Neste trabalho foram estudados os efeitos causados pelo tratamento térmico na argila STx-1b-Li+ na condutividade de filmes argila/alginato de sódio. O argilomineral STx-1b foi submetido à substituição isomórfica do cátion Na+ por Li+ e posteriormente ao tratamento térmico em diferentes temperaturas. As argilas STx-1b-Li+ não tratada e tratada termicamente foram caracterizada por difração de raios-X (DRX) e termogravimetria (TG). As curvas TG mostraram que o argilomineral STx-1b-Li+ apresentou três perdas de massa que podem ser atribuídas à água adsorvida na argila, a água de hidratação dos íons Li+ e a água estrutural da argila. Para as argilas STx-1b-Li+ tratadas termicamente não foi observado a perda de massa associada à água quimicamente ligada aos contra-íons Li+. Estes resultados estão em concordância com os obtidos por DRX, onde observou-se uma diminuição no espaçamento interlamelar nas argilas tratadas termicamente. Em adição, foram preparados filmes de alginato de sódio com as argilas STx-1b-Li+ não tratada e tratada termicamente e estes foram caracterizados por calorimetria exploratória diferencia (DSC) e espectroscopia de impedância eletroquímica (EIE). As curvas DSC mostraram um aumento na temperatura de transição vítrea (Tg) dos filmes com o aumento da temperatura utilizada no tratamento das argilas. Este aumento nos valores de Tg é um indicativo que a mobilidade das cadeias diminuiu nos filmes polímero/argila que contém argilas tratadas em temperaturas mais elevadas. A espectroscopia de impedância eletroquímica (EIE) foi usada para avaliar-se a condutividade iônica dos filmes. Os resultados indicaram que os filmes contendo argilas que foram tratadas com temperaturas mais altas apresentaram menor condutividade. / In this work the effects caused by the heat treatment in STx-1b-Li+ clay on the conductivity of sodium alginate/clay were studied. The clay mineral STx-1b was submitted to isomorphous substitution of the Na+ for Li+ cation and subsequently to heat treatment at different temperatures. The STx-1b-Li+ clays untreated and heats treated were characterized by X-ray diffraction (XRD) and Thermogravimetric Analysis (TG). The TG curve showed that the clay mineral STL-1b-Li+ had three mass losses which can be attributed to adsorbed water in the clay, the water of hydration of the Li+ ions and structural clay water. To STx-1b-Li+ clays heat treated there were no mass loss associated to the water chemically bound to Li+ counter ions. These results are in agreement with those obtained by XRD, which it was observed a decrease in interlayer spacing in the heat treated clay. In addition, they were prepared sodium alginate films with STx-1b-Li+ clays untreated and heat treated and these films were characterized by Differential Scanning Calorimetry (DSC) and Electrochemical Impedance Spectroscopy (EIS). DSC curves showed an increase in glass transition temperature (Tg) of the films with temperature increasing used in the treatment of clays. This increase in Tg value is an indicative that the mobility of the chains had decrease in the polymer/clay films which contains heat treated clays at higher temperatures. The electrochemical impedance spectroscopy (EIS) was used to evaluate the ionic conductivity of the films. The results indicate that films containing clays which have been treated at higher temperatures had lower conductivity.

"Surface contamination during the heat treatment process can greatly affect the quality of the heat treated parts. Although cleaning the post-heat treated parts is considered a value added process in heat treatment, cleaning parts prior to heat treatment is also important and can influence the outcome of subsequent processes. A series of experiments has been designed to determine the effects of the surface contaminants on nitriding. Nitralloy-135 steel was selected to evaluate the cleaning methods and the effects on the result of subsequent nitriding process. The samples were contaminated with a variety of contaminants, including rust preventive oil, cutting fluid and rust. The contaminated samples were cleaned using either acid or alkaline cleaner. Both cleaned and contaminated samples were nitride in the furnace. To determine the effect of contaminants on gas nitriding, weight gain and the surface hardness were measured. Nitrogen flux was also calculated. The results show that the acid cleaning effectively removes the rust layer. Rusted parts had lower nitrogen absorption than that of the cleaned samples. The parts contaminated by the oil did not reveal any effect on the nitrogen uptake. The surface hardness (Rc) did not show a significant difference between the heavily rusted sample and the clean sample. It has been observed that the nitrogen flux is smaller due to the rust layer on the heavily rusted samples."

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / Includes bibliographical references. / M.S.

No presente projeto, foi estudada a viabilidade do purê de manga (Mangifera indica Linn.), variedade 'Haden', para pronto consumo. Inicialmente foi feito o acompanhamento do processo de amadurecimento das mangas para determinar o estágio de maturação adequado para o processamento do purê. Foram feitas análises de firmeza, pH, acidez titulável expressa em porcentagem de ácido cítrico, sólidos solúveis e teor de pectina da polpa das frutas. Os resultados mostraram que a coloração da casca foi um bom indicador do estágio de maturação das mangas. Após acidificação, foram alicados no purê quatro tratamento térmicos diferentes: 25,5 minutos a 65°C; 16,0 minutos a 75°C; 4,0 minutos a 80°C e 2,5 minutos a 95°C. Purê tratado e não tratado termicamente foi mantido sob refrigeração durante 36 dias e análises de pH e acidez titulável, além da contagem de bolores e leveduras, foram realizadas no purê na freqüência de 7 dias. Apesar da análise estatística indicar diferenças significativas entre os valores de pH e acidez titulável em função do tempo de armazenamento e do tratamento térmico, o purê apresentou valores dentro dos limites estabelecidos pela legislação para purê de manga destinado ao consumo como bebida (valor de pH entre 3,3 e 4,5 e acidez titulável mínima de 0,32% de ácido cítrico). Em relação à contagem de bolores e leveduras, o purê tratado termicamente mostrou-se estável, apresentado contagem zero dos microrganismos citados durante todo o período de armazenamento. Estudo do comportamento reológico do purê tratado e não tratado termicamente indicou o seu caráter não-newtoniano, de natureza pseudoplástica. Apesar dos tratamentos térmicos apresentarem valores de F bem distintos, as análises físico-químicas, a contagem de bolores e leveduras e o estudo reológico mostraram que não houve diferença entre os produtos finais. Isso indica que a estabilidade físico-química e microbiológica do purê pode ser alcançada com o tratamento térmico que apresentou o menor valor de F, no caso, o tratamento conduzido a 65ºC durante 25,5 minutos. Em um teste de aceitação do consumidor, o purê tratado nestas condições apresentou um alto indice de aceitação, o que reforça a viabilidade do produto pronto para consumo. / In this research project, the viability of 'Haden' mango puree (Mangifera indica Linn.) as a ready-to-serve product was studied. The ripening process of the fruti was studied to determine the adequate stage for the puree production. Firmness, pH, total acidity expressed as citric acid percentage, soluble solids and pectin content of the fruti pulps were analyzed. results showed that color of skin is a good parameter to indicate the mangoes ripening stage. Four different heat treatments were applied to the acidified puree: 25.5 minutes at 65°C; 16.0 minutes at 75°C; 4.0 minutes at 80°C and 2.5 minutes at 95°C. Non treated and treated puree were maintained under refrigeration for 36 days. pH, titrable acidity, molds and yeast analyses were carried out weekly. Although statistical analyses indicate significant difference among pH and acidity values in relation to storage time and heat treatment, the puree presented acceptable values by Brazilian legislation for mango puree consumed as beverage (pH between 3,3 and 4,5 and mininum total acidity of 0,32% of citric acid). Heat treated puree showed microbiological stability, presenting zero count of these microorganisms during the storage time. The study of rheological behavior of treated and non treated purees revealed non Newtonian character of shear thinning nature. Even though the heat treatments presented very distinct F values, the physical chemical analyses, the mold and yeast counts and the rheological behavior showed that there was difference among the final products. This indicates that the stability os the puree can be achieved applying the heat treatment with the smallest F value, that is 25.5 minutes at 65°C. Consumer acceptance test of puree treated in these conditions presented high level of acceptance, which reinforces the viability of this puree as a ready-to-serve product.

No description available.

The study involves two different approaches to increasing cottage cheese yields by the inclusion of whey proteins in the curd. They were the use of high heat treated skim milk and ultrafiltered skim milk retentates for cottage cheese making. Increasing the pasteurization temperature of skim milk from 61.8 to 79.4 C for 30 minutes resulted in 15.6% increase in cultured cottage cheese yields. However, the high heat cheese exhibited variable quality and was generally inferior to the control. Cheese making from high heat skim milk was done by cutting at the A.C. end point and using 30 ml of rennet per 454 kg of skim milk. There appeared to be no relationship between the rate of heating to 79.4 C and the quality of cottage cheese produced. Skim milk was concentrated by ultrafiltration to 12, 16, and 20% solids. The 20% retentate was produced by concentrating skim milk 5:1 and then subjecting it to diafiltration with an equivalent volume of deionized water. The acidification of the retentates was accomplished by metering concentrated hydrochloric acid into the vortex of the centrifugal Culture growth in 20% retentates was inhibited below and soluble phosphate seemed to be an important factor in this inhibition. The yield trials indicated that the increase in yields over cultured cottage cheese made from skim milk was 12.4, 15.3, 5.6 and 1.6% for 16 % cultured, 16 % direct acid, 20% cultured and 20% direct acid cottage cheeses made from retentates. The lower yield increases from 20% retentates was because of the shattering of the curd while cooking, and the diffusion of the whey proteins. While the quality of cultured cottage produced by ultrafiltration was as good as the cultured cottage cheese from skim milk, the direct acid cottage cheeses were much inferior. Considering both high heat treatment of skim milk and ultrafiltration for increasing cottage cheese yields, ultrafiltration seems to be the better method owing to the much better quality of cheese produced. To obtain maximum benefits from ultrafiltration, problems of lactic culture growth in retentates must be solved and non conventional cooking methods have to be developed for handling curds from high solids retentates.

Health consciousness drives people to drink skim milk. Yet, improving the blue-white appearance and watery texture of skim milk is necessary to make consumers happy with skim milk. In this study, the influence of limited proteolysis with soluble or immobilized proteases, heat treatment, and pH on the whiteness of skim milk were examined to meet this goal. Limited proteolysis with milk-clotting enzymes increased the whiteness of skim milk. the proteases porcine pepsin and chymosin were immobilized onto nonporous ceramic, glass, and controlled pore glass (CPG) beads. The enzymes were coupled to beads either directly or via crosslinker proteins. Pepsin, immobilized onto CPG beads via crosslinker proteins, exhibited the best properties with respect to enzymatic activity, stability, and whitening efficiency. The L value (whiteness) of this immobilized enzyme-treated skim milk was 79.5, which approached the whiteness of 1% fat milk. Immobilized proteases whitened skim milk more effectively than did soluble proteases. The whiteness of skim milk was determined at various temperatures from 4 to 90°C. The L value increased with increasing temperature throughout the range tested. For samples not heated above 50°C, the increases in L values were completely reversible on cooling. Partial reversibility was observed with samples heated at 70°C and above. Milk whiteness was also determined at different pH values ranging from 5.0 to 8.2 at temperatures of 4, 20, and 30°C. The L value increased with decreasing pH and increasing temperature. A maximum L value of 80.0 was obtained at pH 5.0 and 30°C, which is higher than the L value of skim milk at its natural pH at room temperature. The temperature-dependent dissociation of major caseins was investigated by size exclusion chromatography at temperatures from 10 to 40°C. Free soluble β-casein and κ-casein were found only at 10°C.

Graduation date: 1997

This study determined the independent effects of various homogenization cycles and precipitation treatments on the elevated temperature workability and the final ambient temperature mechanical properties of AA2024 aluminum alloy and on the T3 tensile properties of 2014 aluminum alloy as well as T6 tensile properties of 2618 and 2618 (Curich) aluminum alloys. The elevated-temperature tensile and extrusion tests indicate that the workability of AA2024 alloy improves with elevated-temperature precipitation treatment as suggested by earlier investigations. The precipitation treatments do not appear to degrade the ambient-temperature T3 and T8 tensile properties. The time at the precipitation temperature appears to affect the T3 and T8 tensile properties in unextruded ingot, longer times especially providing both relatively high ambient-temperature strength and ductility of AA2024 alloy. The time at the standard homogenization temperature and the heat-up and cool-down rates do not dramatically affect the T3 tensile properties of unextruded ingot of AA2024 and 2014 alloys. However, long soak times at the homogenization temperature and more rapid cooling rates may improve the properties somewhat of AA2024 alloy and longer heat-up times and rapid cooling rates may slightly improve the properties of 2014 alloy. The higher standard solution temperature appears to increase both strength and ductility of 2014 alloy over lower temperatures. The homogenization temperature affects the T6 tensile properties of 2618 and 2618 (Cu-rich) alloys, a high homogenization temperature (compare to standard homogenization temperature) providing both high strength and ductility. Increased manganese and copper appears to increase the strength, but slightly decreases the ductility. The standard aging temperature and time produce higher strength but lower the ductility than lower temperatures at the same or shorter aging times in 2618 (Cu-rich) alloy. / Graduation date: 1993

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