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On the grain boundary character evolution in non equiatomic high entropy alloy during hot rolling induced dynamic recrystallization
No full textGrain boundary character evolution during dynamic recrystallization (DRX) in a non-equiatomic Fe40Mn40Co10Cr10 high entropy alloy has been examined systematically through single pass hot rolling of 30, 50 and 70 pct reduction. It was observed that the extent of DRX is highly dependent upon the hot rolling reduction. The recrystallization area fraction was considerably higher at 50 pct as compared to 30 pct and 70 pct rolling reduction. In recrystallized regions, a significant proportion of coincidence site lattice (CSL) boundaries (?<= 29) were observed regardless of the rolling reductions. Interestingly, a higher proportion of CSL boundaries (particularly ?3 and ?9) were observed amongst the grain boundaries between re-crystallized grains of last and second last necklace layer (L-S); and grain boundaries between recrystallized grains of the last necklace layer (L-L). However, most of the grain boundaries between last necklace layer and the parent deformed matrix (L-D) have been observed to be random high angle grain boundaries (HAGBs). Generation of significant fraction of second order twin boundaries (sigma 9) along with first order twin boundaries (sigma 3) adjacent to the recrystallization front (i.e. behind the migrating grain boundary) is a con-sequence of multiple twinning processes expected to occur during DRX. Here, role of sigma 3 twin boundaries on the recrystallization process has been discussed. Grain boundary character evolution and its influence on DRX in the presently studied High-Entropy Alloy (HEA) has been inferred to be similar to previously re-ported observations on conventional low stacking fault energy materials. (C) 2022 Elsevier B.V. All rights reserved
An Investigation on the Correlation Between Microstructure, Texture, and Mechanical Properties of Mg and its Alloys
No full textThe effects of microstructure and texture on the mechanical properties of Mg and its alloys have been investigated in the present study. Samples, such as pure Mg, AM30 (Mg–3 wt.% Al−0.3 wt.% Mn), and AME300 (Mg–3 wt.% Al–0.3 wt.% Mn–0.2 wt.% Ce) alloys, were used for the investigation. The samples in the form of hot-rolled plates were subjected to annealing to characterize their microstructures, textures, and mechanical properties. The results revealed that the ductility of pure Mg is dependent on the reduction in basal texture intensity, and its tensile strength is dependent on the average grain sizes of the samples. However, the optimum combination of strength and ductility can be achieved in pure Mg after annealing at 300 °C for 15 min. Similarly, the same can be achieved in AM30 alloys after annealing at 400 °C for 480 min, and in AME300 alloys after annealing at 450 °C for 10 min. However, these Mg alloys after annealing at lower temperatures (i.e., 200 and 300 °C) did not show any correlation between grain size, texture, and mechanical properties of the alloys. This has been attributed to the presence of precipitates in the alloys. It was further found that AME300 alloy had the best combination of tensile strength and ductility compared to AM30 and pure Mg after annealing
Effect of microstructure on corrosion behavior of medium manganese steel
No full textIn this work, the corrosion behavior of medium-manganese steel (MMS), with lamellar and globular microstructure having comparable austenite and ferrite fractions is studied using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. It was observed that lamellar morphology had superior corrosion resistance depicted by similar to 44 % lower corrosion current and a greater charge transfer resistance. The superior corrosion resistance of lamellar morphology was attributed to a relatively favorable crystallographic texture and a higher fraction of low energy low angle grain boundaries compared to globular morphology MMS. This work sheds important insights into controlling corrosion resistance of third-generation advanced high-strength MMS through microstructural design
Recovery of Precious Metal Silver from Scrap Computer Keyboards
No full textSilver (Ag) is extensively used in manufacturing of electronic goods due to its low cost and conductivity. In view of the escalating demand, stringent, environment rules, and limited sources of Ag, the present paper is focused on the development of hydrometallurgical process flow-sheet to extract Ag from scrap computer keyboards. These keyboards contain ~0.4% of Ag. Initially, keyboards were dismantled to separate the Mylar sheets scontaining Ag. The same were pyrolyzed at 300 °C for 2 h to get enriched metallic part. About 99.99% Ag was leached using 2 M HNO3 at 60 °C within 30 min in close and proper condensed system. Separation techniques (precipitation/cementation) could be used to obtain pure Ag salt/metal. Based on the
laboratory-scale experiments, the process flow-sheet developed is economical, ecofriendly, and has potential to be translated to industry for commercial exploitation
after scale up/pilot trial
Recovery of Lithium from Black Cathode Active Materials of Discarded Lithium-Ion Batteries
No full textLithium (Li) is the lightest energy critical element used in manufacturing of active cathode material of lithium-ion batteries (LIBs). Thus, the consumption of lithium is constantly increasing in the LIBs. Meanwhile, LIBs become obsolete after reaching its end-of-life resulting in the generation of huge amount of spent LIBs. Present study reports the roasting and leaching process for selective recovery of Li from active cathode material. To optimize the process parameters viz. roasting temperature, time, and mass ratio studies were carried out varying the experimental
conditions for the conversion of lithium oxide to lithium sulfate from the complex of lithium cobalt oxide. It was found that cathode material converted into lithium
sulfate at 750 °C in two hours maintaining mass ratio of LiCoO2/Na2SO4: 1/0.5. Subsequently, 99.1% Li was leached from roasted product at 75 °C in de-ionized water within two hours. Further, Li can be precipitated as lithium carbonate using sodium carbonate
Novel observation of dominant role of strain rate over strain during pre-straining on corrosion behaviour of 304L austenitic stainless steel
No full textPre-straining at different strain-rate is usually carried out during forming of 304L stainless steel (SS) which can affect its corrosion behaviour. A systematic study on the effect of strain-rate in conjunction with pre-strain on electrochemical corrosion behaviour of 304L SS is elucidated for the first time. Prior deformation (10% and 30%) resulted in either beneficial or detrimental effect on the corrosion and pitting resistance depending up on the imposed strain-rate. A novel observation of improved corrosion resistance at higher strain-rate is attributed to differences in strain-rate dependent evolution of microstructure and substructure. This work suggests that the corrosion behaviour of 304L SS is a stronger function of strain-rate compared to the strain and from the microstructure viewpoint, it depends on the complex interplay between dislocation density, deformation-induced martensite, coincidence site lattice (CSL) boundary and, crystallographic texture
Anomalous interfacial stress generation and role of elasto-plasticity in mechanical failure of Si-based thin film anodes of Li-ion batteries
No full textTo understand the reason for mechanical failure and capacity fading of Si-based composite thin film batteries, we have developed a lithiation-induced interfacial stress model. The role of electrochemical charging reaction process, stiffness-induced elasto-plastic deformation and relative change in resistivity in detail through regional material heterogeneity sensitivity exponent has been accounted for anomalous interfacial stress generation. The insight gained from the results of state-of-health of the battery electrodes suggests that the transition of material from elastic to plastic behaviour and cracking at the interface are due to volume expansion, i.e., fully lithiated. Finally, the unified lithiation-induced stress model unravels the effect of embedded material heterogeneity parameters coupled with resistivity and stiffness and its anomalous dynamics at composite electrode-collector interface. The verification with the available experimental data in the literature has also been made and hence providing a better insight into the origin of degradation and the evaluation of advanced battery electrodes
Effect of surfactant, ionic strength, mineralogical composition, and surface morphology on zeta potential of bituminous coals of Indian origin
No full textThe variation of zeta potential of high ash Indian coals in the presence of various surface modifying conditions has rarely been studied in depth. The objective of the present investigation was to perform a detailed comparative study on surface zeta potential of two distinct Indian coals that have substantial differences in their ash content and surface chemistry. Detailed characterization studies of the two coals were performed using FTIR, petrography, and proximate and ultimate analyses, which demonstrated that Topa coal was more hydrophobic in comparison to Kulda coal. Electrokinetic measurements at ambient temperatures demonstrated that the zeta potential of both coals was dependent on pH, ionic strength, and type of surfactant. The surface potential of both coals, irrespective of the extent of mineral association, was only affected by cationic surfactant over a prolonged contact time. XRD analysis of the coal ash samples revealed the presence of quartz, hematite, mica, and zeolite as the predominant minerals. In the present study, the inherent and surface chemistry of mineral-rich coals was correlated through the measurements of zeta potential. It was concluded that the variation in mineral matter content does not impact the zeta potential of coal particles significantly
Continuous hydrocyclization of aqueous levulinic acid to ?-valerolactone over bi-functional Ru/NbOPO4/SBA-15 catalyst under mild conditions
No full textHerein, we demonstrate that surface acid-base properties have marked effect upon the performance (activity, selectivity and stability) of supported Ru catalysts upon tandem hydrocyclization (hydrogenation-dehydration) of aqueous levulinic acid. A mesoporous bi-functional Ru/NbOPO4/SBA-15 catalyst incorporating highly dispersed Ru sites and well balanced strong Bronsted acidic sites (optimum B/L and M+S/W ratio) was identified, which outperformed the benchmark monofuncational (Ru/SBA-15, Ru/MCM-41) and physically blended bifunctional catalysts (Ru catalysts mixed with acid co-catalysts e.g.NbOPO4/Amberlyst-15). Further, the catalyst also demonstrated remarkable stability in a fixed-bed reactor, maintaining steady activity and gamma-valerolactone selectivity (72-86%) during ca. 300 h time on stream (10 bar, 90-100 degrees C), corroborating its industrial potential. The exceptional performance and durability of the bi-functional catalyst was attributed to the presence of well dispersed hydrothermally and chemically stable acid (NbOPO4) and redox (Ru) sites
Recovery of clean coking coal from difficult-to-wash low volatile coking coal fines of Jharia coalfield by multi gravity separator
Get PDFMulti gravity separator (MGS) is a centrifugal gravity separator deployed for beneficiation of fine particles with relatively low concentration. It is for the first time, that a statistical tool was engaged to evaluate effects of the most influencing process variables and their actual impact upon the performance of MGS with respect to its potential to clean the difficult-to-wash low volatile coking (LVC) coal fines. Characteristics of LVC coal sample was analysed and discussed in terms of physical properties, petrographic composition, washability, XRD and SEM analysis. Three different feed sizes such as –500 μm, –250 μm and –150 μm were used for assessing the separation mechanism and efficacy of MGS along with three different process variables such as drum speed, shaking amplitude and wash water rate to study and ascertain the most efficient experimental design for obtaining optimal result. Results revealed that drum speed and feed size turned out to be most significant parameters for reduction of ash concentration. In design of experiments, clean coal ash, combustible recovery and separation efficiency were considered as response functions. Material balance for MGS unravelled that about 74% clean coal produced with 10% ash reduction from the feed ash of 32.8% could be achieved in single stage, in optimized process conditions