Volume 21, Issue 3
June 1998, pages 185-261
pp 185-187 June 1998
Aluminosilicate (mullite) precursor was prepared by mechanochemical treatment of gibbsite and fumed silica mixtures. The effect of grinding on its structure and thermal behaviour was examined by27Al and29Si MAS NMR, XRD, DTA-TG and FTIR. Thermal treatment of this precursor led to the crystallization of mullite at about 1200°C via a spinel-phase.27Al and29Si MAS NMR spectroscopies show lowering of mullitization temperature, which is associated with increased homogeneity of the precursor. Mechanochemical treatment of gibbsite and fumed silica mixtures resulted in the formation of a more homogeneous aluminosilicate precursor.
pp 189-193 June 1998
Tetravalent metal acid (TMA) salt zirconium tungstate (ZW) has been synthesized, followed by its derivatization using ortho chlorophenol (ZWoCP). ZWoCP has been characterized for elemental analysis, spectral analysis (FTIR) and thermal analysis (TGA). Its chemical stability has been assessed in various acidic, basic and organic media. Ion exchange capacity (IEC) has been determined and distribution behaviour towards several metal ions in different electrolyte concentrations studied and a few binary separations achieved.
pp 195-201 June 1998
A simple extension of Beale’s and Lehmann’s models for the formation of porous silicon layer onp-type silicon is proposed with a view to explain the experimental conditions necessary for obtaining either uniform vertical pores or non-uniform pore branching, as desired. A uniformity parameter is defined and correlated with the measured porosity. The dependence of the porosity and the uniformity factor with the various formation parameters of porous layer are studied experimentally and explained qualitatively.
pp 203-206 June 1998
The phase diagram of a binary organic system involving diphenyl and succinonitrile shows the formation of a eutectic (0·968 mole fraction of succinonitrile) and a monotectic (0·074 mole fraction of succinonitrile) with a large miscibility gap in the system, the upper consolute temperature being 53·5°C above the monotectic horizontal. From the enthalpy of fusion of the pure components, the eutectic and the monotectic, determined by the DSC method, the enthalpy of mixing, Jackson’s roughness parameter, interfacial energy, size of the critical nucleus and excess thermodynamic functions were calculated.
pp 207-212 June 1998
Depolarization current characteristics of solution grown pure ethyl cellulose (EC) films of about 20µm thickness have been studied as a function of electrode materials at constant poling field (5 × 104 V/cm) and poling temperature 40°C. Thermally stimulated current (TSC) thermograms of EC consists of two well resolved peaks (located at 60°C and 140°C) for Al-Al system, which are attributed to the deorientation of strongly attached ethoxy groups of glycosidal units and diffusion of space charges either at electrodes or due to their thermal release at higher temperatures from the defect levels. For dissimilar electrode combinations (Al-Ag/Cu/Au/Sn/Pb), an indication of peak of lower magnitude at around (50–70°C) alongwith a higher temperature peak (140–155°C), have been observed. TSC parameters are found to change with the choice of electrode material. The dependence of dark current at 40°C in metal-ethyl cellulose-metal systems on applied voltage in the range (2·0–5·0) × 104V/cm has also been studied. The results of current-voltage measurement on EC have been interpreted to show that the Schottky-Richardson mechanism is the controlling transport mechanism. Zero field current density extrapolated fromI-E1/2 plots are found to vary with metal work function.
pp 213-217 June 1998
Single crystals of zirconium diselenide (ZrSe2) were grown by chemical vapour transport method using iodine as the transporting agent. The crystals were found to exhibit metallic behaviour in the temperature range 77–300 K and semiconducting nature in 300–443 K range. The measurements of thermoelectric power and conductivity enabled the determination of both carrier mobility and carrier concentration. The variation of carrier mobility and carrier concentration with temperature indicates the presence of deep trapping centres and their reduction with temperature in these crystals.
pp 219-226 June 1998
The dielectric properties (dielectric constant and loss) of a single crystal of yttrium iron garnet (Y3Fe5O12) were measured in the temperature range 77–725 K and in the frequency range 100 Hz-1 MHz. AC conductivity was derived from dielectric constant and loss. DC conductivity was measured in the temperature range 30–725 K. Thermoelectric power (TEP) was measured from 77–800 K. On the basis of the results, conduction in this garnet is interpreted as due to small polarons. The nature of conduction at different temperature ranges is discussed in the light of existing reports on defect formation.
pp 227-231 June 1998
Mixed composition thin films of zinc sulphide-thorium fluoride have been deposited on glass and silicon substrates by thermal evaporation of mixtures of these materials in different proportions, from a single resistively heated source. The films are characterized for their optical properties (refractive index and extinction coefficient), mechanical properties (intrinsic stress), surface morphology and chemical composition. It is found that these films have tailorable refractive indices and low losses, and that films with certain compositions have low intrinsic stress and smooth surface morphology, making them suitable for incorporation in thin film multilayers for use in the near infrared region up to at least 10µm.
pp 233-239 June 1998
Magnetization measurements of the ferrite system Mg1+xMnxFe2−2xO4 were undertaken primarily to study variation of the saturation magnetization with manganese concentration and to gain information about the type of magnetic ordering. The observations indicate the existence of Yafet-Kittel (YK) type of magnetic ordering in this system which is well supported by results of Mössbauer effect measurements. A molecular field analysis of the YK spin ordering using the three-sublattice model is shown to explain the experimental data satisfactorily.
pp 241-245 June 1998
The variation of yield strength and fracture toughness was investigated for four different heat treatments attempted on specimens of a near-eutectoid steel. The aim of this study was to optimize the microstructure for simultaneous improvements in strength and toughness. Further, the fracture toughness deduced through empirical relations from tensile and charpy impact tests was compared with those measured directly according to ASTM Designation: E 399. Among the four different heat treatments attempted in this study, the plane strain condition was valid in the fracture toughness tests for (i) normalized and (ii) hardened and tempered (500°C for 1 h) treatments only. The latter of the two heat treatments resulted in simultaneous improvement of strength and plane strain fracture toughness. The finely-dispersed carbides seem to arrest the crack propagation and also increase the strength. The pearlitic microstructure of the former leads to easy crack propagation along cementite platelets and/or cementite/ferrite interfaces. The nature of variation of empirically determined toughness values from tensile tests for different heat treatments is similar to that measured directly through fracture toughness tests, although the two sets of values do not match quantitatively. On the other hand, the toughness data deduced from charpy impact test is in close agreement with that evaluated directly from fracture toughness tests.
pp 247-249 June 1998
Surface modification of metals and alloys using lasers has acquired considerable importance because the changes achieved are highly localized and superficial. In this process the mechanical and structural properties of the bulk are retained as such because of the high temperature gradient and high rate of change of temperature that are unattainable by conventional methods. The present report is on surface hardening of oil-hardened nonshrinking (OHNS) steel using Ruby laser in normal mode. It is found that surface hardening increases thrice the size of base material and the microstructure of the laser-heated zone changes from pearlite phase to martensite phase.
pp 251-255 June 1998
An experimental setup is developed for the measurement of dynamic magnetoelectric effect (ME) in polycrystalline materials, using a time varying DC magnetic field on which an AC magnetic field is superimposed. The experimental data on ME on Bi5FeTi3O15 and a solid solution of (90%)BiFeO3-(10%)BaTiO3 are obtained using this setup. The linear and higher order ME coefficients can be evaluated from the output voltage. The temperature variation of ME data gives additional information corroborating with the data on magnetization.
pp 257-261 June 1998
The conventional methods such as specific gravity bottle method, pyknometer method, and the Westphal-balance method or the capillary tube method where accurate weighing is a problem cannot be employed when liquids are available in micro-quantities. The method described may be employed to determine the density of micro-quantity liquids (even up to 0·5µl) and it is found to be simple and rapid. The method also allows the analyst to retrieve the sample for further analysis.
Volume 42 | Issue 5
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