A small-scale model of a CVD reactor was built. Axial and radial of major species concentrations and temperature profiles were obtained with a micro gas chromatograph and a fine thermocouple. Those temperature and species concentrations revealed detailed thermal and chemical structures of the CVD reactor. The concentrations of argon plus hydrogen, methane, and C2Hx (C2H2 + C2H4 + C2H6) resulting from xylene decomposition were measured along the CVD at different temperatures. Ferrocene was added to xylene to investigate the effect of a catalyst on composition profiles. The results with ferrocene indicated an increase in CH4 and C2Hx concentrations. At 1000 C and above, the increase of C2Hx concentration is higher than that for CH4. The effect of ferrocene was very minor on the concentration of the gases. Finally composition and temperature profiles were measured and plotted for the radial direction at X=75 cm and T=1200 C. The overall rate constant for the gas-phase reaction was calculated based on the measured species concentration data using the Benson and Shaw reaction mechanism. Our study showed that the Benson and Shaw mechanism could be used in the temperature range lower than 800 C. Also the effect of hydrogen in the syntheses of CNTs, in the CVD reactor using xylene and ferrocene, was studied. Both single-step and two-step methods were applied. In the single-step method, the ferrocene was dissolved in the xylene. In the two step-method the catalyst preparation step was performed first; ferrocene powder was placed in the preheater for a certain period of time and carried by a mixture of argon and hydrogen at fixed concentration to get catalyst nanoparticles deposited on the reactor wall. Xylene then was injected to the reactor. To study the effect of hydrogen, the synthesized materials were observed by SEM and TEM. The results showed that the presence of hydrogen is essential for CNTs to be synthesized by the CVD method, and also the concentration of hydrogen in the reactor has a great effect on the quality of CNTs. The yield of CNTs in the two-step method was slightly higher than that in the one-step method.

Du fait de leurs excellentes propriétés mécaniques et de leurs faibles masses spécifiques, l'utilisation des matériaux composites, au sein des structures mécaniques, est en plein essor. Cependant, leur usinage entraine une usure prématurée et aléatoire des outils de coupes en cermet WC-Co. L'origine de cette étude provient de la nécessité de protéger leur surface par un revêtement dur et résistant comme, par exemple, le diamant NCD. Toutefois, le cobalt présent dans le carbure cémenté favorise la formation de graphite au niveau de l'interface avec le film de diamant, ce qui nuit à son adhérence. La méthode retenue afin d'isoler ce métal de la surface a été de réaliser des systèmes interfaciaux multicouches. Ces derniers sont composés d'une barrière de diffusion au cobalt en nitrure de tantale et/ou en nitrure de zirconium et d'une couche favorisant la germination du diamant en acier inoxydable ou en molybdène. Les protocoles de dépôt élaborés au cours de ce travail ont la particularité d'utiliser une polarisation négative et séquencée du substrat durant l'étape de croissance. Cela induit une morphologie originale au revêtement de diamant breveté sous le nom de PyrNCD (Brevet N° :FR0807181). Les objectifs de cette étude sont la compréhension de l'ensemble des mécanismes (influence de la solubilité du carbone sur la germination du diamant, l'effet de la polarisation sur le substrat revêtu et sur la croissance du diamant,...) intervenant durant le dépôt de diamant et l'optimisation du procédé.

L'objectif de cette thèse porte sur la fabrication et la caractérisation de cellules solaires à jonction radiale à base d'assemblée de nanofils de silicium cristallin. Une étude sur la croissance des nanofils à partir de deux catalyseurs métalliques (cuivre et aluminium) dans une machine de dépôt chimique en phase vapeur (CVD) à pression réduite est présentée. L'influence des conditions de croissance sur la morphologie, le dopage et la contamination des nanofils par le catalyseur est analysée par des mesures électriques, chimiques (SIMS, Auger) et structurales (SEM, TEM, Raman). Le cuivre est utilisé pour la fabrication d'une cellule solaire avec des nanofils de type p et une jonction radiale créée avec du silicium amorphe de type n. Les performances photovoltaïques de la cellule solaire sont ensuite mesurées et interprétées. Un rendement de conversion de 5% est mesuré sur une cellule avec des nanofils de hauteur 1,5µm.

Background: In the past 37 years, increased efforts have been directed toward a better understanding of the importance of Hcy in disease and it has now become clear that hyperhomocysteinemia is a major independent risk factor for CVD. Extensive research on the influence of vitamin supplementation leading to reductions in Hcy levels and improvements in cardiovascular function has been done. The importance of exercise in the lowering of cardiovascular risk factors, as well as its favourable influence on cardiovascular function has also been indicated in several studies, however, the limited number of studies investigating the effect of exercise on Hcy concentrations revealed contradicting results. Furthermore, a relationship between Hcy concentration and cardiovascular function with the intervention of an exercise training and a vitamin supplementation programme respectively has also not been investigated. Objective: The objective of this study was to examine the effect of a 12-week exercise training and a 12-week vitamin supplementation intervention respectively on tHcy concentrations and cardiovascular function, and whether the change in tHcy concentration within the different interventions correlated with the change in cardiovascular function. Methods: In a randomised controlled cross-over intervention study, 52 men matched for age, cardiorespiratory fitness levels and cardiovascular risk factors were randomly assigned to one of 3 groups (Group A = exercise training programme, 20-30min. at 70-80% of HRmax; Group B = 400 g folic acid and 25 g vitamin B12 supplement; Group C = control). Group A and B were crossed over for phase 11, and Group C remained the control. The questionnaires were completed, and the body composition variables (BMI, WHR and body fat percentage), cardiovascular function (Finometer), tHcy concentrations and VO2max, were measured before and after each 12-week intervention period. A 6-week washout period separated the crossovers. Results: The ANCOVA, adjusted for age and BMI, showed that the percentage change from baseline to end, corrected for baseline of the tHcy concentration increased significantly (p ≤ .05) by 9.7% with the exercise training intervention and decreased significantly (p ≤ .05) by 12.9%, with the vitamin supplementation intervention. The ANCOVA of the percentage change from baseline to end in cardiovascular function showed that the vitamin supplementation intervention resulted in improvements in cardiovascular function (decreased resting MAP, TPR and increased resting SV, CO, Cw) in comparison to the impairment in cardiovascular function with the exercise training intervention (increased resting DBP, MAP and TPR). The relationship between the tHcy concentration and cardiovascular function at baseline and within each of the different interventions were assessed by partial correlations adjusted for age, BMI and VO2max. Significant (p ≤ .05) relationships only occurred within the vitamin supplementation intervention, where decreased percentage change in tHcy concentration significantly correlated with increased percentage change of resting SV and CO and decreased percentage change of resting TPR. Conclusion: The general conclusion that can be drawn is that a 12-week vitamin supplementation intervention showed increased health related results, e.g. a significant reduction in tHcy concentration, an improvement in cardiovascular function and a significant positive relationship between these b o factors, in comparison to the 12-week exercise training intervention that significantly increased the tHcy concentration and did not show increased health related results. Due to inadequate compliance to the exercise training intervention, no conclusion can be drawn with regard to the effect of exercise training on tHcy concentrations and cardiovascular function. / Thesis (M.Sc. (Human Movement Science))--North-West University, Potchefstroom Campus, 2007

Zeolites are crystalline aluminosilicates with diverse structures and uniform porosities. They are widely used as catalysts, adsorbents and ion-exchangers in industry. Direct or post modifications optimize the performance of zeolites for different applications. In this thesis, IZM-2 and TON-type zeolites were synthesized, modified and studied. In addition, FAU-type zeolite and silicoaluminophosphate (SAPO) molecular sieves were applied as templates for the preparation of microporous carbons. In the first part of this thesis, the IZM-2 zeolite with an unknown structure was synthesized. We focused on the increasing the secondary porosity and the varied framework compositions upon post modifications. The structure determination of this IZM-2 zeolite was hindered by the small size of crystals. In the second part of this thesis, the synthesis composition was directly modified in order to increase the crystal sizes. IZM-2 crystals were enlarged by excluding the aluminium atoms from the framework. The micropores of the obtained pure-silica polymorphs were activated by ion-exchanging alkali-metal ions with protons. Typically, TON-type zeolites that are synthesized at hydrothermal conditions under stirring have needle-shaped crystals. In the third part of this thesis, snowflake-shaped aggregates were produced by using static hydrothermal conditions for the synthesis of TON-type zeolites. The effects of synthesis parameters on the growth and morphology of crystals were discussed in detail. In the last part of this thesis, microporous carbons with a structural regularity were prepared by chemical vapour deposition (CVD) of propylene using a silicoaluminophosphate (SAPO-37) template. Compared to the conventional zeolite templates, the SAPO template could be removed under mild conditions, without using hydrofluoric acid, and the generated carbons had a large specific surface area and a high fraction of ultrasmall micropores. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

A series of ruthenium complexes of the general type Ru(CO)2(P(n-Bu)3)2(O2CR)2 (4a, R = Me; 4b, R = Et; 4c, R = i-Pr; 4d, R = t-Bu; 4e, R = CH2OCH3; 4f, R = CF3; 4g, R = CF2CF3) was synthesized by a single-step reaction of Ru3(CO)12 with P(n-Bu)3 and the respective carboxylic acid. The molecular structures of 4b, 4c and 4e–g in the solid state are discussed. All ruthenium complexes are stable against air and moisture and possess low melting points. The physical properties including the vapor pressure can be adjusted by modification of the carboxylate ligands. The chemical vapor deposition of ruthenium precursors 4a–f was carried out in a vertical cold-wall CVD reactor at substrate temperatures between 350 and 400 °C in a nitrogen atmosphere. These experiments show that all precursors are well suited for the deposition of phosphorus-doped ruthenium layers without addition of any reactive gas or an additional phosphorus source. In the films, phosphorus contents between 11 and 16 mol% were determined by XPS analysis. The obtained layers possess thicknesses between 25 and 65 nm and are highly conformal and dense as proven by SEM and AFM studies. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

L'objectif de cette étude était de réaliser des revêtements de TiO2 présentant une large variété de morphologies et d'établir des corrélations entre la structure de ces couches et leurs propriétés fonctionnelles, notamment la photocatalyse. Deux voies de synthèse employant le même précurseur, le tétra-isopropropoxide (TTIP) de titane, ont été utilisées, le procédé sol-gel et le dépôt chimique en phase vapeur (MOCVD). L'emploi de ces deux techniques permet de produire TiO2 sous une large gamme de morphologies mais avec des variétés polymorphiques similaires. Les revêtements synthétisés ont été caractérises afin de déterminer leur composition polymorphique, la taille des cristallites, la surface spécifique, la rugosité et l'épaisseur. Puis leur activité photocalytique pour la dégradation du bleu de méthylène a été déterminée. Par voie sol-gel, des dispersions de nano-cristallites de TiO2 dans l'eau, stables sur une longue durée (plus d'un an) en termes de composition polymorphique, taille d'agglomérats et de cristallites ont été synthétisées. Les revêtements ont été réalisés par tape-casting et dip-coating. Pour la synthèse en MOCVD, un plan d'expérience (PeX) a été utilisé, à notre connaissance pour la première fois. Il a permis de déterminer, d'une manière efficace et économique (avec un nombre minimum de tests expérimentaux), les paramètres les plus importants du procédé contrôlant les diverses propriétés quantifiables du revêtement. Il a aussi permis de mettre en évidence les interactions entre les paramètres de synthèse et leur effet sur la structure du revêtement. Les conclusions tirées du PeX sont en accord avec les résultats obtenus lors des études précédentes. L'analyse en composantes principales (ACP) a été réalisée pour avoir une vue globale de la façon dont les diverses propriétés des revêtements sont reliées entre elles / The overall objectives of this study was to find an environmental-friendly and simple procedure to synthesize titanium-dioxide, as well as, to determine the relation between the structural and functional properties of titanium dioxide coatings. Both of these objective have been attained in this study. By the sol-gel technique, titanium dioxide sols were synthesized by the hydrolysis of titanium(IV)isopropoxide. Nanocrystalline dispersions of TiO2 in water were prepared that were suitable for coatings and having long-term stability (more than 1 year) in terms of polymorphic composition, crystallite and agglomerate size. A design of experiments (DoE) was utilised, to our knowledge, for the first time in MOCVD for the synthesis of TiO2 coatings. It was employed to determine, in a timely and economical manner, the most significant process parameters for any quantifiable property of the coating and to highlight the interaction between these operating parameters, as well as, the correlation between the structure of the coating and the process. The conclusions drawn from the DoE were compared to results obtained by previous studies and were found to concur. Therefore, the DoE was successful in screening the most important process parameters, with a minimum number of experimental trials. For most of the properties that were under investigation, the DoE showed that, the deposition temperature and reactor pressure were, often-times, the most significant. Therefore, to change the microstructure and composition of MOCVD coatings, changing these process parameters will ensure the highest impact. It has to be stressed that the conclusions drawn from the DoE are restricted to the experimental range that was under investigation. Principal Component Analysis (PCA) was conducted to have an overall view of how the different properties of the coatings related with one another. The interpretations made from this analysis were that the photocatalytic (PC) activity of the coatings produced did not relate strongly to the polymorphic composition, which is contrary to literature review and is explained to be a result of the different morphologies that lead to different porosities and specific surface area. The PC activity did not depend on the mass over a critical mass. With this analysis it appeared to be clear that the porosity and specific surface area played a larger role than polymorphic composition. This hypothesis has to be verified because we did not succeed in determining the specific surface area of our coatings during this study. However, some preliminary tests have been conducted showing that cyclic voltametry could be used to evaluate the surface area of our films

Ce travail expérimental porte sur l'influence des paramètres de synthèse de nanotubes de carbone par CVD sur leurs caractéristiques structurales. Cette étude repose sur des analyses ex situ et in situ par spectroscopie Raman d'échantillons synthétisés sous diverses conditions de croissance. Une étude sur des films de cobalt oxydés a montré qu'il existe une variation de la pression seuil pour la croissance de nanotubes de carbone en fonction de l'épaisseur de cobalt que nous proposons d'attribuer à une pression seuil de réduction des particules.Une étude des bandes D et G' nous a permis d'attribuer les composantes basses fréquences aux nanotubes mono-feuillets et les composantes hautes fréquences à des espèces carbonées co-produites lors de la synthèse. Cette nouvelle approche a permis une étude plus fine des défauts et la proposition d'un modèle de création des défauts dans les nanotubes synthétisés par CVD. Enfin, une étude systématique des RBM nous a permis de mettre en évidence des processus favorisant la croissance de nanotubes mono-feuillets de petits ou de moyens diamètres. Ainsi, le contrôle de l'épaisseur de catalyseur, de la nature du précurseur carboné, de sa pression partielle ou encore de la température de synthèse permet de contrôler la distribution en diamètre des nanotubes mono-feuillets. / This experimental work deals with the influence of CVD growth parameters on carbon nanotube structural properties. The study is based on in situ and ex situ Raman spectroscopy on samples synthesized under various conditions of growth. A work on oxidized cobalt films showed that the threshold pressure for nanotube growth depends on the thickness of the cobalt film. We assign this pressure to a threshold pressure of reduction. A study of the D-band and G'-band allowed to assign low-frequency components to SWNT and high-frequency components to carbonaceous co-products of synthesis. This new approach allowed a fine study of defects which led to a model for defect creation in SWNT grown by CVD. A systematic study of RBM showed the processes leading to the preferential growth of small- or medium-diameter SWNT. Thus, control of catalyst thickness, of carbonaceous precursor nature and partial pressure or of synthesis temperature allows to control the diameter distribution of SWNT.

Este trabalho trata do crescimento de diamante policristalino pela técnica de deposição química a partir da fase vapor (CVD - "Chemical Vapor Deposition"), cuja característica é copiar a superfície do material sobre o qual está sendo crescido. Aliado ao fato do diamante ser material duro e resistente ao desgaste, vislumbra-se a sua aplicação como revestimento interno de bicos de ejeção de água com abrasivos utilizados em máquinas de corte a jato de água com abrasivos, que estão sujeitos a um grande desgaste por abrasão. É feito um estudo preliminar para determinar as condições ótimas de crescimento do filme e adequar os parâmetros de funcionamento do reator, obtendo um filme de boa qualidade morfológica e alta pureza. Os experimentos consistem no recobrimento de substratos cilíndrico de molibdênio de 1mm de diâmetro e comprimento de até 100mm, com superfícies polidas. Após o crescimento, as amostras são submetidas à corrosão do substrato, fornecendo tubos de diamante auto-sustentados. O polimento da superfície do substrato confere aos tubos de diamante uma superfície interna com baixa rugosidade. Estes tubos são ensaiados em um aparato de ejeção de água, dando condições de obter os parâmetros de desempenho hidrodinâmico (cf e cd). Estes resultados são comparados aos resultados obtidos com um tubo de igual geometria feito em cobre extrudado, cuja característica é apresentar um bom acabamento interno. Esta comparação comprova a possibilidade de aplicação do revestimento de diamante para a ejeção de líquidos.

L'objectif de la thèse était de synthétiser des tubes de SiC monolithiques pour améliorer l'étanchéité de la structure composite SiC/SiC d'une gaine de combustible nucléaire. Des revêtements tubulaires de 8 mm de diamètre et quelques centaines de micromètres d'épaisseur ont été produits par dépôt chimique en phase vapeur à pression atmosphérique à partir d'un mélange CH3SiHCl2/H2. Le procédé a été développé de manière à réaliser en continu des tubes de SiC de plusieurs dizaines de centimètres de long. La composition chimique et la microstructure des tubes ont été déterminées par microsonde de Castaing, spectroscopie Raman, DRX et microscopie électronique (MEB, MET). Les propriétés mécaniques des tubes ont été caractérisées par nanoindentation et à travers des essais de compression C-ring. Le comportement thermomécanique a également été étudié. L'étude du procédé comprend une étude thermocinétique, un suivi de la phase gazeuse par IRTF et la modélisation 2D du réacteur. / The goal of this study was to synthesize monolithic SiC tubes to improve sealing of the SiC / SiC composite of a nuclear fuel cladding structure. Tubes of 8 mm inner diameter and several hundred micrometers in thickness have been produced by atmospheric pressure chemical vapor deposition (APCVD) from a mixture CH3SiHCl2/H2. The method has been developed so as to produce continuous SiC tubes of up to thirty centimeters long. The chemical composition and microstructure of the tubes were determined by microprobe, Raman spectroscopy, XRD and electron microscopy (SEM, TEM). The mechanical properties of the tubes were characterized by nanoindentation tests and through compression C -ring . The thermomechanical behavior was also studied. The method includes consideration of a thermokinetic study , followed by a gas phase analysis by IRTF and 2D modeling of the reactor.