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Thermodynamic properties of YRhO3 and phase relations of the system Y-Rh-O
No full textAs part of a larger program of research on physico-chemical aspects of processing Rh catalysts, thermodynamic properties of the ternary oxide YRhO3 are determined in the temperature range from 900 to 1300 K using a solid-state electrochemical cell incorporating yttria-stabilized zirconia as the electrolyte. The standard Gibbs energy of formation of orthorhombically-distorted perovskite YRhO3 from its component binary oxides Y2O3 and Rh2O3 is calculated. Assuming Neumann-Kopp rule, the standard entropy of YRhO3 at 298.15 K is evaluated as 83.51(+/- 1.5) J K-1 mol(-1). The standard enthalpy of formation of the compound from elements at 298.15 K is obtained as -1219.2(+/- 2.8) kJ mol(-1). Using isothermal equilibration technique, YRhO3 is identified as the only inter-oxide compound in the system Y2O3-Rh2O3. Existence of a three-phase field involving Rh + Y2O3 + YRhO3 is confirmed. Based on thermodynamic data phase relations in the system Y-Rh-O are computed at 1200 K. Various phase diagrams at 1200 K are presented
Electrochemical sensor study of TiO2 nanoparticle-graphene composite produced by mechanical milling and sonication-assisted exfoliation
No full textTiO2 nanoparticle-decorated graphene was produced by mechanical milling of TiO2 powder with graphite followed by sonication of the nanocomposite in the presence of sodium lauryl sulfate surfactant. Sonication led to the exfoliation of graphite to produce TiO2 nanoparticle-graphene composite. The as-prepared TiO2-graphite nanocomposite was characterized using X-ray diffraction and scanning electron microscopy and the exfoliated TiO2-graphene nanocomposite was analyzed using Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The results indicated the formation of faceted titanium dioxide particles with an average size of 200 nm. Thickness of the few layered graphene sheets was found to be 2 + 0.8 nm. The glassy carbon electrode coated with the TiO2 nanoparticle-graphene composite was used to detect potassium ferricyanide (K3FeCN6) by cyclic voltammetric method. TiO2 nanoparticle-graphene-coated surface demonstrated improved response with enhanced current for K3FeCN6 detection
Effect of low temperature annealing on the properties of nano Ni-Ti alloys
No full textBinary 1:1 Ni-Ti alloy has been the work horse for many industrial and of late biomedical applications amongst all shape memory alloys. Apart from being employed for endovascular applications like stents and filters, they are also used as orthodontic braces and in endodontic tools. Ni-Ti drills and files are used in a few procedures with sterilization between uses. However, the effect of these sterilizing heat-treatments on the properties of the tools is not clearly investigated. In addition to this, satisfactory metallurgical explanations for the wear resistance of these alloys in absent in the literature. Therefore, this paper attempts to define the transformational temperatures for the Ni-Ti as-received and low temperature heat-treated conditions have been investigated using Differential Scanning Calorimetry (DSC). Attempts are made to justify their suitability for endodontic applications by evaluating their mechanical strength parameters using the Tensile and Wear tests. It was found that the samples showed did not show much variations in strength when subjected to tensile tests whereas the same was not observed for DSC tests. Ambient temperature x-ray diffraction studies indicate the presence of Austenitic and Martensitic phases in all the samples. DSC results are strongly affected by presence of internal stresses but stress-induced-martensitic forms in all the samples with equal facility
Pregabalin peptides: conformational comparison of gamma(3)- and gamma(4)-substituted gamma-amino acids in alpha gamma alpha alpha alpha pentapeptides
No full textGamma-aminobutyric acid (GABA, gammaAbu), an unsubstituted gamma-amino acid, is an important inhibitory neurotransmitter in the mammalian brain. The role of GABA in the treatment of epilepsy has triggered a great deal of interest in substituted gamma-amino acids, which may serve as GABA analogs, acting as inhibitors of GABA aminotransferase. Pregabalin (Pgn), a well-known antiepileptic drug, is also a beta-substituted gamma3-amino acid. Pregabalin and gamma4Leu, an isomer of the pregabalin (Pgn) residue, both carrying the same isobutyryl group in the side chain, were introduced in the present study to have a comparison of their respective conformational differences as well as their role in influencing the overall conformation of the peptides, they are inserted in. Two alpha-gamma-alpha-alpha-alpha hybrid pentapeptides were designed that contain Aib-Pgn and Aib-gamma4Leu segments at the N terminus. The study provides a detailed analysis of the conformational properties and non-covalent interactions observed in the crystal structures of two polymorphs of the pentapeptide monohydrate, Boc-Aib-(S)Pgn-Leu-Phe-Val-OMe (C38H63N5O8 center dot H2O) and the isomeric pentapeptide, Boc-Aib-gamma4(R)Leu-Leu-Phe-Val-OMe (C38H63N5O8), obtained from single crystal X-ray diffraction experiments
Tuning sample length effect on mass transport in current carrying Cu-Si thin-film systems via interfacial engineering
No full textOften, electric current-induced mass depletion at the cathode decreases with a decrease in the sample length; this is known as the Blech length effect. However, we recently demonstrated that coupling between thermomigration and electromigration, which is spontaneously established upon passage of an electric current through thin-film conductors with bends, results in an increase in the mass depletion at the cathode with a decrease in the sample length; we term this behavior inverse Blech length phenomenon. Here, we study the possibility of switching the mass transport in Cu thin films between the above two extreme phenomena by tuning the interlayer placed in between the Cu film and SiO2/Si substrate. Tests were performed by passing electric currents of high density through Cu thin film deposited on SiO2/Si substrate, with Ta or Ti interlayer. While inverse Blech length phenomenon was observed in the Cu-Ta sample, the classic Blech length effect was observed in the Cu-Ti sample. Moreover, partial oxidation of the Ti interlayer resulted in the observation of inverse Blech length phenomenon in the Cu-Ti sample also. The observations have been rationalized through characterization of the structure of the interfacial layer using a transmission electron microscope and estimation of the temperature field using finite element analysis. We also discuss the implications of our findings on the design of robust microelectronic interconnects
Na2MnP2O7 polymorphs as efficient bifunctional catalysts for oxygen reduction and oxygen evolution reactions
No full textIn order to design earth-abundant low cost electrocatalysts, this communication exploits polymorphism in Na2MnP2O7 pyrophosphate sodium insertion materials. Two polymorphs of Na2MnP2O7 have been prepared with a short annealing duration of 30 minutes. These scalable materials exhibit efficient bifunctional electrocatalytic activity stemming from the Mn redox centre and robust structural framework
Cobalt and Nickel Phosphates as Multifunctional Air-Cathodes for Rechargeable Hybrid Sodium-Air Battery Applications
No full textNoble-metal-free bifunctional electrocatalysts are indispensable to realize low-cost and energy-efficient rechargeable metal-air batteries. In addition, power density, energy density, and cycle life of these metal-air batteries can be improved further by utilizing the fast faradaic reactions of metal ions in the catalyst layer together with the oxygen evolution/reduction reactions (OER/ORR) for charge storage. In this work, we propose mixed metal phosphates of nickel and cobalt, NixCo3-x(PO4)(2) (x = 0,1, 1.5, 2, and 3), as multifunctional air-cathodes exhibiting bifunctional electrocatalytic activity and reversible metal redox reaction (M3+/2+, M = Ni and Co). Submicron-sized NixCo3-x(PO4)(2) particles were synthesized by a solution combustion synthesis technique with urea acting as the fuel. Electrocatalytic activity toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in 0.1 M NaOH was systematically tuned by varying the Ni-to-Co ratio. The synthesized NixCo3-x(PO4)(2) with x = 1.5 (NCP11) showed superior bifunctional catalytic activity to other samples. Moreover, the catalyst material delivered a specific capacity of , similar to 110 mAh g(-1) by the redox reactions of its metal sites. The hybrid Na-air battery fabricated using the NCP11 catalyst-loaded aircathode exhibited low overpotential, stable cycling performance, and round-trip energy efficiency exceeding 78% in a 0.1 M NaOH aqueous electrolyte
Rattling-Induced Ultralow Thermal Conductivity Leading to Exceptional Thermoelectric Performance in AgIn5S8
No full textRattling has emerged as one of the most significant phenomenon for notably reducing the thermal conductivity in complex crystal systems. In this work, using first-principles density functional theory, we found that rattlers can be hosted in simpler crystal systems such as AgIn(5)S(8 )and CuIn5S8. Rattlers Ag and Cu exhibit weak and anisotropic bonding with the neighboring In and S and reside in a very shallow anharmonic potential well. The phonon spectra of these compounds have multiple avoided crossing of optical and acoustic modes, which are a signature of rattling motion. This leads to ultralow thermal conductivity, which is inversely proportional to mass and frequency span of rattling modes. Even though Ag atoms contribute to the valence band states, the rattler modes of Ag do not scatter carriers significantly, leaving the electronic transport virtually unaffected. Moreover, AgIn5S8 possesses a combination of heavy and light valence bands resulting in a very high power factor. A combination of favorable thermal and electronic transport results in a very high figure of merit of 2.2 in p-doped AgIn5S8 at 1000 K. The proposed idea of having rattlers in simpler systems can be extended to a wider class of materials, which would accelerate the development of thermoelectric modules for waste energy harvesting
Deposition of Ni-NiO nanoparticles on the reduced graphene oxide filled polypyrrole: evaluation as cathode catalyst in microbial fuel cells
No full textHerein, we fabricated the in situ polymerization of pyrrole (Py) on reduced graphene oxide (rGO), formulated as a nanocomposite support matrix for the deposition of nickel-nickel oxide (Ni-NiO) nanoparticles (NPs), as a cost-effective cathode catalyst for application in microbial fuel cells. In the presence of an oxidant, pyrrole (Py) monomers were electrostatically adsorbed over the negatively charged rGO sheet, where the pi-pi interactions among the Py monomers resulted in its polymerization as polypyrrole (PPy). The synergistic effects of components of the support matrix resulted in durable electrocatalytic activity for the ORR in the prepared Ni-NiO/PPy-rGO composite in neutral media. The prepared composites were characterized by Fourier transform infrared spectroscopy (FTIR), UV spectroscopy, Raman spectrometry (RAMAN), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the results confirmed the presence of Ni+ and Ni2+ ions in the synthesized nanocomposites. In addition, nickel-nickel oxide (Ni-NiO) nanoparticles (NPs) were homogeneously dispersed over this PPy-rGO sheet during their deposition through field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Also, the synthesized nanocomposites, i.e., Ni-NiO/PPy-rGO (70 : 30), were electrochemically analyzed using cyclic voltammetric (CV), chronoamperometric (CA) and impedance spectroscopic (EIS) techniques to highlight its stability and efficacy as a nanocatalyst. In comparison with the conventional Pt/C catalyst (reduction potential at 0.521 V with -0.204 mA current), the superior stability and electrocatalytic activities of Ni-NiO/PPy-rGO (reduction potential of 0.535 V at -0.235 mA current) were observed via CV in the enhanced oxygen reduction reaction (ORR). In the microbial fuel cell (MFC), the cost-effective Ni-NiO/PPy-rGO nanocatalyst exhibited a higher current density and power density of 2134.56 mA m(-2) and similar to 678.79 +/- 34 mW m(-2) in comparison to the commercial Pt/C catalyst (1788.2 mA m(-2) and similar to 481.02 +/- 24 mW m(-2)). Thus, overall, the present study illustrates the preparation and characterization, efficacy and electro-active stability of Ni-NiO/PPy-rGO as a cost-effective nanohybrid catalyst in single chambered MFCs during the ORR
Ions' motion in water
No full textOver the decades, a great deal of attention has been focused on the solvation and transport properties of small rigid monatomic ions such as Na+, K+, Li+, Cl-, and Br- due to their importance in physical chemistry. Much less attention has been devoted to polyatomic ions although many polyatomic ions (such as nitrate, acetate, sulfate, and ammonium) are of great importance in biological and chemical processes. While the translational diffusion of smaller rigid ions shows the remarkable nonmonotonic dependence on inverse ion size (known as the `` breakdown of Walden product''), the intermediate- to large-sized polyatomic ions (such as nitrate, acetate, and sulfate) exhibit different anomalies pointed out only recently. In this Perspective article, we provide an overview of how rotational diffusion and translational diffusion of these ions themselves are coupled to translational and rotational motions of water molecules. We discuss how diffusion of polyatomic ions is different from that of monatomic ions due to the rotational self-motion of the former that enhances diffusion in specific cases because of symmetry. While a continuum hydrodynamic model fails to describe the motion of polyatomic ions, we discuss how a mode-coupling theory approach can capture many aspects of this coupling between the solute ion and solvent water. We discuss how ionic mobility in water and other dipolar solvents are intimately connected to the dipolar solvation dynamics, in particular to its ultrafast component. We point out how the usual thinking on the relation between the diffusion and entropy needs to be modified in the case of ion diffusion