Hydrogen embrittlement is a problem that offers challenges both to technology and to the theory of metallurgy. In the presence of a hydrogen rich environment, applications such as rolling bearings display a significant decrease in alloy strength and accelerated failure due to rolling contact fatigue. In spite of these problems being well recognised, there is little understanding as to which mechanisms are present in hydrogen induced bearing failure. The objective of this thesis are twofold. First, a novel alloy combining the excellent hardness of bearing steels, and resistance to hydrogen embrittlement, is proposed. Second, a new technique to identify the nature of hydrogen embrittlement in bearing steels is suggested. The new alloy was a successful result of computer aided alloy design; thermodynamic and kinetic modelling were employed to design a composition and heat treatment combining (1) fine cementite providing a strong and ductile microstructure, and (2) nano-sized vanadium carbide precipitates acting as hydrogen traps. A novel technique is proposed to visualise the migration of hydrogen to indentation-induced cracks. The observations employing this technique strongly suggest that hydrogen enhanced localised plasticity prevails in bearing steels. While proposing a hydrogen tolerant bearing steel grade, and a new technique to visualize hydrogen damage, this thesis is expected to aid in increasing the reliability of bearings operating in hydrogen rich environments.

ermal desorption spectroscopy (TDS) is a common method for surface analysis of adsorbed molecules. In chapter 1 the work deals with the theoretical background of this method and shows the principles of a desorption process influenced by subsurface diffusion. Chapter 2 first shows application of TDS for detection of surface molecules and determination of binding energy.Experiments were mainly focused on ditermination of surface adsorbents and impurities on Si wafers. The second part of chapter 2 describes desorption of atoms of a Ga layer on Si surface and their subsurface diffusion. A Ga diffusion process was also observed by with secondary ion mass spectrometry (SIMS) and numerically simulated.

No description available.

Room-temperature chemisorption of hexacyclic aromatic hydrocarbons on the 2x1, sputtered, oxidized and H-terminated Si(100) surfaces, as well as those upon post treatments of hydrogenation, oxidization and electron irradiation have been investigated by using thermal desorption spectrometry (TDS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). This work focuses on the effects of the functional groups (phenyl, methyl, vinyl, heteroatom, and H atom) in the chemisorbed aromatic hydrocarbons (benzene, toluene, xylene isomers, styrene and pyridine) on organic functionalization of the Si(100) surface, particularly on such surface processes as cycloaddition, dative adsorption, hydrogen abstraction, desorption, dissociation, diffusion, and condensation polymerization. Unlike the earlier notion that hydrogen evolution in the hydrocarbon/Si(100) systems is the result of hydrocarbon dissociation (into smaller hydrocarbon fragments and H atoms) on the surface, condensation polymerization of the adsorbed aromatic hydrocarbons is proposed in the present work, in order to explain the higher-temperature hydrogen evolution feature in the toluene/Si(100) system. This hypothesis is supported by our TDS results for other hydrocarbon adsorbates, especially in the pyridine/Si(100) system where electron-induced condensation polymerization has been observed at room temperature. The improved techniques in the TDS experiments developed in the present work have enabled us to observe condensation polymerization and the effect of H on the surface processes (via surface reconstruction) on Si(100) for the first time. New analysis methods have also been developed to determine the adsorption coverage from the AES data, and this work has not only improved the accuracy of the elemental-coverage evaluation, but also provided a means to estimate the rate and the order of chemisorption. By using the density functional theory with the Gaussian 98 program, the adsorption geometries and the corresponding adsorption energies of various adsorption phases have been calculated. These computational results have provided useful insights into the chemisorption structures on the Si(100) surface. The present work also presents the development of three kinetics models for hydrogen evolution in the aforementioned aromatic-hydrocarbon systems on Si(100). Based on a modified collision theory with consideration of diffusion, these theoretical models have proven to be quite successful in simulating the observed TDS profiles and in estimating the kinetic parameters for the analysis of condensation polymerization in 2-dimensional diffusion systems. The present work illustrates that TDS experiments can be used effectively with quantum computation and theoretical kinetics modelling to elucidate the intricate nature of organosilicon surface chemistry.

[pt] A presente tese apresenta uma abordagem sobre a técnica de dessorção térmica na remediação de áreas contaminadas, esta tecnologia se baseia no aquecimento direto do solo. A propagação de calor num solo é simulada matematicamente pelo fluxo acoplado de calor. Para que esta simulação seja possível é necessário a identificação dos parâmetros relevantes para o problema: condutividade hidráulica em função da umidade volumétrica, condutividade térmica em função da umidade volumétrica, capacidade de aquecimento volumétrico, e, curva característica de sucção. Uma discussão técnica é apresentada sobre estes parâmetros. Foram estudados dois tipos de solos, uma argilo-arenoso (Campo Experimental da PUC-Rio) e um areno-argiloso (Cidade dos Meninos). É apresentado um estudo físico-químico sobre os efeitos da temperatura nos solos, com ensaios de RaiosX, Microscopia Eletrônica, CTC, Ataque Sulfúrico e de Caracterização para solos não aquecidos e previamente aquecidos até a temperatura de 300 Graus Celsius. São apresentadas metodologias e equipamentos que foram desenvolvidos e/ou adaptados de para o estudo das propriedades termo- hidráulicas necessárias. Foram realizados ensaios de condutividade hidáulica, curvas características de sucção e deformabilidade, levando-se em conta a temperatura. Todos os parâmetros mostraram-se altamente dependente desta. Os parâmetros térmicos, condutividade térmica e calor específico, foram determinados para estes dois de solos. / [en] This thesis presents an introduction on the use of the thermal desorption technique that is based on the direct heating of the soil, for the remediation of contaminated areas. Heat propagation through soils can be mathematically simulated using coupled heat-moisture transfer theories. In order to make this simulation possible it is necessary to identify the required parameters: hydraulic conductivity as a function of volumetric water content, thermal conductivity as a function of volumetric water content, volumetric heat capacity, and soil-water characteristic curve. One technical description of such parameters is presented. Two different kinds of soils were used, one clay- sand (CH) and one sandclay (SC). A study physico-chemical was done talking into consideration the temperature effect on the soils with X-Ray, electron microscopic investigation, CTC, Atterberg Limits and at the particle size distribution. The study was done on pre-heated soils with temperatures ranging from 20 Degrees Celsius to 300 Degrees Celsius. Equipments and methodologies have been especially developed for the study of the thermo-hydraulics proprieties. The laboratory tests program consisted of hydraulic conductivity, retention curves and deformability, taking into account the temperature effects. During the tests it was observed that all parameters were temperature dependent. The thermal parameters, thermal conductivity and heat capacity were studied for both soils.

Room-temperature chemisorption of hexacyclic aromatic hydrocarbons on the 2x1, sputtered, oxidized and H-terminated Si(100) surfaces, as well as those upon post treatments of hydrogenation, oxidization and electron irradiation have been investigated by using thermal desorption spectrometry (TDS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). This work focuses on the effects of the functional groups (phenyl, methyl, vinyl, heteroatom, and H atom) in the chemisorbed aromatic hydrocarbons (benzene, toluene, xylene isomers, styrene and pyridine) on organic functionalization of the Si(100) surface, particularly on such surface processes as cycloaddition, dative adsorption, hydrogen abstraction, desorption, dissociation, diffusion, and condensation polymerization. Unlike the earlier notion that hydrogen evolution in the hydrocarbon/Si(100) systems is the result of hydrocarbon dissociation (into smaller hydrocarbon fragments and H atoms) on the surface, condensation polymerization of the adsorbed aromatic hydrocarbons is proposed in the present work, in order to explain the higher-temperature hydrogen evolution feature in the toluene/Si(100) system. This hypothesis is supported by our TDS results for other hydrocarbon adsorbates, especially in the pyridine/Si(100) system where electron-induced condensation polymerization has been observed at room temperature. The improved techniques in the TDS experiments developed in the present work have enabled us to observe condensation polymerization and the effect of H on the surface processes (via surface reconstruction) on Si(100) for the first time. New analysis methods have also been developed to determine the adsorption coverage from the AES data, and this work has not only improved the accuracy of the elemental-coverage evaluation, but also provided a means to estimate the rate and the order of chemisorption. By using the density functional theory with the Gaussian 98 program, the adsorption geometries and the corresponding adsorption energies of various adsorption phases have been calculated. These computational results have provided useful insights into the chemisorption structures on the Si(100) surface. The present work also presents the development of three kinetics models for hydrogen evolution in the aforementioned aromatic-hydrocarbon systems on Si(100). Based on a modified collision theory with consideration of diffusion, these theoretical models have proven to be quite successful in simulating the observed TDS profiles and in estimating the kinetic parameters for the analysis of condensation polymerization in 2-dimensional diffusion systems. The present work illustrates that TDS experiments can be used effectively with quantum computation and theoretical kinetics modelling to elucidate the intricate nature of organosilicon surface chemistry.

An investigation of binary fluid heat and mass transfer in ammonia-water absorption was conducted. Experiments were conducted on a horizontal-tube falling-film absorber consisting of four columns of six 9.5 mm (3/8 in) nominal OD, 0.292 m (11.5 in) long tubes, installed in an absorption heat pump. Measurements were recorded at both system and local levels within the absorber for a wide range of operating conditions (nominally, desorber solution outlet concentrations of 5 - 40% for three nominal absorber pressures of 150, 345 and 500 kPa, for solution flow rates of 0.019 - 0.034 kg/s.). Local measurements were supplemented by high-speed, high-resolution visualization of the flow over the tube banks. Using the measurements and observations from videos, heat and mass transfer rates, heat and vapor mass transfer coefficients for each test condition were determined at the component and local levels. For the range of experiments conducted, the overall film heat transfer coefficient varied from 923 to 2857 W/m²-K while the vapor and liquid mass transfer coefficients varied from 0.0026 to 0.25 m/s and from 5.51×10^-6 to 3.31×10^-5 m/s, respectively. Local measurements and insights from the video frames were used to obtain the contributions of falling-film and droplet modes to the total absorption rates. The local heat transfer coefficients varied from 78 to 6116 W/m²-K, while the local vapor and liquid mass transfer coefficients varied from -0.04 to 2.8 m/s and from -3.59×10^-5 (indicating local desorption in some cases) to 8.96×10^-5 m/s, respectively. The heat transfer coefficient was found to increase with solution Reynolds number, while the mass transfer coefficient was found to be primarily determined by the vapor and solution properties. Based on the observed trends, correlations were developed to predict heat and mass transfer coefficients valid for the range of experimental conditions tested. These correlations can be used to design horizontal tube falling-film absorbers for ammonia-water absorption systems.

A wide range of organic compounds are released from building and furnishing products and these have the potential to adversely affect indoor air quality. There are growing international requirements for testing and controlling these emissions for the protection of public health. The test methods require specialist analytical chemistry facilities based on thermal desorption/gas chromatography/mass spectrometry (TD/GC/MS). This project has addressed the need for better performance and greater automation of the analysis, as well as development of simpler screening tests. A variety of products were tested using screening techniques, with an emission cell method being used as a reference test. Short duration tests, using a micro-scale chamber at slightly elevated temperature, were shown to have the potential to predict emissions occurring during longer term reference tests. Multi-sorbent air sampling tubes, that have the potential to extend the volatility range of compounds determined by a single TD/GC/MS analysis, were compared with Tenax TA tubes specified by current standard methods. This showed no difference in performance for the range of compounds for which Tenax is optimal, with improved performance for a number of more volatile compounds. The determination of formaldehyde was investigated using 2-hydroxymethylpiperidine as a derivatising agent, followed by TD/GC/MS. The results showed the possibility of this method being developed as an alternative to the current standard method that involves solvent elution and liquid chromatography. The performance of a newly developed time-of-flight mass spectrometer was compared with a standard quadrupole instrument. This showed its potential, with the use of re-collection, to extend the concentration range of compounds quantified from a single air sample, of particular benefit for the determination of carcinogens. New compound identification software was applied to increase automation of analysis of the TD/GC/MS data. Good correlation with manual processing was achieved, demonstrating the possibility of routine application to material emissions testing.

Motivation: The accurate and reliable measurement of the concentration of coal tar pitch volatiles (CTPVs) in ambient air has proved to be a challenge for occupational hygienists. The challenge must however be confronted due to, amongst others, the carcinogenic properties of some poly–aromatic hydrocarbons (PAHs) contained in CTPVs. Aim: To determine the feasibility of a thermal desorption (TD) technique based method as an alternative method to be used for the measurement of the concentration of CTPVs in ambient air by assessing it along criteria such as ease of use, cost, accuracy and precision by comparing it to NIOSH’s Method 5515 and OSHA’s Method 58 and to determine the level of exposure to CTPVs on the anode paste floor of an electric furnace, used for the smelting of platinum group metals (PGMs) concentrate. Methodology: To satisfy the research objective, two accepted methods the National Institute of Occupational Safety and Health’s (NIOSH) method 5515 and the Occupational Safety and Health Administration’s (OSHA) method 58 were used for the measurement of the concentration of CTPVs with a TD technique based method used as a third, alternative method. All three methods were used concurrently to measure the concentration of CTPVs in ambient air, at the anode paste floor of a platinum group metals (PGMs) concentrate smelter. Results and conclusions: The NIOSH method proved to be the most precise method while the TD technique based method proved to be the most accurate. The TD technique based method proved to measure the widest range of individual CTPVs and were able to measure the highest concentration of Benzo(a)pyrene, an individual CTPV that is classified as a Group 1 (carcinogenic to humans) chemical substance by the International Agency for Research on Cancer (IARC). The OSHA method measured on average almost four times less total CTPVs than either the NIOSH or the TD technique based method and failed to readily measure individual CTPVs with a molecular weight lower than that of Phenanthrene. / Thesis (M.Sc. (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2012.

Motivation: The accurate and reliable measurement of the concentration of coal tar pitch volatiles (CTPVs) in ambient air has proved to be a challenge for occupational hygienists. The challenge must however be confronted due to, amongst others, the carcinogenic properties of some poly–aromatic hydrocarbons (PAHs) contained in CTPVs. Aim: To determine the feasibility of a thermal desorption (TD) technique based method as an alternative method to be used for the measurement of the concentration of CTPVs in ambient air by assessing it along criteria such as ease of use, cost, accuracy and precision by comparing it to NIOSH’s Method 5515 and OSHA’s Method 58 and to determine the level of exposure to CTPVs on the anode paste floor of an electric furnace, used for the smelting of platinum group metals (PGMs) concentrate. Methodology: To satisfy the research objective, two accepted methods the National Institute of Occupational Safety and Health’s (NIOSH) method 5515 and the Occupational Safety and Health Administration’s (OSHA) method 58 were used for the measurement of the concentration of CTPVs with a TD technique based method used as a third, alternative method. All three methods were used concurrently to measure the concentration of CTPVs in ambient air, at the anode paste floor of a platinum group metals (PGMs) concentrate smelter. Results and conclusions: The NIOSH method proved to be the most precise method while the TD technique based method proved to be the most accurate. The TD technique based method proved to measure the widest range of individual CTPVs and were able to measure the highest concentration of Benzo(a)pyrene, an individual CTPV that is classified as a Group 1 (carcinogenic to humans) chemical substance by the International Agency for Research on Cancer (IARC). The OSHA method measured on average almost four times less total CTPVs than either the NIOSH or the TD technique based method and failed to readily measure individual CTPVs with a molecular weight lower than that of Phenanthrene. / Thesis (M.Sc. (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2012.