Showing papers by "National Aerospace Laboratories published in 2013"

Effect of Calcination Temperature on Structural, Photoluminescence, and Thermo luminescence Properties of Y2O3:Eu3+ Nanophosphor

Abstract: Red light emitting cubic Y1.95Eu0.05O3 nanophosphors have been synthesized by a low temperature solution combustion method using ethylene diamine tetra acetic acid (EDTA) as fuel. The systematic studies on the effect of calcination temperature on its structural, photoluminescence (PL), and thermoluminescence (TL) properties were reported. The crystallinity of the samples increases, and the strain is reduced with increasing calcination temperature. SEM micrographs reveal that samples lose their porous nature with an increase in calcination temperature. PL spectra show that the intensity of the red emission (611 nm) is highly dependent on the calcination temperature and is found to be 10 times higher when compared to as-formed samples. The optical band gap (E-g) was found to reduce with an increase of calcination temperature due to reduction of surface defects. The thermoluminescence (TL) intensity was found to be much enhanced in the 1000 degrees C calcined sample. The increase of PL and TL intensity with calcination temperature is attributed to the decrease of the nonradiative recombination probability, which occurs through the elimination of quenching defects. The trap parameters (E, b, s) were estimated from Chen's glow peak shape method and are discussed in detail for their possible usage in dosimetry.

Palladium Nanoparticles on Graphite Oxide: A Recyclable Catalyst for the Synthesis of Biaryl Cores

Abstract: The synthesis of life saving drug molecules in a cost-effective and environmentally benign pathway is of paramount significance. We present an environment friendly protocol to prepare core moieties of top selling drug molecules such as boscalid and telmisartan using Suzuki–Miyaura coupling conditions. In contrast to the traditional synthesis of these pharmaceutically important molecules, we have accomplished a graphite oxide (GO) supported palladium nanoparticles (PdNPs) based catalyst which quantitatively produced these core biaryl moieties of top selling drug molecules in a recyclable way. The catalytic activity remained unchanged even after 16 successive catalytic cycles without incorporating any palladium metal impurity in the pharmaceutically significant organic products. A detailed study including IR spectroscopy, solid state NMR spectroscopy, X-ray photoelectron spectroscopy, and DFT calculation was employed to understand the role of solid support on the nondecaying recycling ability of the catalys...

The Aqua-Planet Experiment (APE): CONTROL SST Simulation

Abstract: Climate simulations by 16 atmospheric general circulation models (AGCMs) are compared on an aqua-planet, a water-covered Earth with prescribed sea surface temperature varying only in latitude. The idealised configuration is designed to expose differences in the circulation simulated by different models. Basic features of the aqua-planet climate are characterised by comparison with Earth. The models display a wide range of behaviour. The balanced component of the tropospheric mean flow, and mid-latitude eddy covariances subject to budget constraints, vary relatively little among the models. In contrast, differences in damping in the dynamical core strongly influence transient eddy amplitudes. Historical uncertainty in modelled lower stratospheric temperatures persists in APE.Aspects of the circulation generated more directly by interactions between the resolved fluid dynamics and parameterized moist processes vary greatly. The tropical Hadley circulation forms either a single or double inter-tropical convergence zone (ITCZ) at the equator, with large variations in mean precipitation. The equatorial wave spectrum shows a wide range of precipitation intensity and propagation characteristics. Kelvin mode-like eastward propagation with remarkably constant phase speed dominates in most models. Westward propagation, less dispersive than the equatorial Rossby modes, dominates in a few models or occurs within an eastward propagating envelope in others. The mean structure of the ITCZ is related to precipitation variability, consistent with previous studies.The aqua-planet global energy balance is unknown but the models produce a surprisingly large range of top of atmosphere global net flux, dominated by differences in shortwave reflection by clouds. A number of newly developed models, not optimised for Earth climate, contribute to this. Possible reasons for differences in the optimised models are discussed.The aqua-planet configuration is intended as one component of an experimental hierarchy used to evaluate AGCMs. This comparison does suggest that the range of model behaviour could be better understood and reduced in conjunction with Earth climate simulations. Controlled experimentation is required to explore individual model behavior and investigate convergence of the aqua-planet climate with increasing resolution.

Effect of strain on the thermomechanical behavior of epoxy based shape memory polymers

Abstract: The effect of deformation strain on the thermomechanical (TM) behavior of a commercially available bifunctional epoxy resin modified with 5 % carboxyl-terminated butadiene acrylonitrile (CTBN) was studied. The results were compared with those for the unmodified epoxy SMP. The glass transition temperatures (T g) as well as the moduli of these SMPs were determined. Static tensile tests were carried out at both 25 °C and 115 °C to study the effect of CTBN addition on the failure strain. TM cycling tests were conducted for two prescribed strain values: 15 % and 25 %. Further, the effect of the prescribed strain values and TM cycling on the shape-frozen and recovery responses of these SMPs were studied. In addition, microstructure studies were carried out in order to examine the dispersion of the CTBN and the fracture behavior of the CTBN-epoxy SMP. The results show that adding CTBN to the epoxy matrix leads to a slight reduction in storage modulus and T g. Static tensile tests revealed that there was a noticeable improvement in the failure strain of the CTBN-epoxy SMP when it was tested at 115 °C rather than at 25 °C. The cyclic thermomechanical tests performed here prove that the CTBN-epoxy SMP has a better endurance than the unmodified epoxy SMP, as well as enhanced shape-recovery characteristics.

Characterization of iron impregnated polyacrylamide catalyst and its application to the treatment of municipal wastewater

Abstract: The persistent organic pollutants and bio diversities (pathogenic and non-pathogenic) present in treated municipal wastewater cause environmental deterioration besides adversely affecting human health. In the present investigation, an attempt was made to treat the municipal wastewater using iron impregnated polyacrylamide (IIPA) powder catalyst in a fluidized reactor. The IIPA catalyst was characterized by carbon, 12.23%, hydrogen, 1.63%, nitrogen, 2.93%, iron, 58%, silicon, 15.25%, surface area 96.66 m2 g−1 and pore diameter, 58.32 A. IIPA was crystalline with an energy gap of 1.93 eV and it was capable of generating hydroxyl radicals for the oxidation of dissolved organics in municipal wastewater with minimum sludge yield (0.05 g VSS/g of COD). The oxidation of dissolved organics in municipal wastewater by IIPA was carried out under batch and continuous mode operations. The pseudo first order rate kinetic constants for the oxidation of organics in municipal wastewater were found to be 2.2 × 10−2, 3.01 × 10−2, 3.33 × 10−2 and 3.72 × 10−2 min−1. The activation energy for the oxidation of dissolved organics in municipal wastewater was 13.15 kJ mol−1. The pollution parameters BOD5, COD, ammonia, TKN and sulphide were removed from the municipal wastewater by 72.72%, 82.87%, 71.76%, 65.3% and 86.66% respectively.

Effect of lanthanum, neodymium on piezoelectric, dielectric and ferroelectric properties of PZT

Abstract: The effect of La3+ and Nd3+ on piezoelectric, dielectric and ferroelectric properties of PZT (Pb(Zr0.53Ti0.47)O3) was studied. The powders were prepared by “wet-chemical” route followed by calcination at 800 °C for 4 h. XRD analysis of the calcined powders confirms the tetragonal phase in the undoped PZT, which gradually decreases with the dopant concentration and the appearance of rhombohedral phase simultaneously. SEM study of sintered pellets reveals the decrease in grain size with the increase in dopant concentration beyond 0.02 mol Nd3+ and 0.03 mol La3+ respectively. The piezoelectric constant (d33) and dielectric properties were maximum for 0.02 mol Nd3+ and 0.03 mol La3+ respectively. The remnant polarization of La3+-doped sample was higher than Nd3+-doped sample, and the sample with combined dopants shows intermediate remnant polarization (Pr). Based on the above study, it is concluded that La3+ is more effective than Nd3+, including in a mixture of La3+ and Nd3+ dopants.

The aqua-planet experiment (APE): Response to changed meridional SST profile

Abstract: This paper explores the sensitivity of Atmospheric General Circulation Model (AGCM) simulations to changes in the meridional distribution of sea surface temperature (SST). The simulations are for an aqua-planet, a water covered Earth with no land, orography or sea- ice and with specified zonally symmetric SST. Simulations from 14 AGCMs developed for Numerical Weather Prediction and climate applications are compared. Four experiments are performed to study the sensitivity to the meridional SST profile. These profiles range from one in which the SST gradient continues to the equator to one which is flat approaching the equator, all with the same maximum SST at the equator. The zonal mean circulation of all models shows strong sensitivity to latitudinal distribution of SST. The Hadley circulation weakens and shifts poleward as the SST profile flattens in the tropics. One question of interest is the formation of a double versus a single ITCZ. There is a large variation between models of the strength of the ITCZ and where in the SST experiment sequence they transition from a single to double ITCZ. The SST profiles are defined such that as the equatorial SST gradient flattens, the maximum gradient increases and moves poleward. This leads to a weakening of the mid-latitude jet accompanied by a poleward shift of the jet core. Also considered are tropical wave activity and tropical precipitation frequency distributions. The details of each vary greatly between models, both with a given SST and in the response to the change in SST. One additional experiment is included to examine the sensitivity to an off-equatorial SST maximum. The upward branch of the Hadley circulation follows the SST maximum off the equator. The models that form a single precipitation maximum when the maximum SST is on the equator shift the precipitation maximum off equator and keep it centered over the SST maximum. Those that form a double with minimum on the equatorial maximum SST shift the double structure off the equator, keeping the minimum over the maximum SST. In both situations only modest changes appear in the shifted profile of zonal average precipitation. When the upward branch of the Hadley circulation moves into the hemisphere with SST maximum, the zonal average zonal, meridional and vertical winds all indicate that the Hadley cell in the other hemisphere dominates.

Wear and Corrosion Behavior of Zr-Doped DLC on Ti-13Zr-13Nb Biomedical Alloy

Abstract: Zirconium (Zr)-doped DLC was deposited on biomedical titanium alloy Ti-13Nb-13Zr by a combination of plasma-enhanced chemical vapor deposition and magnetron sputtering. The concentration of Zr in the films was varied by changing the parameters of the bi-polar pulsed power supply and the Ar/CH4 gas composition. The coatings were characterized for composition, morphology, nanohardness, corrosion resistance in simulated body fluid (SBF) and tribological properties. X-ray photoelectron spectroscopy (XPS) studies on the samples were used to estimate the concentration of Zr in the films. XPS and micro-Raman studies were used to find the variation of ID/IG ratio with Zr concentration. These studies show that the disorder in the film increased with increasing Zr concentration as deduced from the ID/IG ratio. Nanohardness measurements showed no clear dependence of hardness and Young’s modulus on Zr concentration. Reciprocating wear studies showed a low coefficient of friction (0.04) at 1 N load and it increased toward 0.4 at higher loads. The wear volume was lower at all loads on the coated samples. The wear mechanism changed from abrasive wear on the substrate to adhesive wear after coating. The corrosion current in SBF was unaffected by the coating and corrosion potential moved toward nobler (more positive) values.

Structural Health Monitoring of Composite Aircraft Structures Using Fiber Bragg Grating Sensors

Abstract: Aircraft industry is continually striving towards reducing the acquisition, operation and maintenance costs. Usage of advanced composite materials in primary aircraft structures have resulted in significant weight savings owing to their higher specific strength and specific stiffness. Composite structures, in spite of their inherent advantages, are prone to various damages. To detect and repair various structural damages that can occur during the service life of the aircraft, a thorough inspection schedule is implemented through conventional visual and Non Destructive Evaluation methods. Such scheduled inspections lead to considerable increase in maintenance cost & down-time of the aircraft. An online structural health monitoring (SHM) system consisting of well-designed sensor networks incorporated in the structure along with necessary hardware and software can provide information about the structure, thereby leading to reporting of flaws or damages in real time. Such a system can provide inputs for condition based maintenance which can result in reduced maintenance cost. This paper presents the work carried out at CSIR-National Aerospace Laboratories towards developing a flight-worthy SHM system and its demonstration on an unmanned aerial vehicle (UAV). Sensor selection, characterization, instrumentation design, algorithm development towards damage detection & load estimation at lab level and implementation of the technology on a UAV are discussed in this paper.

In Vitro Corrosion Behavior and Apatite Growth of Oxygen Plasma Ion Implanted Titanium Alloy β-21S

Abstract: Titanium alloy beta 21S was implanted with oxygen ions by plasma immersion ion implantation. The implanted surface was characterized by micro-Raman, XPS and FESEM before and after potentiodynamic polarization and electrochemical impedance studies in Hanks’ solution and after incubation in Hanks’ solution for 1 and 7 days. The investigations show that the native oxide on the sample is replaced by a compact oxide by implantation and the new oxide layer behaves in a different way in that a two layer model is required to explain the observed electrochemical impedance data. The analysis of layers formed in the electrochemical studies and after incubation in Hanks’ solution by XPS and FESEM shows that the new oxide surface is capable of inducing apatite growth on it.