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Beneficiation of difficult-to-wash Indian low volatile coking coal fines by Falcon concentrator
Get PDFThe fast depleting reserves of high grade Indian coking coal and its resultant dependence on import makes the emerging situation a fit case for exploring innovative and high efficacy techniques such as non-conventional gravity based systems for clean coal recovery viz., advanced centrifugal gravity separators like Falcon concentrators for fine and ultra-fine coal particles processing using enhanced gravitational force. The above methodology has been adopted for low volatile coking (LVC) coal due to the high ash content associated washability characteristics and high NGM content. Attempt was made using laboratory Falcon SB40 concentrator for cleaning the LVC coals assaying 32.6% Ash. Considering the physical properties, Coal petrography and washability studies, as received coal was ground to three size fractions of -500μm, -250μm and -150μm and subjected to separation in Falcon separator. Experiments were conducted using Design Expert software to evaluate the effects of four significant process variables such as feed size, pulp density, gravitational force value and water pressure. The relationship between the response functions (ash content, combustible recovery and separation efficiency) and process variables is presented as empirical model equations. Under the optimum operating conditions, LVC coal was cleaned to 18.4% ash content with 57.8% combustible recovery using Falcon concentrator
Lattice expansion and phase stability in nanocrystalline titanium thin films
No full textCrystallite-size-dependent lattice expansion of the hcp Ti phase has been observed by X-ray diffraction of polycrystalline Ti thin films. X-ray line profile analysis (XLPA) revealed a systematic reduction of crystallite size in the hcp Ti phase with decreasing film thickness. Increase of specific volume (i.e. volume/atom) of the hcp Ti phase with decreasing crystallite size has confirmed such lattice expansion. The observed lattice expansion has been simulated using an existing theoretical model after appropriately incorporating a crystallite-size-dependent width of the grain boundaries. It is further revealed that decreasing crystallite size and accompanying lattice expansion leads to lattice instability of the hcp Ti phase and eventually to a hcp-fcc phase transformation of elemental Ti in these thin films as reported earlier by the author
Comprehending the role of individual microstructural features on electrochemical response and passive film behaviour in type 304 austenitic stainless steel
No full textThe individual implication of sensitization, grain size, residual strain, and grain boundary character distribution on semiconducting response of passive film in 304 stainless steel is investigated. Involvement of higher donor densities in the sensitized specimen deteriorated passive film stability. The greater density of random grain boundaries in fine-grained specimen promoted the defects formation in the passive film. In contrast, higher fraction of ‘special’ boundaries and triple junctions, realized through grain boundary engineering, suppressed the formation of defects in the passive film. Interestingly, defects induced via straining accelerated the oxygen vacancy formation at metal/film-interface, which depreciated the protectiveness of passive film
Effect of thermo-elasto-plastic strain on the mechanism of twin-free microstructure formation in the stainless steel
No full textThe stainless steel with grain growth stagnant microstructure was subjected to rapid heating and quenching cycles repetitively to induce thermo-elasto-plastic strain. The evolving microstructure and grain orientation were analysed using electron microscopy equipped with an EBSD facility. A special emphasis was laid on elucidating the twin evolution mechanism. Multi variant primary and secondary twin (s) formation associated with {001}, {011, {111} and {122} slip planes have been observed by electron microscopy. The possible role of vacancies accumulated during the quenching process and the boundary characteristics on the formation of stacking faults especially in the non-preferred slip planes have been discussed and a logical correlation has also been made on the evolution of crystallographic multi-variant twin (s) within the austenite grains. The result also suggests that the thermo-elasto-plastic strain can have a profound effect in altering the true-twin crystallographic relation of the multi-variant twin(s) within the austenite grains. It has been observed that the grain rotation towards preferred orientation resulted in the formation of twin-free refined grain microstructure at some instances of annealing cycles. The absence of twin(s) was correlated with the rotation and widening of the twinned region to a new grain formation. On further subjecting, this twin free microstructure to annealing cycle, reappearance of the new twin(s) noted
Leaching of Copper from Waste-Printed Circuit Boards (PCBs) in Sulfate Medium Using Cupric Ion and Oxygen
No full textIn the present paper, the leaching of copper from printed circuit boards (PCBs) using sulfuric acid with Cu2+ and O2 is proposed. The effects of various process parameters such as agitation speed, temperature, the type and the flow rate of gas, initial Cu2+ concentration, and pulp density were investigated to examine the dissolution behavior of Cu from PCBs in 1 mol/L sulfuric acid. The
kinetic studies were performed using the obtained leaching data. The leaching rate of Cu from PCBs was found to be higher on addition of Cu2+ and O2 to the leachant in comparison with the addition of O2 or both Cu2+ and N2 in the leachant. The leaching efficiency of Cu was found to be increased with increasing agitation speed, temperature, O2 flow rate, and initial Cu2+ concentration and decreasing pulp density. The 96% of Cu leaching efficiency was obtained under the following conditions: sulfuric acid concentration, 1 mol/L; temperature, 90 °C; agitation speed, 600 rpm; pulp density, 1%; initial Cu2+ concentration, 10,000 mg/L; and O2 flow rate, 1000 cc/min. The leaching data and analyses indicate that the Cu leaching from PCBs followed the reaction-controlled model satisfactorily and determined that the activation energy was found to be 23.8 kJ/mol. Therefore, these results indicate that the sulfuric acid solution with Cu2+ and O2 as a mild leach medium without strong oxidants such as HNO3, H2O2, and Fe3+ is valid for Cu leaching from PCBs
Determination of Non-Recrystallization Temperature for Niobium Microalloyed Steel
Get PDFIn the present investigation, the non-recrystallization temperature (TNR) of niobium-microalloyed steel is determined to plan rolling schedules for obtaining the desired properties of steel. The value of TNR is based on both alloying elements and deformation parameters. In the literature, TNR equations have been developed and utilized. However, each equation has certain limitations which constrain its applicability. This study was completed using laboratory-grade low-carbon Nb-microalloyed steels designed to meet the API X-70 specification. Nb- microalloyed steel is processed by the melting and casting process, and the composition is found by optical emission spectroscopy (OES). Multiple-hit deformation tests were carried out on a Gleeble® 3500 system in the standard pocket-jaw configuration to determine TNR. Cuboidal specimens (10 (L) × 20 (W) × 20 (T) mm3) were taken for compression test (multiple-hit deformation tests) in gleeble. Microstructure evolutions were carried out by using OM (optical microscopy) and SEM (scanning electron microscopy). The value of TNR determined for 0.1 wt.% niobium bearing microalloyed steel is ~ 951 °C. Nb- microalloyed steel rolled at TNR produce partially recrystallized grain with ferrite nucleation. Hence, to verify the TNR value, a rolling process is applied with the finishing rolling temperature near TNR (~951 °C). The microstructure is also revealed in the pancake shape, which confirms TN
Structural and Physico-mechanical Investigations of Mine Tailing-Calcined Kaolinite Based Phosphate Geopolymer Binder
No full textThis work explores the possibility of using Mine tailing (MT) as a feedstock in the synthesis of phosphate geopolymer binder. MT was activated at different concentrations of phosphoric acid (4, 6, 8, 10 and 12 M). The modification of the Si/Al weight ratio was done by the incorporation of 5, 10, 15, 20 and 25 wt% of calcined kaolinite (CK). After 28 days of curing, the products obtained were analyzed using XRD, FTIR, compressive strength and water absorption. The results of the XRD and FTIR analyses reveal a partial dissolution of the crystalline phase of iron oxide in this medium and the formation of aluminium phosphate hydrate as new crystalline phase. The optimum values of compressive strength (45.5 MPa) and water absorption (3.0 %) show that the binder obtained by activation with 6 M phosphoric acid and 10 wt% CK incorporation can be used in the manufacture of structural materials. Acid activation of MT thus appears as an innovative way to recycle these fine wastes in the synthesis of geopolymer
Role of dew points and Fe pre-coats on the galvanizing and galvannealing of dual phase steel
No full textIn this study, the galvanizing and galvannealing ability of dual phase steel sheet (DP 590), with and without Fe pre-coatings, is investigated with varying dew points using a hot dip process simulator (HDPS). Good quality defect free adherent galvanized coating on the substrate surface is obtained by appropriate selection of the inter-critical annealing atmosphere consists of N2-5%H2 gas mixture with +10 °C dew point without substrate pre-coating. However, the production of defect-free coating on DP 590 substrates is highly challenging when the substrates are without any pre-coating. It is observed that the selective oxidation of manganese on the substrate surface during intercritical annealing is primarily responsible for the appearance of bare spots on the galvanized surface in case of the coated specimen produced without pre-coating. A significant improvement in the reactive wetting behaviour between the liquid zinc alloy and pure Fe results in defect free adherent coatings (both galvanized and galvannealed) with electrodeposited Fe pre-coating on the substrate surface irrespective of dew points. Both the galvannealed specimens prepared with and without iron pre-coatings, exhibit partial passive-active metal characteristics in potentiodynamic polarization corrosion test. Iron pre-coating on the substrate surface is observed to improve the quality of galvannealed coatings by reducing defects and enhancing the formation of more compact and dense delta (δ) phase compared to galvannealed coatings produced without pre-coating under identical conditions. This leads to the improvement in corrosion resistance of galvannealed coating produced with pre-coating by lowering the corrosion potential and corrosion current density compared to that of galvannealed specimens produced without iron pre-coating
Assessment of N-(4H-1,2,4-triazol-4-yl)octanamide as hydrochloric acid corrosion inhibitor for mild steel
No full textThe present study demonstrates a method to manipulate the adsorption behavior of corrosion inhibitor molecules through structural modification leading to significant enhancement of the corrosion inhibition efficiency. A weak corrosion inhibitor molecule 4-amino 1,2,4 triazole (AT) was structurally modified to N-(4H-1,2,4-triazol-4-yl) octanamide (OAT) through the attachment of an octanoyl chain as the hydrophobic tail. Probing of the adsorption behavior of both AT and OAT on mild steel in 1 M HC1 using gravimetric, polarization, and electrochemical impedance spectroscopy (EIS) techniques revealed a change of the adsorption mechanism from physisorption to chemisorption due to the structural modification and the corrosion inhibition efficiency i mproved from 65 % (for 10 mM AT) to 99 % (for 0.3 mM OAT). OAT exhibited a temperature-independent inhibition efficiency of more than 99 % in 30-60 degrees C range. X-ray photoelectron spectroscopy (XPS) study indicated chemisorption of OAT molecules on the steel surface through nitrogen atoms of the triazole ring, resulting in the formation of a self-assembled monolayer (SAM). Finally, the efficacy of the OAT SAM to protect mild steel from corrosion in HC1 medium was demonstrated using scanning electrochemical microscopy (SECM) and scanning electron microscopy (SEM)
Phase decomposition in nanocrystalline Cr0.8Cu0.2 thin films
No full textMetastable Cr0.8Cu0.2 alloy thin films with nominal thickness of 360 nm have been deposited on Si(100) substrate by co-evaporation of Cu and Cr using molecular beam epitaxy (MBE). Phase evolution, microstructure, stress development, and crystallographic texture in Cr0.8Cu0.2 thin films have been investigated by X-ray diffraction (XRD), atom probe tomography (APT) and transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDS) during annealing of the films in the temperature range 200-450 degrees C. X-ray diffraction of the as-deposited thin film shows single phase bcc crystal structure of the film whereas APT observation of fine precipitates in the film matrix due to inherent compositional fluctuation indicates onset of phase separation via spinodal decomposition regime. XRD (in-situ) and APT investigation of 300 degrees C annealed film reveals that the early stage of phase separation involves localized formation of metastable intermediate bcc precipitate phase having 60 at% Cr and 40 at% Cu approximately (similar to Cr0.6Cu0.4). For longer duration of annealing at temperature >= 350 degrees C, such metastable bcc precipitates act as heterogeneous nucleation sites for the onset of precipitation of Cu rich fcc Cu(Cr) phase which indicates a change of phase separation mechanism from 'spinodal decomposition' to 'nucleation and growth'. Annealing of the film at temperature >= 400 degrees C for longer duration leads to the formation of a two phase structure with Cu rich fcc precipitate phase in a Cr rich bcc matrix. Observed phase decomposition is accompanied by significant changes in the microstructure, residual stress and crystallographic texture in the Cr rich bcc film matrix which leads to the minimization of both surface and strain energies and thereby a reduction of total Gibbs free energy of the thin film. Thermodynamic model calculation has been presented in order to understand the nucleation pathway of Cu rich stable fcc Cu(Cr) precipitates via non-classical nucleation of metastable intermediate bcc Cr0.6Cu0.4 phase. (C) 2021 Elsevier B.V. All rights reserved