La diffusion des ions et des radionucléides au sein des matériaux cimentaires est l'un des facteurs les plus importants qui déterminent la durabilité et les propriétés de confinement de ces matériaux. Cette étude s'inscrit, en particulier, dans le domaine de confinement des déchets radioactifs de faible et moyenne activité. Elle consiste à mettre en évidence l'influence de la microstructure des mortiers, notamment la présence des granulats, sur la diffusion de l'eau tritiée au sein de ces matériaux. La démarche consiste, dans un premier temps, à sélectionner des formulations de mortiers à base de CEM I afin d'étudier l'influence de la teneur en granulats, de la granulométrie et du rapport eau/ciment sur les paramètres de diffusion. Des différentes techniques expérimentales complémentaires ont été utilisées afin de caractériser la structure poreuse : porosimétrie à l'eau, porosimétrie mercure, perte au feu et imagerie MEB associée à l'analyse d'image. Dans ce contexte, un protocole d'analyse d'images a été mis en place afin de quantifier la porosité à l'interface granulat/pâte. Le lien entre les propriétés de la microstructure et les paramètres de transport a été ensuite examiné. Pour cela, des essais de diffusion à l'eau tritiée (HTO) ont été conduits et des corrélations entre les paramètres de la microstructure et le transport ont été réalisées. Enfin, afin de mettre en avant le rôle des phases mésoscopiques (Matrice/granulats/ITZ) dans le mécanisme de diffusion un modèle 3D a été développé et des calculs de diffusivités équivalentes ont été effectués. La présente étude confirme la présence d'une interface granulat/pâte au voisinage des grains de sable siliceux. Cette auréole de transition (ITZ) se caractérise par une épaisseur qui varie entre 10 et 20 µm et une porosité environ trois fois plus grande que celle de la matrice cimentaire. En dessous de 55% de sable normalisé, l'effet de cette interface sur les propriétés macroscopiques de transport est faible. En effet, l'effet de dilution et de tortuosité liés aux granulats reste dominant. Par conséquent, les données acquises à l'échelle de pâte de ciment restent valables et sont extrapolable à l'échelle des mortiers. Ces résultats ont été confirmés par les calculs analytiques et numériques de la diffusivité homogénéisée. Au-delà de 55% de sable normalisé, d'autres effets liés au grands nombre de grains de sable rentrent en jeu comme les bulles d'air et les taches poreuses dus principalement à la difficulté d'obtenir des matériaux bien compactés. Ceci rend ces formulations extrêmes et ne permettent pas d'approfondir notre compréhension du lien entre la microstructure et les propriétés de transport au-delà de cette teneur en sable

Baigiamajame magistro darbe nagrinėjamos elektrolankiniu purškimu skirtingomis vielomis užpurkštos dangos. Atlikta terminio purškimo dangų, jų technologijų apžvalga ir analizė, pateikta dangų tyrimo metodika. Metalo paviršinis sluoksnis dengiamas siekiant pakeisti jo mechanines bei fizikines savybes, suteikti atsparumą išorės poveikiui ir pagerinti estetinį vaizdą. Atlikti nerūdijančio plieno, jūrinės bronzos bei jų kombinuotos dangų mikrostruktūros, mikrokietumo, dangos tamprumo modulio bei adhezijos tyrimai. Gauti rezultatai pateikti grafiškai. Išnagrinėjus praktinius ir skaitinius terminio purškimo dangų rezultatus, pateikiamos baigiamojo darbo išvados. Darbą sudaro 5 dalys: įvadas, literatūros šaltinių apžvalga ir analizė, elektrolankiniu purškimu gautų dangų tyrimai, išvados, literatūros sąrašas. Darbo apimtis – 59 p. teksto, 55 iliustr., 14 lent., 18 bibliografinių šaltinių. / In the final master thesis examined coatings by arc spraying with different solid wires. The review of thermal spray coatings technology and research methods are described. The metal surface coating was applied to modify it‘s mechanical and physical properties, also resistance to external impact and improve aesthetics view. The research of stainless steel, marine bronze and combined coating microstructures, microhardness modulus of elesticity and adhesion were carried out. The results are presented graphically. The experimental and numerical results of thermal spray coatings were analysed and conclusions were given. Structure of work: introduction, literature review and analysis, research of coatings by arc spraying, coclusions, references. Thesis consist of – 59 p. text, 55 pictures, 14 tables, 18 bibliografical entries.

Cementitious materials such as concrete, cement and gypsum are widely used in construction, as the raw materials of which they are made are abundant on Earth. Such trend is unlikely to change in the coming decades. But these materials suffer from creep. The creep of cementitious materials is a complex issue. On one hand, in cementitious materials creep is often coupled with other phenomena such as drying, hydration and cracking, and can be influenced by various parameters such as temperature, level of stress, water content and mix design. On the other hand, measuring creep by traditional macroscopic creep testing is time-consuming (creep test on concrete is recommended to be carried out over several months in order to provide a reliable characterization of long-term creep) and tedious, since experimental parameters need to be well controlled over extensive periods of time. This thesis studied microindentation at the scale of cement paste or gypsum plaster for the assessment of long-term basic creep properties of cementitious materials, by comparing creep functions obtained by minutes-long microindentation testing with those obtained with macroscopic creep experiments which lasted up to years. For cement paste, the comparison was made at the scale of concrete with the aid of upscaling tools. The study validated that minutes-long microindentation testing can provide a measurement of the long-term creep properties of cementitious materials. With the validated indentation technique, we studied the effect of microstructure (i.e., the distribution and the spatial organization of phases) and of water on long-term basic creep of cementitious materials. The effect of microstructure was studied on materials such as C3S pastes and C2S pastes as well as on compacts of synthetic C-S-H, portlandite (CH) and their mixtures prepared by compaction of powders. For all samples considered, we identified the right micromechanical model that allows predicting the results. The choice of micromechanical model was consistent with microstructural observations. The effect of relative humidity was studied by conditioning and testing some of those materials (i.e., C3S paste, compact of C-S-H, and compact of CH) in various relative humidities ranging from 11% to 94%. Relative humidity had a significant effect on creep: for all materials tested, a greater humidity led to a greater creep. The compact of portlandite was the most sensitive to relative humidity, probably because creep occurs at interfaces between portlandite crystals. For C3S paste, a linear relation was identified between long-term creep properties and water content at relative humidities ranging from 11% to 75%.Finally, we proposed micromechanical models that allow predicting long-term basic creep properties of cementitious materials with a wide range of volume fraction of crystalline phase and over a wide range of relative humidities

This thesis addresses the issue of a potential future microelectronics technology, namely the possibility of utilising the optical properties of nanocrystalline silicon for optoelectronic circuits. The subject is subdivided into three chapters. Chapter 1 is an introduction. It formulates the oncoming problem for microelectronic development, explains the basics of Integrated Optoelectronics, introduces porous silicon as a new light-emitting material and gives a brief review of other competing light-emitting material systems currently under investigation. Examples of existing porous silicon devices are given. Chapter 2 reviews the basic physics relevant to the subject of this thesis and informs on the present situation in this field of research, including both experimental and theoretical knowledge gained up-to-date. The chapter provides the necessary background for correct interpretation of the results reported in Chapter 3 and for a realistic decision on the direction for future work. Chapter 3 describes my own experimental and computational results within the framework of the subject, obtained at De Montfort University. These include: onestep preparation of laterally structured porous silicon with photoluminescence and microscopy characterisation, Raman spectroscopy of porous silicon, a polarisation study of the photoluminescence from porous silicon, computer simulations of the conductivity of two-component media and of laser focused atomic deposition for nanostructure fabrication. Thus, this thesis makes a dual contribution to the chosen field: it summarises the present knowledge on the possibility of utilising optical properties of nanocrystalline silicon in silicon-based electronics, and it reports new results within the framework of the subject. The main conclusion is that due to its promising optoelectronic properties nanocrystalline silicon remains a prospective competitor for the cheapest and fastest microelectronics of the next century.

Nonwoven materials are engineered fabrics, produced by bonding constituent fibres together by mechanical, thermal or chemical means. Such a technology has a great potential to produce material for specific purposes. It is therefore crucial to develop right products with requested properties. This requires a good understanding of the macro and micro behaviours of nonwoven products. In last 40 years, many efforts have been made by researchers to understand the performance of nonwoven materials. One of the main research challenges on the way to this understanding is to link the properties of fibres and the fabric's random fibrous microstructure to the mechanisms of overall material's deformation. The purpose of this research is to study experimentally and numerically the deformation mechanisms of a low-density thermally bonded nonwoven fabric (fibre: Polypropylene; density: 20 gsm). The study started with tensile experiments for the nonwoven material. Specimens with varying dimensions and shapes were tested to investigate the size-dependent deformation mechanisms of the material. Based on obtained results, representative dimensions for the material are determined and used in other experimental and numerical studies. Then standard tensile tests were performed coupled with image analysis. Analysis of the obtained results, allowed the tensile behaviour of the nonwoven material to be determined, the initial study of the effects of material's nonuniform microstructure was also implemented. Based on the experimental results obtained from tensile tests, continuous finite-element models were developed to simulate the material properties of the nonwoven material for its two principle directions: machine direction (MD) and cross direction (CD). Due to the continuous nature of the models, they were only used to establish the mechanical behaviour of the material by treating it as a two-component composite. The effects of bond points, which are a stiffer component within the material, were analysed. Due to the limitations of the continuous FE models, experimental studies were performed focused on the material s microstructure. The latter was detected using an x-ray Micro CT system and an ARAMIS optical strain analysis system. According to the obtained images, the nonwoven fabric is a three-component material. The effects of material's microstructure on stress/strain distributions in the deformed material were studied using advanced image analysis techniques. Based on the experimental results, a new stress calculation method was suggested to substitute the traditional approach, which is not suitable for the analysis of the low density nonwoven material. Then, the fibres orientation distribution and material properties of single fibres were measured due to their significant effects on overall mechanical properties. Finally, discontinuous finite-element models were developed accounting for on the material's three-component structure. The models emphasised the effects of the nonuniform and discontinuous microstructure of the material. Mechanical properties of fibres, the density of fibrous network, the fibres orientation distribution and the arrangement of bond points were used as input parameters for the models, representing features of the material's microstructure. With the use of the developed discontinuous models, the effects of material's microstructure on deformation mechanisms of the low-density nonwoven material were analysed.

The aim of the current study is to develop an efficient model which can predict low-energy compatible microstructures in ferroelectric bulks and film devices and their dynamic behaviour. The results are expected to assist in the interpretation of microstructure observations and provide a knowledge of the possible domain arrangements that can be used to design future materials with optimum performance. Several recent models of ferroelectric crystals assume low energy domain configurations. They are mainly based on the idea of fine phase mixtures and average compatibility, and can require intensive computation resulting in complex domain configurations which rarely occur in nature. In this research, criteria for the exact compatibility of domain structure in the form of a periodic multi-rank laminate are developed. Exactly compatible structure is expected to be energetically favourable and does not require the concept of a fine mixture to eliminate incompatibilities. The resulting method is a rapid and systematic procedure for finding exactly compatible microstructures. This is then used to explore minimum rank compatible microstructure in various crystal systems and devices. The results reveal routes in polarization and strain spaces along which microstructure can continuously evolve, including poling paths for ferro- electric single crystals. Also, the method is capable to generate all possible exactly compatible laminate configurations for given boundary conditions. It is found that simple configurations are often energetically favourable in conditions where previous approaches would predict more complex domain patterns. Laminate domain patterns in ferroelectrics are classified and corre- lated with observations of domains in single crystals, showing good agreement. The evolution of microstructures under applied mechanical and electrical loads is studied. A variational method, which minimises the overall energy of the crystal is developed. A new concept of transitional “pivot states” is introduced which allows the model to capture the feature that the microstructure in ferroelectric crystal switches between possible domain patterns that are energetically favourable, rather than assuming one particular domain pattern throughout. This model is applied to study the hysteresis responses of barium titanate (BaTiO3) single crystals subjected to a variety of loads. The results have good agreement with experimental data in the literature. The relationship between domain patterns and ferroelectric hysteresis responses is discussed.

The rolling-sliding dry-wear behaviour of a series of bainitic steels and a standard pearlitic rail steel have been compared over a range of contact stress and creepage conditions applicable to the British Rail network. A rolling-sliding wear machine has been constructed - LEROS - which allows very high contact stresses to be combined with high creepages under well controlled conditions. Materials were tested on LEROS and on an Amsler machine. Limited vibration analyses were carried out on both machines and compared with the frequencies of disc surface periodic undulations. No direct linkage was determined. Despite better standard mechanical properties, the wear resistance of lower carbon bainitic steels was inferior to that of the pearlitic steel. A bainitic steel with the same carbon content as the pearlitic steel wore a little less, but at considerable expense to the pearlitic wheel steel counter-material in the wear couple. The wear resistance of bainitic steels depends upon the volume fraction of hard phase, such as carbide and martensite-austenite phase, for rolling-sliding as well as other types of dry wear loading. Pearlitic steel performs exceptionally well under certain rolling-sliding conditions, such as the majority seen in these tests, since the lamellar microstructure is modified so as to present a greater area fraction of carbide hard phase at the wear surface, a fraction in excess of bulk volume fraction. Recommendations are made for the dry wear applicability of the steels.

There is growing interest in using additive manufacturing for various alloy systems and industrial applications. However, existing process development and part qualification techniques, both involve extensive experimentation-based procedures which are expensive and time-consuming. Recent developments in understanding the process control show promise toward the efforts to address these challenges. The current research uses the process mapping approach to achieve control of melt pool geometry and microstructure in different alloy systems, in addition to location specific control of microstructure in an additively manufactured part. Specifically, results demonstrate three levels of microstructure control, starting with the prior beta grain size control in Ti-6Al-4V, followed by cell (solidification structure) spacing control in AlSi10Mg, and ending with texture control in Inconel 718. Additionally, a prediction framework has been presented, that can be used to enable a preliminary understanding of melt pool geometry for different materials and process conditions with minimal experimentation. Overall, the work presented in this thesis has the potential to reduce the process development and part qualification time, enabling the wider adoption and use of additive manufacturing in industry.

This thesis is focused on achieving materials with non-equilibrium structures fabricated by high-energy laser sintering. The chosen precursor materials have rigid and inert structures like high-melting point ceramics or metals. It was necessary to use real-time monitoring of temperature and spectrum profiles for selecting the optimal laser parameters for the laser sintering process. This monitoring was done by an off-axial setup that also controls the surface morphologies during the laser irradiation process. The laser focal spot receives very high temperatures and subsequent extreme cooling rates within a short time period. New non-equilibrium structures will emerge ruled by kinetics, huge temperature gradients or stresses and freeze by quenching in solid state. These material structures were found to form at different length scales from nano- to macro-level, frequently by a hierarchical ordering. This opens a method to engineer materials with both hierarchical and non-equilibrium structures by a single operation in both metal and ceramics by laser sintering. In the Co-Cr-Mo alloy system, structures on three levels of lengths were observed, namely i) nano-level structures dominated by the grain boundary segregation; ii) micron-level structures characterized by the interlocked clusters of columns; and iii) macro-level structures defined by the selected laser scan patterns. The non-equilibrium structures of the Co-Cr-Mo alloy are related to mechanical, corrosion and bio-compatibility properties. In ZrO2 ceramics, the final product had a non-equilibrium nano- and micron-sized structure created by uneven absorption of laser energy and rupture. The structure inside the micron-sized grains is formed through ordered coalescence of nano-crystals. Properties of the laser sintered materials were established and related to the observed structures. The materials properties might be tailored by controlling the structures in different levels and potential applications of the new materials will be given. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Accepted. Paper 4: Submitted. Paper 5: Manuscript.</p>

<p>Promene komponenata i strukture mleka ispitane su tokom fermentacije kori&scaron;ćenjem inokuluma kombuhe kultivisane na crnom čaju zaslađenom saharozom<br />u koncentraciji 10%. Fermentacija mleka sa 2,2% mlečne masti izvr&scaron;ena je na dve različite temperature (37&deg;C i 42&deg;C) i uzorci su analizirani na sledećim pH vrednostima: 6,1; 5,8; 5,4; 5,1; 4,8 i 4,6. Urađena je determinacija i identifikacija produkata fermentacije laktoze kao &scaron;to su: &scaron;ećeri, organske kiseline i masne kiseline. Ispitane su teksturalne i reolo&scaron;ke karakteristike i mikrostruktura uzoraka. Pored toga, utvrđene su sličnosti i razlike uticaja inokuluma kombuhe na proces fermentacije mleka u poređenju sa delovanjem jogurtne, odnosno probiotske starter kulture.<br />Tokom fermentacije mleka u različitim fazama procesa pri odabranim pH vrednostima na 42&deg;C transformi&scaron;e se 14,6% laktoze odnosno 18,2% na 37&deg;C. Sadržaj galaktoze i glukoze koje nastaju fermentacijom i hidrolizom laktoze raste između prve i druge tačke fermentacije (pH=6,07 i pH=5,8). Dominantne organske kiseline tokom fermentacije su L&ndash;mlečna kiselina i sirćetna kiselina. Nije utvrđena značajna razlika u sadržaju masnih kiselina tokom fermentacije mleka kombuhom na 37&deg;C i 42&deg;C. Sadržaj palmitinske kiseline u mleku i uzorcima tokom fermentacije je najveći, zatim slede miristinska, stearinska i oleinska kiselina.<br />Praćenjem procesa fermentacije mleka uz primenu kombuhe na 37&deg;C i 42&deg;C od početne pH vrednosti 6,07 do zavr&scaron;ne 4,6, najznačajnije promene teksturalnih karakteristika (čvrstoće, konzistencije, kohezivnosti i indeksa viskoziteta) i reolo&scaron;kih svojstava zabeležene su između pH=5,4 i 5,1, &scaron;to je u korelaciji sa mikrostrukturom.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Promene viskoziteta u svim uzorcima pokazuju istu regresionu liniju, sa različitim koeficijentima i visokom vredno&scaron;ću r2, osim uzorka proizvedenog primenom jogurtne kulture na pH 5,4. Uzorak dobijen kori&scaron;ćenjem inokuluma kombuhe imao je najveće vrednosti kompleksnog modula, &scaron;to je rezultiralo boljim reolo&scaron;kim karakteristikama gotovog proizvoda.<br />Da bi se definisao empirijski model procesa fermentacije laktoze u mleku delovanjem kombuhe formulisana su prethodno dva matematička modela za kinetiku fermentacije saharoze u tradicionalnom kombuha napitku (na crnom čaju) &ndash; jedan koji opisuje promenu koncentracije saharoze tokom fermentacije, i drugi koji opisuje brzinu fermentacije. Promena koncentracije laktoze na ispitivanim temperaturama 37&deg;C i 42&deg;C sastoji se od dve lag faze između kojih je faza izraženog pada koncentracije. Krive zasićenja pokazuju sigmoidalnu kinetiku na nižim koncentracijama laktoze, ukazujući na kompleksni ne&ndash;Michaelis&ndash;Mentenov tip kinetike.<br />Generalno može se istaći da su primenom inokuluma kombuhe tokom fermentacije mleka u različitim fazama procesa ustanovljene specifične promene komponenata i strukture u poređenju sa efektima delovanja jogurtne odnosno probiotske starter kulture.</p><p>&nbsp;</p> / <p>Changes of milk components and structure were examined during fermentation by kombucha inoculum cultivated on black tea switened with saccharose in a concentration of 10%. The fermentation of milk with 2.2% of milk fat was carried out at two different temperatures (37&deg;C i 42&deg;C) and samples were analyzed at the following pH values: 6.1; 5.8; 5,4; 5.1; 4.8 and 4.6. Determination and identification of the lactose fermentation products, such as: sugars, organic acids and fatty acids were carried out. Textural and rheological characteristics and microstructure of the samples were investigated. Furthermore, the effect of kombucha on the milk fermentation process was compared with the effect of yoghurt and probiotic starter culture.<br />During milk fermentation at various stages of the process 14.6% of lactose content was transformed at 42&deg;C and 18.2% at 37&deg; C. The galactose and glucose content, which are formed by lactose hydrolyses and fermentation, increased between first and second pH point of fermentation (pH = 6.07 and pH = 5.8). Dominant organic acids during fermentation are L&ndash;lactic acid and acetic acid. There is no significant difference between samples in fatty acids content during fermentation on 37&deg;C and 42&deg;C. The level of palmitic acid in milk and samples was the highest of all fatty acids, followed by myristic, stearic, and oleic acid.<br />The most significant changes in textural properties (firmness, consistency, cohesiveness and viscosity index) and viscosity during milk fermentation by kombucha at 37&ordm;C and 42&deg;C, from the initial pH value 6.07 to a final 4.6, were recorded between pH=5.4 and 5.1, which is in correlation with microstructure.<br />Viscosity changes in all samples showed the same regression line with the different coefficients and a rather high r2 except for the sample produced with standard yoghurt culture at the pH 5.4. Samples produced with kombucha had the highest values of the complex modulus, which indicates better rheological characteristics of the final product.<br />In order to define an empirical model of lactose fermentation process in milk by kombucha, two mathematical models (one for the change of saccharose concentration, during its fermentation by kombucha, and the other for the rate of the mentioned fermentation) previously were formulated. Change of lactose concentrations at 37&ordm;C and 42&ordm;C consists of two retaining stages and very steep descend in-between. Saturation curves show a sigmoidal kinetics at low lactose concentrations, indicating a complex non&ndash;Michaelis&ndash;Menten type kinetics.<br />Generally it can be concluded that specific changes in the components and structure of milk by application of kombucha inoculum during fermentation at different stages of the process were established in comparison with the effects of yoghurt and probiotic starter culture.</p>