Department of Chemical Engineering
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Item Phase transformations in sol-gel prepared PZT and PLT thin films upon isothermal treatments at different temperatures(Taylor & Francis, 1998-08-24) Roy, BanasriPhases formed upon isothermal treatments of sol-gel prepared PZT andPLT films at different temperatures have been determined. In PZT, the sequence of phase formation with increased temperature is found to be: Amorphous → Amorphous + Pyrochlore + PbO → Pyrochlore + PbO → Pyrochlore + PbO + Perovskite → PbO + Perovskite → Perovskite. In the PLT films no PbO phase is found to form and the region in which the pyrochlore phase forms is very limited. TIT diagrams for both the films are proposed.Item Effect of rare earth doping on sol-gel derived PZT thin films(Taylor & Francis, 2000-09-04) Roy, BanasriWe have studied the effect of rare earth dopants (Nd, Gd and Ce) on the phase formation behavior and electrical properties of sol-gel derived Pb1.05(Zr0.53Ti0.47)O3 thin films. In all these films the perovskite phase is obtained up to 5 at% doping and beyond that pyrochlore phase was found to coexist with the perovskite phase. Ce and Gd doping(1-2 at%) exhibited improved ferroelectric and dielectric properties as compared to the undoped PZT films. Nd doping (2 at%) was found to be effective to increase the retained switchable polarization of undoped PZT from 63% to 84%. The transition temperature of undoped PZT film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxor behavior and a diffuse phase transition, characteristic of the relaxor material. Introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO3 lattice which causes the observed relaxor behaviorItem Raman scattering and x-ray diffraction studies of rare earth-doped Pb0.90La0.15TiO3 thin films prepared by the sol–gel method(Wiley, 2000-11-07) Roy, BanasriThe structural modification and phase transition in rare earth (Gd3+ and Ce3+)-doped Pb0.90La0.15TiO3 films, prepared by the sol–gel technique on Pt substrates, were studied utilizing x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate an increase in lattice tetragonality with increasing content of Gd and Ce in these films. Raman spectra exhibited features characteristic of bulk PbTiO3, including the observation of the soft mode. Variations in the phonon mode wavenumber, especially that of the lowest soft mode, for Pb0.90La0.15−xCexTiO3 (x = 0.00–0.07) and Pb0.90La0.15−xGdxTiO3 (x = 0.00–0.15) as a function of the composition x and temperature corroborate the increase in tetragonality caused by rare earth doping. As a result, the ferroelectric transition temperature was found to increase almost linearly from 480 to 630 K with increasing Gd content from x = 0.00 to 0.15. In Ce-doped films, the solubility limit was found at about x = 0.05; the transition temperature increases up to 5 doping then it decreases above that composition, probably owing to Ce precipitation.Item Effect of acceptor and donor dopants on polarization components of lead zirconate titanate thin films(AIP, 2001-01-11) Roy, BanasriABSTRACT We have compared the magnitudes of reversible and irreversible polarization components of sol–gel-derived Nd3+- and Fe3+-doped PZT (53/47) thin films on platinized silicon substrates. Beyond the switching field, it was found that the reversible component of the polarization remains almost constant both for donor- (Nd3+) and acceptor- (Fe3+) doped PZT films. The irreversible polarization component reduces with the increase in Nd3+ content, whereas it increases until 3 at. % Fe3+-doped PZT thin films. The dielectric behavior of these films at subswitching fields was analyzed in terms of Rayleigh law. The inverse of the Raleigh coefficient (υ) was considered as a measure of the obstacle for the domain-wall motion. In the case of Fe-doped PZT, the inverse of the Raleigh coefficient (υ) shows a declining linearity with Fe content, which may be found exactly opposite to that observed for Nd-doped PZT. The observed results are explained in terms of the nature of the defect-domain-wall interaction of acceptor-and-donor-doped PZT thin films. Studies indicated that in the case of Fe-doped PZT films, the possible defect interaction initiates only above 2 at. % and it was found to be much lower in magnitude in comparison with the Nd doping.Item Effect of neodymium (Nd) doping on the dielectric and ferroelectric characteristics of sol-gel derived lead zirconate titanate (53/47) thin films(AIP, 2001-01-12) Roy, BanasriThe results of the studies on the effect of rare earth Nd doping on the phase formation behavior and electrical properties of sol-gel derived Pb1.05(Zr0.53Ti0.47)O3 (PZT) thin films are presented. The perovskite phase is obtained up to 5 at. % doping and beyond that pyrochlore phase was found to coexist with the perovskite phase in all the films. The transition temperature of undoped lead zirconate titanate (PZT) film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxor-type behavior and a diffuse phase transition, similar to that observed in relaxor materials. The introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO3 lattice, which causes the observed dielectric relaxation. Efforts were made to isolate the irreversible component contributions in low field dielectric and high field polarization switching behavior. REFERENCESItem Investigation on the Dielectric and Polarization Behavior of Sol-Gel Derived Erbium Doped Pb(Zr 0.53 Ti 0.47 )O 3 Thin Films(Taylor & Francis, 2002) Roy, BanasriWe have studied the effect of Er 3+ doping on the dielectric and polarization hysteresis behavior of sol-gel derived Pb 1.05 (Zr 0.53 Ti 0.47 )O 3 thin films. Up to 1 at% Er doping, the dielectric constant of undoped PZT increases from 1245 to 1477 (measured at 50 kHz, 500 mV oscillation voltage), whereas the remnant polarization increases from 30 to 41 w C/cm 2 . Under the subswitching external field, the dielectric permittivities follow the Rayleigh law. The Rayleigh coefficient ( f ) was considered as a measure of the ease of domain wall motion. Up to 1 at% Er doping, the increase of f indicates minimal defect-domain wall interaction due to lower defect concentration. Under the switching field, the irreversible part of the switchable polarization was estimated from the C-V and hysteresis measurements. At the saturation field it was observed that up to 1 at% Er doping the irreversible component at switchable polarization increases and reversible component remains low. The improvements of dielectric and ferroelectric properties for up to 1 at% Er doping have been correlated to the relative site occupancy of Er 3+ as a function of Er content in PZT host lattice.Item A Framework for Implementation of Occupational Healthand Safety Management Systems in Process Industry(UDYOG PRAGATI JOURNAL, 2003) Kale, Samir R.The paper throws light on understanding the proactive role that Occupational, Health and Safety (OH&S) plays in process related unit operations. It focuses on various hazardsoccuring in workplace of a process industry and how to mitigate this hazards through theapplication of various tools that drives OH&S with the help of real life examples. It alsodescribes the implementation stages of OH&S in a process industry. A case study has beenillustrated to understand the consequences of overlooking the safety aspects. The paper concludes that inculcating safety culture right from design to development, results in reduced accident rates and keep employers and employees safeItem Non-vacuum and PLD growth of next generation TCO materials(Elsiever, 2003-12-15) Roy, BanasriTransparent conducting oxides represent a key component in a number of important opto-electronic technologies. The demand for improved materials is increasing. It is increasingly important to develop improved materials and process techniques. We report on the PLD growth of both Mo doped In-O, an n-type material with enhanced mobilities, and p-type Ca–CuInO2 films with improved conductivity. In both cases, very high quality films have been obtained with improved opto-electronic properties. We also report on a solution based route to p-type Cu2SrO2 which has produced phase pure films.Item Application of Wavelet Transform in Controls: A Review(IUP, 2005-03) Mohanta, Hare KrishnaWavelet analysis is an emerging field of mathematics that has provided new tools and algorithms suited for the type of problems encountered in process monitoring and control. In this paper, a review is presented for the applications of wavelet transform in advanced control systems, particularly in Model Predictive Control, Intelligent Control, Robust Control, Adaptive Control, Nonlinear Control, Process Modeling and Control, Process Identification and Control, Process Monitoring, Diagnosis and Control, Statistical Process Control and Optimal Control. The underlying principles in each of these control strategies have also been briefly discussed. Over the past few years, wavelets and wavelet-based analysis have found their way into many different fields of science and engineering. The wavelet transform is a tool that provides descriptions of functions or signals in the time-frequency plane (Daubechies, 1992). Using traditional mathematical tools, one can study the properties of a phenomenon either in time domain or frequency domain. Although the Fourier transform and its inverse allow a passage from one domain to another domain, it does not give a simultaneous view of the phenomenon in both domains. Wavelets, on the other hand, are the basis functions, which are localized in both time and frequency domains. A basis, which preserves the time-frequency information of the signal, is of significant advantage in control system synthesis and analysis. Wavelets, because of their time-frequency localization and multiresolution properties offer an efficient framework for representation and characterization of signals, especially that non-stationary in nature. Wavelets can also be useful in obtaining process models that describe the process behavior on different time scales. These properties are very attractive from process identification and controller design prospective and recently have been shown to be of significant advantage for some of the process engineering problems (Bakshi and Stephanopoulos, 1993; Palavajjhala et al., 1994).Item Modeling And Simulation Of Fixed Bed Adsorption Column: Effect Of Velocity Variation(iManager, 2005-08) Gupta, SureshThe kinetic behavior of a fixed-bed adsorber can be explained and the characteristic breakthrough curve of the adsorption phenomena can be obtained through mathematical models. In the earlier models, the kinetics is explained using a mathematical model that takes into account of external and internal mass-transfer resistances with a nonideal plug flow behavior. The variation of fluid velocity along the column is an important aspect, which has not been accounted so far. In the present study, a mathematical model is proposed for explaining the kinetic behavior of adsorption phenomena incorporating the fluid velocity variation along the column length also. Internal mass-transfer resistances due to pore diffusion mechanism are considered in the model. The proposed mathematical model for fixed-bed adsorption is solved numerically and compared with earlier model reported in literature. The results show that the breakpoint is obtained earlier which represents the realistic behavior in adsorption phenomena. Initially the sharp front of the breakthrough curve is seen followed by broadening of tail of the breakthrough curve. Simulations are carried out using the present model for a systematic parametric study. The effects of various important and influencing parameters such as flow rate, bed height, inlet adsorbate concentration and particle diameter on breakthrough curve are studied in detail.Item Ergonomic and workplace assessment of an integrated fiber industry using quantitative methods(2006) Kale, Samir RamdasErgonomic Design and Workplace Assessment are the major disciplines that govern the Occupational Health and Safety of a Process Industry.This paper highlights the various factors that are vital to these disciplines in the context of an Integrated Fiber Industry (combined chemical and spinning operations). A Questionnaire was designed to cover all aspects related to Ergonomics and Workplace. It included feedback from the workers at the Spinning and After-treatment sections (heart of the fiber industry). Based on the workers response quantification was done on the marks allocated to each one of the factors. This methodology aimed at finding the deviations from the desired norms and regulations. This approach is discussed in detail in the article. Certain inferences can be made from the study. • No of Training hours to be increased • Use of Personal Protective Equipment to be encouraged • Comfort conditioning to be calculated & maintained (Based on 8 hours working)Item Simulation Studies on Transient Model for Biofilter operated in Periodic Mode(JET, 2006) Raghuvanshi, SmitaBiofiltration of off-gases containing Volatile Organic Compounds (VOCs) is a reliable and cost effective technology for VOCs removal. Due to many inherent advantages, most of the industries operate biofilters under the periodic conditions (highly transient). Taking the importance of such operation into account, a model is developed based on the transient conditions. In this study, a Linear Driving Force (LDF) model is used, which takes into account both mechanisms (adsorption and biodegradation) involved in biofiltration process. The rate equation is given by the modified three-parameter Monod-type expression. The results obtained from the present model are validated with the experimental data and the results obtained from earlier model reported in the literature. The simulations are also carried out to understand the influence of various important parameters such as inlet VOCs concentrations, bed height and gas velocity on the biofiltration process operated in the periodic mode.Item Rapid thermal annealing of hot wire chemical-vapor-deposited a-Si:H films: The effect of the film hydrogen content on the crystallization kinetics, surface morphology, and grain growth(AIP, 2006-01) Roy, BanasriThe ability to crystallize thin amorphous Si layers into large grain Si can lead to significant improvements in Si solar cells and thin-film transistors. Here we report on the effect of the hydrogen content in as-grown films on the crystallization kinetics, surface morphology, and grain growth for hot wire chemical-vapor-deposited a-Si:H films crystallized by rapid thermal annealing (RTA). At RTA temperatures >750°C for high-hydrogen-content films, we observe the explosive evolution of hydrogen, with a resultant destruction of the film. Little or no damage is observed for films containing low hydrogen content. At a lower RTA temperature (600°C), the films remain intact with similar morphologies. At this same lower RTA temperature, both the incubation time and crystallization time decrease, and the grain size as measured by x-ray diffraction increases with decreasing hydrogen film content. Measurements of the crystallization time versus H evolution time indicate that the vast majority of the hydrogen must evolve from both films before crystallization commences. To examine the relationship between hydrogen evolution and crystallization, a two-step annealing process was utilized. For the high hydrogen content films, the final grain size increases if a large portion of the hydrogen is driven out at temperatures well below the crystallization temperatureItem Improvement of the degradation characteristics of sol-gel derived PZT (53/47) thin films : Effect of conventional and graded iron doping(Taylor & Francis, 2006-09-03) Roy, BanasriSeveral approaches are evident in the literature to improve the fatigue resistance and lower the leakage current densities of PZT thin films for nonvolatile random access memory (NVRAM) application. We have undertaken an approach of doping (conventional and graded) of PZT (53/47) thin films with Fe cation, which tend to occupy B-site in the AB03 unit cell. Our studies indicated several improvements in the electrical characteristics. The graded doped Fe film of similar dopant concentrations exhibited even better fatigue behavior up to -lo9 cycles. In addition, the Ohmic behavior in I-V characterization extended up to 250 kV/cm for graded doped films, while the non-linearity sets at much lower field (lSOkV/cm) for undoped films at room temperature. Conventional doping improved the electrical behavior as compared to undoped films. However, the graded doped films exhibited even further improved electrical behavior in terms of reducing leakage current by at least an order of magnitude under an applied electric fields of about 150 kV/cm.Item Modeling and Simulation of Reduction Zone of Downdraft Biomass Gasifier: Effect of Air to Fuel Ratio(JET, 2007) Sheth, P.N.Biomass mainly in the form of wood is the oldest form of energy used by humans. Biomass generally means a relatively dry solid of natural matter that has been specifically grown or has originated as waste or residue from handling such materials. The thermochemical conversion of biomass (pyrolysis, gasification, combustion) is one of the most promising non-nuclear forms of future energy. In the present study, the model reported in literature is simulated to study the effects of pyrolysis fraction on the outlet gas concentration in a downdraft biomass gasifier. It is found that the air to fuel ratio is one of the key parameters in the reduction zone of downdraft biomass gasifier. It effects the value of pyrolysis fraction in the model, and indirectly proportional to the pyrolysis fraction. Steady state composition and temperature profiles for the reduction zone of the downdraft biomass gasifier are also predicted for various values of air to fuel ratio.Item Two-step annealing of hot wire chemical vapor deposited a-Si:H films(Springer, 2008) Roy, BanasriA two-step annealing process was used to investigate the effect of dehydrogenation on crystallization and grain growth of low and high hydrogen content hot wire chemical vapor deposited (HWCVD) a-Si:H films. A low temperature pre-annealing followed by a rapid thermal annealing step at 600 °C was carried out. For the high hydrogen content film XRD (111) peak narrowed quite a bit, while opposite effect was observed for the low hydrogen content film. According to the grain sizes as calculated from TEM images, grain sizes of both of the two-step annealed high and low hydrogen content films are smaller than that of the single stage annealed film.Item Adsorption of Cr(VI) using activated neem leaves: kinetic studies(Springer, 2008) Gupta, SureshIn the present study, adsorbent is prepared from neem leaves and used for Cr(VI) removal from aqueous solutions. Neem leaves are activated by giving heat treatment and with the use of concentrated hydrochloric acid (36.5 wt%). The activated neem leaves are further treated with 100 mmol of copper solution. Batch adsorption studies demonstrate that the adsorbent prepared from neem leaves has a significant capacity for adsorption of Cr(VI) from aqueous solution. The parameters investigated in this study include pH, contact time, initial Cr(VI) concentration and adsorbent dosage. The adsorption of Cr(VI) is found to be maximum (99%) at low values of pH in the range of 1-3. A small amount of the neem leaves adsorbent (10 g/l) could remove as much as 99% of Cr(VI) from a solution of initial concentration 50 mg/l. The adsorption process of Cr(VI) is tested with Langmuir isotherm model. Application of the Langmuir isotherm to the system yielded maximum adsorption capacity of 62.97 mg/g. The dimensionless equilibrium parameter, R L, signifies a favorable adsorption of Cr(VI) on neem leaves adsorbent and is found to be between 0.0155 and 0.888 (0Item Removal of heavy metal pollutants from wastewater using low cost absorbents(Atlantic, 2008-01) Gupta, SureshItem Preparation and characterization of sol–gel derived copper–strontium–oxide thin films(Elsiever, 2008-04-30) Roy, BanasriP-type transparent conductive oxides have potential applications in photovoltaics, transparent electronics, and organic optoelectronics. In this paper, results are presented on the synthesis of Cu2SrO2 thin films, a p-type transparent conducting oxide by a sol–gel route. Cu(II)methoxide and Sr-metal dissolved in anhydrous isopropanol were used as precursor for the sol preparation. For potassium (K) doping, K-acetate dissolved in anhydrous isopropanol was used as the precursor. Films were spin-coated onto substrates and partially pyrolysed in air at 225°C. After partial pyrolization, a two stage annealing sequence was used to achieve the final film microstructure and composition. Although combinations of oxygen pressure, annealing time, and annealing temperature were used to obtain phase pure Cu2SrO2 thin films, X-ray diffraction consistently showed the presence of Cu2O as a second phase with Cu2SrO2−the desired phase. Microstructural studies showed similar phase separation in the films and confirmed the microcrystalline nature. The best conductivities obtained for the undoped and 1% K-doped films were 2 × 10− 3 and 1.2 × 10− 2 S/cm, respectively. Both films showed a broad optical absorption edge in the visible range.