Дисертації з теми "Thermodynamic instabilities and phase transition"

In dieser Arbeit wird mit Hilfe der Gitter-Methode der Phasenübergang/Crossover bei nicht verschwindender Temperatur der Quantenchromodynamik mit zwei Quark Flavour untersucht sowie die thermodynamische Zustandsgleichung berechnet. Es wird dabei die Wilson twisted-mass Formulierung der Quark-Wirkung verwendet, welche hinsichtlich des Kontinuum-Limes eine automatische Verbesserung birgt. Erste belastbare Resultate mit dieser Wirkung bei endlicher Temperatur werden in dieser Arbeit gezeigt. Mehrere kleine Werte der Pion-Masse werden betrachtet mit dem Ziel, Aufschluss über die Ordnung des Phasenüberganges im chiralen Limes zu erhalten. Im Bereich der von uns simulierten Pion-Massen zwischen 300 und 700 MeV wird hierbei lediglich ein Crossover-Übergang beobachtet. Die Abhängigkeit der gemessenen Crossover-Temperatur von der Masse wird für eine Extrapolation zu verschwindender Masse hin verwendet unter der Annahme verschiedener Szenarien für den chiralen Limes. Dazu komplementär wird das chirale Kondensat, der Ordnungsparameter der spontanen Brechung der chiralen Symmetrie, vor dem Hintergrund der so genannten magnetischen Zustandsgleichung untersucht, welche das universelle Verhalten in der Nähe des Phasenüberganges für die Universalitätsklasse des O(4) Modells angibt. Hinsichtlich der Thermodynamik wird ausgehend von der Spur-Anomalie und unter Benutzung der Temperatur-Integral Methode der Druck und die Energiedichte im Crossover-Gebiet berechnet. Der Kontinuum-Limes der Spur-Anomalie wird mit mehreren Gitterdiskretisierungen der Temperatur Nt sowie unter Zuhilfenahme einer tree-level Korrektur untersucht.
In this thesis we report about an investigation of the finite temperature crossover/phase transition of quantum chromodynamics and the evaluation of the thermodynamic equation of state. To this end the lattice method and the Wilson twisted mass discretisation of the quark action are used. This formulation is known to have an automatic improvement of lattice artifacts and thus an improved continuum limit behaviour. This work presents first robust results using this action for the non-vanishing temperature case. We investigate the chiral limit of the two flavour phase transition with several small values of the pion mass in order to address the open question of the order of the transition in the limit of vanishing quark mass. For the currently simulated pion masses in the range of 300 to 700 MeV we present evidence that the finite temperature transition is a crossover transition rather than a genuine phase transition. The chiral limit is investigated by comparing the scaling of the observed crossover temperature with the mass including several possible scenarios. Complementary to this approach the chiral condensate as the order parameter for the spontaneous breaking of chiral symmetry is analysed in comparison with the O(4) universal scaling function which characterises a second order transition. With respect to thermodynamics the equation of state is obtained from the trace anomaly employing the temperature integral method which provides the pressure and energy density in the crossover region. The continuum limit of the trace anomaly is studied by considering several values of Nt and the tree-level correction technique.

In view of the important applications of carbides and carbo-nitrides of transition metals in the heat-resistant and hard materials industries, the thermodynamic activities of Cr and Mn in the Cr-C, Fe-Cr-C, Mn-Ni-C and Mn-Ni-C-N systems have been studied in the present work by the use of the galvanic cell technique. CaF₂ single crystals were used as the solid electrolyte. The phase relationships in selected regions of the systems in question were investigated by the use of the equilibration technique. The phase compositions and microstructures of the alloys were analysed by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).

In the Cr-C system, the Gibbs energy of formation of Cr3C2 were obtained from ElectroMotive Force (EMF) measurements conducted in the temperature range 950-1150 K. The values of the enthalpy of formation of Cr₃C₂ were evaluated by the third-law method. The ground-state energy of the hypothetic end-member compound CrC3, in the bcc structure at 0 K, was calculated by use of the Ab-initio method. Based on the obtained results the Cr-C system was reassessed by use of the CALPHAD approach.

In the Fe-Cr-C system, 16 different alloys were quenched at 1223 K and their equilibrium phases identified by XRD. The experimental results show that the substitution of Cr by Fe in the (Cr,Fe)₇C₃ carbide changes the lattice parameters of the phase. A slight decrease of the lattice parameters with an increase in the Fe content was established. The lattice parameters of the γ-phase in the Fe-Cr solid solution did also show a decrease with an increase of the Fe content. The activities of chromium in Fe-Cr-C alloys were investigated in the temperature range 940-1155 K. The activity of chromium decreases with an increase in the Fe content when the ratio of C/(Cr+C) was constant. It was also established that the activity of chromium decreases with an increase of the carbon content when the iron content was constant. The experimental results obtained were compared with the data calculated by use of the Thermo-Calc software.

In the Mn-Ni-C system the phase relationships were investigated at 1073 K as well as at 1223 K. The experimental results obtained showed that the site fraction of Ni in the metallic sublattice of the carbides M₂₃C₆, M₇C₃ and M₅C₂ (M=Mn and Ni) was quite low (approximately 2~3 percent). The activities of manganese in Mn-Ni-C alloys were investigated in the temperature range 940-1165 K. The three-phase region γ/M₇C₃/graphite was partly constructed at 1073 K.

In the Mn-Ni-C-N system, nitrogen was introduced into Mn-Ni-C alloys by equilibrating with N2 gas. It was established that the solubility of nitrogen in the investigated alloys was effected by the carbon content, and that a (Mn,Ni)₄(N,C) compound was formed in the nitrided alloys. EMF measurements were performed on Mn-Ni-C-N alloys in the temperature interval 940-1127 K. The addition of nitrogen to Mn-Ni-C alloys was found to decrease the activity of manganese. The negative effect of nitrogen on the activity of manganese was found to decrease as the carbon content increased.

Keywords: Thermodynamic activity; Galvanic cell technique; Transition metal carbides; Transition metal nitrides; Phase equilibrium; Thermodynamics; Differential thermal analysis; Scanning electron microscopy; Transmission electron microscopy; Ab-initio calculations; CALPHAD approach;

Materials in proximity to quantum critical points (QCPs) experience strong fluctuations in the order parameter associated with the transition and often, as a result, display interesting properties. In this dissertation, we have used a variety of experimental probes such as Shubnikov-de Haas quantum oscillations, thermal conductivity and heat capacity, to better understand two such materials — $A_3T_4$Sn$_{13}$ and YFe$_2$Ge$_2$. $A_3T_4$Sn$_{13}$ ($A$ = Ca, Sr; $T$ = Ir, Rh) is a family of quasi-skutterudite superconductors with moderate $T_c$’s between 4 and 8 K. Although the superconductivity is believed to be phonon-mediated with s-wave pairing symmetry, an unusual second-order structural transition makes this material family fascinating to study. Whether this structural transition is a result of three distortions with perpendicular wavevectors resulting in a cubic-to-cubic transformation, or each wavevector acting independently giving rise to cubic-to-tetragonal transformations and formation of twinned domains is a disputed issue. We have measured quantum oscillations in the resistivity of Sr3Ir4Sn13 and compared it to density functional theory (DFT) calculations for both scenarios. Our results strongly suggest that the former interpretation is correct. The structural transition temperature $T^*$ in $A_3T_4$Sn$_{13}$ can be suppressed to zero by tuning with physical or chemical pressure. In (Ca$_x$Sr$_{1−x}$)$_3$Rh$_4$Sn$_13$, the quantum critical point can be accessed purely by chemical substitution at x ~ 0.9. In the vicinity of the QCP, we expect large fluctuations of the order parameter at low temperatures, which for a structural transition could manifest as a structural disorder. We have measured thermal conductivity at temperatures much lower than $T_c$ and found that it is well described by a single power law with suppressed exponents near the QCP. The heat capacity, however, remains ~ $T^3$. After excluding conventional phonon scattering mechanisms, we propose the possibility of intrinsic quasi-static spatial disorder that is related to the structural QCP. YFe$_2$Ge$_2$ is closely linked to the “122” family of iron-based superconductors like KFe$_2$As$_2$, although it has a significantly lower $T_c$ ~ 1 K. It has a rather three-dimensional Fermi surface which closely resembles that of KFe$_2$As$_2$ in the pressure-induced collapsed tetragonal phase. YFe$_2$Ge$_2$ is in proximity to several types of magnetic order which are predicted by DFT calculations to have lower energy than the non-spin polarised case. Even though YFe$_2$Ge$_2$ is non-magnetic, its superconductivity could be strongly affected by magnetic fluctuations. Through a collaboration with researchers at the University of Waterloo, we have measured the thermal conductivity of YFe$_2$Ge$_2$ down to millikelvin temperatures and up to 2.5 T in field. Our results suggest that YFe$_2$Ge$_2$ is a nodal superconductor. This result could assist in the explanation of the unconventional superconductivity in iron-based superconductors.

This study gives our calculations for the temperature-pressure and temperature-concentration phase diagrams using the mean field models applied to ammonium halides (NH4Cl, ND4Cl), ammonium sulfate ((NH4)2SO4/H2O), lithium potassium rubidium sulfate (LiK1-xRbxSO4), potassium pyrosulfate-potassium hydrogensulfate (K2S2O7-KHSO4), cholestanyl myristate-cholesteryl myristate (CnM-CrM), cholestanyl myristate-cholesteryl oleate (CnM-CO), benzene (C6H6) and ice. The phase line equations are derived from the free energies expanded in terms of the order parameters and they are fitted to the experimental data. Some thermodynamic quantities are calculated close to phase transitions in these crystalline systems. We also calculate the specific heat CV using the Raman frequency shifts for NH4Br on the basis of an Ising model close to the lambda-phase transition. A linear relationship is obtained between the specific heat CP and the frequency shifts (1/v)(dv/dT)P near the lambda-point in NH4Br.

In this dissertation, we will study solvent-vapor induced spherulitic growth in multicomponent thin films modeled as prestressed elastic solids. The interface between the crystalline phase and the amorphous phase will be treated as an evolving thermodynamic system and no diffusion of any component will be considered. The dissertation is divided into three parts. In Part I we will determine necessary conditions of thermodynamic equilibrium between the two solid phases, the inter- face, and the vapor. In Part II we will derive the thermodynamic driving force for spherulitic growth in multicomponent elastic thin films. In Part III we will investigate the effect of prestress on the directional dependence of the growth. There a formula that delineates how the prestress affects the shape of the spherulite will be proposed.

Orientador: Wei-Liang Qian
Resumo: Uma característica vital da cromodinâmica quântica (QCD) está relacionada à simetria quiral. Isso é particularmente intrigante devido ao papel crítico da simetria quiral não abeliana dos spinores de Lorentz na física teórica moderna. Muitos esforços teóricos foram dedicados à sua quebra espontânea no vácuo, bem como a restauração da mesma no ambiente extremamente quente ou denso. Além disso, quarks e glúons tornam-se os graus de liberdade relevantes por meio da transição de desconfinamento do estado dos hádrons. O significado desta última está intimamente ligado às implicações da equação de Callan-Symanzik e à teoria do grupo renormalizado. No entanto, em princípio, ambas as transições acima podem ser descritas pela QCD. Os estudos da QCD na rede demonstraram que a transição do sistema é um cruzamento suave com a densidade bariônica nula e a massa de quarks estranhos grandes. No potencial químico finito, por outro lado, uma variedade de modelos prevê a ocorrência de uma transição de fase de primeira ordem entre a fase hadrônica e o plasma de quarks e glúons (QGP). Esses resultados indicam que um ponto crítico (CEP) pode estar localizado em algum lugar no diagrama de fases da QCD no qual a linha de transições de fase de primeira ordem termina. Espera-se que a transição seja de segunda ordem neste caso. De fato, entre outros objetivos estabelecidos, o programa Beam Energy Scan (BES) em andamento no Relativistic Heavy Ion Collider (RHIC) é impulsionado pela busca do CEP. Nesta t... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: One vital characteristic of the quantum chromodynamics (QCD) is regarding the chiral symmetry. This is particularly intriguing owing to the critical role of non-abelian gauge symmetry of Lorentz spinors in modern theoretical physics. Many theoretical efforts have been devoted concerning its spontaneously breaking in the vacuum, as well as the restoration at the extremely hot or dense environment. Furthermore, quarks and gluons become the relevant degrees of freedom through the deconfinement transition from the hadron state of matter. The significance of the latter is closely connected to the implications of the Callan-Symanzik equation and the theory of the renormalized group. Nonetheless, in principle, both of the above transitions can be described by the QCD. Lattice QCD studies demonstrated that the transition of the system is a smooth crossover at vanishing baryon density and large strange quark mass. At finite chemical potential, on the other hand, a variety of models predict the occurrence of a first-order transition between the hadronic phase and quark-gluon plasma (QGP). These results indicate that a critical endpoint (CEP) might be located somewhere on the QCD phase diagram at which the line of first-order phase transitions terminates. The transition is expected to be of second-order at this point. As a matter of fact, among other established goals, the ongoing Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC) is driven by the search for th... (Complete abstract click electronic access below)
Doutor

In dieser Arbeit werden Zufallsfeld-Ising-Modelle mit einem eingefrorenen dichotomen symmetrischen Zufallsfeld für den eindimensionalen Fall und das Bethe-Gitter untersucht. Dabei wird die kanonische Zustandssumme zu der eines einzelnen Spins in einem effektiven Feld umformuliert. Im ersten Teil der Arbeit werden das mulktifraktale Spektrum dieses effektiven Feldes untersucht, Übergänge im Spektrum erklärt und Ungleichungen zwischen lokalen und globalen Dimensionsbegriffen bewiesen, die eine weitgehend vollständige Charakterisierung des multifraktalen Spektrums durch eine Reihe von Schranken erlauben. Ein weiterer Teil der Arbeit beschäftigt sich mit einer ähnlichen Charakterisierung des Maßes der lokalen Magnetisierung, das aus dem Maß des effektiven Feldes durch Faltung hervorgeht. In diesem Zusammenhang wird die Faltung von Multifraktalen in einem allgemeineren Rahmen behandelt und Zusammenhänge zwischen den multifraktalen Eigenschaften der Faltung und denen der gefalteten Maße bewiesen. Im dritten Teil der Dissertation wird der Phasenübergang von Ferro- zu Paramagnetismus im Modell auf dem Bethe Gitter untersucht. Neben verbesserten exakten Schranken für die Eindeutigkeit des paramagnetischen Zustands werden im wesentlichen drei Kriterien für die tatsächliche Lage des Übergangs angegeben und numerisch ausgewertet. Die multifraktalen Eigenschaften des effektiven Felds im Modell auf dem Bethe-Gitter schließlich erweisen sich als trivial, da die interessanten Dimensionen nicht existieren
In this work random field Ising models with quenched dichotomous symmetric random field are considered for the one-dimensional case and on the Bethe lattice. To this end the canonical partition function is reformulated to the partition function of one spin in an effective field. In the first part of the work the multifractal spectrum of this effective field is investigated, transitions in the spectrum are explained and inequalities between local and global generalized fractal dimensions are proven which allow to characterize the multifractal spectrum bei various bounds. A further part of the work is dedicated to the characterization of the measure of the local magnetization which is obtained by convolution of the measure of the effective field with itself. In this context the convolution of multifractals is investigated in a more general setup and relations between the multifractal properties of the convolution and the multifractal properties of the convoluted measures are proven. The phase transition from ferro- to paramagnetismus for the model on the Bethe lattice is investigated in the third part of the thesis. Apart from improved exact bounds for the uniqueness of the paramagnetic state essentially three criteria for the transition are developped and numerically evaluated to determine the transition line. The multifractal properties of the effective field for the model on the Bethe lattice finally turn out to be trivial because the interesting dimensions do not exist

Arctic climate is changing fast, but weather forecast and climate models have serious deficiencies in representing the Arctic atmosphere, because of the special conditions that occur in this region. The cold ice surface and the advection of warm air aloft from the south result in a semi-continuous presence of a temperature inversion, known as the “Arctic inversion”, which is governed by interacting large-scale and local processes, such as surface fluxes and cloud formation. In this thesis these poorly understood interactions are investigated using observations from field campaigns on the Swedish icebreaker Oden: The Arctic Summer Cloud Ocean Study (ASCOS) in 2008 and the Arctic Clouds in Summer Experiment (ACSE) in 2014. Two numerical models are also used to explore these data: the IFS global weather forecast model from the European Center for Medium-range Weather Forecasts and the MIMICA LES from Stockholm University. Arctic clouds can persist for a long time, days to weeks, and are usually mixed-phase; a difficult to model mixture of super-cooled cloud droplets and ice crystals. Their persistence has been attributed to several mechanisms, such as large-scale advection, surface evaporation and microphysical processes. ASCOS observations indicate that these clouds are most frequently decoupled from the surface; hence, surface evaporation plays a minor role. The determining factor for cloud-surface decoupling is the altitude of the clouds. Turbulent mixing is generated in the cloud layer, forced by cloud-top radiative cooling, but with a high cloud this cannot penetrate down to the surface mixed layer, which is forced primarily by mechanical turbulence. A special category of clouds is also found: optically thin liquid-only clouds with stable stratification, hence insignificant in-cloud mixing, which occur in low-aerosol conditions. IFS model fails to reproduce the cloud-surface decoupling observed during ASCOS. A new prognostic cloud physics scheme in IFS improves simulation of mixed-phase clouds, but does not improve the warm bias in the model, mostly because IFS fails to disperse low surface-warming clouds when observations indicate cloud-free conditions. With increasing summer open-water areas in a warming Arctic, there is a growing interest in processes related to the ice marginal zones and the summer-to-autumn seasonal transition. ACSE included measurements over both open-water and sea-ice surfaces, during melt and early freeze. The seasonal transition was abrupt, not gradual as would have been expected if it was primarily driven by the gradual changes in net solar radiation. After the transition, the ocean surface remained warmer than the atmosphere, enhancing surface cooling and facilitating sea-ice formation. Observations in melt season showed distinct differences in atmospheric structure between the two surface types; during freeze-up these largely disappear. In summer, large-scale advection of warm and moist air over melting sea ice had large impacts on atmospheric stability and the surface. This is explored with an LES; results indicate that while vertical structure of the lowest atmosphere is primarily sensitive to heat advection, cloud formation, which is of great importance to the surface energy budget, is primarily sensitive to moisture advection.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Une série de calculs de premier principe pour étudier la transformation martensitique des alliages Ni-Mn-In a été mise en œuvre en utilisant la méthode du pseudopotentiel de VASP et la méthode de densité de charge complète par EMTO-CPA dans le cadre de la théorie de la fonctionnelle de la densité (DFT). Pour l'alliage stoechiométrique Ni50Mn25In25, l'effet de Coulomb efficace et des paramètres d'échange (U + J) sur la stabilité de phase, les propriétés structurelles et magnétiques a été étudié. Les paramètres du réseau et la stabilité de phase varient avec les différents couplages U et J dans l'austénite cubique L21. Cependant, la bande interdite présente toujours une liaison métallique dans l'alliage cubique Ni50Mn25In25. Pour déterminer l'effet des atomes de Mn en excès sur la préférence de la structure martensitique, la distorsion tétragonale a été utilisée dans les alliages Ni50MnxIn50-x avec différentes teneurs en Mn. La distorsion tétragonale à l'état fondamental, résolue en énergie, révèle que l'excès de Mn change la structure stable préférée de la structure cubique parfaite L21 en structures déformées tétragonales. De plus, pour découvrir une préférence plus précise de la structure de la martensite, les énergies de formation ont été calculées. Les résultats montrent que la structure orthorhombique est préférée aux concentrations de Mn faibles (entre 29 at.% et 40 at.%), Tandis que la structure tétragonale L10 est plus stable aux concentrations Mn plus élevées (supérieures à 40 at.%). De plus, l'effet de la concentration en Mn sur les propriétés magnétiques a également été étudié. Avec l'augmentation de la teneur en Mn en excès, le moment magnétique augmente linéairement dans la structure ferromagnétique cubique L21, alors qu'il varie dans les deux types de martensite. L'excès de Mn pourrait conduire à la coexistence du ferromagnétisme et de l'antiferromagnétisme. L'apparition de l'antiferromagnétisme pourrait être attribuée à l'interaction antiferromagnétique Ni-Mn dans la martensite tétragonale. De plus, les effets de la concentration en Mn et des contributions excitées thermiquement (y compris les contributions vibratoires, électroniques et magnétiques) sur la stabilité de phase de l'austénite et de la martensite de 0 K à des températures finies dans les alliages à mémoire de forme Ni50MnxIn50-x typés Heusler ont également été étudiés. Les résultats montrent qu'à 0 K, les différences d'énergie entre la martensite non modulée (NM) et l'austénite deviennent négatives lorsque du Mn supplémentaire est ajouté, indiquant que le Mn ajouté stabilise la martensite et favorise la transformation martensitique. Aux températures finies, il a été révélé que les entropies vibrationnelles des deux phases augmentent avec l'augmentation de la température pour toutes les teneurs en Mn. Sous les deux effets (température et teneur en Mn), l'austénite a une entropie vibrationnelle plus grande que la martensite, ce qui indique que l'entropie vibrationnelle contribue à favoriser la transformation martensitique. La teneur en Mn et la température montrent une influence similaire sur les entropies électroniques des deux phases. Et les moments magnétiques augmentent linéairement avec la teneur en Mn, cependant, l'influence de la température est relativement faible. Au-dessus de 100 K, le moment magnétique de l'austénite est plus élevé que celui de la martensite dans l’alliage ferromagnétique Ni50Mn29.25In20.75, suggérant que l'entropie magnétique contribue de manière similaire à favoriser la transformation martensitique, comme les entropies vibratoires et d'excitation électronique. Le présent travail fournit des connaissances fondamentales pour comprendre la transformation martensitique des alliages Ni-Mn-In stœchiométriques, qui pourraient être utilisés pour concevoir des alliages ferromagnétiques à mémoire de forme avec des performances fonctionnelles améliorées
A series of first-principle calculations to discover the martensitic transition of the Ni-Mn-In alloys were implemented using the pseudopotential method by VASP and the full charge density method by EMTO-CPA within the framework of the Density Functional Theory (DFT). In the stoichiometric Ni50Mn25In25 alloy, the effect of effective Coulomb and exchange parameters (U + J) on the phase stability, structural and magnetic properties was studied. The lattice parameters and the phase stability vary with the U and J couplings in the cubic L21 austenite. However, the bandgap is still showing metallic bonding in the cubic Ni50Mn25In25 alloy. To figure out the effect of excess Mn atoms on the preference of the martensite structure, the tetragonal distortion was employed in the off-stoichiometric Ni50MnxIn50-x alloys with different Mn contents. The calculations were conducted with the optimization of the magnetic structure, where the stoichiometric Ni50Mn25In25 alloy was served as the reference. The ground state-energy-resolved tetragonal distortion reveals that the excess Mn changes the preferred stable structure from the perfect cubic L21 structure to the tetragonally distorted structures. Furthermore, to find out more accurate preference of the martensite structure, the formation energies were calculated. The results show that, the orthorhombic structure is preferred at lower Mn concentrations (between 29 at. % and 40 at. %), whereas the tetragonal L10 structure is more stable at the higher Mn concentrations (above 40 at. %). Moreover, the effect of the Mn concentration on the magnetic properties was also studied. With the increase of the excess Mn content, the magnetic moment increases linearly in the ferromagnetic cubic L21 structure, whereas it varies in the two kinds of martensite. The excess Mn could lead to the coexistence of ferromagnetism and antiferromagnetism. The appearance of the antiferromagnetism could be attributed to the Ni-Mn antiferromagnetic interaction in the tetragonal martensite. Furthermore, the effects of Mn concentration and thermally excited contributions (including the vibrational, electronic excitation and magnetic contributions) on the phase stability of austenite and martensite from 0 K to finite temperatures in Heusler type Ni50MnxIn50-x shape memory alloys were also studied. Results show that at 0 K, the energy differences between the non-modulated (NM) martensite and the austenite become negative when extra Mn is added, indicating that the added Mn stabilizes the martensite and promotes martensitic transformation. At finite temperatures, the three thermal contributions (the vibrational, electronic excitation and magnetic contributions) were further calculated based on the equilibrium structure at 0 K. It was revealed that the vibrational entropies of the two phases increase with the increase of the temperature for all Mn contents. Under the two effects (temperature and Mn-content), the austenite has a larger vibrational entropy than the martensite, which indicates that the vibrational entropy contributes to promoting the martensitic transition. The Mn content and the temperature show a similar influence on the electronic entropies of the two phases. And the magnetic moments increase linearly with the Mn content, however, the influence of temperature is relatively small. Above 100 K, the magnetic moment of the austenite is higher than that of the martensite in ferromagnetic Ni50Mn29.25In20.75 alloy, suggesting that the magnetic entropy makes a similar contribution to promote the martensitic transformation, like the vibrational and electronic excitation entropies. The present work provides fundamental knowledge to understand the martensitic transition of off-stoichiometric Ni50MnxIn50-x alloys, which could be used for the design of ferromagnetic shape memory alloys with improved functional performances

Phase transitions in minerals are transformations naturally occurring when environmental conditions, such as pressure and temperature, change. So, studying their evolution means to understand the modifications of the physical and structural properties of a compound, which can be controlled through industrial processes and exploited in technological applications. On this ground, the present thesis is divided into two big sectors of material science: after a short overview on the basic theory of thermodynamics and kinetics (Part I), the first branch deals with traditional ceramics (Part II), where interest is focused on quartz-cristobalite-tridymite-involving reactions; after that, the field of functional ceramics is discussed in Part III, analysing the behaviour at the nano scale of two widely studied technological materials: the half-doped La and Ca manganite and the tetragonal zirconia stabilized at room temperature by size reduction. All these subjects of study are treated considering the effect of varying the particle size. It is well known, indeed, that reactions are promoted when particles have a greater surface to volume ratio. Therefore, when investigating phase transitions, solid state reactivity and kinetics must reflect the effect of the reduction of grain size. Knowing the mechanisms and the behaviour of materials undergoing high or low temperature processes is essential for industrial procedures to be developed. Thus, phase transitions of the cited compounds are here discussed, in the light of three completely different but complementary approaches: X-Ray Powder Diffraction, performing both reciprocal-space and real-space refinements, and Resonant Ultrasound Spectroscopy, investigating the elastic and anelastic properties of the material of interest.

Cette étude traite de l'existence de concentration Gaussienne pour des états d'équilibre suffisamment mélangeant sur réseau. De plus, nous montrons qu'une telle condition assure l'unicité de ceux-ci.Dans le premier chapitre, nous montrons que si un état d'équilibre associé à un potentiel invariant par décalage et absolument sommable satisfait la concentration Gaussienne alors il est à fortiori mélangeant et unique i.e. il ne peut y avoir transition de phase.Par la suite, nous étudions numériquement un modèle physique particulier autorisant une transition de phase à savoir le modèle d'Ising ferromagnétique en dimension deux. Nous évaluons les constantes de la concentration grâce à la simulation d'observables classiques à toute température. Grâce au comportement de ces paramètres, nous mettons spécialement en lumière la divergence de la constante de concentration Gaussienne à la température critique et nous en déduisons qu'une telle propriété ne peut exister.Puis, nous prouvons que l'existence de la concentration Gaussienne est satisfaite pour toute température supérieure à la température critique pour ce modèle.Ensuite, nous étudions un système dynamique symbolique unidimensionnel sur un alphabet fini: les chaînes à liaisons complètes. Nous étudions en particulier les propriétés de concentration de l'unique état d'équilibre associé à un potentiel (ou probabilité de transition) satisfaisant la condition de Walters.Enfin, nous traitons le régime de haut bruit pour des automates cellulaires probabilistes. Nous prouvons notamment que dans ce régime, ils satisfont la concentration Gaussienne pour une certaine classe d'observables spatio-temporelles
This thesis deals with the existence of Gaussian concentration for sufficiently mixing equilibrium states for lattice systems. Moreover, we show that such a property ensures uniqueness.In the first chapter, we show that if an equilibrium state associated to a shift-invariant and absolutely summable potential satisfies a Gaussian concentration bound then it is à fortiori mixing and unique em i.e. there is no phase transition.Thereafter, We study numerically a particular physical model which allows phase transition to occur: the ferromagnetic Ising model in two dimensions. We evaluate concentration constants through classical estimates at all temperature. Thank to the behavior of these parameters, we emphasize divergence of the Gaussian concentration constant at the critical temperature deduce that such property doesn't hold.Later on, we prove that the Gaussian concentration behavior holds for all temperature above the critical one for this model.Then, we dedicate a chapter to the study of an unidimensional symbolic dynamics on a finite alphabet: chains with complete connections. In particular, we study the concentration properties of a unique equilibrium state associated to a potential (or transition probability) satisfying Walters' condition.In the end, we review the high-noise regime in probabilistic cellular automata. In particular, we prove that in this regime, the probabilistic cellular automata satisfies a Gaussian concentration for a certain class of spatio-temporal observables

Dans ce mémoire, deux problèmes liés aux écoulements multiphasiques compositionnels en milieux poreux ont été traités. La première partie est consacrée au développement d'une nouvelle approche alternative aux calculs flash, qui permet de résoudre les équations d'équilibre thermodynamique analytiquement. Cette méthode est basée sur des équations d'état (EOS) dissymétriques, ainsi, les comportements du gaz, du liquide et du fluide diphasique sont décrits par des EOS individuelles simples. La Capacité d'une EOS à capturer l'état diphasique est appelé : conditions de consistance. Ces conditions ont été formulées dans cette partie pour les systèmes multi-composants. La deuxième partie est consacrée au développement de la méthode de saturations négatives qui a été proposé précédemment par notre groupe pour le cas d'un mélange diphasique binaire. Tout d'abord, nous avons présenté la théorie analytique de la méthode pour les mélanges idéaux puis sa généralisation pour des mélanges réels avec un nombre arbitraire de composants chimiques et de phases. Nous avons obtenu les nouvelles équations multiphasiques uniformes qui contiennent des termes supplémentaires responsables de la diffusion et de la gravité à travers les interfaces de transition de phase
In this thesis, two problems related to compositional multiphase flow in porous media have been treated. The first part is devoted to develop a new approach which gives a form of equilibrium equations which can be solved analytically even for multi-component non ideal systems and even in the presence of capillary effects, which reduce significantly computational time. In this approach, separate behaviors of gas, liquid and two phase fluid may be described using very simple equations of state (EOS). Capacity of EOS?s to capture two phase state is called: consistency conditions. These conditions are formulated in this part for multi-components systems. The second part is devoted to develop the negative saturations method which was proposed earlier by our group for the case of two-phase binary mixtures. First, we have developed the mathematical theory of the method for ideal mixtures in 1D case. Next, we have generalized the method for the case of any number of phases and chemical components. We have obtained the new equivalent uniform multi-phase equations which contain additional non-classical terms responsible of diffusion and gravity across the interfaces of phase transition

Observation de l'apparition de modes oscillants amortis, ondes de spin, pour la diffusion d'aimantation dans l'helium 3 gazeux polarise par pompage optique, dans l'intervalle 2-6k; bon accord entre les mesures du coefficient caracterisant la surtension de ces ondes et des calculs numeriques ab initio a partir du potentiel interatomique he-he. Mise au point d'une technique de condensation rapide de **(3)he oriente permettant d'obtenir un echantillon liquide a spin polarise; etude rmn de l'aimantation du systeme liquide-gaz a l'equilibre

Etude de petrologie experimentale sur les transformations a hautes pressions et hautes temperatures, de silicates et de germanates a structure olicine et pyroxene. Il a ete determine en fonction de la pression et de la temperature, la distribution du magnesium, du fer et du calcium entre mineraux mantelliques. Un modele thermodynamique coherent est construit et a permis de determiner le champ de stabilite de la perovskite silicatee et de proposer une interpretation de la discontinuite sismique des 670 km. Des mecanismes microscopiques de transformations de phase de l'olivine sont proposes. De quelques composes etudies par spectroscopie raman, a ete tire des parametres thermodynamiques harmoniques et anharmoniques de ces phases

Mise au point d'un nouveau calorimètre pouvant fonctionner depuis la température ambiante jusqu'à 1800K. Application à des mesures de capacité calorifique et d'enthalpie de formation ainsi qu'à l'analyse thermique différentielle. Caractérisation de l'enthalpie de 27 composés binaires de métaux de transition. Étude à partir des résultats de plusieurs modèles de prévision des enthalpies de formation d'alliages. Discussion des résultats. Proposition d'un modèle prévisionnel de stoechiométries et des structures des phases binaires susceptibles d'apparaître dans un système métallique

Mesure de l'enthalpie de formation du composé GAMO::(3) et du liquide (MO, GA) riche en gallium. Détermination du diagramme de phases du système (MO, GA) grâce à un calcul complet auto cohérent. Mise au point d'un logiciel d'exploitation des données calorimétriques de mesure de CP en programmation discontinue sur le calorimètre DSC 111 de SETARAM

Дисертацію присвячено дослідженню процесів межового тертя в рамках термодинамічної моделі плавлення ультратонкого мастила, затиснутого між двома атомарно-гладкими твердими поверхнями. Описано поведінку двох простих механічних аналогів трибологічних систем – при зсуві верхньої поверхні тертя в одному напрямку та при зовнішньому знакозмінному впливі. Установлено, що залежно від керуючих параметрів мастила можуть реалізуватись режими сухого, переривчастого та рідинного тертя. Проведена модифікація термодинамічного потенціалу, яка дала змогу описати фазові переходи першого роду в системі. Показано, що наявність пружньої взаємодії між блоком та зовнішнім приводом суттєво змінює гістерезис на залежності сили тертя від температури та швидкості зсуву. Проведено врахування універсальної залежності в’язкості неньютонівського мастила від температури та градієнта швидкості. При цьому досліджено властивості мастила при низьких температурах і швидкостях зсуву. За допомогою врахування залежності в’язкості від температури та градієнта швидкості вдалося описати квазістатичну компоненту сили тертя. Змодельовано ефекти пам’яті межового мастила. Проведено подальшу модифікацію термодинамічного потенціалу, а саме враховано лінійний доданок в розвиненні вільної енергії. Розраховано критичні значення плавлення і тверднення мастила в цьому випадку для фазових переходів першого та другого родів. Знайдено співвідношення між параметрами розкладення при яких в системі реалізується фазовий перехід першого роду, і при яких – другого. Отримані результати розрахунку якісно співпадають з експериментальними даними інших авторів.
Диссертация посвящена исследованию процессов граничного трения в рамках термодинамической модели плавления ультратонкой пленки смазки, зажатой между двумя атомарно-гладкими твердыми поверхностями. Плавление и затвердевание смазки описываются как фазовые переходы первого и второго рода. Описано поведение двух механических аналогов трибологических систем – при сдвиге верхней поверхности в одну сторону и при внешнем знакопеременном воздействии. Показано, что в зависимости от параметров системы возможна реализация режимов сухого, прерывистого и жидкостного трения. Выяснено, что увеличение температуры смазки и/или скорости сдвига приводит к уменьшению максимальных значений силы трения. Изучено влияние коэффициента пропорциональности между вязкостью и скоростью сдвига, коэффициента жесткости пружины, циклической частоты, различных типов смазок (псевдопластических, дилатантных и ньютоновских) на поведение трибологических систем. Анализ термодинамического потенциала позволил выделить критические значения температур плавления и затвердевания смазки, которые совпадают при реализации в системе фазового перехода второго рода, и различны при протекании фазового перехода первого рода. Установлено, что ширина гистерезиса по температуре значительно увеличивается при наличии пружины между блоком и внешним приводом. Гистерезис по скорости сдвига в таком случае отсутствует. Проведен учет универсальной зависимости вязкости полимерных смазок от температуры и градиента скорости. Эта зависимость показывает, что логарифм эффективной вязкости пропорционален логарифму скорости сдвига. Коэффициент пропорциональности изменяет свое значение от 1 в твердоподобном состоянии до 0 в жидкоподобном (ньютоновская жидкость). При этом исследованы свойства смазки при низких температурах и скоростях сдвига. Построена трехмерная зависимость силы трения от температуры и скорости сдвига. С помощью учета зависимости вязкости от температуры и градиента скорости удалось описать квазистатическую компоненту силы трения. Построена зависимость силы трения от времени при продолжительной остановке внешнего привода. Смоделированы эффекты памяти граничной смазки, которые проявляются в том, что поведение системы в последующий момент времени зависит от предыдущего состояния. Изучено поведение при различных значениях внешней нагрузки. Построены зависимости для параметров смазок, состоящих из алканов различной длины, продемонстрированы и объяснены отличия для различных типов смазок. Проведена дальнейшая модификация термодинамического потенциала путем учета линейного слагаемого в разложении свободной энергии по степеням параметра порядка. Рассчитаны критические значения температуры и скоростей плавления и затвердевания смазки в этом случае для фазовых переходов первого и второго рода. Найдено соотношение между параметрами разложения при которых в системе реализуется фазовый переход первого либо второго рода. Показано, что расплавленному состоянию смазки может отвечать ненулевое значение параметра порядка. Такой вид потенциала дал возможность описать квазистатическую силу трения базируясь на новом подходе. На его основе изучено поведение трибологической системы при различных временах остановки внешнего привода для различных времен релаксации параметра порядка. Полученные результаты расчета качественно совпадают с экспериментальными данными других авторов.
The thesis is devoted to the boundary friction processes investigation using thermodynamic model of ultrathin lubricant melting, which is grabbed between two atomically-smooth solid surfaces. The behavior of two simple mechanical analogues of tribological systems have been described: during the shearing of upper block in one direction and during the external periodical influence. It has been found out that depending on lubricant control parameters, regimes of dry, interrupted and sliding friction can be realized. Further thermodynamical potential modification allows us to describe first-order phase transition in the system. The presence of the elastic connection between block and external drive significantly changes temperature and shear velocity hysteresis’s. The universal dependence of viscosity of lubricant on temperature and velocity gradient has been took into consideration. Herewith, the lubricant characteristics have been investigated at the low temperatures and low shear velocities. The guasi-static friction force was described using the viscosity dependence. The further thermodynamic potential modification has been performed. For this purpose, the linear term was added in the free energy expansion into series. The critical values of lubricant melting and solidification were calculated for the phase transitions of the first- and second-order. The relation was found between expansion parameters for which first- or second-order phase transition are realized in the system. Obtained results qualitatively coincide with experimental data.

We study compensation functions for an infinite-to-one factor code $\pi : X \to Y$ where $X$ is a shift of finite type. The $p$-Dini condition is given as a way of measuring the smoothness of a continuous function, with $1$-Dini corresponding to functions with summable variation. Two types of compensation functions are defined in terms of this condition. Given a fully-supported invariant measure $\nu$ on $Y$, we show that the relative equilibrium states of a $1$-Dini function $f$ over $\nu$ are themselves fully supported, and have positive relative entropy. We then show that there exists a compensation function which is $p$-Dini for all $p > 1$ which has relative equilibrium states supported on a finite-to-one subfactor.
Graduate
0405
antoniol@uvic.ca

Very specific protein-salt interactions are involved in a multitude of biological phenomena such as protein folding/stability, enzymatic activity, and signal transduction events. In this work, we used two very simple, protein-mimic model biopolymers to obtain a better understanding of specific cation effects operating in aqueous protein environments. The two biopolymers used were Elastin-like Polypeptides (ELPs) and poly(N-isopropylacrylamide) (PNIPAM). ELPs are an especially an ideal model system as these polypeptides can be easily genetically engineered to observe the effect of specific amino acid residues and peptide chain length on these salt interactions. Both of these biopolymers are also highly thermoresponsive as their aqueous solutions undergo a hydrophobic collapse/aggregation induced phase transition process above a lower critical solution temperature (LCST). Thermodynamic measurements of these biopolymers were carried out under various salt solution conditions. Additionally, both of these biopolymers are suitable for making surface specific spectroscopic measurements. Vibrational sum frequeny spectroscopy (VSFS), a non-linear interface sensitive spectroscopic technique, was employed here to investigate biologically relevant cation interactions which occur at peptide/protein surfaces. First, the LCST response of a non-polar ELP and a neutral biopolymer, PNIPAM, was investigated in the presence of 12 different alkali, alkaline-earth metal and transition metal chloride salts. Even though the salt interactions for uncharged proteins are dominated by anions, subtle specific cation effects were also observed. The results followed a direct Hofmeister series for cations. Most alkali cations are excluded from the polar amide regions of proteins. More polarizable cations, however, can solvate the hydrophobic moieties and somewhat counter the salting-out effect of the chloride anion. More charged and hydrated ions like lithium and divalent cations showed a weak interaction to the amide moiety through their hydration shell. The role of acidic amino acid residues in inducing cation specificities was investigated using an aspartate-rich ELP system. Both thermodynamic and spectroscopic data conclusively proved that the negative charge on protein surfaces is the main driving force for cation partitioning and specificity under physiological relevant concentration regimes. Apparent binding constants of carboxylate moieties with cations were determined. This is the first quantitative and thoroughly systematic study of such biologically relevant cation-carboxylate interactions prevalent in enzyme active sites and protein surfaces.

In dieser Arbeit werden Zufallsfeld-Ising-Modelle mit einem eingefrorenen dichotomen symmetrischen Zufallsfeld für den eindimensionalen Fall und das Bethe-Gitter untersucht. Dabei wird die kanonische Zustandssumme zu der eines einzelnen Spins in einem effektiven Feld umformuliert. Im ersten Teil der Arbeit werden das mulktifraktale Spektrum dieses effektiven Feldes untersucht, Übergänge im Spektrum erklärt und Ungleichungen zwischen lokalen und globalen Dimensionsbegriffen bewiesen, die eine weitgehend vollständige Charakterisierung des multifraktalen Spektrums durch eine Reihe von Schranken erlauben. Ein weiterer Teil der Arbeit beschäftigt sich mit einer ähnlichen Charakterisierung des Maßes der lokalen Magnetisierung, das aus dem Maß des effektiven Feldes durch Faltung hervorgeht. In diesem Zusammenhang wird die Faltung von Multifraktalen in einem allgemeineren Rahmen behandelt und Zusammenhänge zwischen den multifraktalen Eigenschaften der Faltung und denen der gefalteten Maße bewiesen. Im dritten Teil der Dissertation wird der Phasenübergang von Ferro- zu Paramagnetismus im Modell auf dem Bethe Gitter untersucht. Neben verbesserten exakten Schranken für die Eindeutigkeit des paramagnetischen Zustands werden im wesentlichen drei Kriterien für die tatsächliche Lage des Übergangs angegeben und numerisch ausgewertet. Die multifraktalen Eigenschaften des effektiven Felds im Modell auf dem Bethe-Gitter schließlich erweisen sich als trivial, da die interessanten Dimensionen nicht existieren.
In this work random field Ising models with quenched dichotomous symmetric random field are considered for the one-dimensional case and on the Bethe lattice. To this end the canonical partition function is reformulated to the partition function of one spin in an effective field. In the first part of the work the multifractal spectrum of this effective field is investigated, transitions in the spectrum are explained and inequalities between local and global generalized fractal dimensions are proven which allow to characterize the multifractal spectrum bei various bounds. A further part of the work is dedicated to the characterization of the measure of the local magnetization which is obtained by convolution of the measure of the effective field with itself. In this context the convolution of multifractals is investigated in a more general setup and relations between the multifractal properties of the convolution and the multifractal properties of the convoluted measures are proven. The phase transition from ferro- to paramagnetismus for the model on the Bethe lattice is investigated in the third part of the thesis. Apart from improved exact bounds for the uniqueness of the paramagnetic state essentially three criteria for the transition are developped and numerically evaluated to determine the transition line. The multifractal properties of the effective field for the model on the Bethe lattice finally turn out to be trivial because the interesting dimensions do not exist.

Celem niniejszej pracy było szczegółowe opracowanie warunków elektrochemicznego otrzymania stopów palladu z rutenem (Pd-Ru) w postaci elektrod o ograniczonej objętości, tj. cienkich powłok stopowych osadzonych na podłożu przewodzącym oraz zbadanie ich podstawowych właściwości elektrochemicznych ze szczególnym uwzględnieniem procesu elektrochemicznej absorpcji wodoru. Badania obejmowały wpływ potencjału elektrody i składu stopu oraz temperatury na procesy elektrochemicznej sorpcji wodoru oraz utleniania powierzchni. Stopy Pd-Ru są szczególnie ważne w kontekście wykorzystania ich w układach hybrydowych do ogniw wodorkowych, ponieważ – zgodnie z wynikami niniejszej pracy – są zdolne do magazynowania nawet do 20% więcej wodoru niż czysty pallad. Jeszcze do niedawna uważano, że dodatek innego metalu szlachetnego do palladu może jedynie spowodować spadek jego zdolności do magazynowania wodoru (z wyjątkiem układu Pd-Rh). Ponadto w literaturze dostępne są jedynie niepełne informacje dotyczące stopów Pd-Ru i żadna z nich nie dotyczy próbek osadzanych elektrochemicznie i określenia ich szczegółowych właściwości. Przeprowadzone eksperymenty pozwoliły na opracowanie warunków osadzania (składy kąpieli galwanicznych, wartości potencjałów osadzania) stopów o grubości ok. 1 μm o powtarzalnym składzie. Otrzymanie powłok o wskazanej grubości pozwoliło na pracę z tzw. elektrodami o ograniczonej objętości – LVE (limited volume electrodes). Proponowane podejście umożliwiło wyodrębnienie w sposób szczegółowy sygnałów od procesów elektrochemicznych zachodzących w głębi i na powierzchni badanej próbki. Stopy Pd-Ru analizowane były w odniesieniu do dwóch procesów: (1) absorpcji wodoru w głębi stopu (również wraz z jednoczesną adsorpcją wodoru na powierzchni stopu); (2) utleniania powierzchni stopu. Pierwszy z nich odpowiada za właściwości wodorochłonne (magazynowanie wodoru), natomiast drugi za właściwości elektrokatalityczne (katalizator). Otrzymane wyniki wskazują, że zastosowana elektrochemiczna metoda osadzania stopów pozwala z powodzeniem otrzymać cienkie warstwy stopowe w szerokim zakresie składów (jednorodne w objętości, o powierzchniowym wzbogaceniu w Ru). Stopy Pd-Ru scharakteryzowane zostały kilkoma technikami fizykochemicznymi: skaningową mikroskopią elektronową (SEM) z mikroanalizą rentgenowską (EDS), mikroskopią sił atomowych (AFM), rentgenowską spektroskopią fotoelektronów (XPS) i dyfrakcją rentgenowską (XRD) oraz metodami elektrochemicznymi: chronoamperometrią (CA) i chronowoltamperometrią cykliczną (CV), a także elektrochemiczną mikrowagą kwarcową (EQCM). W związku z różnicami w składzie objętościowym i powierzchniowym zaproponowana została nieniszcząca metoda szacowania składu powierzchniowego oparta na liniowej zależności składu powierzchniowego stopu, otrzymanego z rentgenowskiej spektroskopii fotoelektronów (XPS), i potencjału redukcji tlenków powierzchniowych, odczytanego z danych chronowoltamperometrii cyklicznej (CV). W ten sposób przy wykorzystaniu jedynie danych CV możliwe jest określenie składu powierzchniowego stopów Pd-Ru bez konieczności wykonywania analizy XPS. W ramach realizacji pracy została potwierdzona hipoteza, że nie tylko stopy pallad-rod (Pd-Rh) mogą absorbować więcej wodoru niż czysty Pd, bowiem okazało się, że stopy Pd-Ru o zawartości jedynie ok. 1% obj. Ru zdolne są do zaabsorbowania aż o ok. 20% (maksymalny stosunek wodoru do metalu: H/M=0,88) więcej wodoru niż czysty Pd (H/M=0,74). W przypadku stopów Pd-Ru zdolność do tworzenia wodorku (faza β) zostaje utracona już dla próbek zawierających jedynie 7-8% obj. Ru. Domieszkowanie palladu rutenem pozwoliło także na ułatwienie procesu desorpcji wodoru, jak również, w większości przypadków, na skrócenie czasu sorpcji wodoru. Zbadanie absorpcji wodoru w zakresie temperatur 283-313 K pozwoliło na wyznaczenie wartości funkcji termodynamicznych (zmiana entalpii swobodnej, zmiana entalpii, zmiana entropii) procesu sorpcji wodoru w stopach. Obliczone wartości zmian entropii wskazują, że w strukturze krystalicznej stopu wodór zajmuje luki w sąsiedztwie atomów Pd. Eksperymenty wykonane przy wykorzystaniu elektrochemicznej mikrowagi kwarcowej pozwoliły stwierdzić, że zarówno (nawet jednokrotna) absorpcja wodoru jak i dodatek Ru wpływają na zwiększenie odporności stopów na elektrochemiczne roztwarzanie. Wykonane tą metoda eksperymenty pozwoliły także na wyznaczenie poziomu naprężeń (pozornej masy molowej wodoru), jakie towarzyszą procesowi absorpcji wodoru w stopach Pd-Ru. Wraz ze wzrostem zawartości wodoru w stopach wzrastała wielkość naprężeń w ich sieci krystalicznej, przy czym maksymalna wartość częstotliwości odpowiadającej istnieniu naprężeń zmniejszała się ze wzrostem zawartości Ru w stopie. Przebiegi krzywych odpowiadających procesowi absorpcji i desorpcji w stopach nie pokrywały się, co świadczyło o różnym rozkładzie naprężeń w stopach w zależności od rodzaju zachodzącego procesu. Przeprowadzenie powyższych badań dostarczyło brakujących i niezbędnych informacji, które pozwolą na szczegółowe opisanie właściwości stopów palladu z rutenem. Oczekuję, że wyniki tych badań okażą się pomocne w interpretacji procesów zachodzących na materiałach elektrodowych o potencjalnym znaczeniu dla ogniw wodorkowych i paliwowych oraz superkondensatorów elektrochemicznych, zarówno w aspekcie zagadnień podstawowych jak i aplikacyjnych. Otrzymane wyniki będą mogły posłużyć m.in. do projektowania układów, w których badany materiał będzie mógł współpracować z komercyjnymi stopami wodorochłonnymi tworząc sprzężony układ do absorpcji i magazynowania wodoru oraz będą mogły zostać z powodzeniem wykorzystane jako katalizatory w etanolowych ogniwach paliwowych, które coraz większe znaczenie zyskują w przemyśle samochodowym i militarnym. W literaturze naukowej pojawiły się już pierwsze prace, korzystające z opublikowanych wyników niniejszego projektu, co świadczy o ważności przeprowadzonych badań i aktualności podjętej tematyki.
In the framework of this dissertation the specific conditions of the electrochemical deposition of the palladium-ruthenium (Pd-Ru) alloys as limited volume electrodes (thin coatings deposited on the conducive substrate) were elaborated and their electrochemical properties were examined with the special emphasis on the process of hydrogen electrochemical absorption. Research included the influence of the potential value, alloy composition and temperature on the process of electrochemical sorption of hydrogen and surface oxidation. Pd-Ru alloys are particularly important in the context of its utilization in hybrid hydride cells, since – according to the results of this study – Pd-Ru alloys are able to store even 20% more hydrogen than the pure palladium. Until recently it has been thought that the addition of the other noble metal to the pure palladium could only result in the decrease in its hydrogen storage ability (with the exception of the Pd-Rh system). Furthermore in the literature, there is available only residual information on Pd-Ru alloys and none of articles concerns the electrochemical deposition and examination of detailed properties of Pd-Ru samples. Experiments that have been conducted, allowed to describe the conditions of deposition (galvanic baths compositions, deposition potentials) of 1 µm thick samples with reproducible compositions. Receiving samples of the indicated thickness gave ability to work with limited volume electrodes. This approach allowed to distinguish, in the detailed manner, the signals from the electrochemical processes taking place in the bulk and on the surface of the sample. Palladium-ruthenium alloys were analyzed with respect to two processes: (1) hydrogen absorption in the bulk (also with simultaneous hydrogen adsorption on the surface); (2) alloy surface oxidation. The first one is responsible for hydrogen absorbing properties (hydrogen storage), while the second one – for electrocatalytic properties (catalyst). Received results indicate that the applied electrochemical method of the alloys deposition gives ability to obtain successfully thin alloy layers in the wide range of compositions (homogeneous in the bulk, with the surface enrichment with Ru). Pd-Ru alloys were characterized with several physicochemical techniques, such as: scanning electron spectroscopy (SEM) with energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction and electrochemical techniques such as: chronoamperometry (CA), cyclic chronovoltammetry (CV), as well as electrochemical quartz crystal microbalance (EQCM). In the connection with the differences in the bulk and surface compositions of alloys the non-destructive method of surface composition estimation, based on the linear dependence of the surface composition (obtained from the X-ray photoelectron spectroscopy – XPS) and the reduction potential of surface oxides (received from the cyclic chronovoltammetry – CV), was proposed. Thereby only on the basis of CV data it is possible to obtain surface composition without the need of XPS analysis. In the framework of this dissertation the hypothesis, that not only Pd-Rh alloys are able to absorb more hydrogen than Pd, was confirmed. It was found that Pd-Ru alloys containing only 1% of Ru (in the bulk) are able to absorb 20% (maximum hydrogen to metal atomic ratio: H/M=0,88) more hydrogen than Pd (H/M=0,74). Pd-Ru alloys lose their ability to form hydrides already for samples containing only 7-8% of Ru. Alloying palladium with ruthenium allows also for facilitation of the process of hydrogen desorption as well as in the most cases for the reduction of hydrogen sorption time. Hydrogen sorption experiments conducted in temperature range 283-313 K gives ability to estimate the value of thermodynamic functions (the change of Gibbs energy, the change of enthalpy and the change of entropy) of hydrogen sorption. Calculated values of entropy changes indicate that in the crystal structure of alloy hydrogen occupies preferably Pd neigbouring interstices. Experiments performed by the use of the electrochemical quartz crystal microbalance indicates that both (even single) hydrogen absorption and Ru addition influence on the increase in alloy resistance on the electrochemical dissolution. EQCM experiments also allowed to determine the level of stresses (apparent molar mass) in the crystal lattice that accompanied the process of hydrogen absorption in Pd-Ru alloys. With the increase in the hydrogen content the magnitude of stresses in Pd-Ru alloys increase, wherein the maximum value of frequency (originating from stresses) decrease with the increase in Ru content in the sample. The course of hydrogen absorption-desorption curve did not overlap, what implies that the distribution of stresses varies depending on the type of the sorption process. Results of these studies provide missing and necessary information, which allows to describe in details properties of Pd-Ru alloys. I expect that the results of these experiments appeared to be helpful in the interpretation of the processes occurring on the electrode materials on the potential importance for hydride and fuel cells and electrochemical supercapacitors in the aspect of basic application issues. Obtained results can be helpful i.a. to design systems where tested material will cooperate with commercial hydrogen-absorbing alloys forming coupled system for hydrogen absorption and storage and will be successfully utilized as a catalyst in ethanol fuel cell, which becoming more and more important in the automotive and military industry. In the scientific literature the first few articles using the published results of the project have appeared. It provides proof of the validity of the conducted research and the topicality of taken subject.