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  • 1
    Digitale Medien
    Digitale Medien
    A crusher for single particle testing (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1553-1556 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: For the investigation of particle failure in abrasive processes a single particle crusher has been developed. Basically the apparatus consists of two approaching diamond anvils between which a particle is positioned. Both the force and displacement can be either measured or controlled during an experiment. The force is determined by the current through the voice coil with a resolution of 0.5 mN. The vertical displacement of the lower anvil is measured by three inductive displacement transducers, each with a resolution of 0.1 μm. Single abrasive particles in the size range 10–500 μm can be used. The crushing process can be monitored through the upper anvil by a long distance microscope and recorded video. Preliminary experiments show that three different failure mechanisms can be distinguished: chipping, breaking, and fragmentation. By far the most dominant failure mechanism is chipping. The data of the crushing experiments are represented in a Weibull plot. The generally low value for the Weibull modulus indicates a large variability in strengths of the abrasive particles. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147644
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  • 2
    Digitale Medien
    Digitale Medien
    Adhesion of electrolessly deposited Ni(P) layers on alumina ceramic. I. Mechanical properties (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3402-3413 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The adhesion mechanism of electrolessly deposited Ni(P) on alumina ceramic substrates has been investigated. The adhesion was measured by direct pull-off tests and by 90° peel tests, which provided information on adhesion strength and fracture energy, respectively. An assessment is made of quantitative aspects of both adhesion measurement techniques. The observed mechanical behavior is rationalized using the Griffith–Irwin theory. Two types of alumina substrates with different roughnesses were used. Ni(P) was deposited from two types of electroless Ni(P) solutions, one with glycine and one with acetate as the complexing agent. The fracture surfaces were analysed with scanning electron microscopy, combined with energy dispersive analysis of x rays. The adhesion strength of the glycine-type Ni(P) was much higher and the fracture energy was lower than that of the acetate-type Ni(P), for both substrate types. This implies that the difference in adhesion strength is not caused by differences in interfacial chemical bonding, but rather by differences in flaw sizes. Since high adhesion strength was measured on smooth substrates, along with low peel strength, it is concluded that strong adhesion can be obtained without making use of mechanical interlocking. Further research should be aimed at controlling the interfacial flaw sizes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.356100
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  • 3
    Digitale Medien
    Digitale Medien
    Adhesion of electrolessly deposited Ni(P) layers on alumina ceramic. II. Interface characterization (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3414-3422 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The interface microstructure and interface chemistry of electrolessly deposited Ni(P) on alumina ceramics is studied in order to obtain insight into the influence of molecular interactions upon the adhesion. Detailed static secondary-ion-mass spectrometry, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy (TEM) analyses have been carried out with samples with various roughnesses, of which the mechanical analyses are described in the companion article. TEM cross-section micrographs showed a close contact between the two phases on a nanometer scale for all sample types. In addition, a 1–2-nm-thick interfacial layer was observed. This layer consists of nucleation material and compounds from the metallization solution. Fracture surface analyses showed that fracture takes place through this layer, which is therefore considered to be the weak boundary layer in this system. The presence of this weak boundary layer explains the importance of substrate surface roughness and mechanical interlocking for the fracture energy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.356101
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  • 4
    Digitale Medien
    Digitale Medien
    Crack nucleation at the surface of stressed fibers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3890-3900 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A model is proposed for crack initiation on a pristine surface. In this model failure starts from a flat surface and the crack develops during the strength or lifetime experiment. Both energy and kinetic arguments are used. The model is applied to lifetime calculations of pristine optical fibers. Surface energy and bulk elastic energy are calculated for a fiber with a flat and a slightly distorted surface. When a small amount of elastic energy is removed locally from the fiber, e.g., by dissolution, the distorted state is more stable. Like cracks in brittle materials, the stable distortions for pristine optical fibers have local radii of curvature at atomic dimensions. In this model the lifetime of a pristine fiber is mainly determined by the time needed to pass from a flat surface to a relatively small surface distortion. From the derived expression for the lifetime, the exponent n in the empirical power law expression for subcritical crack growth can be interpreted. It is shown that n is stress dependent. The discrepancy in n value observed for silica glass fibers (n(approximately-equal-to)20) and bulk fused silica (n(approximately-equal-to)40) is removed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.341343
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  • 5
    Digitale Medien
    Digitale Medien
    Dielectric properties of fine-grained barium titanate ceramics (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 1619-1625 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Dielectric properties, lattice- and microstructure of ceramic BaTiO3 showing grain sizes of 0.3–100 μm were studied. At grain sizes 〈10 μm the width of ferroelectric 90° domains decreases proportionally to the square root of the grain diameter. The decreasing width of the domains can be theoretically explained by the equilibrium of elastic field energy and domain wall energy. The smaller the grains, the more the dielectric and the elastic constants are determined by the contribution of 90° domain walls. The permittivity below the Curie point shows a pronounced maximum εr ≈5000 at grain sizes 0.8–1 μm. At grain sizes 〈0.7 μm the permittivity strongly decreases and the lattice gradually changes from tetragonal to pseudocubic.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.336051
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  • 6
    Digitale Medien
    Digitale Medien
    Electrical transport and defect properties of Ca- and Mg-doped yttrium aluminum garnet ceramics (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2627-2632 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electrical transport properties of a sintered yttrium aluminum garnet (YAG) doped with Ca or Mg have been investigated as a function of temperature and partial pressure of oxygen. Conductivity and ionic transport measurements show Ca- and Mg-doped YAG to be mixed ionic-electronic p-type conductors exhibiting an activation energy of about 2 eV. Thermally stable inclusions of alumina, which were found to be present in sintered YAG powders, act as a source of Al vacancies. Al vacancies are dominating the defect chemistry at high oxygen partial pressure. The electronic contribution to total conductivity becomes more pronounced when the temperature increases. At low pO2 a hole-release from O⋅O centers (trapped holes) influences the transport behavior. We developed a possible defect model which explains the experimental data qualitatively. This model considers the influence of dispersed particles of constant activity over a pO2 regime ranging from 105 to 10−12 Pa and their influence on the defect chemistry.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.344485
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  • 7
    Digitale Medien
    Digitale Medien
    The Influence of Water on the Fracture of Magnesium Aluminate (MgAl2O4) Spinel (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The influence of water on the fracture of magnesium aluminate (MgAl2O4) ceramics and spinel single crystals is investigated in order to determine whether adsorption plays an important role during subcritical crack growth as it does for MnZn ferrites, a compound with the same spinel structure. The fracture toughness of porous and dense polycrystalline ceramic and single crystal specimens are determined using a single edge notched beam setup at different crosshead velocities and humidities. Furthermore, in order to investigate whether a preferred plane of fracture is present, electron backscattered diffraction (EBSD) has been performed. It is found that the fracture toughness decreases with increasing humidity for dense ceramics, indicating that adsorption plays an important role as it does for MnZn ferrites. However, porous ceramics only show a sharp decrease between 0% and 2–10% relative humidity (RH) and hardly decreases onwards. This implies that the pores inhibit in some way the effect of adsorption during fracture. The exact mechanism remains unclear. EBSD measurements indicated that a preferred plane is absent. Therefore, the fracture of spinel single crystal along the (100) and (111) planes was chosen for further detailed investigation. It is revealed that between 2% and 40% RH both planes show a reduction in fracture surface energy of ∼46%. Using reported computer simulations results, it can be concluded that the surfaces are partially hydrated when being fractured.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00110.x
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  • 8
    Digitale Medien
    Digitale Medien
    Geometry of {001} Surfaces of Spinel (MgAl2O4): First-Principles Simulations and Experimental Measurements (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Maschinenbau , Physik
    Notizen: The geometry of {001} surfaces of spinel (MgAl2O4) was investigated by first-principles simulations within density-functional theory (DFT). The calculations show that the structure relaxation or reconstruction occurs for a depth of about 0.5 nm. The (001)-Mg surface shows moderate relaxations and the (001)-Al surface shows reconstruction: a new surface was formed with half of the subsurface oxygen atoms moved to the top. The surface energy was calculated to be about 1.7 J/m2 for the relaxed (001)-Mg surface and about 3.0 J/m2 for the relaxed (001)-Al surface. The chemical composition of a freshly fractured (001) surface of a spinel single crystal was measured using Low Energy Ion Scattering. The measured Al/Mg ratio indicates that the (001)-Mg surface is more stable, in good agreement with the calculations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00315.x
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  • 9
    Digitale Medien
    Digitale Medien
    A test on the statistics of derived intensities (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 1011-1013 
    Details
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Variances of X-ray reflexions calculated with the procedure as proposed by McCandlish, Stout & Andrews [Acta Cryst. (1975), A31, 245-249] have been tested against variances determined in an independent way. A satisfying agreement is obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S056773947600209X
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  • 10
    Digitale Medien
    Digitale Medien
    Thermal expansion of oxamide (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 353-354 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The thermal expansion tensor of oxamide (oxalic acid–diamide, C2N2O2H4) has been calculated from the changes of the lattice constants with temperature, as measured with X-ray diffraction. The principal components of the thermal expansion tensor at 293 K are α1 = 207 (10), α2 = 27 (6) and α3 = −3.0 (6) x 10 −6 K−1 respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889877013612
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