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Synergistic protection of borate and silicate salts composite for controlling the chloride-induced pitting and uniform corrosion of steel reinforcement bars embedded in mortars
No full textIn this study, the efficacy of the combined effect of borate and silicate alkali metal salts added to mortars for controlling the chloride-induced uniform and localized corrosion of embedded steel rebars is examined. The individually added salts in mortars are found to have insignificant effects in terms of reducing the uniform corrosion rate and localized damage. However, their combination (0.50% sodium tetra borate + 0.10% sodium silicate added with respect to the weight of the binder) provides complete protection to reinforcements tested for long durations under wet/dry treatments with mortars in saline water and laboratory atmospheres. Electrochemical impedance spectroscopy, direct current cyclic polarization, polarization resistance, and visual observations are used for quantitative and qualitative evaluations of the protective effects of the tested additives. X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analysis of the corrosion products formed on the embedded steel surfaces help explain the possible mechanisms behind the considerable improvement in the inhibitive effects of a mixed composition of borate and silicate. This combination also improves the compressive strength and workability of the mixed concrete. The results reveal that the synergistic protection provided by a mixture of borate and silicate can be attributed to the co-deposition of an iron-boron + ferrosilicate + cortensitite (an iron-silicon phase) film on the rebar surface
Optimization of the Leaching Kinetics for Uranium Recovery from a Boltwoodite Ore as Emerging Solution to Nigerian Power Sector
No full textThe continuous rise of the population cum standard of living has resulted in Nigerians looking for a profound solution to the fast-growing demand for electrical energy with sustainability concerns including greenhouse gas emissions limitation. Thus, the investigation of uranium leaching kinetics and thermodynamics has become one of the most crucial topics in leach technology, where many distinct results have been obtained. In this study, the influence of sulfuric acid concentration, reaction temperature, solid-to-liquid ratio, and leaching time were all investigated. At established experimental conditions (2.5 mol/L H2SO4, 75 degrees C, 75 mu m), the uranium ore dissolution efficiency recorded was 89.1% within 120 min. The kinetic and thermodynamic tests of the leaching process coupled with the reaction mechanism between sulfuric acid and uranium were discussed. Hence, the results confirm that the dissolution mechanism of uranium was diffusion-controlled, exothermic, and spontaneous
Hydrophobicity and high-temperature mechanical behaviour of hard and optically transparent nanocomposite Al-Si-N thin films
No full textNanocomposite Al-Si-N thin films were deposited on SS 304, silicon and quartz substrates through magnetron sputtering. Silicon addition in AlN has transformed the coating structure from a single-phase coating into a nanocomposite structured film. It affected the phase formation and interband electronic transition in the Al-Si-N thin film. XPS study suggests the formation of Al-N, Si-N and composite Al-Si-N phases in the Al-Si-N film. The Urbach energy increases from 535 to 763 meV with addition of Si, for nanocomposite Al-Si-N film. No significant change in hardness and microstructure were observed up to 400 degrees C. The Al-Si-N film showed good hydrophobicity on both SS 304 and quartz substrates along with high hardness values. Low wettability and high strength make them a potential candidate for protective optical coatings as they are optically transparent too
Experimental and numerical study on the fatigue behaviour of pre and post heat treated additively manufactured SS 316L specimens
No full textThe success of 3D printing relies on developing components with desired strength that heat treatment processes can further improve. While SS 316L is a widely used structural material for several industrial applications, the fatigue behaviour of its 3D-printed version is investigated herein. The low cycle fatigue (LCF) behaviour of heat-treated (HT) 3D-printed SS 316L specimens was carried out and compared with the without heat-treated (WHT) specimens thereof. The heat treatment considerably affected its LCF behaviour, which can be attributed to the microstructural changes post heat treatment. The cyclic softening is observed in both HT and WHT specimens. However, the degree of softening is lower (12.35 %) for HT compared to WHT specimens (25.30 %) and 62 % higher fatigue life for HT compared to WHT specimens. Further, the hardness values obtained are 176 and 169 HV for WHT and HT, respectively, while it is 238 and 223 HV for the same, before and after fatigue tests. Fractography revealed fewer pores and reduced fatigue striations in the HT specimens. Considering the Chaboche non-linear model, finite element modelling was employed to capture the specimens' fatigue behaviour. The proposed model is found to be suitable for predicting the cyclic behaviour of 3D-printed austenitic steels
ZnO Nanorod: An Efficient Reusable Catalyst for One-pot Multicomponent C-C Bond Formation Reactions Involving Isatins
No full textIn the present study we have disclosed here that ZnO nanorod (ZnO-NR) can effectively be used as a catalyst for various C-C bond formation reactions, i. e. allylation, as well as one-pot three components conjugate addition and Knoevenagel-allylation of isatins. The corresponding products were obtained with good to excellent yields under solvent-free conditions in most cases at RT. The catalyst was successfully recycled for up to five cycles for allylation reaction and one pot three components Knoevenagel-allylation reaction of isatin. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the catalyst. The present study demonstrated the catalytic efficacy of ZnO nanorod for allylation reaction, one-pot three-component conjugate addition, and Knoevenagel -allylation of isatins under ambient conditions. imag
Red Mud Neutralisation by CO2 Promotes Alkali Recovery and Higher Scandium Extraction
No full textTo ensure the complete utilization of red mud and parallel reduction in carbon footprints from alumina production, it is very important to tackle the alkalinity in red mud which poses problems in the processing of bauxite residue. Despite various methods, this article stresses the use of CO2 neutralization which has been employed to address alkalinity (2176 ppm) and simultaneously recovers the alkali under atmospheric pressure, which assisted in improved scandium extraction. Under conditions of particle size < 50 mu m, 20% pulp density, 3-4 atm pressure, room temperature, in 30 min brought down the pH from 9.99 to 6.26, with 36-37% alkali recovery and capturing 28.8 g CO2/kg red mud. The neutralized red mud serves as an excellent feed for acid leaching to extract Ti and REEs. With 2 M sulfuric acid at 10% pulp density and 90 degrees C, 96% La, 95% Ce, and similar to 90% Sc were recovered in 2 h. The residue after the second stage operation was rich in Fe, Al and Si and thus can be processed by a hybrid pyro-hydro-metallurgical process, for achieving complete valorization of red mud while recovering critical metals
Enhanced electrocatalytic overall alkaline water splitting induced by interfacial electron coupling of Mn3O4 nano-cube@CeO2/γ-FeOOH nanosheet hetero-structure
No full textThe development of efficient and durable transition metal-based bifunctional electrocatalysts for overall water splitting and cost-effective production of green hydrogen is highly necessary to overcome the adverse environmental effect of non-renewable energy sources. Herein we have developed an aqueous solution-based simple, scalable and one-pot strategy for the synthesis of arrayed gamma-FeOOH nanosheets and CeO2 nanoparticle loaded Mn3O4 nano-cubes (Mn3O4@CeO2/gamma-FeOOH) at room temperature. The synthesized Mn3O4@CeO2/gamma-FeOOH showed superior HER and OER activities at both lower and higher current density (eta 10: 190 mV and eta 1000: 300 mV for OER, and eta 10: 180 mV and eta 1000: 420 mV for HER) and excellent stability of 50 hours at a current density of 1 A cm(-2). The respective two-electrode electrolyser with the developed catalyst in both anode and cathode demanded a potential of 1.55 V and 2.06 V to drive 10 mA cm(-2) and 1 A cm(-2) current density, respectively. Most importantly, it also showed outstanding water splitting performance in a 2 cm x 2 cm prototype anion exchange membrane (AEM) electrolyser and reached a current density of 366 mA cm-2 at an applied potential of 2 V. The developed catalyst showed outstanding stable performance for 100 hours at a current density of 1 A cm(-2) in both the two electrode electrolyser as well as the prototype AEM electrolyser. Characterization results revealed that the origin of enhanced electrocatalytic activity is not only from the microstructure and high surface area (313 m2 g-1) but also due to the interfacial partial electron transfer between the constituent components Mn3O4, CeO2 and gamma-FeOOH. Thus, the simple and scalable synthesis strategy of the catalyst and its superior and stable electrocatalytic activity, particularly in AEM electrolyser, suggest that the developed catalyst Mn3O4@CeO2/gamma-FeOOH might be an alternative to the PGM-based catalyst for large-scale hydrogen production through AEM electrolyser
Nanostructure-induced inhibition of oxygen evolution and enhancement of methanol electrooxidation on engineered anodized brass
No full textTo capitalize the improved electrical contact feature, a self-supported hybrid binary/ternary copper and zinc oxides (i.e., ZnOeCu2O and Cu2OeZnOeCuO) nanostructures have
been generated via a simple potentiostatic mode of anodaization on alpha brass in an alkaline medium. The catalyst nanostructuring i.e., wheat-grain-like to nanograss type structure has improved the mass transport, sluggish kinetics of methanol electrooxidation reaction process, and hindered the competitive oxygen evolution reaction (OER) of direct methanol fuel cell. The catalytic poisoning phenomenon has not been noticed due to twodifferent reaction processes in two potential regions. Interestingly, a significant reduction in overpotential (hOERCH3OH
10 mAcm2 ) has been noticed for S125@A1 and S125@A2 samples i.e., 236 mV and 350 mV, respectively. The enhancement of current density has been explained through inductive circuit perspective. So, the present study provides a better insights to design and utilize non-precious metal/alloy based catalyst with hindered OER and enhanced methanol electrooxidation reaction activit
An innovative approach to replace bentonite in hematite ore pelletizing with organic binder
No full textThere is a continuous endeavor to replace bentonite with any other suitable inorganic or organic binders.Organic binders generally burn at around 300–350°C and lose their binding property and cause crumblingin most cases. This study aimed to develop a process to use a suitable organic binder for the developmentof blast furnace quality pellets using some additives which can overcome the strength loss pelletsduring induration. The wastes generated from pulp industries viz. Ca-lignosulphonate (Ca-LS) and Na-lignosulphonate (Na-LS) have been used as binders in hematite ore pellets. To alleviate the strength loss at300–350°C, lower iron oxide (FeO and Fe3O4) containing materials viz. Linz-Donawitz (LD) sludge and millscale have been added. FeO and Fe3O4 in these materials will be oxidized at the mild oxidizing atmo-sphere of the induration strand and initiate diffusion bonding at around 300°C. Therefore, the strengthloss due to burning will be compensated by the strength gain due to diffusion bonding. From theexperimental study, it has been found that Ca-LS is a better binder than Na-LS and LD-sludge (LDS) isa better additive than mill scale. A combination of 0.4% Ca-LS with 5% LDS addition can prevent strengthdeterioration at 300–350°C during drying and gives a good-quality pellet in terms of strength, thermalshock resistance, reducibility, reduction degradation, and swelling index, which is comparable withbentonite added pellet. Thus, 04% Ca-LS with 5% LDS shows its good application potential to replacebentonite in hematite ore pelletizing
Development of Spherical Eutectic Si Particles through M-SIMA Process and Its Effects on the Tensile Properties of Al-7Si-0.05Sr Alloy
No full textThis paper investigates the microstructure and mechanical behavior of modified strain-induced melt activation (M-SIMA) processed Al-7Si-0.05Sr alloy. The M-SIMA process involves multiple warm rolling at 150 °C (below recrystallization temperature) to reduce its thickness by 60% to its original dimension, followed by semi-solid isothermal treatment at 585 °C for 30 min. The microstructure was characterized by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, and transmission electron microscopy. During the early stage of the experiment, Sr-containing as-cast alloy showed a better hardness value than that of Sr-free alloy; the former was attributed to the formation of the SrSi2Al2 phase and uniform distribution of fine fibrous Si particles, which was triggered by the Sr addition. The mechanical properties of SIMA-treated samples in a semi-solid state were studied by tensile test. The higher ultimate tensile strength (UTS) of the Sr-containing M-SIMA processed alloy (267 MPa) than that of the Sr-free M-SIMA processed alloy (204 MPa) was associated with the highly dense and uniformly distributed Si particles (with Feret diameter of ~ 300 nm) in the former one. However, both specimens had the nearly equal size of primary α-Al grains. The UTS was ~ 31% higher while the elongation (%) was ~ 53% higher than that of the Sr-free alloy, manifesting the benefits of thermally stable SrSi2Al2 phase at the grain boundaries, and the interdendritic regions and reduction in porosities, blow holes and shrinkage cracks