Antibacterial Applications of Silver Nanoparticles Synthesized by Aqueous Extract of Azadirachta Indica (Neem) Leaves

Silver nanoparticles are known to have bactericidal effects. A new generation of dressings incorporating antimicrobial agents like silver nanoparticles is being formulated to reduce or prevent infections. The particles can be incorporated in materials and cloth rendering them sterile. Recently, it was found that aqueous silver ions can be reduced by aqueous extract of plant parts to generate extremely stable silver nanoparticles in water. Apart from being environmentally friendly process, use of Neem leaves extract might add synergistic antibacterial effect of Neem leaves to the biosynthesized nanoparticles. With this hypothesis the biosynthetic production of silver nanoparticles by aqueous extract of Neem leaves and its bactericidal effect in cotton cloth against E. Coli were studied in this work. Silver nanoparticles were synthesized by short term (1 day) and long term (21 days) interaction of Neem extract (20% w/v) and 0.01 M AgNO3 solution in 1:4 mixing ratio. The synthesized particles were characterized by UV visible spectroscopy, transmission electron microscopy, and incorporated into cotton disks by (i) centrifuging the disks with liquid broth containing nanoparticles, (ii) in-situ coating process during synthesis, and (iii) coating with dried and purified nanoparticles. The antibacterial property of the nanoparticles coated cotton disks was studied by disk diffusion method. The effect of consecutive washing of the coated disks with distilled water on antibacterial property was also investigated. This work demonstrates the possible use of biologically synthesized silver nanoparticles by its incorporation in cloths leading them to sterilization.

Some studies on TiO2 films deposited by sol-gel technique

TiO2 films are extensively used in various applications including optical multi-layers, sensors, photo catalysis, environmental purification, and solar cells etc. These are prepared by both vacuum and non-vacuum methods. In this paper, we present the results on TiO2 thin films prepared by a sol-gel spin coating process in non-aqueous solvent. Titanium isopropoxide is used as TiO2 precursor. The films were annealed at different temperatures up to 3000 C for 5 hours in air. The influence of the various deposition parameters like spinning speed, spinning time and annealing temperature on the thickness of the TiO2 films has been studied. The variation of film thickness with time in ambient atmosphere was also studied. The optical, structural and morphological characteristics were investigated by optical transmittance-reflectance measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The refractive index and extinction coefficient of the films were determined by envelope technique and spectroscopic ellipsometry. TiO2 films exhibited high transparency (92%) in the visible region with a refractive index of 2.04 at 650 nm. The extinction coefficient was found to be negligibly small. The X-ray diffraction analysis showed that the TiO2 film deposited on glass substrate changes from amorphous to crystalline (anatase) phase with annealing temperature above 2500 C. SEM results show that the deposited films are uniform and crack free.

Hydrocarbon oxidation and three-way catalytic activity on a single step directly coated cordierite monolith: High catalytic activity of Ce0.98Pd0.02O2−δ

Catalytic activity of cordierite honeycomb by a completely new coating method for the oxidation of major hydrocarbons in exhaust gas is reported here. The new coating process consists of (a) dipping and growing γ-Al2O3 on cordierite by combustion of monolith dipped in the aqueous solution of Al(NO3)3 and oxalyldihydrazide (ODH) (or glycine) at 600 °C and active catalyst phase Ce0.98Pd0.02O2−δ on γ-Al2O3-coated cordierite again by combustion of monolith dipped in the aqueous solution of ceric ammonium nitrate, ODH and 1.2 × 10−3 M PdCl2 solution at 500 °C. Weight of active catalyst can be varied from 0.02 wt% to 2 wt% which is sufficient but can be loaded even up to 12 wt% by repeating dip dry combustion. Adhesion of catalyst to cordierite surface is via oxide growth, which is very strong. ‘HC’ oxidation over the monolith catalyst is carried out with a mixture having the composition, 470 ppm of both propene and propane and 870 ppm of both ethylene and acetylene with the varying amount of O2. Three-way catalytic test is done by putting hydrocarbon mixture along with CO (10 000 ppm), NO (2000 ppm) and O2 (15 000 ppm). Below 350 °C full conversion is achieved. In this method, handling of nano-material powder is avoided.

Dual functional performance of fiber Bragg gratings coated with metals using flash evaporation technique

Metallic and other type of coatings on fiber Bragg grating (FBG) sensors alter their sensitivity with thermal and mechanical stress while protecting the fragile optical fiber in harsh sensing surroundings. The behavior of the coated materials is unique in their response to thermal and mechanical stress depending on the thickness and the mode of coating. The thermal stress during the coating affects the temperature sensitivity of FBG sensors. We have explored the thermal response of FBGs coated with Al and Pb to an average thickness of 80 nm using flash evaporation technique where the FBG sensor is mounted in a region at room temperature in an evacuated chamber having a pressure of 10(6) Torr which will minimize any thermal stress during the coating process. The coating thickness is chosen in the nanometer region with the aim to study thermal behavior of nanocoatings and their effect on FBG sensitivity. The sensitivity of FBGs is evaluated from the wavelengths recorded using an optical sensing interrogator sm 130 (Micron Optics) from room temperature to 300 degrees C both during heating and cooling. It is observed that the sensitivity of the metal coated fibers is better than the reference FBG with no coating for the entire range of temperature. For a coating thickness of 80 nm, Al coated FBG is more sensitive than the one coated with Pb up to 170 degrees C and it reverses at higher temperatures. This point is identified as a reversible phase transition in Pb monolayers as the 2-dimensional aspects of the metal layers are dominant in the nanocoatings of Pb. On cooling, the phase transition reverses and the FBGs return to the original state and for repeated cycles of heating and cooling the same pattern is observed. Thus the FBG functions as a sensor of the phase transitions of the coatings also. (C) 2012 Elsevier Inc. All rights reserved.

Zinc acetylacetonate hydrate adducted with nitrogen donor ligands: Synthesis, spectroscopic characterization, and thermal analysis

We report synthesis, spectroscopic characterization, and thermal analysis of zinc acetylacetonate complex adducted by nitrogen donor ligands, such as pyridine, bipyridine, and phenanthroline. The pyridine adducted complex crystallizes to monoclinic crystal structure, whereas other two adducted complexes have orthorhombic structure. Addition of nitrogen donor ligands enhances the thermal property of these complexes as that with parent metal-organic complex. Zinc acetylacetonate adducted with pyridine shows much higher volatility (106 degrees C), decomposition temperature (202 degrees C) as that with zinc acetylacetonate (136 degrees C, 220 degrees C), and other adducted complexes. All the adducted complexes are thermally stable, highly volatile and are considered to be suitable precursors for metal organic chemical vapor deposition. The formation of these complexes is confirmed by powder X-ray diffraction, Fourier transform infrared spectroscopy, mass spectroscopy, and elemental analysis. The complexes are widely used as starting precursor materials for the synthesis of ZnO nanostructures by microwave irradiation assisted coating process. (c) 2015 Elsevier B.V. All rights reserved.

Effect of sintering on optical, structural and photoluminescence properties of ZnO thin films prepared by sol-gel process

Zinc oxide (ZnO) thin films have been deposited on glass substrates via sol-gel technique using zinc acetate dihydrate as precursor by spin coating of the sol at 2000 rpm. Effects of annealing temperature on optical, structural and photo luminescence properties of the deposited ZnO films have been investigated. The phase transition from amorphous to polycrystalline hexagonal wurtzite structure was observed at an annealing temperature of 400 degrees C. An average transmittance of 87% in the visible region has been obtained at room temperature. The optical transmittance has slightly increased with increase of annealing temperature. The band gap energy was estimated by Tauc's method and found to be 3.22 eV at room temperature. The optical band gap energy has decreased with increasing annealing temperature. The photoluminescence (PL) intensity increased with annealing temperature up to 200 degrees C and decreased at 300 degrees C. (c) 2010 Elsevier B.V. All rights reserved.

Quasicrystalline Coatings Through Laser Processing: A Study on Process Optimisation and Microstructure Evolution

Composite coatings containing quasicrystalline (QC) phases in Al-Cu-Fe alloys were prepared by laser cladding using a mixture of the elemental powders. Two substrates, namely pure aluminum and an Al-Si alloy were used. The clad layers were remelted at different scanning velocities to alter the growth conditions of different phases. The process parameters were optimized to produce quasicrystalline phases. The evolution of the microstructure in the coating layer was characterized by detailed microstructural investigation. The results indicate presence of quasicrystals in the aluminum substrate. However, only approximant phase could be observed in the substrate of Al-Si alloys. It is shown that there is a significant transport of Si atoms from the substrate to the clad layer during the cladding and remelting process. The hardness profiles of coatings on aluminum substrate indicate a very high hardness. The coating on Al-Si alloy, on the other hand, is ductile and soft. The fracture toughness of the hard coating on aluminum was obtained by nano-indentation technique. The K1C value was found to be 1.33 MPa m1/2 which is typical of brittle materials.

Optical, electrical and dielectric properties of TiO(2)-SiO(2) films prepared by a cost effective sol-gel process

Titanium dioxide (TiO(2)) and silicon dioxide (SiO(2)) thin films and their mixed films were synthesized by the sol-gel spin coating method using titanium tetra isopropoxide (TTIP) and tetra ethyl ortho silicate (TEOS) as the precursor materials for TiO(2) and SiO(2) respectively. The pure and composite films of TiO(2) and SiO(2) were deposited on glass and silicon substrates. The optical properties were studied for different compositions of TiO(2) and SiO(2) sols and the refractive index and optical band gap energies were estimated. MOS capacitors were fabricated using TiO(2) films on p-silicon (1 0 0) substrates. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated for the films annealed at 200 degrees C for their possible use in optoelectronic applications. (C) 2011 Elsevier B.V. All rights reserved.

Process and properties of electroless Ni-Cu-P-ZrO2 nanocomposite coatings

Electroless Ni-Cu-P-ZRO(2) composite coating was successfully obtained on low carbon steel matrix by electroless plating technique. Coatings with different compositions were obtained by varying copper as ternary metal and nano sized zirconium oxide particles so as to obtain elevated corrosion resistant Ni-P coating. Microstructure, crystal structure and composition of deposits were analyzed by SEM, EDX and XRD techniques. The corrosion behavior of the deposits was studied by anodic polarization, Tafel plots and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution. The ZRO(2) incorporated Ni-P coating showed higher corrosion resistance than plain Ni-P. The introduction of copper metal into Ni-P-ZRO(2) enhanced the protection ability against corrosion. The influence of copper metal and nanoparticles on microhardness of coatings was evaluated. (C) 2011 Elsevier Ltd. All rights reserved.

Influence of Sn doping on structural, optical and electrical properties of ZnO thin films prepared by cost effective sol-gel process

Tin (Sn) doped zinc oxide (ZnO) thin films were synthesized by sol-gel spin coating method using zinc acetate di-hydrate and tin chloride di-hydrate as the precursor materials. The films were deposited on glass and silicon substrates and annealed at different temperatures in air ambient. The agglomeration of grains was observed by the addition of Sn in ZnO film with an average grain size of 60 nm. The optical properties of the films were studied using UV-VIS-NIR spectrophotometer. The optical band gap energies were estimated at different concentrations of Sn. The MOS capacitors were fabricated using Sn doped ZnO films. The capacitance-voltage (C-V), dissipation vs. voltage (D-V) and current-voltage (I-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated. The porosity and surface area of the films were increased with the doping of Sn which makes these films suitable for opto-electronic applications. (C) 2012 Elsevier B.V. All rights reserved.

Process Development for Functionalization of Cotton with Silver Nanoparticles Synthesized by Bio-based Approaches

Cotton is a widely used raw material for textiles but drawbacks regarding their poor mechanical properties often limit their applications as functional materials. The present investigation involved process development for one step coating of cotton with silver nanoparticles (SNP) synthesized using Azadirachta indica and Citrus limon extract to develop functional textiles. Addition of starch to functional textiles led to efficient binding of nanoparticles to fabric and led to drastic decrease in release of silver from fabricated textiles after ten washing cycles enhancing their environment friendliness. Differential scanning calorimetry, scanning electron microscopy, FT-IR analysis and mechanical studies demonstrated efficient binding of nanoparticles to fabric through bio-based processes. The functionalized textiles developed by the bio-based methods showed significant antibacterial activity against E. coli and S. aureus (with 99% microbial reduction). Present work offers a simple procedure for coating SNP using bio-based approaches with promising applications in specialized functions.

Manipulating Crystallographic Texture of Sn Coatings by Optimization of Electrodeposition Process Conditions to Suppress Growth of Whiskers

The effects of two major electrodeposition process conditions, electrolyte bath temperature and current density, on the microstructure and crystallographic texture of pure tin coatings on brass and, ultimately, on the extent of whisker formation have been examined. The grain size of the deposited coatings increased with increasing electrolyte bath temperature and current density, which significantly affected the dominant texture: (211) or (420) was the dominant texture at low current densities whereas, depending on deposition temperature, (200) or (220) became the dominant texture at high current densities. After deposition, coatings were subjected to different environmental conditions, for example isothermal aging (room temperature, 50A degrees C, or 150A degrees C) for up to 90 days and thermal cycling between -25A degrees C and 85A degrees C for 100 cycles, and whisker growth was studied. The Sn coatings with low Miller index planes, for example (200) and (220), and with moderate aging temperature were more prone to whiskering than coating with high Miller index planes, for example (420), and high aging temperature. A processing route involving the optimum combination of current density and deposition temperature is proposed for suppressing whisker growth.

Electrochemical behavior of Sn-graphene composite coating

The electrochemical properties of pure Sn and Sn-graphene composite coating have been determined and compared. Coatings were electrodeposited on mild steel substrates. Graphene was synthesized by the electrochemical exfoliation process using SO42- ion as the intercalating agent. Morphological and structural characterization results revealed a clear effect of graphene on altering the texture, grain size and morphology of the coating. Corrosion behavior was analyzed through potentiodynamic polarization and electrochemical impedance spectroscopic methods. A significant improvement in the corrosion resistance in terms of reduction in corrosion current and corrosion rate and increase in polarization resistance was noted in case of Sn coating containing graphene.

Wave propagation in elastic solids undergoing damage and growth process

Modeling and analysis of wave propagation in elastic solids undergoing damage and growth process are reported in this paper. Two types of diagnostic problems, (1) the propagation of waves in the presence of a slow growth process and (2) the propagation of waves in the presence of a fast growth process, are considered. The proposed model employs a slow and a fast time scale and a homogenization technique in the wavelength scale. A detailed analysis of wave dispersion is carried out. A spectral analysis reveals certain low-frequency bands, where the interaction between the wave and the growth process produces acoustic metamaterial-like behavior. Various practical issues in designing an efficient method of acousto-ultrasonic wave based diagnostics of the growth process are discussed. Diagnostics of isotropic damage in a ductile or quasi-brittle solid by using a micro-second pulsating signal is considered for computer simulations, which is to illustrate the practical application of the proposed modeling and analysis. The simulated results explain how an estimate of signal spreading can be effectively employed to detect the presence of a steady-state damage or the saturation of a process.

A High-Resolution Transmission of the Precipitation Process in a Electron Microscopy Study Dilute Ti-N Alloy

The precipitation processes in dilute nitrogen alloys of titanium have been examined in detail by conventional transmission electron microscopy (CTEM) and high-resolution electron microscopy (HREM). The alloy Ti-2 at. pct N on quenching from its high-temperature beta phase field has been found to undergo early stages of decomposition. The supersaturated solid solution (alpha''-hcp) on decomposition gives rise to an intimately mixed, irresolvable product microstructure. The associated strong tweed contrast presents difficulties in understanding the characteristic features of the process. Therefore, HREM has been carried out with a view to getting a clear picture of the decomposition process. Studies on the quenched samples of the alloy suggest the formation of solute-rich zones of a few atom layers thick, randomly distributed throughout the matrix. On aging, these zones grow to a size beyond which the precipitate/matrix interfaces appear to become incoherent and the alpha' (tetragonal) product phase is seen distinctly. The structural details, the crystallography of the precipitation process, and the sequence of precipitation reaction in the system are illustrated.