Concentration and oxidative potential of on-road particle emissions and their relationship with traffic composition : Relevance to exposure assessment

Particles emitted by vehicles are known to cause detrimental health effects, with their size and oxidative potential among the main factors responsible. Therefore, understanding the relationship between traffic composition and both the physical characteristics and oxidative potential of particles is critical. To contribute to the limited knowledge base in this area, we investigated this relationship in a 4.5 km road tunnel in Brisbane, Australia. On-road concentrations of ultrafine particles (<100 nm, UFPs), fine particles (PM2.5), CO, CO2 and particle associated reactive oxygen species (ROS) were measured using vehicle-based mobile sampling. UFPs were measured using a condensation particle counter and PM2.5 with a DustTrak aerosol photometer. A new profluorescent nitroxide probe, BPEAnit, was used to determine ROS levels. Comparative measurements were also performed on an above-ground road to assess the role of emission dilution on the parameters measured. The profile of UFP and PM2.5 concentration with distance through the tunnel was determined, and demonstrated relationships with both road gradient and tunnel ventilation. ROS levels in the tunnel were found to be high compared to an open road with similar traffic characteristics, which was attributed to the substantial difference in estimated emission dilution ratios on the two roadways. Principal component analysis (PCA) revealed that the levels of pollutants and ROS were generally better correlated with total traffic count, rather than the traffic composition (i.e. diesel and gasoline-powered vehicles). A possible reason for the lack of correlation with HDV, which has previously been shown to be strongly associated with UFPs especially, was the low absolute numbers encountered during the sampling. This may have made their contribution to in-tunnel pollution largely indistinguishable from the total vehicle volume. For ROS, the stronger association observed with HDV and gasoline vehicles when combined (total traffic count) compared to when considered individually may signal a role for the interaction of their emissions as a determinant of on-road ROS in this pilot study. If further validated, this should not be overlooked in studies of on- or near-road particle exposure and its potential health effects.

Meaningful musical engagement : the potential impact of generative music systems on learning experiences

In order to create music, the student must establish a relationship with the musical materials. In this thesis, I examine the capacity of a generative music system called jam2jam to offer individuals a virtual musical play-space to explore. I outline the development of an iteration of software development named jam2jam blue and the evolution of a games-like user interface in the research design that jointly revealed the nature of this musical exploration. The findings suggest that the jam2jam blue interface provided an expressive gestural instrument to jam and experience musicmaking. By using the computer as an instrument, participants in this study were given access to meaningful musical experiences in both solo and ensemble situations and the researcher is allowed a view of their development of a relationship with the musical materials from the perspective of the individual participants. Through an iterative software development methodology, pedagogy and experience design were created simultaneously. The research reveals the potential for the jam2jam software to be used as a reflective tool for feedback and assessment purposes. The power of access to ensemble music making is realised though the participants’ virtual experiences which are brought into their physical space by sharing their experience with others. It is suggested that this interaction creates an environment conducive to self-initiated learning in which music is the language of interaction. The research concludes that the development of a relationship between the explorer and the musical materials is subject to the collaborative nature of the interaction through which the music is experienced.

Removal of toxic metals in a multi metal system using sorbents for potential application to urban stormwater treatment

In the context of increasing demand for potable water and the depletion of water resources, stormwater is a logical alternative. However, stormwater contains pollutants, among which metals are of particular interest due to their toxicity and persistence in the environment. Hence, it is imperative to remove toxic metals in stormwater to the levels prescribed by drinking water guidelines for potable use. Consequently, various techniques have been proposed, among which sorption using low cost sorbents is economically viable and environmentally benign in comparison to other techniques. However, sorbents show affinity towards certain toxic metals, which results in poor removal of other toxic metals. It was hypothesised in this study that a mixture of sorbents that have different metal affinity patterns can be used for the efficient removal of a range of toxic metals commonly found in stormwater. The performance of six sorbents in the sorption of Al, Cr, Cu, Pb, Ni, Zn and Cd, which are the toxic metals commonly found in urban stormwater, was investigated to select suitable sorbents for creating the mixtures. For this purpose, a multi criteria analytical protocol was developed using the decision making methods: PROMETHEE (Preference Ranking Organisation METHod for Enrichment Evaluations) and GAIA (Graphical Analysis for Interactive Assistance). Zeolite and seaweed were selected for the creation of trial mixtures based on their metal affinity pattern and the performance on predetermined selection criteria. The metal sorption mechanisms employed by seaweed and zeolite were defined using kinetics, isotherm and thermodynamics parameters, which were determined using the batch sorption experiments. Additionally, the kinetics rate-limiting steps were identified using an innovative approach using GAIA and Spearman correlation techniques developed as part of the study, to overcome the limitation in conventional graphical methods in predicting the degree of contribution of each kinetics step in limiting the overall metal removal rate. The sorption kinetics of zeolite was found to be primarily limited by intraparticle diffusion followed by the sorption reaction steps, which were governed mainly by the hydrated ionic diameter of metals. The isotherm study indicated that the metal sorption mechanism of zeolite was primarily of a physical nature. The thermodynamics study confirmed that the energetically favourable nature of sorption increased in the order of Zn < Cu < Cd < Ni < Pb < Cr < Al, which is in agreement with metal sorption affinity of zeolite. Hence, sorption thermodynamics has an influence on the metal sorption affinity of zeolite. On the other hand, the primary kinetics rate-limiting step of seaweed was the sorption reaction process followed by intraparticle diffusion. The boundary layer diffusion was also found to limit the metal sorption kinetics at low concentration. According to the sorption isotherm study, Cd, Pb, Cr and Al were sorbed by seaweed via ion exchange, whilst sorption of Ni occurred via physisorption. Furthermore, ionic bonding is responsible for the sorption of Zn. The thermodynamics study confirmed that sorption by seaweed was energetically favourable in the order of Zn < Cu < Cd < Cr . Al < Pb < Ni. However, this did not agree with the affinity series derived for seaweed suggesting a limited influence of sorption thermodynamics on metal affinity for seaweed. The investigation of zeolite-seaweed mixtures indicated that mixing sorbents have an effect on the kinetics rates and the sorption affinity. Additionally, the theoretical relationships were derived to predict the boundary layer diffusion rate, intraparticle diffusion rate, the sorption reaction rate and the enthalpy of mixtures based on that of individual sorbents. In general, low coefficient of determination (R2) for the relationships between theoretical and experimental data indicated that the relationships were not statistically significant. This was attributed to the heterogeneity of the properties of sorbents. Nevertheless, in relative terms, the intraparticle diffusion rate, sorption reaction rate and enthalpy of sorption had higher R2 values than the boundary layer diffusion rate suggesting that there was some relationship between the former set of parameters of mixtures and that of sorbents. The mixture, which contained 80% of zeolite and 20% of seaweed, showed similar affinity for the sorption of Cu, Ni, Cd, Cr and Al, which was attributed to approximately similar sorption enthalpy of the metal ions. Therefore, it was concluded that the seaweed-zeolite mixture can be used to obtain the same affinity for various metals present in a multi metal system provided the metal ions have similar enthalpy during sorption by the mixture.

Studies on the surface properties of biodegradable polymer carriers in respiratory delivery of drug from Dry Powder Inhaler formulations

Dry Powder Inhaler (DPI) technology has a significant impact in the treatment of various respiratory disorders. DPI formulations consist of a micronized drug (<5ìm) blended with an inert coarse carrier, for which lactose is widely used to date. DPIs are one of the inhalation devices which are used to target the delivery of drugs to the lungs. Drug delivery via DPI formulations is influenced by the physico-chemical characteristics of lactose particles such as size, shape, surface roughness and adhesional forces. Commercially available DPI formulations, which utilise lactose as the carrier, are not efficient in delivering drug to the lungs. The reasons for this are the surface morphology, adhesional properties and surface roughness of lactose. Despite several attempts to modify lactose, the maximum efficient drug delivery to the lungs remains limited; hence, exploring suitable alternative carriers for DPIs is of paramount importance. Therefore, the objective of the project was to study the performance of spherical polymer microparticles as drug carriers and the factors controlling their performance. This study aimed to use biodegradable polymer microspheres as alternative carriers to lactose in DPIs for achieving efficient drug delivery into the lungs. This project focused on fabricating biodegradable polymer microparticles with reproducible surface morphology and particle shape. The surface characteristics of polymeric carriers and the adhesional forces between the drug and carrier particles were investigated in order to gain a better understanding of their influence on drug dispersion. For this purpose, two biodegradable polymers- polycaprolactone (PCL) and poly (DL-lactide-co-glycolide) (PLGA) were used as the carriers to deliver the anti-asthmatic drug - Salbutamol Sulphate (SS). The first study conducted for this dissertation was the aerosolization of SS from mixtures of SS and PCL or PLGA microparticles. The microparticles were fabricated using an emulsion technique and were characterized by laser diffraction for particle size analysis, Scanning Electron Microscopy (SEM) for surface morphology and X-ray Photoelectron Spectroscopy (XPS) to obtain surface elemental composition. The dispersion of the drug from the DPI formulations was determined by using a Twin Stage Impinger (TSI). The Fine particle Fraction (FPF) of SS from powder mixtures was analyzed by High Performance Liquid Chromatography (HPLC). It was found that the drug did not detach from the surface of PCL microspheres. To overcome this, the microspheres were coated with anti-adherent agents such as magnesium stearate and leucine to improve the dispersion of the drug from the carrier surfaces. It was found that coating the PCL microspheres helped in significantly improving the FPF of SS from the PCL surface. These results were in contrast to the PLGA microspheres which readily allowed detachment of the SS from their surface. However, coating PLGA microspheres with antiadherent agents did not further improve the detachment of the drug from the surface. Thus, the first part of the study demonstrated that the surface-coated PCL microspheres and PLGA microspheres can be potential alternatives to lactose as carriers in DPI formulations; however, there was no significant improvement in the FPF of the drug. The second part of the research studied the influence of the size of the microspheres on the FPF of the drug. For this purpose, four different sizes (25 ìm, 48 ìm, 100 ìm and 150 ìm) of the PCL and PLGA microspheres were fabricated and characterized. The dispersion of the drug from microspheres of different sizes was determined. It was found that as the size of the carrier increased there was a significant increase in the FPF of SS. This study suggested that the size of the carrier plays an important role in the dispersion of the drug from the carrier surface. Subsequent experiments in the third part of the dissertation studied the surface properties of the polymeric carrier. The adhesion forces existing between the drug particle and the polymer surfaces, and the surface roughness of the carriers were quantified using Atomic Force Microscopy (AFM). A direct correlation between adhesion forces and dispersion of the drug from the carrier surface was observed suggesting that adhesion forces play an important role in determining the detachment potential of the drug from the carrier surface. However, no direct relationship between the surface roughness of the PCL or PLGA carrier and the FPF of the drug was observed. In conclusion, the body of work presented in this dissertation demonstrated the potential of coated PCL microspheres and PLGA microspheres to be used in DPI formulations as an alternative carrier to sugar based carriers. The study also emphasized the role of the size of the carrier particles and the forces of interaction prevailing between the drug and the carrier particle surface on the aerosolization performances of the drug.

Identifying familiarity to facilitate intuitive interaction for older adults

Almost every nation on the planet is experiencing increases in both the number and proportion of older adults. Research has shown that older adults use technology less intuitively than younger adults, and have more difficulty with using products effectively. With an ever-increasing population of older adults, it is necessary to understand why they often struggle to use technology, which is becoming more and more important in day to day living. Intuitive use of products is grounded in familiarity and prior experience. The aims of this research were twofold: (i) to examine the differences in familiarity between younger and older adults, to see if this could explain the difficulties faced by some older adults; (ii) to develop investigational methods to assist designers in identifying familiarity in prospective users. Two empirical studies were conducted. The first experiment was conducted in the field with 32 participants, divided across four age groups (18 – 44, 45 – 59, 60 – 74, and 75+). This experiment was conducted in the participants’ homes, with a product they were familiar with. Familiarity was measured through the analysis of data collected through interviews, observation and retrospective protocol. The results of this study show that the youngest group demonstrated significantly higher levels of familiarity with products they own than the 60 – 74 and the 75+ age groups. There were no significant differences between the 18 – 44 age group and the 45 – 59 age group and there were also no significant differences between the three oldest age groups. The second experiment was conducted with 32 participants, across the same four age groups. Four everyday products were used in this experiment. The results of Experiment 2 show that, with previously unused products, younger adults demonstrate significantly higher levels of familiarity than the three older age groups. The three oldest age groups had no significant differences between them. The results of these two studies show that younger adults are more familiar with contemporary products than older adults. They also demonstrate that in terms of familiarity, older adults do not differ significantly as they get older. The results also show that the 45 – 59 age group demonstrate higher levels of familiarity with products they have owned, in comparison with those they have not. The two older age groups did not demonstrate such differences. This suggests that interacting with products over time increases familiarity more for middle-aged adults than for older adults. As a result of this research, a method that can be used by designers to identify potential users’ product familiarity has been identified. This method is easy to use, quick, low cost, highly mobile, flexible, and allows for easy data collection and analysis. A tool has been designed that assists designers and researchers to use the method. Designers can use the knowledge gained from this tool, and integrate it into the design process, resulting in more intuitive products. Such products may lead to improvements in the quality of life of older adults, as a result of improved societal integration, better health management, and more widespread use of communications technology.

The potential influence of Neoliberalism on the capacity and form of spatial adaptation

Human spatial environments must adapt to climate change. Spatial planning is central to climate change adaptation and potentially well suited to the task, however neoliberal influences and trends threaten this capacity. This paper explores the potential interaction of emerging research areas, the first of which pursues climate change adaptation through spatial planning and the second of which has observed the neoliberalisation of urban planning, The potential capacity and form of spatial adaptation within the context a planning environment influenced by neoliberal principles is evaluated. This influence relates to the themes of spatial scale, temporal scale, responsibility for action, strategies and mechanisms, accrual of benefits, negotiation of priorities and approach to uncertainty. This paper presents a conceptual framework of the influence of neoliberalism on spatial adaptation and presents examples of this approach in documents which underpin adaptation in Australia. It identifies the potential characteristics and the challenges and opportunities of spatial adaptation under a neoliberal frame. The neoliberal frame does not entirely preclude spatial adaptation but significantly influence its form. Neoliberal approaches involve individual action in response to private incentives and near term impacts while collective action, regulatory mechanisms and long term planning is approached cautiously. Challenges concern the degree to which collective action and a long term orientation are necessary, how individual adaptation relates to collective vulnerability and the prioritisation of adaptation by markets. Opportunities might involve the operability of individual and local adaptation, the existence of private incentives to adapt and the potential to align adaptation with entrepreneurial projects.

Emergent participant interaction

Emergence has the potential to effect complex, creative or open-ended interactions and novel game-play. We report on research into an emergent interactive system. This investigates emergent user behaviors and experience through the creation and evaluation of an interactive system. The system is +-NOW, an augmented reality, tangible, interactive art system. The paper briefly describes the qualities of emergence and +-NOW before focusing on its evaluation. This was a qualitative study with 30 participants conducted in context. Data analysis followed Grounded Theory Methods. Coding schemes, induced from data and external literature are presented. Findings show that emergence occurred in over half of the participants. The nature of these emergent behaviors is discussed along with examples from the data. Other findings indicate that participants found interaction with the work satisfactory. Design strategies for facilitating satisfactory experience despite the often unpredictable character of emergence, are briefly reviewed and potential application areas for emergence are discussed.

Selective reductions using visible light photocatalysts of supported gold nanoparticles

Photocatalytic synthesis using visible light is a desirable chemical process because of its potential to utilize sunlight. Supported gold nanoparticles (Au-NPs) were found to be efficient photocatalysts and the effects of the supports were identified including CeO2, TiO2, ZrO2, Al2O3, and zeolite Y. In particular Au/CeO2 exhibited the high catalytic activity to reduce nitroaromatics to azo compounds, hydrogenate azobenzene to hydroazobenzene, reduce ketones to alcohols, and deoxygenate epoxides to alkenes at ambient temperatures, under irradiation of visible light (or simulated sunlight). The reac-tive efficiency depends on two primary factors: one is the light adsorption of catalysts and another is the driving ability of catalysts corresponding to the reactants. The light absorption by Au-NPs is due to surface plasmon resonance effect or inter-band electron transition; this is related to the reduction ability of the photocatalysts. Irradiation with shorter wavelengths can excite the conduction electrons in Au-NPs to higher energy levels and as a result, induce reduction with more negative reduction potentials. It is known when irradiated with light the Au-NPs can abstract hydrogen from isopropanol forming Au-H species on the Au-NP surface. Hence, we proposed that the active Au-H species will react with the N=O, N=N, C=O double bonds or epoxide bonds, which are weakened by the interaction with the excited electrons in the Au-NPs, and yield the final reductive products. The reacting power of the Au-H species depends on the energy of the excited electrons in Au-NPs: the higher the electronic energy, the stronger the reduction ability of the Au-H species. This finding demonstrates that we can tune the reduction ability of the photocatalysts by manipulating the irradiation wavelength.

Cryo-electron tomography of Marburg Virus particles and their morphogenesis within infected cells

Several major human pathogens, including the filoviruses, paramyxoviruses, and rhabdoviruses, package their single-stranded RNA genomes within helical nucleocapsids, which bud through the plasma membrane of the infected cell to release enveloped virions. The virions are often heterogeneous in shape, which makes it difficult to study their structure and assembly mechanisms. We have applied cryo-electron tomography and sub-tomogram averaging methods to derive structures of Marburg virus, a highly pathogenic filovirus, both after release and during assembly within infected cells. The data demonstrate the potential of cryo-electron tomography methods to derive detailed structural information for intermediate steps in biological pathways within intact cells. We describe the location and arrangement of the viral proteins within the virion. We show that the N-terminal domain of the nucleoprotein contains the minimal assembly determinants for a helical nucleocapsid with variable number of proteins per turn. Lobes protruding from alternate interfaces between each nucleoprotein are formed by the C-terminal domain of the nucleoprotein, together with viral proteins VP24 and VP35. Each nucleoprotein packages six RNA bases. The nucleocapsid interacts in an unusual, flexible "Velcro-like" manner with the viral matrix protein VP40. Determination of the structures of assembly intermediates showed that the nucleocapsid has a defined orientation during transport and budding. Together the data show striking architectural homology between the nucleocapsid helix of rhabdoviruses and filoviruses, but unexpected, fundamental differences in the mechanisms by which the nucleocapsids are then assembled together with matrix proteins and initiate membrane envelopment to release infectious virions, suggesting that the viruses have evolved different solutions to these conserved assembly steps.

Negotiating teacher identities : dialogic reflections on classroom interaction in a transnational context

This study investigates the development of teacher identity in a transnational context through an analysis of the voices of sixteen preservice teachers from Hong Kong who engage in interaction with primary students in an Australian classroom. The context for this research is the school-based experience undertaken by these preservice English as a second language teachers as part of their short language immersion (SLIM) program in Brisbane, Australia. Such SLIM programs are a genre of study abroad programs which have been gaining in popularity within teacher education in Australia, attended by preservice and inservice teachers from China, Hong Kong, Korea, and other Asian countries. This research is conducted at a time when the imperative to globalise higher education provision is a strategic factor in the educational policies of both Australia and Hong Kong. In Australia, international educational services now constitute the country’s third largest export with more than 400,000 students coming to Australia to study annually. In order to maintain Australia’s current global position as the third most popular Englishspeaking study destination, the government is now focusing on sustainability and the quality of the study experience being offered to international students (Bradley Review, 2008). In Hong Kong, the government sponsors both preservice and inservice English as a second language (ESL) teachers to undertake SLIM programs in Australia and other English-speaking countries, as part of their policy of promoting high levels of English proficiency in Hong Kong classrooms. Transnational teacher education is an important issue to which this study contributes insights into the affordances and constraints of a school-based experience in the transnational context. Second language teacher education has been defined as interventions designed to develop participants’ professional knowledge. In this study, it is argued that participation in a different community of practice helps to foreground tacit theories of second language pedagogy, making them visible and open to review. Questions of pedagogy are also seen as questions of teacher identity, constituting the way that one is in the classroom. I take up a sociocultural and poststructural framework, drawing on the work of James Gee and Mikhail Bakhtin, to theorise the construction of teacher identity as emerging through dialogic relations and socially situated discursive practices. From this perspective, this study investigates whether these teachers engage with different ways of representing themselves through appropriating, adapting or rejecting Discourses prevailing in the Australian classroom. Research suggests that reflecting on dilemmas encountered as lived experiences can extend professional understandings. In this study, the participants engage in a process of dialogic reflection on their intercultural classroom interactions, examining with their peers and their lecturer/researcher selected moments of dissonance that they have faced in the unfamiliar context of an Australian primary classroom. It is argued that the recursive and multivoiced nature of this process of reflection on practice allows participants opportunities to negotiate new understandings of second language teacher identity. Dialogic learning, based on the theories of Bakhtin and Vygotsky, provides the theoretic framing not only for the process of reflection instantiated in this study, but also features in the analysis of the participants’ second language classroom practices. The research design uses a combined discourse analytic and ethnographic approach as a logic-of-inquiry to explore the dialogic relationships which these second language teachers negotiate with their students and their peers in the transnational context. In this way, through discourse analysis of their classroom talk and reflective dialogues, assisted by the analytic tools of speech genres and discourse formats, I explore the participants’ ways of doing and being second language teachers. Thus, this analysis traces the process of ideological becoming of these beginner teachers as shifts in their understandings of teacher and student identities. This study also demonstrates the potential for a nontraditional stimulated recall interview to provide dialogic scaffolding for beginner teachers to reflect productively on their practice.

Electron microscopy of stratospheric particles

A recent NASA program to collect stratospheric dust particles using high-flying WB57 aircraft has made available many more potential candidates for the study of extraterrestrial materials. This preliminary report provides an interpretation of the types of particles returned from one flag (W7017) collected in August, 1981 using a subset of 81 allocated particles. This particular collection period is after the Mt. St. Helen's eruptions. Therefore, the flag may contain significant quantities of volcanic debris in addition to the expected terrestrial contaminants [1]. All particles were mounted on nucleopore filters and have been examined using a modified JEOL100CX analytical electron microscope. For most of the particles, X-ray energy dispersive spectra and images were obtained at 40kV on samples which have not received any conductive coating. However, in order to improve resolution (to ~30A) some images are recorded at 100kV. In addition, 16 samples have been coated with a thin layer (<50A) of Au/Pd.

Antiproton induced DNA damage : proton like in flight, carbon-ion light near rest

Biological validation of new radiotherapy modalities is essential to understand their therapeutic potential. Antiprotons have been proposed for cancer therapy due to enhanced dose deposition provided by antiproton-nucleon annihilation. We assessed cellular DNA damage and relative biological effectiveness (RBE) of a clinically relevant antiproton beam. Despite a modest LET (~19 keV/μm), antiproton spread out Bragg peak (SOBP) irradiation caused significant residual γ-H2AX foci compared to X-ray, proton and antiproton plateau irradiation. RBE of ~1.48 in the SOBP and ~1 in the plateau were measured and used for a qualitative effective dose curve comparison with proton and carbon-ions. Foci in the antiproton SOBP were larger and more structured compared to X-rays, protons and carbon-ions. This is likely due to overlapping particle tracks near the annihilation vertex, creating spatially correlated DNA lesions. No biological effects were observed at 28–42 mm away from the primary beam suggesting minimal risk from long-range secondary particles.

In situ observation of structural changes in polycrystalline silver catalysts by environmental scanning electron microscopy

Morphology changes induced in polycrystalline silver catalysts as a result of heating in either oxygen, water or oxygen-methanol atmospheres have been investigated by environmental scanning electron microscopy (ESEM), FT-Raman spectroscopy and temperature programmed desorption (TPD). The silver catalyst of interest consisted of two distinct particle types, one of which contained a significant concentration of sub-surface hydroxy species (in addition to surface adsorbed atomic oxygen). Heating the sample to 663 K resulted in the production of 'pin-holes' in the silver structure as a consequence of near-surface explosions caused by sub-surface hydroxy recombination. Furthermore, 'pin-holes' were predominantly found in the vicinity of surface defects, such as platelets and edge structures. Reaction between methanol and oxygen also resulted in the formation of 'pin-holes' in the silver surface, which were inherently associated with the catalytic process. A reaction mechanism is suggested that involves the interaction of methanol with sub-surface oxygen species to form sub-surface hydroxy groups. The sub-surface hydroxy species subsequently erupt through the silver surface to again produce 'pin-holes'.

A combined environmental scanning electron microscopy and Raman microscopy study of methanol oxidation on silver(I) oxide

The techniques of environmental scanning electron microscopy (ESEM) and Raman microscopy have been used to respectively elucidate the morphological changes and nature of the adsorbed species on silver(I) oxide powder, during methanol oxidation conditions. Heating Ag2O in either water vapour or oxygen resulted firstly in the decomposition of silver(I) oxide to polycrystalline silver at 578 K followed by sintering of the particles at higher temperature. Raman spectroscopy revealed the presence of subsurface oxygen and hydroxyl species in addition to surface hydroxyl groups after interaction with water vapour. Similar species were identified following exposure to oxygen in an ambient atmosphere. This behaviour indicated that the polycrystalline silver formed from Ag2O decomposition was substantially more reactive than silver produced by electrochemical methods. The interaction of water at elevated temperatures subsequent to heating silver(I) oxide in oxygen resulted in a significantly enhanced concentration of subsurface hydroxyl species. The reaction of methanol with Ag2O at high temperatures was interesting in that an inhibition in silver grain growth was noted. Substantial structural modification of the silver(I) oxide material was induced by catalytic etching in a methanol/air mixture. In particular, "pin-hole" formation was observed to occur at temperatures in excess of 773 K, and it was also recorded that these "pin- holes" coalesced to form large-scale defects under typical industrial reaction conditions. Raman spectroscopy revealed that the working surface consisted mainly of subsurface oxygen and surface Ag=O species. The relative lack of sub-surface hydroxyl species suggested that it was the desorption of such moieties which was the cause of the "pin-hole" formation.

In situ imaging of catalytic etching on silver during methanol oxidation conditions by environmental scanning electron microscopy

Polycrystalline silver is used to catalytically oxidise methanol to formaldehyde. This paper reports the results of extensive investigations involving the use of environmental scanning electron microscopy (ESEM) to monitor structural changes in silver during simulated industrial reaction conditions. The interaction of oxygen, nitrogen, and water, either singly or in combination, with a silver catalyst at temperatures up to 973 K resulted in the appearance of a reconstructed silver surface. More spectacular was the effect an oxygen/methanol mixture had on the silver morphology. At a temperature of ca. 713 K pinholes were created in the vicinity of defects as a consequence of subsurface explosions. These holes gradually increased in size and large platelet features were created. Elevation of the catalyst temperature to 843 K facilitated the wholescale oxygen induced restructuring of the entire silver surface. Methanol reacted with subsurface oxygen to produce subsurface hydroxyl species which ultimately formed water in the subsurface layers of silver. The resultant hydrostatic pressure forced the silver surface to adopt a "hill and valley" conformation in order to minimise the surface free energy. Upon approaching typical industrial operating conditions widespread explosions occurred on the catalyst and it was also apparent that the silver surface was extremely mobile under the applied conditions. The interaction of methanol alone with silver resulted in the initial formation of pinholes primarily in the vicinity of defects, due to reaction with oxygen species incorporated in the catalyst during electrochemical synthesis. However, dramatic reduction in the hole concentration with time occurred as all the available oxygen became consumed. A remarkable correlation between formaldehyde production and hole concentration was found.