The aim of this thesis is to investigate the effects of interstellar processing using presolar samples. Dust in the interstellar medium is predicted to have experienced grain-grain and grain-gas collisions, cosmic-ray bombardment, or the formation of ices on their surfaces. Each process is likely to have altered presolar grains. The grains are extracted from meteorites and can be analyzed in the laboratory to try and understand these processes. The main analytical tool used in this research was a new time-of-flight secondary ion mass spectrometry instrument equipped with a Au-cluster primary ion source. Analysis of presolar grains required that a rigorous experimental procedure was developed. A depth-profiling technique for the analysis of micron-sized samples was produced and the limitations of the technique considered. Secondary ion mass spectrometry suffers from matrix effects, so homogeneous silicate glass standards were analyzed. The use of Au-cluster primary ions was shown to enhance practical secondary ion yields relative to those with Au+, consistent with increased sputter rates. Relative sensitivity factors for major and trace elements in the standards were obtained using both normal and delayed secondary ion extraction techniques. Depth-profiles of Li, B, Mg, Al, K, Ca, Ti, V, Cr and Fe were obtained from eleven presolar SiC grains. In some SiC grains, the abundances of several elements were up to orders-of-magnitude higher in the outer ~200nm relative to the grain cores. This was attributed to the implantation of interstellar matter, accelerated to velocities of ~1000kms-1 by supernovae shockwaves. Other SiC grains contained homogeneously distributed trace elements, or evidence of elemental zoning, which could be explained by condensation processes around the grains' parent stars. These grains must have experienced minimal processing in the interstellar medium. It is suggested that the two populations represent SiC grains whose residence times in the interstellar medium significantly differed, consistent with previous findings of noble gas and Li isotopic studies. A further study investigated carbonaceous grains isolated from the Murchison meteorite using a size and density procedure adapted for presolar graphite. No graphite grains were found and possible reasons for this are discussed. The structural and isotopic natures of thirty-three carbonaceous grains were determined by correlated, multi-instrument analyses. The grains contained solar C, N and O isotopic compositions. Deuterium was enriched in the grains with δD values up to +333 ± 110‰. These enrichments suggest exchange of H with cold interstellar gas in the outer part of the early solar nebula or interstellar medium. Raman spectroscopic and transmission electron microscopic analysis showed the grains to be composed of carbon more structurally disordered and amorphous than most carbonaceous phases observed in extra-terrestrial samples. It is argued that amorphization of the grains occurred through solar wind ion irradiation in the proto-solar nebula. This model is supported by previous studies of terrestrial soot and carbon-rich ices irradiated by H⁺ and He⁺ ion doses of ~10¹⁵ - 10¹⁶ ions cm⁻². Implantation and mixing of H⁺ ions is likely to have diluted the grains' original H isotopic composition.

No description available.

Factors that may govern diesel particulate matter (DPM) oxidation at low temperatures (~200°C) were studied using reactivity and TP-ToFSIMS analysis. Best-case scenarios that give maximum gasification rates were determined for DPM impregnated with KOH and non-catalyzed DPM using temperature programmed oxidation and isothermal experiments. Conditions of intimate catalyst-carbon contact (K/C molar ratio=1/50) and high NO2 concentrations (1%) to improve the reactivity of the carbon reactive sites were unable to meet the steady state gasification rate needed for particulate filter regeneration for a modern diesel engine at 200°C. Oxygen-free thermal annealing (>500°C) caused reactivity losses of a maximum of 40% that correspond to changes to surface morphology and/or concentration of oxygen-containing functional groups. TP-ToFSIMS identified surface functional group changes with temperature on non-dosed and NOX pre-dosed (1.5%NO, 1%NO2, 4.5%O2, balance helium) diesel soot and sucrose char. Detailed analysis of the NOX dosed sucrose char spectra using both inspection and principal component analysis techniques revealed that the 1200 ion fragments created could be reduced to five sets of ions that are chemically and kinetically distinct. These sets presumably represent surface functional groups on the carbon. For example, Set IV may represent carboxylic acid, lactone, or carboxylic anhydride functional groups. Based on these results a mechanism for the surface reaction of NO2 with carbon under vacuum conditions was postulated. At temperatures less than 200°C the ion fragments contain primarily carbon-NO2 type ions. As temperature increases between 200 and 400°C the ion fragments are primarily carbon-NO and carbon-N type fragments. At higher temperatures (>500°C) the surface is enriched with nitrogen containing functional groups. A surface reaction mechanism is proposed where NO2 is bonded to an armchair site and with increasing temperatures and molecular rearrangements the N is incorporated into the carbon ring. The initial surface composition of NOx containing functional groups changes within the area of relevance of low temperature soot regeneration (i.e. between 25° and 200°C). Further studies are needed to understand the effect of N-incorporation on carbon reactivity. No rate processes either in reactor studies or based on surface functional groups met the rate criteria for low temperature DPM oxidation.

Factors that may govern diesel particulate matter (DPM) oxidation at low temperatures (~200°C) were studied using reactivity and TP-ToFSIMS analysis. Best-case scenarios that give maximum gasification rates were determined for DPM impregnated with KOH and non-catalyzed DPM using temperature programmed oxidation and isothermal experiments. Conditions of intimate catalyst-carbon contact (K/C molar ratio=1/50) and high NO2 concentrations (1%) to improve the reactivity of the carbon reactive sites were unable to meet the steady state gasification rate needed for particulate filter regeneration for a modern diesel engine at 200°C. Oxygen-free thermal annealing (>500°C) caused reactivity losses of a maximum of 40% that correspond to changes to surface morphology and/or concentration of oxygen-containing functional groups. TP-ToFSIMS identified surface functional group changes with temperature on non-dosed and NOX pre-dosed (1.5%NO, 1%NO2, 4.5%O2, balance helium) diesel soot and sucrose char. Detailed analysis of the NOX dosed sucrose char spectra using both inspection and principal component analysis techniques revealed that the 1200 ion fragments created could be reduced to five sets of ions that are chemically and kinetically distinct. These sets presumably represent surface functional groups on the carbon. For example, Set IV may represent carboxylic acid, lactone, or carboxylic anhydride functional groups. Based on these results a mechanism for the surface reaction of NO2 with carbon under vacuum conditions was postulated. At temperatures less than 200°C the ion fragments contain primarily carbon-NO2 type ions. As temperature increases between 200 and 400°C the ion fragments are primarily carbon-NO and carbon-N type fragments. At higher temperatures (>500°C) the surface is enriched with nitrogen containing functional groups. A surface reaction mechanism is proposed where NO2 is bonded to an armchair site and with increasing temperatures and molecular rearrangements the N is incorporated into the carbon ring. The initial surface composition of NOx containing functional groups changes within the area of relevance of low temperature soot regeneration (i.e. between 25° and 200°C). Further studies are needed to understand the effect of N-incorporation on carbon reactivity. No rate processes either in reactor studies or based on surface functional groups met the rate criteria for low temperature DPM oxidation.

No description available.