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Microstructural Evolution and Mechanical Properties of Fe-Containing High and Medium Entropy Alloys: Recent Advances and Future Prospects
No full textSince the first report on high entropy alloys (HEAs) in the year 2004, HEA systems have opened up new avenues in the development of novel materials, where the formation of simple structures could be realized in the multi-principal element alloys. Due to their concentrated alloying concepts, these alloys have shown many exciting properties compared to conventional ones. Despite the promise of HEAs, the research community is still struggling to utilize the concept to design processes and to develop superior alloys. The biggest challenge is the paucity of data and the vast possibility of alloys from where one needs to find the best. These challenges pertain to composition screening of the alloys for specific applications, alloy processing, thermodynamic database, and overall cost. In the present work, we have discussed the status and the challenges related to fundamental issues and prospects of Fe-containing high and medium entropy alloys to meet industrial requirements. The results of the selected Fe-containing medium entropy alloys will be discussed with their microstructural evolution and promising mechanical properties
A Mini Review on Flotation Techniques and Reagents Used in Graphite Beneficiation
No full textDue to its numerous and major industrial uses, graphite is one of the significant carbon allotropes. Refractories and batteries are only a couple of the many uses for graphite. A growing market wants high-purity graphite with big flakes. Since there are fewer naturally occurring high-grade graphite ores, low-grade ores must be processed to increase their value to meet the rising demand, which is predicted to increase by >700% by 2025 due to the adoption of electric vehicles. Since graphite is inherently hydrophobic, flotation is frequently used to beneficiate low-grade ores. The pretreatment process, both conventional and unconventional; liberation/grinding methods; flotation methods like mechanical froth flotation, column flotation, ultrasound-assisted flotation, and electroflotation; and more emphasis on various flotation reagents are all covered in this review of beneficiation techniques. This review also focuses on the different types of flotation reagents that are used to separate graphite, such as conventional reagents and possible nonconventional environmentally friendly reagents
Tuneable magnetic properties of single-domain oxidation-resistant core/shell FeCo/Cu nanostructures
No full textThe displacement reaction technique was used to produce a nanostructured core/shell FeCo/Cu composed of FeCo core and copper (Cu) shell. The formation of the core-shell structure and thickness of the Cu layer is established and determined by analyzing the X-ray diffraction (XRD) pattern. The transmission electron microscope and selected area diffraction pattern analysis corroborate the results of the XRD studies. Magnetic force microscopic studies reveal that the FeCo/Cu particle shows single-domain characteristics. Oxidation studies indicate that Cu serves as a protective layer and provides a better oxidation resistance to the FeCo core even at high temperatures. Heat-treated FeCo/Cu particles show the possibility of tuning the magnetic properties of this core-shell structure to fit specific application requirements
A comprehensive review on recycling of critical raw materials from spent neodymium iron boron (NdFeB) magnet
No full textThe present paper focuses on the importance of critical raw materials (CRMs) of green energy technologies especially, wind mill and electric vehicle (EVs) sectors. The Neodymium-Iron-Boron (NdFeB) magnet is one of the essential components of these green energy technologies. The rare earth elements (neodymium, praseodymium, and dysprosium) present in NdFeB magnet, due to their increasing demand, high-tech application, and limited availability, fall under the critical category. In the present review paper, the supply risk associated with these critical raw materials has been examined. To meet the demand of these critical rare earth metals, the end-of-life NdFeB magnets have emanated as a potential secondary resource of rare earths. Therefore, the recycling aspects of critical rare earth metals from spent NdFeB magnets have been comprehensively reviewed in the present paper under (i) Direct recycling of spent NdFeB magnets (ii) Extraction of critical rare earth metals using pyrometallurgical, hydrometallurgical, electrometallurgical methods. The advantages and limitations of different methods have been critically examined. The review indicated that the effectiveness of a recycling method depends on the type of spent NdFeB magnet (scrap, sludge or spent magnet) and their level of contamination. Particularly, direct recycling method suitable only for non-oxidized magnets (low contamination). Pyrometallurgical methods use high temperature processes recovering rare earths in the form of alloy or mixed compound, which require subsequent processing for purification. The yield and purity are in trade-off situation. Consumption of large amount of chemicals and loss of rare earths during purification of leach solution is one of the major drawbacks for hydrometallurgical processing of waste NdFeB magnet. Very few processes have been studied at a large scale from a commercialization aspect. Thus, there is a scope that exists in the coming future to develop a robust, eco-friendly, and energy-efficient process for selective extraction and separation of critical rare earth from spent NdFeB magnets. The efficient recovery of rare earth from spent NdFeB magnet will be very much helpful to avoid the supply risk associated with critical raw materials of green energy technologies
Operational Failure of Vertical Roller Attached to a Grinding Mill: Root Cause Analysis
No full textIn the present incident, one of the rollers of
the grinding mill in the cement plant failed during operation, exhibiting longitudinal cracking over the inner surface. Deposition welding was carried out just before the incident to match the worn-out profile of the roller. Investigation revealed that the subsurface of the cracked region contained discontinuities like blow holes (B1.0 mm) and fine cracks (0.2–2.0 mm length). Chemical analysis of the alloy showed low nickel (0.5 wt.%) and high tungsten
(*1.0 wt.%) concentration. The deviation in composition
reduced the ductility of the component. The microstructure of the alloy consisted of complex carbides (50–200 lm)
embedded in a martensite–austenite matrix. Under cyclic
loading, the fatigue crack was initiated from the subsurface
containing discontinuities and bulky carbides. Low
toughness (*2 J) and high residual tensile stress
(*170 Mpa) of the material facilitated crack propagation
in the thickness direction. The final failure of the component occurred due to overload
Distribution, mode of occurrence, and significance of rare-earth elements in coal from Samaleswari open cast coal blocks, Odisha, India with their provenance and paleodepositional environment
No full textThis study aims to thoroughly examine the distribution, concentration, and occurrence of a broad selection of REEs and major elements in coal samples from Samaleswari coal block, IB valley, Odisha, India using advanced geochemical tools. A total of 85 coal samples from four boreholes were characterized using proximate analysis and calorific value measurements. The corresponding ash samples were examined using X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Electron Probe Microanalyzer (EPMA), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS).The coal ash samples were delineated to be rich in SiO2 (42-65%) along with a lower proportion of Al2O3 (24-41%), Fe2O3 (5-6%), and TiO2 (1-2%). The average concentration of REEs in the four boreholes was found to be 510 ppm, with the distribution pattern being Ce > La > Nd > Y > Pr > Sc > Sm > Gd > Dy > Er > Yb > Eu > Ho > Tb > Tm > Lu. The concentration of critical REEs varied in the range of 100-300 ppm, and outlook coefficient (C-outl) ranged from 0.7 to 1.0, demonstrating our coal seams' suitability as a promising source of REEs. A higher concentration of REEs in BH1 was correlated with a relatively higher proportion of apatite. The increment in REE concentration with depth was speculated to be due to their close association with hematite, especially in BH1 and BH2. A strong positive correlation of all the REEs with clay minerals and specifically TiO2 reinstates their abundance in fine-grained clastic sedimentary rocks which are not significantly affected by weathering. Point analysis using EPMA and Scanning Electron Microscope-Energy Dispersive Analysis X-ray (SEM-EDAX) confirmed the co-existence of La, Ce, Pr, and Nd in the Fe-containing aluminosilicate matrix. In addition, the major oxide ratio and their plot entail terrestrial depositional environment in the basin during coal formation and deposited in semi-arid climatic conditions
Effect of Structural Refinement and Modification on the Mechanical Properties of Al-7Si Alloy
No full textIn this present research, the effects of grain refiner (Ti-B) and eutectic modifier (Sr) on the microstructural feature, casting defects, and mechanical properties of Al-7Si alloys are studied. Addition of grain refiner (0.1 wt.% Ti) into Al-7Si melt can significantly change the morphology of dendritic alpha-Al phase to finer equiaxed grains and eutectic modifier (0.05 wt.% Sr) changes the plate-type eutectic Si particles into fine fibrous-/spherical-type particles leads to improve mechanical properties. AFM analysis reveals that combined effect of grain refiner and eutectic modifier on Al-7Si alloy can easily reduce the surface roughness and casting defects such as porosity and shrinkage. The formation of TiAl3 and Ti7Al5Si14 precipitates refines the alpha-Al grains, and SrSi2Al2 precipitate modifies eutectic Si particles during solidification. Both the precipitates are identified by XRD and TEM analysis. The ultimate tensile strength (UTS, MPa), yield strength (YS, MPa), and elongation to fracture (El, %) of developed AS4 alloy are 164, 91 MPa, and 30%, respectively, which are significantly higher than those of developed as-cast AS1 alloy (UTS: 117 MPa, YS: 78 MPa, and El: 16%). The developed microstructural features are correlated with mechanical properties of the alloy by using a liner equation. This correlation suggests that SDAS and morphology of eutectic Si particles play a vital role in the enhancement of mechanical properties (UTS, MPa) of the developed alloys. The grain-refined and eutectic modified alloy exhibit more dimple formation on the fracture surface indicating more ductility
Microstructural evolution and phase selection during solidification of AlCrCuFeNi high entropy alloy
No full textAn equiatomic AlCrCuFeNi high entropy alloy (HEA) was synthesized by arc melting. The as-cast material exhibits the formation of the two-phase structure consisting of BCC and FCC phases. Different heat-treatment schedules were adopted in this investigation for the systematic understanding of the elemental distribution, microstructural evolution and solidification behavior of the alloy. Light microscope and scanning electron microscope (SEM) with EDS analysis was extensively used to characterize the alloy. The results indicate the as-cast material has the primary phase of dendritic structure. The heat-treated sample at 1300 °C, followed by water quenching as well as furnace cooling, primarily showed the Fe-Cr rich BCC phase formation in the dendritic region. The interdendritic space is enriched in Al-Ni rich B2 phase and the Cu rich phase. These outcomes have proximity to the equilibrium phase predictions performed based on the CALPHAD approach. The element Cu plays a crucial role in affecting the solidification behavior of the alloy in the temperature range of 900–1100 °C. This work has shown why understanding the microstructure evolution and solidification behavior is more important in HEAs for their potential future applications
Design and Optimization Study of Metal Recovery from Scrap NdFeB Magnets Using Response Surface Methodology
No full textThe worldwide production of NdFeB magnets has outpaced all other types of magnets owing to their low cost and enhanced magnetic properties. The critical elements required for the production of these magnets are Nd, Pr, and Dy along with other metals. However, rare earth elements (REEs) come with substantial supply risk. Recycling REEs from obsolete NdFeB may be a promising alternative to address the supply chain pressure. The purpose of this work is to optimize the water leaching process for the selective recovery of Nd, Pr, Co, and from chloride-roasted waste NdFeB magnets, using a statistical approach, and to simultaneously study the effect of significant process variables on the extraction of metals from end-of-life (EOL) magnets. Process optimization was carried out by performing a minimum number of bench-scale operations specifically designed for leaching experiments. It was observed that the temperature, time, and pulp density were the most significant process parameters. Tuning of operational parameters was carried out, and model equations were generated for all the response variables with the help of Design Expert software. The response surface methodology (RSM) was used to generate optimized conditions for the leaching process (temperature: 95 & DEG; C; pulp density: 100 g/L; time: 60 min), which were further validated by repeating the leaching experiments in triplicate. The extraction efficiency of metal ions was found to be maximum under the optimized leaching conditions
Curcumin-capped gold nanorods as optical sensing platform for sequence-specific detection of DNA based on their self-assembly
No full textWe are reporting curcumin-induced gold nanorods as an optical sensing platform for the detection of sequence-specific DNA targets through their self-assembly. The combined effect of eco-friendly reducing agent (i.e., curcumin) and silver nitrate in a basic medium (i.e., pH 10) has been attributed to the formation of small gold nanorods (AuNRs) having approximate length and diameter i.e., 19.7 +/- 0.8 nm and 6.0 +/- 0.5 nm, respectively, and lower longitudinal surface plasmon resonance (SPR) enable to detect and analyze different biomarkers. Further, for evaluating cellular uptake of as-synthesized AuNRs, the cytotoxicity study has been carried out by 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay on A549 cells and HEPG2 cell lines, respectively, and shown approximately similar cytotoxicity. Interestingly, an as-synthesized optically and electronically active AuNRs-based nano biosensing platform enables to detection of sequence-specific DNA targets with a low level of detection limit i.e., LOD 8.6 +/- 0.15 pM for the complementary target (CT) DNA with higher sensitivity and better selectivity. Finally, this study suggests a simplistic bio-mediated approach to tuning the shape and size of AuNRs for sensitive, selective, and reliable nano-biosensing platforms for sequence-specific DNA detection related to cancer cells