Showing papers by "National Aerospace Laboratories published in 2021"

A review on metal-oxide based p-n and n-n heterostructured nano-materials for gas sensing applications

Abstract: Gas sensor is a device that converts the information of an analyte species into electrical signals using various detection principles. Electrical conductivity is one of the crucial properties of sensing materials. This basic property is modified with the formation of p-n and n-n heterostructures or by the inclusion of dopants. Surface morphology of a sensing material plays a vital role in the adsorption of analyte species for effective gas sensing behavior, further this can be improved with proper surface treatment viz., surface reactions by decorating with nanoparticles composed of various noble metals. The sensing mechanism differs owing to various morphologies with sensing materials. Sensing materials can either be polymers, metal oxides, nanoparticles or pertinent combination of these constituents. The sensor properties like selectivity, sensitivity, stability, response time and detection limits are influenced by morphology, material exposed to target gas and operating conditions. This review focusses on sensing mechanism and monitoring of nanostructures (nanorods, nanosheets, nanobelts, nanoribbons, nanowires, nanoflowers, spinel etc.) by appropriate combination of materials and dopants. The performance of numerous metal oxide-based gas sensing devices and their market trends are reviewed.

Poly (ε-caprolactone)-based electrospun nano-featured substrate for tissue engineering applications: a review

Abstract: The restoration of normal functioning of damaged body tissues is one of the major objectives of tissue engineering. Scaffolds are generally used as artificial supports and as substrates for regenerating new tissues and should closely mimic natural extracellular matrix (ECM). The materials used for fabricating scaffolds must be biocompatible, non-cytotoxic and bioabsorbable/biodegradable. For this application, specifically biopolymers such as PLA, PGA, PTMC, PCL etc. satisfying the above criteria are promising materials. Poly(e-caprolactone) (PCL) is one such potential candidate which can be blended with other materials forming blends, copolymers and composites with the essential physiochemical and mechanical properties as per the requirement. Nanofibrous scaffolds are fabricated by various techniques such as template synthesis, fiber drawing, phase separation, self-assembly, electrospinning etc. Among which electrospinning is the most popular and versatile technique. It is a clean, simple, tunable and viable technique for fabrication of polymer-based nanofibrous scaffolds. The design and fabrication of electrospun nanofibrous scaffolds are of intense research interest over the recent years. These scaffolds offer a unique architecture at nano-scale with desired porosity for selective movement of small molecules and form a suitable three-dimensional matrix similar to ECM. This review focuses on PCL synthesis, modifications, properties and scaffold fabrication techniques aiming at the targeted tissue engineering applications.

Insights from a Pan India Sero-Epidemiological survey (Phenome-India Cohort) for SARS-CoV2.

Abstract: To understand the spread of SARS-CoV2, in August and September 2020, the Council of Scientific and Industrial Research (India) conducted a serosurvey across its constituent laboratories and centers across India. Of 10,427 volunteers, 1058 (10.14%) tested positive for SARS-CoV2 anti-nucleocapsid (anti-NC) antibodies, 95% of which had surrogate neutralization activity. Three-fourth of these recalled no symptoms. Repeat serology tests at 3 (n = 607) and 6 (n = 175) months showed stable anti-NC antibodies but declining neutralization activity. Local seropositivity was higher in densely populated cities and was inversely correlated with a 30-day change in regional test positivity rates (TPRs). Regional seropositivity above 10% was associated with declining TPR. Personal factors associated with higher odds of seropositivity were high-exposure work (odds ratio, 95% confidence interval, p value: 2.23, 1.92-2.59, <0.0001), use of public transport (1.79, 1.43-2.24, <0.0001), not smoking (1.52, 1.16-1.99, 0.0257), non-vegetarian diet (1.67, 1.41-1.99, <0.0001), and B blood group (1.36, 1.15-1.61, 0.001).

Development of vanadium impregnated flat absorber composite PEO coating on AA6061 alloy

Abstract: The formation of black plasma electrolytic oxidation (PEO) coating on aluminium alloy using vanadyl sulphate as additive in a silicate-based electrolyte is investigated. A brief discussion on the mechanism of incorporation of vanadium in PEO coating starting with a cationic species of vanadium (i.e., VO2+) in solution is attempted. The coating formation with respect to morphology and composition is systematically studied as a function of process time. With increase in process time, incorporation of vanadium ions in the coating increases and the formation of black colour is attributed to the presence of V3+ and V4+ species in the coating. A 55 ± 5 μm thick flat absorber black coating with high solar absorptance (0.92) and high infrared emittance (0.88) is obtained with a process time of 10 min.

Improved Corrosion Protection of Magnesium Alloys AZ31B and AZ91 by Cold-Sprayed Aluminum Coatings

Abstract: Magnesium (Mg) alloys have a high strength/weight ratio, high dimensional stability, good machinability, and the ability to be recycled. However, their poor corrosion resistance in humid environments limits their usage for exterior aerospace components. This study aims to improve the corrosion resistance of two Mg alloys (AZ31B and AZ91) by using aluminum coatings. The latter have been deposited by a low pressure and temperature cold spray process. An aluminum powder (60 wt%) with a particle size ranging between 1 and 8 µm and nickel powder (40 wt%) with a particle size of about 70 µm were blended and used as feedstock powder. The coating thickness was about 240 μm. Its densification was achieved by the in-situ hammering effect of the nickel particles. The shot-peening effect also resulted in an enhanced coating hardness. The microstructure, mechanical properties, and corrosion resistance of the coatings have been investigated. They showed that the aluminum had a face centered cubic structure. Potentiodynamic polarization tests were performed along with a combination of materials characterization techniques to assess the corrosion resistance of the coatings when immersed in a 3.5 wt% NaCl solution for long durations. The results revealed that the corrosion resistance increased with the immersion time because of the formation of a protective oxide layer on the surface. These results were supported by elemental and structural analyses. This study shows that cold-sprayed aluminum coatings are a promising candidate for enhancing the corrosion resistance of AZ31B and AZ91Mg alloys compared to other thermal spray processes.

Silica-alumina based sol-gel coating containing cerium oxide nanofibers as a potent alternative to conversion coating for AA2024 alloy

Abstract: The current work demonstrates a study on the improved corrosion protection efficiency of a defect-free sol-gel hybrid coating consisting of cerium oxide nanofibers vis-a-vis sol-gel coating containing commercial nanosize ceria particles as corrosion inhibitors. The less researched organically modified silica-alumina (Si-Al) hybrid sol-gel coating containing cerium oxide nanofibers and commercial ceria are synthesized from 3-glycidoxypropyltrimethoxysilane and aluminum-tri-sec-butoxide. The sol-gel matrix containing cerium oxide nanofibers exhibiting Ce mainly in +3 oxidation state exhibits improved corrosion resistance as corroborated by electrochemical impedance spectroscopy. The corrosion property of this sol-gel coating commensurates well with the conventional chromate conversion coating (CCC) as evidenced by the neutral salt spray test. The developed coating exhibits good compatibility with the top primer layer and thus ascertains that the developed Si-Al based sol-gel coating containing cerium oxide nanofibers is a potent alternative to conventional CCC.

Mahalanobis-ANOVA criterion for optimum feature subset selection in multi-class planetary gear fault diagnosis:

Abstract: The empirical analysis of a typical gear fault diagnosis of five different classes has been studied in this article. The analysis was used to develop novel feature selection criteria that provide a...

Electrospun polyacrylonitrile nanofiber membranes for air filtration application

Abstract: Polyacrylonitrile (PAN) nanofiber membranes of varied thicknesses (20–100 µm) were electrospun at a polymer concentration of 14% (w/v) in N,N-Dimethylformamide (DMF); characterized for porosity, pressure drop, air permeability and particle filtration efficiency (PFE). Densities of membranes are found very less (0.11 to 0.21 g/cm3), with porosities in the range of 80–92%, higher porosity was for higher thickness. Membranes were used to measure air pressure drop, which was higher for thicker membranes due to the torturous path encountered by air. Air permeability of membranes decreased with increasing thickness for the same reason. The PFE was higher for thin samples due to less porosity and was lower for thicker samples due to higher porosities and cushion effect. The 20-µm-thick membranes achieved highest PFE of > 99.7% for clearing 0.3 µm particles. Above experiments suggested that PAN nanofiber membranes prepared in this study could be used for face mask in addition to non-woven fabrics.

Nd2Ti2O7 (NTO) with high curie temperature (TC) for high temperature sensor applications

Abstract: Perovskite-like layered structured (PLS) materials with A2B2O7 structure are promising materials for high temperature applications because of their high curie temperatures. These materials show linearity in resistivity vs. temperature, therefore, are preferred for high temperature sensor applications. Neodymium titanate (Nd2Ti2O7) is one of the prominent PLS materials with high curie temperature (TC ≥ 1500 °C). Nd2Ti2O7 (NTO) was synthesized by mixed oxide route and the powder was calcined at 1250 °C for 2 h. NTO samples were sintered in the temperature range of 1325–1400 °C for 2 h. The sintered samples were characterized for dielectric constant (K), P-E hysteresis loop and DC electrical resistivity (ρ) from 100 to 900 °C. The sintered density was highest at 1375 °C for NTO samples (>94.85% Th.). DC resistivity was found to decrease linearly from 1014 to 106 Ω cm with the rise in temperature from 100 to 900 °C, therefore, confirming as a prospective high temperature sensor material.

High-temperature flexural strength of I-CVI processed Cf/SiC composites with variable interphases

Abstract: The effect of single-layer pyrocarbon (PyC) and multilayered (PyC/SiC)n=4 interphases on the flexural strength of un-coated and SiC seal-coated stitched 2D carbon fiber reinforced silicon carbide (Cf/SiC) composites was investigated. The composites were prepared by I-CVI process. Flexural strength of the composites was measured at 1200 °C in air atmosphere. It was observed that irrespective of the type of interphase, the seal coated samples showed a higher value of flexural strength as compared to the uncoated samples. The flexural strength of 470 ± 12 MPa was observed for the seal coated Cf/SiC composite samples with multilayered interphase. The seal coated samples with single layer PyC interphase showed flexural strength of 370 ± 20 MPa. The fractured surfaces of tested samples were analyzed in detail to study the fracture phenomena. Based on microstructure-property relations, a mechanism has been proposed for the increase of flexural properties of Cf/SiC composites having multilayered interphase.

Preliminary results on the simulation of the 1999 Orissa super cyclone using a GCM with a new boundary layer code

Abstract: We present here preliminary results from the simulation of the Orissa supercyclone using a new AGCM code (named Varsha) written as part of a NMITLI project. The simulation is initialized at 00 UTC, 26 October 1999, using ECMWF T-106 initial conditions. The control run is made using the Varsha code at a T-80 resolution with a standard Monin-Obukhov boundary layer code incorporating a gustiness factor. With the horizontal resolution improved to 120 spectral modes with a 78 km grid spacing, and a new boundary layer parameterization at low winds, the code shows substantial improvements: the maximum error is reduced from 350 to 234 km at 36 h after initialization, 310 to 34 km at 48 h, and 410 to 55 km at 96 h. It is suggested that part of the explanation for this improvement lies in the improved estimation of surface forces and torque in the new boundary layer code. The role of torque is particularly interesting as the major contribution to it comes from the outer regions of the cyclone where the winds are relatively low but the area on which the surface force acts and its moment arm are both high. Intriguingly the higher surface forces arise also from the higher winds predicted by the new code. An interesting finding is that, on both track and minimum pressure, the improvement due to higher resolution is greater with the new boundary layer module. Further analysis is necessary to assess the effect of other eddy fluxes (sensible heat, moisture) on cyclone track prediction.

Lignin addition to polyacrylonitrile copolymer solution and its effect on the properties of carbon fiber precursor

Abstract: Polyacrylonitrile copolymer (PAN) fiber and PAN/lignin (PL) fiber were wet spun from the PAN copolymer solution and PAN/Lignin blend solution using dimethyl sulphoxide (DMSO) solvent. A blend of 90% by weight (wt %) PAN terpolymer and 10wt% lignin dissolved in DMSO was used in wet spinning of PL fiber. Viscoelastic properties of PAN solution and PAN/lignin solution in DMSO were determined by rheometer. The properties of precursor fiber with and without lignin were evaluated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and mechanical testing. The diffusion of lignin out of coagulated filament was observed during wet spinning of PL solution and was quantitatively estimated by UV–Vis studies. DSC results showed that blending lignin with PAN copolymers can improve the thermal oxidation performance of the precursor fiber and accelerate the thermal stabilization process. A schematic illustration has been deduced for the decrease in tensile strength of PL fiber compared to that of PAN fiber.