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Evolution of 3D microstructure and correlation with deformation behavior of as-cast Mg-4Zn-xCa alloys
No full textIn this study, X-ray microtomography results aided with fractography have been utilized to elucidate the effect of the distribution of the secondary phases on the damage mechanism of the Mg-4Zn-xCa (x = 0, 0.2, 0.4, 0.6, 1.0 wt%) alloys. The alloy Mg-4Zn exhibited a 2 -a phase microstructure comprising of alpha-Mg matrix and the second phase (MgZn), which converted to an interconnected network of Ca2Mg6Zn3 phase along grain boundaries with an increase in Ca content. The compressive strength increased with the increase in Ca content up to 0.4 wt% due to the formation of the Ca2Mg6Zn3 phase. However, it further decreased due to easier crack propagation through the 3D network of Ca2Mg6Zn3 at grain boundaries
A comparative study on the association and extractability of rare earth elements from laboratory ash, bottom ash, fly ash: A perspective on Indian coals
No full textThe conditions under which coal ash is formed largely dictate the association of valuables within its matrix. Optimum utilization of coal waste at the commercial level is only feasible upon performing an in-depth comparative study of fly ash (FA), bottom ash (BA), and laboratory ash (LA). In the present study, two coal ash samples were acquired from a power plant in India (1200-1300 degrees C), whereas the one under laboratory conditions was prepared at 815 degrees C. The total concentrations of rare earth elements (hereafter abbreviated as REEs) were LA (873 ppm), FA (509 ppm), and BA (373 ppm) and their respective outlook coefficients were LA (0.78), FA (0.87), and BA (0.88). Sequential extraction revealed that the chosen LA possessed 40 % of the total REE in extractable form, whereas both FA and BA possessed only 10 % of the total REE in extractable form. Magnetically isolated Fe-containing matrix with 50 % Fe2O3 was observed in the case of FA. Alkaline pre-treatment to enhance the extractability of REEs was performed using both NaOH and Na2CO3, under varying temperatures from 400-850 degrees C. The optimum condition was deduced to be using NaOH at 400 degrees C. Sodium silicate was eliminated during water leaching, from which Si was precipitated at neutral pH. The leaching parameters were optimized on these alkali roasted coal ash samples, and 0.5 M tartaric acid at 90 degrees C stirred for 60 min demonstrated a 75-80 % increase in leaching of REEs as compared to baseline leaching of 27 % (LA), 5 % (FA), 12 % (BA). Significant morphological change was observed post-alkaline pre-treatment and acid leaching. NaOH roasting resulted in cracks and fractures on the surface of spherical BA and FA samples followed by the development of pores during the leaching process. Solvent extraction was performed with 10 % (v/v) D2EHPA (di-(2-ethylhexyl) phosphoric acid) in kerosene with an additional scrubbing stage (5 % oxalic acid solution) to enhance the purity of REE extraction
Nanocomposites of Magnesium Metal Matrices with Potential Medicinal Uses: A Review
No full textThere is growing interest in biomedical applications of magnesium (Mg) and its nanocomposites due to their superior biodegradability, stiffness, and lower elastic modulus than other implant materials. However, the quick deterioration of magnesium alloys results in a rapid decline in mechanical properties, restricting their clinical application. Recent advancements, particularly in the integration of nanoparticle reinforcement, have enhanced mechanical strength while preserving the inherent toughness. These composites also show impressive corrosion resistance and compatibility with biological systems. However, uniformly dispersing nanoparticles as reinforcements within the Mg matrix and achieving the desired properties present significant challenges. Consequently, selecting appropriate magnesium nanocomposite production methods and identifying biodegradable, biocompatible, and osteogenic reinforcements are of utmost importance to overcome these obstacles and enhance mechanical, corrosion, and cytotoxic properties relevant to specific applications becomes imperative. This review investigates a range of fabrication techniques and types of reinforcement, analyzing their impact on the mechanical properties, corrosion resistance, and biocompatibility of magnesium nanocomposites. Additionally, it investigates potential applications and proposes future research avenues for magnesium nanocomposites
Creep rupture properties of dissimilar welded joint of ferritic/ martensitic P92 steel and Inconel 617 alloy
No full textThe dissimilar welded joint (DWJ) comprising P92 steel and Inconel 617 (IN617) is frequently utilized in advanced ultra-supercritical (AUSC) boilers. In present work the creep rupture behaviour, rupture mechanism and microstructure evolution of DWJ of P92 steel and IN617 with Ni-based ERNiCrCoMo-1 filler, were examined at 650 degrees C under the stress range of 120-200 MPa. The results of the creep test indicated that the location of creep rupture varied across different testing conditions, encompassing areas such as P92 base metal and the fine-grained heat-affected zone (FGHAZ). The creep tested specimens within the stress range of 180-200 MPa exhibited failure originating from P92 base metal, predominantly influenced by plastic deformation. The failure manifested in a transgranular mode, driven by the formation, growth, and eventually coalescence of microvoids. The creep tested specimens within the stress range of 120-150 MPa displayed the characteristic ofType IV failure, primarily attributed to matrix softening and the absence of adequate precipitates to pin the PAGBs. Microstructural characterization unveiled the presence of microvoids along the PAGBs, facilitating microvoid nucleation primarily owing to the existence of the coarse brittle carbide phase. The growth of these microvoids over a period of time during tertiary stage of creep which lead to their coalescence and the formation of microcracks, ultimately resulting in premature intergranular failure. The specimen creep exposed at 650 degrees C under the lower stress of 120 MPa exhibited higher creep rupture life for 432 h. The SEM/EDS study of the crept sample of 120 MPa is also confirmed the presence of intermetallic laves phases in regions near the fracture tip and in the heat-affected zones (HAZs). Although the creep tested specimens at 150 MPa and 120 MPa exhibited failure in the FGHAZ and their elemental SEM/EDS analysis confirmed the presence of an oxide layer and notch formation near the interface of P92 base metal and ErNiCrCoMo-1 filler weld. The FESEM study revealed the growth of the oxide layer in the notch region, and it also showed the presence of multiple cracks and microvoids in the oxide layer. The formation and propagation of the oxide notch mainly led to the interfacial failure. The crept specimens subjected to 180 MPa and 200 MPa did not exhibit any cracks or microvoids in HAZs. However, specimens that failed under applied stresses of 120 MPa and 150 MPa revealed the presence of a high density of microvoids in the FGHAZ, inter-critical heat affected zone (ICHAZ), and in the region of the coarse-grained heat-affected zone (CGHAZ) adjacent to the interface attached with an oxide layer
Investigation on modified Linz-Donawitz slag for the treatment of Pb2+ion-laden wastewater - A slag utilization sustainable approach
No full textThe present study investigated the adsorptive chemistry of Pb 2 + ions eradication using modified Linz-Donawitz slag (LDS), a byproduct of steelmaking industries. The processing of LDS was carried out using a magnetic separation technique followed by planetary micro-crushing. The morphology of surface texture and elemental composition of LDS were examined using SEM and EDS techniques, respectively. XRD and FTIR analysis revealed that the divalent cation of Pb 2 + was replaced by Ca 2 + to form metal silicate (Pb 2 SiO 4 ) and ferrite (Pb 2 Fe 2 O 5 ) through ion exchange and finally precipitated. The experiment data best fitted Langmuir isotherm and showed excellent adsorption capacity of LDS for Pb 2 + adsorption (479 mg/g). Thermodynamic parameters, Gibbs free energy ( Delta G o ), and enthalpy change ( Delta H o ) indicated the adsorption was spontaneous and endothermic. The leachability study done by the ICP-OES technique suggested the possibility of immobilizing Ca and Si due to the dissolution of CaO and SiO 2 . The study demonstrated the potential of LDS for treating Pb 2 + ions as part of the waste utilization of the steel industry for a sustainable approach
Evaluation of Shot Peened SS 347 Tubes Through a Magnetostrictive Sensing (MsS) Device
No full textImpact of shot peening on SS347 tube has been investigated using MagStrics, a magnetostrictive sensing (MsS) device comprising of rapidly quenched ribbon as sensor element. Two tubes of SS347 have been considered in pre- and post-shot peened state. Annealed ribbon as sensor element showed enhanced MsS signal. Using the annealed ribbon as sensor element, the MsS signal amplitude in shot peened tube was found to be distinctly different from un-peened sample. This was associated to magnetic phase evolutions in the pipe internal surface due to shot peening. Such phenomena have been endorsed through SEM–EDX compositional analysis and correlated through simulations using COMSOL Multiphysics
Inorganic-organic hybrid geopolymers: evolution of molecular and pore structure, and its effect on mechanical and fire-retardant properties
No full textIn order to overcome the brittle behavior of conventional geopolymers, of late, a paradigm shift towards development of hybrid geopolymers has commenced. This study describes hybrids synthesized by co-milling metakaolin and solid organics (epoxy resin: diglycidyl ether of bisphenol A and hardener: dicyandiamide) followed by alkali activation. The developed hybrid geopolymers exhibit enhanced mechanical and physical properties. Physical and mechanical properties of such hybrids depend on the extent of molecular-level interactions and microstructural evolution during geopolymerisation. Evolution of molecular structure from precursor stage (co-milled samples) to hybrid geopolymers is studied using transmission electron microscopy (TEM) and 27Al, 13C, 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy. NMR and TEM analyses of the hybrid geopolymers illustrate the formation of Si-O-C bonds and uniform C distribution (with no phase separation); this confirms inorganic-organic chemical interactions during geopolymerisation. Detailed assessment of pore characteristics using TEM, mercury intrusion porosimeter, and Brunauer-Emmett-Teller reveal formation of a dense gel (with reduced pore size and pore volume) in hybrid geopolymer vis-& agrave;-vis MK-based inorganic geopolymer. The implication of such microstructural features on mechanical and physical properties is discussed. Lastly, the suitability of developed hybrids as fire-retardant materials used in mass transit applications is highlighted
On the influence of austenite content in orientation selectivity and shear texture evolution during hot rolling of Fe-3 wt% Si grain-oriented electrical steel
No full textA systematic investigation of the development of shear textures during hot rolling of Fe - 3 wt% Si steel has been carried out in the present work with a special focus on the influence of austenite in preferential orientation selectivity. This orientation selectivity was anticipated owing to the fact that texture evolution during thermomechanical processing is entirely an effect of crystallographic rotations and such rotations may experience constraining effects because of surrounding austenite. The influence of austenite on shear texture evolution was studied over a range of finish rolling temperatures (FRTs). The evolution of microstructure and microtexture within the surface-subsurface zone was studied adopting EBSD. Sharp Goss orientation was observed at lower FRT, while texture intensities of Brass and Copper were observed to be high at higher FRT. Additionally, it was inferred that in the surface-subsurface zone, next to the austenite, the ease of rotation about ND contributed to the higher observed frequency of the Brass orientation despite of its overall lesser fraction as compared to Copper orientation. The less observed frequency of Copper orientation near the austenite has been attributed to the resistance offered by the austenite to its adjacent ferrite grains while rotating about TD. This constraining effect of austenite has been shown to be consistent over the entire range of studied FRTs. Moreover, it has been shown that at higher rolling temperatures, the lower constraining effect by austenite paves the way for Goss orientation formation, which acts as the precursor to the formation of Brass at the FRT
Lattice distortion in nanocrystalline Fe powder studied by positron annihilation and X-ray diffraction
No full textX-ray diffraction and positron annihilation measurements
were performed on the ball-milled nanocrystalline Fe
powder over a wide range of crystallite sizes (9–90 nm).
With increasing milling time, the crystallite size reduction
was accompanied by a monotonic increase of the lattice
parameter of Fe (i.e. lattice expansion). The positron
lifetime increased significantly due to enhanced positron
annihilation from the defects (excess vacancies, vacancyclusters, etc.) generated at the Fe grain boundaries and intercrystalline regions with progressive milling up to 24 h (crystallite size ∼ 12 nm). The observed lattice expansion has been successfully simulated using a theoretical model taking account of the excess free volume associated with the excess vacancies/vacancy-clusters at the grain boundaries in nanocrystalline Fe. Prolonged ball milling up to 36 h (crystallite size < 10 nm) led to an anomalous decrease of all positron lifetime parameters. The X-ray diffraction line profiles of ball-milled Fe powder exhibited anisotropic broadening due to the high density of
dislocations in Fe. Milling duration ≥ 24 h further led to
asymmetric broadening of Fe diffraction peaks indicating
heterogeneous dislocation structure in the severely
plastically deformed ball-milled Fe. Further analysis of
asymmetrically broadened peak reflections revealed
deformation induced tetragonal distortion of body
centered cubic Fe lattice in the 36 h ball-milled Fe powder
Ru‑supported mesoporous melamine polymers as efcient catalysts for selective hydrogenation of aqueous 5‑hydroxymethylfurfural to 2,5‑bis‑(hydroxymethyl)furan
No full textA Ru-decorated porous melamine polymer is found to be an active catalyst upon selective hydrogenation of aqueous 5-hydroxymethylfurfural to 2,5-bis-(hydroxymethyl)furan (yield>99%) under mild (20 bar H2, 30–90 °C), base/additive free conditions. Owing to its porous structure and unique surface chemistry presenting abundant weakly basic N-sites (amine and triazine), the polymeric catalyst could outperform various benchmark Ru catalysts (viz. Ru/AC, Ru/SBA-15, Ru/Nb2O5, Ru/ NbOPO4, Ru/NC, and Ru/g-C3N4) in terms of activity and desired product selectivity. The catalytic material was also found to be reusable and maintained good performance during multiple recycles under kinetic regime in batch mode. Furthermore, the polymeric catalyst also showed good performance for selective HMF hydrogenation under intensifed conditions in a fxed-bed reactor achieving constant BHMF yield during 20-h steady-state operation under relatively mild conditions (70 °C,
20 bar, WHSV 0.2 h−1)