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  • 1
    Electronic Resource
    Electronic Resource
    The substitution of cobalt for nickel in stoichiometric nickel-zinc ferrite : 35th annual conference on magnetism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6192-6194 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the past, cobalt (II) ions have been added to nickel-zinc ferrites to capitalize on the anisotropic character of Co+2 in stabilizing domain walls and reducing magnetic losses. This paper emphasizes increasing losses. The effect of Co+2 on the real permeability (μ') and magnetic loss (μ‘) when cobalt was sequentially substituted for nickel in stoichiometric nickel-zinc ferrite was measured at 50–1500 MHz. The compositions examined were included in the formulation CoxNi0.5−xZn0.5Fe2O4. in which the cobalt atom fraction x took values from x=0.032 to 0.50. Air density of the measured toroids decreased from 4.52 g/cm3 at x=0.032 to 4.28 g/cm3 at x=0.50. A maximum for μ‘ was found in the region x=0.03–0.04, depending upon the frequency. This increase was marked at the lower frequencies, but it essentially disappeared by 800 MHz. The magnetic loss spectrum for cobalt-zinc ferrite was described by a single relaxation dispersion with a relaxation time of 6.22×10−10 s. As nickel replaced cobalt, the relaxation time increased to 14.9×10−10 s at x=0.032. An earlier analysis of nickel-zinc ferrite (x=0) yielded a relaxation time of 11.9×10−10 s, confirming the approximate coincidence of maxima in both μ‘ and relaxation time. The fact that μ‘ decreases at x(approximately-greater-than)0.04 (as cobalt replaces nickel) does not mean that the reflected attenuation must decrease. Sample thickness also influences the result. For shorted samples 0.250 in. thick, the replacement of nickel by cobalt increased attenuation despite decreasing values of μ‘, and shifted the frequency of maximum attenuation to higher values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348803
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  • 2
    Electronic Resource
    Electronic Resource
    The variation of permeability with ferrite tile density : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6195-6197 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effectiveness of ferrites as specular radar absorbers may be related to the volumetric concentration of ferrite in the absorber. This relationship is indicated when the performances of ferrite composites are compared, and when the composites are compared with ferrite tiles. The density of a ferrite tile is dependent on both composition and the conditions of preparation. A series of samples with the composition Ni0.5Zn0.5Fe2O4 was prepared by seven different methods to yield ferrites with densities varying from 3.82 to 5.33 g/cm3. Micrographs are presented to illustrate the structural dissimilarities. The highest density was produced by hot isostatic pressing, a procedure that produced two regions of differing grain size. There was relatively little grain growth in the exterior region, but grains in the interior nearly doubled in size. The greatest effects of density on permeability were noted in the 100–200-MHz region. There, the real part of permeability (μ') increased with density up to 5.1 g/cm3. The imaginary part (μ‘) also increased with ferrite density. Since the microstructure greatly influences the magnetic loss, and the many processes used resulted in greatly varying microstructural differences, the increase of both μ' and μ‘ with density was conclusive. The presence of linewidth broadening as a result of energy absorption by various spin-wave modes was confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348804
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  • 3
    Electronic Resource
    Electronic Resource
    The Mechanism of Uranium Extraction by Tributyl Phosphate (1957)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 79 (1957), S. 4625-4629 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja01574a013
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic loss in the nickel-zinc-iron oxide system (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5650-5652 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of cubic inverted spinel structures in the nickel-zinc-iron oxide system produces ferrites with high initial magnetic permeability. However, the electrical conductivity of nickel-zinc ferrites, when prepared under oxidizing conditions, is extremely low. Consequently, the imaginary part of the dielectric constant is correspondingly low, and the resultant rf electric loss is small. Most loss is, therefore, associated with the imaginary part of the magnetic permeability, which declines inversely with frequency in the VHF-UHF frequency regime. In this work, dielectric constant and magnetic permeability were measured for a series of nickel oxide-zinc oxide-ferric oxide compositions in order to identify the region of the ternary diagram associated with higher values of magnetic loss. Ferrites were prepared under identical conditions by a reactive sintering process at 1200 °C. Compositions corresponded to stoichiometric spinels (NixZn1−xFe2O4), or to spinels with the presence of excess or insufficient ferric oxide. Toroids were machined for coaxial analysis. Variation of the imaginary part of permeability with ferric oxide concentration indicated that larger values of magnetic loss were obtained when a relatively large excess of Fe2O3 was absent. When values of the imaginary part of magnetic permeability were plotted versus the nickel-zinc atom ratio, the sensitivity was relatively weak near and above unity. Below a ratio of 0.75, magnetic loss decreased rapidly, disappearing below the ratio Ni/Zn(approximately-equal-to)0.2. Reasons for this behavior are discussed. The largest μ‘ obtained with the stoichiometric iron oxide series was at Ni0.5Zn0.5Fe2O4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342259
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  • 5
    Electronic Resource
    Electronic Resource
    Validation of mixture equations for dielectric-magnetic composites (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3768-3770 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mixture equations relate the effective macroscopic electromagnetic properties (dielectric constant and magnetic permeability) of a composite material to the intrinsic microscopic electromagnetic properties of its constituents. The predictions of mixture equations in popular use generally agree with each other when particles are widely separated (small volume fraction), but begin to diverge when the volume fraction of particles in the composite is greater than 10%. This paper reviews the assumptions and characteristics of different representative mixture equations. The validity of these mixture equations for application to magnetic composites was tested by comparing their predictions of macroscopic electromagnetic properties to VHF and UHF measurements of these properties for a series of well-characterized dielectric-magnetic composite samples comprised of ferrite particles in an epoxy binder. The investigation emphasized the parameter regimes where large disparities between the predictions of the various equations exist, namely, large volume fraction of particles, complex dielectric constant and magnetic permeability (lossy material), and large contrast ratio between particle and binder properties. Correlation and lack of correlation between the mixture equation predictions and experimental data are shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340662
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  • 6
    Electronic Resource
    Electronic Resource
    Uranium Oxide–Liquid Metal Slurries (1959)
    s.l. : American Chemical Society
    Industrial & engineering chemistry 51 (1959), S. 197-199 
    Details
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ie50590a049
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  • 7
    Electronic Resource
    Electronic Resource
    An adaptive time domain deconvolution technique to characterize planar flaws in highly attenuative composites (1994)
    Springer
    Journal of nondestructive evaluation 13 (1994), S. 101-109 
    Details
    ISSN: 1573-4862
    Keywords: Deconvolution ; flaw characterization ; signal processing ; waveform prediction ; nondestructive evaluation ; polyurethane ; composite materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract To identify planar heterogeneities or flaws inside a structure using ultrasonic tests, it is necessary to characterize reflections originating from the boundaries of the heterogeneities. However, for composite materials with high, frequency-dependent wave attenuation, it is often not possible to clearly identify the reflections with either A-scan signals or conventional deconvolution techniques due to the combined effect of signal distortion and overlap. To enable deconvolution of a distorted propagating wave, a new time domain deconvolution technique which includes the frequencydependent acoustic properties of the host material has been developed. This approach is shown to be superior to conventional time domain deconvolution with L1 norm minimization in resolving flaw reflections in highly attenuative glass fiber reinforced polyurethane composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728249
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  • 8
    Electronic Resource
    Electronic Resource
    Interfacial stress state present in a “thin-slice” fibre push-out test (1992)
    Springer
    Journal of materials science 27 (1992), S. 3821-3826 
    Details
    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 An analysis of the stress distributions along the fibre-matrix interface in a “thin-slice” fibre push-out test is presented for selected test geometries. For the small specimen thicknesses often required to displace large-diameter fibres with high interfacial shear strengths, finite element analysis indicates that large bending stresses may be present. The magnitude of these stresses and their spatial distribution can be very sensitive to the test configuration. For certain test geometries, the specimen configuration itself may alter the interfacial failure process from one which initiates due to a maximum in shear stress near the top surface adjacent to the indentor, to one which involves mixed mode crack growth up from the bottom surface and/or yielding within the matrix near the interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00545464
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  • 9
    Electronic Resource
    Electronic Resource
    Crack-tip damage and fracture toughness of borsic/titanium composite (1980)
    Springer
    Experimental mechanics 20 (1980), S. 334-344 
    Details
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The fracture behavior of center-notched unidirectional borsic/titanium composites under uniaxial tensile loading has been investigated. Load-crack-opening displacement (COD) curves were obtained for crack length-to-width ratios ranging from 0.05 to 0.5. The COD was measured across the crack surfaces by means of laser interferometric displacement gage (gage length of 500 μm). As expected, the interferometric displacement gage (IDG) was very sensitive to the appearance of damage at the crack tip, yielding nonlinear load-COD curves. The crack-tip damage in borsic/titanium was found to grow coplanarly with the original crack and consist of fiber breaks and matrix plastic deformation, the former preceding the latter. The failure mode and the crack-tip-damage growth were found to be different from those observed in unidirectional boron/aluminum and these differences are discussed. The examination techniques include radiography, SEM, photomicrographs, interference microscope and optical-interferometry technique. It was found that the fracture strengths and crack-tip-damage growth can be analyzed by the analytical models proposed in the literature. The resistance-curve method was also tried and found to be applicable. A correlation has been established among the fracture strength, crack-opening displacement and failure mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02321120
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  • 10
    Electronic Resource
    Electronic Resource
    Plane-strain fracture toughness of epoxies at different loading rates (1989)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 523-530 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The plane-strain fracture toughness of two common epoxy systems of different ductility were determined at different loading rates, according to ASTM E 399 for metallic materials. The ASTM standard was applicable, but underestimated slightly the specimen thickness required for KIc. KIc decreased with an increasing loading rate and with an increasing yield stress. The fracture surfaces were all very smooth as long as plane-strain conditions prevailed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760290806
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