb, and W alkoxides. It was found that WO3 and Nb2O5 were effective in suppressing the grain growth of PLZT, which lead to the enhancement of photovoltaic and photostrictive properties. Photovoltaic and photostrictive responses show ed a maximum for samples with 0.5 at% WO3 doped sol–gel PLZT. It has been shown that the sol–gel derived PLZT ceramics with proper density possess the possibility of enhancing the photostriction over ceramics produced by conventional oxide mixing process.
    Materialart: Digitale Medien
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