Methane and water are important trace gases in the stratosphere and by discussing their sources, sinks, chemistry and transport a case will be made for improved measurements in the lower stratosphere and upper troposphere. Various methods of measuring water vapour and methane will be described and a novel technique for measuring combustable hydrocarbons and hydrogen will be introduced. It will be demonstrated that methane and hydrogen can be catalytically oxidising into a stoiciometric amount of water vapour which can then be measured using a frost point hygrometer. The catalyst will need to be kept at ~450°C to get 100% oxidation of the available methane. The experiment results will be complimented with modelling of the oxidation process in the reactor. A laboratory instrument with suitable characteristics to form the basis of a balloon sondé will be presented as will a prototype balloon instrument.

A probe for the continuous on-line measurement of hydrogen dissolved in liquid aluminium has been developed using the perovskite proton conductor <i>CaZrO₃</i>-<i>In</i>, in conjunction with a <i>Zr,ZrH₂</i> solid state reference. The probe has been designed to an industrial prototype standard, and measurements were in good agreement with established (but cumbersome) hydrogen measurement methods such as the AISCAN analyser, LECO analysis, and the Straube-Pfeiffer technique. The electrolytic domain of <i>CaZrO₃</i>-<i>In </i>has been investigated using a novel double-cell arrangement to simultaneously fix the chemical potential of both hydrogen and oxygen at the electrodes of a pellet of the electrolyte. As predicted from the defect equilibria, the electrolyte makes the transition from the hydrogen ion conduction domain to the oxygen ion domain under conditions of low oxygen partial pressure and high hydrogen partial pressure. The <i>pO₂</i> corresponding to the <i>Zr,ZrO₂</i> equilibrium is low enough to locate <i>CaZrO₃</i>-<i>In</i> in the oxygen ion conduction domain. Sodium <i>b-</i>alumina was employed to measure the <i>pO₂</i>developed under operating conditions at the sensor reference electrode by a sample zirconium containing dissolved oxygen. This was found to be many orders of magnitude higher than the <i>pO₂</i> corresponding to the <i>Zr,ZrO₂</i> equilibrium, and was five magnitude higher than the <i>pO₂</i> marking the <i>H⁺</i>/<i>O^2-</i> conduction domain boundary for <i>CaZrO₃</i>-<i>In</i>, suggesting that <i>Zr, ZrH₂</i> may be suitable as a reference material. Hydrogen sensors manufactured using <i>CaZrO₃</i>-<i>In </i>as the solid electrolyte and a <i>Zr,ZrH₂</i> solid state reference were found to provide stable, reproducible <i>emfs </i>at constant temperature and <i>pH₂</i>, and showed full Nernstian response following a change in <i>pH₂</i> at the measuring electrode. The recently developed Current Reversal Mode can accurately determine the <i>emf </i>of a solid electrolyte sensor, and also provides additional information in the form of the sensor resistance. A detailed study has identified how the CRM parameters should be selected in order to make accurate measurements. The sensor resistance measurement was used to improve measurement accuracy and stability of an internally heated yttria stabilised zirconia oxygen sensor. When applied to a commercially available probe for measuring hydrogen dissolved in liquid aluminium it was found that erroneous <i>emf</i> readings, measured after prolonged use in the melt, were accompanied by a corresponding increase in the sensor resistance, opening up the possibility of using CRM as an on-line diagnostic tool.

Samples of Ba β-Al<SUB>2</SUB>O<SUB>3</SUB> with the stoichiometries BaAl<SUB>9</SUB>O<SUB>15 </SUB>to BaAl<SUB>14</SUB>O<SUB>22</SUB> were prepared. Mixed β-Al<SUB>2</SUB>O<SUB>3</SUB> materials consisting of Na β-Al<SUB>2</SUB>O<SUB>3</SUB> + Ba β-Al<SUB>2</SUB>O<SUB>3</SUB> or Na β-Al<SUB>2</SUB>O<SUB>3</SUB> + strontium magnetoplumbite were also produced. Some samples of Ba β-Al<SUB>2</SUB>O<SUB>3</SUB> with 12.5 wt.% zirconia added were also produced. All materials were prepared using a solid state route using Al<SUB>2</SUB>O<SUB>3 </SUB> and the relevant carbonate as the starting materials. After rationalising the calcining and sintering route for Baβ-Al<SUB>2</SUB>O<SUB>3</SUB> these materials and the mixed ionic conductors were tested by XRD, Impedance Spectroscopy and thermodynamic methods to determine the structure, phase composition or conduction characteristics. Although 2 distinct β-alumina phases (β(I) and β(II) can be identified within the BaO-xAl<SUB>2</SUB>O<SUB>3</SUB> (4.5 < x < 7) composition by XRD, galvanic cell measurements reveal only a single phase within the above composition. This can be explained if we consider β(I) and β(II) structures as part of a single phase but intergrown as stacking defects, made up of a sufficient number of unit cells within each stack to be revealed as distinct (although related) structures by XRD. A consequence of this is a decrease in conductivity and increase in activation energy from BaAl<SUB>14</SUB>O<SUB>22</SUB> (Ea = 1.8eV) to BaAl<SUB>9</SUB>O<SUB>15</SUB> (Ea = 2.3eV) with BaAl<SUB>12</SUB>O<SUB>19 </SUB>having a roughly intermediate value for both conductivity and activation energy. Thermodynamic experiments for calculating activity of Na<SUB>2</SUB>O in the mixed β-Al<SUB>2</SUB>O<SUB>3</SUB> suggest that these are single phases for both the Na-Ba and the Na-Sr systems, and that the variations of activity of Na<SUB>2</SUB>O with composition exhibit positive deviation from ideality. Despite the similarities in structures between the different β-Al<SUB>2</SUB>O<SUB>3</SUB>, it is possible to distinguish between the Na and the Baβ in the Na-Ba mixed β-Al<SUB>2</SUB>O<SUB>3</SUB> and likewise for the Na-Sr β-Al<SUB>2</SUB>O<SUB>3</SUB>. Therefore it is suggested that in mixed β-Al<SUB>2</SUB>O<SUB>3</SUB>, the two structures can intergrow by sharing the spinel blocks into unit cells large enough to be identified by XRD, yet dissolve into each other to form a single phase in the thermodynamic sense.

We have employed reflection-absorption infrared spectroscopy (RAIRS) as the principal technique as well as low energy electron diffraction (LEED) and thermal programmed desorption (TPD) as diagnostic tools to study the adsorption of CO, NO, NO/O, NO/O+N, and NO/K on Co{1010}. A novel reversible order-order phase transition is revealed by studies of a chemisorbed monolayer of CO on Co{1010} between 100 and 150 K. The high temperature phase consists of tilted 2-fold bridging CO molecules in the well established p(2x1)g structure, while the low temperature phase involves the movement of one-third of the CO molecules into 3-fold hollow sites to produce a new p(6x1)g structure. The temperature-induced site switching is attributed to a vibrational-entropy-driven secondary-order displacive phase transition. The high coverage structures of CO on Co{1010} have also been investigated over the temperature range for 100 to 250 K. This has revealed a curious anomaly. As the coverage is increased above 0.5 monolayer (ML) at temperatures below 250 K, a p(2x1) phase, with atop CO, is incompletely converted to a p(2x1) phase with a local coverage of 1 ML, and CO in bridge sites. At temperatures below 180 K, one third of the surface is converted into the energetically most stable structure, c(2x6), with Co in two types of bridge sites, local coverage1.17 ML, and the remaining two thirds remains in the p(2x1)g phase. On cooling to 100 K, the stable c(2x6) phase is unchanged, still occupying one third of the surface, and the p(2x1)g phase is transformed to a p(6x1)g phase, driven by vibrational entropy. At these low temperatures, this phase transition occurs between two ordered phases which are both metastable with respect to the high coverage (c(2x6) phase. This is attributed to kinetic constraints within the close-packed adsorbed overlayer associated with frozen-in antiphase domains. For the interaction of NO with clean Co{1010} at 100 K, NO is found to absorb molecularly on the Co{1010} surface with an estimated 0.5 ML coverage at saturation. At low coverages, three adsorption sites, on-top, two-fold and three-fold, are occupied; while from moderate coverage to saturation, bridge-bonded NO becomes dominant. A sharp c(2x4) LEED pattern is observed at saturation, and a corresponding surface structure is proposed for the pattern. For all precoverages of NO dissociation is complete on heating the surface, but the temperature at which dissociation occurs depends critically on NO coverage and on the presence of the dissociation products. TPD spectra indicate that no species other than N<SUB>2</SUB> desorbs below 630K; c(2x6) and p(2x3) LEED patterns are observed after annealing to 600 K, and removal of O adatoms by H<SUB>2</SUB> show that these are due to N adsorption. A first-order unimolecular reaction mechanism is proposed for NO dissociation on Co{1010}, with a strong dependence of the activation energy for surface dissociation on both NO coverage and the coverage of the dissociation products, N and O. For the adsorption of NO/O on Co{1010} at 100 K, the presence of oxygen adatoms greatly attenuates the occupation of two-fold sites in favour of atop sites, but O adatoms do not show any significant blocking effect for NO adsorption, and the NO coverage is close to 0.5 ML, as found on the clean surface. The coadsorption of NO with various precoverages of oxygen (0.15 - 1.0 ML) including three ordered oxygen overlayers, c(2x4) (θ ≈ 0.5 ML); p(2x1) (θ ≈ 0.5 ML) and p(2x1)-g (θ ≈ 1.0 ML) , reveals a NO-induced surface restructuring process, in which O adatoms are driven from overlayer to underlayer sites at high NO coverages, and this restructuring process increases the O effective diameter to up to ~ 10 Å.

Formaldehyde (HCHO) is a highly irritating, toxic and presumably carcinogenic chemical widely used in industry and the health-care sector. Exposure to formaldehyde in the workplace is hence an important health concern. Occupational health legislation requires employers to monitor workforce HCHO exposure at regular intervals. Methods for formaldehyde monitoring currently endorsed by the regulatory bodies are essentially laboratory based and as such, time and labor intensive. Development of simpler, more cost-effective methods which can be used in-the-field has so far been limited by the fact that most known detection techniques are not specific for formaldehyde or dependent on either exotic equipment or hazardous chemicals. This thesis describes the development of a new colorimetric method which can be used to detect formaldehyde in the 0.03 to 2ppm range. Unlike available techniques, this method is selective for HCHO and also easy and safe to use. It was discovered that 6-amino-1-napththol-3-sulfonic acid (j-acid) reacts with formaldehyde under relatively mild aqueous conditions and at room-temperature to form the easily detectable yellow dye 2,2'-bis(6-amino-1-napththol-3-sulfonic acid)methane. Dye formation was found to be specific for HCHO. Reaction with higher aldehydes and other substances is prevented sterically by the sulfonic acid groups in the C-3 position of j-acid. The kinetics of this reaction were investigated and optimal reaction conditions regarding j-acid concentration, pH and temperature were determined. It was discovered that the mechanism of the reaction is complicated by a reversible side-reaction which is competing for available HCHO. Ways to improve the j-acid reaction were investigated. Eight j-acid derivatives were synthesised and tested. None of these compounds was found to be reactive at the same mild conditions used with j-acid. Two compounds, however, 6-N-acetylamino-1-naphthol-3-sulfonic acid and 6-N-methyl-amino-1-naphthol-3-sulfonic acid where identified which can be used in acid (1M HCl and above). With those compounds, dyes with a higher extinction coefficient are formed. Based on the j-acid reaction a new analytical device for the detection of gaseous HCHO was developed. This device utilises an optical technique called attenuated reflection spectroscopy and was built using solid state optoelectronics.

Laser and optical emission spectroscopies have been employed to study the gas phase chemistry in the growth environment for diamond chemical vapour deposition (CVO) in a microwave (MW) reactor. Computational investigations have also been used to explore the energetics of elementary reactions on a diamond surface, to give insight into which species are likely to incorporate into a growing diamond film. The focus of this thesis is on 0 and N containing CIH plasmas.

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