Navegando por Assunto "Infravermelho"

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Acesso aberto (Open Access)
Diferenciação catiônica de bentonitas por infravermelho: um estudo dos efeitos da hidratação dos cátions trocáveis
(Universidade Federal do Pará, 2020-04-13) RODRIGUES, Andréia Oliveira; PAZ, Simone Patrícia Aranha da; http://lattes.cnpq.br/5376678084716817; https://orcid.org/0000-0002-5880-7638
In the bentonite industry, the most common procedure for quality control of the ore and the sodium activation process is the swelling method. However, this tool is restricted only to the differentiation of the sodium and non-sodium types, not considering the other cationic varieties. The analysis of the composition of exchangeable cations requires laborious procedures, with daily cationic exchanges (between 3 and 6 days) and chemical analysis Via Humid, which would be unfeasible for this type of industry. Despite this, knowledge of the cationic type is of paramount importance, as it would help in the implementation of a technological route of better quality and efficiency of sodium activation. In this context, he sought in this work to establish cationic differentiation parameters for bentonites based on near and medium infrared spectroscopy for the investigation of hydration of exchangeable cations. Particle size distribution (DTP) and N2 BET adsorption-desorption isotherms were also used. Eleven smectites were studied, including one Mg-montmorillonite and two from the Clay Minerals Society repository: SWy-2 (Na-montmorillonite) and SAz-1 (Ca-montmorillonite). The clay fraction obtained by granulometric separation was characterized by FRX, DRX, CTC and PCZ. Previous heat treatment by drying at 105 ºC for 24 h and dehydration at 400 ºC for 2 h. Exchangeable cations and hydration influenced the absorption bands of water molecules in the near and medium spectral region, showing that they are strongly influenced by the size and charge of the ions (monovalent and divalent). The cationic differentiation was observed by the intensity of these bands. Absorptions close to 3620 cm-1 were attributed to water directly linked to cations, however, differentiation was only possible in samples dried at 105 ºC, because at this temperature they still remain hydrated. The reduction in the intensity of this band is due to the decrease in the water content, due to dehydration of the interlayer after heating to 400 ºC, which does not favor differentiation. The absorptions close to 3430 cm-1 were attributed to the adsorbed water molecules, as well as the complex band in 7072 cm-1, obtaining a spectrum, in descending order, Ca, Mg and Na. DRIFT spectroscopy in the nearby region was considered a simple, fast and low-cost analysis technique that allowed to distinguish different types of bentonites.
Acesso aberto (Open Access)
Influência de Gd e de elementos de transição nas propriedades físico-químicas da goethita (x-FeOOH)
(Universidade Federal do Pará, 1998-12-09) GANHEN, José Henrique de Melo; SCHELLER, Thomas; http://lattes.cnpq.br/5712304485190137
Goethite is a common mineral, easily found in surface environments, typically forming under oxidizing conditions as a product of chemical weathering of iron-bearing minerals. Several non-ferric metals have already been found in its structure, such as, for example, Cd, Co, Ni, V, Zn and Mn. The presence of these foreign elements in the structure of goethite can lead to variations in its physicochemical properties. To study variations in the following properties: unit cell dimensions, position of infrared bands, thermal properties, mineral color, degree of crystallinity and solubility product, synthetic goethite samples were prepared under mildly acidic conditions (pH ~ 4.5 ), incorporating Mn3+, Cd2+, V3+, Zr4+, Nb5+ and Gd3+ in its structure. The systematic changes in dimensions a, b and c of the unit cell, with the increase in the concentration of foreign elements in the structure, suggest that such elements replace Fe3+ in the octahedral structure of goethite and can be related to the ionic radius of the incorporated metals. The dispersion of values for the crystallographic axis a may result from distortion of the octahedron with the incorporation of non-ferric metals or structural defects. The crystallinity of the samples decreases with the increase in the concentration of foreign elements in the structure. The vibrations of the O-H bonds, out of plane, increased from 794 to 798 cm -1, indicating a slight shortening in the length of the M-OH bond (M = metal), with the increase in the concentration of incorporated metals. M-O bond vibrations, for M = Cd, Mn, V, Nb, Zr and Gd, were obtained in the region of 50 - 500 cm -1. The appearance of new vibration frequencies, compared to the pure synthetic goethite sample, and the disappearance of others, indicate the presence of metals other than iron in the structure. Data from differential thermal analysis (DTA) demonstrate that there is greater disorder in the structure, or less crystallinity of the samples, as the content of non-ferric metal in the octahedral structure of goethite increases.
Acesso aberto (Open Access)
Técnicas para avaliação do desempenho térmico e lumínico associado a sistemas de prateleira de luz em clima quente e úmido
(Universidade Federal do Pará, 2013-09-27) SILVA, Marcelle Vilar da; FRANCO, Irving Montanar; http://lattes.cnpq.br/4254203203850909
When using a daylight system in a hot and humid climate region, with a elevated number of hours of insolation and high intensity of solar radiation, it is mandatory to evaluated the effects on the thermal performance and environmental luminosity, to identify their potential for use in a controlled and appropriate manner. The aim is to carry out a performance analysis, but more specifically ensure a critic and carefull approach to methodology for assessing the increase of heat, light gains -in hot and humid climate-, through fenestrations with shading protection systems, the comparative studies of efficiency where done to compared systems with and without shading protection through the calculation of solar heat gains using the CSTB method (adapted by Frota e Schiffer), internal illuminance levels where done with computer simulations (RELUX 2006), variation of internal temperatures (ECOTEC v.2) and measurements under real sky condition, with reduced scale models, air temperature measurement, globe temperature and internal and external illuminance, using data loggers, for calculating the daylight coefficient (CLD), infrared thermal imaging to monitor the internal and external surface temperatures. Processing data with auxiliary of regression curves where used to ensure the accuracy of the measurements and identify the quality of the equipment and data refinement. Where verified as results that the systems had very similar performance, but with some relative indicative differences levels for internal illuminance. The shading method analyses shown similar analytical angle generated by the solar protections adopted the prototypes, offering a 40.14% reduction on the thermal load for the north façade. The simulations indicate that the proposed lightshelf could reveal potencial for luminance levels improvements at the center portion of the environment when compared to the tradicional shading device, indicative of potential for future studies. The internal temperature measurements generated very close values between the shelf and the traditional light shading device, what was not enough to demonstrate differential heating. Studies in infrared shown to be efficient to identify surfaces temperatures conditions as thermal energy – heat gains -, drived inside by the boards of the shading device and the lightshelf. For the light shelf the internal illuminance measurements showed significantly increased levels near the window, and at the more inner illuminance measurement point presented an difference of 500lux , this specifically occurred regarding the traditional shading device only 11:00 to 13:30. The DLF – Day Light Factor - indicated that the availability of light in the environment of the center position of the prototype is higher with light shelf than with the traditional shading device and in the more inner illuminance measurement point both indicate mostly similar performances.