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Ru‑supported mesoporous melamine polymers as efficient 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 intensified conditions in a fixed-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)
Enhancement of Molten Salt Corrosion Resistance of Ni-Based Superalloy Through Adding Inhibitor
No full textRecently, molten salt corrosion of metallic alloys in concentrated solar power (CSP) industries is one of the important and unavoidable issues among others. In this investigation, the role of inhibitor (i.e., Mg powder) on the hot corrosion behavior of Inconel 617 superalloy in molten chloride salts mixture has been examined through immersion corrosion test method and electron microscopic analysis. Post-corrosion observations revealed that Cr at the grain boundary is preferentially depleted, which leads to severe grain boundary corrosion. By addition of 1 wt% Mg powder (as inhibitor), the corrosion rate (derived through percolation depth) was observed to be remarkably minimized by similar to 40% compared with the immersion test without Mg powder addition. The notable increase in corrosion resistance by the addition of Mg powder could be attributed to the reduction of oxidizing impurities in the molten salts mixture, which is considered to be the main culprit for the corrosion promoter
Probing dimensional consistency during multi-track multi-layer gas metal arc directed energy deposition of aluminium alloys
No full textThe dimensional consistency of multi-track multi-layer parts fabricated by gas metal arc-directed energy deposition is by far the most critical challenge. A systematic investigation is presented here to examine the influence of the important process variables such as wire feed rate, printing travel speed, and resulting energy input per unit length on the dimensional consistency and surface waviness of multi-track and multi-layer parts made by gas metal arc directed energy deposition using an aluminum alloy filler wire. The current and voltage transients are monitored in real time to realize a quantitative measure of the arc power and energy input per unit length of deposition on the build profile and its dimensional consistency. The dimensional consistency and the surface waviness of the build profile are measured by optical microscopy. The microhardness distribution of the sample builds along the tracks and layers is also examined for different process conditions and the effect of energy input per unit length on microhardness distribution has been examined. The evaluation of the experimentally measured results shows that the dimensional inconsistency and surface unevenness of the deposited profiles can be reduced significantly by increasing the energy input per unit length for gas metal arc-directed energy deposition
Investigating the influence of various tool path trajectories on the anisotropic behavior of bulk NiCrMo-3 alloy fabrication by WADED process
No full textThis study delves into the Wire Arc directed energy Deposition (WADED) process, exploring the impact of four tool path trajectories designated as bidirectional contour (S1), bidirectional spiral (S2), Fermat's spiral (S3), and Fermat's zigzag (S4) on the deposition of a regular cubic solid structure of NiCrMo-3 alloy. The research focuses on understanding how these trajectories influence both microstructural heterogeneity and anisotropic mechanical response. It has been shown that the WADED processed NiCrMo-3 alloy displays prominent dendritic microstructure, with varying dendritic arm spacing and growth orientation angle across S1 to S4. S2 and S4 favor more columnar to equiaxed transition due to relatively lower cooling rates and G/R values along with a higher extent of Laves and carbide precipitation compared to S1 and S3. Texture analysis reveals S1 and S3 exhibit a predominant cube {001} texture, while S2 transitions to Goss {110} texture, and S4 displays a more random texture with higher intensity in copper {112} and brass {110} . Microhardness exhibited slight anisotropy (within 3%), with S4 (227.77HV0.5) having the highest microhardness. The YS and UTS were lower in the build direction ( (S)) compared to the horizontal direction ( (S)) in all samples. S2 showcased maximum YS (334.5 MPa) and UTS (655 MPa) values while minimum anisotropy (<= 2%) was observed in S4 along with comparable YS (330 MPa) and UTS (645.5 MPa
Slag-Metal- Refractory Interactions During Dissolution of Hydrogen-Based Directly Reduced Iron (H-DRI) in Liquid Iron Melt
No full textThe steel industry is regarded as the most critical industry in the nation and is crucial to economic prosperity; however, its high energy use and carbon emissions significantly impact climate change and global warming. In view of achieving carbon neutrality, one of the most promising technologies is using green hydrogen gas as a reductant for producing carbon emission-free direct reduced iron (H-DRI) from iron ores/pellets. Moreover, the produced H-DRI is subsequently used for steel making in the induction furnace/electric arc furnace. However, the study on the melting behavior of H-DRI, interaction among slag and metal produced from H-DRI with refractory during the steel making in induction furnace/electric arc furnace has yet to be thoroughly studied. Therefore, in this study, DRI's dissolution/melting behavior in the liquid iron at 1600 +/- 10 degrees C has been studied. Then, interactions among slag generated during the melting/dissolution of DRI, refractory of the induction furnace, and metal produced from H-DRI have been studied using the SEM backscatter electron method. The thermodynamics modeling for the slag formation and interactions among slag-metal-refractory systems have been studied using FactSage 8.2. The penetration of iron from a liquid melt into porous refractory and the formation of complexes like mullite, spinal, and olivine has been observed. The boundaries between the slag-metal-refractory system and the dissolution of Mg and Fe have been identified using backscattered electron mode. Thermodynamics modeling has been validated with experimental observations
Efficient Adsorption and Desorption of Uranium(VI) Using a Polymeric Adsorbent: A Combined Theoretical and Experimental Approach with Real-Life Alkaline Leach Liquor
No full textAlkaline leaching is used for the extraction of uranium from rarely available carbonate ore. A hyperbranched cross-linked polymeric adsorbent (HCPA) was developed for selective recovery of uranium(VI) (U) from real-life alkaline leach liquor. HCPA was synthesized using the free radical copolymerization of acrylamide and N, N-methylene bis(acrylamide). In addition, potassium persulfate (as the initiator) and dodecanethiol (as the brancher) were used to transfer the radicals for faster chain formation and smooth branching of the long-chain polymer. Several methods were used extensively to characterize the adsorbent. The Langmuir maximum U adsorption capacity of HCPA was 1012 mg/g at 303 K, and 98% of U was removed from alkaline leach liquor. U was adsorbed at pH 8.5 in the presence of various interfering co-ions and desorbed at pH 11.5 in the form of sodium diuranate (Na2U2O7) precipitate. The adsorption was monolayer, exothermic, and spontaneous in nature. The C-N, CO-NH2, and C-OH groups of HCPA interacted with uranyl ions initiating the coordinative and electrostatic interactions leading to U adsorption. Continuous fixed-bed column runs were performed using the actual leach liquor, and a fundamental kinetic model was used to quantify the performance of columns. The transport parameters were estimated from the model, and scaling-up calculations were performed using these parameters. Five adsorption-desorption cycles were conducted to determine the reusability and structural stability of the synthesized polymeric adsorbent
Structural and optical properties of Iodine doped zinc oxide nanoparticles
No full textIodine-doped zinc oxide (viz., ZnO1-xIx) nanoparticles were prepared using the sol-gel method. The samples were treated at 700 degrees C in air for 1h. The structural, morphological, and optical properties were measured using an X-ray diffractometer (XRD), a field emission scanning electron microscope (FE-SEM), UV-visible spectroscopy (UV/vis), and Raman spectroscopy, respectively. XRD results showed that the pure and doped samples have a wurtzite hexagonal structure, indicating the presence of some impurities in doped samples. The lattice parameters a and c were observed to be closer to the reported values for pure ZnO. The average crystalline size values of samples were calculated and found to be between 84 +/- 18 and 177 +/- 53 nm. The FE-SEM micrographs reveal that the particle sizes decreased from 77 to 57 nm with an increasing I concentration from x = 0.0 to x = 0.4, respectively. The morphologies of the samples were changed from particle to flask shape at higher I concentrations of 0.6 and 0.8 with average diameters of 213 and 427 nm. The increasing I concentration from 0.0 to 0.8 narrows the optical energy gap (Eg) from 3.271 to 3.242 eV due to the presence of oxygen vacancies or the lattice expansion caused by doping. Raman spectra of samples consist of the E2(high) mode, which confirmed the wurtzite hexagonal structure and it is located between 435 and 436 cm-1 except for x = 0.6, where the E2(high) mode was shifted to the higher wavenumber could be due to defects or anisotropic internal strains consistent to different growth directions
Mechanistic investigation of hydrogen generation from water and magnesium catalyst reaction: Advanced reactive molecular dynamics simulation
No full textMagnesium is an effective catalyst for producing hydrogen through thermochemical water splitting. However, the slow reaction between Mg and water prevents this catalyst from being commercially useful. In this study, reactive MD simulations with accurate force fields and reactive potential energy surfaces are used to comprehend the slow kinetics of the Mg water reaction. At room temperature, water is split when it interacts with Mg nanoparticles and forms a Mg-H bond. Furthermore, at temperatures above 1200 K, Mg-H bonds begin to dissociate, resulting in the generation of hydrogen radicals from the Mg-H bond. The percentage of H-H bonds is almost zero until the reaction pathway reaches temperature 2000K, after which H radicals combine to form hydrogen gas. The analysis of temperature-dependent data reveals that oxygen and hydrogen atoms combine with Mg elements to form massive stable linear and branched chains, resulting in slow Mg-water reaction kinetics for hydrogen production. Therefore, current studies utilizing reactive molecular dynamics can provide a means of improving the kinetics of the Mg-water reaction. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
Dissolution kinetics and thermodynamics of uranium from a boltwoodite ore for nuclear fuel cycle application
No full textThe demand for pure uranium and uranium compounds of an industrial standard is tremendously increasing due to its wide array of utilities in electron microscopy, catalysis, armor-piercing, and nuclear explosions, among others. The raw ore and some of the products after alkaline leaching were characterized by X-ray fluorescence, X-ray diffraction, inductively coupled plasma mass spectroscopy, and scanning electron microscopy analyses. Dissolution kinetics and thermodynamics were examined under the experimental conditions at different sodium hydroxide concentrations, reaction temperature, and particle size towards purified uranyl leach liquor which could further be processed to industrial ammonium diuranate. The experimental results affirmed that the best parameters comprised a residence time of 120 min, reaction temperature of 75 degrees C, sodium hydroxide concentration of 2.5 mol/L, and particle size of 75 mu m, yielding a dissolution efficiency of 96.1% with an activation energy of 41.39 kJ/mol
Effect of Quenching and Partitioning on Microstructure and Mechanical Properties of High-Carbon Nb Microalloyed Steel
No full textIn this study, high-carbon Nb micro alloyed hot rolled steel plates are subjected to quenching and partitioning (Q&P) treatment at different temperatures and time durations. Dilatometry results show that increasing cooling rate (CR) leads to suppression of transformation start and finish temperatures of high-temperature transformation products like pearlite (P) or bainite (B), whereas martensite (M) transformation triggers with increasing cooling rate from 5 to 50 degrees C/s. The observations made by optical (OM), scanning (SEM), and transmission electron microscopy (TEM) reveal mixed-phase microstructures consisting of preformed/tempered martensite (PTM), retained austenite (RA), twin martensite (TM), and lower bainite (LB) for the isothermally heat-treated (IHT) samples subjected to Q&P at 200 degrees C and 180 degrees C for 30 minutes. The maximum volume percentage of RA (V-gamma) and C content in RA (C-gamma) are witnessed in the IHT samples subjected to Q&P for 30 minutes at 200 degrees C and 180 degrees C, respectively, followed by the hot rolled air-cooled (HRAC) sample. The formation of very fine NbC precipitates (similar to 17 to 33 nm) is also evident in HRAC and Q&P at 160 degrees C for 30-minute samples, which are expected to contribute significantly to precipitation strengthening. Hardness shows an increasing trend from 36 HRC to 65 HRC with increasing CR from 0.5 to 50 degrees C/s. The best combinations of the ultimate tensile strength (UTS) and total elongation (TEL) in Q&P 200 samples (36043 MPa pct) followed by Q&P 180 samples (32759 MPa pct) can be correlated with their higher values of V-gamma and C-gamma