Volume 10, Issue 3
May 1988, pages 1-261
pp 1- May 1988
Thick films of the highTcsuperconducting oxides, LnBa2Cu3O7, Ln = Eu, Y, have been fabricated by screen printing on alumina and SrTiO3 substrates. Conditions for optimum superconductivity behaviour of the films have been established.Tconset varies from 90–94 K for all the films but zero resistance was observed only in a few cases.
pp 181-185 May 1988
Boric oxide, used as an encapsulant, prevents loss of volatile components in the growth of compound semiconductors. As the material readily absorbs moisture, and as moisture content has to be kept below a certain level, preparation and handling of this material becomes an involved process. In the present paper we report the process developed for preparing boric oxide from boric acid and growth of cylindrical rods of the desired diameter. The grown boric oxide is characterized by thermal analysis. Infrared characterization is also a powerful method and the advantages of this technique as well as the problems faced in taking the IR spectrum are discussed.
pp 187-197 May 1988
The growth of orthorhombic disphenoidal and long needle habit single crystals of ammonium hydrogen tartrate (AHT) in silica gels under the influence of an externally applied uniform field is described. The properties resulting from different growth parameters are reported. Variation in the electrical conductivities of AHT is illustrated. Two distinct electrical conductivity processes are reported. The polarization effect contributing to the dielectric constants is studied. The mechanism of dielectric behaviour which is different in lower and higher temperature ranges is discussed.
pp 199-203 May 1988
Hydrothermal phase reaction studies in the systemsβ-MnO2-H2O,γ-Mn2O3H2O andγ-MnO2-H2O have been carried out. Based on the experimental data and the reported phase diagrams in Mn2O3-H2O and MnO-H2O systems, hydrothermal stability temperature of some of the manganese oxide minerals has been defined.
pp 205-216 May 1988
Variations in the halfwidth values of X-ray reflections from fatigue-cycled, polycrystalline aluminium samples have been analysed. An oscillatory variation of the halfwidths with fatigue cycling has been observed. Analysis of the diffraction line profiles indicates that broadening arises mainly because of the build-up of microstrains during fatigue cycling. The present data indicate that (i) broadening due to fatigue cycling increases with glancing angle; (ii) changes in halfwidth and integral widths, due to fatigue cycling, are comparable and (iii) (b/b0) versusN curves for fatigue cycling under constant stress amplitude and flight loading conditions are comparable.
pp 217-222 May 1988
The effect of thermomechanical ageing (TMA) treatment on the microstructure and mechanical properties of 2218 Al alloy has been studied. This was followed by hardness measurements and transmission electron metallography (TEM). The 2218 Al alloy was given various thermomechanical ageing treatments including partial peak ageing, warm rolling and further ageing to peak hardness level. Without thermomechanical treatment the peak hardness value was 130 VHN. With thermomechanical treatment there was an overall improvement in hardness. This is attributed to the combined effect of dislocation precipitate networks and the fineness ofθ′ particles.
pp 223-231 May 1988
Different stages of iron films evaporated under a vacuum of about 10−5 torr were investigated with and without the addition of aluminium impurity at different percentages. Micrographs of such films heated at 623 K for 2 h show similar network spreading of oxide growth. Addition of aluminium significantly improves the oxidation resistance of iron films by the formation of Al2O3 layer.
pp 233-239 May 1988
Electron microscopic investigations have been carried out on superconducting YBa2Cu3 O7−δ, NdBa2Cu3 O7−δ and related oxides. All these orthorhombic oxides exhibit twin domains. Based on high resolution electron microscopy, it is shown that there is no significant change in the structure across the twins. Oxides of the La2−xSrx(Bax)CuO4 system do not show twins, but exhibit other types of defects. Twins appear to be characteristic of only the orthorhombic 123 structures.
pp 241-243 May 1988
YBa2Cu3 O7−δ samples stored in different environments have been studied over a period of 30 days employing TGA, electrical resistivity and X-ray diffraction measurements. Oxygen content andTcdo not change significantly in samples stored in the normal laboratory environment, in a sealed tube or in a vacuum desiccator. Superconductivity is lost only in samples stored in a very humid atmosphere around 320 K.
pp 245-250 May 1988
Seebeck coefficient and DC resistivity of the solid solution La1 −x NaxCo1 −xNbxO3 (0·01 ⩽x ⩽ 0·99) have been measured in the temperature range 300–900 K. Seebeck coefficient is positive for all compositions over the temperature range of measurements. Conduction is due to 3d electrons of cobalt ions in the compositions withx ⩽ 0·60. Conduction occurs among localized sites for compositions withx ⩾ 0·70.
pp 251-255 May 1988
An ultrasonic technique has been used to evaluate the degradated fatigue life of glass fibre/zirconia hybrid composites in different concentrations of sodium chloride and sulphuric acid. Results indicate that reduction in fatigue life of hybrid composites increases with increase in ultrasonic attenuation. Ultrasonic attenuation can be used to predict the fatigue life of hybrid composites before and after service.
pp 257-261 May 1988
γ-radiation treatment of radiation sterilized polycarbonate biomaterials has been carried out to ensure efficient disposal by incineration. Low molecular weight polycarbonate sterilized with 2·5 Mrad dose ofγ-radiation was further treated with different doses ofγ-radiation. The radiation-treated samples were subjected to thermogravimetry. The sterilized sample and the 7·5 Mrad-treated sample showed similar properties. These samples do not leave any residue during thermal decomposition.
Volume 42 | Issue 6
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