L’élaboration de combustible nucléaire UO2-30%PuO2 pour les nouveaux réacteurs nucléaires de Génération IV repose sur l’utilisation de plutonium issu du recyclage des combustibles MOX (Mélange d’OXydes UO2-PuO2) des réacteurs actuels. Par rapport au Pu initial, ce plutonium présente une proportion d’isotopes fissiles beaucoup plus faible et une quantité plus importante (x30) en 238Pu dont l’activité spécifique alpha et la puissance thermique sont importantes. Le procédé d’élaboration du combustible qui consiste à mettre en forme les poudres d’oxydes par pressage met en jeu un lubrifiant organique, le stéarate de zinc. L’objectif de la thèse est d’étudier le comportement en température et sous irradiation de ce composé. Un effet de la montée en température et du vieillissement en température a été observé sur les propriétés cristallographiques du stéarate de zinc, avec une amorphisation partielle du matériau qui engendre une détérioration de ses propriétés de lubrification dès 110°C. La dégradation radiolytique du stéarate de zinc a été étudiée à travers l’analyse des gaz produits par irradiation alpha au contact de poudres de PuO2 ou par irradiation externe aux hélions, complétée par des analyses physico-chimiques du stéarate irradié. Les rendements de production de gaz sont calculés et permettent d’établir un mécanisme de radiolyse. Il a été montré que l’impact de la radiolyse sur les propriétés de lubrification est moindre que l’effet de la température. Le couplage des dégradations a un effet synergique, avec une détérioration des propriétés de lubrification observée à des températures plus faibles que sur le matériau non irradié. A partir de ces résultats, des recommandations d’utilisation du stéarate de zinc ont été proposées. / The manufacturing of nuclear fuels UO2-30%PuO2 for the Gen IV nuclear reactors is based on the use of plutonium coming from MOX (Mixed OXides) fuel recycling from actual reactor. This plutonium would contain a few quantities of fissionable isotopes and a significant amount (x30) of 238Pu compared to initial Pu. This isotope possesses a strong alpha activity and a great thermal power. The manufacturing process which consists in powders pressing will use zinc stearate, an additive used as lubricant. The aim of this PhD is to study the behaviour in temperature and under irradiation of this compound. An effect of temperature increasing and thermal ageing has been observed on crystallographic properties with a material amorphisation and a deterioration of lubricant properties from 110°C. Radiolytic degradation of zinc stearate has been studied through the analysis of gases produced by alpha radiation at the contact of PuO2 powders or by external radiation by helions, with the support of chemical analysis of irradiated solid. Gaz production yields are calculated and enable establishment of a radiolysis mechanism. It has been showed that impact of radiolysis on lubricant properties is less important than temperature effect. The coupling of degradations has a synergic effect, with a deterioration of lubricant properties observed at lower temperature compared to non-irradiated material. From these results, recommendations for use of zinc stearate have been proposed.

At the start of this project, the possible choices of metal soaps had already been narrowed to include some of the zinc soaps used in this project. These zinc soaps are mixtures of zinc stearate and zinc palmitate of varying ratios purchased from a supplier. Zinc soap was chosen as result of its common use in various industries as a lubricant and mold release, which implied potential benefits in an electrophotographic printing system. These potential benefits include, but are not limited to, a more efficient transfer from a photoconductive drum and protection of the drum from mechanical and chemical degradation. Nanoindentation of these soaps was implemented in an effort to characterize each soap mixture and compare how the soap types differed from one another. Each sample was indented under a variety of different maximum loads and at different holding times to observe effects on the modulus, hardness, and, creep. The mechanical properties measured were then used to help distinguish differences between each type and provide an insight as to how or why one mixture may be preferable over another. The data could be utilized in conjunction with further testing to be used in a simulation of an interface of interest.

This thesis deals with the conformation and phase-transitions in anchored alkyl chain bilayer assemblies in organic-inorganic hybrids. The alkyl chain bilayers in organic-inorganic hybrids bear a striking resemblances to the lipid bilayers that are an integral part of biomembranes. However, unlike the lipid bilayer where individual lipid molecules can undergo the total absence of translational mobility. The anchored bilayer are, therefore, the simplest model system for understanding the structure, organization and thermal behaviour of alkyl-chain assemblies. The anchored bilayer in the organic-inorganic hybrids also offer the advantage that unlike the lipid bilayers that are essentially fluid like, these are solids and therefore, amenable to study by a variety of solid-state spectroscopic techniques. The objective of the present works was to determine the organization, conformation and thermal behaviour of alkyl chains in these class of materials- the alkyl ammonium layered pervoskites and in zinc soaps of saturated and unsaturated fatty acids. The preparation, conformation and orientation of alkyl chains assemblies in the layered(CH3CH2)nNH3)2PbI4 is described in chapter 2 and the phase-transitions and associated changes in conformation in presented in chapter 3. In chapter 4 the preparation, structure, conformation and phase-transitions of alkyl chains in the m = 2 member of the layered (CH3NH3)m-1(CH3CH2)nNH3)2PbmI3m+1 Ruddleson-Popper series is discussed. The thermal behavior of zinc soaps of saturated fatty acids is discussed in chapter 5 and formation and phase-transitions in solid solution between saturated zinc soaps of differing chain lengths, zinc stearate and zinc myristate is presented in chapter 6. The effect of a rigid link or double bond on the evolution of conformational disorder and phase-transitions of other-wise flexible hydrocarbon chains is explored in chapter 7 by comparing the thermal behavior of zinc oleate and zine elaidate with that of zinc stearate. A unique feature of the zinc soaps is that they form solid solutions over the entire composition range feature of the zinc soaps is that they form solid solutions over the entire composition range between soaps of saturated and unsaturated fatty acids. The formation and conformation of alkyl chains in the solid solution of zinc stearate and zinc oleate is discussed in chapter 8.