IR@CGCRI - Central Glass and Ceramic Research Institute (CSIR)
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Silver nanoparticles enhanced photoluminescence and the spectroscopic performances of Nd3+ ions in sodium lanthanum borate glass host: Effect of heat treatment
No full textSilver nanoparticles (NPs) impact on the emission attributes of Nd3+ activated Na2O-La2O3-B2O3 vitreous host matrix has been studied and discussed in detail. The effect of nucleation and growth of Ag NPs occurred due to the different heat-treatment durations at the temperature of 450 degrees C has been discussed. Transmission electron microscopy measurement revealed the formation of spherically shaped Ag NPs in the studied samples. The median Ag NPs size was increased from 2 to 9 nm with heat-treatment durations. Utilizing the absorption spectra of Nd3+ ions, the phenomenological Judd-Ofelt (J-O) parameters (omega lambda= 2, 4, 6) were estimated. The optimized luminescence intensity at 1056 and 875 nm have realized for 10 h of annealing at 450 degrees C, with an enhancement factor of 160%. Moreover, the quantum efficiency for 1056 nm increased steadily with the heat-treatment duration. The stimulated emission cross-section and gain bandwidth for 1056 nm laser transition has shown to be 2.92 x 10-20 cm2 and 9.19 x 10-26 cm3 for the Ag NPs embedded glass-composite. The results exemplifies the suitability of Ag NPs embedded glass-composites for the fabrication of compact solid-state infrared lasers
Site-specific microstructure, porosity and mechanical properties of LENSTM processed Ti-6Al-4V alloy
No full textIn the present study, pre-alloyed Ti-6Al-4V powder is deposited on CP-Titanium substrate by laser engineered net shaping (LENSTM) process using parameters optimized for best adhesion and densification. The optical montages from the three surfaces (front, side and top) show columnar beta grains growing along the building direction due to conductive heat transfer through the substrate. The as-deposited microstructure contains thin lamellar (alpha+beta)-colonies besides prior beta grain boundaries and basket-weave (alpha+beta)-structure inside prior beta grains. Narrow band-like structure forms between consecutive layers due to re-melting of previously deposited layers, thereby creating additional interfaces in the microstructure. In addition, tiny isolated pores appears in negligible fraction throughout the LENSTM-processed specimen due to gas entrapment, shrinkage during cooling and unmelted or partially melted powder particles. Both the number and volume of the pores increase along the building direction. Hardness on different surfaces (front, side and top) differs considerably due to the presence of different heating/cooling zones, residual stresses and variations in the thermal cycles and consequent change in the alpha'-martensite phase fraction. Larger variation in the hardness between these surfaces is observed in nanoindentation technique signifying for inhomogeneity in nano-scale structure. These microstructural variations also resulted in measurable changes in the coefficient in friction (COF) during scratch testing from the substrate along the building direction due to presence of different heating/cooling zones (diffused vs. reheating/re-melting zones). The variation in hardness and COF along different directions can ultimately lessen the in-service performance of the as-deposited parts
Factors affecting properties of Ti-6Al-4V alloy additive manufactured by metal fused filament fabrication
No full textThis paper aims to break the current material-process-property tradeoffs in metal fused filament fabrication (MF3) to effectively fabricate Ti-6Al-4V alloy specimens beyond 90% relative density without any post-processing with consistent mechanical properties and microstructure, which are critical for aerospace and medical applications. Existing knowledge gaps in MF3 3D printing fail to address how properties scale from the filament processing stage to green part printing to sintering and what contributing factors cause significant deviation in mechanical properties in samples having the same sintered densities. To tackle these gaps, this work holistically investigates four key aspects specifically for MF3 of Ti-6Al-4V to address a) influence of filament extrusion conditions on filament density variance and diameter control, b) use of the design of experiments to identify factors influencing MF3 3D printed green sample density and dimensions, c) identifying sintering time and temperature conditions that yield densities beyond 90% and mechanical properties close to literature and d) powder attributes (size and interstitial concentrations) and its effect on sintered density andmechanical properties for MF3 samples. (C) 2021 Elsevier B.V. All rights reserved
Partial replacement of metakaolin with red ceramic waste in geopolymer
No full textMetakaolin was incrementally replaced (33.3%, 50% and 66.6%) by red ceramic waste in geopolymer formulation to study the effect on geopolymerisation and its resultant properties. The geopolymer binders composed of two calcined aluminosilicates (viz. Metakaolin and Red ceramic waste), NaOH and sodium silicate. In the experimental compositions, metakaolin was replaced gradually up to 66.6% in the clay fraction, the Si/Al increased from 3.36 to 5.16 and Na/Al increased from 0.93 to 1.38. The FTIR spectroscopic studies of geopolymer pastes along with XRD analysis indicated that the red ceramic waste partly reacts with alkali and takes part in geopolymer formation. Replacement of 33.3% metakaolin by the red ceramic waste in geopolymer binder did not reduce the compressive strength with respect to the pure metakaolin geopolymer here. Additional replacement resulted in a drastic decrease in the compressive strength of the geopolymer binder. However, the compressive strength of geopolymer mortars revealed interesting synergy between the amount of binder and particle packing in the mortar. Despite having a lower amount of binder phase, mortars with 33% and 50% red ceramic waste exhibited maximum compressive strength values. This has been attributed to improved particle packing through incorporation of red ceramic waste particles
Hydrogel-integrated 3D-printed poly(lactic acid) scaffolds for bone tissue engineering
No full textThere is currently a high demand for synthetic biodegradable scaffolds with enhanced osteogenic and angiogenic performance for the regeneration of large-size bone defects. Here, hybrid scaffolds were prepared by integrating either alginate or alginate-bioglass composite hydrogels with a 3D-printed poly(lactic acid) (PLA) porous structure. The as-deposited PLA scaffolds were surface treated with polyacrylic acid (PAA), which significantly enhanced the PLA scaffold's wettability. The surface-modified PLA scaffolds integrated well with hydrogels and provided shape and mechanical rigidity to the hydrogel. In phosphate-buffered saline, the lowest weight loss during 21-days immersion was measured for the PLA scaffold, while alginate-bioglass scaffolds lost similar to 1.9% weight during the first 7 days of immersion. In vitro cytocompatibility tests indicated good cell viability and cell proliferation on the scaffolds. The bioglass-containing hybrid scaffold promoted osteogenic differentiation and calcium mineralization. The excellent biocompatibility, good mechanical stability of the hydrogel, and shape retention of the novel hybrid scaffolds with cell-laden alginate could make them attractive for large bone regeneration
Effect of heavy metal oxides on photoluminescence and spectroscopic attributes of Eu3+ activated borate glasses
No full textInfluence of Heavy Metal Oxides (HMOs: PbO and Bi2O3) on structural and photoluminescence (PL) properties Eu3+ activated lanthanum borate glasses has been analyzed and discussed in thoroughly here. When the PbO is loaded more and more in the glass system, the luminesce intensity and lifetime values of D-5(0) -> F-7(2) transition of Eu3+ were improved for the excitation at 464 nm due to enhanced covalency of Eu-O bonds arose from the dual function of lead oxide in the structure of PbO varied glasses. The betterment in luminescence features are also attributed to the decrease of effective network phonon energy occurred because of the incorporation of lead oxide in the glass composition. On the other hand, the luminesce (emission intensity and lifetime values of 614 nm emission of Eu3+ under 464 nm excitation) results are completely upending as the Bi2O3 content increased gradually in the glass matrix. This reduction in luminescence properties are ascribed to the decrease of covalency of Eu-O and thus crystal field in the vicinity of Eu3+ site. The reduction of covalent character of Eu-O is due to two facts, one being the newly generated NBOs owing to the generation of BiO6 units with the incorporation of Bi2O3 in the glass matrix and the second, the development of Bi-O-Bi and Bi-O-B linkages. The luminescence and spectroscopic attributes evidently reveal the lead varied borate glass hosts are more beneficial than Bi2O3 varied borate glass hosts for optoelectronic applications
Confinement creates a 9 GPa ambience: emergence of cristobalite phases in a silica film
Get PDFWe present here the results of the x-ray fluorescence (XRF), x-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Analysis of x-rays (EDAX), x-ray Reflectivity (XRR), Secondary Ion Mass spectroscopy (SIMS) and x-ray Diffraction (XRD) studies of silica films spin-coated from a Tetraethyl Orthosilicate (TEOS) precursor on native and hydrophilized Al substrates. It is observed that the substrates are mainly porous (porosity similar to 33%) AlO(OH), there is a diffuse interlayer of highly porous (porosity similar to 90%) AlO(OH), essentially a modification of the substrate, and a top layer of silica composed of nanocrystals with in-plane dimensions of 100-300 nm and thickness of 2.5 nm with a sharply defined silica-hydrated alumina interface. The silica nanocrystals were found in the metastable high pressure cristobalite phases with the tetragonal or alpha-phase co-existing in its low (0.77 GPa) and high (9 GPa) pressure structures. This indicates a high normal stress developed from the confinement and provides a basis for the quantitative assessment of the confinement force, which comes out to be higher in value than the van der Waals force but weaker than the Hydrogen bonding force
Effect of low temperature structural phase transitions in BaTiO3 on electrical transport through a metal-ferroelectric-metal multilayer of AuCr/BaTiO3/Nb:SrTiO3
No full textIn this paper we report an investigation of electronic transport through the metal-ferroelectric-metal (MFM) multilayer consisting of AuCr/BaTiO3/Nb:SrTiO3 over a temperature range of 100 K-300 K where BaTiO3 (BTO) shows a series of structural phase transitions leading to change of magnitude as well as the orientation of the polarization (P)over-right-arrow. We observed that the bias dependent barrier heights associated with the interfaces carry strong signature of the phase transitions in the BTO layer which lead to a strong temperature dependent asymmetric transport, when cooled down below room temperature. Specifically, it is observed that the temperature dependence is closely correlated to low temperature transitions in the BTO layer as revealed through the temperature dependent x-ray diffraction (XRD), capacitance as well as resistivity behavior of the BTO layer. There is substantial enhancement of the asymmetry in the device current that occurs at or close to temperatures T-2 similar to 190 K where BTO shows a crystallographic phase change to the low temperature rhombohedral phase. The temperature dependent changes occur due to barrier modulation at the interfaces of AuCr/BaTiO3 as well as BaTiO3/Nb:SrTiO3 that softens on cooling due to inhomogenities present there. The change in barrier on change of the bias direction has been observed below T-2 which arises from alignment of the polarization in-plane or out-of-plane as determined by tensile or compressive character of the in-plane strain in the BTO film. We also discuss the effect of space charge determined by the oxygen vacancies in the interface region, regulated by the applied bias
Comparative analysis for the prediction of WEDM responses for machining spark plasma sintered boron carbide ceramic sample by RSM and ANFIS
No full textUnconventional wire electrical discharge machining (WEDM) process is successfully used to cut different metals, alloys, composites and recent addition is engineered ceramics which possess sufficient electrical conductivity. Boron carbide is one of the hardest ceramic materials that unable to be processed with conventional machine tools and can be machined by WEDM compulsorily with proper selection of machine parameters. This study is based on boron carbide samples which were prepared using spark plasma sintering (SPS) furnace and machined with WEDM. Five machining parameters were analyzed such as pulse on time, pulse off time, peak current, water pressure and servo feed rate. Surface roughness (R-a) and machining speed were considered as output parameters and design of experiment was derived using central composite design (CCD) of response surface method (RSM) with 32 numbers of different test runs. Adaptive neuro-fuzzy inference system (ANFIS) was used with a new set of 16 numbers of experiments to predict results and seen to be more reliable than predicted results of response surface method. (C) 2019 Elsevier Ltd. All rights reserved
Parakeet Hemoglobin - Its Crystal Structure and Oxygen Affinity in Relation to Some Avian Hemoglobins
No full textBackground: ``Avians'' often show efficient oxygen management to meet the demands of their metabolism. Hemoglobin, a transporter protein consists of four non-covalently linked subunits contain haem binding hydrophobic pocket serves as a site of allosteric cooperativity. The physiology and anatomy of both mammals and avian are functionally different, in birds, the respiratory system formed by small air sacs that serve as tidal ventilation for the lungs and have no significant exchange across their cells. Parakeet (Psittacula krameri) a tropical and non-migrating species and it is easily adapted to living in disturbed habitat. The sequence analysis reveals that alpha and beta chain of parakeet hemoglobin highly similar grey lag goose and bar headed goose hemoglobin respectively. Thus it has been tempted us to study in to analyzing the sequence and structural comparison of this hemoglobin to find out the physiological capabilities of parakeet hemoglobin. Objective: The structure determination studies of parakeet hemoglobin by X-ray diffraction. The sequence and structure are compared with goose, chicken and human Hb, emphasizing the role of amino acids in the subunit contacts that facilitate survival by low oxygen demand. Methods: The Hb was purified and crystallized by hanging drop vapor diffusion method using polyethylene glycol (PEG) 3350 and sodium phosphate buffer. X-ray diffracted data set was collected at 3 angstrom resolution, the data was processed in Automar and molecular replacement, refinements, model building was carried out in CCP4i program package. The final refined model was deposited in protein data bank with accession id 2zfb. Results: The tertiary structure of Parakeet Hb is compared with the met form of BHG Hb (1c40) and oxy form of GLG (1faw) and oxy form of human Hbs (1hho). Superimposing parakeet Hb alpha(1)beta(1) subunit with `R' state human Hb shows an r.m.s.d of 0.98 angstrom and for BHG and GLG Hb, the r.m.s.d shows 0.72 and 0.61 angstrom. The replacement of alpha 115Asp in parakeet Hb as against the alpha 115Glu in human Hb results in the movement of GH corners. The amino acid proline at alpha 50 present only in Parakeet Hb and Chicken HbD and not present in any other avian family which includes human Hb. The residue alpha 78Thr located in EF corner loop region, which slightly diverge when superimposing with human and BHG Hb and also replacement of alpha 113Asn present only in Parakeet Hb placed near the FG helix corner. Conclusion: The present study describes the structure determination of parakeet hemoglobin and its structural features to understand its oxygen affinity characteristics. The crystals were obtained by buffered low-salt conditions, like those of chicken HbD, carbonmonoxy and cyanomet human Hb. The present study reveals several interesting and unique modifications in the finer aspects of the quaternary structure of parakeet Hb, which are involved in oxygen affinity characteristics and the alpha(1)beta(1) subunit contacts. Crystallization of parakeet Hb with allosteric effectors like Inositol pentaphosphate may bring further understanding of the influence of physiological and environmental factors on the quaternary structure