8369 research outputs found
Sort by
Oxidation and Hot Corrosion Studies of Laser Hybrid Welded IN617 and P91 Alloys
No full textThe present investigation aimed to evaluate the
effect of similar laser hybrid welds on the oxidation and hot corrosion behavior of IN 617 and P91 alloys. The oxidation studies were carried out on the base and welded IN617 and P91 alloys in air in the temperature range 600–800 °C for 100 h. At the same time, hot corrosion tests with or without synthetic coal ash coatings were conducted in a flue gas environment for 1000 h. The oxidation and hot corrosion
kinetics revealed that the change in mass is lower for the
base and welded IN 617 than the P91 alloys at all the expo
sure temperatures. The post-characterization of oxide scales
formed on the surface of the base and welded alloys later to
oxidation and hot corrosion, was done using XRD and SEM
EDS techniques. The oxide phase were identified as NiO and
Cr2O3 on welded IN617 alloys at 600–700 °C and 800 °C,
respectively, whereas as Fe2O3 and Fe2O3–Fe3O4 on welded
P91 alloy at 700 °C and 800 °C, respectively. In the case of
coal ash-coated samples, additional Al2O3 & SiO2 phases
were identified for both base and welded IN 617 and P91
alloys. The non-protective Fe2O3 in the outer scale allowed
oxygen to pass through, thus yielded into much thicker oxide
scales and higher mass gains for P91 alloys, while protective NiO or Cr2O3 oxide scales yielded into low scale thicknesses and mass gains for IN617 alloys
Utilizing a sustainable surfactant from Cucurbita pepo seeds for eco-friendly flotation of non-coking coal in sustainable energy applications
No full textFatty acids are being explored as promising collectors in coal flotation as they consist of both polar heads and non-polar aliphatic tails. In the present study, the fatty acid-rich oil extracted from Cucurbita pepo (Cp) seeds by Soxhlet extraction was used as a bio-based surfactant to reduce ash in non-coking coal by flotation. The FTIR and GCMS were used to investigate the functional groups and free fatty acid composition of the extracted oil respectively. The molecular conformation was identified using NMR spectroscopy. The extracted Cp oil was primarily composed of linoleic acid (64.17%) and oleic acid (11.54%). The extracted oil was utilized as a bio-based surfactant to float high ash non-coking coal, taking advantage of the oil's fatty acid content. Taguchi's design of experiments was used to optimize flotation process parameters such as collector dosage (extracted Cp oil), frother dosage (MIBC), and airflow rate. ANOVA analysis was conducted to determine the significance of the process parameters. It was observed that frother dosage played the most significant role in achieving optimal ash rejection, followed by collector dosage and airflow rate. The optimized conditions for combustible recovery were an airflow rate of 2.0 lpm, collector dosage of 3.5 ml, and frother dosage of 0.35 ml. For optimal combustible recovery (92.15) and separation efficiency (67.77), the airflow rate had the highest impact, followed by collector and frother dosages. From the XRD analysis, it was found that the major gangue, namely, quartz and kaolinite present in the non-coking coal, were significantly reduced in the final concentrate (float). Thus, the oil extracted from the seeds of Cucurbita pepo can be used as a bio-based surfactant in high ash, non-coking coal flotation
Base free HMF oxidation over Ru-MnO2 catalysts revisited: Evidence of Mn leaching to Mn-FDCA complexation and its implications on catalyst performance
No full text2,5-furan dicarboxylic acid (FDCA) is a high-value bio-based chemical useful for the production of next-generation renewable polymers, epoxy resins, and surfactants. Herein, we show that the performance and stability of MnO2-based oxidation catalysts used in FDCA production are considerably influenced by process conditions (especially initial HMF conc. and the presence of base additives). Although base-free aerobic oxidation of HMF to FDCA is known to be highly effective over Ru-modified MnO2 catalysts, our experiments showed considerable leaching of the MnO2 phase under reaction conditions with the formation of insoluble Mn-FDCA complexes. The formation of the Mn-FDCA complex and Mn leaching was also supported by control experiments between FDCA and various Mn oxides under hydrothermal conditions and its structure was confirmed by single crystal XRD. Formation of Mn-FDCA and Mn leaching was also identified as the underlying reason for carbon balance deficit, catalyst mass loss, and deactivation observed upon reuse
Fostering Charge Carrier Transport and Absorber Growth Properties in CZTSSe Thin Films with an ALD-SnO2 Capping Layer
No full textThe present study demonstrates that precursor passivation is an effective approach for improving the crystallization process and controlling the detrimental defect density in high-efficiency Cu2ZnSn(S,Se)(4) (CZTSSe) thin films. It is achieved by applying the atomic layer deposition (ALD) of the tin oxide (ALD-SnO2) capping layer onto the precursor (Cu-Zn-Sn) thin films. The ALD-SnO2 capping layer was observed to facilitate the homogeneous growth of crystalline grains and mitigate defects prior to sulfo-selenization in CZTSSe thin films. Particularly, the Cu-Zn and Sn-Zn defects and deep defects associated with Sn were effectively mitigated due to the reduction of Sn2+ and the increase in Sn4+ levels in the kesterite CZTSSe film after introducing ALD-SnO2 on the precursor films. Subsequently, devices integrating the ALD-SnO2 layer exhibited significantly reduced recombination and efficient charge transport at the heterojunction interface and within the bulk CZTSSe absorber bulk properties. Finally, the CZTSSe device showed improved power conversion efficiency (PCE) from 8.46% to 10.1%. The incorporation of ALD-SnO2 revealed reduced defect sites, grain boundaries, and surface roughness, improving the performance. This study offers a systematic examination of the correlation between the incorporation of the ALD-SnO2 layer and the improved PCE of CZTSSe thin film solar cells (TFSCs), in addition to innovative approaches for improving absorber quality and defect control to advance the performance of kesterite CZTSSe devices
Dislocation density-based constitutive model for cyclic deformation and softening of Ni-based superalloys
No full textA physically-based constitutive modeling framework is proposed for the cyclic deformation and softening of Ni-based superalloys. The constitutive model accounts for underlying mechanisms of grain size strengthening, dislocation strengthening, solid solution strengthening, and precipitate strengthening, commonly observed in these alloys. A constitutive model is proposed for the shearing of precipitates on their interaction with glide dislocations during cyclic deformation. This is the primary contributor to the experimentally observed cyclic softening behavior in Ni-based superalloys. Model predictions of the cyclic stress-strain response and the cyclic softening (quantified in terms of the peak stress) are compared with the experimental counterparts for a range of strain amplitudes under fully-reversed cyclic loading of Inconel 718 (IN 718). Further, model predictions of precipitate size are also compared with the experimentally measured transmission electron micrographs of precipitate sizes at the end of deformation. Concurrence in the cyclic stress-strain response, peak stress, and precipitate size provides validation for our constitutive modeling framework.
Development of a physically-based constitutive modeling framework for cyclic deformation. Microstructure-based strengthening mechanisms are considered in the model. Model incorporated the physical mechanisms of cyclic softening due to precipitate shearing
Coal derived highly fluorescent N-Doped graphene quantum dots with graphitic and chemisorbed nitrogen
No full textGraphene quantum dots (GQDs) constitute a novel category of quantum dots distinguished by their distinctive properties. The introduction of nitrogen heteroatom in GQD is an effective strategy for tuning its intrinsic properties and band gap toward its optoelectronic application. This work explores the synthesis and characterization of nitrogen-doped graphene quantum dots (N-GQDs) derived from low-cost precursor coal. The synthesized N-GQD contains both graphitic and chemisorbed nitrogen states along with pyrollic and pyridinic nitrogen states which is the key responsible factor for excellent photoluminescence properties. The excitation dependent photoluminescence of the synthesized N-GQD exhibited excellent emission at 520 nm in neutral and basic pH due to the additional conjugation provided by the doped nitrogen on the surface and functional groups as well. The pH dependent photophysical properties support the existence of doped graphitic and chemisorbed nitrogen states which is also well supported by the high resolution N1s XPS peaks at 402 eV (graphitic N) and 406 eV (chemisorbed N/N2). DFT calculations further showed the decrease in fermi energy level by introducing chemisorbed-N. TEM analysis evident the formation of quantum dots with an average diameter of 3 - 7 nm with d-spacing of 0.20-0.34 nm. Additionally, the cyclic voltammetry analysis of the synthesized N-GQDs sheds light on the participation of doped nitrogen in redox reactions
Impact of thermally induced stress gradient on magneto-impedance sensitivity of As-quenched and Joule annealed microwires
No full textThe investigation addresses the dependence of rapidly quenched (Co 94 Fe 6 ) 72.5 Si 12.5 B 13 Cr 2 microwire diameters on their phase transformation evidenced during devitrification and consequent giant magneto -impedance (GMI) behavior. Phase segregation / nucleation in thicker microwires as compared to thinner ones were detected through thermal studies. In addition to such nucleation, the stress effect was more pronounced in thinner microwires as evidenced from GMI output. Structural relaxation through Joule annealing further enhanced the properties. Appropriate choice of operating frequency, alternating current and Joule heating current density vis`a-vis microwire diameter is essential for sensor design
Investigation into the Characteristics of Nanoporous Carbon/Silica-Nickel Nanocomposite for high-frequency Applications
No full textThe synthesis process involved integrating nickel oxide nanoparticles into a Carbon/Silica host matrix using the sol-gel method, resulting in the formation of a Carbon/Silica-Nickel nanocomposite. This nanocomposite was subjected to pyrolysis at 650 degrees C for two hours. The XRD diffractogram revealed a broad diffraction peak characteristic of amorphous silica and carbon phases, alongside three distinct peaks attributed to nickel. The XPS analysis identified five prominent peaks corresponding to Si 2p, Si 2s, C 1s, O 1s, and Ni 2p. SEM and TEM images showcased the porous texture and agglomeration of nanoparticles, respectively. FTIR spectroscopy indicated the presence of three major peaks associated with Si-O-Si, C-C, and Ni-O vibrations. Raman spectroscopy showed that electrical conduction is facilitated by the graphite nanoparticles. The direct current electrical conductivity (sigma dc) was exploited using Variable Range Hopping and Nearest Neighbor Hopping conduction models. The alternating current electrical conductivity (sigma ac) suggested the dominance of the Overlapping Large Polaron Tunnelling model. The complex impedance and electrical modulus were studied to determine the equivalent circuit and understand the electric relaxation process. The dielectric properties explained the occurrence of Maxwell-Wagner interfacial polarization
Optimizing Microstructure and Mechanical Properties of Cold-Rolled Medium-Mn Steel Through Intercritical Annealing and Warm Rolling
No full textThis study investigates the influence of intercritical annealing (IA) and warm-rolling (WR) parameters on the microstructure and mechanical properties of a cold-rolled medium-Mn steel (CR-MMnS). IA was conducted between temperatures of 620 degrees C and 740 degrees C, while warm rolling was carried out after IA to improve mechanical properties. To calculate the parameters for the IA and IA + WR treatments, thermodynamic model calculations were conducted using the ThermoCalc database, TCFE9. The microstructural analysis of CR-MMnS revealed that IA promoted the formation of globular morphology of ferrite/martensite and retained austenite along with the formation of carbides, while warm rolling resulted in refined grain sizes and the breakup of coarser carbides with lamellar morphology. Mechanical testing demonstrated that the combination of intercritical annealing and warm rolling (IA + WR) achieved improved tensile strength and yield strength compared to the individual intercritical annealing. The findings provide valuable insights into the optimization of intercritical annealing and warm-rolling parameters for enhancing microstructure and mechanical properties in medium-Mn steel. This research contributes to the development of advanced steel materials with enhanced performance for various engineering applications
Tunnel Kiln: A Technoeconomic Route of Sponge Iron Making
No full textThe conventional coal-based sponge iron process (Rotary Kiln) used for the production of sponge iron (DRI- Directly Reduced Iron) requires high-grade ferruginous materials in the form of lump or pellets and quality coal. Moreover, these Rotary Kiln processes require pre-indurated pellets to sustain the mechanical abrasion during reduction and suffer from low thermal and chemical efficiency. To overcome these problems, CSIR-National Metallurgical Laboratory, Jamshedpur, has developed a process for production of sponge iron utilizing mining and steel plant ferruginous waste such as iron ore fines, mill scale, LD sludge, BF sludge, etc. and lean grade coal in Tunnel Kiln. Pellets were made utilizing these ferruginous wastes in their suitable proportion, and reduction kinetics studies were carried out with non coking coal in a muffle furnace simulating Tunnel Kiln conditions. Process parameters were optimized w.r.t. blending ratio, reduction temperature and time. Based on the laboratory scale investigation, pilot plant trials were carried out in a commercial tunnel kiln on a 5-tpd scale. Fine tuning of the process parameters was carried out to obtain optimum metallic yield in the commercial production. After fine tuning of the process parameters in the commercial tunnel kiln, continuous production at the rate of 18 TPD is carried out to ascertain the techno-economics of the process. Techno-economic evaluation of the process reveals that the sponge iron produced from the Tunnel Kiln process is much cheaper (30-40%) than the conventional process of sponge iron making. Patents have been filed, and technology has been transferred to user industries