Phase equilibria in the ZnO-rich area of the Fe-Zn-O system in air

The phase equilibria in the Fe-Zn-O system in the range 900-1580degreesC in air have been experimentally studied using equilibration and quenching techniques. The compositions of the phases at equilibrium were determined using electron probe X-ray microanalysis (EPMA). The ferrous and ferric bulk iron concentrations were measured with a wet chemical analysis using the ammonium metavanadate technique. X-ray powder diffraction analysis (XRD) was used to characterise the phases. Iron oxide dissolved in zincite was found to be present principally in the ferric form. The XRD analysis and the composition measurements both indicate that zincite is the only phase stable in the ZnO-rich area in the range of conditions investigated. The solubility of the iron oxide in zincite rapidly increases at temperatures above 1200degreesC; the morphology of the zincite crystals also sharply changes between 1200 and 1300degreesC from rounded to plate-like crystals. The plate-like zincite forms a refractory network-the type of microstructure beneficial to the Imperial Smelting Process (ISP) sinter performance. The software program FactSage with a thermodynamically optimised database was used to predict phase equilibria in the Fe-Zn-O system.

A reinvestigation of phase equilibria in the system Al2O3-SiO2-ZnO

The phase equilibria and liquidus temperatures in the binary SiO2-ZnO system and in the ternary Al2O3-SiO2-ZnO system at low Al2O3 concentrations have been experimentally determined using the equilibration and quenching technique followed by electron probe X-ray microanalysis. In the SiO2-ZnO system, two binary eutectics involving the congruently melting willemite (Zn2SiO4) were found at 1448 +/- 5 degrees C and 0.52 +/- 0.01 mole fraction ZnO and at 1502 +/- 5 degrees C and 0.71 +/- 0.01 mole fraction ZnO, respectively. The two ternary eutectics involving willemite previously reported in the Al2O3SiO2-ZnO system were found to be at 1315 +/- 5 degrees C and 1425 +/- 25 T, respectively. The compositions of the eutectics are 0.07, 0.52, and 0.41 and 0.05, 0.28, and 0.67 mole fraction Al2O3, SiO2, and ZnO, respectively. The results of the present investigation are significantly different from the results of previous studies.

A trace element study of siderite-jasper banded iron formation in the 3.45 Ga Warrawoona Group, Pilbara Craton - Formation from hydrothermal fluids and shallow seawater

Shale-normalised rare earth element and yttrium (REE + Y) patterns for siderite-jasper couples in a banded iron formation of the 3.45 Ga Panorama Formation, Warrawoona Group, eastern Pilbara Craton, display distinct positive Y and Eu anomalies and weak positive La and Gd anomalies, combined with depleted light REE relative to middle and heavy REE. Ambient seawater and hydrothermal fluids are identified as major sources of REE + Y for the BIF. In the case of siderites, strong correlations between incompatible trace elements and trace element ratios diagnostic of seawater indicate variable input from a terrigenous source (e.g. volcanic ash). We propose a volcanic caldera setting as a likely depositional environment where jasper and siderite precipitated as alternating bands in response to episodic changes in ambient water chemistry. The episodicity was either driven by fluctuations in the intensity of hydrothermal activity or changes in magma chamber activity, which in turn controlled relative sea level. In this context, precipitation of jasper probably reflects background conditions during which seawater was saturated in silica due to evaporative conditions, while siderites were deposited most likely during intermittent periods of enhanced volcanic activity when seawater was more acidic due to the release of exhalative phases (e.g. CO2). © 2005 Elsevier B.V. All rights reserved.

Thermal stability of ion-implanted ZnO

Zinc oxide single crystals implanted at room temperature with high-dose (1.4x10(17) cm(-2)) 300 keV As+ ions are annealed at 1000-1200 degrees C. Damage recovery is studied by a combination of Rutherford backscattering/channeling spectrometry (RBS/C), cross-sectional transmission electron microscopy (XTEM), and atomic force microscopy. Results show that such a thermal treatment leads to the decomposition and evaporation of the heavily damaged layer instead of apparent defect recovery and recrystallization that could be inferred from RBS/C and XTEM data alone. This study shows that heavily damaged ZnO has relatively poor thermal stability compared to as-grown ZnO which is a significant result and has implications for understanding results on thermal annealing of ion-implanted ZnO. (c) 2005 Americian Institute of Physics.

Preparation of high purity ZnO nanobelts by thermal evaporation of ZnS

High purity one-dimensional ZnO nanobelts were synthesized by thermally evaporating commercial ZnS powders in a hydrogen-oxygen mixture gas at 1050 degrees C. It was found that these ZnO nanobelts had a single crystal hexagonal wurtzite structure growing along the [0001] direction. They had a rectangle-shaped cross-section with typical widths of 20 to 100 nanometers and lengths of up to hundreds of micrometers with lattice constants of a = 0.325 nm and c = 0.520 nm. The self-catalytic hydrogen-oxygen assisted growth of ZnO nanobelt is discussed. The photoluminescence (PL) characterization of the ZnO nanobelts shows strong near-band UV emission (about 383 nm) and one broad peak at 501 nm, which indicates that the ZnO nanobelts have good potential application in optoelectronic devices.

Cost-effective and eco-friendly synthesis of novel and stable N-doped ZnO/g-C3N4 core-shell nanoplates with excellent visible-light responsive photocatalysis

N-doped ZnO/g-C3N4 hybrid core–shell nanoplates have been successfully prepared via a facile, cost-effective and eco-friendly ultrasonic dispersion method for the first time. HRTEM studies confirm the formation of the N-doped ZnO/g-C3N4 hybrid core–shell nanoplates with an average diameter of 50 nm and the g-C3N4 shell thickness can be tuned by varying the content of loaded g-C3N4. The direct contact of the N-doped ZnO surface and g-C3N4 shell without any adhesive interlayer introduced a new carbon energy level in the N-doped ZnO band gap and thereby effectively lowered the band gap energy. Consequently, the as-prepared hybrid core–shell nanoplates showed a greatly enhanced visible-light photocatalysis for the degradation of Rhodamine B compare to that of pure N-doped ZnO surface and g-C3N4. Based on the experimental results, a proposed mechanism for the N-doped ZnO/g-C3N4 photocatalyst was discussed. Interestingly, the hybrid core–shell nanoplates possess high photostability. The improved photocatalytic performance is due to a synergistic effect at the interface of the N-doped ZnO and g-C3N4 including large surface-exposure area, energy band structure and enhanced charge-separation properties. Significantly, the enhanced performance also demonstrates the importance of evaluating new core–shell composite photocatalysts with g-C3N4 as shell material.

Defects in ZnO nanoparticles laser-ablated in water-ethanol mixtures at different pressures

The effect of liquid medium and its pressure on the photoluminescence of ZnO nanoparticles prepared via laser ablation of Zn targets in various water-ethanol mixtures is studied. As the ethanol content increases, the photoluminescence of the product changes, while metallic zinc is observed to emerge in nanomaterials prepared in ethanol-rich environments. The applied pressure had a less profound effect, mainly affecting materials produced in water or water-ethanol, and much less those generated in pressurized ethanol. Tuning the reactivity of the liquid and pressurizing it during laser ablation is demonstrated to be promising for tailoring the emission properties of the product.

Hierarchical ZnO “rod like” architecture synthesized via reverse micellar route for improved photocatalytic activity

Hierarchical ZnO “rod like” architecture was successfully synthesized via reverse micellar route and characterized by various techniques. The FESEM studies show controlled decomposition of zinc oxalate into ZnO “rod like” architecture at 500 °C with slow heat rate at 1°/min. Interestingly, improved photocatalytic activity was observed for the degradation of Rhodamine B, due to the self assembly of hexagonal nanoparticles of zinc oxide forming hierarchical ZnO “rod like” architecture which can greatly enhance the light utilization rate due to its special architecture and enlarge the specific surface area, providing more reaction sites and promoting mass transfer. More importantly, the reusability studies of this architecture were most economical.

Toxicity assessment of industrial- and sunscreen-derived ZnO nanoparticles

Lo scopo della presente tesi è l’analisi della tossicità di nanoparticelle di ossido di zinco (nano-ZnO) verso gli organismi acquatici. In particolare, il presente studio valuta per la prima volta l'inibizione della crescita della diatomea Thalassiosira pseudonana indotta sia da nanoparticelle di dervazione industriale, che da nanoparticelle auto-estratte in laboratorio da un filtro solare. Gli esperimenti, condotti presso il Laboratorio di Ingegneria dell'Università di Miami, hanno mostrato che la tossicità indotta dalle nanoparticelle di ossido di zinco è influenzata dal tipo di nanoparticelle, nonché dalla loro concentrazione nella soluzione acquosa e dal tempo di esposizione. In particolare le nanoparticelle di derivazione industriale, più piccole rispetto alle nanoparticelle estratte dal filtro solare, hanno indotto un’inibizione della crescita superiore, specialmente a concentrazioni inferiori. Questo andamento suggerisce che ad alte concentrazioni la tossicità di nano-ZnO potrebbe essere influenzata dall’aggregazione di nanoparticelle (indipendentemente dalle dimensioni di partenza delle nanoparticelle), mentre a concentrazioni inferiori la tossicità potrebbe essere influenzata dalle dimensioni di partenza delle nanoparticelle, così come dal tipo di nanoparticelle e dal tempo di esposizione.