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The Influence of Cobalt Acetate on Sol-gel Derived Mullite Densification Behaviour

Journal of Wuhan University of Technology(Materials Science) 2012年第5期27卷 836-840页

作者： debasis roy Biswajoy Bagchi Alakananda Bhattacharya Sukhen Das Papiya Nandy Physics Department Jadavpur University

Monophasic mullite （3Al2O3？2SiO2） samples doped with 0.002 M, 0.02 M, 0.1 M, 0.15 M and 0.2 M of cobalt were prepared by a sol-gel process. Prepared gels were then dried, grinded, pressed into pellets and sintered at 1 000 °C and 1 300 °C for 4 h. Phase formation and densification behavior has been investigated as a function of the cobalt content and sintering temperature. Mullite densification behavior was analyzed .The density of the sintered ceramics was measured using Archimedes method. CoO and Co related compounds were detected by the analysis for G3, G4 and G5 doping levels. The mullite X-ray diffraction suggests predominant incorporation of Co in the glassy phase, whose quantity increased with the doping level.

关键词： sol-gel processes nanocomposite XRD FESEM mullite

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Abrupt change of dielectric properties in mullite due to titanium and strontium incorporation by sol-gel method

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Journal of Advanced Ceramics 2014年第4期3卷 278-286页

作者： Biplab Kumar PAUL Kumaresh HALDAR debasis roy Biswajoy BAGCHI Alakananda BHATTACHARYA Sukhen DAS Physics Department Jadavpur UniversityKolkata-700032India

Highly crystallized mullite has been achieved at temperatures of 1100℃and 1400℃by sol-gel technique in presence of titanium and strontium ions of different concentrations:G_(0)=0 M,G_(1)=0.002 M,G_(2)=0.01 M,G_(3)=0.02 M,G_(4)=0.1 M,G_(5)=0.2 M and G6=0.5 M.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscopy(FESEM),LCR meter characterized the *** formation was found to depend on the concentration of the *** dielectric properties(dielectric constant,loss tangent and AC conductivity)of the composites have been measured,and their variation with increasing frequency and concentration of the doped metals was *** the experiments were performed at room *** composites showed maximum dielectric constants of 24.42 and 37.6 at 1400℃of 0.01 M concentration for titanium and strontium ions at 2 MHz,*** to the perfect nature of the doped mullite,it can be used for the fabrication of high charge storing capacitors and also as ceramic capacitors in the pico range.

关键词： mullite sol-gel technique X-ray diffraction(XRD) dielectric properties field emission scanning electron microscopy(FESEM)

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Reduced Activation Energy of Iron and Copper Ion Doped Mullite which Can Be Used as a Substrate in Electronic Industry

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Journal of Surface Engineered Materials and Advanced Technology 2013年第3期3卷 11-17页

作者： debasis roy Kumaresh Haldar Biplab Kumar Paul Alakananda Bhattacharya Sukhen Das Papiya Nandy Physics Department Jadavpur University Kolkata India.

The crystallized mullite composite has been synthesized via sol-gel technique in the presence of transition metal ions such as iron and copper. The electrical resistivity and activation energy of the composites have been measured and their variation with concentration of the metal ion has been investigated. The resistivity of doped mullite decreases rapidly in the shorter temperature range and sharply in the higher temperature range. The decreasing resistivity is due to the 3d orbital electrons and the concentration of metal ions present. X-ray analysis confirms the presence of metal ions in mullite, which entered in the octahedral site. The Fe2+ and Cu2+ ions will substitute Al3+ ion in the octahedral site of mullite structure and most probably will be responsible for reducing the resistivity as well as the activation energy. Transition metal ion doped mullite-based ceramic can be considered as promising material as a substrate in the electronic industry, because of its reasonable atom density, its low activation characteristics, low thermal expansion coefficient and high mechanical strength. The present material we have developed has an activation energy of resistivity/band gap energy, Eg, 1.11 eV at 0.04 M concentration for Cu2+ ion.

关键词： Nanostructures Sol-Gel Growth X-Ray Diffraction Scanning Electron Microscopy (SEM) Electrical Conductivity

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An approach towards estimating critical value of waiting time at transit stops

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Journal of Traffic and Transportation Engineering(English Edition) 2021年第2期8卷 257-266页

作者： Subhojit roy debasis Basu School of Infrastructure Indian Institute of Technology BhubaneswarOdisha 752050India

Waiting time at transit stops is found to be an influential policy variable for a passenger’s decision on whether to undertake a given transit service. With regard to policy framework for improvement of operational service headway of a transit service and thereby its waiting time, the necessity to have knowledge on its critical value becomes inevitable. The critical value of waiting time for passengers waiting at transit stops is that duration beyond which passengers are found to be no more interested to wait for a that transit service. The paper demonstrates an approach for estimating the critical value of waiting time at urban transit stops with reference to public transport services such as city bus and shared-auto operational in Bhubaneswar, India. The critical value of waiting time is estimated from the point on cumulative distribution curve of waiting time frequency distribution, at which the maximum rate of change of the slope of curve occurs. The work assumes two positively skewed distributions such as gamma and log-normal for observed distributional pattern of waiting time. The work identifies that gamma distribution is comparatively fitting the observed data better than log-normal distribution. The study reveals that the critical value of waiting time for city bus passengers is about twice than that of shared auto ***, the study presents new information on critical values of waiting time with reference to an urban area of a developing country, it also demonstrates an experience on application of probability distribution functions for understanding distributional pattern of waiting time.

关键词： Traffic engineering Waiting time at transit stop Critical value of waiting time Probability density function Gamma and log-normal distribution

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