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Comparison of feldspar and meta-halloysite geopolymers by alkaline and acidic activation
No full textGeopolymerisation, a sustainable route to advanced binders, has traditionally been explored using common activators and single precursors such as metakaolin. Although previous investigations have explored the potential of feldspathic minerals, particularly with metakaolin as a partial replacement, there remains a gap in understanding the nuances of feldspar-phosphate-based geopolymers. This study seeks to fill this gap by providing an in-depth investigation of the properties and reactivity behavior of three different feldspar quarry wastes, each modified with meta-halloysite at a 15% inclusion rate. This research not only evaluates the effects of both acidic and alkaline activators on the resulting geopolymer properties but also explores the broader implications of such modifications in different environments at ambient conditions. Using a series of experimental assessments, we have explored how the mineralogical and crystalline identities of these feldspars influence key aspects such as reaction kinetics, physico-mechanical performance, structural and microstructural properties, and even thermal behavior. The results of the physicomechanical properties showed that lower water absorption (i.e. less than 9.2%) as well as higher flexural (i.e. about 30 MPa) and compressive strength (i.e. about 40 MPa) can be achieved with the feldspar-based geopolymer in alkaline medium. In acidic medium, the highest flexural and compressive strengths were less than 10 and 19 MPa, respectively, with about 13.5% of water absorption. In acidic to basic medium, the highest cumulative pore volume of the geopolymers increases from 26.5 to 75.2 mm3/g, respectively. The outcomes of this study hold promise for tailoring geopolymer properties for various applications and provide a basis for further work in this area
Effect of maximum applied cyclic stress on fretting fatigue stress distribution of flat-on-flat modified 9Cr-1Mo steel contact: Finite element analysis
No full textFretting fatigue experiments were conducted on a modified 9Cr-1Mo (P91) steel under flat-on-flat contact with maximum applied cyclic stress (σmax) levels of 450 MPa, 500 MPa and 550 MPa at a stress ratio of 0.3 and a contact pressure of 100 MPa. A decrease in the cyclic life was observed with an increase in σmax. Chaboche model with isotropic and kinematic hardening was employed in finite element analysis to evaluate the stress distribution near the contact pad and along the contact surface under fretting fatigue conditions. In addition, the contact-related parameters such as contact pressure, contact shear stress and relative tangential motion were also assessed. The relative tangential motion was found to increase with increasing σmax. Besides, the peak values of normal stress (parallel to the applied loading direction) and maximum principal stress were observed around the leading and trailing edges of the contact pad at the σmax. The amplitude of relative tangential motion and slip zone increases with σmax. The orientations of the principal plane and shear plane to the applied cyclic loading direction are − 89.5◦ and − 134.5◦, irrespective of the σmax. The fracture surface of the failed specimen revealed that the direction of the crack was nearly perpendicular to the applied stress. Smith-Watson-Topper parameter was used for estimating the crack initiation life with σmax. It has been noticed that the fraction and dominance of crack initiation or propagation phase depend on the imposed cyclic condition for the steel
Waste remediation: Low-temperature synthesis of hybrid Cu(OH)2/CuO and CuO nanostructures from spent printed circuit boards and their dye degradation studies
No full textThe demand for environmentally friendly and sustainable resource utilization techniques for recycling waste printed circuit boards is significant due to their status as valuable secondary resources, containing high-purity copper and precious metals. In this context, Cu(OH)2/CuO and CuO nanostructures were fabricated using alkaline precipitation and low-temperature aging methods using the strip solution originated from laboratory-scale spent mobile phone printed circuit board recovery process. XRD, FTIR, FESEM-EDX, and TEM were utilized to characterize the as-recovered nanoproducts. A hybrid structure of Cu(OH)2/CuO was formed at 70°, and monoclinic CuO phase was formed at 80 °C aging time. The results show that Cu(OH)2/CuO nanoflakes have an average crystallite size of 24.06 nm and a particle width of 22 ± 3 nm. Cu(OH)2/CuO nanoflakes formed at 70 °C aging temperature and 24-h residence time have finer crystallite and particle sizes than CuO-ridged nanospheres formed at 80 °C aging temperature. The optical band gap energy of Cu(OH)2/CuO and CuO nanostructures formed was found to be 2.28 eV and 2.22 eV, respectively. The hybrid Cu(OH)2/CuO nanostructure photocatalyzed the decomposed 97.28% rhodamine blue using a visible light source, whereas the CuO nanostructure degraded only 14.64% rhodamine blue dye under similar conditions. A surfactant-less hybrid structure is developed without the use of any chemical precursor. Thus, a high value-added product is produced using one waste material to remove another waste in wastewater treatment
Sustainable Process to Recover Metals from Waste PCBs Using Physical Pre-Treatment and Hydrometallurgical Techniques
No full textPrinted Circuit Boards (PCBs) are an essential component of electronic devices. The digitalization and upgrading of gadget generates lots of PCB-containing electronic waste. Conserving resources and protecting the environment requires the recycling of such e-waste. This paper focuses on the recovery of metals from waste PCBs using physical pre-treatment and hydrometallurgical processes. Initially, the waste PCBs were pre-treated and beneficiated to separate the metallic and non-metallic fractions. The metallic concentrate obtained was leached using nitric acid (a strong oxidative agent) to dissolve the metals. The system was fully jacketed with a scrubber and condenser to prevent the emission of toxic gases into the environment. The process parameters, such as the effect of acid concentration, pulp density, temperature, time, etc., were studied, optimized, and scientifically validated. The kinetics of leaching fitted well with the following shrinking core models: XB = kc.t for Cu, (1 - (1 - XB)1/2) for Ni, and 1 - 3(1 - XB)2/3 + 2(1 - XB) for Pb. The activation energy was 19.42 kJ/mol. The tin left in the residue was treated separately. The developed process is useful for recovering metals from waste PCBs and has the potential to be commercialized after conducting scale-up studies
Mixed-valent cobalt phosphate/borophene nanohybrids for efficient electrocatalytic oxygen evolution reaction
No full textDeveloping efficient, low-cost, non-precious, and stable electrocatalysts is necessary for sustainable electrocatalytic water splitting. Recently, borophene has emerged as a novel two-dimensional material with exciting properties. Although several researchers have theoretically predicted its applicability towards effective electrocatalytic water splitting, studies on its practical applications are still limited. In this regard, a mixed-valent cobalt phosphate/borophene nanohybrid (BCoPi) was synthesized using the hydrothermal method, and its activity towards oxygen evolution reaction (OER) was systematically studied. The electron-deficient nature of borophene enables the activation of catalytic sites and facilitates electron transport owing to its highly conductive nature. It can act as a proton acceptor along with phosphate groups, as well as provide multiple secondary active sites in addition to Co, breaking the scaling relation of OER. For BCoPi, achieving a current density of 50 mA cm -2, 100 mA cm- 2 and 500 mA cm -2 requires an overpotential of 337 mV, 357 mV, and 401 mV, respectively, in an alkaline medium, which is superior to pristine cobalt phosphate (CoPi). It also exhibits a low Tafel slope of 61.81 mV dec- 1, suggesting faster OER kinetics and excellent long-term stability. This study will extend the development and application of borophene-based heterostructures for highly active and stable electrocatalysts for various applications
Development of environment-friendly reduced graphene oxide coating and corrosion behavior on cold-rolled interstitial-free (IF) steel
No full textMany different processes have been developed to grow graphene film to protect metals. These processes are primarily based on chemical vapour deposition and are challenging to scale. In this paper, we have attempted to grow the reduced graphene oxide (rGO)-like film using the natural resin 'shellac' as a precursor through the simple process of dip coating of shellac varnish and annealing of coated substrates in a reducing atmosphere. X-ray diffraction (XRD) analysis and Raman spectroscopy were used to establish the rGO phases grown in the coating. The corrosion studies of rGO films grown on cold-rolled interstitial-free steel are investigated with different loadings of shellac in the varnish solution and subsequent heat treatments. Scanning electron probe micro-analysis was done to do elemental analysis, and potentiometric studies were done to investigate the corrosion behavior of the coatings. The structure-property correlation of the film has established the corrosion mechanism using different microscopy techniques
Exploitation of pyrazole C-3/5 carbaldehydes towards the development of therapeutically valuable scaffolds: a review
No full textOver the past decades, pyrazole has displayed significant importance in various areas of chemistry and industry owing to its unique nature, reactivity, and properties. Pyrazole is a versatile compound with a wide range of applications in pharmaceuticals, agriculture, materials science, and various branches of science. Specifically, pyrazole C-3/C-5 carbaldehydes can be used as a building block in organic synthesis to create more valuable and bioactive molecules. In this context, pyrazole C-3/C-5 carbaldehydes may be explored for achieving pyrazole fused/linked heterocyclic skeletons by employing different organic transformations. The investigation of pyrazole C-3/C-5 carbaldehydes has resulted in the formation of a range of biologically potent heterocyclic structures, which include pyrazole C-3/C-5-based silicon derivatives, pyrazole C-3/C-5-based Schiff base derivatives, pyrazole C-3/C-5-based metal complexes, pyrazole C-3/C-5-based imidazo[1,2-a]azines, pyrazole C-3/C-5-based sulphur containing derivatives, and pyrazole C-3/C-5-based thioamide and amides, as well as other pyrazole fused/tethered polycyclic systems. Previous reports have shown that derivatives synthesized from the pyrazole C-3/C-5 carbaldehyde have demonstrated favorable biological uses like 5-HT3A receptor antagonists, allosteric inhibitors, insecticidal activity, antioxidant, antifungal, antiproliferative and antimicrobial. Pyrazole C-3/C-5 carbaldehydes have the potential to be highly utilized in the medical field as well as material science if studied judiciously. This review focuses on the exploration of pyrazole C-3/C-5 carbaldehydes towards the synthesis of highly diversified pyrazole-based molecular hybrids till 2023 and describes their promising utilization in the field of pharmaceutical science
Evaluation of Post-Weld Heat-Treated 2.25Cr-1Mo Steel Joint Behaviors by Electromagnetic NDE Parameters
No full textA P22 (2.25Cr-1Mo) steel pipe is machined into two separate plates and then joined across with a V-groove by manual arc welding. The welded plate is further cut into three pieces and each piece is post-weld heat-treated (PWHT) at temperatures of 680 degrees C, 700 degrees C, and 720 degrees C for different holding times of 0.5, 1, and 2 h at each temperature. The welding area is typically categorized into three regions: base metal (BM), heat-affected zone (HAZ), and weld fusion (WF). As-weld and PWHT samples are characterized by destructive techniques of microscopy and hardness measurement and non-destructive evaluation (NDE) of magnetic behaviors. The WF region shows a bainitic lath structure, correlated to its high hardness and coercivity and low Barkhausen voltage. In contrast, the change in microstructure towards HAZ and BM decreases dislocation density, displaying a continuous decrease of hardness and coercivity and increasing Barkhausen voltage. This is endorsed by a decrease in magnetic and mechanical softness profiles, sequentially proceeding from WF towards HAZ and BM, while this softening behavior changes with PWHT temperatures and holding time. After PWHT at 720 degrees C for 2-h holding time, the magnetic softening along the welding region indicates an actual trend compared to mechanical softening. The electromagnetic parameters are considerable to identify the correct PWHT conditions necessary to maintain the accurate stress-relieving operation of weldments
Fe–Al core-shell structure as an efficient catalyst for dual hydrogen production and storage by thermochemical water splitting: A reactive molecular dynamic simulation
No full textatalysts with dual functions in hydrogen production and storage are desired for the low-cost technology. In the preceding view, we used reactive force molecular dynamics to demonstrate how effective the Fe–Al core-shell structure is at breaking up water molecules and storing hydrogen free radicals via thermochemical water splitting. The results show that at T ∼600 K, water molecules begin to dissociate in the presence of a Fe–Al catalyst, releasing OH and H free radicals. It is worth noting that the produced OH free radicals are bonded to the Al-shell, whereas the H free radicals move to the Fe-core and stores via chemical bond. Interestingly, at T 3000 K, the number of Fe–H bonds decreases while the number of H–H bonds increases, indicating that the stored H atom desorbs and forms an H2 molecule. Temperature can thus be used to monitor the ability of Fe–Al catalysts to dissociate water, store hydrogen, and produce hydrogen. This research shows that developing core-shell type catalysts can provide an effective solution for hydrogen generation, storage, and transportation
Influence of texture on anomalous yielding behavior of thermomechanically processed nickel-based superalloy 720Li
No full textPrecipitation-strengthened Ni-base superalloys are extensively used for high-temperature load-bearing applications due to their unique combination of yield stress anomaly (YSA), excellent creep, fatigue, and corrosion resistance. However, in line with the previous reported results, it is shown in the present study that 720Li alloy does not exhibit YSA during uniaxial deformation. The investigation explores the role of anti-phase boundary (APB) energy, Zener ratio and break away stress of Kear-Wilsdrof (KW) lock on YSA behavior. It is shown that in spite of meeting all the energetic requirements necessary for YSA (viz. energy for octahedral to cubic cross slip along with high break away shear stress, i.e. similar to 80 MPa); the thermo-mechanically processed 720Li alloy does not exhibit YSA. In support of the observed absence of YSA, a plausible mechanism is provided for the first time through this work. This unusual absence of YSA has been attributed to the crystallographic texture of the alloy (specifically, the loading direction (LD) being parallel to [111]), which prevents the formation of KW-locks in the first place. The [111] texturing has been shown to rather lead to direct cubic plane slip i.e. {001} , thereby paving way for suppression of KW-locks (and hence YSA). In order to validate this postulate, the study also examines a vacuum induction melt and cast Ni-75(Al-11, Ti-14), L1(2) compound. The presence of YSA in the L1(2) compound under conditions of LD not being parallel to [111], confirms that texturing impacts the occurrence of YSA