The contribution of energy from biomass sources is projected to increase in Britain to assist in meeting renewable energy targets and reducing anthropogenic CO2 emissions. With increasing concerns over the sustainability of food crop-based biofuels, purpose-grown lignocellulosic biomass crops such as Miscanthus and short rotation coppice (SRC) willow have been promoted as more sustainable feedstocks for the production of heat and electricity as well as for the future production of liquid biofuels. With the introduction of the Energy Crops Scheme, land-use change (LUC) for lignocellulosic biomass crop production has become increasingly common in Britain in recent decades. However, there is limited understanding of the impact this has on soil organic carbon (SOC) stocks and limited predictability concerning the overall trajectory, magnitude and rate of SOC changes under a range of different conditions. Using a chronosequence of 93 biomass crop plantations in England and Wales, mainly of 1 to 14 years age, empirical models were developed to determine the short term trajectory of SOC stocks following LUC from arable and grassland to SRC willow and Miscanthus production. SOC stocks were calculated for each site using a fixed sampling depth of 30 cm and estimated changes were inferred by comparing with typical pre-change SOC stocks. These results indicate that only LUC from arable crops to SRC willow demonstrated an overall increase in SOC stocks, by an estimated 15.3 ± 2.2 t C ha-1 (± 95% confidence intervals) after 14 years and 68.8 ± 49.4 t C ha-1 after 22 years. LUC from arable crops to Miscanthus and from both arable crops and grassland to SRC willow and Miscanthus demonstrated no overall net effect on SOC stocks. Soil texture and climate data were measured for each site and multivariable models were created to assess the influence of different environmental conditions on SOC trajectory. In most cases the addition of these explanatory variables improved the model fit, and the models provide some preliminary estimates of more region-specific changes in SOC following LUC. Since LUC to biomass crops often causes a loss of SOC, at least in the short term, the potential for pyrogenic carbon (PyC) to ameliorate this effect was investigated. Studies indicate that PyC can interact with and stabilise native SOC, a process termed negative priming, although the potential for PyC to reduce LUC-induced losses of SOC by negative priming has not yet been assessed. Although negative priming has been observed in many studies, most of these are long term incubation experiments which do not account for the impact of environmental weathering of PyC on interactions with native SOC. Here the aim was to assess the impact of environmentally weathered PyC on native SOC mineralisation at different points in LUC from arable crops to SRC willow. Soil was sampled to a 5 cm depth from multiple recently established SRC willow plantations approximately 2 years after amendment with PyC. Cumulative CO2 flux was measured weekly from incubated soil and soil-surface CO2 flux was also measured in the field. The results demonstrate a PyC-induced increase in CO2 flux for the surface 5 cm of soil. However, no net effect on soil-surface CO2 flux was observed in the field. Although the mechanisms for these contrasting effects remain unclear, they do not suggest that PyC can reduce LUC-induced SOC losses through negative priming.

A simple rule for the optimal global price of carbon is presented, which captures the geophysical, economic, and ethical drivers of climate policy as well as the effect of uncertainty about future growth of consumption. There is also a discussion of the optimal carbon budget and the amount of unburnable carbon and stranded fossil fuel reserves and a back-on-the-envelope expression are given for calculating these. It is also shown how one can derive the end of the carbon era and peak warming. This simple arithmetic for determining climate policy is meant to complement the simulations of large-scale integrated assessment model, and to give analytical understanding of the key determinants of climate policy. The simple rules perform very well in a full integrated assessment model. It is also shown how to take account of a 2 °C upper limit on global warming. Steady increases in energy efficiency do not affect the optimal price of carbon, but postpone the carbon-free era somewhat and if technical progress in renewables and economic growth are strong leads to substantially lower cumulative emissions and lower peak global warming.

Les composites C/C sont principalement utilisés dans les applications à très haute température et notamment dans le domaine du spatial. Savoir concevoir ces matériaux est essentiel pour améliorer leurs performances et diminuer les coûts de production. Ce mémoire présente le développement d’un modèle multiéchelle basé images du comportement thermomécanique d’un composite C/C à renfort 3Daiguilleté. L’utilisation de méthodes classiques ne permet pas de décrire correctement cette architecture très complexe. La méthode CEPI (Computing Effective Properties using Images) présentée s’appuie d’une part sur les propriétés des constituants, dont certaines ont été caractérisées au laboratoire, etd’autre part sur l’architecture de ces matériaux, qui a été obtenue à partir d’une image tomographique.Les propriétés mesurées des constituants ont été directement utilisées dans un modèle microscopique de fil idéal, le modèle macroscopique étant lui directement basé sur l’image de tomographie. Les paramètres des calculs aux différentes échelles ont ensuite été étudiés et discutés pour en déterminer l’influence et permettre de valider certaines hypothèses. La comparaison des résultats numériques et expérimentaux a enfin permis de valider la méthode CEPI sur le comportement mécanique linéaire et de mettre en avant les principaux axes d’améliorations pour le comportement en dilatation des ces composites. / C/C composites are used in very high temperature applications, especially in space activities. The ability to design these materials is essential in order to enhance their performances and lower their production costs. This work introduces an images-based multiscale modeling of the thermomechanical behavior of a C/C needled composites. Standard methods cannot describe this very complex architecture.The CEPI model (Computing Effective Properties using Images) is based on one hand on the components properties, some of them having been characterized in the laboratory, and on the other hand on the architecture of the material which is directly obtained using tomography images. The components properties were used on a microscopic model of an idealistic yarn, while the macroscopic model was based on the CT scan data itself. The influence of the internal parameters of the method was studied and discussed, and allowed validating some hypotheses. Finally, the comparison between the numerical and experimental results validates the CEPI model on the linear mechanical behavior and stressed the key axes of improvement for the thermal expansion behavior of these composites.

A number of investigators have reported enhancement in oxidation and wear resistant of carbon-carbon composites (CCC) in the presence of protective coating layers. However, application of a surface and subsurface coating system that can preserve its oxidation and wear resistance along with maintaining lubricity at high temperature remains unsolved. To this end, thermodynamically stable protective oxides (ZnO/Al2O3/ZrO2) have been deposited by atomic layer deposition (ALD) to infiltrate porous CCC and graphite foams in order to improve the thermal stability and wear resistance in low and high speed sliding contacts. Characterization of microstructural evolution was achieved by using energy dispersive x-ray spectroscopy (EDS) mapping in scanning electron microscope (SEM) coupled with focused ion beam (FIB), x-ray tomography, high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD). Evaluation of the tribological properties of CCC coated with abovementioned ALD thin films were performed by employing low speed pure sliding tribometer and a high speed/frequency reciprocating rig to simulate the fretting wear behavior at ambient temperature and elevated temperatures of 400°C.It was determined with x-ray tomography imaging and EDS mapping that ALD ZnO/Al2O3/ZrO2 nanolaminates and baseline ZrO2 coatings exhibited excellent conformality and pore-filling capabilities down to ~100 μm and 1.5 mm in the porous CCC and graphite foam, respectively, which were dependent on the exposure time of the ALD precursors. XRD and HRTEM determined the crystalline phases of {0002} textured ZnO (wurtzite), amorphous Al2O3, and {101}-tetragonal ZrO2. Significant improvements up to ~65% in the sliding and fretting wear factors were determined for the nanolaminates in comparison to the uncoated CCC. A tribochemical sliding-induced mechanically mixed layer (MML) was found to be responsible for these improvements. HRTEM confirmed the presence of a high density of ZnO shear-induced basal stacking faults inside the wear tracks responsible for intrafilm shear velocity accommodation that mitigated friction and wear.

L’objectif de ce travail est d’étudier quantitativement l’évolution des propriétés de surface des matériaux carbonés et leur réactivité dans les conditions proches de celles rencontrées lors du taxiage des avions. Les essais de freinage ont été réalisés à l’aide d’un Banc d’Essai Tribométrique à Simulation Inertielle. Les composites C/C frottés et les débris d’usure sont caractérisés par des techniques non-conventionnelles multi-échelles. Les composites frottés (dans leur totalité) et les débris d’usure sont caractérisés par thermo-désorption programmée et chimisorption d’oxygène. Ces analyses permettent de déterminer la nature et la quantité de groupes fonctionnels et la teneur en sites actifs, caractéristique de la réactivité intrinsèque du carbone et responsable de l’interaction avec les espèces gazeuses de l’environnement. Ces caractérisations sont complétées par des analyses morphologiques, structurales et texturales par microscopies, diffractions des rayons X, adsorption de gaz. L’analyse des caractéristiques physico-chimiques des débris d’usure et des disques frottés permet de remonter aux réactions tribochimiques ayant eu lieu dans le contact : des réactions chimiques entre l’oxygène ou l’eau et les liaisons C-C rompues ont été mises en évidence. Un modèle permettant de justifier les différences de propriétés tribologiques lors des essais de taxiage a été proposé. Ce modèle, basé sur la réactivité du système et sur les propriétés de l’interface de frottement, permet d’élucider les problématiques liées à la température dans ce type de système. / The objective of this work is to study quantitatively the evolution of carbon materials surface properties and reactivity under breaking conditions similar to those encountered during taxiing. The breaking tests were carried out using a Tribometric Test Bench. The rubbed C/C composites and the wear debris collected are then characterized by mutiscale unconventional techniques. The whole rubbed composites and the wear debris are characterized by Temperature-Programmed Desorption and by oxygen chemisorption. These analyzes are used to determine the nature and amount of functional groups and the content of active sites that is characteristic of the reactivity of the carbon material and also responsible of its interaction with the surrounding environment. The characterizations are completed by morphological, structural and textural analysis, such as Electron Microscopy, X-Ray Diffraction and gas adsorption. The analysis of the physic-chemical characteristics of wear debris and of the rubbed discs enables to evidence the tribochemical reactions occurring in the mechanical contact: chemical reactions between oxygen or water and the broken C-C bonds have been evidenced. A model is finally proposed, justifying the differences in the tribological properties during taxiing tests. The later is based on the carbon reactivity and on the interface properties and justify the temperature dependence of this system.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18997号 / 工博第4039号 / 新制||工||1622(附属図書館) / 31948 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 辻 康之, 教授 大江 浩一, 教授 杉野目 道紀 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19239号 / 工博第4074号 / 新制||工||1628(附属図書館) / 32238 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 村上 正浩, 教授 吉田 潤一, 教授 松田 建児 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20192号 / 理博第4277号 / 新制||理||1615(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 依光 英樹, 教授 丸岡 啓二, 講師 西村 貴洋 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20409号 / 工博第4346号 / 新制||工||1674(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 村上 正浩, 教授 吉田 潤一, 教授 杉野目 道紀 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The body of information concerning carbon-carbon spin-spin coupling constants now includes a large number of coupling constants, the establishment of a dihedral angular dependence on 3JCC, and the application of 3JCC to conformational analysis. This study adds another dimension to the growing wealth of information associated with 13 C-NMR: the influence of some non-bonded interactions on 3JCC Four types of non-bonded interactions that could influence vicinal carbon-carbon NMR coupling constants were investigated. To facilitate the NMR studies, a variety of 13C-labeled compounds were synthesized.