Infiltration of highly concentrated solutions into unsaturated sand is suspected to be affected by the liquid-gas interfacial tension between the resident water and that of the infiltrating solution. The wetting of non-porous solid surfaces by liquids is commonly quantified by contact angle measurements. However, it is well known that wettability of porous solids cannot be accurately obtained by optical inspection because the liquid is penetrating into the pores of the solid in question. The main objective of this investigation was to find an effective method to measure contact angle in coarse porous media such as sandy soils. In this study, we compare both static and dynamic methods to estimate the contact angle formed by solutions of varying surface tension on silica sands. In addition, the contact angle of the imbibing solutions is estimated in both dry and water-wetted sand. Experiments in this study employed three clear acrylic columns of known volume to determine contact angles using two methods, one static method and one dynamic method. The three acrylic columns were packed with the same mass of each grade of Accusand�� (40/50, 30/40, 20/30, and 12/20 grades respectively) for triplicate measurements. The solutions used in this study included (1) pure water and (2) 5 molal NaNO��� and (3) n-hexane as a reference. The static method estimated contact angles in initially dry sand of 23�� for 40/50 sand, and 30�� to 33�� for 12/20, 20/30, and 30/40 sands, with the same values obtained for both solutions. Contact angles of these solutions observed in the dynamic test, were twice those found in the static test (averaging 45�� and 62�� respectively). In the case of pre-wetted sands, dynamic imbibition with water provided an estimated contact angle of 2��, while the NaNO��� solution yielded 21�� contact. Based on relative surface tensions of water and the 5 molal NaNO���, the Young's equation predicts a contact angle of 25��. These results strongly support recent claims of effective contact angles between these miscible, but contracting, fluids. The observed data suggest that the zero contact angle assumption is a poor one even for clean dry silica sand. In a dynamic system, gravitational forces cannot be ignored in course porous media. An analytical method, used to model imbibition of the solutions into the silica sands, was both accurate and useful for estimating contact angle. / Graduation date: 2002

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Made available in DSpace on 2014-06-11T19:25:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-03-06Bitstream added on 2014-06-13T20:53:37Z : No. of bitstreams: 1 saliba_lf_me_ilha.pdf: 2689127 bytes, checksum: 77157443fa70337c82aeb80e43ec516e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A sílica mesoporosa do tipo MSU-4 foi sintetizada a partir do agente direcionador de estrutura Tween 20, utilizado como molde, e do precursor inorgânico tetraetilortosilicato (TEOS). Estruturas mesoporosas tem sido aplicadas em estudos luminescentes por apresentarem alto índice de organização, grande área superficial e distribuição regular de tamanho de poros. Nesse trabalho a sílica mesoporosa foi funcionalizada com 3-aminopropiltrietoxisilano (APTES) para aplicação luminescente. A sílica mesoporosa funcionalizada foi caracterizada por difração de raios-X a baixo ângulo (SAXS), espectroscopia no infravermelho (FT-IR) e adsorção e dessorção de nitrogênio (BET). O material luminescente foi preparado pela formação do complexo [Eu(tta)3] em meio metanólico e impregnado nos canais da sílica mesoporosa. Para a impregnação, o íon Eu3+ foi primeiramente encapsulado na sílica e posteriormente foi adicionado o ligante 2- tenoiltrifluoroacetona (tta). Esse procedimento foi realizado para as sílicas lavada, calcinada e funcionalizada. Uma amostra de sílica funcionalizada foi preparada com a impregnação do complexo já pronto. Todas as amostras foram caracterizadas por espectroscopia luminescente. O estudo espectroscópico foi realizado à temperatura ambiente e os espectros de excitação mostraram a absorção de energia pelo ligante tta na faixa do ultravioleta. Os espectros de emissão mostraram as transições características do íon Eu3+, dos estados de maior energia 5D0 para os de menor energia 7F0-4. Foi observado que a transferência de energia do ligante para o íon Eu3+ foi eficiente. A transição hipersensitiva 5D0→7F2 mostrou o efeito das diferentes superfícies da matriz de sílica. PALAVRAS CHAVE: Sílica mesoporosa, luminescência, európio. / MSU-4 type mesoporous sílica has been synthesized with polyoxyethylenesorbitan monolaurate (Tween 20) as structure-directing agent (MTS) as a template and tetraethyl orthosilicate Si(OEt)4 (TEOS) as silica source. The mesoporous structures have a wide application in the luminescence study because of their organization, large surface area, and size of pores. In this work, MSU-4 mesoporous silica was functionalized with 3-amino-propyl-triethoxysilane (APTES) for luminescence applications. Mesoporous silica and amino-functionalized silica was characterized by small-angle X-ray scattering (SAXS), infrared spectroscopy (FT-IR) and nitrogen adsorption/desorption isotherms at 77 K (BET). A luminescent material was prepared by formation of the complex Eu(tta)3 in methanolic medium within the channels of MSU-4 type ordered mesoporous silica. Using simple wet impregnation methods, the europium ion was first encapsulated followed by ligand 2-thenoyltrifluoracetonate (tta) addition. This process it was done for washed, calcined and functionalized mesoporous silica. Analogous one sample of functionalized silica was impregnated with the complex already ready. All samples were characterized by photoluminescence spectroscopy. The spectroscopy studies in room temperature showed the energy absorption of the ligand range ultraviolet in excitation spectra. The emission spectra this materials displayed the typical Eu3+ intra-4f6 lines ascribed to transitions between the 5D0,1 excited states and the ground multiplet (7F0-4). Negligible emission from the organic part of the encapsulated species was observed, indicating that energy transfer from the ligands to the Eu3+ ion was quite efficient. The hypersensitive 5D0→7F2 line showed the mesoporous silica effect in luminescence europium chelate.

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This thesis addresses the tensile capacity and load-deflection behavior of wedge-type expansion and undercut anchors in concrete affected by alkali-silica reaction (ASR). ASR is a chemical reaction that occurs between alkalis in the cement and silica in the aggregates. The reaction occurs with the presence of moisture, forming a gel which expands and causes micro-cracking in the concrete. Researchers conducted 85 static unconfined tensile tests on control and ASR-affected specimens. The results indicate that anchors in concrete cracked due to ASR perform like anchors in concrete cracked due to other mechanisms. Up to a threshold value of the Comprehensive Crack Index (CCI) of at least 1.5 mm/m, all cracking, regardless of cause, has the same effect on the tensile breakout capacity of mechanical and undercut anchors. / text

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A selective sloped silicon dioxide etching method has been studied using a temperature controlled diode-type reactive ion etch system with CHCl₃, C₂F₆, H₂ and N₂ gases. The SiO₂ was covered by a polyimide mask with vertical sidewalls and window openings from 1.25-4 microns. Control of the sidewall slope in SiO₂ is possible through varying the ratios of CHCl₃ and C₂F₆. High percentages (95-100%) of CHCl₃ resulted in low etch rates of 420 angstroms/min. Large slopes of up to 65 degrees are possible. With C₂F₆ above 5%, larger etch rates close to 2000 angstroms/min. occur and etching becomes vertical with purely anisotropic profiles at 10% C₂F₆. In a simulation study, SiO₂ sidewall slope was found to be controlled by the isotropic deposition rate as well as the anisotropic etch rate. Optical Multichannel Analysis of the discharge showed an increase in silicon dioxide removal when the percentage of C₂F₆ was increased. (Abstract shortened with permission of author.)

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