Dissimilar welding of steel and aluminium alloys has attracted widespread attention in the automobile industry to make lighter parts for better fuel efficiency and reduced emissions. Fusion welding processes are not suitable for dissimilar welding due to various issues. Friction stir welding (FSW) is a solid-state welding process that can overcome these issues. The present work focuses on the dissimilar FSW of aluminium alloy (AA6082-T6) and dual-phase steel (DP780) of different thicknesses in a lap configuration. Different process parameters, such as tool rotation speed, transverse speed, and plunging depth, were considered to establish the process parameter window based on microstructural analysis and mechanical property evaluation. The effect of intermetallic compounds (IMCs) formed at the joint interface was also evaluated. 1250 rpm, 40 mm/min, and 3 mm plunge depth yielded the highest shear strength but also resulted in tunnel defects. Increasing the rotation speed to 1500 rpm, along with a concomitant increase in traverse speed (50 mm/min) and plunge depth (3.1 mm), eliminated the tunnel defect but resulted in lower shear strength. This can be attributed to IMC layer thickness, which increased with increasing tool rotation speed. Consequently, the weld made with 1750 rpm exhibited the lowest strength and elongation. The interlocking effect of steel hook fragments formed in the Al matrix and refined grain size also contributed to the enhanced strength in the 1250 rpm, 40 mm/min, 3 mm sample.

In this work, microstructure evolution in friction stir-processed (FSP) AA6061 aluminium alloy was studied under different initial temper conditions (T6, O, W), and the age hardening behaviour in two different temperatures was investigated before and after FSP. Microstructural evolution pathway during FSP was found to differ in different tempers, leading to differences in grain refinement. FSP led to a significant increase in strength compared to the base metal (BM), however, the ductility was lower, and it reduced further upon over-ageing. The peak hardness was higher, and the peak ageing time was lower in the stir zone (SZ) at both the ageing temperatures (150 °C and 170 °C), with higher temperature yielding higher peak hardness. The precipitates were finer and more closely spaced in the SZ compared to the BM, resulting in higher strength in the SZ in peak-aged condition.

Newly developed (Al, Zn, Mg)–Fe cast alloys have been found to exhibit properties of wrought alloys while displaying the shape casting characteristics of cast alloys and thus have the potential for making near net shape light-weight structural components. The alloy is based on a dilute hypoeutectic Al–Fe system with Zn and Mg as strengtheners and Ti as a grain refiner. The alloy is also precipitation hardenable but the precipitation behavior and the evolution pathway of the precipitates during the manufacturing process are not well known. In this work, systematic studies were carried out to elucidate the evolution pathways for the microstructure and the precipitates in a manufacturing process like friction stir welding (FSW), which is commonly used for aluminum alloys. It also involved microstructure–property correlative studies through ThermoCalc simulation and microstructural characterization to gain insights on different types of metastable Al–Fe-based eutectic phases present in the as-cast alloy and their evolution during FSW affecting the properties. AlmFe intermetallic phases underwent morphological changes from skeleton type to particulate form and were also partially transformed to Al6Fe during FSW. The grain size of the alloy was also refined significantly during FSW. The studies on aging behavior revealed the existence of homogeneously distributed Zn-rich nanoclusters and Zn–Mg-based GP zones, which did not evolve into stable equilibrium precipitates, in the stir zone (SZ) during long-term natural aging post-FSW. The heat-affected zone (HAZ), on the other hand, exhibited accelerated growth of η-type precipitates due to localized solute microsegregation and thermally induced dislocations.

Friction stir-based additive manufacturing has shown promising results and has the full potential to fabricate near-net-shaped 3D metallic structures. Most existing research has focused on discontinuous multilayer deposition of nickel-based superalloys using friction surfacing (FS). In this study, a semi-automatic friction stir welding machine operating in vertical position control mode was used to continuously build up multiple layers of Inconel 718 alloy. The process parameters were optimized based on the single-layer deposition of Inconel 718 alloy with different parameter combinations (rotational speed, axial feed, and traverse speed), which resulted in uniform microstructure and hardness. At high axial feed, changes in process path direction in the multilayer process resulted in variations in the axial force and temperature during deposition. Electron back-scattered diffraction (EBSD) analysis revealed the occurrence of discontinuous dynamic recrystallization (DDRX), which led to refined grains during multilayer deposition. Among the evaluated axial feeds (10, 13, and 16 mm/min), 16 mm/min yielded defect-free deposition with optimal microstructure and hardness. Microstructure analysis also revealed banded structures with variations in the grain size, resulting in hardness variation across the layers. The high axial feed showed less variation in grain size in all layers, while few coarser grains were observed at the maximum axial load. The microtexture analysis revealed that at 13 and 16 mm/min axial feed, C texture component {001}(110) evolved in all layers, and the selective grain growth mechanism resulted in a sharp recrystallization texture.

Recycling and recovery of metals from e-waste help develop a circular economy. Current methods of recovering metals from e-waste employ strong inorganic acids and generate harmful byproducts and effluent streams. Besides, the metals are recovered in the form of salts, requiring further purification. Green solvents such as deep eutectic solvents (DES) are capable of dissolving metals. Here, we focus on using a hydrophobic thymol-capric acid DES to study the dissolution and recovery of metallic copper through controlled studies. The extraction efficiency of dissolved Cu metal from DES into an aqueous solution of trisodium citrate (TSC) was 98.4

A multiphase phosphate based ceramic dielectric material was prepared by treating Indian bauxite residue (BR) with phosphoric acid. Various concentrations of phosphoric acid namely, 1 M, 3 M, 5 M and 8 M, were used. The phases formed out of the treatment were studied using X-ray diffraction. Aluminum, iron and silicon phosphates were observed as major phases along with sodium and calcium compounds. Pellets of treated BR formed by cold compaction were sintered at 900°C, and the dielectric properties were studied using ac impedance spectroscopy in the temperature range of 250–350°C. An optimum combination of dielectric constant and loss tangent was observed in the 1 M sample, whereas the 3 M, 5 M and 8 M samples exhibited higher dielectric loss. Furthermore, the optical properties of the phosphate samples were studied using UV-visible spectroscopy and photoluminescence spectroscopy. The chromaticity index diagram showed that the emission occurred in the visible region for all the samples. Especially, the 3 M sample exhibited emission in the pure white region, which is attractive for light-emitting applications.

Al-Zn-Mg-Fe (HE700) is a new generation cast alloy based on dilute Al-Fe hypoeutectic system. Being a new member, the precipitation behavior of the HE700 alloy is not fully understood unlike its conventional 7xxx series counterparts. Moreover, presence of Fe and friction stir welding (FSW) used to join such alloys add to the complexity of the precipitation phenomenon. The present study captured the microstructural features with atomic-scale resolution that provided new insights into the nature, distribution, and evolution of precipitates in this alloy. The stir zone (SZ) and heat-affected zone (HAZ) exhibited significantly different natural aging behavior. Finer precipitates identified as GPI and GPII (Guinier Preston zones) were found to coexist with very fine zinc-rich solute clusters in the SZ. The GP zones evolved gradually and transitioned into strengthening precipitates. The HAZ, on other hand, exhibited heterogeneous distribution of coarse pre-existed particles and fine MgZn2 precipitates that were heterogeneously nucleated by localized solute supersaturation and thermally induced dislocations. Hardness variations can be correlated to precipitates evolution thereby helping design a suitable post-weld heat treatment (PWHT) process.

Traditional photocatalysts suffer from inferior utilization of solar light. Therefore, developing novel photocatalyst for better solar light harvesting is much required in the wake of current environmental problems arising from conventional energy technologies. Here we report synthesis and characterization of photocatalysts based on TiO 2 nanorods (TNR) and Zeolitic Imidazolate Framework -9 (ZIF-9) and their photoelectrochemical properties. The TNRs were sensitized by ZIF-9 through solvothermal method. The presence of ZIF-9 on TNR formed a p -n heterojunction which assisted in initiating efficient charge separation and promoting injection of these carriers into the electrolyte. The heterojunction catalysts also exhibited enhanced optical properties in terms of extended absorption with reduced bandgap in comparison to the TNR film. The aforementioned properties manifested in improved photoelectrochemical performance with a current density of 0.94 mA/cm 2 , which is four times better than TNR and an applied bias photon to current efficiency (ABPE) of 0.27 %, which is five times better than TNR film alone. These superior properties of the processed ZIF-TNR demonstrate their potential for photoelectrochemical catalysis, thus paving the way for green hydrogen generation.

A microfluidic paper-based analytical device (μPAD) for detection of biopesticide - azadirachtin (Aza).

Polyethylene glycol-6000 (PEG-6000) and trisodium citrate dihydrate (TSC) form an aqueous two-phase system (ATPS). This ATPS has been explored for synthesis and separation of silver nanoparticles (AgNPs). However, synthesis of stable nanoparticles using high TSC concentration corresponding to generic ATPS composition is not possible as high ionic strength of TSC causes aggregation and precipitation of silver nuclei. In the current study, this problem was overcome by synthesizing AgNPs at low concentrations of TSC. A two-step process was used for simultaneous synthesis and separation of AgNPs. Once stable nanoparticles were synthesised at low TSC concentration, the solution was taken to biphasic ATPS composition by mixing higher concentrations of TSC and PEG-6000 solutions to ensure particle entrapment. A silver to TSC (Ag+:TSC) molar ratio ≥ 67 × 10–3 that corresponds to lower TSC concentrations resulted in the formation of stable silver nanoparticles. The synthesis was carried out in batch and continuous modes. Spherical particles of average size 9.1 ± 3.4 nm were obtained in batch mode while in the continuous mode, the size was 10.6 ± 2.5 nm. Addition of polyvinylpyrrolidone (PVP) helped in sterically stabilizing the particles. Spontaneous formation and stabilization of AgNPs were observed within 15 min of reaction time as opposed to several hours reported in literature. The adopted synthesis route thus, is an effective green process to synthesise stable nanoparticles of silver which can be used in biological applications.

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a vital role in the functioning of Zn-air batteries and similar energy storage systems. These reactions are kinetically sluggish, which limits the performance of rechargeable Zn-air batteries. An effective bifunctional electrocatalyst that can replace the current noble metal based expensive systems is the need of the hour. In this study, Mn-doped cobalt oxide was synthesized using a cobalt zeolitic imidazolate framework (Co-ZIF) as a template. Mn-doped Co-ZIFs with different Co : Mn ratios (0.5, 1, and 2) were prepared using a single-pot technique and converted into corresponding Mn-doped cobalt oxides via calcination. Structural features were studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Mn-Co3O4 displayed a high Brunauer-Emmett-Teller (BET) surface area of 69 m2 g-1 and a high pore volume. Among all the studied compositions, Mn-Co3O4-1 (Co : Mn = 1) exhibited the best performance, illustrating the crucial role of an optimum level of Mn doping. Mn-Co3O4-1 displayed a low ORR onset potential of 0.94 V and high mass transfer limited current density of 5.65 mA cm-2. The catalyst exhibited a low overpotential of 330 mV at a current density of 10 mA cm-2 for the OER. It also exhibited excellent ORR and OER stability and good bifunctionality, with a potential difference of 0.71 V. This study illustrates the excellent performance of Mn-doped cobalt oxides produced using ZIF templates in oxygen electrocatalysis. Mn-doped cobalt oxide prepared by utilizing Co-ZIF as the precursor produced a porous nanocage structure and exhibited excellent ORR and OER activity.

Development of photocatalysts for hydrogen generation is highly imperative in the current scenario for resolving the worldwide energy crisis. Continuous efforts are being made to find low-cost and durable photocatalysts with better light absorption capacity to mitigate energy issues. Herein, a new p-n heterojunction photocatalyst has been synthesized successfully using a polyoxometalate (POM), phosphomolybdic acid (PMo12), and zeolitic imidazolate framework (ZIF-9). Photoelectrochemical studies under visible-light irradiation revealed that ZIF9-PMo12 exhibits a higher photocurrent density than pure ZIF-9. The support of ZIF-9 prevented the instability of PMo12 in aqueous solutions and improved the photoresponse ability of ZIF-9. The p-n junction formation impedes the recombination of electrons and holes, resulting in the improved photocatalytic property. Photoelectrochemical experiments confirmed the photocatalytic features, and thus this work paves the way for the development of an efficient, stable, and low-cost photocatalyst for green H2 generation.

Bauxite residue (BR) is an industrial waste from alumina refineries. Despite being comprised of valuable secondary materials, utilization of BR is limited owing to its high alkalinity and presence of some toxic constituents. Acid neutralization is widely used as a pre-treatment step to mitigate the problems caused by the alkalinity of BR. In this work, BR was treated with various concentrations of phosphoric acid (1 M, 3 M, 5 M, 8 M) followed by thermal treatment to recover the valuables (metals) in terms of metal phosphates. Phosphates of Al and Si were the main constituents of the residue while the supernatant contained mainly Fe and Al. The supernatant solution was acidic (pH between 1.5 and 1.9) and hence can be used to treat BR in place of phosphoric acid to obtain the metal phosphates as before. The 1 M sample residue showed presence of P2O5 like superphosphate fertilizer. The water leaching test showed insignificant levels of metal dissolution in the 8 M sample, thus exhibiting its ability toward immobilizing the constituents of BR. Additionally, the phosphates can be melted at 1000–1100 °C indicating their suitability for glass forming. Thus, phosphoric acid treatment of BR can result in phosphates that can be used in a range of applications.

Light weighting of automobiles would improve fuel efficiency and reduce emissions. Newly developed highstrength, high-elongation (Al-Zn-Mg)-Fe alloys for structural shape casting applications have the potential to fulfill the demand for significant lightweighting of components. Joining such shape casting alloys to form a high integrity component assembly is a critical process in structural lightweighting. Friction stir welding has recently emerged as an effective joining method for aluminium alloys. In this work, friction stir welding was used to join these new-generation (Al-Zn-Mg)-Fe cast alloys. The critical process parameters such as rotation and traverse speed were optimized through a detailed microstructural study and mechanical property evaluation of the welds. Three different tool rotation speeds (600, 800, and 1000 rpm) and traverse speeds (25, 50, and 75 mm/min) were the independent parameters. The welds made with 800 rpm and 25 mm/min traverse speed showed the best properties with no weld/microstructural defects. Friction stir welding also refined the microstructure and uniformly distributed the agglomerated Al-Fe-based intermetallic particles. The microhardness and tensile properties (longitudinal direction) of the stir zone increased significantly (Ultimate tensile strength = 380 MPa, Yield strength = 250 MPa) with appreciable ductility (31%) due to the microstructural refinement despite the dissolution of the strengthening precipitates such as Guinier-Preston zones and & eta;ꞌ phases. The study was able to establish a viable window of processing parameters for joining the new generation Al-Zn-Mg-Fe alloys for structural lightweight components.

The polymorphs (alpha - Bi2Mo3O12, beta - Bi2Mo2O9, gamma - Bi2MoO6) of bismuth molybdate (BMO) exhibit photo-catalytic activity. Among them, the beta phase exhibits good photo electrochemical (PEC) performance but suf-fers from stability issues. In this work, mixed-phase BMO compounds were synthesized using a facile co-precipitation route. The processed BMO showed a band gap of 2.46 eV. The sample with predominantly gamma-BMO (gamma - Bi2MoO6) with lower alpha and beta content exhibited better photo-electrochemical performance with a photocurrent density of 1.12 mu A/cm2 and lower charge transfer resistance compared to the BMO-1 sample with a larger amount of alpha and beta phases. Both the samples displayed n-type conductivity and excellent photoresponse under chopped illumination.

Zinc vanadium oxide (ZVO), Zn0.25V2O5 center dot H2O, was synthesized by a facile hydrothermal synthesis and was evaluated as the positive electrode for Zn-ion batteries (ZIBs). The hydrothermal reaction time had a profound influence on the phase formation and morphology. Short reaction times (12, 24 h) lead to the formation of shorter nanobelts and secondary phases in the Zn0.25V2O5 center dot H2O cathode. A reaction time of 48 h yielded a singlephase material with a multilayered ultralong nanobelt structure. The intercalation of water molecules into the interlayer space of ZVO increased with increasing reaction time. Cyclic voltammetry (CV) revealed that the diffusion-controlled reaction is dominant in the 48 h sample below 0.4 mV s(-1) scan rate and the surface-controlled reaction is dominant above 0.4 mV s(-1) scan rate. Owing to the high crystal water content and consequently increased intercalation sites, the 48 h electrode sample delivered a high capacity of 275 mAh g(-1) with 99.6% coulombic efficiency at 1 C current rate and impressive cyclic stability over 200 cycles with 94% capacity retention. The 48 h electrode exhibited excellent structural and morphological stability after the Zn2+ insertion/extraction cycles, while the 24 h sample displayed degradation after the cycles as revealed by ex situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The study thus demonstrates the rate capability of ZVO and a facile synthesis route that leads to a single-phase and unique morphology, thereby providing a high-performing positive electrode for improved zinc-ion batteries.

The present work demonstrates the feasibility of friction surfacing as a tool to repair surface cracks. An artificial crack, made on Inconel 718 plate was repaired by depositing a self-mating coating by friction surfacing. The crack was completely filled and the coating exhibited sound bonding with the substrate. For complete filling of the crack, the optimized process parameters depends on the crack dimensions. The coating microstructure was characterized by equiaxed fine grains with an average grain size of 1-3 mu m and with a high fraction (>78%) of high angle grain boundaries. The microstructure in the coating evolves through dynamic recrystallization process, driven by combination of high strain rate and high temperature during friction surfacing. The method opens up a new way of repairing surface cracks and enhancing the service life of engineering components.

Solid oxide fuel cell (SOFC) is a green energy technology that directly coverts chemical energy into electricity. Scandia stabilized zirconia (SSZ) shows the highest conductivity among zirconia based electrolytes for SOFCs. However, the stability of the cubic phase, which is the desirable phase for high conductivity, can be an issue in SSZ electrolytes due to its transformation to other low-conducting phases at higher temperatures. In the present investigation, SSZ electrolyte was co-doped with ytterbia, gadolinia and ceria with an objective of improving the high-temperature phase stability. Both the doped and co-doped compositions exhibited a single cubic phase in the as-processed condition. The phase stability at high temperature was studied by aging the sintered pellets at 900 degrees C for 500 h in air. X-ray diffraction and transmission electron microscopy analysis revealed formation of small amount of the low-conducting tetragonal phase in 1 mol % ytterbia and gadolinia co-doped compositions on ageing which resulted in conductivity degradation. Increasing the doping level to 2 mol% prevented the formation of the tetragonal phase. The ceria co-doped composition (1 mol%), on the other hand, was clean without any sign of the secondary phases even after high-temperature ageing. The rhombohedral 'beta' phase formed in the binary composition (SSZ) after sintering but was absent in all the co-doped compositions. The conductivity of the co-doped samples was higher than the binary SSZ. Thus, it can be said that rare earth co-doping is an effective way of improving the phase stability and conductivity of SSZ electrolytes. (C) 2020 Elsevier B.V. All rights reserved.

Here we report a new process termed reverse friction deposition, wherein the parent rod used as a consumable tool in a friction stir welding machine curls up and gets deposited as a seamless tube over itself. The process parameters were optimized and oxide dispersed strengthened (ODS) ferritic stainless tube was processed. The formed tube exhibited a fine-grained structure and improved oxidation behavior. The weight gain after oxidation was lower in the tubes compared to that in the parent rod. The dispersion of oxide (zirconia) particles in the ODS alloy retarded the outward chromium diffusion by pinning down the grain boundaries which might have been the faster diffusion paths for Cr in absence of the particles. When used in the intended application as an interconnect for solid oxide fuel cells (SOFC), this can prevent Cr poisoning of the cathode which will be in contact with the outer surface of tube. (Cr,Mn)O4 spinel formed in the inner diameter of the ODS tube during oxidation. Such spinels are highly conductive electrically and hence are beneficial for the interconnect.

Oxide dispersion-strengthened AISI 430 alloy was fabricated using a novel thermomechanical processing route for potential application as interconnect in solid oxide fuel cells. The process can be termed as reverse friction deposition wherein the final product is formed by curling up as a seamless tube on the surface of the parent rod which is used as a consumable tool in a friction stir welding machine. The oxide dispersion alloy is obtained by incorporating 8 mol% yttria-stabilized zirconia powder in drilled holes in the rod. The number and spatial distribution of holes were optimized for a sound product and uniform distribution of the particles. The oxidation behavior of the formed tube was remarkably different from that of the parent rod. The dispersion of zirconia particles on the outer surface of the tube retards Cr diffusion owing to their grain boundary pinning effect which also refines the Fe2O3 crystal size. (Cr, Mn)O4 spinel, which is known to be electrically conductive, formed in the inner surface of the tube. The tube thus can be used as an interconnect in tubular solid oxide fuel cells and potentially prevent Cr poisoning of the cathode.