Electrical, Thermal and Optical Diagnostics of an Atmospheric Plasma Jet System

Plasma diagnostics of atmospheric plasmas is a key tool in helping to understand processing performance issues. This paper presents an electrical, optical and thermographic imaging study of the PlasmaStream atmospheric plasma jet system. The system was found to exhibit three operating modes; one constricted/localized plasma and two extended volume plasmas. At low power and helium flows the plasma is localized at the electrodes and has the electrical properties of a corona/filamentary discharge with electrical chaotic temporal structure. With increasing discharge power and helium flow the plasma expands into the volume of the tube, becoming regular and homogeneous in appearance. Emission spectra show evidence of atomic oxygen, nitric oxide and the hydroxyl radical production. Plasma activated gas temperature deduced from the rotational temperature of nitrogen molecules was found to be of order of 400 K: whereas thermographic imaging of the quartz tube yielded surface temperatures between 319 and 347 K.

Correlation Between the Electrical and Optical Properties of an Atmospheric Pressure Plasma During Siloxane Coating Deposition

The effect of varying process parameters on atmospheric plasma characteristics and properties of nanometre thick siloxane coatings is investigated in a reel-to-reel deposition process. Varying plasma operation modes were observed with increasing applied power for helium and helium/oxygen plasmas. The electrical and optical behaviour of the dielectric barrier discharge were determined from current/voltage, emission spectroscopy and time resolved light emission measurements. As applied power increased, multiple discharge events occurred, producing a uniform multi-peak pseudoglow discharge, resulting in an increase in the discharge gas temperature. The effects of different operating modes on coating oxidation and growth rates were examined by injecting hexamethyldisiloxane liquid precursor into the chamber under varying operating conditions. A quenching effect on the plasma was observed, causing a decrease in plasma input power and emission intensity. Siloxane coatings deposited in helium plasmas had a higher organic component and higher growth rates than those deposited in helium/oxygen plasmas.

Applications of colloidal gas aphrons for pollution remediation

This work reviews the use of micron sized bubbles made from aqueous surfactant solution in environmental remediation. This is a novel technique and offers a low cost treatment option.

Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds

Tree ring Delta C-14 data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric Delta C-14 varied on multi-decadal to centennial timescales, in both hemispheres, over the period between AD 950 and 1830. The Northern and Southern Hemispheric Delta C-14 records display similar variability, but from the data alone is it not clear whether these variations are driven by the production of C-14 in the stratosphere (Stuiver and Quay, 1980) or by perturbations to exchanges between carbon reservoirs (Siegenthaler et al., 1980). As the sea-air flux of (CO2)-C-14 has a clear maximum in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the interhemispheric gradient. In this study, model simulations are used to show that Southern Ocean winds are likely a main driver of the observed variability in the interhemispheric gradient over AD 950-1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980-2004). This interpretation also implies that there may have been a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds at the Medieval Climate Anomaly to Little Ice Age transition remain unknown. Our process-focused suite of perturbation experiments with models raises the possibility that the current generation of coupled climate and earth system models may underestimate the natural background multi-decadal- to centennial-timescale variations in the winds over the Southern Ocean.

An Investigation into the Optimum Thickness of Titanium Dioxide Thin Films Synthesized by Using Atmospheric Pressure Chemical Vapour Deposition for Use in Photocatalytic Water Oxidation

Twenty eight films of titanium dioxide of varying thickness were synthesised by using atmospheric pressure chemical vapour deposition (CVD) of titanium(IV) chloride and ethyl acetate onto glass and titanium substrates. Fixed reaction conditions at a substrate temperature of 660 degrees C were used for all depositions, with varying deposition times of 5-60 seconds used to control the thickness of the samples. A sacrificial electron acceptor system composed of alkaline sodium persulfate was used to determine the rate at which these films could photo-oxidise water in the presence of 365 nm light. The results of this work showed that the optimum thickness for CVD films on titanium substrates for the purposes of water oxidation was approximate to 200 nm, and that a platinum coating on the reverse of such samples leads to a five-fold increase in the observed rate of water oxidation.

In situ, continuous monitoring of the photoinduced superhydrophilic effect: Influence of UV-type and ambient atmospheric and droplet composition

A controlled-atmosphere chamber, combined with a CCTV system, is used to monitor continuously the change in shape of water droplets on the self-cleaning commercial glass, Activ, and a sol-gel TiO2 substrate during their irradiation with either UVA or UVC light. This system allows the photoinduced superhydrophilic effect (PSH) exhibited by these materials to be studied in real time under a variety of different conditions. UVA was less effective than UVC in terms of PSH for both titania-coated glasses, and plain glass was unaffected by either form of UV irradiation and so showed no PSH activity. With UVA, ozone increased significantly the rate of PSH for both substrates, but had no effect on the wettability of plain glass. For both titania substrates and plain glass, no PSH activity was observed under an O-2-free atmosphere. A more detailed study of the PSH effect exhibited by Activ revealed that doping the water droplet with either an electron acceptor (Na2S2O8), electron donor (Na2S2O4), or simple electrolyte (KCl) in the absence of oxygen did not promote PSH. However, when Activ was UV irradiated, while immersed in a deoxygenated KCl solution, prior to testing for PSH activity, only a small change in contact angle was observed, whereas under the same conditions, but using a deoxygenated persulfate-containing immersion solution, it was rendered superhydrophilic. The correlation between organic contaminant removal and surface wetting was also investigated by using thick sol-gel films coated with stearic acid; the destruction of SA was monitored by FTIR and sudden wetting of the surface was seen to coincide with the substantial removal of the organic layer. The results of this work are discussed in the context of the current debate on the underlying cause of PSH.

Photocatalytically active gamma-WO3 films from the atmospheric pressure CVD of WOCl4 with ethyl acetate or ethanol

Communication: Coatings Of Yellow gamma-WO3 are deposited on glass by APCVD of WOCl4 and either ethanol or ethylacetate at 350-450degreesC. The yellow films show significant photoactivity for the destruction of stearic acid, and photoinduced superhydrophilicity. Preparation of blue reduced WO2.92 films from the same reaction at higher substrate temperatures of 500-600degreesC (Figure) is also found to be possible. These films show no photoactivity, but can be converted into the fully stoichiometric photoactive form simply by heating in air.

Atmospheric Pressure Chemical Vapour Deposition of thin Films of Nb2O5 on Glass

A novel route involving atmospheric pressure chemical vapour deposition (APCVD) is reported for coating Nb2O5 onto glass substrates via the reaction of NbCl5 and ethyl acetate at 400-660degreesC. Raman spectroscopy is shown to be a simple diagnostic tool for the analysis of these thin films. The contact angle of water on Nb2O5-coated glass drops on UV irradiation from 60degrees to 5-20degrees. XPS Analysis showed that the Nb:O ratio of the film was 1:2.5. Glancing angle X-ray diffraction showed that all films were crystalline, with only a single phase being observed; this has some preferred orientation in the (201) plane of Nb2O5. The niobium(V) oxide materials show minimal photocatalytic ability to degrade organic material.

Atmospheric pressure chemical vapour deposition of titanium dioxide coatings on glass

Atmospheric pressure chemical vapour deposition of titanium dioxide coatings on glass substrates was achieved by the reaction of TiCl4 and a co-oxygen source (MeOH, EtOH, (PrOH)-Pr-i or H2O) at 500-650degreesC. The coatings show excellent uniformity, surface coverage and adherence. Growth rates were of the order of 0.3 mum min(-1) at 500degreesC. All films are crystalline and single phase with XRD showing the anatase TiO2 diffraction pattern; a = 3.78(1), c = 9.51(1) Angstrom. Optically, the films show minimal reflectivity from 300-1600 nm and 50-80% total transmission from 300-800 nm. Contact angles are in the range 20-40degrees for as-prepared films and 1-10degrees after 30 min irradiation at 254 nm. All of the films show significant photocatalyic activity as regards the destruction of an overlayer of stearic acid.

Increasing the accuracy of Nitrogen Dioxide (NO2) pollution mapping using geographically weighted regression (GWR) and geostatistics.

Nitrogen Dioxide (NO2) is known to act as an environmental trigger for many respiratory illnesses. As a pollutant it is difficult to map accurately, as concentrations can vary greatly over small distances. In this study three geostatistical techniques were compared, producing maps of NO2 concentrations in the United Kingdom (UK). The primary data source for each technique was NO2 point data, generated from background automatic monitoring and background diffusion tubes, which are analysed by different laboratories on behalf of local councils and authorities in the UK. The techniques used were simple kriging (SK), ordinary kriging (OK) and simple kriging with a locally varying mean (SKlm). SK and OK make use of the primary variable only. SKlm differs in that it utilises additional data to inform prediction, and hence potentially reduces uncertainty. The secondary data source was Oxides of Nitrogen (NOx) derived from dispersion modelling outputs, at 1km x 1km resolution for the UK. These data were used to define the locally varying mean in SKlm, using two regression approaches: (i) global regression (GR) and (ii) geographically weighted regression (GWR). Based upon summary statistics and cross-validation prediction errors, SKlm using GWR derived local means produced the most accurate predictions. Therefore, using GWR to inform SKlm was beneficial in this study.