Suchitra Sen

Characterization of porous core layer for controlling rare earth incorporation in optical fiber

The porous core layer deposited by modified chemical vapour deposition process has been analyzed in terms of thickness, pore size distribution, homogeneity and characteristics of the soot particles to investigate their variation with deposition temperature and input vapour composition. The compositions selected were SiO(2), SiO(2)-GeO(2) and SiO(2)-P(2)O(5). Rare earth ions were incorporated into the deposit by a solution doping technique. The analysis of deposited microstructures was found to provide a quantitative indication about the rare earth incorporation and its variation with respect to process conditions. Thus the characterization provides a method of controlling rare earth doping and ultimate preform/fiber properties.

Preparation and thermal evolution of sol-gel derived transparent ZrO2 and MgO-ZrO2 gel monolith

Transparent gel monoliths of pure and MgO-doped zirconia having dopant concentrations in the range 0 to 15 mol % were prepared by chemical polymerization of zirconium n-propoxide and magnesium acetate tetrahydrate using 2-methoxy ethanol as solvent. The thermal evolution of amorphous gels was studied by differential thermal analysis, X-ray diffraction and transmission electron microscopy. The crystallization of pure and doped zirconia gels occurred in the temperature range 360 to 450° C. The first crystalline phase to appear is tetragonal for pure and 2 mol % doped zirconia, and cubic for 3 to 15 mol % doped samples. Both crystallization and decomposition temperatures are found to increase with increasing dopant concentration, approaching a saturation value for 10 mol % doped samples. It has been established that the transformation of the cubic to the monoclinic phase takes place via a metastable tetragonal phase. A linear relationship between the lattice parameter of cubic zirconia and MgO concentration has been established. X-ray diffraction studies have also revealed that the entire amount of MgO used in preparing doped zirconia gels remains in a single MgO-ZrO2 crystalline phase formed initially by thermal treatment.[/p]

Rietveld analysis of polymorphic transformations of ball milled anatase TiO2

Rietveld’s whole powder profile fitting method based on crystal structure refinement is applied to extract the microstructure information of several polymorphic TiO2 phases grown simultaneously during high energy vibratory ball milling of anatase phase. Warren–Averbach’s method of X-ray line profile analysis is also made for comparison of above results. The X-ray powder patterns of four TiO2 phases along with α-Al2O3 (contamination) are simulated simultaneously for the first time to fit the experimental X-ray powder patterns of multiphase materials. The structural details of monoclinic TiO2 (B) phase are also reported first time in this paper. The advantages of the present method of analysis over the other methods of X-ray line profile analysis are discussed in details.

The formation of intermetallics in Cu/In thin films

The kinetics of the formation of intermetallics in the Cu–In bimetallic thin film couple have been studied from room temperature to 432 K by measuring the evolution of composite and contact electrical resistance with time and temperature. The resistivity measurements have been supplemented by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Copper reacts with indium even at room temperature to form CuIn intermetallic and assuming a model of defect assisted diffusion into the grains, the activation energy averaged over five different samples is found to be 0.40 eV. The grain boundary diffusion is found to occur with an average activation energy of 0.55 eV. XRD confirms the growth of CuIn intermetallic and on annealing at higher temperature, for copper-rich films copper further reacts with CuIn to form Cu 9 In 4 . Further evidences of solid state reactions and grain boundary diffusion through Cu grain boundaries have been obtained from SEM study. TEM indicates the growth of the grain size on annealing and confirms the presence of the CuIn phase.

THE STRUCTURAL TRANSFORMATION OF ANATASE TIO2 BY HIGH-ENERGY VIBRATIONAL BALL MILLING

The structural transformation of anatase TiO2 by high-energy vibrational ball milling was studied in detail by different analytical methods of x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This structural transformation involves both phase transition and nanoparticle formation, and no amorphization was observed. The crystallite size was found to decrease with milling time down to nanometer size similar to 13 nm and approaching saturation, accompanied by phase transformation to metastable phases, i.e., TiO2(II), which is a high-pressure phase and TiO2(B), which was identified in ball-milled powder reported for the first time in this paper. These phases eventually started transforming to rutile by further milling.

The synthesis, characterization and sintering of sol-gel derived cordierite ceramics for electronic applications

Cordierite ceramics were synthesized by sol-gel processing using alkoxides and acetate with an aim to use the material as substrate and packaging material. Preparation conditions were optimized by varying the amount and pH of water added and the amount of acetic acid as chelating agent. The powders were characterized by different analytical techniques such as thermogravimetric analysis, differential thermal analysis, surface area by BET, X-ray diffraction, transmission and scanning electron microscopies and infrared spectroscopy. The best product was obtained using 19.6 mol water and 0.34 mol acetic acid with respect to silicon ethoxide. The pH of the water added did not make any significant difference. Sintered materials were characterized by measuring different physical properties such as density, electrical and dielectric properties, thermal expansion, microstructure and composition. Well-sintered bodies could be achieved at 1000 °C in air with a soaking time of 2 h having a density of ∼ 99% theoretical, electrical resistivity of ∼1014 Ωcm, dielectric constant of 5, dielectric loss ∼0.008 and thermal expansion coefficient of 28.5 × 10−7 °C−1, 25–200 °C. X-ray diffraction studies show the phase evolution in these materials is predominantly μ-cordierite (hexagonal high cordierite) and some β-quartz. SEM reveals a uniformly dense microstructure with crystals of granular habit. X-ray photoelectron spectroscopy indicates that the surface composition of the sintered material is slightly enriched with aluminium and deficient in silicon.

Interfacial reactions in bimetallic Ag-Sn thin film couples

Abstract Interfacial reactions in bimetallic Ag-Sn thin film couples have been investigated by measurement of electrical resistance and contact resistance as a function of time and temperature in order to understand kinetic behaviour in the above system where the intermetallic phase γ-Ag3Sn is formed. Since the reaction is found to start at room temperature, the conventional vacuum coating unit has been modified for preparing such films and conducting subsequent measurements without breaking the vacuum. The results from the above different methods of resistance measurement indicate that interfacial reactions are characterized by a mean diffusion coefficient of 10-13 cm2 s-1 at room temperature. X-ray diffraction indicates growth of the γ-Ag3Sn phase immediately after deposition. Scanning electron microscopy confirms the diffusion of tin into silver by grain boundary diffusion rather than by bulk diffusion. The results from transmission electron microscopy confirm the presence of a γ-Ag3Sn phase.

Phase-transformations in amorphous 3Al2O3-2SiO2 system prepared by Sol-Gel method

Binary gels of SiO2-Al2O3 of different compositions were prepared, using alkoxides, by the sol-gel technique. In this communication, we report the preparation and phase-transformations of 3Al2O3-2SiO2 (mullite) gel. The material obtained was dried and heat-treated at different temperatures for dehydration-polymerization. Further heat-treatment above 900°C promoted crystallization, a metastable phase first being formed leading to the stable mullite phase. The kinetics and the microstructural evolution of these transformations were studied by X-ray diffraction, differential thermal analysis, electron microscopy, infrared spectroscopy and refractive index measurements. It was found that in this gel material the high-temperature heat-treatment at 1450°C produced pure well-crystallized mullite (particle size ∼ 0.07–0.15 μm) of prismatic shape contrary to its characteristic acicular habit.

Energy Efficient Melting of Glass for Nuclear Waste Immobilization Using Microwave Radiation

A base glass suitable for immobilization of nuclear waste was prepared by melt quenching technique using microwave radiation as a heating source. Microwave absorption behavior of major raw materials was studied and presented. The glass was also prepared in a conventional resistance heating furnace using the same batch composition. X-ray diffraction analysis of the sample prepared in microwave furnace has confirmed glass formation, which is in a similar agreement with that of glass prepared in the conventional resistance heating furnace. Comparative property analysis indicated identical glass prepared in both the routes. In microwave furnace, total power consumption was found to be ˜5 kWh with the maximum power demand of 1.5 kW. Electrical power consumption in resistance heating furnace was studied in three different capacities of furnaces and compared with that of microwave furnace. Energy saving in the range ˜60% was recorded in microwave heating compared to resistance heating furnace. Further, the time needed to melt the glass in a microwave furnace was recorded less than 2 hr compared to 6–7 hr needed in resistance heating furnace. Thus, microwave heating yields identical glass consuming substantially less electrical power and time, signifying possibility of drastic reduction of cost in glass melting.

Electrically conducting polyaniline and polyaniline/polycarbonate composite films: Preparation, characterization and electrical conductivity measurements

Polyanilinc (PAN) films and composites of polyaniline with poly bisphenol A carbonate (PC) have been prepared electrochemically. The electrical conductivity measured from room temperature down to 77 K is larger in air than in vacuum and obeys a ID variable range hopping (VRH) mechanism. From DTA analysis of the composite film, an extra peak at 210 °C apart from the usual peaks of PC and PAN has been identified. It is believed to be the result of a chemical interaction between PAN and PC, that is further confirmed from the shift in the carbonyl peak in the FTIR spectra of the composite films. From XPS studies and electrical conductivity measurements of different films it seems that it is the proportion of ionic chlorine rather than covalent chlorine to nitrogen that is more important in determining the conductivity. SEM pictures clearly indicate the formation of a fibrilar network in the composite film, especially inside the craters seen on the surface.