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Rozprawy doktorskie na temat „Microstructural modification”

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Data publikacji: 6 września 2023

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1

Illing, Cyprian A. W. "Chemical Mechanisms and Microstructural Modification of Alloy Surface Activation for Low-Temperature Carburization". Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1521753968828438.

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Nafisi, Shahrooz. "Effects of grain refining and modification on the microstructural evolution of semi-solid 356 alloy = Effets de l'affinage des grains et de la modification sur l'évolution microstructurale de l'alliage 356 semi-solide /". Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2006. http://theses.uqac.ca.

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3

Longworth, Hai Pham. "Microstructural modification of thin films and its relation to the electromigration-limited reliability of VLSI interconnects". Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13114.

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4

Liu, Xiaorui. "Crystallographic and microstructural study of as-cast and heat-treated Srmodified Al-12.7Si alloys". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0103/document.

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Les alliages aluminium-silicium (Al-Si) ont attiré une attention considérable en raison de leur importance pour les applications industrielles. Dans le présent travail, des alliages à haute pureté (Al-12.7 wt. % Si) avec et sans ajout de strontium (400 ppm), solidifiés lentement en creuset ou de façon dirigée (DS), ont été préparés et traités thermiquement. L'influence de l'ajout de strontium et des post-traitements thermiques sur les caractéristiques microstructuraux et cristallographiques des phases eutectiques a été étudiée de façon systématique. Les caractéristiques de croissance du silicium eutectique (Si) dans l'alliage non modifié ainsi que dans l'Al-12.7Si Sr-modifié ont été étudiés. Pour le cas du non-modifié, la formation répétée de variantes de macles mono-orientées permet une croissance rapide du silicium eutectique selon le mécanisme twin plane re-entrant (TPRE). Microscopiquement, les cristaux de silicium ont une forme de plaque allongée dans la direction <1 1 0> non conforme à la croissance selon <1 1 2> présumée par le modèle TPRE. L'élongation selon <1 1 0> est réalisée par des paires en zigzag <1 1 2> sur des plans de maclage parallèles, conduisant à une disparition alternative et à la création de macles rentrantes à 141°. Ce mécanisme de croissance permet aux cristaux de silicium de n'exposer que les plans {1 1 1} à faible consommation d'énergie à la consolidation. Pour les alliages modifiés au strontium, des changements importants de morphologie apparaissent dans le silicium eutectique, attribuable à la croissance de TPRE restreinte et au maclage induit par les impuretés (IIT). Ce dernier améliore la croissance latérale en formant de nouvelles macles avec des plans de macles parallèles, tandis que le second conduit à une croissance isotrope en formant des macles orientées différemment. Le traitement thermique provoque l'affinement des grains des deux phases eutectiques. L'affinement de l'α-Al se produit en même temps que la fragmentation et la sphéroïdisation du silicium et est principalement lié à la fracture des grains de silicium en raison de leur capacité limitée à accommoder la très grande dilatation thermique l'α-Al, ainsi qu'à la diffusion des atomes d'aluminium au cours du traitement thermique. La rupture du silicium génère une force de "capillarité" qui active la diffusion d'atomes d'aluminium dans la fissure. En raison du caractère de substitution de la diffusion de l'aluminium, la migration des lacunes vers l'intérieur de l'α-Al est induite lorsque l'aluminium se déplace dans les fissures, ainsi les vides de la fracture du silicium sont transférés à l'α-Al. De cette façon, les cristaux d'α-Al sont altérés et déformés. Les défauts cristallins produits, à leur tour, initient la restauration et même la recristallisation du α-Al, ce qui entraîne une diminution de taille de grain. La phase α-Al dans l'alliage de Al-12.7Si-0.04Sr solidifiée directionnellement, affiche une forte texture de fibre <1 0 0> parallèle à la direction de solidification. De très gros grains <1 0 0> α-Al sont principalement formés à la périphérie de l'échantillon cylindrique en raison des directions d'évacuation de chaleur favorables disponibles pour les trois directions [1 0 0]. Après traitement thermique, l'intensité de la texture de la phase α-Al diminue en raison de la restauration et de la recristallisation, mais le type de texture ne change pas. Pour la phase de silicium eutectique dans l'alliage de coulée, il y a deux fibres principales de texture, <1 0 0> et <1 1 0> parallèles à la direction de solidification, accompagnées de deux composantes faibles, <2 2 1> et <1 1 3> dans la même direction. Les fibres <1 0 0> et <1 1 0> correspondent à des grains de silicium situés sur la périphérie et dans le centre de l'échantillon. Les composantes <2 2 1> et <1 1 3> proviennent de plusieurs macles de grains orientés <1 1 0> et <1 0 0>. Les faibles intensités de ces deux composantes sont liées à leur fraction volumique mineure [...]
Al-Si alloys have attracted considerable attention due to their importance to industrial applications. In the present work, both crucible slowly solidified and slowly directionally solidified (DS) high-purity Al-12.7 wt. % Si alloys with and without 400 ppm Sr addition have been prepared and heat treated. The influence of Sr addition and post heat treatments on the microstructural and crystallographic features of the eutectic phases has been systematically studied. The growth characteristics of eutectic Si in the unmodified and the Sr-modified Al-12.7Si alloys were investigated. For the non-modification case, the formation of repeated single-orientation twin variants enables rapid growth of eutectic Si according to the twin plane re-entrant (TPRE) mechanism. Microscopically, Si crystals are plate-like elongated in one <1 1 0> direction that is not in accordance with the <1 1 2> growth assumed by the TPRE model. The <1 1 0> extension is realized by paired <1 1 2> zigzag growth on parallel twinning planes, leading to alternative disappearance and creation of 141° re-entrants. This growth manner ensures Si crystals to expose only their low-energy {1 1 1} planes to the melt. For the Sr-modification case, substantial changes appear in eutectic Si morphology, attributable to the restricted TPRE growth and the impurity induced twinning (IIT) growth. The first enhances lateral growth by forming new twins with parallel twinning planes, while the second leads to isotropic growth by forming differently oriented twins. Heat treatment brings about refinement of both eutectic phases. The refinement of the α-Al occurs concomitantly with the fragmentation and spheroidization of Si and is mainly related to the fracture of the Si crystals due to their limited capacity to accommodate the giant thermal expansion of the α-Al and the diffusion of Al atoms to the cracks during the heat treatment. The Si fracture generates “capillarity” force that activates the diffusion of Al atoms to the gap of the crack. Due to the substitutional feature of Al diffusion, the migration of vacancies toward the interior of the α-Al is induced when Al moves to the gaps, thus the voids of the Si fracture are transferred to the α-Al. In this way, the crystals of α-Al are distorted and defected. The produced crystal defects, in turn, initiate recovery and even recrystallization of the α-Al, resulting in grain refinement. The α-Al phase in the directionally solidified Al-12.7Si-0.04Sr alloy, displays a strong <1 0 0> fiber texture in the solidification direction. Giant <1 0 0> α-Al grains are mainly formed in the outer circle region of the cylindrical specimen due to the favorable heat evacuation directions available for the three <1 0 0> directions. After heat treatment, the texture intensity of the α-Al phase decreases due to the recovery and recrystallization, but the texture type does not change. For the eutectic Si phase in the as-cast alloy, there are two main fiber texture components, <1 0 0> and <1 1 0> in the DS direction, accompanied by two weak components, <2 2 1> and <1 1 3> in the same direction. The <1 0 0> and <1 1 0> components are from Si crystals located in the outer circle and center regions of the cylindrical specimen. The <2 2 1> and the <1 1 3> components are from multiple twins of the <1 1 0> and <1 0 0> oriented crystals. The weak intensities of these two components are related to their minor volume fraction. Once heat treated, the twinned parts with minor volume fractions enlarge at the expense of their twin related matrix, thus the <1 1 0> component is weakened and accompanied by the intensification of the components from the twins. The disappearance of the <1 1 3> component and the appearance of the <1 1 5> component are due to crystallographic rotation of Si crystals during their fragmentation
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5

Hecht, Matthew David. "Effects of Heat Treatments and Compositional Modification on Carbide Network and Matrix Microstructure in Ultrahigh Carbon Steels". Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1023.

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This dissertation investigates microstructure/property relations in ultrahigh carbon steel (UHCS) with the aim of improving toughness while retaining high hardness. Due to high C contents (ranging from 1 to 2 wt%), UHCS exhibit high strength, hardness, and wear resistance. Despite this, applications for UHCS are currently limited because they typically contain a continuous network of proeutectoid cementite that greatly reduces ductility and toughness. In previous research, thermomechanic processing had seen considerable success in breaking up the network. However, the processing is difficult and has thus far seen very limited industrial application. Chemical modification of the steel composition has also seen some success in network break-up, but is still not well understood. There have been relatively few fundamental studies of microstructure evolution in UHCS; studies in the literature typically focused on lower C steels (up to 1 wt% C) or on cast irons (>2.1 wt% C). Thus, this work was undertaken to gain a better understanding of microstructural changes that occur during heat treatment and/or chemical modification of UHCS with a focus on the distribution of proeutectoid cementite within the microstructure. This dissertation is composed of eight chapters. The first chapter presents an introduction to phases found in UHCS, descriptions of research materials used in each chapter, and the hypotheses and objectives guiding the work. The second chapter describes a study of the microstructure found in a 2C-4Cr UHCS before and after an industrial-scale austenitizating heat treatment that increased hardness and toughness and also produced discrete carbide particles in the matrix. The third chapter establishes and demonstrates a metric for measuring connectivity in carbide networks. The fourth chapter describes a series of heat treatments designed to investigate kinetics of spheroidization and coarsening of carbide particles and denuded zones near cementite network branches in 2C-4Cr UHCS. The fifth chapter describes an additional series of heat treatments comparing coarsening kinetics in 2C-1Cr and 2C-4Cr UHCS. Lowering the Cr content caused clustering of cementite particles near grain boundaries, in contrast to the denuded zones observed in the higher Cr UHCS. The fifth chapter details four in situ confocal laser scanning microscopy heat treatments of 2C-4Cr UHCS. The seventh chapter investigates the effects of a 2wt% Nb addition on 2C-4Cr UHCS. The eighth and final chapter summarizes the findings of all the experiments of the previous chapters and revisits the objectives and conclusions.
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6

Zamani, Mohammadreza. "Al-Si Cast Alloys - Microstructure and Mechanical Properties at Ambient and Elevated Temperature". Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Material och tillverkning – Gjutning, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-26805.

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Aluminium alloys with Si as the major alloying element form a class of material providing the most significant part of all casting manufactured materials. These alloys have a wide range of applications in the automotive and aerospace industries due to an excellent combination of castability and mechanical properties, as well as good corrosion resistance and wear resistivity. Additions of minor alloying elements such as Cu and Mg improve the mechanical properties and make the alloy responsive to heat treatment. The aim of this work is studying the role of size and morphology of microstructural constituents (e.g SDAS, Si-particles and intermetalics) on mechanical properties of Al-Si based casting alloy at room temperatures up to 500 ºC. The cooling rate controls the secondary dendrite arm spacing (SDAS), size and distribution of secondary phases. As SDAS becomes smaller, porosity and second phase constituents are dispersed more finely and evenly. This refinement of the microstructure leads to substantial improvement in tensile properties (e.g. Rm and εF). Addition of about 280 ppm Sr to EN AC- 46000 alloy yields fully modified Si-particles (from coarse plates to fine fibres) regardless of the cooling conditions. Depression in eutectic growth temperature as a result of Sr addition was found to be strongly correlated to the level of modification irrespective of coarseness of microstructure. Modification treatment can improve elongation to failure to a great extent as long as the intermetallic compounds are refined in size. Above 300 ºC, tensile strength, Rp0.2 and Rm, of EN AC-46000 alloys are dramatically degraded while the ductility was increased. The fine microstructure (SDAS 10 μm) has superior Rm and ductility compared to the coarse microstructure (SDAS 25 μm) at all test temperature (from room to 500 ºC). Concentration of solutes (e.g. Cu and Mg) in the dendrites increases at 300 ºC and above where Rp0.2 monotonically decreased. The brittleness of the alloy below 300 ºC was related to accumulation of a high volume fraction damaged particles such as Cu- Fe-bearing phases and Si-particles. The initiation rate of damage in the coarse particles was significantly higher, which enhances the probability of failure and decreasing both Rm and εF compared to the fine microstructure. A physically-based model was adapted, improved and validated in order to predict the flow stress behaviour of EN AC- 46000 cast alloys at room temperature up to 400 ºC for various microstructures. The temperature dependant variables of the model were quite well correlated to the underlying physics of the material
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7

Liu, Jing. "Mechanisms of lifetime improvement in Thermal Barrier Coatings with Hf and/or Y modification of CMSX-4 superalloy substrates". Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3423.

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In modern turbine engines for propulsion and energy generation, thermal barrier coating (TBCs) protect hot-section blades and vanes, and play a critical role in enhancing reliability, durability and operation efficiency. In this study, thermal cyclic lifetime and microstructural degradation of electron beam physical vapor deposited (EB-PVD) Yttria Stabilized Zirconia (YSZ) with (Ni,Pt)Al bond coat and Hf- and/or Y- modified CMSX-4 superalloy substrates were examined. Thermal cyclic lifetime of TBCs was measured using a furnace thermal cycle test that consisted of 10-minute heat-up, 50-minute dwell at 1135C, and 10-minute forced-air-quench. TBC lifetime was observed to improve from 600 cycles to over 3200 cycles with appropriated Hf- and/or Y alloying of CMSX-4 superalloys. This significant improvement in TBC lifetime is the highest reported lifetime in literature with similar testing parameters. Beneficial role of reactive element (RE) on the durability of TBCS were systematically investigated in this study. Photostimulated luminescence spectroscopy (PL) was employed to non-destructively measure the residual stress within the TGO scale as a function of thermal cycling. Extensive microstructural analysis with emphasis on the YSZ/TGO interface, TGO scale, TGO/bond coat interface was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning electron microscopy (STEM) as a funcion of thermal cycling including after the spallation failure. Focused ion beam in-situ lift-out (FIB-INLO) technique was employed to prepare site-specific TEM specimens. X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) were also employed for phase identification and interfacial chemical analysis. While undulation of TGO/bond coat interface (e.g., rumpling and ratcheting) was observed to be the main mechanism of degradation for the TBCs on baseline CMSX-4, the same interface remained relatively flat (e.g., suppressed rumpling and ratcheting) for durable TBCs on Hf- and/or Y-modified CMSX-4. The fracture paths changed from the YSZ/TGO interface to the TGO/bond coat interface when rumpling was suppressed. The geometrical incompatibility between the undulated TGO and EB-PVD YSZ lead to the failure at the YSZ/TGO interface for TBCs with baseline CMSX-4. The magnitude of copressive residual stress within the TGO scale measured by PL gradually decreased as a function of thermal cycling for TBCs with baseline CMSX-4 superalloy substrates. This gradual decrease corrsponds well to the undulation of the TGO scale that may lead to relaxation of the compressive residual stress within the TGO scale. For TBCs with Hf- and/or Y-modified CMSX-4 superalloy substrates, the magnitude of compressive residual stress within the TGO scale remained relatively constant throughout the thermal cycling, although PL corresponding to the stress-relief caused by localized cracks at the TGO/bond coat interface and within the TGO scale was observed frequently starting 50% of lifetime. A slightly smaller parabolic growth constant and grain size of the TGO scale was observed for TBCs with Hf- and/or Y- modified CMSX-4. Small monoclinic HfO2 precipitates were observed to decorate grain boundaries and the triple pointes within the alpha-Al2O3 scale for TBCs with Hf- and/or Y-modified CMSX-4 substrates. Segregation of Hf/Hf4+ at the TGO/bond coat interfaces was also observed for TBCs with Hf- and/or Y-modified CMSX-4 superalloys substrates. Adherent and pore-free YSZ/TGO interface was observed for TBCs with Hf- and/or Y-modified CMSX-4, while a significant amount of decohesion at the YSZ/TGO interface was observed for TBCs with baseline CMSX-4. The beta-NiAl(B2) phase in the (Ni,Pt)Al bond coat was observed to partially transform into gama prime-Ni3Al (L12) phase due to depletion of Al in the bond coat during oxidation. More importantly, the remaining beta-NiAl phase transformed into L10 martensitic phase upon cooling even though there was no significant difference in these phase transformations for all TBCs. Results from these microstructural observations are documented to elucidate mechanisms that suppress the rumpling of the TGO/bond coat interface, which is responsible for superior performance of EB-PVD TBCs with (Ni,Pt)Al bond coat and Hf- and/or Y-modified CMXS-4 superalloy.
Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Materials Science & Engr PhD
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8

Anyango, Joseph Ochieng. "Physico-chemical modification of kafirin microstructures for application as biomaterials". Thesis, University of Pretoria, 2012. http://hdl.handle.net/2263/29708.

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Microparticles produced from kafirin, the sorghum grain prolamin protein, by molecular selfassembly using coacervation with acetic acid solvent are vacuolated. They have shown considerable potential for encapsulation of antioxidants and for preparation of high quality free-standing bioplastic films. However, the functional quality of these kafirin microstructures needs to be improved to exploit their potential application, particularly as biomaterials. Wet heat, transglutaminase and glutaraldehyde treatments were used to modify the physical structure and chemical properties of the kafirin microstructures. Heat treatment (50–96°C) increased microparticle average size by up to four-fold to ≈20 μm, probably due to disulphide cross-linking of kafirin proteins. The vacuoles within these microparticles enlarged up to >10-fold, probably due to greater expansion of air within the microparticles with higher temperature, as the vacuoles are probably footprints of air bubbles. As with heat treatment, glutaraldehyde (10–30%) treatment resulted in oval microparticles, up to about four-fold larger than the control, probably due to covalent glutaraldehyde-polypeptide linkage. Transglutaminase (0.1–0.6%) treatment had only slight effect on the size and shape of microparticles, probably because kafirin has very low lysine content, inhibiting transglutaminase-catalysed cross-linking through ε-(-glutamyl)-lysine bonding. Surface morphology using atomic force microscopy indicated that the microparticles apparently comprised coalesced nanostructures. With heat and transglutaminase treatments, the microparticles seemed to be composed of round nanostructures that coalesced into random irregular shapes, indicative of non-linear protein aggregation. In contrast, with glutaraldehyde treatment, the nanostructures were spindle-shaped and had a unidirectional orientation, probably due to linear alignment of the nanostructures controlled by glutaraldehyde-polypeptide linkage. Thin (<50 μm) films prepared from kafirin microparticles and conventional cast kafirin films were compared in terms of their water stability and other related properties. Films cast from microparticles were more water-stable compared to conventional kafirin films, probably because the large vacuoles within the kafirin microparticles may have enhanced protein solubility in the casting solution, thereby improving the film matrix cohesion. The films prepared from microparticles treated with glutaraldehyde were more water-stable compared to the control, despite the loss of plasticizer, probably due to formation of the covalent glutaraldehyde-polypeptide linkages. The potential of modified kafirin microparticles to bind bone morphogenetic protein-2 (BMP- 2) was investigated. Compared to a collagen standard, the BMP-2 binding capacity of control, heat-treated, transglutaminase-treated and glutaraldehyde-treated kafirin microparticles were 7%, 18%, 34% and 22% higher, respectively, probably mainly due to the vacuoles within the microparticles creating greater binding surface area. The safety, biodegradability and effectiveness of kafirin microparticle film and kafirin microparticle film-BMP-2 system in inducing bone growth were determined by a subcutaneous bioassay using a rat model. Kafirin microparticle film and kafirin microparticle film-BMP-2 system was non-irritant to the animals, probably because kafirin is non-allergenic. The kafirin microparticle film implants showed signs of some degradation but a large proportion of these implants was still intact by Day 28 post implantation, probably because of the low susceptibility of kafirin to mammalian proteolytic enzymes. Kafirin microparticle film-BMP-2 system did not induce bone growth, probably mainly due to low BMP-2 dosage and short study duration. Modification of kafirin microparticles by wet heat or glutaraldehyde treatment both result in increased size of the microparticles with similar gross structure. However, it is apparent that with both treatments the proteins within the pre-formed kafirin microparticles undergo some form of further assisted-assembly through different mechanisms. It seems that heat-induced disulphide cross-linking reinforces a layer around the nanostructures, probably rich in γ- kafirin polypeptides, that stabilizes the structure of the nanostructures. In contrast, glutaraldehyde-treatment appears to destabilize this structure-stabilizing layer through formation of γ-kafirin polypeptide-glutaraldehyde covalent bonding. This probably offsets the balance of attractive and repulsive forces between the different kafirin subclasses within the nanostructures, thereby resulting in collapsed nanostructures and linear realignment. A deeper understanding of the mechanism of kafirin self-assembly will be important for further development of kafirin microstructures for different applications.
Thesis (PhD)--University of Pretoria, 2012.
Food Science
unrestricted
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9

Valko, N., S. Anufric, A. Ivanov i S. Vasiliev. "Laser Modification of the Microstructure of Zn-Co Electroplating Alloys". Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42658.

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In this study we report the experimental results of researches of the effect on the microstructure of the Zn-Co coatings with laser radiation generated by a ruby laser operating of free oscillators regime (1.2 ms pulse duration, wavelength 0.69𝜇𝑚 and the power density of 104 to 106 W / cm2). It is shown how the microstructure of the investigating alloys after its modification by an impulse laser radiation depends on the power density.
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10

Díez, Escudero Anna. "Tuning the biological performance of calcium phosphates through microstructural and chemical modifications". Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/620730.

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Bone is the most transplanted tissue after blood. As pointed out by the World Health Organization, musculoskeletal diseases can potentially rise as the fourth largest cause of disability within the next years. Unfortunately, despite the natural ability of bone to self-heal it cannot bridge large bone defects without the help of a material. Still today the gold standard to restore bone function remains the use of natural bone grafts. However, they have several limitations that need to be overcome to accommodate the high demands of a global ageing population. Calcium phosphate (CaP) bone grafts have been known since the 1970s and stand as excellent synthetic candidates due to their composition, similar to the mineral phase of bone which consists of approximately 70 wt% of hydroxyapatite (HA). CaPs, and in particular HA, possess outstanding intrinsic properties such as biocompatibility, bioactivity and the ability to support bone growth. However, HA is too stable and once implanted it hardly degrades. Ideal synthetic bone grafts should integrate in the bone remodelling cycle, balancing implant resorption with its progressive replacement by new bone. This can be achieved either by modulating the material¿s physicochemical properties, or by combining the substrate with biological molecules capable of adequately orchestrating the various cells involved in the bone healing process. The present thesis seeks to explore, on the one hand, the feasibility of modulating the physicochemical properties of CaPs towards improving its degradation behavior, and, on the other hand, to investigate the potential CaP functionalization with heparin as a strategy to improve their biological performance at the various stages of bone healing: during the initial phase of inflammation, and during the stages of bone resorption and bone growth. The first part of the present thesis deals with the in vitro degradation of CaPs in a solution mimicking the osteoclastic environment, focusing specifically on the effect of some properties like porosity, specific surface area, microstructure and composition. The interrelation of all these parameters sometimes masks the relative importance of textural over compositional features, making difficult the prediction of their degradation behavior. Additionally, part of the work explores different strategies to incorporate carbonate ions in the crystal structure of HA as a route to obtain materials that more closely mimic natural bone. To further mimic the biological environment of bone, the second part of the thesis is focused on grafting heparin, a highly sulfated glycosaminoglycan present in the bone extracellular matrix, to CaPs. The affinity of heparin for growth factors (GF) makes this molecule an excellent candidate to capture endogenous GF bringing many benefits in the regulation of cell behavior. It is hypothesized that heparin, given its anti-inflammatory role, together with the known involvement in osteoblasts differentiation (bone forming cells) and osteoclastogenesis (bone resorbing cells formation) could enhance the biological performance of synthetic bone grafts. To this aim, CaPs were heparinized and their biological performance was assessed using human immune system cells, bone forming cells and bone resorbing cells, in an attempt to elucidate the synergies of both immune cells and cells of the skeletal system.
L'os és el teixit més trasplantats desprès de la sang. L'organització Mundial de la Salut ha posat de relleu l'increment de les malalties musculoesquelètiques, les quals esdevindran la quarta causa mundial de discapacitat en el següents anys. Malgrat la capacitat natural de l'ós per autoregenerar-se, els defectes ossis de grans dimensions necessiten l'ajuda de materials per restaurar-se completament. Actualment, l'ús d'empelts naturals és l'alternativa més emprada clínicament. Tot i això, els autoempelts comporten certes limitacions que requereixen ser adreçades per tal de fer front a les elevades demandes d'una població mundial amb un grau d'envelliment creixent. Els empelts basats en fosfats càlcics (CaPs) són coneguts des de la dècada del 1970 i són uns excel·lents candidats per a la regeneració òssia donada la seva composició, similar a la fase mineral de l'os, que consisteix en aproximadament un 70% d'hidroxiapatita (HA). Els CaPs, en particular l'HA, posseeixen unes propietats intrínseques excepcionals com ara la biocompatibilitat, bioactivitat o la capacitat de suportar el creixement de nou os. Malgrat la seva semblança amb l'os, l'HA és massa estable químicament, i un cop implantada es degrada molt lentament. L'empelt ossi sintètic idealment s'hauria d'integrar en el cicle de remodelació òssia, el que requereix d'un balanç entre la seva reabsorció i la progressiva substitució per os nou. Aquesta capacitat es pot modular mitjançant propietats inherents del material o per mitjà de la combinació de substrats amb molècules capaces d'orquestrar adequadament les respostes de les diverses cèl·lules implicades en la restauració o regeneració òssia. La present tesis cerca explorar, per una banda, la possibilitat de modular les propietats físico-químiques dels CaPs per tal de millorar la seva degradació, així com investigar el potencial de funcionalitzar els CaPs amb heparina, amb la finalitat de millorar les interaccions biològiques a les diferents etapes de la restauració òssia, tant durant la primera etapa inflamatòria, com durant la resorció i el creixement d'os nou. Concretament, la primera part de la present tesi explora la manera en què la modificació de propietats com la porositat, la superfície específica, la microestructura o la composició dels CaPs pot ser emprada per regular la degradació d'aquests materials en una solució acídica similar a l'emprada pels osteoclasts durant la resorció òssia. La interrelació de totes aquestes propietats emmascara de vegades la importància relativa de les propietats texturals, molt lligades a les composicionals, dificultant la predicció dels nivells de degradació dels materials depenent de cada propietat. Per tal de mimetitzar encara més la composició de l'os, s'estudiarà també diferents estratègies per incorporar ions carbonat en l'estructura cristal·lina de l'HA. El segon bloc de la tesi explora la funcionalització dels CaPs amb heparina, un tipus de glicosaminoglicà altament sulfonat present en la matriu extracel·lular de l'os. L'afinitat de l'heparina per captar factors de creixement fan d'aquesta molècula un candidat excel·lent per capturar factors de creixement endògens capaços de regular la resposta cel·lular. Així doncs, partint de les propietats anti-inflamatòries de l'heparina, i de la seva implicació en els processos d'osteogènesi i osteoclastogènesi s'ha formulat la hipòtesi de que aquesta biomolècula podria contribuir a millorar les prestacions dels empelts ossis sintètics. Amb aquest objectiu, s'ha posat a punt un procés d'heparinització de CaPs i s'ha avaluat el seu efecte sobre la resposta de cèl·lules humanes del sistema immune, cèl·lules osteogèniques i osteoclàstiques, per tal d'escatir les possibles sinèrgies de tots dos sistemes, l'immune i l'ossi en la regeneració.
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11

Hua, Bin. "Studies on microstructure modification in transparent materials by femtosecond laser pulses". 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/136159.

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12

Wu, Tso-chang. "Laser Surface Modification of AZ31B Mg Alloy Bio-Implant Material". Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1248459/.

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Magnesium and its alloys are considered as the potential biomaterials due to their biocompatibility and biodegradable characteristics but suffer from poor corrosion performance. Various surface modification techniques are employed to improve their corrosion resistance. In present case, laser surface melting was carried out on AZ31B Mg alloy with various laser energy densities using a continuous wave ytterbium laser. Effect of laser treatment on phase and microstructure evolution was evaluated by X ray diffraction and scanning electron microscopy. Multi-physics thermal model predicted time temperature evolution along the depth of the laser treatment zone. Additionally, electrochemical method and bio-immersion test were employed to evaluate the corrosion behavior in simulated body fluid medium. Microstructure revealed grain refinement and even distribution of Mg17Al12 phase along the grain boundary for laser treated samples leading to substantial enhancement in the corrosion resistance of the laser treated samples compared to the untreated alloy. The laser processed samples also possessed a superior wettability in SBF solution than the untreated sample. This was further reflected in enhanced bio-integration behavior of laser processed samples. By changing the parameters of laser processing such as power, scanning speed, and fill spacing, a controllable corrosion resistance and bioactivity/biocompatibility of the implant material was achieved.
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13

Hauptstein, Anneliese Materials Science &amp Engineering Faculty of Science UNSW. "The effects of electron irradiation on the morphology, modification and microstructure of talc powder". Awarded by:University of New South Wales. School of Materials Science and Engineering, 2007. http://handle.unsw.edu.au/1959.4/27303.

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Electron irradiation may be a useful method for treating inorganic cosmetic powders such as talc for undesirable microorganisms if it can be established that no loss of quality or efficacy results as a consequence of the technique. A commercial electron accelerator was used to prepare bulk samples by exposure to electron irradiation under different conditions. A morphological characterisation of the control talc was carried out using microscopy techniques and focused on the particle size, shape and surface features of individual particles. Asperity dimensions vs. Roughness values were compared. Assessment of the bulk properties of the powders as a function of absorbed dose showed no serious impact on the quality or efficacy of the powder for cosmetic applications. The particle size and the level of dust expelled during impact were maintained. Changes to the surface chemistry of the irradiated powders were apparent from an increase in pH and water retention with increasing dose. Improvements to the fragrance retention occurred for both irradiated powders tested. Importantly a satisfactory microorganism level was achieved with the lowest absorbed dose level tested i.e. 5 kGy. Analysis of the crystallography did not show the development of a new phase. Mechanical testing using a slip-peel tester found an increase in the stick-slip behaviour occurred for the powder exposed to the highest absorbed dose only. Atomic force microscopy (AFM) testing of the lift-off force showed an increase in adhesion with increasing dose. Surface roughness increased with dose, while no change in elastic properties was found using nanoindentation suggesting the differentiating factor is due to surface features. Microstructural analysis used the transmission electron microscope (TEM). Voids were observed, which decrease in size, yet increase in number with increasing voltage. Prior to void development a loss of crystalinity is seen using electron diffraction. Explorative data analysis using factor analysis and Independent Component Analysis was performed on the void development data to discover the controlling mechanisms. Two distinct normally distributed populations were identified, each driven by 2-3 critical mechanisms. The distinct behaviour differences of the mechanisms may be utilised for characterisation of more complex properties of crystal microstructures.
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14

Kniep, Benjamin-Louis. "Microstructural modifications of copper zinc oxide catalysts as a function of precipitate ageing". [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975886851.

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15

Korthals, Brigitte [Verfasser]. "Nanoparticles of Polybutadiene with Unconventional Microstructures and their Post-Polymerization Modification / Brigitte Korthals". Konstanz : Bibliothek der Universität Konstanz, 2010. http://d-nb.info/1017236089/34.

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16

Horvat, Frank E. "A Numerical and Experimental Investigation for the Modification and Design of a Gerolor Using Low Viscoscity Fluids". University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1342585429.

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Catrin, Rodolphe [Verfasser]. "Effects of microstructure modification induced by laser interference patterning of thin films / Rodolphe Catrin". Aachen : Shaker, 2012. http://d-nb.info/1069044512/34.

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18

Chen, Weijie. "Microstructure modification and mechanical behaviour of an investment cast near ã-TiAl intermetallic alloy". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0016/NQ57605.pdf.

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19

Contino, Anna Rita. "Modification of Anode Microstructure to Improve Redox Stability of Solid Oxide Fuel Cells (SOFCs)". Doctoral thesis, Università degli studi di Trento, 2010. https://hdl.handle.net/11572/369234.

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In the last decade the increase in energy demand, the awareness of limited availability of fossil fuels and the need to reduce green house gases emission impelled governments and research institutions to focus on the study of renewable energy sources such as solar, wind and biomass derived energy and on the increase in the energy production devices efficiency. Within such scenario a relevant contribution is given by fuel cells technologies as advanced power generation system. Fuel cells are high efficiency devices and comply with the request of environmental friendly source of energy. They convert directly fuel energy into power and heat by electrochemical reactions without the need for combustion as intermediate step. The possibility to use Hydrogen makes fuel cells virtually zero-emission devices being water the only reaction product; nevertheless, also the use of hydrocarbons as fuel reduces considerable CO2 emissions. Among the different systems, solid oxide fuel cells (SOFCs) operate at high temperatures (650-1000°C) and allow to achieve the highest electrical efficiency, from 45 to 60% for common fuels, values not attainable by traditional electrical power generation methods, and up to 70% in combination with a gas turbine for Hybrid Power System generation, with an overall electrical and thermal efficiency higher than 90%. Moreover, such technology presents many advantages such as the possibility to be fed with different fuels, the absence of moving parts, modularity and limited emissions. These characteristics make SOFC suitable for application in the distributed generation market. Despite all the mentioned advantages, SOFCs show problems that make these devices not suitable for the production on industrial scale yet. In particular they present low reliability and are not competitive with traditional powers sources. SOFCs are constituted by single cells (consisting of an anode and a cathode separated by a solid electrolyte) that are collected together in a stack by interconnects in order to obtain the required power. This means that a stack is a multilayer assembly of materials with different thermal, mechanical and chemical properties that need to fulfil many prerequisites for their own function. Moreover, some of these properties must match for other connected components; for instance they have to show similar thermal expansion coefficients, to be stable at high temperatures and during thermal transients. Due to the high working temperature, stack components are necessarily subjected to degradation phenomena, which reduce their long term reliability. Among them, poisoning of cathode by Chromium evaporation from metallic interconnects, chemical interactions between glass–ceramic sealants and ferritic steel interconnects, anode poisoning caused by carbon or sulphur deposition, reduction of electrical conductivity are worthy of mention. Furthermore, various cycling conditions such as thermal cycle, redox cycle, and load cycle affect stability of SOFCs. All these degradation phenomena must be minimized in order to increase SOFC reliability. All these issues are object of intense research. The research work of the present thesis has been focused on the increase of redox stability of anode supported cells, which is considered one of the key point to improve stack reliability. The state of the art materials for the anode is Ni/YSZ cermet due to its high performance. Nevertheless, this cermet is prone to severe degradation upon redox cycling. Due to the high operating temperatures, Nickel particles tend to coalesce and coarsen. Fuel supply interruptions, over-potentials and leakages can cause the re-oxidation of Ni to NiO with a consequent volumetric expansion that can generate internal stresses and lead to cracks formation within the YSZ network and the electrolyte resulting in cell failure. Different approaches can be taken in account in order to minimize redox instability. In order to study redox phenomena and produce redox stable cells many aspects related to the modification of anodic microstructure were analyzed. Among these, one of the most promising method is to modify the anode microstructure by increasing its porosity. The present thesis is divided in two parts. In the first section the theoretical background of fuel cells, specifically SOFCs, is reported. A particular attention is dedicated to describe redox phenomenon and the state of the art of the research in this field. The second experimental part concerns with the production of anodes with improved microstructure. The modification of microstructure was realized by using different powders and by adding different pore formers and doping elements. A detailed study of the effects on redox stability of the microstructure modifications induced by the addition of each of the aforesaid substances is described.
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20

Contino, Anna Rita. "Modification of Anode Microstructure to Improve Redox Stability of Solid Oxide Fuel Cells (SOFCs)". Doctoral thesis, University of Trento, 2010. http://eprints-phd.biblio.unitn.it/349/1/Modification_of_Anode_Microstructure_to_Improve_Redox_Stability_of_Solid_Oxide_Fuel_Cells_(SOFCs).pdf.

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In the last decade the increase in energy demand, the awareness of limited availability of fossil fuels and the need to reduce green house gases emission impelled governments and research institutions to focus on the study of renewable energy sources such as solar, wind and biomass derived energy and on the increase in the energy production devices efficiency. Within such scenario a relevant contribution is given by fuel cells technologies as advanced power generation system. Fuel cells are high efficiency devices and comply with the request of environmental friendly source of energy. They convert directly fuel energy into power and heat by electrochemical reactions without the need for combustion as intermediate step. The possibility to use Hydrogen makes fuel cells virtually zero-emission devices being water the only reaction product; nevertheless, also the use of hydrocarbons as fuel reduces considerable CO2 emissions. Among the different systems, solid oxide fuel cells (SOFCs) operate at high temperatures (650-1000°C) and allow to achieve the highest electrical efficiency, from 45 to 60% for common fuels, values not attainable by traditional electrical power generation methods, and up to 70% in combination with a gas turbine for Hybrid Power System generation, with an overall electrical and thermal efficiency higher than 90%. Moreover, such technology presents many advantages such as the possibility to be fed with different fuels, the absence of moving parts, modularity and limited emissions. These characteristics make SOFC suitable for application in the distributed generation market. Despite all the mentioned advantages, SOFCs show problems that make these devices not suitable for the production on industrial scale yet. In particular they present low reliability and are not competitive with traditional powers sources. SOFCs are constituted by single cells (consisting of an anode and a cathode separated by a solid electrolyte) that are collected together in a stack by interconnects in order to obtain the required power. This means that a stack is a multilayer assembly of materials with different thermal, mechanical and chemical properties that need to fulfil many prerequisites for their own function. Moreover, some of these properties must match for other connected components; for instance they have to show similar thermal expansion coefficients, to be stable at high temperatures and during thermal transients. Due to the high working temperature, stack components are necessarily subjected to degradation phenomena, which reduce their long term reliability. Among them, poisoning of cathode by Chromium evaporation from metallic interconnects, chemical interactions between glass–ceramic sealants and ferritic steel interconnects, anode poisoning caused by carbon or sulphur deposition, reduction of electrical conductivity are worthy of mention. Furthermore, various cycling conditions such as thermal cycle, redox cycle, and load cycle affect stability of SOFCs. All these degradation phenomena must be minimized in order to increase SOFC reliability. All these issues are object of intense research. The research work of the present thesis has been focused on the increase of redox stability of anode supported cells, which is considered one of the key point to improve stack reliability. The state of the art materials for the anode is Ni/YSZ cermet due to its high performance. Nevertheless, this cermet is prone to severe degradation upon redox cycling. Due to the high operating temperatures, Nickel particles tend to coalesce and coarsen. Fuel supply interruptions, over-potentials and leakages can cause the re-oxidation of Ni to NiO with a consequent volumetric expansion that can generate internal stresses and lead to cracks formation within the YSZ network and the electrolyte resulting in cell failure. Different approaches can be taken in account in order to minimize redox instability. In order to study redox phenomena and produce redox stable cells many aspects related to the modification of anodic microstructure were analyzed. Among these, one of the most promising method is to modify the anode microstructure by increasing its porosity. The present thesis is divided in two parts. In the first section the theoretical background of fuel cells, specifically SOFCs, is reported. A particular attention is dedicated to describe redox phenomenon and the state of the art of the research in this field. The second experimental part concerns with the production of anodes with improved microstructure. The modification of microstructure was realized by using different powders and by adding different pore formers and doping elements. A detailed study of the effects on redox stability of the microstructure modifications induced by the addition of each of the aforesaid substances is described.
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21

Lomello, Fernando. "Optimization of nanostructured oxide-based powders by surface modification". Lyon, INSA, 2010. http://theses.insa-lyon.fr/publication/2010ISAL0028/these.pdf.

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This thesis is divided into two parts. The first part deals with the study of surface modification of a transition alumina nanopowder and the second part is devoted to the production and mechanical characterization at room- and high-temperature of Alumina 5 vol. % YAG nanocomposites. In order to study, the effect of the dispersion on a transition alumina several physico-chemical characterization techniques were employed such as the DTA-TG analysis, XRD, BET Specific Surface Area, HR-TEM and the FT-IR spectroscopy. In particular, the transition aluminas present metastable phases which suffer transformations during sintering and induce the formation of a vermicular microstructure, consisting of a network of large pores. As a consequence, the final density and the microstructure have been improved thanks to the dispersion which allowed to achieved higher densities and promotes the transformation into alpha-phase. Moreover , the influence of the dispersion on the transformation kinetics (Kissinger Method), as well as, on the sintering kinetics (SID Method) has been evaluated. In the second part, it is presented the development of Alumina/YAG nanocomposites from two commercial nanopowders naturally sintered and sintered by non-conventional methods, such as HP and SPS. The mechanical characterization at room temperature (Hardness, Toughness, Elastic modulus) has been correlated to a microstructural study (ESEM). Interesting values regarding hardness and toughness have been measured in samples sintering by SPS and HP, around 20GPA and 7 MPA. M1/2, respectively. For the characterization at the high temperature, creep tests were carried in a 4-point bending fixture at 1200°C and an applied stress of 100 Mpa. The results show that mechenical properties depend on the second phase distribution into the alumina matrix. In all cases, the obtains results were interesting
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22

Vieille, Laetitia. "Modifications microstructurales en température de la phase hydrocalumite et des dérivés hydrocalumite-polymères". Clermont-Ferrand 2, 2004. http://www.theses.fr/2004CLF22531.

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Dans ce travail, l'accent a été mis sur le suivi in situ de la décomposition thermique des phases [Ca2Al(OH)6Cl. 2H2O] et [Ca2Fe(OH)6Cl. 2H2O] par diffraction et absorption des rayons X, permettant ainsi de décrire de manière la plus fine possible la réversibilité de l'étape de déshydratation et le greffage des anions chlorure aux feuillets hydroxydes. Notre étude est la première concernant le greffage d'anions halogénure i. E. Non oxygénés. Des expériences couplées DSC-Quick XANES ont également pu être réalisées permettant ainsi de suivre la décomposition du matériau en temps réel. Le second volet de cette thèse est l'étude des matériaux hydrocalumite-polymères avec une approche comparative hydrotalcite/ hydrocalumite pour une meilleure compréhension des mécanismes qui régissent la formation de nanocomposites HDL-polymères. Le vinyle benzène sulfonate (VBS) et le polystyrène sulfonate (PSS) trouvent une application dans le domaine des ciments. Après un traitement thermique à 200° C sous air, une forte contraction de la distance interlamellaire (deltad = 3,9 A°) est observée provenant de la polymérisation in situ des monomères entre les feuillets d'HDL
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23

De, Carvalho Pinheiro Bianca. "Étude par diffraction des rayons X des modifications microstructurales en cours de fatigue". Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10063/document.

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Le travail présenté ici a pour but d’évaluer les mécanismes microstructuraux liés à l’amorçage de l’endommagement par fatigue d’un acier à usage pétrolier. Les microdéformations et les contraintes résiduelles (macrocontraintes) ont été déterminées par diffraction des rayons X en temps réel pendant des essais de fatigue en flexion alternée sur des éprouvettes plates prélevées dans la paroi d’un tube neuf. Les microdeformations sont estimées à partir de mesures de la largeur de corde à mi-hauteur (LCMH) d’un pic de diffraction et les contraintes résiduelles à partir du déplacement du pic. Les essais de fatigue sont réalisés pour cinq niveaux de contraintes différents. On observe trois stades de variation pendant l’évolution des microdeformations. On montre que leur amplitude et leur durée sont proportionnelles au niveau de contrainte alternée. Des variations similaires sont observées pour les contraintes résiduelles, avec des durées identiques à celles des microdéformations. Des évolutions dans la densité et la répartition des dislocations ont été observées par microscopie électronique en transmission à l’aide de la technique du faisceau d’ions focalisés. Pour comprendre le rôle de la structure initiale, des essais de fatigue sur éprouvettes recuites ont été réalisés dans les mêmes conditions d’essai. Là encore trois stades d’évolution sont observées mais avec un premier stade inversé du fait de l’état initial du réseau de dislocations. Les résultats obtenus sont très encourageants pour la prise en compte des évolutions microstructurales dans l’établissement d’un futur indicateur de dommage de la phase d’amorçage en fatigue à grand nombre de cycles des matériaux
The present work aims to evaluate the microstructural mechanisms associated with the initiation of fatigue damage of steels used in the oil and gas industry. Microdeformations and residual stresses (macrostresses) were evaluated by X-ray diffraction in real time during alternating bending fatigue tests performed on flat test pieces taken from a pipe sample. Microdeformations were estimated from measurements of the full width at half maximum (FWHM) of the diffraction peak and residual stresses from the peak displacement. The fatigue tests were performed at five different stress levels. Three stages of changes during the evolution of microdeformation were detected. We show that their amplitude and duration are proportional to the level of alternating stress. Similar variations were observed for the residual stresses, with duration identical to those of the microdeformation. Changes in the density and distribution of dislocations were observed by transmission electron microscopy using the technique of focused ion beam. To understand the role of the initial structure, fatigue tests on annealed samples were performed under the same test conditions. Again, three stages of changes are observed but with an increase of the microdeformations instead of a decrease during the first stage due to the initial state of the dislocation network. The results are very encouraging for the consideration of the microstructural evolutions in the construction of a future counter of fatigue damage initiation in materials
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24

Eyidi, Dominique. "Microstructures d'oxydes supraconducteurs à haute température critique à base de mercure ; modification par déformation plastique". Poitiers, 1999. http://www.theses.fr/1999POIT2317.

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Ce travail porte sur l'etude par microscopie electronique en transmission des microstructures de defauts dans les materiaux supraconducteurs a haute temperature critique (hg, m)ba 2ca n 1cu no 2 n + 2 +. Le materiau hg 0. 8 2re 0. 1 8ba 2ca 2cu 3o 8 + (t c = 135 k) brut de synthese renferme une grande variete de phases secondaires (oxydes) et de fortes densites de fautes d'intercroissances (hg, re)-1212 dans le plan basal. Les systemes de glissement sont (001)100 et (001)110. Des dislocations parfaites et des fautes d'intercroissances sont egalement presentes dans les materiaux non substitues hg-1212 et hg-1223. La deformation d'echantillons (hg, re)-1223 a temperature ambiante par compression uniaxiale sous pression de confinement provoque l'activation substantielle des systemes de glissement (001)100 et (110)110, en meme temps qu'une augmentation sensible de la densite de dislocations et de microfissures. Les dislocations nucleees au cours de la deformation presentent de longs segments vis rectilignes qui suggerent l'existence de fortes contraintes de peierls le long des directions <100> et <110>. Les dislocations de vecteur de burgers 110 sont sujettes a des dissociations par montee et a des evenements de glissement devie vers (001). La deformation plastique entraine une diminution du volume supraconducteur par reduction de la taille des grains. Des mesures d'aimantation et de susceptibilite alternative montrent que pour des taux inferieurs a 20%, la densite de courant critique decroit legerement, alors qu'on note une amelioration nette pour les echantillons deformes a 63%. Cette hausse du courant critique a ete attribuee a l'accroissement de la densite de dislocations, et en particulier a celle des segments coins des dislocations de vecteurs de burgers <100>. Ces segments sont susceptibles d'ancrer efficacement les vortex par un effet de taille.
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25

Chollet, Sébastien. "Étude des modifications microstructurales de superalliages à base nickel induites par nitruration assistée plasma". Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2293/document.

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Les turbines aéronautiques et terrestres utilisent comme matériaux de structure les superalliages à base nickel. Ils sont confrontés en utilisation à des environnements agressifs à très hautes températures, conduisant à l'usure et la corrosion, et à des sollicitations mécaniques qui entraînent fatigue et fluage. Pour permettre l'utilisation de ces matériaux dans des conditions toujours plus sévères de fonctionnement et augmenter la durée de vie des pièces, divers traitements de nitruration ont été proposés pour durcir la surface tout en conservant ou en améliorant la tenue mécanique et la résistance chimique. Les modifications induites par la nitruration, leur stabilité et l'influence de la microstructure initiale sont encore mal comprises dans ces matériaux complexes. Au cours de ces travaux, nous avons étudié les effets d'une nitruration assistée plasma en fonction de la microstructure et de la composition chimique des alliages. Différents types de superalliages à base nickel ont été choisis, de microstructures variées, comprenant éventuellement des précipités de type Ni3(Al,Ti,Nb) et/ou Ni3 (Nb). Nous avons alors caractérisé les modifications induites par l'introduction de l'azote dans les matériaux suite à un traitement de nitruration à basse température (400°C) : expansion de la maille, génération de contraintes résiduelles, comportement des précipités, formation de nitrures, plasticité, anisotropies... Les résultats obtenus suggèrent des effets différents selon la composition des précipités. Ces modifications structurales et leurs évolutions ont ensuite été étudiées lors d'un recuit à plus haute température (650°C) afin d'étudier la stabilité des couches formées
Nickel-based superalloys are commonly used in pressurized water heat exchangers or in the hottest sections of aeroengines or industrial gas turbines, where they are subjected to high temperature and severe mechanical solicitations (fatigue, creep). To allow use of those materials in more and more difficult operating conditions and to improve their duration, different nitriding treatments have been proposed to harden the surface while maintaining or improving their mechanical strength and chemical resistance. However, modifications induced by nitriding, resulting stability in time and influences of the initial microstructure are still poorly understood in these complex materials. In this work, we investigated the behavior of plasma nitriding on superalloys according to their initial microstructure and chemical composition. Thus, different types of Nickel-based superalloys were selected with various microstructures, possibly including precipitates like Ni3(Al, Ti, Nb) and/or Ni3(Nb). Then, we have characterized the modifications induced by nitrogen introduction in the materials after nitriding treatment at low temperature (400°C): lattice expansion, generation of residual stress, precipitates behavior, nitrides formation, plasticity, anisotropy... The results suggest different behaviors depending on the composition of precipitates. Finally, these structural modifications and their evolutions have been studied during an annealing at higher temperature (650°C) in order to study the stability of the nitrided layers
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26

Graziani, Alessandro. "Chemical composition modification of casting aluminium alloys for engine applications". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10018/.

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The research activities were focused on evaluating the effect of Mo addition to mechanical properties and microstructure of A354 aluminium casting alloy. Samples, with increasing amount of Mo, were produced and heat treated. After heat treatment and exposition to high temperatures samples underwent microstructural and chemical analyses, hardness and tensile tests. The collected data led to the optimization of both casting parameters, for obtaining a homogeneous Mo distribution in the alloy, and heat treatment parameters, allowing the formation of Mo based strengthening precipitates stable at high temperature. Microstructural and chemical analyses highlighted how Mo addition in percentage superior to 0.1% wt. can modify the silicon eutectic morphology and hinder the formation of iron based β intermetallics. High temperature exposure curves, instead, showed that after long exposition hardness is slightly influenced by heat treatment while the effect of Mo addition superior to 0,3% is negligible. Tensile tests confirmed that the addition of 0.3%wt Mo induces an increase of about 10% of ultimate tensile strength after high temperature exposition (250°C for 100h) while heat treatments have slight influence on mechanical behaviour. These results could be exploited for developing innovative heat treatment sequence able to reduce residual stresses in castings produced with A354 modified with Mo.
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Bakare, Mayowa Sunday. "The effects of microstructural modifications on corrosion resistance of metallic corrosion resistant materials Inconel 625 and FeCrMoCB". Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546474.

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Ahmed, Nauman. "Characterisation of different forms of Inconel 625 for determining the effects of microstructural modifications on electrochemical behaviour". Thesis, University of Nottingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493327.

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Thermal spraying is widely used to produce application-based superior surfaces on relatively cheap bulk materials, thus saving materials and cost. The concept is based on the assumption that the coating offers the same superior properties as the bulk material of the same composition. However, the use of thermal spray coatings for corrosion protection requires an awareness regarding microstructural modification during coating deposition and due to which, a performance gap may exist between coating and the bulk material.
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Shahid, Hafiz Rub Nawaz [Verfasser], Jürgen [Gutachter] Eckert i Prashanth Konda [Gutachter] Gokuldoss. "Strengthening of Al-based composites by microstructural modifications / Hafiz Rub Nawaz Shahid ; Gutachter: Jürgen Eckert, Prashanth Konda Gokuldoss". Dresden : Technische Universität Dresden, 2019. http://d-nb.info/1226896995/34.

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Catrin, Rodolphe Verfasser], i Frank [Akademischer Betreuer] [Mücklich. "Effects of microstructure modification induced by laser interference patterning of thin films / Rodolphe Catrin. Betreuer: Frank Mücklich". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2012. http://d-nb.info/1052339565/34.

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Catrin, Rodolphe [Verfasser], i Frank [Akademischer Betreuer] Mücklich. "Effects of microstructure modification induced by laser interference patterning of thin films / Rodolphe Catrin. Betreuer: Frank Mücklich". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:291-scidok-47993.

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Donley, Carrie Lynn. "Interfaces in organic electronic devices: Surface characterization and modification and their effect on microstructure in molecular assemblies". Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280407.

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This dissertation has focused on (i) the characterization and optimization of the near-surface region of indium-tin oxide (ITO) thin films, and (ii) the characterization of the microstructure and electrical properties of thin films of several new self-organizing liquid crystalline phthalocyanines (Pcs). Commercial ITO surfaces were explored through a combination of high resolution X-ray photoelectron spectroscopy and electrochemical techniques. It was determined that sputter-deposited ITO films undergo hydrolysis immediately upon exposure to atmosphere, creating InOOH and In(OH)₃ species, which appear to inhibit charge transfer reactions. The surface coverage of these InOOH and In(OH)₃-like species can be controlled by various solution and vacuum pretreatments, including etching with EDTA solutions, and RF-plasmas. Characterization of new discotic mesophase Pc materials has focused on modifications of the original Pc in this series, CuPc(OCH₂CH₂OBz)₈, including a polymerizable version, CuPc(OCH₂CH₂OCH₂CH=CH-Ph)₈, and the sulfur analogs of these molecules, CuPc(SCH₂CH₂OBz)₈ and CuPc(SCH₂CH₂OCH₂CH=CH-Ph)₈. The self-organizing properties of these new Pcs are altered by the changes in side chain composition, but still show the same "column-forming" tendencies as the parent Pc, with long range order. The polymerizable Pc materials can be photolithographically patterned with features as small as 2 microns. Electrical anisotropies in these films were measured with a conductive tip AFM and with OFETs, and anisotropies in current (j(∥)/j(⊥)) were ca. 10 on the micron scale, and up to 1000 on the submicron scale. OFET measurements showed low hole mobilities, which are attributed to poor contact between the Pc column and the Au electrodes. Chemical modification of these electrodes shows that considerable improvements in OFET performance result from this modification strategy. Understanding and controlling the microscopic structure of these Pc films is important for optimizing their electrical properties. A considerable effort was focused on developing a quantitative protocol to combine transmission and reflectance vibrational spectroscopic data to determine the three Euler angles that determine the orientation of these Pcs in an LB-deposited film on a planar substrate. Changes in orientation upon annealing and polymerization were observed, but in general these molecules display tilt angles away from the surface normal of <20° and twists about the surface normal of ca. 25°.
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Ormston, Marcus Winston. "Deposition and interface modification of thin magnetic multilayer films by closed-field unbalanced magnetron sputtering". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343533.

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34

Thibault, Simon. "Modifications des propriétés physico-chimiques et de la microstructure de l'aluminium après nitruration par implantation d'ions multichargés". Phd thesis, Université de Caen, 2009. http://tel.archives-ouvertes.fr/tel-00403112.

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L'implantation ionique d'azote dans l'aluminium a pour conséquence d'améliorer certaines de ses propriétés superficielles et peut donc entre autre être utilisée comme traitement de surface pour les alliages d'aluminium. Cette étude fait suite au développement d'une nouvelle technologie d'implantation basée sur l'utilisation de microaccélérateurs de particules qui permettent l'implantation d'ions multichargés (jusqu'à N4+). L'objectif de la thèse a été dans un premier temps de cibler les paramètres d'implantation permettant d'obtenir les meilleurs résultats, notamment lors de tests de corrosion et d'usure. Une analyse microstructurale a été menée afin de comprendre les mécanismes rentrant en jeu dans le renforcement des surfaces implantées. On a ainsi, pu mettre en évidence la nécessité d'une interpénétration des couches nitrurées et oxydées pour une amélioration significative de la résistance aux sollicitations superficielles. Les mécanismes de durcissement ont également été étudiés ce qui a permis de mettre à jour un durcissement par écrouissage régi par effet Hall-Petch apparaissant lors de l'implantation. Une étude du comportement mécanique d'éprouvettes implantées a montré que malgré les faibles épaisseurs d'implantations (~0,5 µm) des effets pouvaient se faire sentir sur tout le volume des éprouvettes. Le comportement élastique ainsi que le mode d'endommagement de ces pièces ont en effet été modifiés après implantation.
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Acera, Fernandez José. "Modification of flax fibres for the development of epoxy-based biocomposites : Role of cell wall components and surface treatments on the microstructure and mechanical properties". Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS218.

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Les fibres végétales peuvent être considérées comme une alternative intéressante aux fibres de verre pour la fabrication de matériaux composites. En effet, elles présentent des caractéristiques physiques intéressantes, telles que leur faible densité et leurs bonnes propriétés mécaniques spécifiques, qui peuvent rivaliser avec les composites renforcés de fibres de verre. En outre, les fibres végétales sont obtenues à partir de ressources renouvelables, et présentent généralement moins d'impacts environnementaux lors de leurs phases de production, d’utilisation et en fin de vie. Contrairement aux fibres de verre, les fibres végétales, telles que des fibres de lin, présentent des structures hiérarchiques complexes composées essentiellement de cellulose, hémicellulose, lignine, ciments peptiques et extractibles lipophiliques (cires, acides gras, etc.). Cette composition varie selon les espèces, le lieu et les conditions de croissance, la maturité de la plante, etc. De la même façon, la composition biochimique et la structure des produits et des sous-produits issus du lin sont soumis à de grandes variations selon les étapes successives de transformation réalisées à partir des tiges de lin jusqu’aux fils et tissus. Cela influence fortement les propriétés finales des fibres de lin et de leurs biocomposites. La première partie de cette étude se concentre sur la caractérisation de fibres de lin au cours de leurs étapes successives de transformation. Une homogénéisation de la composition chimique est observée dans les étapes finales de transformation, ainsi qu’une augmentation des propriétés en traction longitudinale des mèches de fibres de lin. La deuxième partie traite de l'utilisation de différents traitements de lavage appliqués sur des tissus d’étoupes de lin et leur influence sur l'extraction des composants de la paroi cellulaire des fibres, ainsi que sur la microstructure et les propriétés mécaniques de biocomposites époxy/lin. Il est montré que les composants de la paroi cellulaire jouent un rôle clé dans la dispersion des mèches et des fibres élémentaires de lin et sur le comportement mécanique transversal de leurs biocomposites. Enfin, l'application de différents traitements de fonctionnalisation sur des tissus de fibre de lin est étudiée afin d'améliorer l'adhérence interfaciale entre les fibres et la matrice. L'utilisation de molécules de type organosilanes (aminosilane, époxysilanes) et de molécules biosourcés (acides aminés et polysaccharides) est étudiée. Une augmentation de la rigidité en traction longitudinale et de la rigidité et de la contrainte maximale en traction transverse est observée en raison de l'amélioration de l'adhésion interfaciale par la fonctionnalisation de surface des fibres avec des molécules d'origine biosourcé et non-biosourcé
Natural fibres can be considered as a relevant alternative to glass fibres in the manufacture of composite materials. Indeed, they present interesting physical characteristics, such as low density and good specific mechanical properties, which can compete with glass fibre reinforced composites. Moreover, natural fibres are obtained from renewable resources, and generally present lower environmental impacts during their production and use phases and their end of life. Unlike glass fibres, natural fibres, such as flax fibres, are complex hierarchical materials composed essentially of cellulose, hemicellulose, lignin, peptics cements and lipophilic extractives (waxes, fatty acids, etc.). This composition varies among species, collection site, plant maturity, batches, etc. Besides, the biochemical composition and structure of flax products and sub-products undergo wide variations according to the transformation steps from stems to yarns and fabrics. This influences greatly the final properties of flax fibres and their biocomposites. The first part of this study is focused on the characterization of flax fibres during their successive transformation steps. A homogenization of the chemical composition is observed at the final transformation steps, as well as an increment of the longitudinal tensile properties of flax yarns. The second part deals with the use of different washing treatments applied on flax tow fabrics and their influence on the extraction of flax cell wall components and the resulting microstructure and mechanical properties of epoxy/flax fibres reinforced biocomposites. It is shown that cell wall components play a key role in the flax yarns and elementary fibres dispersion and transverse mechanical behaviour of biocomposites. Finally, the application of different functionalization treatments onto flax fibres fabrics is investigated in order to improve the interfacial adhesion between fibres and matrix. The use of non-bio-based organosilane molecules (aminosilane, epoxysilane) and bio-based molecules (amino-acids and polysaccharides) is studied. Improvedstiffness in longitudinal tension test and stiffness and tensile strength in transverse tension test are observed due to the improvement of interfacial adhesion by surface functionalization of the fibres with both bio-based and non-bio-based molecules
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36

Mitwally, Mohamed Elwi. "Surface modification and mechanical reliability enhancement of free-standing single crystal silicon microstructures using localized KrF excimer laser annealing". 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/200447.

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37

Dargent, Éric. "Evolution de la microstructure de films polyester soumis à un traitement thermomécanique". Rouen, 1994. http://www.theses.fr/1994ROUES074.

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L'évolution de la microstructure de films de poly(éthylène téréphtalate) (polymère thermoplastique amorphe et cristallisable) a été étudiée lorsqu'ils sont soumis à un traitement mécanique (mono ou bi-étirage) et à un traitement thermique. L'étirage est effectué entre les températures de transition vitreuse et de cristallisation. A partir d'une valeur critique du taux d'étirage (2,8), il apparaît une phase cristalline induite. L'évolution de la texture cristalline a été étudiée par diffraction des rayons X (Debye-Scherrer et figures de pôles). Les chaines s'orientant selon la/les direction/s d'étirage, les figures de pôles montrent le développement d'une forte texture de fibres. De plus, dans le cas des films bi-étirés, les plans cristallins les plus denses s'orientent parallèlement aux faces des films. Dans tous les cas, la taille des cristaux induits par l'étirage est plus petite que celle des sphérolites initiés par le chauffage. Les différents films ont été étudiés par analyse enthalpique différentielle, analyse mécanique dynamique et courants de dépolarisation thermostimulés. Il a été mis en évidence l'existence d'une phase supplémentaire mésomorphe (à partir d'un taux d'étirage égal à 2). Cette phase amorphe rigide prend naissance dans la phase amorphe. Elle est transformée en une phase cristalline anisotrope si le matériau subit une contrainte mécanique ou thermique supplémentaire. L'analyse thermique des films pré-cristallisés par étirage, ayant des taux d'étirage inférieurs à 4,2, montre l'existence d'une cristallisation supplémentaire initiée par la chaleur. L'influence de l'étirage sur la topologie de la phase amorphe a également été étudiée. Nous avons mis en évidence l'existence de deux relaxations apparaissant a des températures inférieures à la température de transition vitreuse. L'analyse par courants de dépolarisation thermostimulés montre que l'augmentation du taux d'étirage s'accompagne d'une localisation de la mobilité moléculaire
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38

Le, Gloannec Brendan. "Modifications microstructurales sous sollicitations thermomécaniques sévères : application au soudage par résistance des gaines de combustibles en aciers ODS". Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0367/document.

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Les aciers renforcés par dispersion d’oxydes (ODS) sont des matériaux candidats pourconstituer les gaines de combustibles des réacteurs nucléaires de IVème génération refroidis au sodium(RNR-Na). Le soudage par résistance en bout de ces gaines est étudié dans ce travail, avec pourobjectif la détermination et la compréhension des effets du procédé sur l’évolution de la microstructuredes aciers ODS à 9 % et 14 % de chrome à l’échelle des grains et des oxydes nanométriques. Uneapproche couplant caractérisations microstructurales sur soudures, simulation numérique et simulationphysique du procédé, à l’aide d’un simulateur thermomécanique Gleeble 3500, est adoptée. Le soudagepar résistance en bout impose localement des conditions de sollicitations sévères en termes dedéformation, vitesse de déformation et température. Ces sollicitations induisent un affinement de lamicrostructure dont l’origine peut être attribuée à un mécanisme de recristallisation dynamique (acier à14 % de chrome) ou à l’association de la recristallisation dynamique et des transformations de phase(acier à 9 % de chrome). Les conditions d’occurrence de la recristallisation dynamique sont étudiéessur ces matériaux. On montre notamment la possibilité d’une transition entre recristallisation dynamiquecontinue et discontinue sur l’acier à 14 % de chrome en fonction des conditions de sollicitation. Il estégalement observé que ces sollicitations thermomécaniques sévères induisent une augmentation de lataille des oxydes nanométriques associée à une diminution de leur fraction volumique
Oxide dispersion strengthened (ODS) steels are considered as candidate materials for thedevelopment of fuel cladding for sodium-cooled fast reactors (SFR). Resistance upset welding of thecladding is studied in this work. The aim is to determine and to understand the process effects on themicrostructure of ODS steels with 9% and 14% of chromium at the scales of the grains and thenanometric oxides. An approach coupling microstructural characterization of welds, numericalsimulation and physical simulation of the process, using a thermomechanical simulator Gleeble 3500,is proposed. Resistance welding locally imposes severe thermomechanical conditions in terms of strain,strain rate and temperature. Refinement of the microstructure is noted and correspond to a dynamicrecrystallization mechanism (14 % Cr steel) or the combination of dynamic recrystallization and phasetransformations (9 % Cr steel). The conditions of occurrence of dynamic recrystallization are studied.The possibility of a transition between continuous and discontinuous dynamic recrystallization is shownfor the 14 % Cr steel according to the loading conditions. Such severe thermomechanical conditionsinduce an increase in the size of nanoscale oxides associated with a decrease of their volume fraction
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Sipple, Ernst-Michael. "Réarrangements structuraux et modifications microstructurales associés aux transformations de phases dans le système CaSO 4(s) - H 2O (g)". Dijon, 1999. http://www.theses.fr/1999DIJOS039.

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Les décompositions endothermiques du type solide1solide2+gaz laissent généralement inchangée une fraction importante des liaisons atomiques constitutives de la structure du solide1. Par conséquence la morphologie et les dimensions externes de chaque particule sont préservées (la particule de solide2 est dite pseudomorphe de celle de solide1). Cependant le départ de gaz entraine, en général, une contraction du volume molaire du solide précurseur, il en résulte une fissuration de celui-ci et l'apparition d'une porosité intra-particulaire. Ce travail est consacré à l'étude d'une réaction de ce type : la déshydratation du gypse (CaSO 4,2H 2O) en sous-hydrates (CaSO 4,0. 6H 2O OU CASO 4,0. 5H 2O SH) ou en phases anhydres (gammaCaSO 4 [AIII] dénommé anhydrite soluble ou bétaCaSO 4 [AII] l'anhydrite dit insoluble). Les sous-hydrates et l'anhydrite [AIII] sont les constituants du plâtre. Les recherches ont été menées selon trois approches expérimentales différentes mais complémentaires dont les résultats constituent les trois chapitres expérimentaux du mémoire. La première est une analyse cristallographique, réalisée en vue de préciser le mécanisme des réarrangements structuraux qui accompagnent les déshydratations. La deuxième est consacrée à l'examen microscopique des pseudomorphes. L'objectif est alors d'établir le lien entre les modifications morphologiques induites par les déshydratations et les structures cristallines du gypse et des phases produites. La troisième est une étude de la microstructure poreuse des pseudomorphes. Son but est d'évaluer les parts respectives de la fissuration et de la contraction de l'enveloppe des particules initiales dans la réduction de volume qui accompagne les déshydratations. La compilation des résultats des trois approches expérimentales a permis de préciser la cristallochimie du mécanisme reactionnel et l'influence des paramètres physico-chimiques du solide précurseur et des conditions réactionnelles sur la microstructure finale.
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40

Achilli, Matteo. "Modification de la microstructure et des propriétés mécaniques d'échafaudages à base de gels de collagène pour la régénération du tissu vasculaire". Thesis, Université Laval, 2012. http://www.theses.ulaval.ca/2012/28722/28722.pdf.

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Le besoin de substituts pour vaisseaux sanguins de petit calibre a attiré une attention considérable sur le développement de constructions artérielles dans des bioréacteurs à partir de systèmes d’échafaudage. Les gels formés à partir de collagène reconstitué représentent des substrats idéaux pour le remodelage du à l’activité cellulaire, mais leur faible résistance et élasticité limitent leur utilisation comme échafaudages pour la régénération du tissu vasculaire. Ces caractéristiques proviennent de la perte d’organisation structurelle liée au processus d’extraction du collagène. Dans ce contexte, l’objectif de ce projet était d’améliorer les propriétés mécaniques des gels de collagène afin de supporter la croissance et la maturation du tissu vasculaire sous contrainte cyclique. En considérant l’importance de l’état d’agrégation du collagène pour les propriétés mécaniques des tissus natifs, la stratégie de ce projet a été de modifier la microstructure des matrices de collagène reconstitué en agissant sur trois aspects : 1) les interactions intermoléculaires et la fibrillogenèse ont été ajustées en variant les paramètres expérimentaux (pH, température, force ionique et concentration du collagène); 2) des liaisons covalentes ont été introduites afin de fixer des fibrilles voisines; 3) les gels ont été compactés et les fibrilles alignées grâce à l’action de remodelage des cellules. Des mesures de spectrophotométrie et des images par MEB ont confirmé les effets des conditions expérimentales et du remodelage sur la microstructure des gels. Notamment, la présence des cellules a permis la formation de matrices plus compactes et orientées, surtout en présence de contraintes mécaniques. Des essais mécaniques ont démontré que les stratégies adoptées ont engendré le renforcement de la structure. En particulier, des essais cycliques ont établi que la variation des conditions expérimentales combinée à la réticulation ont produit des matrices dont l’hystérèse diminue et l’élasticité augmente. En conclusion, l’ensemble de ces études a permis la réalisation à court terme (24-48 h) de structures à base de collagène présentant une résistance mécanique, une rigidité et une élasticité accrues. Ces résultats suggèrent que ces matrices sont de bons candidats comme supports pour la régénération de tissus vasculaires sous conditionnement cyclique.
The need for small-caliber vascular replacements has attracted considerable attention on the development of scaffold-based vascular constructs in bioreactors. Reconstituted collagen gels represent ideal substrates for cell-mediated remodeling, but their low strength and low elasticity, limits their application as scaffold for the regeneration of the vascular tissue. These features result from collagen extraction and the consequent loss of structural organization. The objective of this project was to improve the mechanical performances of collagen gels in order to support the growth and the maturation of the vascular tissue under cyclic conditioning. Considering how fundamental collagen assembly is for the mechanical behavior of native tissues, the microstructure of reconstituted collagen lattices was modified by working on three aspects: 1) The intermolecular interactions and the aggregation of collagen monomers were tailored by modulating the experimental conditions, including pH, temperature, ionic strength and collagen concentration; 2) Inter-fibril crosslinking was carried out in order to fix neighboring collagen fibrils through their reactive side chains; 3) Gels were compacted and fibrils were aligned through cell-mediated remodeling. Spectrophotometric analyses and SEM confirmed the effects of changes in experimental conditions and cell-mediated remodeling on collagen gels microstructure. Notably, the presence of SMCs lead to tighter and highly oriented lattices, moreover in the presence of mechanical constraints. Mechanical tests showed that the adopted procedures contributed to the stiffening of collagen lattices. In particular, the modulation of the experimental conditions combined with crosslinking lead to lattices presenting lower hysteresis and higher elasticity as shown by cyclic tests. In conclusion, this study produced, in a short time (24-48 h), collagen gel-based lattices with improved stiffness, strength, and elastic recoil. The results suggest that these lattices are serious candidates for the role of temporary supports during the maturation period under cyclic loading.
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41

Thiery, Mickaël. "Modélisation de la carbonatation atmosphérique des matériaux cimentaires : prise en compte des effets cinétiques et des modifications microstructurales et hydriques". Phd thesis, Ecole des Ponts ParisTech, 2005. http://pastel.archives-ouvertes.fr/pastel-00001517.

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La carbonatation atmosphérique est un des facteurs parmi les plus importants de la durabilité du béton armé. Elle repose sur l'action du CO2 de l'atmosphère qui diffuse à travers le béton et se dissout en acide au contact de la solution interstitielle. Cette acidification du milieu induit une dissolution de la portlandite qui constitue la réserve de basicité du béton. La baisse du pH, d'une valeur de l'ordre de 13 à une valeur inférieure à 9, peut conduire à la corrosion des aciers du béton armé qui ne sont passivés et protégés qu'en milieu fortement basique. L'objectif de la thèse est de construire un modèle physico-chimique de carbonatation des matériaux cimentaires permettant de prédire la chute du pH de la solution interstitielle, variable pertinente pour appréhender la corrosion des armatures. Une riche campagne d'analyses thermogravimétriques, de gammadensimétries et de porosimétries par intrusion de mercure, réalisées sur 3 bétons différents et plusieurs pâtes de ciment à base de CEM I, permet de comprendre les mécanismes physico-chimiques, de déterminer les conséquences de la carbonatation sur la microstructure et l'état hydrique des matériaux, de calibrer et enfin de valider le modèle proposé à partir d'essais de carbonatation accélérée.
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42

Perrot, Philippe. "Modifications morphologiques et microstructurales du matériau actif des cathodes de batteries à l'ion lithium induites par broyage et traitement thermique". Poitiers, 1998. http://www.theses.fr/1998POIT2264.

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L'objectif de ce travail est d'apporter des améliorations au mélange cathodique linio#2 + graphite + suie des cathodes des batteries à l'ion lithium : les principaux résultats obtenus sont les suivants : - une étude préliminaire de la microstructure des cathodes a montré que les grains de linio#2 étaient micrométriques et présentaient des dislocations. - le broyage du linio#2 dans un conteneur en agate permet d'améliorer la percolation électrique macroscopique du mélange cathodique associe tout en évitant une pollution du matériau (optimisation de la morphologie de la poudre avec notamment une forte augmentation de la surface spécifique). - le broyage modifie la microstructure des grains de linio#2 : -il est susceptible de désordonner la structure cristalline. -les domaines cohérents de diffraction sont nanométriques ce qui améliore la diffusion intergranulaire des cations li#+. -des microdistorsions importantes du réseau apparaissent au sein de ces domaines ce qui constitue vraisemblablement un handicap au déplacement intragranulaire des li#+. - un traitement thermique sous argon permet de réarranger les dislocations en sous joints et de relaxer fortement les microdéformations introduites lors du broyage ce qui doit faciliter la diffusion intragranulaire des ions li#+. - divers mélanges cathodiques ont été sélectionnés pour préparer des piles boutons soumises à des cyclages galvanostatiques (charge et décharge). Les performances en puissance et en cyclabilité sont nettement augmentées dans le cas d'une pile où le linio#2 broyé et recuit possède une morphologie optimum et une microstructure idéale. L'ensemble de ces résultats montre les rôles indissociables des configurations macroscopique et microscopique du linio#2 sur les performances des batteries. Les phénomènes qui se produisent lors des divers traitements subis par la poudre ouvrent la voie à de nouveaux champs d'investigation scientifique et à de nouvelles applications industrielles.
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43

Lee, Jiho. "Impact of process parameter modification on poly(3-hexylthiophene) film morphology and charge transport". Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50409.

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Organic electronics based on π-conjugated semi-conductor raises new technology, such as organic film transistors, e-paper, and organic photovoltaic cells that can be implemented cost-effectively on large-area applications. Currently, the device performance is limited by low charge carrier mobility. Poly(3-hexylthiophene) (P3HT) and organic field effect transistors (OFET) is used as a model to investigate morphology of the organic film and corresponding electronic properties. In this thesis, processing parameters such as boiling points and solubility are controlled to impact the micro- and macro-morphology of the film to enhance the charge transport of the device. Alternative approach to improve ordering of polymer chains and increase in charge transport without post-treatment of P3HT solution is studied. The addition of high boiling good solvent to the relatively low boiling main solvent forms ordered packing of π-conjugated polymers during the deposition process. We show that addition of 1% of dichlorobenzene (DCB) to the chloroform based P3HT solution was sufficient to improve wetting and molecular structures of the film to increase carrier mobility. Systematic study of solvent-assisted re-annealing technique, which has potential application in OFET encapsulation and fabrication of top-contact OFET, is conducted to improve mobility of OFET, and, to suggest a cost-effective processing condition suitable for industrial application. Three process parameters: boiling point, polarity, and solubility are investigated to further understand the trend of film response to the solvent-assisted technique. We report the high boiling non-polar solvents with relatively high RED values promote highest improvement in molecular packing and formulate crystalline structure of the thin film, which increases the device performance.
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44

Vempaire, David. "Modification des propriétés magnétiques de couches minces de nickel et de manganèse et réalisation de microstructures magnétiques par implantation ionique en immersion plasma". Université Joseph Fourier (Grenoble), 2004. http://www.theses.fr/2004GRE10252.

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Nous avons tout d'abord etudie le depot de couches minces de manganese et de nickel sur silicium 100 par pulverisation ionique assistee par plasma micro-onde mul tidipolaire. Les couches de nickel et de manganese deposees ont ensuite ete implantees par de l'azote en utilisant la technique d'implantation ionique en immersion plasma assistee par plasma micro-onde decr. Cette technique nous a permis de synthetiser les nitrures ni3n et mn4n malgre la metastabilite du ni3n et la forte reactivite chimique a l'oxygene du manganese. Nous avons ensuite implante de l'azote dans une double couche ni sur mn pour les nitrurer simultanement en formant l'empilement ni3n sur mn4n. Le caractere metastable de ni3n et la forte affinite du manganese pour l'azote, traduit par une grande difference d'enthalpie de formation des composes ni3n et des nitrures de manganese, a conduit l'azote implante a diffuser entierement dans le manganese lors du recuit post implantation. Pour finir, nous avons initier l'etude de la realisation d'une microstructure magnetique par implantation d'azote dans une couche de nickel a travers un masque organique
WE FIRST OF ALL STUDIED THE DEPOSIT OF THIN LAYERS OF MANGANESE AND NICKEL ON SILICON 100 USING THE PULVERIZATION ASSISTED BY MICROWAVE MUL TIDIPOLAR PLASMA TECHNIQUE. THE LAYERS OF NICKEL AND MANGANESI DEPOSITED WERE TH EN IMPLANTED WITH NITROGEN BY USING THE PLASMA BASED IMMERSION IMPLANTATION TECHNIQUE ASSISTED BY A MICROWAVE DE CR PLASMA. THIS TECHNIQUE ENABLED TO SYNTHESIZE THE NITRIDES NI3N AND MN4N lN SPITE OF THE METASTABILITY OF NI3N AND THE STRONG CHEMICAL REACTIVITY OF MANGANESE WITH OXYGEN. THEN WE HAVE IMPLANTED NITROGEN lN A DOUBLE LAYER NI ON MN SIMUL TANEOUSL Y TO NITRIDE THEM BY MAKING NI3N STACKING ON MN4N. THE METASTABILITY OF NI3N AND THE STRONG AFFINITY OF MANGANESE FOR NITROGEN, HAVE MADE NITROGEN IMPLANTED ENTIREL Y DIFFUSING lN MANGANESE DURING THE ANNEALING. THEN, WE HAVE INITIATED THE STUDY OF THE REALIZATION OF A MAGNETIC MICROSTRUCTURE BY NITROGEN IMPLANTATION lN A LAYER OF NICKEL THROUGH AN ORGANIC MASK
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45

Sharma, Anurag. "Effects of Advanced Surface Treatments on Microstructure, Residual Stress and Corrosion-Fatigue Behavior of Aluminum Alloy 7075-T6". University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin162765884039947.

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46

Jagtap, Rohit. "The Effects of Ultrasonic Nano-crystal Surface Modification on Residual Stress, Microstructure and Fatigue Behavior of Low-Modulus Ti-35Nb-7Zr-5Ta-0.3O Alloy". University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1479823317088871.

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47

Laroche, Marine. "Rôle des ondes de surface dans la modification des propriétés radiatives de matériaux microstructurés : application à la conception de sources infrarouges et à l'effet thermophotovoltaïque". Phd thesis, Ecole Centrale Paris, 2005. http://tel.archives-ouvertes.fr/tel-00011615.

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La présence d'ondes de surface sur certains matériaux (métaux, semiconducteurs dopés, cristaux polaires, cristaux photoniques) modifie leurs propriétés radiatives.
La 1ère partie de cette thèse est consacrée au phénomène d'émission thermique cohérente et amplifiée par plasmon-polaritons de surface. Nous avons tout d'abord conçu et réalisé une source thermique de tungstène avec une directivité exceptionnelle dans le proche infrarouge. Nous avons ensuite étudié le refroidissement radiatif du silicium dopé grâce à l'amplification d'émission thermique par plasmons de surface. Nous avons comparé les performances de ces sources cohérentes avec celles d'un système anti-réfléchissant : l'écran de Salisbury.
Dans la 2ème partie, nous étudions l'impact du transfert radiatif en champ proche sur la conversion thermophotovoltaïque (TPV). L'excitation d'ondes de surface sur la source éclairant la cellule TPV engendre un transfert radiatif amplifié et quasi-monochromatique. Nous présentons un modèle quantitatif permettant de calculer le photocourant et le rendement. Nous montrons que l'on peut obtenir une augmentation significative de la puissance électrique extraite et du rendement d'un dispositif TPV éclairé en champ proche.
La 3ème partie porte sur les propriétés radiatives des cristaux photoniques induites par ondes de surface. Deux phénomènes connus en plasmonique ont pu être obtenus : la transmission résonante à travers un film opaque et l'émission thermique cohérente. Un avantage des cristaux photoniques est la possibilité de modifier la fréquence d'excitation des ondes de surface en faisant varier les paramètres du cristal.
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48

Jaradeh, Majed. "The Effect of Processing Parameters and Alloy Composition on the Microstructure Formation and Quality of DC Cast Aluminium Alloys". Doctoral thesis, KTH, Materialvetenskap, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4205.

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The objective of this research is to increase the understanding of the solidification behaviour of some industrially important wrought aluminium alloys. The investigation methods range from direct investigations of as-cast ingots to laboratory-scale techniques in which ingot casting is simulated. The methods span from directional solidification at different cooling rates to more fundamental and controlled techniques such as DTA and DSC. The microstructure characteristics of the castings have been investigated by optical and Scanning Electron microscopy. Hardness tests were used to evaluate the mechanical properties. The effects of adding alloying elements to 3XXX and 6XXX aluminium alloys have been studied with special focus on the effects of Zn, Cu, Si and Ti. These elements influence the strength and corrosion properties, which are important for the performance of final components of these alloys. Solidification studies of 0-5wt% Zn additions to 3003 alloys showed that the most important effect on the microstructure was noticed at 2.5 wt% Zn, where the structure was fine, and the hardness had a maximum. Si addition to a level of about 2% gave a finer structure, having a relatively large fraction of eutectic structure, however, it also gave a long solidification interval. The addition of small amounts of Cu, 0.35 and 1.0 wt%, showed a beneficial effect on the hardness. Differences have been observed in the ingot surface microstructures of 6xxx billets with different Mg and Si ratios. Excess Si compositions showed a coarser grain structure and more precipitations with possible negative implications for surface defect formation during DC casting. The comparison of alloys of different Ti content showed that the addition of titanium to a level of about 0.15 wt% gave a coarser grain structure than alloys with a normal Ti content for grain refinement, i.e. < 0.02 wt%, although a better corrosion resistance can be obtained at higher Ti contents. The larger grain size results in crack sensitivity during DC casting. A macroscopic etching technique was developed, based on a NaOH solution, and used in inclusion assessment along DC cast billets. Good quantitative data with respect to the size and spatial distribution of inclusions were obtained. The results from studied billets reveal a decreasing number of inclusions going from bottom to top, and the presence of a ring-shaped distribution of a large number of small defects in the beginning of the casting. The present study shows how composition modifications, i.e. additions of certain amounts of alloying elements to the 3xxx and 6xxx Al alloys, significantly change the microstructures of the materials, its castability, and consequently its mechanical properties
QC 20100901
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49

Riestra, Martin. "High performing cast aluminium-silicon alloys". Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Material och tillverkning, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-38005.

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The need to produce lighter components due to environmental aspects and the development of electrical vehicles represents an opportunity for cast aluminium-silicon alloys. With high specific strength, good castability, high corrosion resistance and recyclability, these alloys offer an attractive combination of properties as an alternative to steel, cast iron and titanium-based components in certain applications. To take advantage of such a combination of properties, there is a need to ensure that they can be reliably achieved. In other words, high performing components need to be produced. For that, the production cycle, from alloy selection and melt preparation, to the casting and heat treatment of the component must be understood and controlled as a whole. The different steps in the production cycle will affect the microstructure of the components and hence the resulting mechanical properties. Understanding the relation between the different steps in the production cycle, its consequences on the microstructural features and on the mechanical properties constitutes the aim of this thesis. Experiments applying state-of-the-art knowledge regarding effect of casting process, alloying system and post-process variables were performed aimed at achieving properties similar to those of high pressure die casting (HPDC) components. Different melt quality determination tools were evaluated on three different EN AC-46000 melt qualities. The influence of modification, grain refinement and both treatments together was assessed on an Al-10Si alloy solidified under different cooling rates. The tensile behaviour and the impact of features such as secondary dendrite arm spacing (SDAS) or grain sizes was quantified. It was corroborated that by appropriate selection and control of such alloying system, process and post-process variables it is possible to achieve HPDC EN AC-46000 tensile and fatigue properties through a T5 treated sand cast EN AC-42100 alloy. On the other hand, the available techniques for melt quality assessment are inadequate, requiring further analysis to successfully identify the melt quality. Additionally, it was observed that decreasing the melt quality by additions of 25 wt.% of machining chips did not significantly decrease the tensile properties but slightly increased the variation in them. In relation to the modification and grain refinement of Al-10Si alloys it was concluded that with the slowest cooling rate tested, additions of only grain refiner did not successfully produce equiaxed grains. For cooling rates corresponding to dendrite arm spacings of 15 μm and slower, combined additions of grain refiner and modifier can lead to higher tensile properties compared to the corresponding separate additions. SDAS was observed to describe flow stress through the Hall-Petch equation but grain size did not show a physically meaningful relationship. Furthermore, beginning of cracking was detected in the plastic deformation region at dendrite/eutectic boundaries and propagated in a trans-granular fashion.
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50

Sedighi, Moghaddam Maziar. "Wettability of modified wood". Doctoral thesis, KTH, Yt- och korrosionsvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-175875.

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Despite many excellent properties of wood which make it suitable for many applications, it suffers from a number of disadvantages limiting its use. For instance, modification is needed to reduce water sorption and to improve decay resistance, dimensional stability and weathering performance. In addition, wood/liquid interaction such as water wettability on wood plays an important role in design and characteristics of many processes and phenomena such as adhesion, coating, waterproofing, wood chemical modification, and weathering. This thesis focuses on enhancing the understanding of wetting of wood, with emphasis on modified wood. The influence of surface chemical composition of wood and its microstructural characteristics on wetting and swelling properties has also been studied. A multicycle Wilhelmy plate technique has been developed to evaluate wetting properties of porous materials, such as wood, in which the samples were subjected to repeated immersions and withdrawals in a swelling liquid (water) and in a non-swelling liquid (octane). This method was utilized to dynamically investigate contact angle, sorption and swelling properties, as well as dimensional stability of unmodified, chemically and surface modified wood samples. Scots pine sapwood and heartwood samples were utilized to establish the principles of the technique. Acetylated and furfurylated wood samples with different level of modification were thereafter examined utilizing the developed technique for wetting measurements. A perimeter model based on a linear combination of the measured force and final change in sample perimeter was suggested to evaluate the dynamic dimensional stability of wood veneers. The feasibility of this method for studying dynamic wettability was investigated by measuring the changes of advancing and receding contact angles over repeated cycles on surface modified wood samples, created by combining liquid flame spray and plasma polymerisation methods. X-ray photoelectron spectroscopy (XPS) and X-ray computed tomography (XCT) were employed to study the surface chemical composition and microstructural properties of the samples, respectively. Three different kinetic regimes were observed in the wetting measurements: i) fast wetting and spreading of the liquid on the wood surface, ii) void filling and wicking and iii) swelling, which was the slowest of the three. The multicycle Wilhelmy plate method was found to be suitable for studying liquid penetration, sorption, and dimensional stability of swelling materials. The results demonstrate that the wetting properties of wood are highly affected by surface chemistry and microstructure. It was shown that using both swelling and non-swelling liquids in wetting measurements allow to distinguish between capillary liquid uptake and swelling. Based on this, for chemically modified samples, it was demonstrated that acetylation mostly reduces swelling, while furfurylation reduces both swelling and capillary uptake. This is in line with the microstructural study with X-ray computed tomography where a significant change in the porosity was found as a result of furfurylation, conversely acetylation left the total porosity values unchanged. Wetting results for hydrophobised wood samples demonstrate that the multi-scale roughness obtained by combination of nanoparticle coating and plasma polymerization increased both the hydrophobicity and the forced wetting durability compared to the micro-scale roughness found on wood modified with plasma polymerisation alone.

QC 20151029


Sustainable wood modification
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