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Cathodic corrosion induced selective nano-crystallization of Nickel oxo/ hydroxo complex on (NiFeCr)SiB amorphous ribbon for alkaline oxygen evolution reaction and methanol oxidation reaction
No full textThe study focuses on the development and optimization of (Ni87Fe4Cr9)78Si8B14 amorphous ribbons as selfsupported electro-catalysts for oxygen evolution reaction (OER) and methanol oxidation reaction (MOR). Electro-catalytically active nano alpha-Ni(OH)2 phase (5-10nm) was generated in the amorphous ribbon surface through potentiostatic cathodic corrosion for different time intervals (0-120 min). The X-ray diffraction and scanning electron microscopy results shows the favourable occurrence of dense nanocrystallization of alpha-Ni(OH)2 between 45 and 90 min of corrosion time. For OER in 1 M KOH, the 60-min surface modified ribbon exhibits an overpotential of 295 mV at 10 mA/cm2 current density and tafel slope of 51 mV dec-1. In case of MOR in 1 M KOH +1 M MeOH, the 90-min corroded ribbon shows lowest potential of 1.38 V vs RHE, at 10 mA/cm2 and tafel slope of 34 mV dec-1. In addition to superior electro-catalytic activity, the optimal surface-modified ribbons show superior long-term stability for OER and MOR studies, indicating its potential application in hydrogen generation and direct methanol fuel cell
Understanding the Formation Mechanism of Al-Rich Interfacial Layer during Galvanizing of Cu Pre-coated High-Strength Steel Sheet
No full textThis work aims at understanding the formation of a beneficial thin continuous aluminum (Al)-rich interfacial layer with uniform distribution of fine equiaxed Fe-Al crystals formed at the substrate/coating interface during the initial stages of interfacial reactions as well as hindrance of Fe dissolution in Zn layer as soon as copper (Cu) pre-coated high-strength steel substrate is immersed into the molten zinc (Zn) bath containing 0.2 wt.% Al. Pre-coated Cu does not allow the immediate interaction and interdiffusion of Fe and Zn because of the positive heat of mixing between Fe and Cu. As the Cu dissolves in liquid Zn, counterdiffusion of Al and Zn toward the steel interface allows Fe to react with Al and Zn forming the thin Fe-Al
inhibition layer with finer equiaxed grains. Moreover, dissolved Cu in the Zn layer would also prevent Fe diffusion in Zn in the time span during dipping, which is beneficial. Atom probe tomography (APT) analysis at the substrate/coating interface location reveals the presence of 56.22 ± 1.36 at.% Al, 35.01 ± 1.31 at.% Fe, 6.33 ± 0.66 at.% Zn, and 0.032 ± 0.01 at.% Cu, similar to the intermetallic compound of Fe2Al(5-x)Znx, as well Cu in the Zn layer supporting the above reasoning
Beneficiation of lithium bearing pegmatite rock: a review
No full textThe need for lithium in energy storage systems has risen dramatically due to the development of renewable energy technology, portable devices, and electric cars. The current review focuses on the existing worldwide resources of lithium ore, along with the production, demand, and mineralogy of lithium-bearing minerals, in addition to lithium recovery from hard pegmatite ore using different bene-ficiation techniques. Lithium ore is beneficiated using various methods, including magnetic separation, gravity concentration, electrostatic separation, and flotation to separate gangue minerals. Flotation is the most frequently utilized beneficiation technique. It is found that gravity concentration and flotation are the main beneficiation methods used in many plants around the world. In flotation, reagent chemistry, surface properties, and water quality were critical in spodumene’s efficient recovery. A summary of several reagent regimes, surface properties, flotation conditions, and prospective future studies for technical viability are provided. The current review paper also discusses the beneficiation flowsheet widely used to recover spodumene, lepidolite, and petalite from pegmatite ore. Also, it is tried to discuss the key future research areas along with the cost economics aspect of processing such ore deposits to recover lithium
Enhancing Recycling Potential: Exploring Reduction and Metal Separation Behavior of Iron-Rich Slag in Electric Arc Furnace Smelting for a Sustainable Future
No full textThe electric arc furnace steelmaking route is essential for sustainable steelmaking through hydrogen-based direct reduced iron. About 30% of the global steel production currently follows the scrap/direct reduced iron-electric arc furnace (DRI-EAF) route, which is bound to increase given decarburization efforts by the steel industry. We investigated DRI-EAF slag recycling simulated in laboratory EAF smelting tests to lower its environmental impact. Several aspects of process development were explored, such as process conditions, specific energy consumption, and the settling behavior of iron particles. Significant reductions occur in the first 15 min, ranging from 73.4% to 83.34%. About 97% iron was recovered under optimum conditions: basicity-1.2, carbon/oxygen ratio-1, and time-40 min. The settling velocities of iron particles decreased with increasing slag basicity, reaching values of 3.13 x 10-5 m/s, 1.95 x 10-5 m/s, and 0.89 x 10-5 m/s for basicities 0.9, 1.2, and 1.5, respectively. The effects of basicity on slag viscosity, phase formation, and energy consumption are critically discussed. Compared to 0.9, basicities of 1.2 and 1.5 increase power consumption by 17.6% and 23.5%, respectively. The findings potentially contribute to managing DRI-EAF-based slag, repositioning it as a potential resource, and reducing associated pollution
Metallurgical Failure Analysis of Economizer Tube of Thermal Power Plant
No full textIn present investigation, failure investigation of
failed economizer tube of boiler of the thermal power plant
was analyzed through visual inspection, dimensional
measurement, bulk chemical analysis, mechanical properties evolution and metallurgical analysis. Failure of the
economizer tube was occurred in the form of cavity having
one longitudinal hairline crack passing through the cavity
on the external surface of economizer tube. Metallurgical
failure analysis of an economizer tube was carried out by
visual observation, chemical analysis, optical microscopy
(OM), scanning electron microscopy, SEM-EDS analysis,
x-ray diffraction (XRD) and mechanical properties evaluation. Ash deposit and surface corrosion were on outer
surface were observed. Severe corrosion and thinning were
observed on the external surface of economizer tube. SEMEDS analysis on the fractographic samples near failure
zone showed good amount of Cu deposition on the inner
surface of the tube and ash-related corrosion products on
the outer surface of the tube. Localized reduction/thinning
of wall thickness of the economizer tube happened due to
combined effect of ash corrosion-erosion from outside and
pitting/galvanic corrosion from inner surface due to Cu
deposition and finally resulted in failure of the tube.
However, outer corrosion on the tube is significantly
dominant due to ash corrosion. Therefore, ash corrosion is
major cause of failure of economizer tube. Ash corrosion
was due to use of poor-quality coal. To mitigate the
problem, removal of ash deposition on outer surface and
Cu deposition on inner surface of tube should be carried
out by periodically by proper cleaning and use of good
quality coal is suggested
An investigation into the effect of various parameters on oilagglomeration process of coal fines
No full textIn the present study, the authors have performed oil agglomeration of coal fines using castor oil and combination of castor oil and turpentine oil in various proportions. The coal samples were collected from three different mines of Mahanadi Coalfields Limited having high ash content(27–39%). From the post proximate analysis it was revealed that in caseof Mine 1 coal, the moisture content reduced by 83%, for Mine 2 it was94% and for Mine 3 the moisture reduced by 90% from the initial values. Grade achieved after oil agglomeration process was G5 grade for Mine 2coal and G3 grade for Mine 1 & 2 coal. The effect of various parameters such as oil dosage, pulp density, pH, on yield, ash rejection and organic matter recovery were studied. The parameter with the highest relative importance was found to be oil dosage (normalized importance of100%) whereas agitation time and pulp density were found to have normalized relative importance of 74% and 70%, respectively. A non-linear regression model in the form of quadratic equation has also been proposed for ash rejection (%) based on the independent variables such as pulp density, oil dosage and agitation time
Sour Service Domains of 13Cr Martensitic Stainless Steels: A Review of State-of-Art Knowledge vis-à-vis ANSI/NACE MR0175/ISO 15156
No full textHydrocarbons, water, carbon dioxide, hydrogen sulfide, chloride, high temperatures, and pressures are all involved in oil and gas production. Thus, corrosion, particularly sulfide stress cracking (SSC), poses a great threat to the integrity of well components such as tubing, casing, packer, and wellhead assembly. Sometimes, SSC can lead to catastrophic failures and must be addressed due to operational security and environmental concerns. Localized corrosion, including SSC, can be reduced greatly with the appropriate material selection and optimization of critical operational parameters. The material selection is performed according to service environments vis-a-vis mechanical/ metallurgical attributes of the alloys as prescribed in standards such as API 5CT and ANSI/NACE MR0175/ISO 15156. Currently, corrosion-resistant alloys (CRAs) such as martensitic and duplex stainless steels, nickel, titanium and other precipitation hardened alloys are available and used in oil and gas industries because of their superior mechanical and corrosion properties. Owing to the operating environmental reasons, designer often opt for more expensive CRAs as compared to relatively less expensive materials which fall close to the performance boundary of materials selection criteria, thereby increasing overall cost of crude oil production. Thus, there is a paramount requirement to ascertain the candidate materials appropriately without bearing the cost penalties of over-specifications or the performance shortfalls of under-specified alloys when new fields are discovered. In this paper, the application domains of 13Cr martensitic stainless steels are reviewed vis-a-vis limits prescribed in ANSI/NACE MR0175/ISO 15156 standard. The paper will aid in the selection of cost-effective materials for oil and gas production when temperature, pressure, hydrogen sulfide concentration, pH, and salinity vary in different directions and cannot be well defined within standard limits
Comparative interplay of C and Mn on austenite stabilization and low temperature impact toughness of low C medium Mn steels
No full textTo expand the use of medium Mn steels for the production of automotive and structural components intended for cryogenic applications, the present study focuses on attaining an enhanced low temperature impact toughness in two inter-critically annealed medium Mn steels with varying C and Mn contents without sacrificing the strength. In both 'low-C, high-Mn' and 'high-C, low-Mn' steels, the key role in regulating the impact toughness is mainly attributed to the volume fraction of stable retained austenite. Mn is found to stabilize austenite more effectively than C while allowing the attainment of near-equilibrium composition. Except for the 'low-C, high-Mn' steel, inter-critically annealed at lower temperature, Mn redistribution occurs in other samples, leading to a reduction of stable austenite fraction. The filmy shaped Mn enriched retained austenite is more thermally and mechanically stable in 'low-C, high-Mn' steel sample on inter-critical annealing at lower temperature than the other samples. The presence of fine dispersion of the filmy austenite at various substructural boundaries of 'low-C, high-Mn' steel after low temperature inter-critical annealing results in significant structural (Bain width) refinement and thereby, remarkably improves its impact toughness
The effects of microstructure and temperature on the deformation heterogeneities and fatigue behavior of a Ni-based superalloy
No full textThis research investigates the coupling effect of microstructure and temperature on the fatigue performance of an equiaxed Ni-base superalloy, EA, at design-significant temperatures (750-930 degrees C) for different strain amplitudes (Delta epsilon/2). It is observed that distinguishing damage features (specific to the temperature and Delta epsilon/2) remarkably affect the extent and distribution of strain localization, leading to the divergence in associated fatigue behaviour. The strain is uniformly distributed at lower Delta epsilon/2 for all temperatures. Compared to the 850 and 930 degrees C, the strain localizations at 750 degrees C are more effectively alleviated, accounting for the highest fatigue life. Moreover, this alloy exhibited a bilinear Coffin-Manson (C-M) relationship. It is ascertained that the strain localization resulting from the dislocation and precipitates (gamma ', Cr6C23, and gamma-gamma ' eutectic) interactions are mainly responsible for the dual-slope C-M behaviour
Limitations Associated with Proximate Analysis-Based Gross Calorific Value Modeling for Coals
No full textThis study aims to investigate the limitations associated with proximate analysis-based gross calorific value (GCV) modeling for coals. Toward this, a dataset comprising proximate analysis and GCV data of 4792 coal samples collected from various Indian coal basins was generated, and then a GCV prediction model was developed using the popular multivariate linear regression (MLR) technique. Although the developed model appeared to be acceptable in terms of a prediction R2 value of 0.934, through rigorous statistical analysis, it has been shown that grade misclassification and source-specific biases are inherent limitations associated with such GCV prediction models. It was found that the grade classification accuracy associated with a GCV prediction model was inversely and linearly proportional to the model's associated mean absolute error (MAE) value. It has further been demonstrated that even well-validated GCV prediction models available in literature may perform sub-optimally when utilized for grade classification tasks. The analysis presented in this study also confirms that a source-specific bias can be introduced in the GCV prediction models developed using coal samples from varied geographical sources. It has further been shown that the incorporation of a categorical representation of the sample sources in the GCV prediction model could successfully eliminate the source-specific biases