Precursor Dependent Microstructure Evolution and Nonstoichiometry in Nanostructured Cerium Oxide Coatings Using the Solution Precursor Plasma Spray Technique

A solution precursor plasma spray (SPPS) technique has been used for direct deposition of cerium oxide nanoparticles (CNPs) from various cerium salt solutions as precursors. Solution precursors were injected into the hot zone of a plasma plume to deposit CNP coatings. A numerical study of the droplet injection model has been employed for microstructure development during SPPS. The decomposition of each precursor to cerium oxide was analyzed by thermogravimetric-differential thermal analysis and validated by thermodynamic calculations. The presence of the cerium oxide phase in the coatings was confirmed by X-ray diffraction studies. Transmission electron microscopy studies confirmed nanocrystalline (grain size <14 nm) characteristic of the coatings. X-ray photoelectron spectroscopy studies indicated the presence of a high concentration of Ce3+ (up to 0.32) in the coating prepared by SPPS. The processing and microstructure evolution of cerium oxide coatings with high nonstoichiometry are reported.

Direct Growth of Gold Nanorods on Gold and Indium Tin Oxide Surfaces: Spectral, Electrochemical, and Electrocatalytic Studies

The surfactant-assisted seed-mediated growth method was used for the formation of gold nanorods (GNRs) directly on gold (Au) and indium tin oxide (ITO) surfaces. Citrate-stabilized similar to 2.6 nm spherical gold nanoparticles (AuNPs) were first self-assembled on ITO or Au surfaces modified with (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film and then immersed in a cationic surfactant growth solution to form GNRs. The growth of GNRs on the MPTS sol gel film modified ITO surface was monitored by UV-visible spectroscopy. The ITO surface with the attached spherical AuNPs shows a surface plasmon resonance band at 550 nm. The intensity of this absorption band increases while increasing the immersion time of the AuNP-modified ITO surface into the growth solution, and after 5 h, an additional shoulder band around 680 nm was observed. The intensity of this shoulder band increases, and it was shifted to longer wavelength as the immersion time of the AuNP-modified ITO surface into the growth solution increases. After 20 h, a predominant wave at 720 nm was observed along with a band at 550 nm. Further immersion of the modified ITO surface into the growth solution did not change the absorption characteristics. The bands observed at 550 and 720 nm were characteristics of GNRs, corresponding to transverse and longitudinal waves, respectively. The AFM images showed the presence of GNRs on the surface of the MPTS sol gel modified ITO surface with a typical length of similar to 100-120 nm and a width of similar to 20-22 nm in addition to a few spherical AuNPs, indicating that seeded spherical AuNPs were not completely involved in the GNRs' formation. Finally, the electrocatalytic activity of the surface-grown GNRs on the MPTS sol gel film modified Au electrode toward the oxidation of ascorbic acid (AA) was studied. Unlike a polycrystalline Au electrode, the surface-grown GNR-modified electrode shows two well-defined voltammetric peaks for AA at 0.01 and 0.35 V in alkaline, neutral, and acidic pHs. The cause for the observed two oxidation peaks for AA was due to the presence of both nanorods and spherical nanoparticles on the electrode surface. The presence of spherical AuNPs on the MPTS sol gel film oxidized AA at more positive potential, whereas the GNRs oxidized AA at less positive potential. The observed 340 mV less positive potential shift in the oxidation of AA suggested that GNRs are better electrocatalysts for the oxidation of AA than the spherical AuNPs.

A2MoTiO7−x (Atriple bond; length as m-dashrare earth or Y): a new series of oxide pyrochlores prepared by topochemical reduction of A2MoTiO8 scheelites

A series of anion-deficient pyrochlore oxides of the formula A2MoTiO7−x (xless-than-or-equals, slant0.5), where Atriple bond; length as m-dashSm, Gd, Tb, Dy, Ho, Er, Lu and Y, has been prepared by reduction of A2MoTiO8 scheelites. The scheelite-to-pyrochlore conversion is reversible, indicating that the reaction is likely to be topochemical. The oxidation states of molybdenum and titanium are most probably Mo(III) and Ti(IV) for the limiting composition of the pyrochlores A2MoTiO6.5. The new pyrochlores are non-metallic and paramagnetic as expected.

4-Nitro 2-picoline-l-oxide complexes of lanthanide perchlorates

4-Nitro 2-picoline-l-oxide (NPicO) complexes of the formulae La (NPicO)5 (CIO4)3, Ln2 (NPicO)9 (C1O4)6 (Ln = Pr, Nd, and Gd) and Ln (NPicO)4 (CIO4)3 (Ln == Tb, Dy, Ho and Yb) have been synthesised and characterised by analysis, electrolytic conductance, infrared, proton NMR and electronic spectral data. A tentative coordination number of 6 for all the complexes have been assigned

Ball wear and its control in the grinding of a lead-zinc sulphide ore

Marked ball grinding tests were carried out in the laboratory with a lead-zinc sulphide ore under different experimental conditions using high carbon low alloy steel (cast and forged) and high chrome cast iron balls. Relative ball wear as a function of grinding period and milling conditions was evaluated for the different types of ball materials. The role of corrosion and abrasion-erosion in the wear of grinding media is brought out. Methods to minimise ball wear through control of mill atmosphere and addition of reagents are discussed.

Design and fabrication of an automated thermal desorption gas-solid reaction system: Oxidation of ammonia and methanol over YBa2Cu3O7−δ(123) oxide systems

A fully automated, versatile Temperature Programmed Desorption (TDP), Temperature Programmed Reaction (TPR) and Evolved Gas Analysis (EGA) system has been designed and fabricated. The system consists of a micro-reactor which can be evacuated to 10−6 torr and can be heated from 30 to 750°C at a rate of 5 to 30°C per minute. The gas evolved from the reactor is analysed by a quadrupole mass spectrometer (1–300 amu). Data on each of the mass scans and the temperature at a given time are acquired by a PC/AT system to generate thermograms. The functioning of the system is exemplified by the temperature programmed desorption (TPD) of oxygen from YBa2Cu3−xCoxO7 ± δ, catalytic ammonia oxidation to NO over YBa2Cu3O7−δ and anaerobic oxidation of methanol to CO2, CO and H2O over YBa2Cu3O7−δ (Y123) and PrBa2Cu3O7−δ (Pr123) systems.

Effect of zinc content on the processing map for hot working of α brass

The hot deformation behavior of α brass with varying zinc contents in the range 3%–30% was characterized using hot compression testing in the temperature range 600–900 °C and strain rate range 0.001–100 s−1. On the basis of the flow stress data, processing maps showing the variation of the efficiency of power dissipation (given by Image where m is the strain rate sensitivity) with temperature and strain rate were obtained. α brass exhibits a domain of dynamic recrystallization (DRX) at temperatures greater than 0.85Tm and at strain rates lower than 1 s−1. The maximum efficiency of power dissipation increases with increasing zinc content and is in the range 33%–53%. The DRX domain shifts to lower strain rates for higher zinc contents and the strain rate for peak efficiency is in the range 0.0001–0.05 s−1. The results indicate that the DRX in α brass is controlled by the rate of interface formation (nucleation) which depends on the diffusion-controlled process of thermal recovery by climb.

Electrical properties of cobalt‐zinc ferrites

The electrical properties of Co1−xZnxFe2O4 (x=0–1) spinel ferrites were investigated by impedance spectroscopy. The grain‐boundary resistance was found to increase as a function of composition up to x=0.6, and decreases beyond x=0.6. The variation in the bulk resistance and the activation energy as a function of composition is found to exhibit a similar trend whereas the grain resistance appears to be an independent parameter. The observed results suggest that the bulk properties of solid solution spinel ferrites are primarily controlled by the grain‐boundary phase.

Fe-57 Mössbauer and Mo K-EXAFS Investigations of MoxFe3-xO4, an Interesting Mixed-Valent Oxide System

Ferrites of the formula MoxFe3-xO4, prepared by a soft-chemistry route, show mixed valence states of both iron and molybdenum cations. Mössbauer studies show that Fe2+ and Fe3+ ions are present on both the A and B sites, giving Fe an average oxidation state between 2+ and 3+. Molybdenum is present in the 3+ and the 4+ states on the B sites. The presence of Mo in the 3+ state has been established by determining the Mo3+-O distance (2.2 Å), for the first time, by Mo K-EXAFS. The mixed valence of Fe on both the A and B sites and of Mo on the B sites is responsible for the fast electron transfer between the cations. All the Mössbauer parameters including the line width show a marked change at a composition (x ? 0.3) above which the concentration of Fe2+A increases rapidly.

K1-xLaxCa2-xNb3O10, a Layered Perovskite Series with Variable Interlayer Cation Density, and LaCaNb3O10, a Novel Layered Perovskite Oxide with No Interlayer Cations

A series of layered perovskite oxides of the formula K1-xLaxCa2-xNb3O10 for 0 < x ≤ 1.0 have been prepared. All the members are isostructural, possessing the structure of KCa2Nb3O10. The interlayer potassium ions in the new series can be ion-exchanged with protons to give H1-xLaxCa2-xNb3O10. The latter readily forms intercalation compounds of the formula (CnH2n+1NH3)1-x LaxCa2-xNb3O10, just as the parent solid acid HCa2Nb3O10. The end member LaCaNb3O10 containing no interlayer cations is a novel layered perovskite oxide, being a n = 3 member of the series An-1BnX3n+1.