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Scrap computer keyboards a sustainable resource for silver (Ag) and low density oil (L D Oil)
No full textThe most neglected part of the scrap computers are the keyboards, which are generally incinerated by the informal
recycling sectors creating environmental pollution and leading to the wastage of precious metallic contents present
in it. The present paper is focused on a novel chemical processing technique developed to recover silver (Ag) as a value-added product and low-density oil (L D Oil) from computer keyboards. Initially, scrap keyboards were
manually dismantled to separate Mylar sheets, and the same were pyrolyzed at 300 ◦C for 2 h to recover L D Oil.
The obtained pyrolyzed Mylar sheets were further crushed, milled, and homogenized to reduce particle size (− 100
mesh). The crushed sample was leached using 2 M HNO3 at 60 ◦C in a mixing time of 20 min and the pulp density of
100 g/L to achieve maximum dissolution of Ag. The leaching kinetics for Ag dissolution well fitted with chemical
reaction control dense constant size cylindrical particles, 1-(1-X)1/2 = kct. The obtained leach liquor was put into
the cementation process using metallic copper (Cu). Almost 99% of Ag gets cemented as Ag powder in 15 min at a
constant solution temperature of 60 ◦C and pH 1.1. The developed bench scale process has applications orientation to the industry after piloting the process
Computational skills in geosciences higher education system for the 21st century
No full textThere has been a lot of research worldwide on what the education of the future will look like. We are witnessing a growing number of indicators of the slow collapse of education as we know it. It is likely that higher education is approaching a major turning point. Thereafter, the speed and flexibility of adapting to global change will be the main determinants. Ubiquitous digitalisation, new trends, and sustainability will be the key concepts of business models in the future. Alongside computer skills, the new generations will need programming skills as well. The higher education system must take this task as seriously and urgently as possible. Without the mentioned knowledge and skills, it will be difficult for future employees to compete in the labour market and/or further professional career advancement. This article addresses the question of what the future directions of the geoscience education ought to be as the technology is evolving while datasets become richer. Hence, machine learning will have more success in the field. The application of computer and mathematical methods in geosciences, incorporated in the concept of computational geosciences, will determine the future of geology and related disciplines
Utilization of Limestone Mineral Wastes for Developing Self-compacting Micro Concrete
Get PDFThis study aims at investigating the feasibility of replacing cement and fine aggregate by lime stone mineral wastes in developing Self Compacting Micro Concrete (SCMC). SCMC is highly flowable and can be used in places where there is no access to vibrators for compaction. Hence, these types of micro concretes are used mainly for repair purposes. The novelty of the work is that fines and coarse form of limestone mineral wastes generated during the beneficiation of low-grade limestone ore have been studied for its utility as cement and fine aggregate substitute respectively in the preparation of SCMC. The main requirement of repair concrete such as flowability has been studied along with other mechanical properties. Flowability of mixes were assessed by mini slump test and V-funnel test. Mechanical properties namely compressive strength, flexural strength and split tensile strength tests were also studied to evaluate the performance efficacy. It was found that with 100% coarse limestone waste of less than 1mm in size as fine aggregate, it is possible to achieve about 25 MPa and 45 MPa compressive strength at 3 and 28 days respectively. As high flowability and early age strength are of significant parameter for the development of micro concrete, the mix made of 100% limestone wastes as fine aggregate is found to be a successful mix for sustainable development of micro concrete
Realization of Band Convergence in p-Type TiCoSb Half-Heusler Alloys Significantly Enhances the Thermoelectric Performance
No full textBand engineering is a promising approach that proved successful in enhancing the thermoelectric performance of several families of thermoelectric materials. Here, we show how this mechanism can be induced in the p-type TiCoSbhalf-Heusler (HH) compound to effectively improve the Seebeck coefficient. Both the Pisarenko plot and electronic band structure calculations demonstrate that this enhancement is due to increased density-of-states effective mass resulting from the convergence of two valence band maxima. Our calculations evidence that the valence band maximum of TiCoSb lying at the Gamma point exhibits a small energy difference of 51 meV with respect to the valence band edge at the L point. Experimentally, this energy offset can be tuned by both Fe and Sn substitutions on the Co and Sb sites, respectively. A Sn doping level as low as x = 0.03 is sufficient to drive more than similar to 100% increase in the power factor at room temperature. Further, defects at various length scales, which include point defects, edge dislocations, and nanosized grains evidenced by electron microscopy (field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM)), result in enhanced phonon scattering which substantially reduces the lattice thermal conductivity to similar to 4.2 W m-1 K-1 at 873 K. Combined with enhanced power factor, a peak ZT value of similar to 0.4 was achieved at 873 K in TiCo0.85Fe0.15Sb0.97Sn0.03. In addition, the microhardness and fracture toughness were found to be enhanced for all of the synthesized samples, falling in the range of 8.3-8.6 GPa and 1.8-2 MPamiddotm-1/2, respectively. Our results highlight how the combination of band convergence and microstructure engineering in the HH alloy TiCoSb is effective for tuning its thermoelectric performance
Critical investigation of up-conversion and dual emission from nitrogen functionalized graphene quantum dots
No full textUp-conversion photoluminescence (UCPL) and dual-band photoluminescence (DBPL) are two widely-reported, exotic properties of graphene quantum dots (GQDs). However, both these phenomena can be associated with measurement artefacts. In case of excitation with monochromatic radiation derived from a white light source, the second order of the excitation or the emission signal can cause misleading impressions of UCPL and DBPL. Laser excitations can also generate spurious UCPL and/or DBPL signals due to leaking radiations. Using a spatially separated femtosecond pulsed laser, we find that in nitrogen-functionalized GQDs there is no evidence for DBPL although a real UCPL is hidden behind spurious signals
Investigation of the microstructure and mechanical properties of the laser welded joint of P22 and P91 steel
No full textThe present manuscript investigates the microstructural aspects and mechanical properties of laser beam welded ASTM A335 Grade P91 and P22 steel joint for power plant applications. Detailed microstructure characterization of the weld metal (WM) and heat-affected zone (HAZ) were carried out in as-welded and post-weld heat treatment (PWHT) conditions. A variation in microstructure was observed along the welded joint. This resulted in inhomogeneity in mechanical properties. The PWHT resulted in the formation of the stabilized microstructure in weldments and reduced heterogeneity in mechanical properties along the weldments. Tensile strength of weld joint in as-welded (AW) and PWHT condition was found slightly higher (617 MPa and 628 MPa, respectively) than the tensile strength of P22 steel (610 MPa). The fracture location for both AW and PWHT was observed in the P22 base region, which indicates that welded joint is stronger than the base material. Maximum tensile strength of the WZ was found 864 MPa in the as-welded condition. The hardness of WM, P91 CGHAZ and P22 CGHAZ were found 376 HV, 420 HV and 302 HV, respectively. After the PWHT, the hardness of the WM, P91 CGHAZ, P91 ICHAZ, P22 CGHAZ and P22 ICHAZ were measured 237 HV, 264 HV, 212 HV, 208 HV and 190 HV, respectively. The reduction in hardness is attributed to the tempering reaction, which results in the formation of the tempered martensite in WM and HAZ of P91 and tempered bainite in P22 HAZ. The impact toughness of the weld metal in as-welded condition was measured 85 J, which was lower than P22 and P91 steel. PWHT resulted in a drastic increase in impact toughness of WM and it was 145 J. The impact toughness of the P22 and P91 HAZ was measured 146 J and 92 J, respectively, for AW and 168 J and 140 J, respectively, after PWHT. The optimum microstructure and mechanical properties of the dissimilar welded joint were obtained after the PWHT
Selective Separation of Iron and Cobalt from Leached Tungsten Carbide Scrap by Solvent Extraction
No full textChloride leaching of the oxidized tungsten carbide scrap generated a leach liquor of composition(g/L): Fe-7.54, Co-15 & HCl-150, which was used to investigate the selective separation of iron and cobalt by its liquid-liquid interaction with 12.5%(v/v) Alamine-336 +10%(v/v)isodecanol in kerosene. Effect of various parameters such as solution acidity, solvent concentration, phase modifier concentration, iron and cobalt concentration(externally) in the feed solution, were optimized. McCabe-Thiele plots for maximum Fe extraction and stripping were made to decide the number of stages at desired O/A ratio. The pure iron and cobalt solutions obtained can be used to synthesize desired product. Remaining acid and regenerated solvent could be recycled to the leaching tank and re-extraction. The overall process has been attempted to function in a close-loop mode.
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Factors influencing the extent of hydrogen-enhanced brittle cracking in a Cu-strengthened HSLA steel during monotonic loading
No full textThe extent of brittle crack as a function of hydrogen charging conditions was studied for a HSLA steel using circumferentially notched cylindrical tensile samples. Two different notch depths were used. The effect of hydrogen could be well represented by an effective hydrogen potential which was defined using a representative hydrogen concentration and a diffusive time parameter, for relatively faster strain rates. The high triaxiality in deep-notched samples led to the initiation of ductile failure mechanisms overwhelming the brittle cracking process
Influence of Dynamic Strain Aging on Ratcheting Deformation Behavior of SA333 Gr-6 Steel
No full textSA333 Gr-6 steel is a candidate material for the primary cooling system in nuclear power plants. During service, piping components experience asymmetrical stress or strain cycling, resulting in plastic strain accumulation and a drastic reduction in fatigue life compared to symmetrical loading. This investigated steel is prone to the dynamic strain aging phenomenon. The present investigation deals with DSA and its influence on ratcheting deformation. Ratcheting tests were conducted at fixed load (sigma(m )= 50 & sigma(a )= 400 MPa) with varying temperatures from room temperature to 350 degrees C and stress rates (20-700 MPa s(-1)). Result reveals that the steel shows greater resistance to ratcheting strain and increased fatigue life at DSA dominant temperature regimes. The DSA is active at a temperature between 250 and 350 degrees C and the DSA regime gets shifted to a higher temperature with the increase in stress rate. Transmission electron microscopy (TEM) studies reveal severe dislocations activities and dislocation forest at DSA dominant specimen, whereas the arrangement of dislocations into well-developed cell structures at the non-DSA regime. TEM result is corroborated by calculating dislocation density from x-ray diffraction analysis, and it was found greater dislocation density at DSA dominant and lower at the non-DSA regime
Influence of temperatures on structure, thermoelectric, and mechanical properties of nanocrystalline SnSe thin films deposited by thermal evaporation
No full textThe Tin Selenide (SnSe) thermoelectric materials' high heat-electricity inter-conversion capability makes it a potential energy resource material to tap the waste heat from different industrial processing. The present work has optimized parameters for the deposition of single-phase nanocrystalline SnSe thin films using the thermal evaporation technique. The XRD, Raman Spectroscopy, SEM, EDS, Seebeck Coefficient, Electrical Conductivity, and Thermal Conductivity data analyses were used to optimize and establish the structure-thermoelectric property relationship for nanocrystalline SnSe films. The phase analysis of the SnSe thin films deposited at various substrate heating temperatures (Ts) reveals a significant influence of Ts in the evolution of a single phase of SnSe film. The films deposited at Ts & LE; 200 C evolved with the phases of Sn, Se, and SnSe, whereas films deposited at Ts & GE; 300 C grew with single-phase polycrystalline SnSe. An increase in crystallite size with a shape transformation from circular to elongated grains was observed with Ts. The maximum ZT value of 0.64 with a power factor value of-2.2 mu Wcm-1K-2 at 750 K measuring temperature (Ta) was obtained for the SnSe film deposited at Ts = 300 C. The change in thermoelectric properties with Ta, including a p-type to n-type transition observed at-600 K, was correlated with the alteration of structure and the elemental composition of the deposited films after heating at 350 C. The heating temperature significantly influenced the hardness and elastic modulus values of the films deposited at Ts & LE; 300 C