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Microstructural investigations on simulated intercritical heat-affected zone of boron modified P91-steel
No full textConventional P91 and boron modified P91-steels were considered in the present investigation. Using Gleeble, weld intercritical heat-affected zone (ICHAZ) was processed. Conventional microscopy was done along with electron back-scattered diffraction for both specimens. Lath boundary of martensite was more, and preferably oriented for P91B-ICHAZ than P91-ICHAZ. Lattice strain was high and lath mobility was low for P91B-ICHAZ in comparison to P91-ICHAZ. Large fraction of ferritic grain structure (39.1%) and small fraction of fresh martensitic grain structure (9.5%) in P91-ICHAZ, whereas small fraction of ferritic grain structure (10.7%) and large fraction of fresh martensitic grain structure (32.7%) in P91B-ICHAZ was observed. However, tempered martensite exhibited meager variation. These differences between ICHAZ simulations were attributed to the presence of 100ppm-boron in P91B-steel
Potentiodynamic Polarization Behavior and Microscopic Examination of Tungsten Carbide Hard Metal Materials in Supported Ammoniacal Medium
No full textElectrochemical methods for the recycling of tungsten carbide (WC-10Co) resources suffer from passivation in the acidic medium caused by WO3 and also in NaOH electrolytes, due to hydroxide formation. We found that an ammoniacal solution is apromising electrolyte for sustainable electrochemical dissolution of both tungsten (W)and cobalt (Co). The ammoniacal medium performs greatly when supported with Cl-,SO42- and CO32- ions. Poor dissolution/corrosion tendency of WC-10Co in a dilutedNH4OH solution enhanced many folds in the presence of Cl-, SO42- and CO32- ions.Among these supporting ions, Cl- emerged as the most suitable for the electrochemical leaching of W and Co from the WC-10Co, accompanying the least noble behavior of WC-10Co. An electrolyte composed of 150 g/L of ammonia and 5% (w/v) of NH4Cl yielded the maximum anodic current density. Microscopic examination of the electrochemically treated samples shows scattered active sites responsible for the oxidative dissolution of WC-10Co. The usefulness of W and Co dissolution in ammonia-additive salt followed the order NH4OH-NH4Cl>NH4OH-(NH4)2SO4>NH4OH-(NH4)2CO3.
An opinion on hydroxyapatite based bio-composites as bone-scaffolds
No full textHydroxyapatite (HA, Ca10(PO4)6(OH)2) is regarded as one among most bioactive materials for bone and hard-tissue replacement due to its chemical and structural similarity as that of apatite with Ca/P ratio of 1.67. But, the use of HA is limited due to its poor fracture toughness to the order of 0.5-1.5 MPa.m1/2. Therefore, usually, some additives, such as Al2O3, YSZ, ZnO, Fe3O4, TiO2, Ti, Ag, carbon nanotubes (CNTs), Ti, etc have been incorporated. It is observed that the metallic reinforcement is a better toughening agent than the ceramic reinforcement, but the release of metal ions may also hamper the key metabolic pathways of human cell. Further,β-tricalcium phosphate (β-TCP) and bio glass addition can be used for attaining controlled resorption of material under in vivo conditions so the natural bone can replace the artificial scaffold during healing process. Many additives, such as Ag, ZnO, CuO, TiO2, etc have been incorporated to provide antibacterial efficacy to the scaffolds. The aspect of antioxidant activity obtained from aliovalent ceramics (such as CeO2) may also assist in expedited healing. The design of porosity at multi-length scales can also be envisaged as means of incorporating cell-material interaction at bulk scale (~150-250 µm size, for vascularisation), at micrometer length scale (~10s of µm for cellular alignment) and at molecular length scale (~ few nm for surface protein interaction with implant substrate). Hence, the onus is on interdisciplinary biomedical engineers to aspire and design multifunctional bone-scaffolds with required mechanical integrity, antibacterial efficacy, bioactive response, biosorption for accommodating natural healing, and inducting expedited restoration
Synthesis of fully interconnected multiporous hydroxyapatite block for orthopedic application
No full textIn the present work, three dimensional multiporous hydroxyapatite block has been synthesized by a
novel process which comprises of two steps. At first, three dimensional polymer-hydroxyapatite nanocomposite
was synthesized by mimicking matrix mediated in situ biomineralization process. Second is sintering step
where synthesized polymer-hydroxyapatite composite was sintered at 1200°C under atmospheric pressure. After
sintering, a structurally stable fully interconnected multiporous hydroxyapatite block was obtained. Detailed
structural and chemical characterization revealed the role of polymer matrix in the formation of three dimensional
multiporous hydroxyapatite block. Cytocompatibility of sintered hydroxyapatite block was evaluated by MTT
assay and cell adhesion test. Results evidenced the non-toxic nature of sintered hydroxyapatite block
Recent advances in photodetection applications of two dimensional MoS2 nanostructures
No full textTwo-dimensional transition metal dichalcogenides (TMDs) with unique properties have received a great attention of scientific community in recent years. Among the TMDs family, MoS2 has been already stablished as an intriguing building block for the next generation optoelectronics, such as photodetectors. The optoelectronic device performance of TMDs are known to be layer dependent. The MoS2 shows excellent light absorption and is found stable in natural environment, which make it suitable for optoelectronic devices. In the present review article, we discuss different synthesis processes for 2D-MoS2 and have summarized few important studies on the photodetection application of different morphologies of MoS2 nanostructures. Here, we discuss the different MoS2 based photodetectors comprising of p-n junction photodiode and the metal-semiconductor-metal (MSM) junction
Environmental impact of spent lithium-ion batteries and green recycling perspectives by organic acids - A review
No full textThe huge usage of rechargeable batteries in electronics has added to a recurrent problem worldwide in generating tonnage of spent lithium-ion batteries (LIBs). The inadequacy of the resources of the depleting critical metals has also been described in vogue. The environmental assessment of the life cycle of the LIBs has been elucidated vis-a-vis the effects of raw material supply, transportation, and recycling. Based on the available work for recycling technologies, this review also attempts to elicit the various methods practiced in discharging/dismantling, classification, and separation of components followed by metal
recovery. The authors have reviewed the major developments in the area of recycling of cathode material by using various acids for extraction of metals from spent LIBs, compared the merits and demerits of acids used and presented a comprehensive outlook to the processes formulated vis-a-vis imperative
need for using green techniques. The necessity for benign recycling methods is stressed upon to alleviate the need for high temperature and oxidative acid leaching conditions. The various green lixiviants (organic acids) attempted to extract metals from spent LIBs have been discussed in detail with respect to the mechanism, efficacies as well as the various factors (selectivity, cost, etc.) that govern the use of organic acids in battery recycling. It was ascertained that the GHG emissions to extract Co using organic acids stand 1/8 of that using an inorganic acid leaching process. Efforts need to be envisaged in separating
the leached metals from these lixiviants ensuring economics and environmental benefits
Life cycle assessment of sintering process for carbon footprint and cost reduction: A comparative study for coke and biomass-derived sintering process
No full textIron ore sintering is an energy-intensive process that converts iron ore fines into an agglomerated porous mass. Sintering plays a prominent pre-processing role in blast furnace smelting operations because of its unsuitability with finer ores. In recent years, the conventional sintering method using coke/coal is being gradually discarded due to environmental degradation. As a result, there is a need for extensive research on sustainable technologies and cleaner fuel sources with lesser carbon footprints. The recent trend is towards the use of biomass. Although biomass is carbon neutral and environmentally friendly energy source, its energy value is comparatively low and inferior. Nevertheless, biomass is emerging to be a viable alternative. In the present study, life cycle assessment has been carried out between the conventional and eco-friendly method of sintering to reveal comparative economic and environmental aspects. The assessment witnessed a 10% reduction in the production cost which is offered with biomass incorporation. Moreover, biomass addition ensured a reduction in emissive indices by 6% for COx, 15.25% for NOx and 20.79% for SOx. Although these reported values are only for the 30% biomass replacement and are subject to enhance with higher biomass proportions
Formation and growth of iron-zinc intermetallics during annealing treatment of galvanized steel
No full textThe development of desired microstructure of galvannealed sheet requires in-depth understanding of the formation and growth kinetics of various Fe-Zn intermetallic phases in the coating during post-treatment after hot dipping of the strip in liquid zinc alloy bath. Keeping this in view, annealing treatment of as-received commercial galvanized sheets, obtained from low (0.135 wt.% Al) and high (0.2 wt.% Al) aluminium containing zinc bath, is carried out to examine the microstructure of annealed sheet with varying strip annealing duration at a fixed galvannealing temperature. The effect of the bath aluminium concentration on the formation of the inhibition layer and on the formation mechanisms of various Fe-Zn intermetallics during subsequent galvannealing (GA) treatment is investigated. Strip annealing simulation is performed using Gleeble® 3800 thermo-mechanical simulator. A detailed characterization of the annealed specimens is carried out to study the galvannealed microstructure produced with varying annealing parameters for both the galvanized specimens obtained from commercial liquid zinc alloy bath with varying aluminium content. A systematic study of annealing treatment of galvanized sheet is performed to enhance the understanding of the role of reacted aluminium present at the interface of the substrate and coating in controlling the nucleation and growth kinetics of Fe-Zn phases to obtain the optimum galvannealed structure. It is observed that high aluminium galvanized bath hinders the formation of the desired sequence of Fe-Zn intermetallics in the coating during annealing treatment. However, galvannealed coating formed using low Al-containing zinc bath shows the desired sequence of various Fe-Zn intermetallics with favourable galvannealed microstructure mainly consisted of compact delta (d) phase, particularly after annealing for 20s at 470°C
Tensile creep and rupture behavior along with evolution of microstructure in a Zr-2.5Nb alloy
No full textTensile creep behavior of the Zr-2.5Nb alloy has been studied through tests under constant load (stress range ~ 137–371 MPa) between 275 and 375 °C. The minimum creep rate of the alloy is found to vary with applied stress and temperature following a power-law relation. The values of stress exponent (n) obtained in the range of 5.3–6.8 in the temperature interval of 300–375 °C; whereas it is calculated as 1.2 and 7.0 under low and high stresses, respectively at 275 °C. The apparent activation energy of creep and stress exponent have been determined by analyzing the experimental data. The obtained (~198.5 ± 10.7 kJ/mol) is found to be higher than the lattice self-diffusion activation energy of pure zirconium (113 kJ/mol). Using this value, stress exponent ~5.6 ± 0.23 is obtained by the temperature-compensated power law. Microstructural characterization by transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) analysis has confirmed coarsening of β-(Nb, Zr) precipitates with compositional changes during creep. The dislocation-precipitate interaction as evidenced by TEM observations is considered to be the origin of threshold stress, which decreases with increasing temperature. Considering the threshold stress, true activation energy of creep and true stress exponent are found as ~160.4 ± 6.9 kJ/mol and ~4.8 ± 0.22, respectively. Analysis of creep data has confirmed the role of dislocation climb as the rate-controlling mechanism, along with validity of Monkman-Grant and modified Monkman-Grant relations. Scanning electron microscopy (SEM) of creep fracture surfaces has revealed evidence for prominent ductile fracture. Further, the obtained creep damage tolerance factor value of 1.9, indicating the predominance for cavitation during creep
On the Study of Batch Annealing Parameter Optimization for Higher Lankford Value in High Phosphorus Interstitial Free High Strength Steel
No full textIFHS grades best known for their superior strength and high formability are conventionally processed through batch annealing. However, high phosphorus contents, which are responsible for rendering the high strength property to IFHS grades, have also been proved to impair the formability of these steels, mainly because of the formation of FeTiP precipitates during batch annealing process. In the present study, two different categories of high phosphorus-containing IFHS steels, viz. (i) Ti and (ii) Ti + Nb stabilized, were subjected to batch annealing simulations targeting r¯ > 2.0. Uniqueness in the present effort lies in the usage of a custom-designed annealing simulator wherein annealing conditions akin to those prevailing in steel industry could be maintained. Processed specimens were characterized for microstructure, texture, tensile properties, and r¯ measurements. Through careful and iterative optimization of annealing parameters and physical simulations, it was possible to achieve r¯ values higher than 2.0 in both the categories of IFHS steels. The optimization of parameters was based upon maximization of γ-fiber texture along with proper recrystallized microstructure. It has been shown that soaking temperature of 710 and 740 °C leads to the achievement of r¯ > 2.0 in case of Ti-stabilized and Ti + Nb-stabilized grades, respectively