Formation of zinc oxide films using submicron zinc particle dispersions

The thermal oxidation of submicron metallic Zn particles was studied as a method to form nanostructured ZnO films. The particles used for this work were characterized by electron microscopy, x ray diffraction, and thermal analysis to evaluate the Zn-ZnO core shell structure, surface morphology, and oxidation characteristics. Significant nanostructural changes were observed for films annealed to 400 °C or higher, where nanoflakes, nanoribbons, nanoneedles, and nanorods were formed as a result of stress induced fractures arising in the ZnO outer shell due to differential thermal expansion between the metallic Zn core and the ZnO shell. Mass transport occurs through these defects due to the high vapor pressure for metallic Zn at temperatures above 230 °C, whereupon the Zn vapor rapidly oxidizes in air to form the ZnO nanostructures. The Zn particles were also incorporated into zinc indium oxide precursor solutions to form thin film transistor test structures to evaluate the potential of forming nanostructured field effect sensors using simple solution processing

Measurement of trace metals in powder activated carbon (PAC) using proton induced x-ray emission (PIXE)

We have used proton-induced x-ray emission (PIXE) to quantify ppm level of arsenic adsorbed in powder activated carbon (PAC), during the exposure of PAC to arsenic solutions. To evaluate different aspects of adsorption mechanisms in PAC, we have carried out equilibrium and kinetic adsorption experiments. After the exposure, arsenic concentration in adsorbent was quantified by means of PIXE (with 1.0 mm diameter ion beam). The As concentrations determined using PIXE compared favourably to those determined from inductively coupled plasma (ICP) measurements. 1. Introduction: Quantification of trace metals in any adsorbent directly with high accuracy and sensitivity is a challenging task. A rapid, high-sensitivity, non-destructive, quantitative, multi-elemental analytical method is best suited to investigate the issues associated with detecting trace elements. Proton induced x-ray emission (PIXE) is such an analytical tool and it is suitable for simultaneously quantifying trace elements with sensitivity of at least parts per million (ppm) [1]. In this study, trace arsenic concentrations in drinking water were investigated by PIXE. Since activated carbon (AC) can effectively remove hazardous trace elements from the drinking or wastewater, it is commonly being used to treat wastewater [2, 3]. As such, activated carbon is an excellent adsorbent for the investigation of the analysis of trace arsenic concentrations in water by characterisation techniques such as PIXE. In this work, PAC has been used as an adsorbent to remove arsenic from drinking water. The amount of arsenic adsorbed was measured by PIXE. Various adsorption experiments were conducted to evaluate both the different aspects of adsorption mechanisms in PAC; and the detection limit and accuracy of PIXE measurements. The results are compared with those from inductively-coupled-plasma (ICP) measurements

Investigation of misfit dislocations at the Fe₂O₃/Al₂2O₃ interface

Recent studies of buried interface α-Fe2O3(0001)/α-Al2O3 using high resolution transmission electron microscopy (HRTEM) and ion scattering techniques reveal the existence of disordering at the interface due to the misfit dislocations. Molecular dynamics (MD) calculations were carried out to understand the formation of misfit dislocations and the interface structural features. The misfit dislocations are formed because of the lattice mismatch between the substrate and the film. Ion scattering simulations were carried out using VEGAS code, in which the atomic positions generated by the MD calculations were used. The hitting probabilities determined from these simulations were compared with the experimental surface and interface peaks obtained from the aligned RBS spectrum

Comparison of analytical techniques for analysis of arsenic adsorbed on carbon

Activated carbon (AC) has been used extensively to treat arsenic-contaminated groundwater for a number of years. To date, attempts to quantify directly the amount of arsenic removed by the activated carbon using nondestructive methods has been limited. High-energy ion beam based proton induced x-ray emission (PIXE) is ideally suited to investigate the issues regarding the quantification of trace metals in solids. In this study, after the adsorption of arsenic on activated carbon, arsenic concentration in granular activated carbon (GAC) and powder activated carbon (PAC) were quantified using Pixe. The PIXE results were compared with atomic absorption spectrometry (AAS) and inductively coupled plasma optical emission spectrometry (ICP-OES) measurements. Some differences are observed between these measurements. The differences are greater in the case of GAC compared to PAC. These differences are mainly due to the inhomogeneous structure of GAC and PAC, which includes the variable surface properties such as surface area and pore sizes in each granule or particle. The larger differences are mainly due to the increased particle dimensions of GAC compared to PAC and the nature of the internal pore structure of GAC, which results in different amounts of arsenic adsorbed on different granules of GAC or even in different regions of one granule. This inhomogeneity of arsenic concentration is clearly visible in the arsenic concentration map generated for a single GAC particle using microbeam PIXE. Copyright © 2006, CAWQ

Quantification of arsenic in activated carbon using particle induced X-ray emission

To date, the trace elemental analysis of solids with inhomogeneous internal structure has been limited, particularly in the case of adsorbents. High-energy ion beam based particle induced X-ray emission (PIXE) is an ideal analytical tool suitable for simultaneous quantification of trace elements with high accuracy. In this study, PIXE was used to quantify arsenic in the adsorbents, granular activated carbon (GAC) and powder activated carbon (PAC). Pelletized and unmodified GAC and PAC samples were analyzed along with powder samples deposited on thin teflon filters. These sample preparation methods resulted in samples of various thicknesses and densities. PIXE measurements taken from these samples were compared to results from neutron activation analysis (NAA) and atomic absorption spectroscopy (AAS). There is a good agreement between the values from the NAA and pelletized PIXE measurements and some AAS measurements