Reverse osmosis (RO) and ultrafiltration (UF) retentates were ultra-high temperature (UHT) processed and compared for storage life at room temperature. Viscosity studies indicated that UHT-treated, RO retentate delayed age gelation longer than UF retentate at the same total solids level (26% TS). When compared at 6.4% protein level (2x RO vs 2.7x UF where x=ratio of the feed volume to concentrate volume), the storage life for both RO and UF retentates was about 6 to 8 months. Sodium hexametaphosphate (SHMP) and disodium phosphate (DSP) at 1, 3, 5, 10, and 20 mM concentrations were incorporated prior to UHT processing of each sample to improve the shelf life. SHMP at 1 and 3 mM concentrations was effective in delaying age gelation, whereas all levels of DSP accelerated gelation. However, SHMP accelerated age gelation at concentrations of 10 and 20 mM. SHMP at 1 mM in RO retentate was more effective in delaying age gelation than the same SHMP level in two UF samples (22 and 26% TS). Analysis showed that RO/UHT-treated samples had higher soluble calcium and ionic calcium than did UF/UHT-treated samples. The coefficient of determination (R2) was .80 between soluble calcium-to-protein ratio and shelf life.

Sterile ceramic plates and the surface of beef steaks were inoculated with the pathogenic microorganisms Listeria monocytogenes, Campylobacter jejuni, Escherichia coli and Salmonella typhimurium. Samples were also inoculated with nonpathogenic microorganisms Clostridium sporogenes ATCC 7955, Pseudomonas aeruginosa, and Bacillus stearothermophilus. Concentrations of organisms in the pure culture used to inoculate the samples were selected within the range of 106 to 108 colony forming units/ml (CFU/ml). Samples were treated with ultra-high temperature (UHT), and· the surviving organisms were recovered and counted. Meat samples were exposed to 1100°C for 22 seconds. Beef steaks inoculated with pathogenic microorganisms had low survival rates. The percent destruction ranged from 99.9 to 99.8. Sixteen percent of the spores from putrefactive anaerobe 3679 were destroyed. UHT was not found to be effective in destroying the spores of this organism. UHT destroyed 99.9 to 100 percent of the nonpathogenic microorganisms Pseudomonas and Bacillus stearothermophilus, respectively, inoculated on the surface of beef steaks prior to treatment. UHT pasteurization technology proved to be an effective method of controlling vegetative pathogens and vegetative spoilage organisms on meat surfaces.

Ultra-high temperature (i.e., greater than 2500°C) engineering applications present continued materials challenges. Refractory metal/ceramic composites have great potential to satisfy the demands of extreme environments (e.g., the environments found in solid rocket motors upon ignition), though general scalable processing techniques to fabricate complex shaped parts are lacking. The work embodied in this dissertation advances scientific knowledge in the development of processing techniques to form complex, near net-shape, near net-dimension, near fully-dense refractory metal/ceramic composites with controlled phase contents and microstructure. Three research thrusts are detailed in this document. First, the utilization of rapid prototyping techniques, such as computer numerical controlled machining and three dimensional printing, for the fabrication of porous tungsten carbide preforms and their application with the Displacive Compensation of Porosity process is demonstrated. Second, carbon substrates and preforms have been reactively converted to porous tungsten/tungsten carbide replicas via a novel gas-solid displacement reaction. Lastly, non-oxide ceramic solid solutions have been internally reduced to create intragranular metal/ceramic micro/nanocomposites. All three techniques combined have the potential to produce nanostructured refractory metal/ceramic composite materials with tailorable microstructure for ultra-high temperature applications.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18087号 / 理博第3965号 / 新制||理||1572(附属図書館) / 30945 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 三宅 亮, 教授 土`山 明, 准教授 河上 哲生 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Ultra-high temperature ceramics (UHTCs) are a class of materials that maintain their structural integrity at high temperatures, e.g. 2000 °C. They have been limited in their aerospace applications because of their relatively high density and the difficulty involved in forming them into complex shapes, like leading edges and inlets. Recent advanced processing techniques have made significant headway in addressing these challenges, where the introduction of multiscale porosity has resulted in lightweight UHTCs dubbed multiscale porous UHTCs. The effect of multiscale porosity on material properties must be characterized to enable design, but doing so experimentally can be costly, especially when attempting to replicate hypersonic flight conditions for relevant testing of selected candidate samples. As such, this dissertation seeks to computationally characterize the thermomechanical properties of multiscale porous UHTCs, specifically titanium diboride, and validate those results against experimental results so as to build confidence in the model. An implicit quasi-static variant of the Material Point Method (MPM) is developed, whose capabilities include intrinsic treatment of large deformations and contact which are needed to capture the complex material behavior of the as-simulated porous UHTC microstructures. It is found that the MPM can successfully obtain the elastic thermomechanical properties of multiscale porous UHTCs over a wide range of temperatures. Furthermore, characterizations of post-elastic behavior are found to be qualitatively consistent with data obtained from uniaxial compression experiments and Brazilian disk experiments. / Doctor of Philosophy / This dissertation explores a class of materials called ultra-high temperature ceramics (UHTCs). These materials can sustain very high temperatures without degrading, and thus have the potential to be used on hypersonic aircraft which routinely experience high temperatures during flight. In lieu of performing experiments on physical UHTC specimens, one can perform a series of computer simulations to figure out how UHTCs behave under various conditions. This is done here, with a particular focus what happens when pores are introduced into UHTCs, thus rendering them more like a sponge than a solid block of material. Doing computer simulations instead of physical experiments is attractive because of the flexibility one has in a computational environment, as well as the significantly decreased cost associated with running a simulation vs. setting up and performing an experiment. This is especially true when considering challenging operating environments like those experienced by high-speed aircraft. The ultimate goal with this research is to develop a computational tool than can be used to design the ideal distribution of pores in UHTCs so that they can best perform their intended functions.

The aim of this work is to research milk and kefir microbiological indicators according to microbiological risk factors in the milk processing company A. Work tasks: to analyze drinking milk, ultra high temperature pasteurized milk and kefir descriptions and factors of the risk in technological process schemes; microbiological factors of the risk control schemes; samples of these products microbiological indicators according to company’s self-control plan. Conclusion: The main microbiological risk factors in drinking milk is total bacterial count, coliform bacteria, Salmonella; in the kefir – coliform bacteria, yeasts and moulds. Principals control points in drinking milk, ultra high temperature pasteurized milk and kefir technological schemes are: reception of the raw cow’s milk; freezing of the raw cow’s milk, storage and keeping; pasteurization of milk and freezing, pasteurized milk compound storage and keeping; milk warming, deaeration, homogenization, sterilization and refreshing (only for ultra high temperature pasteurized milk); repeated thermal treatment, cooling up to inoculation temperature (only for kefir); inoculation and incubation (only for kefir); storage. In the company’s A self-control plan preview principal control points microbiological risk factors are controlled by keeping a check of heating and freezing stages temperature and duration, monitoring of microbiological parameters are made not less than 4 times per year. Coliform bacteria and total bacteria... [to full text]

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Hypersonic aerospace vehicles are severely limited by the lack of adequate high temperature materials that can withstand the harsh hypersonic environment. Tantalum carbide (TaC), with a melting point of 3880°C, is an ultrahigh temperature ceramic (UHTC) with potential applications such as scramjet engines, leading edges, and zero erosion nozzles. However, consolidation of TaC to a dense structure and its low fracture toughness are major challenges that make it currently unviable for hypersonic applications. In this study, Graphene NanoPlatelets (GNP) reinforced TaC composites are synthesized by spark plasma sintering (SPS) at extreme conditions of 1850˚C and 80-100 MPa. The addition of GNP improves densification and enhances fracture toughness of TaC by up to ~100% through mechanisms such as GNP bending, sliding, pull-out, grain wrapping, crack bridging, and crack deflection. Also, TaC-GNP composites display improved oxidation behavior over TaC when exposed to a high temperature plasma flow exceeding 2500 ˚C.

Pour améliorer la durée de vie des matériaux à haute température et sous atmosphère oxydante, une solution est l’utilisation d’une protection de surface constituée de matériaux ultra réfractaires non oxydes. Un des objectifs principaux de cette thèse est la sélection et la validation expérimentale de nouvelles compositions chimiques de revêtements utilisés en condition oxydante et corrosive à ultra haute température. Les recherches s’appuient sur une démarche expérimentale physico-chimique se basant sur une approche thermodynamique et thermochimique menée au préalable pour choisir les composés. Les revêtements doivent être stables chimiquement, compatibles thermomécaniquement avec le substrat et adhérent de la température ambiante à celle d’utilisation. De plus, Ils doivent jouer le rôle de barrière environnementale et/ou de barrière thermique.Des tests d’oxydation sont réalisés au four solaire sur les systèmes de matériaux non oxydes massifs élaborés par frittage flash. En parallèle, des composites modèles constitués d’une fibre de carbone revêtue par PVD d’un revêtement métallique ultra réfractaire ont été élaborés puis chauffés par effet Joule afin de réaliser des tests d’oxydation. La compréhension des mécanismes entrant en jeu lors de l’oxydation de ces « nouveaux » revêtements est aussi un des challenges de ce manuscrit. Par ailleurs, elle aide à la classification de ces matériaux selon leur résistance à l’oxydation. / In order to improve material’s lifetime used at a temperature above 2500°C and under oxidizing atmosphere, a solution is to use a surfacing protection constituted of non oxide refractory materials. One of the main objectives of this thesis is to select and experimentally validate new chemical coating compositions which will be used under corrosive and oxidizing atmosphere at ultra high temperature (more than 2000°C). A preliminary thermodynamic and thermo-chemical study aims to select compounds. These compounds are then analyzed with physic-chemical tests. Coatings have to be chemically stable, thermo-mechanically compatible with the substrate and have to stick to the substrate from ambient temperature to more than 2000°C. Moreover, coatings have to act as an environmental barrier and/or as a thermal barrier.Two kinds of oxidation tests are made. On one hand, non oxide massive material’s systems are fabricated by spark plasma sintering in order to be tested at the solar furnace. On the other hand, composite models are fabricated by PVD. A carbon fiber is covered with ultra refractory metallic coating by PVD. Then, these composite models are heated by Joule effect in order to realize oxidation tests. Understanding mechanisms at work during the oxidation of these new coatings is another main objective of this thesis. This understanding will be also useful to classify these materials regarding their resistance to oxidation.

Les composites de type Cf/C sont utilisés en tant que pièces structurales dans les propulseurs spatiaux du fait de leurs excellentes propriétés mécaniques dans le domaine des très hautes températures. Néanmoins, l’atmosphère oxydante et corrosive créée lors du décollage des lanceurs et les hauts flux gazeux dégradent ces matériaux. Afin d’améliorer les performances de ces matériaux vis-à-vis de l’oxydation/corrosion, une protection composée de céramiques ultra-réfractaires (dites UHTC) peut être appliquée. Pour une efficacité de protection optimale, des phases UHTC ont été introduites en tant que constituants de la matrice. Dans ces travaux de thèse, la matrice a été réalisée par l’intermédiaire d’un procédé d’élaboration en phase liquide combinant : (i) l’introduction de poudres et (ii) la densification par infiltration réactive d’un métal fondu. La composition de la matrice appartient au système (B;C;Si;Zr). La caractérisation des matériaux après élaboration a permis de comprendre les mécanismes d’infiltration et les réactions permettant de mieux contrôler la composition chimique et la répartition des phases. Des essais sous torche oxyacétylénique ont été utilisés pour se placer dans des conditions proches de l’application visée. La caractérisation post-test des matériaux a permis d’évaluer l’efficacité de la protection dans le cas d’une utilisation unique et également d’une possible réutilisation. Les résultats en oxydation/corrosion ont permis de classer les matériaux en fonction de leur efficacité de protection. / Since many decades, Carbon/Carbon composites are used as structural parts in rocket engines due to their excellent thermomechanical properties. However, under highly oxidizing/corrosive atmosphere and high gas flow rates, carbon suffers from severe oxidation. To improve oxidation resistance of these composites, Ultra High Temperature Ceramics (UHTC) can be used as a protection. To protect the whole composite, the introduction of UHTC as a matrix has been done using a liquid phase process combining: (i) slurry infiltration process and (ii) reactive melt infiltration. Matrix constituents belong to the (B;C;Si;Zr) system. Material characterisation allowed a better understanding of the infiltration mechanisms and of the phase distribution and composition in respect to the processing conditions. To select the best composition, oxyacetylene torch testing has been done to recreate spacecraft launch environmental conditions. Post-test characterisation has been done to evaluate protection efficiency of each matrix composition for single use and possible reuse. Finally, advantages and drawbacks assessment of each composition allowed to highlight the most protective composition and phase distribution.