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A novel approach to envisage effects of boron in P91 steels through Gleeble weld-HAZ simulation and impression-creep
No full textThis paper induced a novel methodology for the characterization of creep behavior of weld heat-affected zone (HAZ) for boron-free P91 (PM) and boron modified P91B (B-PM) steels. Gleeble-3800 thermo-mechanical simulator replicated specimens, representing coarse-grain HAZ (CGHAZ), fine-grained HAZ (FGHAZ), and inter-critical HAZ (ICHAZ). Short-term impression creep tests were conducted at 625 degrees C/270-410MPa on PM/B-PM and their simulated HAZs after being subjected to post-weld heat treatment (PWHT) of 760 degrees C/3 h. Microstructural characterization and local strain analyses were accomplished by electron back-scattered diffraction. Simulated microstructures of P91B-FG/ICHAZ after PWHT exhibited lath martensitic structure and large prior-austenite grain size as regards P91-FG/ICHAZ, correspondingly. Average values of local microstructural strain from local average misorientation were relatively high in B-PM and P91B-ICHAZ than PM and P91-ICHAZ, respectively. Similar observations were found for P91-CG/FGHAZ with their counterparts. Stress dependent steady-state creep-rate (SSCR) followed power-law for all specimens except PM. The minimum and maximum ranges of SSCR for P91B specimens were observed to be in a narrower range than P91 specimens. The value of stress exponent for all specimens was evaluated, and corresponding mechanisms were discussed. The analyses of microstructures and corresponding impression creep behavior of P91/P91B samples suggested that modification of 100 ppm boron to P91 steel improved creep-rupture ductility that delayed type IV failure at outer HAZ of P91 steel weldments
Scalable preparation of graphene from graphite ore via mechano-chemical ball milling
No full textMechanical exfoliation can generate graphene, but a consistent and scalable preparation of few-layer
graphene (FLG) continues to be a challenge. We employed a mechanochemical milling technique to
achieve maximum shear and frictional force by dual drive mode operation for preparation of FLG directly
from beneficiated graphite ore. Low-grade graphite ore from Jharkhand, India, with a carbon content of
9%, was subjected to primary beneficiation by froth flotation technique using the naturally hydrophobic
property of graphite as opposed to the associated impurities. The obtained graphite concentrates with an
enriched carbon content above 90% after flotation was subjected to chemical treatment process including
alkali roasting and acid leaching, which yielded an enriched graphite powder with fixed carbon of
about 98.16%. A comparative study regarding the leaching efficiency was carried out between sulfuric
acid and hydrochloric acid. The few-layered graphene was successfully prepared by mechanical milling of
beneficiated graphite ore with oxalic acid at 20 hours with optimized critical speed. At various milling
hours, the amplitude of the peak (002) decreased continuously, suggesting that the graphite size and
thickness had decreased. Raman Spectroscopy confirmed the 20 h milled graphite is having single and
few layered (<4 layers) graphene sheets
Flotation of low-grade graphite ore using collector derived from low density polyethylene waste
Get PDFThe increasing wide range of applications of graphite for electrode, lubricants, refractory applications especially the recent surging electric automobile industry, resulting in significant need of graphite in future. Graphite demand in the energy storage industry is expected to grow 15 times faster than today's demand by 2030. Due to depleting high-grade ore, utilization of low-grade ore by beneficiation becomes utmost importance for sustainable development and resource management. In this work, low-grade graphite ore from Tamil Nadu, India with 86.84% ash was beneficiated by flotation technique for recovering graphite with lower ash content. Flotation, a surface phenomena, based on the surface hydrophobicity of the mineral surface to be separated and since graphite is naturally flotation mineral, this technique is adopted for beneficiation. The mostly commonly used collector in graphite flotation is diesel. In view of continuous cost escalation of diesel, an alternate collector was developed utilizing the low-density polyethylene (LDPE) waste paving way for plastic waste utilization. The flotation efficacy of this new collector (Collector PE) derived from LDPE waste was compared with that of diesel in graphite flotation. The run-of mine graphite ore was initially size reduced for liberation of values from its associated impurities, followed by flotation. The mesh-of-grind, dosages of collector (diesel and PE) and frother (Methyl Isobutyl Carbinol, MIBC) were optimized for better process efficiency for increasing the surface hydrophobicity of graphite particles leading to better separation efficacy. The ore characterization by x-ray diffraction revealed that graphite was accompanied predominantly by quartz with minor fractions of pyrites and several other phyllosilicates such as kaolinite and muscovite. Exfoliated morphology of graphite with thick layers were observed from SEM images. Flotation reagents such as diesel, collector PE and MIBC were characterized by FTIR to analyze their functional groups that enhances the efficiency of the separation process. A graphite float (rougher concentrate) with 15.2% weight recovery and 17.7% ash content was obtained after 10 minutes of grinding (d80: 240.5µm) with 0.85kg/t of collector (diesel) and 0.07kg/t of frother (MIBC) dosages and on two-stage cleaning, a final concentrate with 12.66% weight recovery and 8.70% ash content was obtained. A graphite final concentrate with 13.04% weight recovery and 8.90 % ash was achieved with two-stage cleaning, when treated with 0.57 kg/t of collector PE and 0.07 kg/t of MIBC. These results indicate that the flotation efficiency of the collector PE derived from LDPE wastes is comparable with that of diesel and would be economical when used in large scale industrial graphite flotation
Selective extraction and separation of Li, Co and Mn from leach liquor of discarded lithium ion batteries (LIBs)
No full textNovel route has been developed to selectively extract lithium (Li), cobalt (Co) and manganese (Mn) from the leach liquor of discarded lithium ion batteries (LIBs) containing 1.4 g/L Cu, 1.1 g/L Ni, 11.9 g/L Co, 6.9 g/L Mn and 1.2 g/L Li. Initially, Cu and Ni were extracted by solvent extraction techniques using 10% LIX 84-IC at equilibrium (Eq.) pH 3 and 4.6, respectively. Subsequently, precipitation studies were carried out at different conditions such as pH, reaction time, precipitant concentration etc., to optimize the parameters for selective precipitation of Co from the leach liquor. Result showed that 99.2% Co was precipitated from the leach liquor (11.9 g/L Co, 6.9 g/L Mn and 1.2 g/L Li) after extraction of Cu
and Ni in a range of pH 2.9 to 3.1 using un-diluted ammonium sulfide solution (10% v/v) as a precipitant at 30 C, while only 0.89% Mn and 0.62% Li were co-precipitated. After Co precipitation, 98.9% Mn was extracted from the filtrate using 10% D2EHPA at equilibrium pH 4.5, and Li remained in raffinate. From the obtained purified solution, metals could be recovered either in a form of salt/metals by precipitation/ evaporation/ electrolysis method
Processing of Chromite Overburden by Soda Roasting to Recover Chromium as Sodium Chromate
No full textSukinda overburden is dumped with chromite ore tailing which contains about 17% Cr2O3. The other constituent with overburden is iron, silica and alumina. Because of its complex nature and large amount of gangue material it is not suitable for the extraction of valuable chromium by conventional route. The author of the present investigation has tried to recover chromium as sodium chromate from chromite overburden. In this investigation the ore is mixed with sodium carbonate. The mixture is heated in a raising hearth furnace at 1123 K. Before roasting, TG/DTA analysis has been done to fix the operating temperature. After roasting at 90 min, the roasted product is ground and sieved. The rate-determining step of roasting for the conversion into sodium chromate has also been investigated and it shows that the required activation energy at the temperature range 923-1123 K is 60 kJ/mole. The roasted product is leached in hot water condition at an optimum pulp density of 1:5 to obtain the chromium recovery. After leaching, solid liquid separation is done. The leach liquor containing sodium chromate is vaporized and a bright yellow crystal of sodium chromate is obtained. A recovery of 85% chromium is obtained at the optimum condition and the purity of sodium chromate is found to be 99.5%. This chromate is suitable for the use in chemical and tanning industries. A portion of ore, roasted product and leached residue are subjected to XRD and EPMA studies to know the mode of conversion and phases present in different stages of reaction
Critical assessment of the strain-rate dependent work hardening behaviour of AISI 304 stainless steel
No full textIn the present work, the effect of strain rate on the micro-mechanism of plastic deformation and ensuing work hardening behaviour of AISI 304 stainless steel has been critically investigated. The defining role of the early stage of deformation (alpha' in 3% strained specimen at HSR was higher contributing to lower transition strain from stage 1 to 2 of work hardening compared to SSR, the extent of work hardening was higher in the latter case during the stage 2 due to a combined effect of extensive twinning and deformation induced martensite formation, which was limited in HSR due to occurrence of cross-slip. These differences in the work hardening mechanisms were manifested as an improvement in UTS/YS ratio from 2.66 to 2.99 in HSR and SSR specimens, respectively. Furthermore, changes in the mechanism of plastic deformation was also reflected as similar to 4 fold increase in dislocation density for SSR specimen compared to HSR specimen at any given strain level and nearly 27% increase in hardness at the point of fracture. A significant improvement in UTS/YS ratio and ductility for SSR specimen left its signature on the fracture surface in form of three-fold increase in the number density of finer dimples compared to HSR specimen
Hydrometallurgical recycling strategies for recovery of rare earth elements from consumer electronic scraps: a review
No full textThe global demand for rare earth elements (REEs) for use in hi-tech applications is constantly rising, yet their supply is a matter of concern given high rates of disposal. However, urban waste such as consumer electronic scrap (CE-Scrap) has remarkable potential to come to the rescue and meet this growing demand, in line with circular economy principles. Notwithstanding this, globally, their commercial extraction and recovery are yet to be adopted, as <1% of REEs are obtained from recycled CE-Scrap, with the rest removed from the materials cycle. Considering the economic importance and industrial applicability of REEs, the current status of the potential CE-Scrap resources for REEs recycling is presented herein. The summarized availability of all REEs, their mode of occurrence and the prospects of relevant recycling processes, typically by the hydrometallurgical route, are discussed. The feasibility of using established REE extraction and recovery technologies is discussed concerning CE-Scrap such as spent fluorescent lamps, spent NiMH hybrid batteries, computer monitor scrap, and scrap NdFeB magnets. Furthermore, the pros and cons associated with their separation are discussed along with the future directions of research and policies to be envisaged in urban resource recycling. (c) 2021 Society of Chemical Industry (SCI)
Physical and mechanical characteristics of composite briquette from coal and pretreated wood fines
No full textMelina wood torrefied at 260 C for 60 min was agglomerated with lean grade coal fines into composite
briquettes using pitch as binder. Torrefied biomass (3%–20%) and coal fines (80%–97%) were blended together to produce
the composite briquettes under a hydraulic press (28 MPa). The briquettes were cured at 300 C. Density, water resistance,
drop to fracture, impact resistance, and cold crushing strength were evaluated for the composite briquettes. The proximate,
ultimate, and calorific value analyses were carried out according to different ASTM standards. Microstructural studies were
carried out using scanning electron microscope and electron probe microanalyzer equipped with energy dispersive x-ray.
Fourier Transform Infrared Spectrophotometer (FTIR) was used to obtain the functional groups in the raw materials and
briquettes. The density of the composite briquettes ranged from 0.92 to 1.31 g/cm3 after curing. Briquettes with \ 10%
torrefied biomass has good water resistance index ([ 95%). The highest cold crushing strength of 4 MPa was obtained for
briquettes produced from 97% coal fines and 3% torrefied biomass. The highest drop to fracture (54 times/2 m) and impact resistance index (1350) were obtained for the sample produced from 97% coal and 3% torrefied biomass. The fixed and elemental carbons of the briquettes showed a mild improvement compared to the raw coal. The peaks from FTIR spectra for the briquettes shows the presence of aromatic C=C bonds and phenolic OH group. The composite briquettes with up to 20% torrefied biomass can all be useful as fuel for various applications
Fracture toughness behavior of dissimilar metal (SA508 Gr.3 Class 1 and SA312 Type 304LN) weld joint: With and without stress relieving treatment
No full textDissimilar metal welds (DMW) are used to connect the low-alloy steel (LAS) pressure vessel and austenitic stainless steel (ASS) piping in nuclear power reactors. DMWs inherently have high gradient of carbon content across fusion boundary (LAS-ASS), leading to carbon migration from LAS to ASS. Nickel-based alloy is the preferred buttering and welding consumable to minimize carbon migration. Stress-relieving treatment after buttering of LAS also enhances the carbon migration, which may lead to a reduction in local fracture toughness in heat affected zone (HAZ) of LAS. Therefore, this paper aims to study the effect of stress-relieving treatment on the fracture toughness behavior of DMW. Fracture toughnesses of different zones of DMWs have been quantified in as-welded and stress-relieved conditions. It has been shown that stress-relieving leads to lowering of fracture toughness with respect to as welded condition. This is attributed to increase in the microstructural heterogeneity in HAZ (LAS) and near fusion boundary of the DMW
Adsorption isotherm modeling for methylene blue removal onto magnetic kaolinite clay: a comparison of two-parameter isotherms
No full textIn this work, kaolinite clay was modified with magnetic magnetite nanoparticles (Fe3O4@MC) by co-precipitation with ferrous and ferric ions as iron precursors to ameliorate its textural and adsorption capacity for methylene blue (MB) dye uptake from synthetic wastewater at low concentrations. The adsorbents were characterized using XRD, BET surface area analysis, VSM, SEM and HRTEM. The BET surface area after chemical treatment increased from 14.616 to 26.913 m2 g−1. The saturation magnetization of Fe3O4@MC was 6.22 emu g−1 and the exhausted adsorbent recoverable by a simple magnet. Adsorption data were modeled using six nonlinear two-parameter isotherm equations, namely Freundlich, Temkin, Fowler–Guggenheim, Elovich, Flory–Huggins and Langmuir model, and the best-fitting model arrived at using three mathematical error functions. MB adsorption onto unmodified clay was best described by the Fowler–Guggenheim isotherm, whereas MB adsorption onto Fe3O4@MC was best described by the Freundlich model. Increase in BET surface area increased the theoretical and experimental maximum adsorption capacit