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Materiais porosos e compósitos quimicamente modificados com zircônio (IV) e ácido fosfórico : preparação e aplicações eletroanalíticas /Silveira, Tayla Fernanda Serantoni da. January 2016 (has links)
Orientador: Devaney Ribeiro do Carmo / Resumo: O presente trabalho descreve as propriedades espectroscópicas e eletroanalíticas de um composto formado entre o Zr (IV) e ácido fosfórico (ZrP), bem como um espongilito inorganofuncionalizado com Zr (IV) (EZr). Em uma primeira etapa, os materiais foram preparados e caracterizados empregando diferentes técnicas, tais como: Espectroscopia de fotoelétrons excitados por raios-X (XPS), Espectroscopia na região do infravermelho (FTIR), Ressonância magnética nuclear no estado sólido (RMN), Microscopia eletrônica de varredura (MEV), Energia dispersiva de raios-X (EDS), Difração de raios-X (DRX), Análise termogravimétrica (TGA) e Análise de área superficial e porosidade. Em uma segunda etapa, realizou-se um estudo sobre as propriedades eletroquímicas desses materiais após a formação de compósitos com complexos metálicos de hexacianoferrato (ZrPAgH e EZrCuH), utilizando um eletrodo de pasta de grafite. O eletrodo de pasta de grafite contendo ZrPAgH mostrou-se sensível a concentrações de hidrazina e também a compostos sulfidrílicos, tais como: N-acetilcisteína, L-cisteína e L-glutationa. O eletrodo de pasta de grafite contendo EZrCuH foi aplicado na detecção de N-acetilcisteína, L-cisteína, nitrito, piridoxina e hidrazina, com sucesso. / Doutor
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Aplicação da espectroscopia na região do visível e infravermelho próximo na avaliação não-destrutiva de materiais cimentícios / Application of visible and near-infrared spectroscopy in the non-destructive evaluation of cement materialsSantos, Rochelle Schneider dos January 2014 (has links)
O século 21 vem sendo caracterizado pela urbanização acelerada em países economicamente emergentes. O aumento das construções em áreas urbanas, quando mal planejado, ocasiona problemas estruturais e espaciais que afetam diretamente os cidadãos e seu entorno. Muitas pesquisas científicas propõem métodos para monitorar a qualidade dos materiais utilizados em obras de engenharia. As inspeções de qualidade mais aplicadas são feitas em materiais relacionados à estrutura, como o concreto. Todo o concreto utilizado em obra é obrigatoriamente submetido ao ensaio à compressão axial, que rompe os corpos-de-prova. Estes ensaios destrutivos não são realizados in loco e todo o material utilizado é descartado após análise. Neste sentido, o sensoriamento remoto pode ser utilizado no mapeamento e monitoramento de materiais de construção, permitindo investigar e identificar diversos componentes de forma não-destrutiva. Os materiais podem ser inspecionados diretamente no local da obra, de uma forma rápida, não-invasiva e de baixo custo, características imprescindíveis no processo contínuo da construção civil. Neste trabalho foi utilizado o equipamento espectrorradiômetro FieldSpec 3 para medir materiais cimentícios à base de cimento Portland (pasta de cimento, argamassa e concreto). Nas amostras de pasta de cimento e argamassa, analisou-se o comportamento espectral de quatro diferentes resistências mecânicas e nas amostras de concreto avaliou-se a diferença entre o comportamento espectral de concretos submetidos a carregamento precoce e concretos de referência. As curvas espectrais geradas pelo registro da radiação eletromagnética refletida e absorvida das amostras foram interpretadas com base na teoria de espectroscopia vibracional e eletrônica. Esta dissertação tem um caráter inovador e a técnica aplicada é extremamente promissora e praticável como um método alternativo. Na literatura não existem estudos que já fizeram esta investigação, nem trabalhos acadêmicos com o propósito de diferenciar resistências mecânicas a partir da análise e interpretação de assinaturas espectrais destes materiais. O objetivo deste trabalho é mostrar uma técnica auxiliar inédita para analisar corpos-de-prova sólidos, utilizando a espectroscopia no visível e infravermelho próximo. O resultado deste estudo constatou que as amostras de pasta e de argamassa apresentaram contraste espectral e detectou a presença e proporção de água nas amostras. Também identificaram-se diferenças entre o comportamento espectral dos concretos de referência e o dos pré-carregados, evidenciando-se a aplicabilidade desta ferramenta na identificação da microfissuração do concreto. Com auxílio da transformada de wavelet foi possível comprovar estatisticamente o contraste espectral e que a profundidade das feições de absorção da água é inversamente proporcional à resistência mecânica, para materiais cimentícios como a pasta e argamassa. A técnica apresentada foi considerada bastante promissora como ferramenta auxiliar na avaliação da qualidade de materiais cimentícios à base de cimento Portland. / The 21st century has been characterized by rapid urbanization in economically emerging countries. The increase of constructions in urban areas, when not planned correctly, causes structural and spatial problems that directly affect citizens and their surroundings. Many scientific researches propose methods to monitor the quality of materials used in engineering works. The quality inspections more applied are made in materials related to the structure, like concrete. All the concrete used in the side work must be submitted to axial compression test, which breakes the samples. These destructive tests are not done in loco and all the material used is discarded after analysis. This way, the remote sensing can be used for mapping and monitoring of construction materials, allowing to investigate and to identify many components in a non-destructive way. The materials can be inspected directly inside the side work, in a quick way, non-invasive and low cost, indispensable characteristics in the ongoing process of civil construction. In this work a piece of equipment FieldSpec 3 spectroradiometer was used to measure cement materials based on Portland cement (cement paste, mortar and concrete). In the cement paste and mortar samples was analyzed the spectral behavior of four different compressive strengths and in the concrete samples was analyzed the difference between the spectral behavior of concretes submitted to early loading and concretes of reference. The spectral curves produced by register of electromagnetic radiation reflected and absorbed of the samples were interpreted based on the theory vibrational and electronic spectroscopy. This dissertation is an innovation and the technique applied is extremely promising and feasible as an alternative method. In the literature there are no studies that have already done this research or academic papers with the purpose of differentiate compressive strengths from the analysis and interpretation of their spectral signatures. The objective of this work is to show an original technique to analyze solid samples using the spectroscopy in the visible and near infrared. The result of this study found that the samples of cement past and mortar showed spectral contrast and detected the presence and proportion of water in the samples. Besides it identified differences between the spectral behavior of early loading and concretes of reference, highlighting the applicability of this tool in the identification of the concrete microcracking. With the help of wavelet transform was possible to prove statistically the spectral contrast and that the depth of water absorption features is inversely proportional to the compressive strength, for cement materials such as paste and mortar. The technique presented was considered very promising as an assistant technique in quality appraisal of cement material based on Portland cement, may complement information obtained by conventional techniques.
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Pozolanicidade do metacaulim em sistemas binários com cimento Portland e hidróxido de cálcio. / Pozzolanic metakaolin in the binary systems with Portland cement and calcium hidroxide.Engler Apaza Medina 23 September 2011 (has links)
O metacaulim é um material pozolânico que vem sendo pesquisado e adotado em vários países. O metacaulim é constituído basicamente de sílica (SiO) e alumina (Al2O3) na fase amorfa, capaz de reagir com o hidróxido de cálcio Ca(OH) gerado durante a hidratação do cimento Portland, formando produtos hidratados similares aos decorrentes da hidratação direta do clinquer Portland. Esta pozolana acelera o processo de hidratação do cimento, formando silicato de cálcio hidratado (C-S-H) adicional. O conhecimento das características do metacaulim que influenciam a interação com a cal, se faz necessário para subsidiar medidas preventivas com relação ao consumo de portlandita. O presente trabalho visa determinar as características físico-químicas relevantes para o entendimento da atividade pozolânica, avaliando as reações propiciadas pelo metacaulim em sistemas binários. Para este propósito, realizaram-se estudos experimentais em pasta e concreto, usando as técnicas de difratometria de raios X e de termogravimetria. As etapas experimentais consistiram: na caracterização do metacaulim, com ênfase na determinação do teor da fase amorfa; a avaliação da cinética da reação em sistema metacaulim/hidróxido de cálcio e análise da evolução da hidratação de cimento com alto teor de metacaulim. Nos sistemas cimenticios de concretos com diferentes teores de substituição de metacaulim com e sem cal hidratada, foi avaliado o comportamento da resistência à compressão. No metacaulim estudado, o teor da fase amorfa foi de 74,60% e o restante (25,40%) atua como material inerte, e o consumo máximo por atividade pozolânica, foi de 1,34 gr de Ca(OH)/grama de fase amorfa de metacaulim. Na evolução das reações, por atividade pozolânica o C-S-H foi formando gradativamente. A adição de 15% de metacaulim e 5% de cal hidratada em concretos proporcionou um ganho de resistência de 17% a mais em função do concreto de referência. / The metakaolin is a pozzolanic material that has been investigated and adopted in several countries. The metakaolin consists primarily of silica (SiO) and alumina (Al2O3) in the amorphous phase, and can react with calcium hydroxide Ca (OH) generated during hydration of Portland cement to form products similar to those obtained during Portland clinker basic hydration. This pozzolana could accelerate the hydration of cement, forming calcium silicate hydrate (C-S-H) additional. The knowledge of the characteristics of metakaolin that influence the interaction with lime provides the necessary subsidize to prevent excessive consumption of portlandite. This paper aims to determine the physical and chemical relevant characteristics in order to understand the pozzolanic activity, evaluating the responses provided by the metakaolin in binary systems. For this purpose, experimental studies were conducted in paste and concrete, using the techniques of X-ray diffraction and thermogravimetry. The experimental steps consisted of: the characterization of metakaolin, with emphasis on determining the amorphous phase content, this evaluation of the kinetics of the reaction system metakaolin and calcium hydroxide; The analysis of the evolution of the cement hydration with high content of metakaolin. In cementitious systems of concrete with different metakaolin replacement levels with and without hydrated lime, was rated the behavior of the compressive strength. The content of amorphous phase In the studied metakaolim was 74.60% and the remainder (25.40%) acts as an inert material, and the máximum consumption by pozzolanic activity was 1.34 g of Ca (OH)/g amorphous phase of metakaolin. During the evolution of pozzolanic reactions, the C-S-H was gradually formed. The addition of 15% metakaolin and 5% hydrated lime in concrete has a strength gain of 17% more depending on the reference concrete.
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Oxido misto de SiO2/SnO2,SiO2/SnO2/Fosfato : propriedades e aplicações / The SiO2/SnO2, SiO2/SnO2/fosfato mixed oxide : properties and applicationsCardoso, William da Silva 08 April 2005 (has links)
Orientador: Yoshitaka Gushikem / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-04T23:27:35Z (GMT). No. of bitstreams: 1
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Previous issue date: 2005 / Doutorado / Quimica Inorganica / Doutor em Ciências
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Desenvolvimento de um eletrodo amperometrico para determinação de glutationa em eritrocitos / Development of an amperometric electrode for determination of glutathione in erythrocytesMarzal, Percy Calvo 08 August 2005 (has links)
Orientadores: Lauro Tatsuo Kubota, Nelci Fenalti Hoehr / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-05T05:16:20Z (GMT). No. of bitstreams: 1
Marzal_PercyCalvo_D.pdf: 1469754 bytes, checksum: 089db3068a7acb221eecbb8dd258a085 (MD5)
Previous issue date: 2005 / Doutorado / Quimica Analitica / Doutor em Ciências
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"Uso de pirrolidinoditiocarbamatos de manganês(II) e vanadila na preparação e aplicação de eletrodos de pasta de carbono modificados"Aline Segnini 26 June 2003 (has links)
Devido à sua baixa solubilidade em água, os pirrolidinoditiocarbamatos poderiam produzir eletrodos livres do problema de lixiviação do modificador, os quais poderiam ser usados como detectores amperométricos, em análises em fluxo e outros procedimentos hidrodinâmicos. O complexo poderia agir como um intermediário de transferência de elétrons entre o analito e a superfície eletródica, aumentando a sensibilidade da resposta analítica do sensor. Desta forma, eletrodos de pasta de carbono modificados (EPCM) com complexos de pirrolidinoditiocarbamatos anidros de diversos metais foram preparados e testados quanto à sua aplicação em técnicas voltamétricas. Os complexos de manganês(II), [MnPyr2] e cobalto(II), [CoPyr2], foram os que apresentaram os melhores resultados em termos de estabilidade e reprodutibilidade de resposta, escolhendo-se o EPCM-[MnPyr2], para uso neste trabalho. O desempenho do eletrodo foi avaliado usando voltametria cíclica, cronoamperometria e análise em fluxo, com detecção amperométrica de peróxido de hidrogênio apresentando regiões lineares de 1,25-14,8; 0,5-41; 1,0-75 x 10-4 mol L-1 e limites de detecção de 11,2; 2,98; 5,40 x 10-5 mol L-1 respectivamente para cada técnica. Na determinação de peróxido de hidrogênio em amostra de alvejante comercial observou-se concordância nos resultados obtidos em voltametria cíclica e análise em fluxo, usando o eletrodo proposto em comparação com a permanganometria clássica, com 95 % de intervalo de confiança. Estes resultados foram obtidos após otimização de parâmetros como velocidade de varredura, pH, eletrólito suporte, entre outros. A oxidação ocorre por meio de um processo eletrocatalítico. O desempenho do pirrolidinoditiocarbamato de vanadila hidratado também foi avaliado como alternativa aos ditiocarbamatos anidros, na preparação de eletrodos modificados com esta classe de complexos, considerando que os complexos hidratados seriam mais fáceis de preparar. Entretanto uma baixa estabilidade e reprodutibilidade de resposta foi observada. O [MnPyr2] mostrou comportamento no qual ocorre oxidação, concordando com a proposta de Schrauzer para ligantes do tipo ímpar, apesar de que a oxidação só ocorreu na presença de oxidantes fortes, como o peróxido de hidrogênio. / Considering their low solubility in water, the dithiocarbamate complexes should produce electrodes without problems of modifier leaching. Such electrodes could be used as amperometric detectors in flow injection analysis and hydrodynamic methods. The complex should act as an electron transfer mediator between the analyte and the electrode surface, improving the response sensitivity of the sensor. Considering these statements carbon paste electrodes modified (EPCM) with anhydrous pyrrolidinedithiocarbamates of several metals were prepared and evaluated in relation to their possible application in voltammetric techniques. Best results regarding response stability and reproducibility were obtained with manganese(II), [MnPyr2] and cobalt(II), [CoPyr2] complexes. The first one was chosen to develop the present work. The electrode performance was evaluated in cyclic voltammetry, chrono amperometric and flow injection analysis with amperometric detection. Linear dynamic ranges of 1,25-14,8; 0,5-41; 1,0-75 x 10-4 mol L-1 and limits of detection of 11,2; 2,98; 5,40 x 10-5 mol L-1 were found respectively for each technique in the determination of hydrogen peroxyde. The methods were used for the determination of H2O2 in bleaching formulation and presented agreement with the classical titration with potassium permanganate within 95% confidence level. Such results have been obtained after optimization of experimental parameters such as scan rate, pH, supporting electrolyte, and others. The oxidation occurred by an electrocatalytic process. Finally the performance of a carbon paste electrode modified with a hydrated vanadyl pyrrolidinedithiocarbamate complex was evaluated as an alternative to the anhydrous complex in the preparation of the modified electrode, since the hydrated complexes are easier to prepare. However a low response stability and reproducibility have been observed. The [MnPyr2] presented an oxidation behavior in agreement with Schrauzers predictions, although the oxidation of the metal center occurred only in the presence of strong oxidative agents as the hydrogen peroxide.
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\"Preparação e aplicação de eletrodos de pasta de carbono modificados com ditiocarbamatos para análise de fármacos\" / \"Preparation and application of modified carbon paste electrodes with dithicarbamates for analysis of farmacos\"Rita de Cassia da Silva 16 October 2006 (has links)
O morfolinoditiocarbamato (Mor); o piperidinoditiocarbamato (Pip) e o pirrolidinoditiocarbamato (Pyr) de rutênio derivados respectivamente da morfolina, piperidina e pirrolidina, três aminas alifáticas cíclicas foram preparados e caracterizados por análise elementar, espectroscopia vibracional na região do infravermelho, espectrometria de massa e análise térmica (termogravimetria TG e análise térmica diferencial DTA). A análise elementar mostrou que os compostos de fórmula geral Ru2DTC5.XH2O foram obtidos (DTC = Mor, Pip e Pyr e X = 4, 1,5 e 2 respectivamente); assim como a IV revelou que os complexos são monodentados, com duas bandas de absorção em torno de 1000 cm-1. A espectrometria de massas mostrou as estruturas moleculares e a estabilidade dos complexos, pois requerem alta energia de colisão para fragmentarem-se; alguns fragmentos puderam ser identificados. A análise térmica mostrou que após desidratação os DTC decompõem-se gerando sulfato e óxido de rutênio (III), dependendo da temperatura. Após caracterização, os complexos foram usados com modificadores na preparação de eletrodos de pasta de carbono modificados e seu desempenho avaliado por voltametria cíclica em diferentes meios e intervalos de potencial e em diferentes composições do material do eletrodo. Com base na melhor definição dos picos referentes aos processos anódicos e catódicos, assim como pela menor corrente residual, optou-se em usar como modificador o Ru2Pip5.1,5H2O, na proporção de 10% (m/m) na pasta. Eletrodos preparados com este modificador foram usados na determinação voltamétrica de carbamazepina (CBZ), usando CV. Na presença do analito a corrente do modificador aumenta proporcionalmente à concentração de CBZ no intervalo de 1,30 x 10-8 e 6,62 x 10-6 mol L-1, com limite de detecção de 3,18 x 10-7 mol L-1. O método foi aplicado na determinação de CBZ em urina sintética, usando procedimento de adição de padrão com recuperação da ordem de 97 104% e concordância com o método espectrofotométrico recomendado pela farmacopéia brasileira no intervalo de confiança de 95%. / The morpholinedithiocarbamate (Mor); piperidinedithiocarbamate (Pip) and pirrolidinedithiocarbamate (Pyr), three cyclic amines derived respectivelly from morpholine, piperidine and pirrolidine complex of Ruthenium (III) were synthesized and characterized by elemental analysis, infra-red spectroscopy, mass spectrometry and thermal analysis (thermogravimetry TG and differential thermal analysis DTA). Elemental analysis showed that complexes of general formula Ru2DTC5.XH2O ((DTC = Mor, Pip e Pyr e X = 4, 1,5 e 2 respectively) were obtained. IR spectra revelead that the ligant behaves as a monodentate one with a duplet around 1000 cm-1. Mass spectrometry showed the molecular structures and the stability of the complexes, therefore they require high energy of collision to be broken up; some fragments could have been identified. Thermal analysis showed that after dehydration the complexes decomposed generating Ru2(SO4)3 and Ru2O3 as residues depending on the temperature, according to XDR analysis. After characterization the complexes were used as modifiers in the preparation of carbon paste electrodes. The performance of the modified electrodes (MCPE) was evaluated by cyclic voltammetry at different electrode composition and supporting electrolytes and potential intervals. On basis of peak definition and background current, the MCPERu2Pip5.1,5H2O, containing 10% of the complex, was chosen for further studies. The electrode was used in the determination of carbamazepine (CBZ) cyclic voltammetry. In the presence of CBZ the modifier current increased proportionally, to the analyte concentration in the 1,30 x 10-8 and 6,62 x 10-6 mol L-1. The method was applied in the determination of CBZ in synthetic urine sample spikes with the analyte with recoveries of 97 104%. Whem compared with a standart spectrophotometric procedure the results of the prposed method agreeded within 95% of confidence, according to the t-Student test.
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Alteração do comportamento reológico da suspensão cimentícia aplicada sobre substratos porosos. / Modification of rheological behavior of cementitious paste applied on porous substrates.Waleska da Silva Barbosa 01 July 2010 (has links)
As argamassas de revestimento são amplamente utilizadas na construção civil e, suas propriedades no estado endurecido são fortemente influenciadas pelas propriedades no estado fresco, as quais dependem de fatores como: materiais empregados; forma de aplicação; e interação entre substrato e argamassa. Os ensaios utilizados para caracterização reológica das argamassas não contemplam as alterações que ocorrem devido o contato com o substrato, gerando discordâncias nas teorias sobre os fenômenos pelo qual ocorre a resistência de aderência. Sendo assim, o presente trabalho visa identificar as alterações do comportamento reológico de suspensões cimentícias aplicadas em substratos porosos por meio do ajuste do método do squeeze-flow. Para tanto, foram utilizadas duas configurações do squeeze-flow, com e sem confinamento do fluxo radial; três tipos de base, sendo uma metálica e duas porosas; e, pastas com diferentes materiais, a saber: cimento; cal e filler calcário. A escolha da pasta ao invés da argamassa foi basicamente por duas razões: primeiro, porque a pasta é a parcela da argamassa mais suscetível aos efeitos de sucção capilar do substrato; e segundo, para simplificar o cenário de análise, eliminando a variável areia. Ambas as configurações apresentaram-se viáveis na identificação da alteração do comportamento reológico da pasta, devido aos fatores como: tipo de substrato; o tempo de contato entre pasta e substrato; perda de água da pasta; e energia de mistura. Além disso, observou-se que os procedimentos adotados, assim como o auxílio de outros ensaios, podem colaborar em estudos da influência de fatores como: temperatura; rugosidade; ângulo de contato; distribuição granulométrica de pastas e argamassas; e, principalmente, compreender os fenômenos que ocorre no período denominado como tempo de puxamento, ao passo que este influencia diretamente na resistência de aderência. / Mortar renderings are used in most of the constructions and their properties in the hardened state are strongly influenced by the properties in the fresh state, which depend on factors such as materials used; application form; and interaction between substrate and mortar. The determination of rheological parameters of fresh mortars doesn\'t include the changes that occur due to contact with the substrate. It generates disagreements in the theories about the phenomena of formation of the bond strength. Therefore, this study aims to identify changes in the rheological behavior of cementitious paste applied to porous substrates by adjusting the squeeze flow method. For this, two configurations of squeeze flow were used, with and without confinement of the radial flow; three substrate types; and pastes with different materials, namely cement, lime and sand. The choice of paste instead of mortar was basically for two reasons: first, because the paste is the portion of mortar more susceptible to the effects of capillary suction of substrate; and second, to simplify scenario analysis, eliminating the variable sand. Both configurations were viable in the identification of the alteration of rheological behavior of paste, due to factors such as substrate type; the contact time between paste and substrate; loss of water from paste; and mixing energy. In addition, it was observed that the procedures adopted as well as the aid of the other tests can collaborate on studies of the influence of factors such as temperature, roughness, contact angle, particle size distribution of pastes and mortars; and above all to understand the phenomena that occurs in the initial periods of contact paste/substrate and consequently in the bond strength.
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Analysis of surface mount technology solder jointsHui, Ip Kee January 1996 (has links)
The factors determining the quality of surface mount technology (SMT) solder joints are numerous, and complex. The exploration of these factors, and how they may affect the reliability and quality of the joints can only be achieved through continuous research. In this project, essential areas of SMT joints were selected for study and analysis, with the intention of providing additional design and process guidelines for the production of quality SMT joints. In the infrared reflow process, one of the common defect phenomena is the occurrence of tombstoning; that is after soldering only one end of the component is soldered while the other is lifted up, assuming a position like a tombstone. The initiation of tombstoning during reflow was analysed based on the forces acting on the component. A model was developed to predict the initiation of this phenomenon. The model shows that, under vibration-free conditions, the surface tension of the molten solder is the source of the force causing the initiation of tombstoning. The contact angle, which varies with the length of the printed circuit board solder land, has a significant effect on the value of the surface tension acting as a force pulling upward on the component. The model further shows that tombstoning initiation is due to the combined effects of the surface tension; the weight of the component; the dimensions of the component; the length of the solder underneath the component; and the length of the solder protruding from the end of the component. Selected components were used as examples for predicting the conditions of initiation, and these conditions were further substantiated by a series of experiments. Another area of study was a method which directly pulled the components off printed circuit boards and this was used as a means for testing the bond quality of surface mount technology leadless chip solder joints. Components D7243, CC1206, RC1206, RC121O, and CC1 812 were selected for this study. It was found that the ultimate tensile force which breaks a component off the printed circuit board has the potential to be used as a parameter for measuring the quality of the solder joint. The effect of solder thickness on the strength of a joint has also been investigated. The shape of joints soldered by two methods, wave soldering and infrared reflow, were compared. Joints at the two ends of a component produced by infrared reflow were found more uniform than the ones produced by wave soldering. A recommendation is made here for the wave soldering approach in achieving uniform solder joints. The effects of solder shape on the joint strength were further investigated by finite element analysis. A convex joint was found marginally more robust than a concave joint. Two aspects of the internal structure of SMT solder joints were investigated, void content and copper/tin intermetallic compounds. The voiding conditions of wave-soldered and infrared reflow joints were compared. No voids were found in all specimens that were produced by wave soldering. However, there were always voids inside joints produced by infrared reflow. Microhardness tests indicated that the hardness of compounds at the copper/solder interface of infrared reflowed joints is lower than that in the wave-soldered joints. It is considered that the lower hardness of the interfacial region of the infrared reflowed joints is due to the presence of voids. Scanning electron microscopy was used to study the formation of copper/tin intermetallic compounds for joints produced by infrared reflow. The results show that Cu 6 Sn5 was the only compound with a detectable thickness. Other compounds such as Cu3 Sn, were virtually not found at all. Aging of the joints at 100°C, shows that both the Cu 6Sn5 and the overall interfacial thickness grew with time. One of the important areas which had been overlooked previously and was studied in some details was the effects of solder paste exposure on the quality of solder paste. The characteristic changes of solder paste due to exposure were investigated in three areas, weight loss, tackiness, and rheology. The evaporation of low boiling point solvents was considered as the main contribution to the loss in the weight of the solder paste. The weight loss against exposure time was found to follow an exponential behaviour. A method was designed to evaluate the tackiness changes of solder paste due to exposure. It was found that the decay of tackiness against exposure time can be expressed by a power law. It is recommended that solder paste manufacturers should provide the necessary characteristic constants so as to enable the characteristics to be calculated after a specific exposure. The rheological changes of the solder paste as a result of exposure were also investigated. The implication on the printability of the solder paste due to these changes was studied and discussed.
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Coupled Thermo-Hydro-Mechanical-Chemical (THMC) Processes in Cemented Tailings Backfill Structures and Implications for their Engineering DesignGhirian, Alireza January 2016 (has links)
The main result of underground mining extraction is creating of large underground voids (mine stopes). These empty openings are typically backfilled with an engineering cementitious material called cemented paste backfill (CPB). The main purpose of CPB application in underground mining is to provide stability and ensure the safety of underground openings, maximize ore recovery, and also provide an environmental-friendly means of underground disposal of potential acid generating tailings. CPB is a mixture of mine tailings, cement binder and water. CPB has a complex geotechnical behaviour when poured into mine voids. This is because of the different thermal (T), hydraulic (H), mechanical (M) and chemical coupled processes and interactions that take place in CPB soon after placement. In addition to these THMC behaviours, various external factors, such as stope geometry, drainage condition and arching effects add more complexity to its behaviour. In order to acquire a full understanding of CPB behaviour, there is a need to consider all of these THMC factors and processes together. So far, there has not been any study that addresses this research need. Indeed, fundamental knowledge of the THMC behaviour of CPB provides a key means for designing safe and cost-effective backfill structures, as well as optimizing mining cycles and productivity of mines. Innovative experimental tools and CPB testing methods have been developed and adopted in this research to fulfill the objectives of this research. In the first phase of the study, experiments with high columns are developed to study the THMC behaviour of CPB from early to advanced ages with respect to height of the column and curing time. The column experiments simulate the mine stope and filling sequence and provide an opportunity to study external factors, such as evaporation, on the THMC behaviour of CPB. However, an important factor is the overburden pressure from the stress due to self-weight that cannot be simulated through column experiments. Therefore, in the second phase of this study, a novel THMC curing under stress apparatus is developed to study the THMC behaviour of CPB under various pressures due to the self-weight of the CPB, drainage conditions, and filling rate and sequence. Comprehensive instrumentation and geotechnical testing are carried out to obtain fundamental knowledge on the THMC behaviour of CPB in different curing conditions from early to advanced ages. The results of these studies show that the THMC properties of CPB are coupled. Important parameters, such as curing stress, self-desiccation due to cement hydration, temperature, pore water chemistry, and mineralogical and chemical properties of the tailings, have significant influence on the shear strength and compressive strength development of CPB. Factors such as evaporation and drying iii shrinkage can also affect the hydro-mechanical properties of CPB. The curing conditions (such as curing stress, drainage and filling rate) also has significant impact on CPB behaviour and performance. The THMC interactions and the degree of influence of each factor should be included in designing backfill structures and planning mining cycles. This innovative curing under stress technique can be replaced the conventional curing of CPB (curing under zero stress and no THMC loadings), in order to optimize CPB mechanical strength assessment, increase mine safety and enhance the productivity.
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