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The influences of polymerization conditions on thermal and structural properties of carbon fiber precursor polymers
No full textThe influences of polymerization conditions, viz. the kind of catalyst, solvent medium and temperature, on thermal, molecular and structural characteristics of carbon fiber precursor polymer were investigated. The dependence of the exothermic peak temperature (Tpk) and heat release rate on the kind of polymerization process was established. An aqueous redox slurry polymer had narrow exothermic peaks (Tpk = 294–297 °C) and relatively high heat release rates (∆H/∆T = 0.96–3.3 J g−1 s−1), and polymers prepared in solid state, solution and bulk had a broader exotherms with Tpk in the range 264–318 °C and low heat release rates in the range 1.15–3.9 J g−1 s−1. Dynamic and thermomechanical analyses indicate three glass transition temperature ranges, i.e., 42–54 °C, 80–98 °C, and 140–142 °C, which are similar irrespective of catalysts. Branching tendency in aqueous redox slurry polymer was notable beyond the intrinsic viscosity of 250 cm3/g. Bulk densities of the polymers were found to be in the range 0.25–0.45 g cm−3
On the structural changes, mechanism and kinetics of stabilization of lignin blended polyacrylonitrile copolymer fiber
No full textPolyacrylonitrile(PAN)/lignin blend fiber prepared by continuous wet spinning process in dimethylsulfoxie(DMSO) was thermally stabilized under oxygen atmosphere in a continuous multizone oven at different heating temperature. The thermal behaviour of PAN/lignin fiber (PL fiber) stabilized were characterized by differential scanning calorimetry(DSC) under nitrogen atmosphere. The cyclization kinetics parameters such as activation energy(Ea), rate constant(k), pre-exponential factor(A) and extent of oxidation reaction (EOR) at different temperature were calculated from Kissinger and Ozawa method. FTIR analysis was used to investigate the structural changes and calculate the cyclization index and dehydrogenation index of stabilized PL fiber. The cyclization index values for the temperature of stabilization from 235 °C to 265 °C varied from 40 to 85%. The variation in density, elemental composition and mechanical properties of PL fiber stabilized at different temperature was determined. The density of the stabilized fiber varied from 1.225 to 1.385 g/cc as the stabilization temperature increased from 235 to 265 °C. The mechanism of thermal stabilization of and a set of temperature profile for a complete stabilization of PL fiber has been deduced from the various characterization
Separation and flow unsteadiness control in a compression corner induced interaction using mechanical vortex generators: Effects of vane size and inter-device spacing
No full textAn experimental investigation was conducted to control separation characteristics of a 24° compression corner induced interaction in a Mach 2.0 flow using an array of mechanical vortex generators (VGs) with rectangular vanes (RRV) placed 6.8δ upstream of the interaction. The objective was to study the effect of (i) inter-VG spacing (s/h = 12, 9.5, 8.0, 6.1, 5.7, 5.5, 4.9, and 4.7), (ii) vane chord length (c/h = 7.2, 4.2, and 3.0), and (iii) vane angle (α = 24°, 20°, 18°, and 16°) in controlling the interaction and on the surface flow topology. These modifications reduce the projected area of VGs in the array from the conventional VG design of RRV2 (c/h = 7.2 and s/h = 9.5) to RRV8 (c/h = 3.0 and s/h = 4.7) by 41%. Reducing s/h also reduces the inter-VG region of the separation significantly that helps to achieve maximum reduction in the streamwise extent of separation up to 83% and in the peak rms value up to 80%. The former improves the overall pressure recovery from 3.0 to 3.4, thereby moving closer toward the inviscid value of 3.8. Surface flow topology shows that the VG array splits a single large spanwise separation bubble for no control into multiple smaller scale individual separation cells placed side-by-side all along the span of the interaction. This helps to reduce the magnitude of mass exchange imbalance across each individual separation cell and, hence, stabilizes the overall interaction relative to no control. The best VG configuration of RRV8 shifts the dominant frequency of fluctuations to approximately 2 kHz or St = 0.19, which is nearly an order of magnitude higher than that for no control
Flow control using single dielectric barrier discharge plasma actuator for flow over airfoil
No full textThe single dielectric barrier discharge (SDBD) plasma actuator has been developed in the present work for high-accuracy, high-performance computing of flow control applications. The present physics-based SDBD model is a significant improvement over the one developed by Bagade et al., [“Frequency-dependent capacitance–based plasma model for direct simulation of Navier–Stokes equation,” AIAA J. 55, 180–194 (2017)], which was used for planar geometry using sequential computation. Based on the physics of SDBD operation, phase-averaged fully developed body force over an ac cycle is computed and stored, which is reused. Thus, the intensive body force computations are bypassed in the new model, and the body force due to the SDBD plasma actuator is incorporated in the compressible Navier–Stokes equation that is solved in a body-fitted curvilinear coordinates. Here, the modified SDBD model enables performing large-scale simulations for the aerodynamic flow control at low speed and transonic flow past airfoils used in unmanned aerial vehicles and executive jets. The flow control by SDBD plasma actuation is finally compared with other forms of flow control strategies
Imaging subsurface geological complexity (2D/3D) beneath the Greater Srinagar region of the Kashmir basin, Northwest Himalaya
No full textA high-resolution microtremor measurement in Greater Srinagar city of the Kashmir valley has been analysed to image 2D and 3D subsurface geological complexities. This region is located in the highly seismogenic Himalayan belt and sits atop a deep sedimentary lake bed with a laterally varying thickness of soft sediments. Srinagar region is a major economic centre and the capital city of the Kashmir valley with 2 million inhabitants living at high seismic risk. To assess the subsurface complexity beneath the city, we present: (1) high-resolution subsurface shear wave velocity Vs structure using the horizontal-to-vertical spectral ratio inversion; (2) shear wave velocity for top 30 metres of soil column (VS30) map with National Earthquake Hazards Reduction Program site classification; (3) comparison of VS30 maps calculated from horizontal-to-vertical spectral ratio inversion and topographic slope methods; and (4) azimuthal behaviour of horizontal-to-vertical spectral ratio peaks, all of which unravel the subsurface spatial heterogeneity and suitability for the building of engineering structures in the study area. In addition, a new matlab code is applied to generate 3D subsurface Vs slices in the study region in different directions using its pre-generated 2D Vs profile data. The presented potentiality of microtremor horizontal-to-vertical spectral ratio technique in Srinagar region, which lies on the eastern edge of the basin with significant topographic irregularities, indicates an uneven distribution of local site effects (primary and secondary) in the case of strong ground motion. The comprehensive results can be promising in engineering analyses of local ground and structural responses in order to mitigate the impact of earthquake occurrence and seismic risk in the city and adjoining regions
Lead-free laminated structures for eco-friendly energy harvesters and magnetoelectric sensors
No full textThe ferromagnetic and ferroelectric laminated structure has been utilized to study the magnetoelectric (ME) effect, which holds great potential to fabricate micro-electro-mechanical devices with a high figure of merit. Designed a laminated heterostructure using ribbons of Metglas (Fe–Co–Si–B alloy) having high magnetic permeability and lead-free piezoelectric composites of 0.92(Na0.5Bi0.5)TiO3-0.08BaTiO3 (NBT-BT) to generate the significant magnitude of direct ME voltage. The displacement-voltage measurements of NBT-BT yield a high response showing the nature of the piezoelectricity effect. The strength of ME coupling is determined from the ME voltage coefficient (αME), ME measurements have been carried out in the range of 0–6 kHz frequencies. The magnitude of the direct ME effect was found about 45–50 mV/Oe.cm over a low magnetic field of less than ±8 kOe. The real-time ME effect produced nearly 274.5 and 280.2 mV of ME voltages for the applied field of 200 and 300 Oe, respectively. It shows that the trilayer composite structure may be used as weak magnetic field sensors and energy harvesters
A state-of-the-art review on the multifunctional self-cleaning nanostructured coatings for PV panels, CSP mirrors and related solar devices
No full textSolar energy-based devices are protected using glass surfaces that need to be cleaned periodically to maintain their desired optimum performance. If these devices are large and placed in remote locations or not easily accessible, manual cleaning is not only difficult but prohibitively expensive, which in turn necessitates suitable self-cleaning coatings to be applied on the glass surfaces. Traditionally, sol-gel processes have been used for such coating developments. However, for large volume production, spray based processes have certain advantages, especially their lower cost and ease of manufacturing. The self-cleaning coatings can be either hydrophobic or hydrophilic determined by the contact angle between water and glass surfaces. Further, care must be taken when selecting coating materials and the corresponding coating parameters to maintain the transparency or reflectivity of such glass surfaces used for the particular device applications. The optical transparency of self-cleaning or anti-soiling coating is of paramount importance in the case of solar photovoltaic panels and related solar devices. Therefore, enhancing their performance by additional cost-effective anti-reflecting coatings, is a plausible solution. A state-of-the-art of this effort is being attempted in this review. It includes the necessary basic principles, cost-effective deposition techniques, performance evaluation standards and life expectancy of such coatings. The scope of the present review has been broadened by including specific issues related to concentrated solar power devices and by highlighting recent advances in atmospheric pressure plasma deposition processes. Additionally, use of non-fluorinated polymer materials and related nanostructured materials has been suggested for the fabrication of the self-cleaning coatings
A Study of Corrosion Behavior of (E)-2-(3,4-dihydroxybenzylidene)hydrazinecarbothioamide and Bis [[3,4-dihydroxyphenylmethylene] Carbonothioicdihydrazide]-Sealed Anodized AA2024-T3
No full textAnodizing is the process of developing an oxide layer on a metal surface. It enhances the corrosion barrier stability of aluminum and its alloys. Chromic acid is universally used as an electrolyte in an anodizing process, but it is not preferred for the anodizing process due to its carcinogenic effect. The aim of present investigation, a chromate-free (E)-2-(3,4-dihydroxybenzylidene)hydrazinecarbothioamide (DHC) or Bis [[3,4-Dihydroxyphenylmethylene]carbonothioicdihydrazide] (DCT)-sealed sulfuric acid anodic oxide coating was developed on AA2024-T3. The 10 wt% H2SO4 was used as an electrolyte in the anodizing process. The results obtained from field emission scanning electron microscopy analysis showed effective surface modification after DHC or DCT sealing. The potentiodynamic polarization curve and electrochemical impedance spectrum were used to study the barrier stability of the created oxide layer on alloy surface against corrosive media (3.5% NaCl). Potentiodynamic polarization results showed a significant difference in corrosion potential value and corrosion current density value after sealing with DHC or DCT. The electrochemical impedance spectrum clearly showed increases in the barrier stability of the sealing oxide layer compared to the plain oxide layer. The salt spray test was used to study the accelerated corrosion of samples. All obtained results confirmed that sealing of organic inhibitors enhances the barrier stability of the anodized aluminum alloy and the order of corrosion protection efficiency is Ox < Ox-DHC < Ox-DCT
Antimicrobial and Free Radical Scavenging Activities of Cellulose/Silver-Nanocomposites with In Situ Generated Silver Nanoparticles Using Cissampelos Pareira Leaf Extract
No full textIn this study, silver nanoparticles (AgNPs) were in situ generated on the surface of cellulose matrix using leaf extract of cissampelos pareira (LCP) by environmentally benign green synthesis. The morphological and structural properties of synthesized cellulose silver nanocomposites (Cel/LCP/Ag-NCs) were characterized by different spectral studies such as UV–visible spectroscopy, SEM, TEM, FT-IR, AFM, DRS, PL, Lifetime, XPS and XRD. Silver nanoparticles were obtained in the cellulose matrix with an average size of 34.26 nm and with antioxidant activity which has been evaluated by ABTS (70.34% at 100 µg/mL) and DPPH (81.65% at 100 µg/mL) methods. The antimicrobial properties of cellulose, Cel/LCP, Cel/LCP (10 mM, 30 mM and 50 mM AgNO3), tested on 13 microorganisms were determined using disk diffusion method. The most effective nanocomposites (Cel/LCP/10, 30 and 50 mM AgNO3), Cel/LCP/50 mM AgNO3 afforded the best antimicrobial properties because increasing the concentration of AgNO3 solution, the zone of inhibition also increased. The prepared cellulose silver nanocomposites synthesized by leaf extract of cissampelos pareira shows the potential to be applied in the future development of therapeutics and biomedical applications
Improved omnidirectional polarisation-insensitive optical absorption and photoelectrochemical water splitting using aperiodic and tapered slanted, kinked and straight silicon nanowires
No full textWe have experimentally demonstrated that slanted, kinked and straight silicon nanowire arrays form a broadband omnidirectional light-harvesting structure. The unique design of kinked and slanted nanowires allows them to trap more light effectively across a wide wavelength range than straight silicon nanowires (SiNWs). We report that the light absorption in slanted, kinked and straight wires is enhanced by controlling their geometrical parameters. The p-type SiNWs have less reflection than n-type SiNWs due to their larger porosity gradient structure. Aperiodic and tapered slanted, kinked and straight SiNWs are remarkably photoactive and promising low-cost materials for photoelectrochemical water splitting applications