No description available.

No description available.

The strive to increase the engine efficiency in terms of fuel consumption and lower emissions have lead to higher demands on materials. In this thesis five different thermal barrier coatings applied using air plasma spraying to three materials commonly used for exhaust application are evaluated. This thesis work was done at Scania CV in Södertälje with main focus on evaluation during thermal cycling. The goal of this thesis is to evaluate the coatings and correlate their behaviour to their characteristic microstructure. The coatings were evaluated through their stability in thermal conductivity, fracture toughness, hardness, porosity and failure modes. The parameters where obtained using laser flash, Vickers indentation, Vickers indentation fracture toughness and microscopic evaluation methods. The evaluation shows that conventionally used zirconia based materials exhibits low thermal conductivity, high hardness, and stable fracture toughness compared to other evaluated materials. One material that can be applicable in diesel exhaust application is mullite, which showed similar performance to zirconia based materials. For the use of TBC together with SiMo51 a different bondcoat than conventional NiCrAlY needs to be evaluated. / Strävan efter att konstruera effektivare motorer för att generera minskade utsläpp och bättre bränsleekonomi har genererat högre krav på konstruktionsmaterialen som används idag. I detta examensarbete som utförts på Scania CV i Södertälje utvärderas fem olika termiska barriärsskikt som belagts med plasma sprayning på tre vanligt förekommande konstruktionsmaterial för grenrör. Målet med detta examensarbete är att utvärdera beläggningarnas beteende under termisk cykling och koppla deras beteende till karakteristiska mikrostrukturer. Beläggningarna utvärderades genom att jämföra deras värmeledningsförmåga, hårdhet, brottseghet och porositet. Materialparametrarna utvärderades genom laser flash, Vickers hårdhetsmätning, Vickers brottseghet samt mikroskopiska bildanalyser. Resultaten visar att kommersiellt använda zirkonium baserade material uppvisar låg värmeledningsförmåga, hög hårdhet och hög brottseghet i förhållande till övriga material. Ett annat material som analyserats, mullit, visar på liknande beteenden som zirkonium baserade material men behöver utvärderas ytterligare. Om SiMo51 används som substratmaterial finns behovet att utvärdera användningen av andra typer av bindskikt än det austenitiska NiCrAlY nu använt.

No description available.

No description available.

No description available.

The focus of this thesis is to develop pectin-based edible films for application of fruits and vegetables to extend their post harvest shelf life. Preliminary research demonstrated that edible coatings could effectively extend the shelf life of based avocado and peach. The respiration rate, moisture loss, firmness, chemical parameters and color changed in a lower rate in coated fruits as compared with the control. Pectin-based film formulations were then evaluated to identify the proper type and concentration of pectin, lipids and plasticizers in the film. The effects of pectin, beeswax and sorbitol concentration on water vapor permeability, mechanical properties and opacity of the films were then evaluated using response surface methodology to identify appropriate levels of different components. Results of studies on film structure revealed that water vapor permeability increased by pectin and sorbitol concentration and was decreased by beeswax concentration. Mechanical properties were mainly affected by pectin and sorbitol concentration. Beeswax was the most influential factor that affected opacity which increased with increasing beeswax concentration. / In order to successfully employ these films, their adsorption behavior, thermal and thermomechanical properties were evaluated as a function of moisture content and sorbitol concentration. The adsorption behavior was strongly influenced by sorbitol concentration. Moisture content and sorbitol concentration increased the films elongation at break, but decreased tensile strength, modulus of elasticity and Tg, and increased water vapor permeability of the films. Finally, avocado was coated with a pectin-based film and the associated quality changes were evaluated during storage. From storage studies, kinetic parameters (rate constants) and activation energy were quantified to help model the quality changes in avocado quality as function of storage temperature and time. Pectin-based coating resulted in slowing down the rate of quality changes in avocado at each storage temperature. In general, most changes were well described by some form of zero or first order rate. Temperature sensitivity of rate constant was adequately described by the Arrhenius model. / A hyperspectral imaging technique was also used to gather additional tools for following quality changes associated with stored avocados. Artificial neural network (ANN) concepts were evaluated as alternated models for predicting quality changes in coated and non-coated avocados during storage at different temperature. Modeling of quality changes in avocado indicated that compared to conventional mathematical models, ANN has more feasibility to predict of these changes. Models developed for firmness, weight loss and total color difference had better fitness than respiration rate. / Finally, the effect of coating on disease severity and different properties of avocados infected by Lasiodiplodia theobromae was studied. The coated fruits demonstrated slower rate of disease progress, respiration rate, softening and color changes. Respiration rate, firmness and color parameters were sensitive to coating and disease severity, and thus these parameters could successfully used to predict fruit quality from disease in coated and uncoated avocados.

Cork has traditionally been the preferred closure for wines. This is attributed to its unique physical properties, which include long lasting flexibility, hydrophobicity, and depending on the quality of the cork, low permeability. However, after bottling, taint compounds originating from the cork, migrate into the wine and cause an “off-musty” odour or taste, which is undesirable. The known taint compounds are geosmin; isoborneol; 1-octen-3-one; 1-octen-3-ol; tetrachloroanisole and finally trichloroanisole, which has been found to be the major cause. Only 7% of all cork-stoppered wines are affected by cork taint. Worldwide, it is estimated that $1 billion per year is lost due to contamination by taint compounds; this does not include other types of food and beverages. Current methods of processing and treating corks have failed to eliminate cork taint entirely. / Thesis (PhDAppliedScience)--University of South Australia, 2002.

Carbon dioxide (CO2) corrosion is a major problem in the oil and gas production industry. The survival of mild steel equipment is to a large extent conditional on the formation and stamina of protective iron carbonate (FeCO3) films. Damage to protective films allegedly leads to accelerated corrosion attacks and increases the risk of failures. In single-phase flows, film removal phenomena are broadly ascribed to two intrinsic mechanisms: mechanical removal by hydrodynamic forces and/or chemical removal by dissolution. The fact that both mechanisms usually act simultaneously in practice puts their combined action in the forefront regarding its significance and relevance for the industry. Yet, virtually no information is available on the exact conjoint mechanism of protective FeCO3 film removal in single-phase environments. The obscurity is largely due to the uncertainty regarding the roles of hydrodynamic forces and mass transfer, where both are closely related to turbulence intensity levels. The aim of this dissertation was to clarify the roles of the two basic FeCO3 film removal mechanisms during the conjoint removal in undisturbed, single-phase flow in terms of their relative contribution and possible synergistic interaction. The proposed aim was accomplished by applying an innovative analytical approach, in which inherently coupled processes of film formation and removal were decoupled. Also, the two intrinsic removal mechanisms were studied separately in the initial stages, before they were combined to provide a complete picture of the conjoint mechanism. An integrated approach to studying film formation/removal mechanisms involved advanced electrochemical techniques for following film growth/removal, complemented by detailedScanning Electron Microscopy/Energy Dispersive Spectroscopy/X-Ray Mapping characterisations of protective/residual films. A single-phase, highly turbulent flow field was attained by employing a rotating cylinder configuration. A standard corrosion experimental setup was extended to accommodate more complex film studies. A comprehensive flow characterisation around the rotating cylinder was carried out by means of flow visualisation and mass transfer measurements under turbulent flow conditions. While the former facilitated proper design of film formation experiments, the latter led to an empirical mass transfer correlation that enabled quantification of film dissolution rates. Furthermore, although some information on film growth kinetics is available, customised experimentation was necessary to identify the key parameters needed to obtain films with desired characteristics. Sound procedures for FeCO3 film growth were established, which led to the reproducible formation of realistic, protective films after a few days. The results of the pure mechanical removal of protective FeCO3 films have shown that its kinetics are rather slow even at high velocities and have caused a delayed, partial macroscopic type of damage. Yet, the findings demonstrate that the currently widely accepted view, that film removal by hydrodynamic forces in the absence of film dissolution in undisturbed, single-phase flows does not occur, is wrong. The strong correlation found between velocity and pure chemical film removal kinetics implicitly followed via corrosion rates suggests that the dissolution of protective FeCO3 films is under mass transfer control. Pure dissolution has faster removal kinetics and is far more detrimental to film integrity even at relatively high pH (just below saturation) than pure mechanical removal at the same Reynolds number. It has been found that the controlled pure dissolution mechanism led to only partial and selective film removal, where the more dissolution-resistant crystalline top film layer and the dissolution-prone inner layer were differently affected both in terms of the type of damage and its severity. A strong synergistic effect between mechanical and chemical film removal mechanisms has been identified during their simultaneous action. The quantified synergistic share in fully established conjoint film removal (during the steady, linear corrosion rate increase) expressed via corrosion rate gradients increased from 19.4% to 29.7% for the corresponding increase in the rotational speed from 7,000 rpm to 10,000 rpm. The synergism comprised two modes of mutual interactions: enhanced mechanical removal due to dissolution (M/D) and enhanced dissolution due to mechanical removal (D/M). In contrast to the independent action of integral removal mechanisms, where dissolution appears to be more destructive, the interaction between the two was primarily dominated by drastically accelerated mechanical film removal kinetics, that is, M/D rather than D/M mode, the latter of which was inferior. A fundamentally improved understanding of film removal mechanisms in single-phase flows has been reached as a result of the present project, thereby creating a solid foundation for future modelling and a more effective prevention and control of flow accelerated corrosion, not only in CO2 corrosive environments, but also in a wide range of industrial settings.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (leaves 175-177). Also available via World Wide Web.