Evaluation of geomembrane UV degradation using melt flow index and oxidative induction time tests

Many factors such as the sunlight, intensity of radiation, temperature, and moisture may influence the degradation process of geosynthetics. UV stabilizers are used especially in polyolefin geomembrane to prevent the degradation process. In these geomembranes the service lifetime is initially governed by the consumption of antioxidants. Tests like MFI and OIT are a alternative to detect the oxidative degradation in polyolefins. This article evaluates HDPE geomembrane degradation after UV exposure through the results of MFI and OIT tests. Two kinds of geomembranes were evaluated: a black and smooth (0.8, 1.0, 1.5, 2.5 mm) and a white and textured (1.0 mm). MFI test showed some levels of superficial degradation (crosslink) in HDPE geomembrane.

Time-course of photosynthetic induction in four tropical woody species grown in contrasting irradiance habitats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Aspects of the kinetics and solubility of silica and calcium oxalate composites in sugar solutions

Fouling of industrial surfaces by silica and calcium oxalate can be detrimental to a number of process streams. Solution chemistry plays a large roll in the rate and type of scale formed on industrial surfaces. This study is on the kinetics and thermodynamics of SiO2 and calcium oxalate composite formation in solutions containing Mg2+ ions, trans-aconitic acid and sucrose, to mimic factory sugar cane juices. The induction time (ti) of silicic acid polymerization is found to be dependent on the sucrose concentration and SiO2 supersaturation ratio (SS). Generalized kinetic and solubility models are developed for SiO2 and calcium oxalate in binary systems using response surface methodology. The role of sucrose, Mg, trans-aconitic acid, a mixture of Mg and trans-aconitic acid, SiO2 SS ratio and Ca in the formation of com- posites is explained using the solution properties of these species including their ability to form complexes.

Sexual reproduction in chydorid cladocerans (Anomopoda, Chydoridae) in southern Finland - implications for paleolimnology

The relationship between sexual reproduction of littoral chydorid cladocerans (Anomopoda, Chydoridae) and environmental factors in aquatic ecosystems has been rarely studied, although the sexual behavior of some planktonic cladocerans is well documented. Ecological monitoring was used to study the relationship between climate-related and non-climatic environmental factors and chydorid sexual reproduction patterns in nine environmentally different lakes that were closely situated to each other in southern Finland. Furthermore, paleolimnological ephippium analysis was used to clarify how current sexual reproduction is reflected in surface sediments of the same nine lakes. Additionally, short sediment cores from two of the lakes were studied with ephippium analysis to examine how recent climate-related and non-climatic environmental changes were reflected in chydorid sexual reproduction. Ephippium analysis uses the subfossil shells of asexual individuals to represent asexual reproduction and the shells of sexual females, i.e. ephippia, to represent sexual reproduction. The relative proportion of ephippia of all chydorid species, i.e. total chydorid ephippia (TCE) indicates the relative proportion of sexual reproduction during the open-water season. This thesis is part of the EPHIPPIUM-project which aims to develop ephippium analysis towards a quantitative climate reconstruction tool. To be able to develop a valid climate model, the influence of the environmental stressors other than climate on contemporary sexual reproduction and its reflection in sediment assemblages must be clarified so they can be eliminated from the model. During contemporary monitoring a few sexual individuals were observed during summer, apparently forced to sexual reproduction by non-climatic local environmental factors, such as crowding or invertebrate predation. Monitoring also revealed that the autumnal chydorid sexual reproduction period was consistent between the different lakes and climate-related factors appeared to act as the main inducers and regulators of autumnal sexual reproduction. However, during autumn, chydorid species and populations among the lakes exhibited a wide variation in the intensity, induction time, and length of autumnal sexual reproduction. These variations apparently act as mechanisms for local adaptations due to the genetic variability provided by sexual reproduction that enhance the ecological flexibility of chydorid species, allowing them to inhabit a wide range of environments. A large variation was also detected in the abundance of parthenogenetic and gamogenetic individuals during the open-water season among the lakes. On the basis of surface sediment samples, the general level of the TCE is ca. 3-4% in southern Finland, reflecting an average proportion of sexual reproduction in this specific climate. The variation in the TCE was much lower than could be expected on the basis of the monitoring results. This suggests that some of the variation detected by monitoring may derive from differences between sampling sites and years smoothed out in the sediment samples, providing an average of the entire lake area and several years. The TCE is always connected to various ecological interactions in lake ecosystems and therefore is always lake-specific. Hypothetically, deterioration of climate conditions can be detected in the TCE as an increase in ephippia of all chydorid species, since a shortening open-water season is reflected in the relative proportions of the two reproduction modes. Such an increase was clearly detected for the time period of the Little Ice Age in a sediment core. The paleolimnological results also indicated that TCE can suddenly increase due to ephippia of one or two species, which suggests that at least some chydorids can somehow increase the production of resting eggs under local environmental stress. Thus, some environmental factors may act as species-specific environmental stressors. The actual mechanism of the increased sexual reproduction seen in sediments has been unknown but the present study suggests that the mechanism is probably the increased intensity of gamogenesis, i.e. that a larger proportion of individuals in autumnal populations reproduce sexually, which results in a larger proportion of ephippia in sediments and a higher TCE. The results of this thesis demonstrate the utility of ephippium analysis as a paleoclimatological method which may also detect paleolimnological changes by identifying species-specific environmental stressors. For a quantitative TCE-based climate reconstruction model, the natural variation in the TCE of surface sediments in different climates must be clarified with more extensive studies. In addition, it is important to recognize the lakes where the TCE is not only a reflection of the length of the open-water season, but is also non-climatically forced. The results of ephippium analysis should always be interpreted in a lake-specific manner and in the context of other paleoecological proxies.

Studies on the brookite-rutile transformation

Brookite, the orthorhombic modification of titanium dioxide, transforms to the tetragonal modification, rutile, on heating. The kinetics and energetics of the transformation have been studied. Below 715±10°C, the rate of transformation is extremely slow. There appears to be little or no induction time. The kinetic data can be fitted reasonably well by the first-order equation. The energy of activation is about 60 kcal/mole and the frequency factor is of the order of 1013 h-1. The entropy of activation from Eyring's theory is about -18 cal/mole deg. at 800°C. The heat of this transformation is -100±75 cal/mole. The kinetic results may be explained qualitatively in terms of various analogies but more clearly by the application of the order-disorder theory to diffusionless transformation in solids. It has been shown that the ratio of propagation rate constant to the nucleation rate constant is small and that there is little or negligible phase aggregation.

Room-temperature synthesis of gold nanoparticles - Size-control by slow addition

We report a simple and rapid process for the room-temperature synthesis of gold nanoparticles using tannic acid, a green reagent, as both the reducing and stabilising agent. We systematically investigated the effect of pH on the size distribution of nanoparticles synthesized. Based on induction time and zeta- potential measurements, we show that particle size distribution is controlled by a fine balance between the rates of reduction (determined by the initial pH of reactants) and coalescence (determined by the pH of the reaction mixture) in the initial period of growth. This insight led to the optimal batch process for size-controlled synthesis of 2-10 nm gold nanoparticles - slow addition (within 10 minutes) of chloroauric acid into tannic acid.

Obtenção de nanocompósitos a partir da co-coagulação da borracha nitrílica e hidrotalcita

Partículas nanoestruturadas têm sido amplamente utilizadas como carga de reforço em matrizes elastoméricas, sendo substitutos eficazes das cargas convencionais, já consagradas, como o negro de fumo, mica, sílica. Em especial, as argilas têm mostrado grande potencial ao que se refere a melhor dispersão na matriz polimérica, em função de sua elevada razão de aspecto. Dentro do vasto universo de argilominerais, as argilas aniônicas, também conhecidas hidróxido duplo lamelar (HDL), apresentam como vantagem a possibilidade de ser projetada estruturalmente para as mais diversas finalidades, ao se modificar os ânions ou os cátions, ou até mesmo combiná-los na estrutura lamelar. E dentre os métodos existentes para se preparar compósitos a base de elastômero/argila, a co-coagulação do látex, é uma forma bastante eficaz e economicamente viável, uma vez que a borracha obtida após processo de coagulação já contém a carga incorporada. Este trabalho se dedicou a avaliar o processo de co-coagulação do látex de NBR e HDL, visando a obtenção de nanocompósitos. Para tanto HDL de composição Mg/Al-CO3 foi modificado com ânions DS, DBS e ST e foram preparadas suspensões aquosas, utilizando como ferramentas de dispersão ultraturrax e ultrassom de ponteira. As variáveis de processo avaliadas foram tipo e teor de HDL, tempo de mistura látex/suspensão aquosa de HDL, quantidade de coagulante e velocidade de agitação. Por fim, os coágulos obtidos foram formulados para avaliar a influência dos HDL na cinética de vulcanização e também para determinação das propriedades mecânicas convencionais. Os resultados obtidos comprovaram que a metodologia de dispersão de hidrotalcita ao látex nitrílico de modo prévio ao processo de coagulação é uma alternativa viável para a obtenção de nanocompósitos. O uso do ultrassom de ponteira como ferramenta na dispersão aquosa de HDL contribuiu para maior estabilidade da suspensão e o ajuste nos parâmetros do sistema de coagulação, levaram a obtenção de grumos uniformes do ponto de vista macroscópico e microscópico. As micrografias dos coágulos não vulcanizados obtidas por MEV-FEG confirmaram as informações apuradas a partir dos difratogramas de raios-X que apontou a formação de um sistema parcialmente esfoliado, em função da ausência dos picos característicos da hidrotalcita, além de indicarem a coexistência de partículas em dimensões micrométrica a nanométricas em uma mesma estrutura. A composição química do HDL, com a presença de átomos de magnésio e alumínio combinados com grupos hidroxila favoreceu a redução tanto o tempo de indução como de pré-cura. As propriedades mecânicas que se mostraram mais sensíveis ao grau de dispersão da carga foram a dureza, a deformação permanente à compressão (DPC) e o módulo de tração a 300% de deformação (E300), em especial para os compósitos contendo 10% m/m de HDL natural e modificado com estearato. A resistência à chama dos nanocompósitos de NBR-HDL vulcanizados apresentou um ligeiro aumento quando comparados à NBR pura, visto que esta é uma característica própria da hidrotalcita, decorrente da sua composição química

纳米流体中HFC134a水合物的生成过程

提出制冷剂气体水合物在纳米流体中快速生成的设想，通过HFC134a气体水合物在纳米铜流体（由0．04％的十二烷基苯磺酸钠（SDBS）水溶液和名义直径为25nm的纳米铜粒子组成）中的生成实验验证了此设想．实验结果表明，与去离子水中HFC134a气体水合物的生成过程相比，纳米铜流体中SDBS是造成HFC134a气体水合物诱导时问明显缩短的主要原因，而纳米铜粒子对诱导时间的影响不大；纳米铜流体中SDBS的乳化作用和纳米铜粒子大比表面积大大促进了HFC134a在水中的溶解；纳米铜粒子的加入明显加强了HFC134a气体水合物生成过程中的传热传质，随着纳米铜粒子数的增加，HFC134a气体水合物生成过程明显缩短．

气体水合物生成特性实验研究

实验研究了添加剂对甲烷气体水合物形成过程的影响。发现微量的表面活性剂降低了甲烷气体水合物在静止反应器中形成的诱导时间，并使水合物快速形成和生长，提高了水合物形成过程中的填充密度。阴离子表面活性剂（十二烷基硫酸钠）对水合物生长的促进作用比非离子表面活性剂（烷基多糖苷）强。液态烃环戊烷降低了水合物形成的诱导时间，但环戊烷不能提高水合物的填充密度。

Effect of microwave on formation/decomposition of natural gas hydrate

Natural gas hydrate (NGH) reservoirs have been considered as a substantial future clean energy resource and how to recover gas from these reservoirs feasibly and economically is very important. Microwave heating will be taken as a promising method for gas production from gas hydrates for its advantages of fast heat transfer and flexible application. In this work, we investigate the formation/decomposition behavior of natural gas hydrate with different power of microwave (2450MHZ), preliminarily analyze the impact of microwave on phase equilibrium of gas hydrate,and make calculation based on van der Waals-Platteeuw model. It is found that microwave of a certain amount of power can reduce the induction time and sub-cooling degree of NGH formation, e.g., 20W microwave power can lead to a decrease of about 3A degrees C in sub-cooling degree and the shortening of induction time from 4.5 hours to 1.3 hours. Microwave can make rapid NGH decomposition, and water from NGH decomposition accelerates the decomposition of NGH with the decomposition of NGH. Under the same pressure, microwave can increase NGH phase equilibrium temperature. Different dielectric properties of each composition of NGH may cause a distinct difference in temperature in the process of NGH decomposition. Therefore, NGH decomposition by microwave can be affected by many factors.

Study on methane hydration process in a semi-continuous stirred tank reactor

The methane hydration process is investigated in a semi-continuous stirred tank reactor. Liquid temperatures and reaction rates without stirrer are compared with those occurring with stirrer, while at the same time better stirring conditions of the methane hydration process are given by the experiments. Some basic data of fluid mechanics, for example, stirring Reynolds number, Froucle number and stirrer power, are calculated during the methane hydration process, which can be applied to evaluate stirrer capacity and provide some basic data for a scaled up reactor. Based on experiment and calculations in this work, some conclusions are drawn. First, the stirrer has great influence on the methane hydration process. Batch stirring is helpful to improve the mass transfer and heat transfer performances of the methane hydration process. Second, induction time can be shortened effectively by use of the stirrer. Third, in this paper, the appropriate stirring velocity and stirring time were 320 rpm and 30 min, respectively, at 5.0 MPa, for which the storage capacity and reaction time were 159.1 V/V and 370 min, respectively. Under the condition of the on-flow state, the initial stirring Reynolds number of the fluid and the stirring power were 12,150 and 0.54 W, respectively. Fourth, some suggestions, for example, the use of another type of stirrer or some baffles, are proposed to accelerate the methane hydration process. Comparing with literature data, higher storage capacity and hydration rate are achieved in this work. Moreover, some fluid mechanics parameters are calculated, which can provide some references to engineering application.

Hydrogen absorption in Ti45Zr35Ni17Cu3 amorphous and quasicrystalline alloy powders

Ti45Zr35Ni17Cu3 amorphous and icosahedral quasicrystal line (I-phase) powders were synthesized by mechanical alloying (MA) and subsequent annealing, the phase structure and hydrogen absorption properties of two powders were investigated. XRD analysis indicated that the MAed powder was an amorphous phase and annealed powder was an I-phase. Two alloy exhibited excellent hydrogen adsorption property and started to absorb hydrogen without induction time. PCT measurement showed that the plateau pressure of the amorphous powders was obviously higher than that of the I-phase powders. After the first hydrogen cycling, the partial amorphous phase changed to (Zr, Ti)H-2 phases, and the I-phase was steady. Similar hydride phases Ti2ZrH4 and (Zr, Ti)H-2 were also formed after the second hydrogen cycling for the amorphous and I-phase alloy powders.

Raman spectroscopic studies of the cure of dicyclopentadiene (DCPD)

The cure of polydicyclopentadiene conducted by ring-opening metathesis polymerisation in the presence of a Grubbs catalyst was studied using non-invasive Raman spectroscopy. The spectra of the monomer precursor and polymerised product were fully characterised and all stages of polymerisation monitored. Because of the monomer's high reactivity, the cure process is adaptable to reaction injection moulding and reactive rotational moulding. The viscosity of the dicyclopentadiene undergoes a rapid change at the beginning of the polymerisation process and it is critical that the induction time of the viscosity increase is determined and controlled for successful manufacturing. The results from this work show non-invasive Raman spectroscopic monitoring to be an effective method for monitoring the degree of cure, paving the way for possible implementation of the technique as a method of real-time analysis for control and optimisation during reactive processing. Agreement is shown between Raman measurements and ultrasonic time of flight data acquired during the initial induction period of the curing process. (c) 2004 Elsevier B.V. All rights reserved.

Geossintéticos em vias de comunicação: influência das condições climáticas

Trabalho de Dissertação de Natureza Científica para obtenção do grau de Mestre em Engenharia Civil na Área de Especialização de Vias de Comunicação e Transportes

Effects of copper on the antioxidant activity of olive polyphenols in bulk oil and oil-in-water emulsions

The antioxidant activity and interactions with copper of four olive oil phenolic compounds, namely oleuropein, hydroxytyrosol, 3,4- dihydroxyphenylethanol- elenolic acid ( 1), and 3,4- dihydroxyphenyl-ethanolelenolic acid dialdehyde ( 2), in olive oil and oil- in- water emulsions stored at 60 degrees C were studied. All four phenolic compounds significantly extended the induction time of lipid oxidation in olive oil with the order of activity being hydroxytyrosol > compound 1 > compound 2 > oleuropein > alpha- tocopherol; but in the presence of Cu( II), the stability of oil samples containing phenolic compounds decreased by at least 90%, and the antioxidant activity of hydroxytyrosol and compounds 1 and 2 became similar. In oil- in- water emulsions prepared from olive oil stripped of tocopherols, hydroxytyrosol enhanced the prooxidant effect of copper at pH 5.5 but not at pH 7.4. The stability of samples containing copper at pH 5.5 was not significantly different if oleuropein was present from that of the control. Oleuropein at pH 7.4, and compounds 1 and 2 at both pH values tested, reduced the prooxidant effect of copper. The lower stability and the higher reducing capacity of all compounds at pH 7.4 could not explain the higher stability of emulsions containing phenolic compounds at this pH value. However, mixtures containing hydroxytyrosol or oleuropein with copper showed higher 1,1-diphenyl- 2- picrylhydrazyl radical scavenging activity at pH 7.4 than at pH 5.5. Moreover, the compound 2- copper complex showed higher radical scavenging activity then the uncomplexed compound at pH 5.5. It can be concluded that the formation of a copper complex with radical scavenging activity is a key step in the antioxidant action of the olive oil phenolic compounds in an emulsion containing copper ions.