The proton exchange membrane fuel cell (PEMFC) is a potential electrochemicalpower device for vehicles, auxiliary power units and small-scale power plants. In themembrane electrode assembly (MEA), which is the core of the PEMFC single cell,oxygen in air and hydrogen electrochemically react on separate sides of a membraneand electrical energy is generated. The main challenges of the technology are associatedwith cost and lifetime. To meet these demands, firstly, the component expensesought to be reduced. Secondly, enabling system operation at elevated temperatures,i.e. up to 120 °C, would decrease the complexity of the system and subsequentlyresult in decreased system cost. These aspects and the demand for sufficientlifetime are the strong motives for development of new materials in the field.In this thesis, MEAs based on alternative materials are investigatedwith focus on hydrocarbon proton-conducting polymers, i.e. ionomers, and newcatalyst supports. The materials are evaluated by electrochemical methods, such ascyclic voltammetry, polarisation and impedance measurements; morphological studiesare also undertaken. The choice of ionomers, used in the porous electrodes andmembrane, is crucial in the development of high-performing stable MEAs for dynamicoperating conditions. The MEAs are optimised in terms of electrode compositionand preparation, as these parameters influence the electrode structure andthus the MEA performance. The successfully developed MEAs, based on the hydrocarbonionomer sulfonated polysulfone (sPSU), show promising fuel cell performancein a wide temperature range. Yet, these membranes induce mass-transportlimitations in the electrodes, resulting in deteriorated MEA performance. Further,the structure of the hydrated membranes is examined by nuclear magnetic resonancecryoporometry, revealing a relation between water domain size distributionand mechanical stability of the sPSU membranes. The sPSU electrodes possessproperties similar to those of the Nafion electrode, resulting in high fuel cell performancewhen combined with a high-performing membrane. Also, new catalystsupports are investigated; composite electrodes, in which deposition of platinum(Pt) onto titanium dioxide reduces the direct contact between Pt and carbon, showpromising performance and ex-situ stability. Use of graphitised carbon as catalystsupport improves the electrode stability as revealed by a fuel cell degradation study.The thesis reveals the importance of a precise MEA developmentstrategy, involving a broad methodology for investigating new materials both as integratedMEAs and as separate components. As the MEA components and processesinteract, a holistic approach is required to enable successful design of newMEAs and ultimately development of high-performing low-cost PEMFC systems. / QC 20100922

<p>The main purpose of this study was to identify and characterize the various sand prone depositional facies in the deepwater Southern Outeniqua Basin which generally tend to form during&nbsp / lowstand (marine regression) conditions producing progradational facies. It made use of sequence stratigraphy and turbidite facies models to predict the probable location of deepwater&nbsp / reservoirs in the undrilled Southern Outeniqua Basin using data from basin margin Pletmos Basin and the deepwater Southern Outeniqua Basin. Basin margin depositional packages were&nbsp / correlated in time and space with deepwater packages. It was an attempt at bridging the gap between process-related studies of sedimentary rocks and the more traditional economic geology&nbsp / f commercial deposits of petroleum using prevailing state-of-the-art in basin analysis. It enabled the most realistic reconstructions of genetic stratigraphy and offered the greatest&nbsp / application in exploration. Sequence stratigraphic analysis and interpretation of seismics, well logs, cores and biostratigraphic data was carried out providing a chronostratigraphic framework of the study area within which seismic facies analysis done. Nine (9) seismic lines that span the shallow/basin margin Pletmos basin into the undrilled deepwater Southern Outeniqua basin were analysed and interpreted and the relevant seismic geometries were captured. Four (4) turbidite depositional elements were identified from the seismic lines: channel, overbank deposits,&nbsp / haotic deposits and basin plain (basin floor fan) deposits. These were identified from the relevant seismic geometries (geometric attributes) observed on the 2D seismic lines. Thinning attributes, unconformity attributes and seismic facies attributes were observed from the seismic lines. This was preceded by basic structural analyses and interpretation of the&nbsp / seismic lines. according to the structural analysis and interpretation, deposition trended NW-SE and NNW-SSE as we go deepwater into the Southern Outeniqua basin. Well logs from six (6)&nbsp / of the interpreted wells indicated depositional channel fill as well as basin floor fans. This was identified in well Ga-V1 and Ga-S1 respectively. A bell and crescent shape gamma ray log&nbsp / signature was observed in well Ga-V1 indicating a fining up sequence as the channel was abandoned while an isolated massive mound-shape gamma ray log signature was observed in&nbsp / Ga-S1 indicating basin plain well-sorted sands. Core analyses and interpretation from two southern-most wells revealed three (3) facies which were derived based on Walker&lsquo / s 1978, turbidite&nbsp / facies. The observed facies were: sandstone, sand/shale and shale facies. Sequence stratigraphic characterisation of petroleum reservoirs in block 11b/12b of the Southern Outeniqua&nbsp / Basin. Cores of well Ga-V1 displayed fine-grained alternations of thin sandstone beds and shales belonging to the thin-bedded turbidite facies. This is typical of levees of the upper fan channel but&nbsp / could easily be confused with similar facies on the basin plain. According to Walker, 1978 such facies form under conditions of active fan progradation. Ga-S1 cores displayed not only classic&nbsp / turbidite facies where there was alternating sand and shale sections but showed thick uninterrupted sections of clean sands. This is typical of basin plain deposits. Only one well had&nbsp / biostratigraphic data though being very limited in content. This data revealed particular depth sections and stratigraphic sections as having medium to fast depositional rates. Such rates are&nbsp / characteristic of turbidite deposition from turbidity currents. This study as well as a complementary study by Carvajal et al., 2009 revealed that the Southern Outeniqua basin is a sand-prone&nbsp / basin with many progradational sequences in which tectonics and sediment supply rate have been significant factors (amongst others such as sea level change) in the formation of these&nbsp / deepwater sequences. In conclusion, the Southern Outeniqua basin was hereby seen as having a viable and unexplored petroleum system existing in this sand prone untested world class.</p>

The phase separation of mixed Langmuir-Blodgett (LB) monolayers was investigated using a combination of atomic force microscopy (AFM), X-ray photoelectron emission microscopy (X-PEEM) and confocal fluorescent microscopy measurements. Shapes of phase-separated domains that formed on solid substrate surfaces depended on a competition between line tension and dipole-dipole interactions. In the mixed LB film of arachidic acid (C19H39COOH) (C20) and perfluorotetradecanoic acid (C13F27COOH) (F14), the components phase separated into elevated hexagonal domains of C20 surrounded by a continuous domain primarily consisting of F14. The underlying molecular arrangement of C20 was found to be an oblique packing. The domains in this system grew via Ostwald ripening and the kinetics of their growth was modeled by twodimensional LifshitzSlyozov equation. In the stearic acid (C17H35COOH) (C18) and F14 mixed films, the C18 domains formed a linear pattern where the F14 molecules filled the areas in between the lines occupied by C18. For the mixed film of palmitic acid (C15H31COOH) (C16) and perfluorooctadecanoic acid (C17F35COOH) (F18), the surfactants phaseseparated into elevated hexagonal domains with hairy extensions radiating from them. These domains were composed of F18 and surrounded by C16. Ostwald ripening was found to be the mechanism of domain growth. Phase separation was controlled by different forces such as line tension and dipole interactions, as well as the diffusion of the molecules, solubility of the surfactant in the sub-phase, temperature and surface pressure. Simple mechanisms regarding phase separation and pattern formation were discussed in these mixed systems. It was observed that all fatty acid / F14 systems in this study were immiscible at all molar fractions examined. The fatty acid / F18 systems were immiscible at short chains of fatty acids (myristic acid (C13H27COOH) C14, C16, C18), whereas at longer fatty acid chains (C20, C22 behenic acid (C21H43COOH)) the components of the mixed system became miscible. When perfluorocarboxylic acid chain combined with fatty acids, the domains changed from large hexagonal domains into narrow lines as the fatty acid chain decreased in length.

The phase separation of mixed Langmuir-Blodgett (LB) monolayers was investigated using a combination of atomic force microscopy (AFM), X-ray photoelectron emission microscopy (X-PEEM) and confocal fluorescent microscopy measurements. Shapes of phase-separated domains that formed on solid substrate surfaces depended on a competition between line tension and dipole-dipole interactions. In the mixed LB film of arachidic acid (C19H39COOH) (C20) and perfluorotetradecanoic acid (C13F27COOH) (F14), the components phase separated into elevated hexagonal domains of C20 surrounded by a continuous domain primarily consisting of F14. The underlying molecular arrangement of C20 was found to be an oblique packing. The domains in this system grew via Ostwald ripening and the kinetics of their growth was modeled by twodimensional LifshitzSlyozov equation. In the stearic acid (C17H35COOH) (C18) and F14 mixed films, the C18 domains formed a linear pattern where the F14 molecules filled the areas in between the lines occupied by C18. For the mixed film of palmitic acid (C15H31COOH) (C16) and perfluorooctadecanoic acid (C17F35COOH) (F18), the surfactants phaseseparated into elevated hexagonal domains with hairy extensions radiating from them. These domains were composed of F18 and surrounded by C16. Ostwald ripening was found to be the mechanism of domain growth. Phase separation was controlled by different forces such as line tension and dipole interactions, as well as the diffusion of the molecules, solubility of the surfactant in the sub-phase, temperature and surface pressure. Simple mechanisms regarding phase separation and pattern formation were discussed in these mixed systems. It was observed that all fatty acid / F14 systems in this study were immiscible at all molar fractions examined. The fatty acid / F18 systems were immiscible at short chains of fatty acids (myristic acid (C13H27COOH) C14, C16, C18), whereas at longer fatty acid chains (C20, C22 behenic acid (C21H43COOH)) the components of the mixed system became miscible. When perfluorocarboxylic acid chain combined with fatty acids, the domains changed from large hexagonal domains into narrow lines as the fatty acid chain decreased in length.

The construction of diverse molecular architecture conceived and created by Nature, continues to be the most exiting and challenging task to the practitioners of organic synthesis. As a result of refinement in isolation and purification techniques, recent advances in the spectroscopic methods particularly two-dimensional NMR spectroscopy and routine use of single crystal X-ray crystallography, the isolation and structural elucidation of the complex natural products has become a routine exercise. Even those natural products which are present in minute quantity, are being unraveled from the newer and exotic sources such as marine flora and fauna, microbial organisms and insect world. This has been a big boon for the synthetic organic chemists, providing them with increasing number of exciting objectives. The recent advances in the field of natural product synthesis testify to the organic chemists endeavors to meet these emerging challenges. Nature's expertise and virtuosity in creating a phenomenal array of carbocyclic frameworks is most notably highlighted in the terpenoid group of natural products. Indeed, the number and type of carbocyclic skeleta among terpenes continues to grow unabated as more and more natural products are being routinely isolated from the various sources. Thus, various polycyclic natural products bearing new and novel fused assemblies of five, six, seven and eight membered rings and replete with dense functionalization and stereogenic centers are being regularly encountered. The present investigation represents synthetic efforts towards some novel and recently isolated terpenoid natural products. Two main themes have been pursued. The first involves the construction of a functionalized hydroazulene framework employing RCM as the key step and its further elaboration to the 5,7,6-tricyclic framework present in diterpene guanacastepene-A and 5,11-fused bicyclic system present in neodolabellane diterpenes. The second theme explores the synthetic versatility of the well-established photo-thermal metathetic approach to linear triquinanes through its application to the total synthesis of novel and recently isolated natural product cucumin E. It further explores the utility of 5-5-5 fused ring system to access 5-8 system. This strategy has led to the stereoselective total synthesis of natural product asterisca-3(15),6~diene belonging to the rare asteriscane family. The present thesis entitled "Towards the Total Synthesis of Terpenoid Natural Products" describes our endeavors towards the synthesis of 5-7-6, 5-11, 5-5-5 and 5-8 fused natural products and has been organized under four chapters. Chapter I. Studies toward the total synthesis of novel diterpene antibiotic guanacastepene A. Chapter EL Synthesis of the novel 5,11-fused bicyclic framework of neodollabellane diterpenoids. Chapter HI. A Stereoselective total synthesis of the novel triquinane sesquiterpene cucumin E. Chapter IV. Total synthesis of 5-8 ring fused sesquiterpene hydrocarbon asterisca-3(15),6-diene. The Chapter I describes a stereoselective approach towards the construction of the novel 5,7,6-rig fused framework present in the diterpene antibiotic guanacastepene A 1, recently isolated from an unidentified fungus growing on the tree Daphnopsis americana by Clardy et al. Besides its structural novelty, guanacastepene A exhibits impressive activity towards methicilline-resistant Staphylococcus aureus and vancomycine-resistant Entereococcusfaecium. Thus, 1 has evoked an unprecedented attention from the synthetic community and we too were enticed to enter this arena. Scheme 1 (structural formula) The synthetic approach towards guanacastepene A 1, envisage in this study, was revealed through a retrosynthetic analysis which identified hydroazulenic core 2 (AB rings) with requisite level of functionalities as an advanced precursor to which a six membered ring could be annulated through appropriate protocols. The hydroazulene core 2 was to be accessed from the substituted cyclopentenone 4 through the intermediacy of 3 and the former in turn could be prepared from the readily available endo tricyclo[5.2.1.026]deca-3,8-diene-5-one 6, Scheme 1. In this approach to the AB ring hydroazulenic core 2 of 1, some essential requirements were recognized at the outset. These were the setting up the key cis relationship of the angular methyl group at C11 and the neighboring bulky-isopropyl group at C12, installation of a desirable level of functionalization in the five membered ring and a functional group handle in seven-membered ring to Scheme 2 (structural formula) append the six membered ring with requisite functionality. Keeping these considerations in mind, readily available endo-tricyclo[5.2.1.02-6]deca-3,8-diene-5-one 6 with well-established propensity toward reactivity on exro-face was identified to be starting point, Scheme 1. Copper(I)mediated stereoselective 1,4-addition of isopropylmagnesium iodide on 6, followed by sequential a-alkylation with allyl bromide and methyl iodide led to 7 as a single diastereomer and correctly installed the methyl and isopropyl groups in the required cis-relationship, Scheme 2* Retro-Diels-^Ider reaction in 7 under flash vacuum pyrolysis (FVP) liberated the cyclopentenone 8. For the annulation of a seven-membered ring to cyclopentenone 8, recourse was taken to a ring closing metathesis-(RCM) based protocol. Barbier-type addition of 4-bromo-1-butene to 8 in the presence of lithium metal and oxidative transposition of the resulting allylic alcohol with PCC furnished enone 9 in good yield. On exposure to Grubbs' catalyst, enone 9 underwent smooth RCM reaction to deliver the desired hydroazulenic framework 10, Scheme 2. The bicyclic hydroazulenic enone 10 was now poised for the elaboration of functionalities in the context of evolution to the natural product 1. Thus, 10 was elaborated to epoxy alcohol 11 in a three step sequence, Scheme 2. TMSOTf mediated opening of epoxide ring to yield cis-enediol, protection of the resultant diol as an acetonide and allylic oxidation furnished the key enone 12, Scheme 2. Attempts to alkylate the enone 12 to install the C16 methyl group and the precursor side chain for six membered ring annulation failed consistently. Recourse was then taken to a-carboethoxylation in 12 using Mander's reagent proved to be quite effective and further alkylation with methyl iodide furnished 13 as a single stereoisomer with the correct stereochemical positioning of the quaternary methyl group at C8. Intermediate 13 was elaborated to tricyclic framework 14 of guanacastepane A in five steps, by setting up NaOEt mediated intramolecular aldol reaction as key step, for the construction of six membered ring, Scheme 2. In tricyclic cross-conjugated dienone 14, complete carbon framework of the natural product guanacastepene A 1, with a copious disposition of functionalities was realized. Further efforts to transform 14 to 1 were not very encouraging. However a variant of ring C annulation on 12 is being investigated by a colleague in the group to achieve the total synthesis of the natural product. In travails towards 1 and 14, several deviations from the expected course, leading to the new tricyclic structural variants of the biologically promising guanacastepene A 1 were encountered and these findings will also be detailed in this chapter of the thesis. In the Chapter n of the thesis, synthetic studies directed towards the bicyclic framework present in novel neodolabellane type diterpenes like a-and (3-neodolabellenol 17a and 17b isolated from an unknown species of Australian soft coral by Coll et al will be delineated. The readily accessible bicyclic hydroazulenic enone 13, also served as an advanced intermediate for the construction of the 5-11 fused bicyclic skeleton 16 of neodollabellane diterpenoids via an oxy-Cope rearrangement. Elaboration of 13 to the divinyl carbinol 15 and its [3.3] sigmatropic rearrangement (oxy-Cope rearrangement) to 16 and related reactions will be described, Scheme 3. Scheme 3(Structral formula) Chapter III describes the first total synthesis of the sesquiterpenoid natural product cucumin E 26 bearing a novel triquinane framework, and reported recently from the mycelial cultures of agaric Macrocystidia cucumis (Pers ex Fr.) by the groups of Steglich and Anke. Synthesis of 26 was accomplished following an interesting variant of the photo-thermal metathetic approach to linear triquinanes delineated by us sometime ago, Scheme 4. Cucumin E 26 attracted our attention as this sesquiterpene [Scheme 4 (Structural formula)] bears an Interesting biogenetic relationship to the related hirsutane group of linear triquinanes from which it can be derived through the migration of a methyl group. Towards the synthesis of 26, the readily available pentacyclic dione 18 was identified as the key starting material and was elaborated to 19 using FVP (flash vacuum pyrolysis) conditions under which 18 underwent [2+2]-cycloreversion of the cyclobutane ring to furnish the cis, syn, cis-triquinane, Scheme 5. On exposure to base, 19 could be equilibrated through back and forth double bond isomerization to furnish the cis,antecis-isorner 20 in reasonable yield. Attention was now turned towards the installation of the network of four methyl groups present in 26 and relevant functional group adjustments. Catalytic hydrogenation of 20, selective mono-Wittig olefination and subsequent gem-dimethylation furnished olefinic ketone 21. At this stage, the carbonyl group in 21 was sought to be removed and recourse was taken to the Barton deoxygenation protocol to furnish 22, Scheme 5. The next task en-route to the cucumin skeleton was the introduction of the angular methyl group at C7 to generate the complete Cis carbon framework. For this purpose, the ketal group in 22 was deprotected to furnish the ketone 23. Angular methylation in 23 exhibited fair regioselectivity to yield 24 as the major product. The enone moiety in 24 was established through allylic oxidation following the Sharpless catalytic selenium dioxide oxidation followed by PDC oxidation to afford 25. Rh(III)-mediated isomerization of the exocyclic double bond in 25 delivered cucumin E 26, whose spectral characteristics were exactly identical to the natural product as established through direct comparison, Scheme 5. In Chapter IV, the total synthesis of the bicyclo[6.3.0]undecane-based sesquiterpene hydrocarbon asterisca-3(15),6-diene 38, isolated from Lippia integrifolia (Griseb) by Konig et al. and representing the simplest member of the asteriscane family, is described. Our approach to the bicyclo[6.3.0]undecane system was based on the 'carbocyclic ring equivalency' concept. Thus, bicyclo[3.3.0]octane ring system is an eight-membered ring equivalent and tricyclo[6.3.0.02'6]undecane (linear triquinane system) is the latent form of the bicyclo[6.3-0]undecane system through the scission of the central bond as shown in Scheme 6. Following this concept a synthesis of 38 was envisaged from the cfe,syn, cis-triquinane bis-enone 28, readily and quantitatively available from the pentacyclic-caged dione 27, through flash-vacuum pyrolysis (FVP), as described earlier. More stable bis-enone 29 was obtained from 28 by relocation of one of the enone moieties in 28 through thermal activation under static conditions. The two double bonds in 29 could be now easily differentiated and hence it served as an appropriate substrate for further elaboration. Thus, bis-enone 29 on selective catalytic hydrogenation and regioselective gem-dimethylation afforded 30, Scheme 7. At this stage, the two-carbonyl functionalities in 30 were sought to be removed and this was achieved in a stepwise manner. The sequence involved chemoselective thioketalisation of the enone carbonyl followed by reductive desulfurization in metal-ammonia milieu and led to a diastereomeric mixture of alcohols (resulting from the concurrent reduction of the saturated ketone under metal-ammonia conditions). The diastereomeric mixture of alcohols was deoxygenated following the Barton protocol to yield tricyclic hydrocarbon 31, Scheme 7. Catalytic ruthenium mediated oxidative fragmentation of the tetrasubstituted olefinic bond in 31 afforded the 5,8-fused os-bicyclic dione 32. Wittig olefination of cis-bicyclic dione 32 proceeded regioselectively at the carbonyl group distant from the ring junction and furnished keto-olefin 33. However, the isomerization of exocyclic double bond in 33 to the desired endo position (corresponding to C6-C7 in the natural product) to yield 34 proved to be difficult due to unwanted transannular cyclization. Consequently, the transformation of 33 to the desired 34 was carried out through a five-step sequence. The sequence involved the reduction of the carbonyl group in 33 to yield alcohol, protection of the resultant alcohol as IMS-ether and RhCb mediated isomerization of the exo-double bond to the desired endo position. Further deprotection of the TMS ether and oxidation led to the acquisition of the expected enone 34, Scheme 7. Finally, the exo- methylene unit present in the natural product was installed by Wittig olefination in 34 to furnish 35, corresponding to the 'assigned structure' of the natural product. However the spectral data of synthetic 35 was distinctly different from that reported for the natural product and a revision of the natural product structure was warranted. A careful analysis of the spectral data led us to the surmise that the natural product could be the trans-isomer and we embarked on its synthesis. Consequently, cis-bicyclic diketone 32 on exposure to base could be readily equilibrated to the more stable trans-isomer 36 in which the later was the major product (1:4). Bicyclic trans-dione 36, like its cis sibling 32 underwent a facile regioselective Wittig olefination to yield keto-olefin 37, Scheme 8. RhCk-mediated double-bond isomerization in 37 proceeded without any complications and gave a readily separable mixture of regiomeric olefinic ketones 38 and 39 in the ratio 2:3, respectively. Wittig olefination on the required keto olefin 39 proceeded smoothly to furnish the bicyclic hydrocarbon 40 whose spectral characteristics [lH NMR, 13C NMR) exactly matched those reported for the natural product, Scheme 8. A total synthesis of the natural product asterisca-3(15),6-diene has been accomplished. These synthetic efforts necessitate the revision of the earlier assigned structure of the natural product from cis-35 to trans-38. (For structural formula pl see the original document)

<p>Dry etching is an important technique for pattern transferin fabrication of most opto-electronic devices, since it canprovide good control of both structure size and shape even on asub-micron scale. Unfortunately, this process step may causedamage to the material which is detrimental to deviceperformance. It is therefore an objective of this thesis todevelop and investigate low damage etching processes for InPbased devices.</p><p>An ion beam system in combination with hydrocarbon (CH₄) based chemistries is used for etching. At variousion energies and gas flows the etching is performed in twomodes, reactive ion beam etching (RIBE) and chemical assistedion beam etching (CAIBE). How these conditions affect both etchcharacteristics (e.g. etch rates and profiles, surfacemorphology and polymer formation) and etch induced damage (onoptical and electrical properties) is evaluated and discussed.Attention is also paid to the effects of typical post etchingtreatments such as annealing on the optical and electricalproperties. An important finding is the correlation betweenas-etched surface morphology and recovery/degradation inphotoluminescence upon annealing in PH₃. Since this type of atmosphere is typical forcrystal regrowth (an important process step in III/Vprocessing) a positive result is imperative. A low ion energy N₂/CH₄/H₂CAIBE process is developed which not onlysatisfies this criteria but also exhibits good etchcharacteristics. This process is used successfully in thefabrication of laser gratings. In addition to this, the abilityof the ion beam system to modify the surface morphology in acontrollable manner is exploited. By exposing such modifiedsurfaces to AsH₃/PH₃, a new way to vary size and density of InAs(P)islands formed on the InP surfaces by the As/P exchangereaction is presented.</p><p>This thesis also proposes a new etch chemistry, namelytrimethylamine ((CH₃)₃N or TMA), which is a more efficient methyl sourcecompared to CH₄because of the low energy required to break the H₃C-N bond. Since methyl radicals are needed for theetching it is presumably a better etching chemistry. A similarinvestigation as for the CH₄chemistry is performed, and it is found that bothin terms of etch characteristics and etch induced damage thisnew chemistry is superior. Extremely smooth morphologies, lowetch induced damage and an almost complete recovery uponannealing can be obtained with this process. Significantly,this is also so at relatively high ion energies which allowshigher etch rates.</p><p><b>Keywords:</b>InP, dry etching, ion beam etching, RIBE,CAIBE, hydrocarbon chemistry, trimethylamine, As/P exchangereaction, morpholoy, low damage, AFM, SCM, annealing</p>

Die Rußbildung in der Pyrolyse von n-Hexan, Benzol und Kohlenwasserstoffen im Stoßrohr wird mit hoher Zeitauflösung absorptionsspektroskopisch beobachtet und Gasproben durch ein besonders schnelles Ventil gesammelt. Vom Beginn der Pyrolyse bis zum Einsetzen der Rußbildung wurde stets eine Induktionszeit beobachtet, deren Dauer von der Temperatur, der Kohlenstoffkonzentration und der Struktur des pyrolysierten Kohlenwasserstoffs abhängt. Dieser Zusammenhang wird mit einem Arrhenius-Ansatz beschrieben. Der Vorfaktor A ist für Aromaten eine Größenordnung kleiner als für Alkane. Die scheinbare Aktivierungsenergie beträgt (220 ± 10) kJ/mol. Das Rußmassenwachstum, das der Induktionsperiode folgt, wird mit einem Gesetz erster Ordnung beschrieben. Durch Normierung der Geschwindigkeitskonstanten auf die Kohlenstoffdichte zeigt, daß das Rußmassenwachstum in Pyrolysen und in vorgemischten Ethylenflammen vergleichbar schnell abläuft. Die Rußausbeute der Aromaten und Acetylen hat bei bei 1800 K ein Maximum. Für Ethylen und Alkane liegt diese charakteristische Temperatur um rund 100 K höher. Neben Ruß und Wasserstoff sind Acetylen gefolgt von Methan und Ethylen die wichtigsten Hauptprodukte. Die polycyclischen Aromaten tragen keine Seitengruppe und enthalten maximal einen Fünfring. Der Rußpartikeldurchmesser ist im Bereich von 30 nm. Der Einfluß von Eisenpentacarbonyl auf die Rußbildung ist gering.

The conventional approach for estimation of in-situ porosity is the combined use of neutron and density logs. These nuclear borehole measurements are influenced by fundamental petrophysical, fluid, and geometrical properties of the probed formation including saturating fluids, matrix composition, mud-filtrate invasion and shoulder beds. Advanced interpretation methods that include numerical modeling and inversion are necessary to reduce environmental effects and non-uniqueness in the estimation of porosity. The objective of this dissertation is two-fold: (1) to develop a numerical procedure to rapidly and accurately simulate nuclear borehole measurements, and (2) to simulate nuclear borehole measurements in conjunction with inversion techniques. Of special interest is the case of composite rock formations of sand-shale laminations penetrated by high-angle and horizontal (HA/HZ) wells. In order to quantify shoulder-bed effects on neutron and density borehole measurements, we perform Monte Carlo simulations across formations of various thicknesses and borehole deviation angles with the multiple-particle transport code MCNP. In so doing, we assume dual-detector tool configurations that are analogous to those of commercial neutron and density wireline measuring devices. Simulations indicate significant variations of vertical (axial) resolution of neutron and density measurements acquired in HA/HZ wells. In addition, combined azimuthal- and dip-angle effects can originate biases on porosity estimation and bed boundary detection, which are critical for the assessment of hydrocarbon reserves. To enable inversion and more quantitative integration with other borehole measurements, we develop and successfully test a linear iterative refinement approximation to rapidly simulate neutron, density, and passive gamma-ray borehole measurements. Linear iterative refinement accounts for spatial variations of Monte Carlo-derived flux sensitivity functions (FSFs) used to simulate nuclear measurements acquired in non-homogeneous formations. We use first-order Born approximations to simulate variations of a detector response due to spatial variations of formation energy-dependent cross-section. The method incorporates two- (2D) and three-dimensional (3D) capabilities of FSFs to simulate neutron and density measurements acquired in vertical and HA/HZ wells, respectively. We calculate FSFs for a wide range of formation cross-section variations and for borehole environmental effects to quantify the spatial sensitivity and resolution of neutron and density measurements. Results confirm that the spatial resolution limits of neutron measurements can be significantly influenced by the proximity of layers with large contrasts in porosity. Finally, we implement 2D sector-based inversion of azimuthal logging-while-drilling (LWD) density field measurements with the fast simulation technique. Results indicate that inversion improves the petrophysical interpretation of density measurements acquired in HA/HZ wells. Density images constructed with inversion yield improved porosity-feet estimations compared to standard and enhanced compensation techniques used commercially to post-process mono-sensor densities. / text

The main objective of this dissertation is to quantify petrophysical properties of conventional and unconventional reservoirs using a mechanistic approach. Unconventional transport mechanisms are described from the pore to the reservoir scale to examine their effects on macroscopic petrophysical properties in hydrocarbon-bearing organic shale. Petrophysical properties at the pore level are quantified with a new finite-difference method. A geometrical approximation is invoked to describe the interstitial space of grid-based images of porous media. Subsequently, a generalized Laplace equation is derived and solved numerically to calculate fluid pressure and velocity distributions in the interstitial space. The resulting macroscopic permeability values are within 6% of results obtained with the Lattice-Boltzmann method after performing grid refinements. The finite-difference method is on average six times faster than the Lattice-Boltzmann method. In the next step, slip flow and Knudsen diffusion are added to the pore-scale method to take into account unconventional flow mechanisms in hydrocarbon-bearing shale. The effect of these mechanisms is appraised with a pore-scale image of Eagle Ford shale as well as with several grain packs. It is shown that neglecting slip flow in samples with pore-throat sizes in the nanometer range could result in errors as high as 2000% when estimating permeability in unconventional reservoirs. A new fluid percolation model is proposed for hydrocarbon-bearing shale. Electrical conductivity is quantified in the presence of kerogen, clay, hydrocarbon, water, and the Stern-diffuse layer in grain packs as well as in the Eagle Ford shale pore-scale image. The pore-scale model enables a critical study of the [delta]LogR evaluation method commonly used with gas-bearing shale to assess kerogen concentration. A parallel conductor model is introduced based on Archie's equation for water conductivity in pores and a parallel conductive path for the Stern-diffuse layer. Additionally, a non-destructive core analysis method is proposed for estimating input parameters of the parallel conductor model in shale formations. A modified reservoir model of single-phase, compressible fluid is also developed to take into account the following unconventional transport mechanisms: (a) slip flow and Knudsen diffusion enhancement in apparent permeability, (b) Langmuir desorption as a source of gas generation at kerogen surfaces, and (c) the diffusion mechanism in kerogen as a gas supply to adsorbed layers. The model includes an iterative verification method of surface mass balance to ensure real-time desorption-adsorption equilibrium with gas production. Gas desorption from kerogen surfaces and gas diffusion in kerogen are the main mechanisms responsible for higher-than-expected production velocities commonly observed in shale-gas reservoirs. Slip flow and Knudsen diffusion marginally enhance production rates by increasing permeability during production. / text

Lanthanum (La)-promoted hydrocarbon activation reactions were carried out in a laser vaporization metal cluster beam source. Reaction products were identified by time-of-flight mass spectrometry, and the approximate ionization thresholds of La-hydrocarbon complexes were located with photoionization efficiency spectroscopy. The accurate ionization energies and vibrational frequencies of the La complexes were measured using mass analyzed threshold ionization (MATI) spectroscopy. Their molecular structures and electronic states were investigated by combing the MATI spectroscopic measurements with quantum chemical and Franck-Condon factor calculations. In this dissertation, La-mediated C-H and C-C bond activation reactions were investigated for several small alkynes (acetylene, propyne) and alkenes (propene, 1,3-butadiene, 1-butene). The C-H bond activation was observed for both alkynes and alkenes and the C-C bond activation for alkenes. The metal-hydrocarbon intermediates formed by the C-H or C-C bond cleavage reacted further with one or more parent hydrocarbon molecules to produce larger species by C-C bond coupling reactions. Structural isomers of the intermediates and products were identified within an energy range of several kilocalories per mole. Reaction pathways for the intermediate and product formations were studied by theoretical calculations. The ground electron configuration of La atom is 4d16s2.Upon the hydrocarbon coordination, La atom is excited to a 4d26s1 configuration to facilitate the formation of two La-C bonds. After the metal-hydrocarbon complex formation, only one electron is left in the 6s orbital of the metal center. Therefore, the most stable electronic state of the La complexes studied in this work is in a doublet spin state. Ionization of the doublet state yields a preferred singlet ion state. Although La is in the formal oxidation state of +2, the ionization energies of the metal-complexes are significantly lower than that of the free atom. This observation suggests that the concept of the formal oxidation state widely used in chemistry textbooks is not useful in predicting the change of the ionization energy of a metal atom upon ligation. Moreover, ionization has a very small effect on the geometry of the hydrocarbon fragment in each complex but significantly reduces the La-C distances as a result of an additional charge interaction.