Volume 15, Issue 2
April 1992, pages 91-188
pp 91-110 April 1992
Drop tube provides a low-cost alternative to study the influence of microgravity in materials processing. In the present paper, the current status of the drop tubes and associated experiments on materials processing are reviewed. Emphasis is placed on the advantages and limitations of these studies. It is pointed out that despite size limitation, large opportunities exist to study the fundamental aspects of the influence of gravity in materials processing.
pp 111-120 April 1992
The free energy difference (ΔG) between an undercooled liquid and its corresponding equilibrium solid has been evaluated on the basis of a method involving Taylor series expansion of ΔG around its value at the equilibrium melting temperature. The resultant expression is shown to be capable of correctly estimating ΔG at temperatures as low as the glass transition temperature. The method is then enlarged to obtain the configurational entropy and used in conjunction with the Adam and Gibbs model to derive a novel expression for the viscosity of undercooled liquids. Most commonly used expressions for the temperature dependence of viscosity are shown to be approximations of the equation obtained in this study.
pp 121-125 April 1992
An empirical relation between lattice parameter and cationic radii for cubic spinels has been established by considering the packing of anions in non-ideal situation and ionic displacement parameter (δ =u−3/8). This relation gives the value ofa, the lattice parameter, which is much closer to the observed value.
pp 127-130 April 1992
Magnetic parameters such as saturation magnetization (σs), coercive force (Hc), remanence ratio (σr/σs) etc of CoxMg1−xFe2O4 (0⩽x⩽1) ferrites were measured at 300 and 80 K. The values ofσs,Hc and (σr/σs) increased as the content of cobalt increased. The magnetic momentμB was calculated using theσs data. The cation distribution has been suggested on the basis of these results.
pp 131-141 April 1992
Al2O3-ZrO2 composites were prepared in two compositional ranges, 15 wt% ZrO2 and 29wt% ZrO2 with or without yttria or magnesia stabilizers. While 1.5 wt% Y2O3 produced tetragonal ZrO2 and fine grain microstructure, the 4.5 wt% Y2O3 developed cubic and tetragonal ZrO2 with similar microstructure. Al2O3 with 29.5wt% ZrO2-1.5wt% Y2O3 composition had the highest strength (3,300 kg/cm2). The bending strength remained more or less the same after the first thermal shock, and then it decreased gradually, but retained some strength after 20 cycles of quench. The load vs displacement curve became nonlinear after thermal shock possibly because of formation of microcracks which could be seen by microstructural studies.
pp 143-148 April 1992
CuInSe2(1-x)S2xthin films were deposited by spray pyrolysis. Lattice parametersa andc, for all composition parametersX, were calculated from the Phillips X-ray diffractometer. The structure remained tetragonal chalcopyrite throughout. Optical band gap (Eg) was determined for the composition parameterX from the transmittance study at room temperature. Variation ofEg,a andc withX was found to be linear.
pp 149-152 April 1992
Barium ferrite thin films with perpendicular anisotropy were grown on (111) oriented GGG substrate by rf diode sputtering method. Their magnetic properties were measured. Faraday rotation was measured in the wavelength range 460–800 nm for such sputtered thin films. These films were found quite suitable for magneto-optical recording applications.
pp 153-159 April 1992
The absorption characteristics of polyimides and polyimide fluorocarbon polymer films were studied at different weathering conditions and after thermal aging. The absorption current increased while the resorption current showed greater time dependence in the presence of humidity. The magnitudes of the residual voltage decreased with increase of humidity and temperature, but increased after thermal aging. The absorption and resorption current also did not satisfy the traditional Curie-Von Schweidler law after weathering and aging.
pp 161-170 April 1992
Natural magnetite and hematite samples taken from iron ore deposits associated with Precambrian banded iron-formation (BIF) at Ari Dongri (20°23′N:81°3°E), Bastar district in Central India have been studied by Mossbauer, XRD and positron annihilation techniques. Three magnetite samples show a genetic association with α-Fe2O3 with a wide range of variations in Fe3O4:α-Fe2O3 ratio. The fourth sample, a typical specular hematite, shows α-Fe2O3 content of the order of 90%, the rest being magnetite. The magnetite present in the samples was found to be stoichiometric. None of the samples contains maghemite (γ-Fe2O3). Some geological implications of the observed variation in the oxidation states of the samples are considered.
pp 171-181 April 1992
Al-Li alloys being developed as lighter, substitutes for conventional high strength Al alloys are to be processed by routine methods. During extrusion of a 8090 Al-Li alloy, the extrusion die container failed causing some alarm. This failed die container was analysed to examine if the failure was caused by interaction of Li diffusing out of Al-Li alloy with the carbides of die steel. The evidence, although not conclusive, is sufficient to exercise caution during such processing.
pp 183-188 April 1992
Photothermal deflection technique was used for determining the laser damage threshold of polymer samples of teflon (PTFE) and nylon. The experiment was conducted using a Q-switched Nd-YAG laser operating at its fundamental wavelength (1-06μm, pulse width 10 nS FWHM) as irradiation source and a He-Ne laser as the probe beam, along with a position sensitive detector. The damage threshold values determined by photothermal deflection method were in good agreement with those determined by other methods.
Volume 42 | Issue 5
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