Highly concentrated micellar casein concentrate (HC-MCC), a potential ingredient for cheese making, containing ~20% casein with ~70% of serum proteins removed by microfiltration, and diafiltration of skim milk, and then further concentrated by vacuum evaporation. The objectives of this research were to investigate solubilization, cold gelation, rennet coagulation properties of recombined HC-MCC and cream for its use in cheese making. In Chapter 3, either mixing thawed HC-MCC in water at high temperature (~50C) or addition of trisodium citrate can achieve complete dispersion and more than 80% solubility of HC-MCC in water (3% protein). Overnight storage helps to fully disperse HC-MCC, but only reaches ~30% of solubility at 20C. Cold-gelation of HCMCC is thermally reversible and reducing protein levels in HC-MCC can decrease its CGT. The HC-MCC with less than 16% of protein does not gel at 5C. We propose that cold-gelation of HC-MCC occurs when the kinetic energy of the casein micelles is sufficiently reduced to inhibit their mobility in relation to adjacent casein micelles. In Chapter 4, the recombined concentrated milk (RCM) by mixing thawed frozen HC-MCC and cream with 12% casein at pH 6.6 does not gel until cooled below 12°C. Addition of either sodium citrate or high levels of calcium increased CGT, although low levels of calcium did not impact CGT. Cold gelation of RCM was thermally reversible, even when citrate was added to partially chelate calcium. We propose that cold gelation of RCM occurs when protein strands that have been partially released from the casein micelles entangle, restrict their mobility and form a fine stranded gel network. The RCM at a casein level of 12% (wt/wt) has potential for use in cheese making. In Chapter 5, reducing rennet level can increase coagulation time of RCM (11% casein) without impact on curd firmness or firming rate. Decreased coagulation temperature helps to increase coagulation time and decrease curd firmness rate, but also increases the initial viscosity of RCM. Pre-acidified RCM has no advantage in increasing coagulation time, decreasing curd firmness or firming rate. Microstructure of RCM and its coagulum indicates that the increased curd firmness probably results from the highly inter-linked and longer protein strands in RCM curd. Reducing rennet level can be applied to slow down rennet coagulation of RCM (11% casein) in cheese making.

A new but relatively simple processing study was conducted to investigate the microstructure-property relationships of alumina/aluminium titanate (AAT) composites. The objectives of this study were: (a) to develop a process for fabricating AAT and β-spodumene modified AAT composites using a solid-state reaction method and functionally-graded AAT using an infiltration technique, and (b) to evaluate the effects of dispersed aluminium titanate (AT) on the phase relations, microstructure and mechanical properties of alumina-based composites. The study has revealed that the processing procedures played an important rule in the microstructural development of AAT composites. The microstructure and properties of AAT composites have been found to be strongly influenced by the presence of dispersed AT. The phase relations in the AAT system have been characterised by x-ray diffraction (XRD) and neutron diffraction (ND). Rietveld analysis showed that the AT content increased in proportion with the amount of rutile added. The dynamic ND study showed that AT commenced to form at ~1310°C The presence of AT caused a reduction of hardness but an improvement in fracture toughness. In addition, the presence of AT hindered the processes or kinetics of sintering and densification. The use of β-spodumene has been investigated as a liquid-phase-sintering aid for the densification of AAT composites. XRD, ND, differential thermal analysis (DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Vickers indentation were used to characterise the effect of β-spodumene on the phase relations, densification, microstructure and mechanical properties of AAT composites. The presence of β-spodumene was found to have a profound influence on the phase relations, densification, microstructure and properties of AAT composites. / The addition of β-spodumene caused a small reduction of AT content and a commensurate increase of alumina phase. Functionally-graded AAT composites have been successfully synthesised through infiltration of porous alumina preform with a solution containing TiCl4. The infiltration kinetics of liquid into porous alumina preform has also been investigated and modelled. It was found that the infiltration rate equation proposed by Washburn was proven to be suitable for describing the kinetics of infiltration in terms of preform sintering temperature, viscosity, and multiple infiltrations. The influence of applied pressure was consistent with the model proposed by Travitzky and Shlayen, where the applied pressure enhanced the rate of infiltration. Pre-sintering of alumina preform at 900, 1000 and 1100°C for 2 h resulted in different rates of infiltration which may be attributed to a varying degree in tortuosity of the pore channels. The graded composition character of functionally-graded AAT composites has been determined by XRD and grazing incidence synchrotron diffraction (GISRD). Graded compositions from Rietveld refinement analysis showed that the concentration of AT decreased with depth. In contrast, the α-A12O3 content increased with depth. Microstructural examination by SEM showed that the content of AT grains was the most abundant near the surface and decreased gradually with an increase in depth. The hardness results showed that FGM had a soft graded-region (AT rich) but hard non-graded alumina region. / The lower hardness in the graded region can be attributed to the presence of intrinsically soft AT phase. The presence of graded AT caused a considerable improvement in damage tolerance. The isothermal decomposition of AT at 1100°C both in air and vacuum has been studied. Both ex-situ and in-situ studies have been conducted to examine the effect of environment on the decomposition behaviour of AT. The addition of MgO was effective in enhancing the thermal stability of AT against decomposition both in air and in vacuum.

Abstract not available

There is an every increasing need to develop more durable and higher performing coatings for use in a range of products including tools, devices and bio-implants. Nano-structured coatings either in the form of a nanocomposite or a multilayer is of considerable interest since they often exhibit outstanding properties. The objective of this thesis was to use advanced plasma synthesis methods to produce novel nano-structured coatings with enhanced properties. Coatings consisting of combinations of aluminum (Al), aluminum nitride (AlN) and amorphous carbon (a-C) were investigated. Cathodic vacuum arc deposition and unbalanced magnetron sputtering were used to prepare the coatings. By varying the deposition conditions such as substrate bias and temperature, coatings with a variety of microstructures were formed. A comprehensive range of analytical methods have been employed to investigate the stoichiometry and microstructure of the coatings. These include Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), Electron Energy Loss Spectroscopy, Auger Electron Spectroscopy, X-ray diffraction and Raman spectroscopy. In addition to the investigation of microstructure, the physical properties of the coatings were measured. Residual stress has been recognized as an important property in the study of thin film coatings since it can greatly affect the quality of the coatings. For this reason, residual stress has been extensively studied here. Hardness measurements were performed using a nano indentation system, which is sensitive to the mechanical properties of thin films. This thesis undertook the most comprehensive investigation of the Al/AlN multilayer system. A major finding was the identification of the conditions under which layers or nanocomposite form in this system. A model was developed based on energetics and diffusion limited aggregation that is consistent with the experimental data. Multilayers of a-C and Al were also found to form nanocomposites. No hardness enhancement as a function of layer thickness or feature size was observed in either the Al/AlN or a-C/a-C systems. It was found that the most important factor which determines hardness is the intrinsic stress, with films of high compressive stress exhibiting the highest hardness. Nano-structured multilayers of alternating high and low density a-C were investigated. For a-C multilayers prepared using two levels of DC bias, evidence of ion beam induced damage was observed at the interfaces of both the low and high density layers. In addition, the structure of the high density (ta-C, known as tetrahedral amorphous carbon) layers was found to be largely unchanged by annealing. These results extend our understanding of how a-C form from energetic ion beams and confirms the thermal stability of ta-C in a multilayer. This thesis also presented the first attempt to synthesis a-C multilayered films with a continuously varying DC bias in sinusoidal pattern. The resulting films were shown to have a structurally graded interface between layers and verified that ion energy and stress are the most important factors which determine the structure of a-C films.

Les Latosols correspondent à environ 40% du Plateau Central brésilien. Ils sont caractérisés par une faible activité de l'argile, une faible différenciation de leurs horizons, une macrostructure peu développée et une microstructure en revanche très développée représentée par des microagrégats de 50 à 300 µm de diamètre. Dix Latosols (L) ont été sélectionnés le long d'une toposéquence régionale d'environ 350 km de long qui recoupe la Surface Sud Américaine (SAS) (L1 à L4) et la Surface Velhas (VS) (L5 à L10). Ces différents Latosols rendent compte de la variabilité de composition granulométrique et minéralogique, et de celle de matériau parental que l'on peut rencontrer dans le Plateau Central brésilien. Nos résultats montrent que la variabilité de proportion de gibbsite et de kaolinite peut s'expliquer à la fois par l'âge de la surface géomorphologique et les conditions hydriques en fonction de la position topographique au sein de chaque toposéquence. Les résultats montrent également que la structure microagrégée ne varie pas en fonction de la composition granulométrique ou minéralogique. Elle est apparue en revanche liée à la bioturbation du sol par les termites. Il a aussi été montré que les microagrégats des Latosols étudiés ne sont pas rigides mais diminuent de volume lors de la dessiccation. De plus, la composition minéralogique de la fraction argileuse ne jouerait qu'un rôle marginal dans les variations du volume poral lors de la dessiccation. Les microagrégats des Latosols situés sur la SAS diminuent moins de volume lors de la dessiccation que les microagrégats situés sur la VS, cette différence serait liée à leur histoire hydrique. Enfin, les propriétés de rétention en eau et la conductivité hydraulique à saturation varient respectivement en fonction de la teneur en argile et du développement des pores de diamètre supérieur à 300 µm, et par conséquent sans lien étroit avec la minéralogie de la fraction argileuse.

Après avoir modélisé les hétérogéniétés intra et intergranulaires se produisant lors de grandes déformations à l'aide d'une loi de comportement micro-mécanique basée sur les dislocations, une évaluation de l'énergie stockée au sein du polycristal a été effectuée. Un modèle de cinétique des joints de grains déduit de la méthode de champ de phase a été implémenté en éléments finis.

This dissertation addresses two critical issues in the deformation of nc metals and alloys: (1) A stress-induced genuine grain growth after the plastic deformation rather than just a change of the grain shape; (2) A systematically quantitative study of micrsostructural evolution during the plastic deformation. These two critical issues point to the deformation of nc materials with the average-grain sizes within the range of 10 to 50 nm, which is the most interesting and controversial region in the current time. The current study provides a systematic and detailed microstructural evolution for this region, which is definitely beneficial for the investigation of the deformation mechanism in this region, especially for the simulation. The main experimental and data-analysis methods employed in this research are synchrotron high-energy X-ray diffraction, X-ray line profile analysis, and texture analysis. The combination of these methods is beneficial to the accurate microstructural interpretation of the bulk materials.

As technological advances occur, many conventional materials are incapable of providing the unique multi-functional characteristics demanded thus driving an accelerated focus to create new material systems such as carbon and graphite foams. The improvement of their mechanical stiffness and strength, and tailoring of thermal and electrical conductivities are two areas of multi-functionality with active interest and investment by researchers. The present research focuses on developing models to facilitate and assess multi-functional carbon foams in an effort to expand knowledge. The foundation of the models relies on a unique approach to finite element meshing which captures the morphology of carbon foams. The developed models also include ligament anisotropy and coatings to provide comprehensive information to guide processing researchers in their pursuit of tailorable performance. Several illustrations are undertaken at multiple scales to explore the response of multi-functional carbon foams under coupled field environments providing valuable insight for design engineers in emerging technologies. The illustrations highlight the importance of individual moduli in the anisotropic stiffness matrix as well as the impact of common processing defects when tailoring the bulk stiffness. Furthermore, complete coating coverage and quality interface conditions are critical when utilizing copper to improve thermal and electrical conductivity of carbon foams.

Cemented carbides based on tungsten carbide and cobalt arecommonly produced by a powder metallurgy route including liquidphase sintering. The pressed compact densifies to almost halfits volume during sintering due to pore elimination. Thesintering behaviour changes with material composition, such ascarbide grain size, binder fraction, carbon content andaddition of cubic carbides. This thesis is devoted to the study of constitutivebehaviour, in particular densification, and the microstructuralevolution during cemented carbide sintering. Dimensionalchanges are monitored using dilatometry with and withoutapplied external load. The microstructural evolution isinvestigated with light optical microscopy and scanningelectron microscopy. Thermodynamic calculations are used asreference. Constitutive relations are derived for uniaxial viscosity,viscous equivalent of Poisson’s ratio and sintering stressbased on relative density and temperature. The relations areextended to a model describing sintering shrinkage withexplicit dependencies on carbide grain size and binder content.The model is divided in three stages of which two pertain tothe solid state and the third to liquid phase sintering. Solidstate shrinkage is suppressed in a material with coarsecarbides and in the stage of liquid phase sintering grain sizestrongly influences the uniaxial viscosity. The binder contentaffects primarily the later densification. The effects of carbon content and grain size distribution onshrinkage have been studied. High carbon content enhancesshrinkage rate, but the effect of grain size distribution israther small. The mean carbide grain size is insufficient todescribe densification for very broad distributions only. Shrinkage occurs through rearrangement andsolution-reprecipitation. Rearrangement is studied through theevolution of the pore size distribution and simulatedgenerically using a discrete element method. Keywords:Cemented carbides, Sintering, Constitutiverelations, Microstructure, Densification, Modelling

Martensitic steels have become very important engineering materials in modern society. Crucial parts of everyday products are made of martensitic steels, from surgical needles and razor blades to car components and large-scale excavators. Martensite, which results from a rapid diffusionless phase transformation, has a complex nature that is challenging to characterize and to classify. Moreover the possibilities for modeling of this phase transformation have been limited, since its thermodynamics and kinetics are only reasonably well understood. However, the recent development of characterization capabilities and computational techniques, such as CALPHAD, and its applicability to ferrous martensite has not been fully explored yet. In the present work, a thermodynamic method for predicting the martensite start temperature (Ms) of commercial steels is developed. It is based mainly on information on Ms from binary Fe-X systems obtained from experiments using very rapid cooling, and Ms values for lath and plate martensite are treated separately. Comparison with the experimental Ms of several sets of commercial steels indicates that the predictive ability is comparable to models based on experimental information of Ms from commercial steels. A major part of the present work is dedicated to the effect of carbon content on the morphological transition from lath- to plate martensite in steels. A range of metallographic techniques were employed: (1) Optical microscopy to study the apparent morphology; (2) Transmission electron microscopy to study high-carbon plate martensite; (3) Electron backscattered diffraction to study the variant pairing tendency of martensite. The results indicate that a good understanding of the martensitic microstructure can be achieved by combining qualitative metallography with quantitative analysis, such as variant pairing analysis. This type of characterization methodology could easily be extended to any alloying system and may thus facilitate martensite characterization in general. Finally, a minor part addresses inverse bainite, which may form in high-carbon alloys. Its coupling to regular bainite is discussed on the basis of symmetry in the Fe-C phase diagram. / <p>QC 20120824</p> / Hero-m