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The objective of this research was to develop and verify a mathematical model that enables the prediction of the effects of heat treatment on cast aluminum alloy components. The model, which uses the commercially available software (ABAQUS), predicts dimensional changes, distortion, and residual stresses in heat treated components. An extensive database is developed for an example aluminum alloy (A356) and includes the mechanical, physical, and thermal properties of the alloy all as functions of temperature. The database is obtained through calculations and measurements made on A356 alloy specimens. In addition, boundary conditions ¨C in the form of heat transfer coefficients for each of the heat treatment steps - are obtained from measurements performed with a special quenching system developed at the Center for Heat Treating Excellence at WPI. The database and boundary conditions were used in the software to predict the dimensional changes, distortions, and residual stresses that develop in a commercial A356 cast component that is subjected to a standard commercial heat treating cycle. In order to verify the accuracy of the software predictions, the predictions were compared to their measured counterparts, where dimensional changes and distortion were measured with a coordinate measuring machine, and residual stresses were measured with x-ray diffraction.

Pour améliorer les paramètres pharmacologiques d’un photosensibilisateur de seconde génération, la méta-tétra(hydroxyphényl)chlorine (mTHPC), plusieurs formules liposomales commerciales ont été élaborées, parmi elles le Foslip, qui correspond à la mTHPC dans des liposomes conventionnels. L’objectif de ce travail est d’étudier les caractéristiques photophysiques et photobiologiques du Foslip. L’exposition des suspensions de Foslip à de petites doses de lumière (10 mJ) a conduit à une baisse significative de la fluorescence, qui a cependant été restaurée après destruction des liposomes. Nous attribuons cette caractéristique au quenching de fluorescence photoinduite. Cet effet a été mis en évidence uniquement pour les concentrations locales élevées de mTHPC dans des bicouches lipidiques. Les résultats ont été interprétés en supposant une migration d’énergie entre les molécules rapprochées de mTHPC avec sa dissipation consécutive par les molécules du photoproduit se comportant comme des pièges d’énergie. Le quenching de fluorescence photoinduite ainsi que les techniques de polarisation et de chromatographie liquide ont été appliquées successivement pour estimer le taux de redistribution des molécules de mTHPC des liposomes vers les protéines du plasma et les membranes lipidiques. Les processus de redistribution de la mTHPC après injection intratumorale de mTHPC dans un modèle de récidive de cancer du sein sont en corrélation avec les résultats obtenus dans une étude in vitro de la redistribution du Foslip dans les liposomes DPPC. Il a été démontré que le phénomène de quenching de fluorescence photoinduite doit être pris en compte lors de l’utilisation de techniques optiques pour l’étude des applications in vivo et in vitro des formulations liposomales de mTHPC. / To improve the pharmacological parameters of a second-generation photosensitizer meta-tetra(hydroxyphenyl)chlorin (mTHPC) several commercial liposomal formulations were designed, among them Foslip, which corresponds to mTHPC in conventional liposomes. The objective of this work was to study photophysical and photobiological characteristics of Foslip. Exposure of Foslip suspensions to small light doses (10 mJ) resulted in a substantial drop in fluorescence, which however, was restored after destruction of liposomes. We attributed this behavior to photoinduced fluorescence quenching. This effect was revealed only for high local mTHPC concentrations in lipid bilayer. The results were interpreted supposing energy migration between closely located mTHPC molecules with its subsequent dissipation by the molecules of photoproduct acting as excitation energy traps. Photoinduced fluorescence quenching together with polarization techniques and liquid chromatography was successfully applied for estimation of the redistribution rate of mTHPC molecules from the liposomes to plasma proteins and lipid membranes. Foslip liposomes were shown to be stable in human blood serum for at least 3 hours. Such increased stability was attributed to incorporation of hydrophobic photosensitiser into lipid bilayer. The processes of mTHPC redistribution after Foslip intratumoral injection in a model of breast cancer recurrence were found to be in good agreement with the results obtained from in vitro study of mTHPC redistribution from Foslip to pure DPPC liposomes. It was demonstrated that photoinduced fluorescence quenching phenomena should be taken into account while using optical techniques for studying in vivo and in vitro applications of liposomal mTHPC formulations.

The cost of an aluminium extrusion die accounts for 35-50% of the total extrusion cost, hence it is important to understand the kinetics of extrusion die heat treatment. The main objective of die heat treatment is to increase the surface hardness so the surface wear property can be enhanced, which extends the die service life. Before the die material is case hardened by processes such as nitriding, the material is first heat treated to certain hardness. Thus the aim of this investigation is to understand the kinetics of carbon diffusion during steel austenitzation because it is significant to steel hardness property.H13 hot work tool steel, a well known material used as a die material for its superior mechanical and hardening properties, was used for the analysis of carbon diffusion during austenization. Samples made of H13 steel were subjected to four different atmospheric conditions: heat treatment without atmospheric control, heat treatment with stainless steel foil wrapping, pack carburization heat treatment and vacuum heat treatment. Three treatment time ranges were also applied for the carbon diffusion modelling. Some samples were further treated by gas nitriding to establish the effect of carbon content on the gas nitriding performance.It was found that decarburization occurred when atmospheric control did not take place during the heat treatment process. Through the carbon diffusion analysis, at austenitizing temperature of 1020ºC, the equilibrium surface carbon content at 1020ºC was 0.157wt%, with activation energy of carbon in H13 steel of 20,200cal/mol, and carbon diffusivity at 1020ºC was 1.97x10-8cm2/s.This study also proved that proper stainless steel foil wrapping on the heat treating material could restrict decarburization process, resulting in a constant hardness profile as vacuum heat treatment does. However the tempering characteristic between this two heat treatment methods are different to each other.For the pack carburization heat treatment, it was noted that the samples suffered from decarburization at early stage of heat treatment as carbon monoxide level was not adequate for carburization process.Results from the gas nitrided samples showed that the thickness and the hardness of the nitrided layer was independent to the carbon content in H13 steel. After 2 rounds of gas nitriding process, further nitriding seemed to have no significant effect on the hardness and thickness of the nitrided layer. Furthermore, the white layer was not observed in the nitrided samples which were heat treated without atmospheric control.

Methyl iodide photolysis has drawn considerable attention over the past years as an ¡§instantaneous¡¨ pseudo-linear dissociation that may be described by a two dimensional potential energy surface. Single photon excitation in methyl iodide results in a direct rupture of the C-I bound, and the dissociation occurs in 〜0.1 ps. The Ã-band photodissocation of methyl iodide yields ground state methyl radicals [CH3 X(2A2˝)] and either ground state iodine atoms [(2P3/2)I¡ÝI] or spin-orbit excited iodine atoms [(2P1/2)I¡ÝI*] . In the present work, we used the IR emission technique to study the kinetics of CH3I photolysis. The intensity of 1.315 £gm infrared fluorescence from I* (2P1/2) is detected and analyzed. We have studied the influences on I* emissions by a variety of quenchers. Their roles in additional reactions and the quenching mechanism were reported.

The cost of an aluminium extrusion die accounts for 35-50% of the total extrusion cost, hence it is important to understand the kinetics of extrusion die heat treatment. The main objective of die heat treatment is to increase the surface hardness so the surface wear property can be enhanced, which extends the die service life. Before the die material is case hardened by processes such as nitriding, the material is first heat treated to certain hardness. Thus the aim of this investigation is to understand the kinetics of carbon diffusion during steel austenitzation because it is significant to steel hardness property.H13 hot work tool steel, a well known material used as a die material for its superior mechanical and hardening properties, was used for the analysis of carbon diffusion during austenization. Samples made of H13 steel were subjected to four different atmospheric conditions: heat treatment without atmospheric control, heat treatment with stainless steel foil wrapping, pack carburization heat treatment and vacuum heat treatment. Three treatment time ranges were also applied for the carbon diffusion modelling. Some samples were further treated by gas nitriding to establish the effect of carbon content on the gas nitriding performance.It was found that decarburization occurred when atmospheric control did not take place during the heat treatment process. Through the carbon diffusion analysis, at austenitizing temperature of 1020ºC, the equilibrium surface carbon content at 1020ºC was 0.157wt%, with activation energy of carbon in H13 steel of 20,200cal/mol, and carbon diffusivity at 1020ºC was 1.97x10-8cm2/s.This study also proved that proper stainless steel foil wrapping on the heat treating material could restrict decarburization process, resulting in a constant hardness profile as vacuum heat treatment does. However the tempering characteristic between this two heat treatment methods are different to each other.For the pack carburization heat treatment, it was noted that the samples suffered from decarburization at early stage of heat treatment as carbon monoxide level was not adequate for carburization process.Results from the gas nitrided samples showed that the thickness and the hardness of the nitrided layer was independent to the carbon content in H13 steel. After 2 rounds of gas nitriding process, further nitriding seemed to have no significant effect on the hardness and thickness of the nitrided layer. Furthermore, the white layer was not observed in the nitrided samples which were heat treated without atmospheric control.

The heat-transfer phenomena in the quenching process have been studied using stainless steel and mild steel specimens in brine (3% by wt. NaCl), water, oil and air, under controlled conditions. The experimental data were analysed using a simple mathematical model of the quenching process to study the relationship between the surface temperature of the specimen and the surface heat-transfer coefficient. The influence on this relationship, of important variables such as initial specimen temperature, quenchant temperature, surface oxidation, etc. has been studied. The results from the experimental data are in good agreement with the results of previous workers. The results obtained in this work, together with Jominy-test data and the mathematical model, were used to determine the necessary quenching conditions required to obtain a desired thermal history or mechanical property at a given position in a 4 inch diameter steel grinding-ball. A steel ball was then quenched under the above determined conditions and an examination of the ball section showed that the desired property was indeed present at the given location. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Due to the penetration of variable renewable energy (VRE) sources, conventional coal fired power plants need to operate with greater flexibility via two-shifting or low load operation whilst remaining reliable and conserving the lifetime of components. Thick sectioned components are prone to thermal fatigue cracking as a result of through-wall temperature gradients during start up and shutdown. These temperature gradients can be significantly amplified during quenching when components at high temperature are unintentionally exposed to colder liquid or steam. Such quench events are known to occur during two-shift operation of a large once-through coal fired tower type boiler, which is the subject of this study. The purpose of this study is to develop and demonstrate a methodology to determine the root cause of quenching in a once-through tower type boiler and provide information that can be used to predict the impact on thick-walled components by estimating the through-wall temperature gradients. The first modelling element in the methodology is a simplified transient heat transfer model for investigating condensation of steam in the superheater. The model is presented and verified by comparison with real plant data. The second element is a liquid tracking model that approximates the liquid level in the superheater as a function of time to predict the location and magnitude of through-wall temperature gradients. The complex geometry of the superheater was divided into a number of control volumes and a dynamic thermo-fluid process model was developed to solve the transient conservation of mass and energy equations for each volume using a semi-implicit time wise integration scheme. The liquid tracking model was verified by comparison with a similar model constructed in Flownex and also by comparison with plant data. Varying levels of discretisation were applied to a particular quench event and the results are presented. The third modelling element is a two-dimensional transient pipe wall conduction model that is used at selected localities to evaluate the temperature gradients within the pipe wall. The temperature gradients and internal heat flux were verified by temperature measurements from the outer surface of a main steam pipe undergoing quenching. The stresses associated with the temperature gradients were also briefly considered. The real plant quenching problem is analysed in detail and found to be caused by liquid overflow from the separators. A particular plant configuration creates a previously unidentified siphon of water from the separating and collecting vessel system into the superheater. This situation is not recognised by plant operators and thus persists for some time and causes flooding of the superheater. Analysis of the resultant through-wall temperature gradients show that quenching causes significant stresses which can be avoided. By understanding the causes and preventing the occurrence of quenching, the life of thick-walled high temperature components can be conserved.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20215号 / 理博第4300号 / 新制||理||1618(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 鹿内 利治, 教授 長谷 あきら, 准教授 小山 時隆 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Investigation of the thermal quenching of photoluminescence (PL) in semiconductors provides valuable information on identity and characteristics of point defects in these materials, which helps to better understand and improve the properties of semiconductor materials and devices. Abrupt and tunable thermal quenching (ATQ) of PL is a relatively new phenomenon with an unusual behavior of PL. This mechanism was able to explain what a traditional model failed to explain. Usually, in traditional model used to explain “normal” quenching, the slope of PL quenching in the Arrhenius plot determines the ionization energy of the defect causing the PL band. However, in abrupt quenching when the intensity of PL decreases by several orders of magnitude within a small range of temperature, the slope in the Arrhenius plot has no relation to the ionization energy of any defect. It is not known a priori if the thermal quenching of a particular PL band is normal or abrupt and tunable. Studying new cases of unusual thermal quenching, classifying and explaining them helps to predict new cases and understand deeper the ATQ mechanism of PL thermal quenching. Very few examples of abrupt and tunable quenching of PL in semiconductors can be found in literature. The abrupt and tunable thermal quenching, reported here for the first time for high-resistivity ZnO, provides an evidence to settle the dispute concerning the energy position of the LiZn acceptor. In high-resistivity GaN samples, the common PL bands related to defects are the yellow luminescence (YL) band and a broad band in the blue spectral region (BL2). In this work, we report for the first time the observation of abrupt and tunable thermal quenching of the YL band in GaN. The activation energies for the YL and BL2 bands calculated through the new mechanism show agreement with the reported values. From this study we predict that the ATQ phenomenon is quite common for high-resistivity semiconductors.