La sollicitation de fretting apparait comme un processus de dégradation très pénalisant dans les multiples systèmes industriels (aéronautique, industrie automobile, industriels du nucléaire, transports ferroviaires etc. …). Ce processus d’usure engendre dans la plupart des cas soit une réparation (rechargement) des surfaces soit le remplacement des composants (situation la plus souvent observée). La sollicitation de fretting est associée à des micro-déplacements alternés entre deux surfaces en contact. On observe généralement ce type de sollicitation dans tous les contacts soumis à des vibrations ou à des cycles thermiques. La sollicitation de fretting usure dans les contacts électriques est particulièrement pénalisante. Outre l’endommagement des surfaces, ce processus induit une augmentation significative de la résistance électrique des contacts et une perte de fonctionnalité du connecteur en particulier dans les connecteurs basses tensions très sensibles aux fluctuations de la résistance électrique. Pour palier ce problème les industriels de la connectique et leurs clients (industriels de l’automobile) cherchent à mettre en place de nouveaux dépôts palliatifs pour résoudre ces problèmes tout en limitant les surcouts liés à l’utilisation de dépôts nobles tels que l’or.Le sujet de cette thèse porte sur cette problématique avec pour objectif de mettre en place une méthodologie de choix des dépôts pour optimiser la durée de vie des connecteurs. L’étude aborde essentiellement l’influence des conditions de chargements mécaniques et plus particulièrement l’amplitude de débattement / The degradation by fretting appears as a very troublesome process in many industrial systems (spatial, automotive, nuclear industry, railway systems etc. …). This wear process makes it necessary to repair or to replace the destroyed component. The process of degradation by fretting is associated with the micro-displacement between two surfaces in contact. This type of degradation is observed in all types of contacts subjected to the vibrations or thermal variations. The degradation by fretting in electrical contact is particularly dangerous. The wear of the contacting surfaces causes a significant increase of the electrical resistance of the contact and the decay of the functional properties of the connector. This situation concerns especially the low tension connectors very sensible to the fluctuations of the electrical resistance. In order to avoid this situation the automotive industry and its suppliers, the manufacturers of the electrical connectors, are looking for new materials and coatings.The objective of this thesis consists to develop the methodology of choice of the coating materials in order to optimise the lifetime of the electrical contact. The study focuses mainly on the influence of the mechanical conditions, the displacement amplitude in particular, on the performance of the electrical connector.

To fully exploit the strengths of La2Zr2O7 pyroclores and promote them as a next-generation thermal barrier coating (TBC), the improvements of their thermally insulating property and fracture toughness are studied in this thesis. A strong phonon scattering source, rattlers, is found in Y3+-doped La2Zr2O7 pyrochlores. Rattlers dramatically flatten k (thermal conductivity)-T curves, or even make k approach the amorphous limit. The presence of rattlers is strongly dependent on (1) oversized atomic cages that are formed in pyrochlores; and (2) the occupation of smaller guest ions in those oversized cages. To maximize the rattling effect, In3+/Sc3+ ions that are much smaller than Y3+ are introduced to the La2Zr2O7 lattice. As envisaged, the smaller ions in the oversized lattice voids make k glass-like at a much lower doping content. Nevertheless, they are still not effective in reducing the high temperature plateau kmin. Instead, oxygen vacancies are very effective in reducing kmin, because they generate an electrostatic repulsion force among cations surrounding them, resulting in stronger lattice anharmonicity and weaker bonds. The plateau kmin is reduced dramatically by the filling of the B-sites in La2Zr2O7 with a 21% larger (and 50% heavier) Ce4+ guest ion rather than a 96% heavier (but similar-sized) Hf4+ ion, suggesting that a large absolute size of substitutional atoms is more effective in reducing kmin than a heavy absolute mass. This is because: (1) kmin is proportional to (E/M)0.5 (where E is the elastic modulus and M is the average atomic mass); (2) a larger size of guest ions tends to produce a weaker ionic bond and consequently, a lower E; and (3) the changing extent of E by introducing larger guest ions is much greater than that of M induced by adding heavier ones. Lastly, the fracture toughness (KIc) has been increased by dispersing the tetragonal 3 mol% Y2O3-stabilized zirconia (t-3YSZ) particulates in the La2Zr2O7 (LZ) matrix. The tendency of the dispersive t-3YSZ second phases transforming to monoclinic (m) phases strongly depends on the volume fraction introduced. For samples made from equilibrium route, they are toughened by phase transformations within the dispersive t-3YSZ second phases and a crack shielding effect arising from the residual compressive stress within the LZ matrix. An anticipated increase of KIc from ferroelastic toughening together with the residual compressive stress toughening highlights a potential to improve coating durability by depositing t’-3YSZ/LZ composite TBCs by the non-equilibrium route.

During this EngD project, two pigmented, anti-corrosion polymer/sol-gel hybrid coatings were developed with the aim of producing an eco-friendly alternative to conventional, toxic hexavalent chromate conversion and anodized anti-corrosion alloy treatments for the aircraft manufacturer; Airbus S.A.S. The polymer/sol-gel hybrid coatings were then tested and validated as anti-corrosion coatings on the AA2024-T3 aluminium aerospace alloy and in certain cases, their performance was compared against that of the hexavalent chromate benchmark (Alocrom 1200). The mechanisms of corrosion inhibition exhibited by the coatings were also studied in depth. The polymer/sol-gel hybrid coatings that were developed in this project are silane based and the first, designated as B2, has polyester-methacrylic functionality and the second, designated as CA/MM, has polyester-amide functionality. Certain inhibitor compounds which were incorporated in the polymer/sol-gel hybrid coatings were chosen by the split-cell technique. The microstructure and elemental compositions of the polymer/sol-gel hybrid coatings and of the AA2024-T3 aluminium alloy were determined by Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopic (SEM-EDS) analysis of the specimens. The anti-corrosion performance and the corrosion protection mechanisms of the polymer/sol-gel hybrid coatings were determined by salt-water and electrochemical testing of the coated alloy specimens. The thermal resistance of the polymer/sol-gel hybrid coatings was ascertained by thermogravimetric analysis (TGA) of the coatings. The polymer/sol-gel hybrid coatings were also analysed by Fourier Transform Infrared (FTIR), Micro-Raman and X-ray Photoelectron (XPS) spectroscopic techniques to determine whether the desired polymer and silane coating networks formed during coating processing. Anti-corrosion performance test results revealed that both polymer/sol-gel hybrid coatings are self-healing due to their ability to implement a precipitation mechanism of corrosion inhibition. Analysis of the polymer/sol-gel hybrid coatings by X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) after salt-water exposure suggested that the B2 coating precipitated the compound tungsten pyrophosphate, W(P2O7), within defects and that the CA/MM coating precipitated the compound iron carbide, Fe2C, within defects. However, anti-corrosion test results also shown that the anti-corrosion performance of the polymer/sol-gel hybrid coatings does not satisfy aerospace industry requirements. Therefore, it can be concluded that although the achievements of this project have not enabled Airbus to eliminate toxic chromium (VI) species from their operations, further optimisation of the polymer/sol-gel hybrid coatings developed during this project could potentially lead to a solution being found.

This project consists of two parts. One area of focus in the first part is understanding the interactions between a non-ionic, block copolymer type dispersant and hydrophobically-modified, ethoxylated urethane (HEUR) associative thickeners in water. The dispersant was mixed at various concentrations (0-2% by weight) with HEUR thickeners at 1% by weight concentration in the aqueous medium. This study is an integral part of our attempts to determine mechanisms of viscosity drop when colorant dispersions are added to latex tint base formulations thickened with associative thickeners. One of the HEUR thickeners is a product that has been available for over three decades (HEUR RM-825), whereas the other, HEUR RM-995 is a product recently introduced to minimize the tint base viscosity drop. The old HEUR showed a definitive viscosity maximum as a function of the dispersant concentration. However, the new generation product did not indicate a viscosity maximum within the dispersant concentration range studied; instead it showed a small, but linear increase in viscosity as dispersant level was increased. The next area of focus was on understanding the phase behavior, rheology, and interactions between polymer latex particles and a hydrophobically-modified, ethoxylated urethane (HEUR) associative thickener in water. The influence of the addition of surfactant in some of the systems was also studied. Several types of dispersions were made using two types of polymer latex, two associative thickeners, and two surfactants. Mixtures containing a small particle size acrylic latex and HEUR RM-825 exhibited the most interesting and complex phase behavior and rheology. In experiments wherein the latex particle volume fraction was kept constant, the addition of HEUR caused stable, followed by phase separated (syneresis) and stable mixtures as HEUR concentration was increased. The observed phase behavior is consistent with previous work reported by other investigators. However, detailed rheological data on systems such as these have not been reported, and this report presents the rheological data and correlate rheology with the phase behavior. The stable latex-HEUR mixtures at low HEUR levels show shear-thinning viscosity with well-defined low-shear Newtonian plateaus. As HEUR level is increased wherein syneresis is observed, erratic rheological profiles with shear-thickening are observed. When HEUR level is increased to a region where no syneresis is observed, low shear Newtonian plateaus re-appeared albeit at higher viscosities. The effects of added non-ionic and anionic surfactants on the dispersion are also studied. The main focus of the second part of this project is hybrid organic-inorganic photovoltaics. They have been the focus of recent studies due to their promising use in low-cost, flexible electronics, which can be processed from solution by printing and coating techniques. Understanding the rheology of these nanocomposites is essential in controlling shear flows during printing and application processes. Through rheology, we can determine different properties of poly(3-hexylthiophene) and dodecanethiol (DDT) modified zinc oxide (ZnO-DDT). Semiconductor nanowires such as ZnO have rigid or rod-like macromolecule geometry. Therefore, they have a tendency to have a lytropic liquid crystal (LLC) phase. LLC orders occur spontaneously in solutions with rod-shaped or anistropic objects from isotropic phase to nematic phase above a critical volume fraction which was studied using ZnO-DDT. The shear-induced alignment of the liquid crystal molecules was analyzed, serving as a guide for LLC printing. Furthermore by using this nanocomposite we are able to induced gelation using the ZnO-DDT nanowires in what is considered as a “good solvent,” dichlorobenzene. The kinetics of this gelation process was determined to be of first-order reaction kinetics. Furthermore, a mechanism of this gelation process is also presented.

Aluminium titanium oxynitrides were studied as candidate materials for high temperature absorbers in solar selective coatings due to their excellent stability and their tuneable optical behaviour. A set of individual AlyTi1-y(OxN1-x) layers with different oxygen content was prepared by cathodic vacuum arc (CVA) deposition. The composition, morphology, phase structure and microstructure of the films were characterized by elastic recoil detection (ERD), scanning and transmission electron microscopy and X-ray diffraction. An fcc phase structure is found in a broad compositional range of AlyTi1-y(OxN1-x). Simultaneously, sample microstructure and morphology undergo systematic changes from a columnar growth to the development of a heterogeneous structure with spherical nanoparticle inclusions when the oxygen concentration is increased. The optical properties were determined by spectroscopic ellipsometry and UV–Vis–NIR and FTIR spectrophotometry. A comprehensive analysis of the film properties allowed an accurate modelling of the optical constants of the AlyTi1-y(OxN1-x) in the whole wavelength range of solar interest (from 190 nm to 25 µm). It points to a transition from metallic to dielectric behaviour with increasing oxygen content. Consequently, it is demonstrated that the optical properties of these AlyTi1-y(OxN1-x) deposited films can be controlled in a wide range from metallic to dielectric character by adjusting the oxygen concentration, opening a huge range of possibilities for the design of solar selective coatings (SSC) based on this material. Complete SSC, including a TiN layer as IR reflector, were designed by applying optical simulations, obtaining excellent optical selective properties of α=94.0% and εRT = 4.8%.

The characterization of work functions and field emission stability for molybdenum and iridium oxide coatings was examined. Single emission tips and flat samples of molybdenum and iridium oxide were prepared for characterization. The flat samples were characterized using X-ray Photoelectron Spectroscopy and X-ray diffraction to determine elemental composition, chemical shift, and crystal structure. Flat coatings of iridium oxide were also scanned by Atomic Force Microscopy to examine topography. Work functions were characterized by Ultraviolet Photoelectron Spectroscopy from the flat samples and by Field Emission Electron Distributions from the field emission tips. Field emission characterization was conducted in a custom build analytical chamber capable of measuring Field Emission Electron Distribution and Fowler-Nordheim I-V plots simultaneously to independently evaluate geometric and work function changes. Scanning Electron Microscope pictures were taken of the emission tips before and after field emission characterization to confirm geometric changes. Measurement of emission stability and work functions were the emphasis of this research. In addition, use of iridium oxide coatings to enhance emission stability was evaluated. Molybdenum and iridium oxide, IrO2, were characterized and found to have a work function of 4.6 eV and 4.2 eV by both characterization techniques, with the molybdenum value in agreement with previous research. The analytic chamber used in the field emission analysis demonstrated the ability to independently determine the value and changes in work function and emitter geometry by simultaneous measurement of the Field Emission Energy Distribution and Fowler-Nordheim I-V plots from single emitters. Iridium oxide coating was found to enhance the stability of molybdenum emission tips with a relatively low work function of 4.2 eV and inhibited the formation of high work function molybdenum oxides. However, the method of deposition of iridium and annealing in oxygen to form iridium oxide on molybdenum emitters left rather severe cracking in the protective oxide coating exposing the molybdenum substrate.

Replacing solventborne coating with waterborne can reduce emission of VOC from paint shops, and decrease the amount of CO2 released from after-burners. The chemistry of 2K WB urethane coatings includes complex kinetics, with a selectivity which is highly dependent on application and curing conditions. To be able to design a coating process producing stable high quality coatings, it is important to know what factors affect the material properties. In this project, the effect of variations in temperature during curing of 2K WB and 2K SB topcoats have been evaluated in order to determine if there are any measurable effects on the material. The significance of these difference have also been evaluated to substantiate the need for thorough design of the curing process. After evaluation of visual, mechanical and chemical properties, as well as the durability of the cured topcoats, it was found that the effect of curing temperature on the level of gloss on 2K WB topcoats could be seen with the naked eye. Effects on colour, hardness, flexibility, adhesion and durability could also be measured, and revealed apparent changes in the material. Increased curing temperature had effects on both cross-linking density and isocyanate conversion. The heightened temperature contributed to the formation of topcoats with significantly decreased level of gloss and reduced stone-chip resistance, but also increased hardness and chemical resistance to an extent that was deemed significant. Varied curing temperature was found to give variations in durability, which with time may give different ageing properties of parts coated under different conditions. Before implementation of this type of waterborne topcoat, it is recommended that several properties be further evaluated, such as the effect of humidity and wet paint viscosity on the material properties. / Genom att ersätta lösningsmedelsburna ytbehandlingar med vattenburna kan man kraftigt reducera utsläppen av VOC från lackeringsverkstäder och minska mängden CO2som frigörs från efterbrännare. Kemin för 2K WB uretanlacker innefattar komplex kinetik med selektivitet som är starkt beroende av applicerings- och härdningsbetingelser. För att kunna konstruera en ytbehandlingsprocess som producerar stabila högkvalitativa ytbehandlingar är det viktigt att känna till vilka faktorer påverkar materialegenskaperna. I detta projekt har effekten av variationer i temperatur under härdning av 2K WB och 2K SB topplack utvärderats för att fastställa om det resulterar i mätbara effekter på den färdiga topplacken. Även signifikansen av dessa skillnader har utvärderats för att bedöma behovet av noggrann utformning av härdningsprocessen. Efter utvärdering av visuella, mekaniska och kemiska egenskaper samt hållbarheten hos de härdade lackerna, fanns det att effekten av härdningstemperaturen på nivån av glans för 2K WB topplacker kunde ses med blotta ögat. Effekter på färg, hårdhet, flexibilitet, vidhäftning och hållbarhet visades också mätbara, och visade på tydliga förändringar i materialet. Förhöjd härdningstemperatur visade sig ha effekter på både tvärbindningsdensiteten och omsättning av isocyanater hos härdaren. En förhöjd härdningstemperatur påvisades även bidra till bildandet av en topplack med avsevärt minskad glansnivå och visst minskad stenskottsbeständighet, men även ökad hårdhet och kemikalietålighet i en omfattning som fanns signifikant. Varierad härdningstemperatur visade sig ge variationer i hållfasthet, som med tiden riskerar att ge olika åldringsegenskaper hos komponenter belagda under olika förhållanden. Innan denna typ av vattenburen täckfärg implementeras i produktion rekommenderas att ytterligare egenskaper utvärderas, såsom inverkan av fukt och våtfärgsviskositet på ytbehandlingens slutegenskaper

Distillate solutions that were derived from concentrated ferment were incorporated into either a carrageenan (CG) and propylene glycol alginate (PGA) gum blend or into a CG, PGA, and xanthan gum (XG) blend. Distillate treatments were compared against a 10% propylene glycol treatment, a gum only control, and negative control using three hams that were cut into 2.5 cm thick slices and then cut into 2.5×2.5×2.5cm cubes (n=50) that were dipped into solutions prior to conducting mite bioassays. Coated and control ham cubes were inoculated with 20 adult mites from the species T. putrescentiae (Schrank), and incubated for 2 and 3 weeks. The distilled treatments with CG + PGA + XG had a greater reduction (P<0.05) in mite populations than all other treatments with the exception of the 10% PG coated treatments. In addition, there were no differences between treatments with respect to sensory texture, flavor, and moistness.

No description available.

In this investigation, four coatings were tested for their ability to increase the wear life of A390 aluminum primary clutch sheaves used in continuously variable transmission (CVT). The coatings tested were: hard chrome, electroless nickel metal, hard coat anodizing and composite ceramic coating. The primary clutch sheave material is a die-cast A390 aluminum. A wear test stand was developed to duplicate wear found on CVTs currently in use. The wear was evaluated using four methods. First, the change in shift characteristics of the CVT while running on the wear test stand, second a change in performance using an ATV and chassis dynamometer, third the amount of material lost, through wear, was measured using a profilometer, and finally a scanning electron microscope which was used to identify the dominate mechanism of wear in the sheave material. All of the tests showed the hard chrome coating to have the lowest wear rates and the best wear characteristics. The electroless nickel metal coating did improve the wear life of the CVT but had very high variation. The hard coat anodized and ceramic composite coatings were eliminated early in testing because of poor performance.