Sutapa Roy Ramanan

Dip coated ITO thin-films through sol–gel process using metal salts

Abstract Indium tin oxide (ITO) thin-films were deposited on soda-lime-silicate glass using sols prepared from alcoholic solutions of indium chloride and stannic chloride with different In:Sn atomic ratios, namely 95/5, 90/10, 85/15 and 80/20. The electrical properties, structure and morphology of the thin-films were investigated. All the films studied, with a thickness range of 10–490 nm were polycrystalline with grain sizes in the range of 25–60 nm. Uniform and dense microstructure apparently devoid of cracks and voids were observed. Only cubic In 2 O 3 phase was observed in the X-ray diffraction (XRD) and transmission electron microscopy (TEM). SnO and SnO 2 phases were not detected. The sheet resistance values decreased with increase in coating thickness. A significant decrease in the resistance values was also noted after annealing in N 2 \H 2 (96–4%) atmosphere. The minimum sheet resistance values were noted for Sn concentration of 10 at.%. The lowest value, 11 ohms per square, was obtained after annealing for a 490-nm film.

Influence of processing variables on the microstructure of sol–gel spun alumina fibres

Abstract High-alumina fibre mats (Al2O3–4 wt.% SiO2) were prepared with and without organic additives using a sol–gel spinning technique. The effect of processing variables during various stages of oxide fibre preparation, including sol spinning, drying and calcination, on the various types of defects generated were studied. The defects formed due to improper spinning can be diameter variations, hollow fibres, fibre sticking, and shots. The defects generated during calcination includes porous fibres, fibre cracking and core–sheath structures. As the organic content increased, surface roughness after calcination increased and the strength of the fibres decreased. Variations in heating schedules used in the calcination of alumina fibres also had a significant effect on properties of alumina fibre mats, either leading to the generation of fibre mats with good strength or dusty products. Fibres having strengths of 1.2 GPa and good handleability were obtained using a heating rate of 240 °C/h.

Spectroscopic studies of Cr-doped silica gels

Abstract Hexavalent chromium was introduced into silica gel monoliths prepared via sols obtained from tetra ethyl orthosilicate and metal salts at a different final sol pH. Gels were heat-treated at temperatures to 1000°C. The UV-visible spectra of the 60°C dried gels indicated a change in the chromium species from Cr 3+ to a combination of Cr 3+ and Cr 6+ with increase in the final sol pH. With increase in the temperature of heat treatment, the conversion C 3+ → C 6+ was promoted. Electronic paramagnetic resonance studies showed Cr 5+ in increasing concentration with increase in the final sol pH and heat treatment temperature. The results indicated that, depending on the final sol pH value and heat treatment temperature, the chromium ions were incorporated as Cr 3+ , Cr 5+ and Cr 6+ in the gel and densified gel matrix.

Green Synthesis of Silver Nanoparticles by Haloarchaeon Halococcus salifodinae BK6

Nanobiotechnology is a multidisciplinary branch of nanotechnology which includes fabrication of nanosized materials using biological approaches. Highly structured metallic and metal sulfide nanoparticles have been reported to be synthesized by numerous bacteria, fungi, yeasts and viruses. However, biosynthesis of nanoparticles by Haloarchaea (salt-loving archaea) of the third domain of life, Archaea, is in its nascent stages. In this study, we report the intracellular synthesis of stable, mostly spherical silver nanoparticles (SNPs) by the haloarchaeal isolate Halococcus salifodinae BK6. The isolate adapted to silver nitrate was found to exhibit growth kinetics similar to that of cells unexposed to silver nitrate. The nitrate reductase enzyme assay and the enzyme inhibitor studies showed the involvement of NADH dependent nitrate reductase in silver tolerance, reduction, and synthesis of SNPs. UV visible spectroscopy, XRD, TEM and EDAX were used for characterization of SNPs. The XRD exhibited characteristic Bragg peaks of face centered cubic silver with crystallite domain size of 26 nm and 12 nm for SNPs synthesized in NTYE and halophilic nitrate broth, respectively. TEM analysis exhibited an average particle size of 50.3 nm and 12 nm for SNPs synthesized in NTYE and halophilic nitrate broth (HNB), respectively. The as synthesized SNPs exhibited antimicrobial activity against both Gram positive and Gram negative organisms.

Low-temperature-processed biocompatible Ag-HAp nanoparticles with anti-biofilm efficacy for tissue engineering applications

Biomaterial-associated infections are the major cause of implant failure and can also develop many years after implantation. Recent advances in nanotechnology and the development of new nano-materials have led to the design of anti-biofilm coatings on implant surfaces. In this study, the inhibition of biofilm formation on silver-doped hydroxyapatite (Ag-HAp) nanoparticles-coated glass slides is reported. Ag-HAp was synthesized using low-temperature-modified sol–gel method. The release of silver ions from the Ag-HAp reduced the adhesion and prevented formation of biofilms of Escherichia coli, Staphylococcus epidermidis and Pseudomonas aeruginosa when studied over a 10-day period. These coatings released an initial high amount of silver ions followed by a slow and gradual release facilitating sustained anti-biofilm activity. This initial high release of silver is beneficial for reducing bacterial adhesion which is the first step in the development of a biofilm. The biocompatibility of silver-doped hydroxyapatite coatings has also been confirmed. As success or failure of an implant depends on the balance between host tissue integration and bacterial colonization, the competitive growth between the mammalian and bacterial cells by inoculating E. coli into actively growing MG63 osteosarcoma cells on Ag-HAp coatings has been investigated. This could mimic the peri-operative contamination model.Graphical AbstractAg-HAp-coated slides exhibit anti-biofilm activity over a period of 10 days, while supporting the growth of osteosarcoma cells (MG63). Co-culturing of MG63 cells with bacteria showed healthy growth of MG63 cells and no growth of bacteria. HAp control did not support growth of MG63 cells in the presence of bacteria.

Sol-Gel Processing of Lead Lanthanum Zirconate Titanate Fibers

ABSTRACT Lead lanthanum zirconate titanate (PLZT) fibers, Pb1 - xLax(Zr1 - yTiy)1 − x/4 O3 were prepared using sol-gel technique with y = 0.35 and x as 0.09. Lead acetate, lanthanum nitrate, zirconium acetate and tetra isopropyl orthotitanate were used as the precursor materials to obtain a sol, which was concentrated to spinnable consistency by polymerizing in a rotary evaporator at 70°C. The gel fibers obtained via spinning method were calcined at 500°, 850° and 1200°C to get the ceramic fibers. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, Thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were used to characterize the fibers. X-ray analysis showed that pure perovskite phases were obtained at 850°C. The microstructure showed the presence of fibers with smooth structure.

Effect of doping on the structural parameters of pure and doped barium titanate nano powders synthesised by sol-gel emulsion technique

Ba1-xDxTiO3, ceramic powders was synthesised using sol-gel-emulsion technique. Structure of the synthesised powders was analysed using X-ray diffractometer from which the lattice parameters were deduced. Effect of doping as a function of atomic radii and the concentration of dopant (D) was studied on these parameters. XRD analysis showed the synthesised material to possess pseudocubic symmetry. Crystallite size of these powders varied between 15.98–40.72 nm. Cell volume shrinkage observed on doping pure BaTiO3 was noted to be between 0.02–2.27%. Change in % tetragonality for the synthesised powders was 16.62–21.57. The experimental lattice parameter values matched more closely when calculated using the empirical formula devised by Jiang et al. than that using Rick Ubic. The |%error| assuming six-fold coordination for the doped BaTiO3 powders was between 0.0168% to 0.9314% using the empirical formula devised by Jiang et al. and 0.0296% to 1.0852% using the formula given by Rick Ubic.