• Volume 22, Issue 7

      December 1999,   pages  1013-1072

    • Decomposition behaviour of Kevlar 49 fibres: Part I. AtTTd

      R V Iyer Kalyani Vijayan

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      The structural changes which accompany decomposition of Kevlar 49 fibres atT=500°C and 550°C, respectively, have been elucidated. At both these temperatures, cumulative thermal exposures of specific durations,tcum(T), are required to result in decomposition. The conspicuous features which characterize isothermal decomposition of the fibres are: (i) progressive reduction and an eventual total loss in fibre crystallinity, (ii) progressive loss in weight, (iii) introduction of surface damages, (iv) introduction of hollowness, and (v) deterioration in tensile properties.

    • Silica fibre-composites obtained using long-chain carboxylic acid as templates

      L Sudheendra A R Raju

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      Fibres of silica-composites having different long-chain carboxylic acids were prepared. The morphology and the composition of these different inorganic-organic composites, thus obtained, were similar owing to their common mechanism of formation. Their morphology was observed to be sensitive to the water content.

    • Effect of corrosive medium on fatigue crack growth behaviour and fracture in high martensite dual phase steel

      K V Sudhakar Asim Bag E S Dwarakadasa K K Ray

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      Fatigue crack growth (FCG) behaviour in both near-threshold and higher stress intensity range (ΔK) in intercritically annealed dual-phase (DP) steel containing martensite between 32% and 76% in ferrite has been studied in 3·5% NaCl solution. It is shown that the amount of martensite content in dual phase steel has a significant effect on threshold (ΔKth) values and FCG rates. Higher content of martensite in ferrite leads to higher threshold values and lower FCG rates. Further, ΔKth is much higher in 3·5% NaCl solution as compared to that in laboratory air. Fractography studies reveal that in the near-threshold region, fracture surfaces are characterized mainly by intergranular cracking in corrosive (3·5% NaCl solution) environment. Higher threshold values in 3·5% NaCl solution is attributed to the higher crack closure induced by rougher fracture surface and by the strong wedge effects of corrosion products.

    • Study on steel corrosion in different seabed sediments

      Yantao Li Baorong Hou

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      A series of simulation experiments on carbon steel (A3 steel) and low alloy steel (16 Mn steel) in marine atmosphere (MA), seawater (SW) and seabed sediment (SBS) including rough sea sand, fine sea sand and seabed mud were carried out indoors for a year or so by means of individually hanging plates (IHP) and electrically connected hanging plates (ECHP). The corrosion of steels in SBS was mainly due to the macrogalvanic cell effect. The steel plates at the bottom of SBS, as the anode of a macrogalvanic cell, showed the heaviest corrosion with a corrosion rate of up to 0·12 mm/a, approximately equal to that of steel plates in marine atmosphere.

      The test results showed that the corrosion rates of A3 and 16 Mn steel in marine environment were in the order: MA>SW>SBS by the IHP method; and MA>SBS>SW by the ECHP method. The corrosion rates of steels in the water/sediment interface were directly proportional to the grain size of the SBS by the ECHP method, but those of steels in the water/sediment interface did not vary with the grain size of SBS by the IHP method. The corrosion rate of low-alloy steel was a little higher than that of carbon steel. The results of this study have important applications for design of offshore steel structures such as oil platform, pier, and port.

    • On the specific heat of Al-Si and Al-Ge alloys—A simulation study

      P Murugan K Ramachandran

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      The large variation in specific heats with concentration between temperatures 50 K and 200 K for Al-Si and Al-Ge alloys are analysed in detail by lattice dynamical and Monte Carlo approaches. The large deviation from linearity at low temperatures does not seem to be due to the Debye’s low temperature contribution. It is shown that an anharmonic vibration in the above solid solutions, particularly at 200 K, is the cause for the small variation in the specific heat.

    • Effect of CuO addition in Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O ceramics

      D R Mishra P N Dheer

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      The effect of adding CuO matrix to Bi1·6Pb0·4Sr2Ca2Cu3Oδ and Y1Ba2Cu3Oδ superconductors was investigated through resistivity, XRD, SEM, thermoelectric power (TEP), and ac magnetization studies. Samples with as low as 20% (by weight) of the superconducting phase showed superconducting transition in resistivity-temperature (R-T), with the superconducting zero around 77 K in thermoelectric power, critical current (Jc) values were evaluated by applying Bean’s critical state model. CuO could be added to the superconducting material without any significant deterioration in the quality of the samples, up to a concentration of as low as 40% (by weight) of the superconducting material.

    • Optical properties of (1-x-y)B2O3-xLi2O-yMCI2 (M=Cd, Zn) glasses

      P S Vijoy M Abdul Khadar

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      Optical absorption and transmission spectra of (1-x-y)B2O3-xLi2O-yMCI2 (M=Cd, Zn) glasses of varying compositions were recorded in the UV-visible region. From the spectra, various optical parameters such as optical energy gap (Eopt), refractive index (n), optical dielectric constant (ɛ′), width of the tail of localized states in the forbidden gap (ΔE), ratio of carrier concentration to the effective mass (N/m*) and the constantB were evaluated. The effects of composition of glasses on these parameters are discussed.

    • Microhardness study of (1-x-y)(B2O3)-x(Li2O)-y(MCI2), (M=Cd, Zn) glasses

      P S Vijoy M Abdul Khadar Cyriac Joseph

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      Results of microhardness measurements on (1-x-y)(B2O3)-x(Li2O)-y(MCI2), (M=Cd, Zn) glasses, in the applied load range 25–500 g, are presented. The microhardness was found to decrease with increase in load up to 50 g, then it increased and finally attained a practically constant value with increase in load. The effects of composition of the glasses on microhardness are discussed.

    • Thermal treatment of the precipitated solid material (PSM) from the waste black liquor (WBL)

      A M A Nada E M A Hamzawy H I Omara S El Gohary

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      Preciptated solid materials (PSM) from waste black liquor (WBL), at pH 8·5–9·0, produced from cooking of rice straw in paper mill factories were thermally treated. The cooking process led to decrease in organic material and partial substitution in silica structure. During this cooking process, three probable stages of mass loss comprise removal of moisture, volatile release, and combustion.

      The chemical analysis depicts the cooking effect on leaching either the high percentage elements (Ca, Na, and K) or some metallic cations (Mn, Cd, Zn and Cu) in the parent rice straw. Silica hydrate, amorphous silica and crystalline silica were obtained at <600°C, 600–700°C and at>800°C, respectively. The infrared spectra show gradual removal of the hydrocarbon bond (C–H), molecular H2O, and sianol group (Si-OH) with temperature. TG, DTA, XRD and SEM were used in this study.

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