• Volume 18, Issue 8

      December 1995,   pages  937-1034

    • Materials engineering for a better global environment

      Kiyotaka Wasa

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      The role of materials engineering including ceramics technology for a better global environment is discussed. Present global environmental issues will be solved by resourceful energy technology and waste management under a minimum pollution of environment. The materials technology will play an important role to mitigate the global environmental issues. Research program on future energy technology and waste management should be considered according to a condition of domestic and/or international regulation. Energy saving and domestic waste management including pollution prevention of atmosphere, water and soil are near term research areas. Medium and long term research areas are non-fossil energy technology and global waste management including removal and/or reuse of greenhouse gas CO2 and nuclear waste management. To mitigate future global environmental issues, traditional materials technology should be reconstructed to build environment benign materials technology which could provide minimum environmental load.

    • Synthesis and characterization of bioactive hydroxyapatite/fluoroapatite solid solutions using corals

      T S Sampath Kumar M Sivakumar N Prasanth Kumar K Senthamil Selvi K Panduranga Rao

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      Hydroxyapatite/fluoropatite solid solutions were prepared by two different methods using Indian coast corals. In the ‘low temperature method’ a known volume (50%) of hydrofluoric acid was added to the coral and an exchange reaction with diammonium phosphate was carried out to form apatite at 250°C under hydrothermal conditions. The coralline derived hydroxyapatite by the above method was reacted with 50 mol% sodium fluoride at 900°C in the ‘high temperature method’. The X-ray powder diffraction, infrared spectroscopy and thermal analysis techniques were employed to characterize the fluorination of the hydroxyapatite.In vitro solubility study in phosphate buffer solution of pH 7·2 indicate the stability of the apatites. The low temperature method of fluorination seems to be advantageous due to betterin vitro stability and absence of impurity phases.

    • Synthesis of high-energy-density Pr2Fe14−xCoxB,x⩽3, magnets for practical applications

      S Haldar S Ram P Ramachandrarao H D Banerjee

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      Stable magnetic powders, of 1–2µm particle size, of partially Co-substituted, Pr2Fe14−xCoxB,x⩽3, alloys together with 2–4 at% excess Pr were prepared by rapidly quenching the associated melts into thin ribbons and then mechanical attriting the ribbons in the refined particle sizes. The saturation magnetizationMs, remanent magnetizationJr, intrinsic coercivityHci and Curie temperatureTc were studied in characterizing the powders for fabricating into sintered or polymer bonded magnets. It is found that the smallx=0·4–0·8 substitution of the Co on Fe sites in this series sensitively leads to an increase in the value ofHci, by as much as 40%, with the optimum value of 21 kOe atx ∼ 0·55, together with an improvement in theTc from 292°C to 325°C, without significantly diluting theMs∼150 emu/g andJr∼8·0 kG values. The Co-substituted Pr2Fe14B alloy particles are better stable and corrosion resistant in ambient atmosphere. The results are discussed with the microstructure and comparison with the data for Nd2Fe14B powders processed under the same conditions.

    • Effect of processing on microstructure and wear characteristics of an Al-4·5Cu-10Pb alloy

      J P Pathak S N Ojha

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      An Al-4·5Cu-10Pb alloy was processed by spray forming as well as impeller mixing followed by chill casting methods. The microstructure, mechanical properties and dry sliding wear characteristics of the alloy were evaluated. The spray formed alloy showed an equiaxed grain morphology with a uniform dispersion of lead particles in the matrix phase. In contrast a cellular-dendritic morphology of the primary phase was the characteristic feature of the alloy processed by impeller mixing and chill casting method. The spray formed alloy indicated its superior mechanical properties and low wear rate particularly at higher applied load and sliding velocity. The possible reason for this behaviour is discussed in the light of microstructure of the alloy and the nature of the worn out surfaces of the wear test specimens.

    • Magnetic study above the curie temperature of γ-Fe2O3 in determining the dispersion nature of Co2+ ions in Co-modified γ-Fe2O3 thin films

      B K Das Sandip Dhara A C Rastogi

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      Gamma (γ) iron oxide thin films containing 6 at% of cobalt atoms selectively dispersed at interstitial and octahedral locations have been prepared by a reactive chemical vapour deposition process. Such dispersion gives microscopic Co-trapped and Co-doped regions inγ-Fe2O3 matrix and introduces magnetocrystalline anisotropy leading to high coercivity values of 64–112 kA/m. Temperature dependence of coercivity and saturation magnetization forγ-Fe2O3 films confirm the dispersion model.

    • Effect of Al3+-substitution on the electrical and magnetic properties of Ni1·05Sn0·05Fe1·9O4 ferrites

      V K Babbar J S Chandel

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      The effect of Al3+-substitution on d.c. resistivity, dielectric constant, initial permeability, saturation magnetization and Curie temperature has been studied for Ni1·05Sn0·05AlxFe1·9−xO4 ferrites, whereinx varies from 0 to 0·5 in steps of 0·1. The d.c. resistivity increases slowly forx⩽0·3 followed by a rapid increase forx>0·3. The variation is explained on the basis of Verwey hopping as well as polaron hopping mechanisms, and the dilution effect of Al3+ ions. The behaviour of dielectric constant is attributed to interfacial polarization and follows the Koops model. The saturation magnetization and the Curie temperature decrease continuously with increasing Al3+ content and are explained using the concepts of sublattice magnetization and exchange interactions. The decrease in initial permeability is attributed primarily to decrease in saturation magnetization. The dispersions in initial permeability and magnetic loss tangent are also discussed.

    • Thermal conductivity measurements at low temperatures

      P Balaya H S Jayanna Hemant Joshi G Sumana V G Narasimha Murthy V Prasad S V Subramanyam

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      We describe briefly the experimental facilities developed for the measurement of thermal conductivity of solids in the temperature range 10K–300K. Different techniques have been used for the determination of thermal conductivity, depending on the relaxation time of the system under investigation. Measurements on stainless steel 304, using steady state and non-steady state methods are presented. Values of thermal conductivity obtained by both these methods agree to each other and are consistent with those reported earlier.

    • Studies on epoxy-polysulfone blend

      D Ratna M Patri B C Chakraborty C Madhavan P C Deb

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      Synthesis of carboxyl terminated poly (ethylene glycol adipate) (CTPA) and amine terminated poly(amide sulfone) (PS) based on the CTPA and an aromatic diamine has been described. The products were characterized by13C NMR and IR spectroscopic analysis, nonaqueous titration, viscosity measurement and solubility characteristic studies. Effect of incorporation of the developed PS on epoxy matrix was studied. Epoxy-PS blends were evaluated with respect to their thermal and dynamic mechanical properties.

    • Short fibre elastomer composites: effect of fibre length, orientation, loading and bonding agent

      R Prasantha Kumar Sabu Thomas

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      A series of short fibre reinforced styrene butadiene rubber (SBR) composites were prepared by incorporating sisal fibres of different lengths and different concentrations. The vulcanization behaviour and the properties of the vulcanizates were measured by the relevant ASTM procedures. The processing characteristics such as green strength and mill shrinkage were improved by the addition of fibres. The properties like tensile strength, tear strength, moduli at 10% and 20% elongations were found to be maximum for composites containing longitudinally oriented fibres of length 6 mm. Mixes containing 35 phr loading of fibres and bonding agent showed better mechanical performance than others. The failure behaviour of tensile and tear specimens have been analysed by scanning electron microscopy techniques.

    • Medium resolution magneto-optical Faraday rotation measurement system

      Sandip Dhara V N Moorthy A C Rastogi B K Das

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      Medium resolution magneto-optic Faraday rotation measurement setup has been reported. Measuremental setup reported is made up of simple polarized laser source, beam expander, analyzer and a bisected cross polarizedp-n detector for single ended measurements. Result of CoO modified yttrium iron garnet (YIG) films showed a rotation of 3 deg/μm which is comparable to earlier reported Co-doped YIG films.

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