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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Ultramicroscopy 19 (1986), S. 409 
    ISSN: 0304-3991
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Analytical transmission electron microscopy (TEM) studies of a dental gallium alloy have been carried out. This commercial Ga alloy was made by triturating a Ag-Sn-Cu-rich alloy powder with a liquid Ga alloy containing Ga, In and Sn. Ga alloys are of increasing interest as an alternative to amalgam. The dental material studied in the present work was found to be a composite consisting of remaining, undissolved particles from the Ag-based alloy powder in a matrix of reaction products with the liquid Ga alloy. The phases in the matrix and the remaining Ag-based alloy particles have been identified by electron diffraction, high resolution electron microscopy and energy dispersive X-ray spectroscopy. the following phases were identified: orthorhombic Ag3Sn, cubic γ-Cu9Ga4, cubic Ag9In4, tetragonal β-Sn and hexagonal Ag2Ga. In addition to these well-known phases Ga-rich regions of Cu-Ga were observed consisting of an intergrowth of the tetragonal CuGa2 and one of the cubic γ-Cu9Ga4 phases.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 1 (1990), S. 94-99 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The mould-filling capacities of an Au-Ag-Cu alloy and a Ni-Cr-Be alloy for dental use have been studied by measuring the lengths of cast helices of a constant cross-section as a function of the supertemperature of the melt. A vacuum-pressure casting machine was applied in the experiments. Assuming that the conduction of heat through the investment is rate-controlling for the heat flow, the heat of fusion was calculated for the two alloys. These values were found to be close to those obtained by differential thermal analysis measurements. The lengths of the helices are strongly influenced by the deliberated heat of fusion during solidification. The substantially higher mould-filling capacity of the Ni-Cr-Be alloy compared with that of the Au-Ag-Cu alloy can be explained to a large extent by the corresponding difference in their latent heat of fusion. A calculation of the lengths of the helices requires a knowledge of the speeds of the melts. So far there are only indications of a higher speed for the Ni-Cr-Be alloy than for the Au-Ag-Cu alloy with the casting machine employed. The highest slope for the length of helix against supertemperature curve was observed for the Au-Ag-Cu alloy, indicating a smaller heat transfer coefficient for this alloy than for the Ni-Cr-Be alloy.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 3 (1992), S. 186-191 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The interface structure and bond strength between Ti and porcelain were studied using various firing times and vacuum levels. During firing an interfacial oxide layer was formed between Ti and porcelain. Fracture occurred between this oxide layer and Ti. A correlation was observed between the thickness of the interfacial layer and the bond strength: the thicker the layer, the weaker was bonding. An improved vacuum was found to increase the bond strength. Oxygen was observed by ESCA to dissolve into Ti, causing brittleness in the uppermost Ti layer with prolonged firing time.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 4 (1993), S. 296-299 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: A vacuum/Ar pressure casting machine was used to study porosity and mould filling of cast bridges of Ti. Two series of experiments were carried out: (1) The melting and the mould chamber were separated by a thin Ti foil until penetrated by the Ti melt. The mould chamber including the mould cavity was evacuated. (2) No separating Ti foil was applied. The pressure in the mould chamber was then controlled by diffusion of Ar through the investment. The moulds were made of two investments with different gas permeability. A standardized wax pattern for a five-unit bridge was used. Mould filling was evaluated by visual inspection and by measuring the missing lengths of the margins of the crowns. The porosity was studied by x-ray radiography and density measurements. In the first series mould filling was satisfactory in all cases, while the porosity was substantial for high Ar pressures. Without a Ti foil (second series) all castings contained little porosity, but the mould filling was adequate only for the high permeability investment. The experiments show that porosity can be avoided by maintaining small pressure differences between the melting chamber and the mould cavity. Adequate mould filling is promoted by minimal back pressures from trapped Ar gas in the mould.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 8 (1997), S. 357-360 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The aim of this work was to study the corrosion of gallium alloys in vivo. Three gallium alloys were tested: GF alloy, Galloy and an experimental GaIn alloy. An amalgam was applied as a control. After ageing for a minimum of two weeks, one disc of each of these alloys was mounted with the polished side up in the buccal surfaces of 17 acrylic dentures. Eight sets of the specimens were retrieved after exposure to the oral cavity for 2–4 months, and another seven were retrieved after 6–9 months. Corrosion of the polished cross-sections of the specimens was studied using scanning electron microscopy (SEM). Only the CuGa2 phase was found to corrode substantially in all three of the alloys investigated, leaving behind holes up to 20 μm deep. This is consistent with the corrosion reported after immersion tests in a solution of 0.1 mol lactic acid and 0.1 mol NaCl for 7 days. Such in vitro tests are also reported to cause distinct corrosion of the Sn phase in the gallium alloys. However, a salient feature of the corrosion in vivo was the lack of detectable dissolution of this phase. Thus, for gallium alloys, the accelerated in vitro immersion method produced results which did not agree with clinical observations. Large variations in the corrosion of the CuGa2 were observed from patient to patient. The amount of corrosion on the Galloy specimens appeared to be less and on a finer scale than on specimens of the two other alloys. The depth of corrosion was thus shallower than for this alloy. This finding indicates that there is room for further improvement of the corrosion resistance by modifying the microstructures. Less overall corrosion was found for the amalgam control than for the gallium alloys.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The microstructure in an as-cast Au-Ag-Cu-Pd alloy has been examined by electron microscopy (TEM) combined with quantitative X-ray microanalysis (EDS). The primary phase formed during solidification is enriched in silver and palladium, while gold and copper segregate to grain boundaries, where substantial amounts of lamellar eutectic colonies are formed. The compositions of the lamellae were determined by EDS analysis to be 56% Au-13% Ag-26% Cu-6% Pd and 50% Au-42% Ag-5.5% Cu-2.5% Pd (wt%). Ordering and decomposition reactions take place during cooling in the solid state: plate-like precipitates of tetragonal AuCu-l on {001} planes were found within the primary phase and in silver-rich lamellae in eutectic colonies.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The microstructure in an as-cast Au-Ag-Cu-Pd alloy has been examined by electron microscopy (TEM) combined with quantitative X-ray microanalysis (EDS). The primary phase formed during solidification is enriched in silver and palladium, while gold and copper segregate to grain boundaries, where substantial amounts of lamellar eutectic colonies are formed. The compositions of the lamellae were determined by EDS analysis to be 56% Au-13% Ag-26% Cu-6% Pd and 50% Au-42% Ag-5.5% Cu-2.5% Pd (wt%). Ordering and decomposition reactions take place during cooling in the solid state: plate-like precipitates of tetragonal AuCu-l on {001} planes were found within the primary phase and in silver-rich lamellae in eutectic colonies.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Glass compositions for double coatings for a Co-Cr-Mo alloy were developed. The glass compositions were chosen to fulfil such requirements as matching thermal expansion, low glass transition temperature and moderate solubility. For the ground coat a fairly high durability is required, whereas the cover coat must be bioactive, i.e. become attached to living bone by a chemical bond. Two compositions of each type were developed by computer-aided optimization. The glasses were chosen in the Na2O−CaO−B2O3−Al2O3−SiO2−P2O5 system. The bioactivity was tested in vitro by immersion in a simulated body fluid. The double coatings on Co−Cr−Mo alloy released hexavalent chromium into the solution as detected by yellow colouration and spectrophotometry. This colouration was strong at the margin between coated and uncoated metal and may be explained by oxidation of trivalent chromium of the alloy in the presence of glass. The released chromium did not have any notable effect on the calcium phosphate formation. After replensihing the solution no coloration was observed. This suggests that the chromate is easily dissolved and that it may be possible to wash it out prior to implantation.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 22 (1987), S. 2542-2548 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The structure of a typical dental Ni-Cr-Be alloy with 1.8 wt% Be has been investigated by SEM and TEM as well as by quantitative X-ray microanalyses in both instruments. Due to its low atomic weight the atomic fraction of Be is as high as 0.10. During solidification beryllium segregates substantially, and a large volume fraction of the casting is made up of a eutectic with coarse (≈ 1 µm diameter) alternating rods of fcc Ni-Cr and NiBe with a CsCl-type structure (ordered bcc). Smaller (≈ 0.1 µm diameter) rods of NiBe are precipitated in matrix in the solid state. Microanalyses of the NiBe rods show that they have a low chromium content (≈ 1.5 wt%). The cube boundary planes of the ordered b cc and fcc structures have a slight difference in orientation of about 7° which is most probably due to a small coherency misfit of the two types of lattices. The 〈100〉 directions in cube boundary plane of the fcc structure are nearly parallel to the 〈110〉 directions of the ordered bcc cube boundary plane. Sometimes another and more complex relationship between the two lattices occurs. The alloy contains 3.9 wt% Al which gives rise to numerous small (≈ 10 nm), spherical, ordered particles of Ni3Al both in matrix as well as in the fcc eutectic rods.
    Type of Medium: Electronic Resource
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