IR@CGCRI - Central Glass and Ceramic Research Institute (CSIR)
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Development of graded composition and microstructure on Inconel 718 by laser surface alloying with Si, Al and ZrB2 for improvement in high temperature oxidation resistance
No full textThe present study evaluates the scope of improvement of oxidation resistance of Inconel 718 (IN718) by laser surface alloying (LSA) with Si, Al and ZrB2 using a 0.5 kW continuous wave Nd-YAG laser. The alloyed zone (AZ) is free of macro-defects (porosity, crack, etc.) and contains microstructural and compositional gradation along vertical depth from the top surface until the AZ-substrate interface. Detailed microstructural and phase evolution studies indicate that the AZ consists of multiple intermetallic phases/compounds of Si, Al or Zr with multi-phase eutectic aggregate including Ni-rich matrix phase. The identity, size, morphology and relative amount of these phases vary with LSA parameters and vertical depth within the AZ. Accordingly, the microhardness profile along depth corroborates such graded microstructure and phase aggregate confined to the AZ. Isothermal oxidation studies at 900 degrees C show significant improvement in oxidation resistance due to LSA in comparison to that of as-received IN718, particularly in case of LSA with Si. Post oxidation studies reveal that the oxide scale consists of adherent oxides like SiO2, Al2O3 or ZrO2, in addition to several intermetallic phases pre-existing in the AZ prior to oxidation. Thus, it follows that the intermetallic phase rich AZ developed by LSA is adherent, defect-free, strong and offers very high resistance to oxidation in IN718 at elevated temperature
Influence of chemical aging on physico-chemical properties of mineral dust particles: A case study of 2016 dust storms over Delhi
No full textThe physico-chemical properties of dust particles collected During Dust Storm (DDS) and After Dust Storm (ADS) events were studied using Scanning Electron Microscope coupled with Energy Dispersive Xray Spectroscopy (SEM-EDS), X-ray Fluorescence Spectroscopy (XRF) and X-ray Photoelectron Spectroscopy (XPS). Morphological and compositional change in dust particles were observed as they react with the anthropogenic pollutants present in the urban environment. The calcite rich particles were observed to transform into calcium chloride, calcium nitrate, and calcium sulfate on reacting with the chlorides, nitrates, and sulfates present in the urban atmosphere. The frequency distributions of Aspect Ratio (AR) for the DDS and ADS particles were observed to be bimodal (mode peaks at 1.2 and 1.5) and monomodal (mode peak at 1.1), respectively. The highly irregular shaped solid dust particles were observed to transform into nearly spherical semisolid particles in the urban environment. XPS analysis confirms the high concentration of oxides, nitrates, and chlorides at the surface of ADS samples which show the signatures of mineral dust particles aging. Species with a high value of imaginary part of refractive index (like Cr metal, Fe metal, Cr2O3, FeO, Fe2O3) were observed at the surface of dust particles. At 550 nm wavelength, the light-absorbing potential of the observed species along with black carbon (BC) was found to vary in the order; Cr metal > Fe metal > Cr2O3> FeO > BC > Fe2O3> FeOOH. The presence of the aforementioned species on the surface of ADS particles will tremendously affect the particle optical and radiative properties compared to that of DDS particles. The present work could reduce the uncertainty in the radiation budget estimations of mineral dust and assessment of their climatic impacts over Delhi. (c) 2020 Elsevier Ltd. All rights reserved
Quasi-Stationary States in Ionic Liquid-Liquid Crystal Mixtures at the Nematic-Isotropic Phase Transition
Get PDFAn open system is a system driven away from equilibrium by a source that supplies an inflow of energy and a sink to maintain an outflow. A typical example of an open system is a system close to its phase transition temperature under irradiation by a laser. This provides a steady flow of energy through a photon flux. The sink in that case is the environment to which energy is lost in the form of heat dissipation. Creation of such a thermodynamically open state suggests that we can expect generation of exotic spatio-temporal structures length-scale independent correlation maintained under the global dissipative forces provided by the surroundings. Internal long-range forces can bring in additional spatio-temporal correlations, giving rise to states with a very long lifetime, the ``quasistationary states'' (QSS). In this communication, we report evolution of quasistationary states, in a mixture of the well-known liquid crystal (N-(4-methoxybenzylidene)-4-butylaniline, MBBA) and an iron-based room temperature ionic liquid (RTIL), namely, 1-ethyl-3-methylimidazolium tetrachloroferrate (EMIF) at the Nematic-Isotropic phase transition, when focused radiation with 532 nm wavelength from a Nd:YAG laser (200-300 mW optical power) is incident on the sample. We explain the QSS by invoking a sharp negative thermal gradient due to the laser photon flux and dipolar interactions. In our model, the dipoles are the charge transfer complexes (CTCs) formed in the RTIL by resonant laser pumping, which create an orientational ordering and balance the fluctuating force of the thermal gradient to create the QSS. In the absence of such CTCs in a mixture of MBBA and a Gallium-based RTIL (1-ethyl-3-methylimidazolium tetrachlorogallate, EMIG), the QSS was not observed
Laser powder bed fusion of in-situ composites using dry-mixed Ti6Al4V and Si3N4 powder
No full textHerein, we report laser powder bed fusion (L-PBF) of dry-mixed Ti6Al4V + Si3N4 powder to create in-situ titanium matrix composites. The dry-mixed Ti6Al4V powder with 5 wt.% Si3N4 was processed using L-PBF at varying laser energy densities, between 44 and 133 J/mm(3), by changing the laser scan speed (400-1200 mm/s) at constant laser power of 96 W, layer thickness of 20 mu m and scan spacing of 90 mu m. The selected samples were examined for microstructural evolution, in-situ reaction products and hardness. The results showed that the in situ reaction between liquid titanium and Si3N4 forms fine TiN and Ti5Si3 reinforcements in these L-PBF processed samples. However, the irregular shape and fine size of Si3N4 reduced the feedstock flowability, and the composites could not be processed with laser energy density (E) < 89 J/mm(3). The amount, distribution and size of the reinforcements were found to depend on the laser energy density. These in-situ composites exhibited high hardness of 860 +/- 49 KHN, which is 110 % higher than that of Ti6Al4V and ex-situ processed Ti-TiN and Ti-TiC composites. Our results show that the dry-mixed Ti6Al4V-Si3N4 feedstock can be processed using L-PBF but further improvement is required through adjusting Si3N4 powder attributes (size, shape) and concentration
Ammonia Sensing by Sn1-xVxO2 Mesoporous Nanoparticles
No full textChemiresistive gas sensing by metal oxide based materials has been usually explained in terms of surface chemistry and band structure modifications due to factors such as chemical composition, particle surface to volume ratio, material morphology, temperature, and surface oxygen vacancy. In this work, keeping parameters such as particle size, morphology, surface area, temperature, and surface oxygen vacancy fixed, we have for the first time attempted to delineate quantitatively the role of crystal structure and surface electronic states in improving gas sensing responses of doped nanosized metal oxide samples. While vanadium-doped tin oxide samples show a nearly 4-fold increase in 10 ppm ammonia sensing responses, the Sn0.696V0.304O2. sample shows similar to 1.2 times more sensing response as compared to Sn0.657V0.343O2. The ammonia sensing behavior has been found to be directly correlated to crystal structures and concentrations of various oxidation states of vanadium dopants present in the studied samples. Detailed comparative analysis of crystal and electronic structures of the samples has revealed the mechanism of enhancement in the ammonia sensing behavior of vanadium-doped tin oxides. It is expected that similar mechanisms might be responsible for enhancement in gas sensing properties of other metal oxide based systems
Influence of ultrasound and magnetic field treatment time on carcinoma cell inhibition with drug carriers: an in vitro study
No full textThe influence of exposing carcinoma cells to a static magnetic field (SMF) and low-intensity pulsed ultrasound (LIPUS), for different durations (15-45 min/d), in the presence of magnetic and non-magnetic drug carriers, on their in vitro inhibition is examined. Increasing the exposure time by 15 min/d decreased the culture duration by 24 h to achieve the same level of inhibition in colon (HCT116) and hepatocellular (HepG2) cells. Cell cycle analysis revealed enhanced cellular blockage in G1 and S phases with SMF + LIPUS exposure, and exposure for 45 min/d completely suppressed the S -> G2 transition. Apoptosis of both types of cells increased with SMF + LIPUS treatment time, and HepG2 cells exhibited elevated necrosis with >30 min/d exposure. HepG2 cells also had higher amounts of reactive oxygen species (seven- to eightfold) than HCT116 cells (two- to sixfold), suggesting treatment effectiveness is cell and drug carrier dependent. The accelerated cellular activities are attributed to the enhanced internalization of drug carriers as a consequence of destabilized cellular membranes caused by the SMF + LIPUS-generated mechanical and electrical stimuli. (E-mail: [email protected]) (C) 2020 World Federation for Ultrasound in Medicine & Biology. All rights reserved
Interfacial and Cross-sectional Studies of Thermally Cycled Alumina-Monel Brazed Joint
No full textAlumina and monel superalloy was successfully joined by active metal brazing technique using Ticusil (68.8Ag-26.7Cu-4.5Ti in wt%) filler alloy in a vacuum furnace at 910oC for 10 min under a vacuum of 5x10(-6)Torr. Phase analysis of the monel-filler alloy and alumina-filler alloy interfaces was conducted by X-ray diffraction analysis. Interfacial and cross-sectional microstructural investigation and determination of elemental composition were performed by scanning electron microscopy and energy dispersive X-ray analysis. No crack was found at the joint interfaces after thermal cycling test for 100 cycles between 50 degrees and 600 degrees C. Microhardness was estimated by Vickers hardness tester at the cross-section of the joint after thermal cycling test. Typical brazing strength of the thermally cycled joint was above 23 MPa. Helium leak tests indicated good hermiticity of the thermally cycled brazed joints
Integration of BiOI and Ag3PO4 nanoparticles onto oxygen vacancy rich-TiO2 for efficient visible-light photocatalytic decontaminations
No full textTo develop an impressive photocatalyst for purification of environmental contaminants, BiOI and Ag3PO4 nanoparticles were adhered on the oxygen vacancy rich-TiO2 (denoted as TOx ) via a facile ultrasonic-assisted procedure to form TiO2-x/BiOI/Ag3PO4 (signify as TOx/BOI/APO) nanocomposites. Then, the physiochemical features of the nanocomposites were characterized via various techniques. It was discovered that the ternary photocatalyst with 10 wt% of APO demonstrates the greatest ability in elimination of RhB, which is almost 44.3, 4.12, and 2.18-folds premier than the bare TiO2, TOx, and TOx/BOI (20 %) materials, respectively. This excellent boosted photoability was ascribed to the p-n-n heterojunctions among the components, great visible-light absorption via BOI and APO semiconductors, and effective segregation of charges. An acceptable mechanism was also suggested through scavenging tests and the results of Mott-Schottky plots. This study displayed that the construction and rational design of p-n-n heterojunctions could be effective for extremely improving visible-light-induced photocatalytic performances for energy and environmental applications
Sintering and characterization of a hard-to-hard configured composite: Spark plasma sintered WC reinforced alpha-SiAlON
No full textIn this study, a composite comprising WC particulate-reinforced alpha-SiAlON was fabricated by spark plasma sintering (1750 degrees C/40 MPa/25 min) in order to develop a hard-to-hard phase configuration and to toughen the hard matrix through particulate reinforcement. Irrespective of the composition, the sintered samples were almost theoretically dense. The nature of the overall sintering process for the composite appeared to be guided by the liquid phase sintering of the SiAlON phase. Microstructural analyses using scanning and transmission electron microscopy indicated the presence of both equiaxed and elongated alpha-SiAlON grains. The WC grains principally appeared equiaxed in nature. A reaction product was not observed at the WC/alpha-SiAlON interface. High-angle annular dark-field scanning transmission electron microscopy imaging indicated the reasonable distribution of the elements within the constituent grains and grain boundary. The presence of an intergranular glassy phase was confirmed, which was principally rich in oxygen and yttrium, with some occasional tungsten in the case of triple junctions. The composite exhibited an acceptable combination of flexural strength, hardness, and fracture toughness with values around 489 MPa, 20 GPa, and 6 MPa-m(0.5), respectively. In contrast to expectations, a decline in hardness was observed up to <= 30 wt% WC. Presumably, the WC grains acted as defects/inclusions with similar dimensions, which eventually resulted in inadequate interfacial performance and reduced hardness. Improvements in the Vickers hardness and fracture toughness were obtained at a WC loading of 40 wt%. The indentation size effect and load dependence of the fracture toughness were also determined for some selected specimens. Higher damage rates for the beta-Si3N4 counterbody against the 40 wt% WC/alpha-SiAlON composite were observed up to 30 N under unlubricated conditions compared with those obtained against the monolithic constituent phases, i.e., alpha-SiAlON and WC. The formation of an adherent tribolayer was observed
Study of Short-range Ordering in Amorphous and Nanocrystalline Materials from Laboratory based Pair Distribution Function (LPDF)
No full textDetermination of local atomic structure at nanoscale for both amorphous and nanocrystalline materials is very difficult and challenging. Local arrangement of atoms needs to be studied for understanding the local or short-range structural information. Pair distribution function (PDF) analysis is a technique used to study the short-range structure of the materials based on local atomic arrangement of atoms using synchrotron and neutron sources. But there is a demand for routine analysis based on laboratory X-ray diffractometer (XRD) using Ag radiation (lambda=0.5608 angstrom) with maximum achievableQvalue of 22 angstrom(-1). An attempt has been taken to study the short-range structure in crystalline Ni, silica glass (SiO2) and nano silica using total scattering experiment to show the capabilities and usefulness of PDF technique in laboratory XRD and are compared with the data from synchrotron radiation to achieve good quality scattering data and optimizing technical feasibility of the optics. PDF results of Ni showed the goodness of optical alignment. The first Si-O distance for both silica samples signified that they hold short- range order within the tetrahedral unit while differences are observed at higher radial distances. Laboratory based PDF experiment helped to get local/short- range structural information for better understanding the multifunctional properties of nano and disordered materials