Detection of explosive markers using zeolite modified gas sensors

Detection of hidden explosive devices is a key priority for security and defence personnel around the globe. Electronic noses, based on metal oxide semiconductors (MOS), are a promising technology for creating inexpensive, portable and sensitive devices for such a purpose. An array of seven MOS gas sensors was fabricated by screen printing, based on WO3 and In2O3 inks. The sensors were tested against six gases, including four explosive markers: nitromethane, DMNB (2,3-dimetheyl-2,3-dinitrobutane), 2-ethylhexanol and ammonia. The gases were successfully detected with good sensitivity and selectivity from the array. Sensitivity was improved by overlaying or admixing the oxides with two zeolites, H-ZSM-5 and TS-1, and each showed improved responses to –NO2 and –OH moieties respectively. Admixtures in particular showed promise, with excellent sensitivity and good stability to humidity. Machine learning techniques were applied to a subset of the data and could accurately classify the gases detected, even when confounding factors were introduced

Variation of Thermochromic Glazing Systems Transition Temperature, Hysteresis Gradient and Width Effect on Energy Efficiency

Due to increasing pressure to reduce the energy demand in buildings, thermochromic thin film based glazing has become a recognized potential solution due to the intrinsic ability to modulate the solar heat gain of a window as a function of the materials temperature. These “intelligent” glazings have been investigated for several years, and it has been found that, through variation of synthetic route, the thermochromic properties (transition temperature, hysteresis gradient and width) can be altered; however, less attention has been applied to how such alterations affect the overall energy savings attributed to the materials. In this study the building simulation software EnergyPlus TM has been used to model a series of idealized thermochromic spectra in a series of different environments to evaluate their energy saving potential against both clear glass systems and industry standards. The idealized spectra are used to see what effect each of the materials thermochromic properties and therefore elucidate which are the most important with respect to the energy saving properties. It was found that the best thermochromic materials were those with a narrow sharp hysteresis and a low transition temperature and result in an increase in energy saving between 30%–45% across the different environments compared to clear glass systems

The effect of transition hysteresis width in thermochromic glazing systems

Thermochromic glazing theoretically has the potential to lead to a large reduction in energy demand in modern buildings by allowing the transmission of visible light for day lighting whilst reducing unwanted solar gain during the cooling season, but allowing useful solar gain in the heating season. In this study building simulation is used to examine the effect of the thermochromic transition hysteresis width on the energy demand characteristics of a model system in a variety of climates. The results are also compared against current industry standard glazing products. The results suggest that in a warm climate with a low transition temperature and hysteresis width energy demand can be reduced by up to 54% compared to standard double glazing

Metal Oxide Semi-Conductor Gas Sensors in Environmental Monitoring

Metal oxide semiconductor gas sensors are utilised in a variety of different roles and industries. They are relatively inexpensive compared to other sensing technologies, robust, lightweight, long lasting and benefit from high material sensitivity and quick response times. They have been used extensively to measure and monitor trace amounts of environmentally important gases such as carbon monoxide and nitrogen dioxide. In this review the nature of the gas response and how it is fundamentally linked to surface structure is explored. Synthetic routes to metal oxide semiconductor gas sensors are also discussed and related to their affect on surface structure. An overview of important contributions and recent advances are discussed for the use of metal oxide semiconductor sensors for the detection of a variety of gases—CO, NOx, NH3 and the particularly challenging case of CO2. Finally a description of recent advances in work completed at University College London is presented including the use of selective zeolites layers, new perovskite type materials and an innovative chemical vapour deposition approach to film deposition

Chemical vapour deposition of metal oxides and phosphides.

This thesis investigates the deposition of thin films of main group metal phosphide and main group metal oxide compounds on glass substrates by the use of dual source atmospheric pressure chemical vapour deposition. Binary phosphide systems with tin, germanium, silicon, antimony, copper or boron have been examined. Binary oxide systems of gallium, antimony, tin or niobium have also been investigated. Additionally these systems were deposited on gas sensor substrates and evaluated as metal oxide semiconductor gas sensors. Halides were used as the metal precursor, RXPH3.X (R = Cychex or Phenyl) were used as phosphorous precursors and either methanol or ethyl acetate were used as oxygen precursors. These coatings showed good uniformity and coverage and the films were adherent passing the Scotch tape test. The tin phosphide films were opaque in appearance with some signs of birefringence due to differential thickness effects. Germanium phosphide and the gallium, antimony, niobium and tin oxide systems were all transparent, once again birefringence was observed. The films produced from the antimony phosphide and silicon phosphide systems were opaque, grey and metallic. Additional work was conducted on the deposition on a variety of alkali metal and alkaline earth metal fluorides on glass substrates using aerosol assisted chemical vapour deposition. In all cases the films were very powdery and were easily wiped off of the substrate. A number of depositions were carried out combining the aerosol and atmospheric pressure methodologies. A tin oxide film was produced from the atmospheric pressure chemical vapour deposition reaction of tin tetrachloride and ethyl acetate. The film contained tungsten, which was introduced into the reaction using a polyoxometalate delivered via aerosol assisted chemical vapour deposition. Films were analysed using Raman microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive analysis of X-rays, electron probe microanalysis, X-ray photoelectron spectroscopy and ultra violet and visible spectroscopy

A study of corruption using the Institutional Analysis and Development framework with an application to the bidding phase of infrastructure procurement

Infrastructure projects are particularly vulnerable to corruption due to the complexity of processes and relationships between private and public entities, and the large-value contracts involved. Corrupt agreements can affect any phase of an infrastructure project, and the outcomes include reduced competition, poor-quality construction or infrastructure that does not meet value-for-money criteria. This PhD thesis brings together insights from economics, sociology and psychology to develop a broad framework of corruption with the focus on individuals, their actions and the settings in which corruption occurs. This framework is then applied to the bidding phase of physical infrastructure procurement. The method used to consolidate and analyse disparate theories and models of corruption across different disciplines is Elinor Ostrom’s Institutional Analysis and Development framework. Key variables of the corruption phenomenon are identified and organised using the IAD framework, and two models are developed. The first is a game-theoretic model analysing the importance of social networks and trust between corrupt partners and the intermediaries who facilitate corrupt exchanges. The second is a simulation model of decision-making processes in corrupt agreements based on a conflict of social norms and individual self-interest. The second model proposes a method of linking legitimacy of institutions, group behaviour status quo, and social network connections, with selfseeking behaviour. Case studies are then developed based on documents filed to support prosecutions under the US Foreign Corrupt Practices Act 1977. The proposed methods of corruption reduction are based on organisational controls and collectiveaction methods

Thin films for advanced glazing applications

© 2016 by the authors.Functional thin films provide many opportunities for advanced glazing systems. This can be achieved by adding additional functionalities such as self-cleaning or power generation, or alternately by providing energy demand reduction through the management or modulation of solar heat gain or blackbody radiation using spectrally selective films or chromogenic materials. Self-cleaning materials have been generating increasing interest for the past two decades. They may be based on hydrophobic or hydrophilic systems and are often inspired by nature, for example hydrophobic systems based on mimicking the lotus leaf. These materials help to maintain the aesthetic properties of the building, help to maintain a comfortable working environment and in the case of photocatalytic materials, may provide external pollutant remediation. Power generation through window coatings is a relatively new idea and is based around the use of semi-transparent solar cells as windows. In this fashion, energy can be generated whilst also absorbing some solar heat. There is also the possibility, in the case of dye sensitized solar cells, to tune the coloration of the window that provides unheralded external aesthetic possibilities. Materials and coatings for energy demand reduction is highly desirable in an increasingly energy intensive world. We discuss new developments with low emissivity coatings as the need to replace scarce indium becomes more apparent. We go on to discuss thermochromic systems based on vanadium dioxide films. Such systems are dynamic in nature and present a more sophisticated and potentially more beneficial approach to reducing energy demand than static systems such as low emissivity and solar control coatings. The ability to be able to tune some of the material parameters in order to optimize the film performance for a given climate provides exciting opportunities for future technologies. In this article, we review recent progress and challenges in these areas and provide a perspective for future trends and developments.Işıl Top thanks TUBITAK for the provision of funding for a studentship. Shuqun Chen thanks the China Scholarship Council for the provision of a studentship

Optimal feature selection for classifying a large set of chemicals using metal oxide sensors

Using linear support vector machines, we investigated the feature selection problem for the application of all-against-all classification of a set of 20 chemicals using two types of sensors, classical doped tin oxide and zeolite-coated chromium titanium oxide sensors. We defined a simple set of possible features, namely the identity of the sensors and the sampling times and tested all possible combinations of such features in a wrapper approach. We confirmed that performance is improved, relative to previous results using this data set, by exhaustive comparison of these feature sets. Using the maximal number of different sensors and all available data points for each sensor does not necessarily yield the best results, even for the large number of classes in this problem. We contrast this analysis, using exhaustive screening of simple feature sets, with a number of more complex feature choices and find that subsampled sets of simple features can perform better. Analysis of potential predictors of classification performance revealed some relevance of clustering properties of the data and of correlations among sensor responses but failed to identify a single measure to predict classification success, reinforcing the relevance of the wrapper approach used. Comparison of the two sensor technologies showed that, in isolation, the doped tin oxide sensors performed better than the zeolite-coated chromium titanium oxide sensors but that mixed arrays, combining both technologies, performed best