Navegando por Orientadores "SCHELLER, Thomas"

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Acesso aberto (Open Access)
Avaliação da reatividade de adições minerais em pasta de cimento Portlan utilizando calorimetria de fluxo de calor (Heat Flow Calorimetry).
(Universidade Federal do Pará, 2005-06-10) LACERDA, Dayane Izabelita Santos; SCHELLER, Thomas; http://lattes.cnpq.br/5712304485190137
The use of mineral additions in the production of cement compounds or in concrete elaboration generates some benefits, either from an economic point of view or when related to the environment preservation. Although limestone deposits are abundant all over the country, the introduction of residues decrease the production costs, besides the fact that the cement industry constitutes an alternative way for reciclation of some other industrial residues. The pozzolan and blast furnace slag are the main raw materials utilized as addition in the ordinary portland cement. The main advantage of their use is the low cost, the durability in aggressive environments and their low hydration heat. As for the hydration reaction, the ordinary portland cement produces hydrated compounds that directly influence its mechanical resistance. The main products are hydrated silicates, portlandite Ca(OH)2 and sulphoraluminates. On the other hand, the presence of addition minerals leads to the combination and reduction of the paste of the portlandite, with the formation of more stable and more resistant hydrated calcium silicates. The use of alternative agglomerate in ordinary portland cement has been the target of investigations in Brazil and abroad. Despite of great number of works on the subject published so far, such as Flores (1989), Marteli (1997), Hildebrando (1998), Barata & Dal Molin (2002) e Carneiro (2003), there are few data about the behavior of these residues when they are mixed to the cement, principally with respect to the study of the heat flux calorimetry of the hydration products of the cement. The isothermal or conduction calorimeter is extensively used in the research of reaction kinematics. Thermal ocouples are used to convert the thermal flow into voltage, which in turn can be monitored. The heat flow calorimeter can be used in the study of limestone carbonatation reactions, hydration reactions and liquid influence, as well as polymerization reactions and glasses, etc. The main objective of this work is the use of the heat flow calorimeter of the Applied Geochemistry and Mineralogy Group (AGMG) laboratory in the study of cement paste behavior with mineral additions, with the aim of comparing and verifying the influence of these materials in the reaction of hydration of the ordinary cement. For the calorimeter analysis, we have used an ordinary portland cement CP I, in which was added rice husk ash, fly ash, blast furnace slag (BFS), red mud, metakaolin, and silica fume in the preparation of the paste, with an water/cement ratio of 0.5, using concentrations of 10, 20, 30%, respectively, with a total duration of 50 hours. Only in the red mud we have added kaolin a calcinated at 900 ˚C, in order to neutralize the sodium hydroxide present in the sample, due to the Bayer process. X-ray diffraction analysis and thermal analysis (ATD/ATG) permitted the identification of the presence of the main products of the hydration reaction and of the portlandite. The results presented indicate that the substitution of part of the cement with mineral additions reduces the hydration heat formed during the reaction of the cement with water. However, the red mud and the metakaolin presented an antecipation of the hydration heat. The metakaolin is highly reactive, since it is composed of fine grains and a large amount of amorphous materials.
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)
Síntese e caracterização de óxidos de manganês: transformação de estruturas em camada para estruturas em túnel
(Universidade Federal do Pará, 2007-04-24) FIGUEIRA, Bruno Apolo Miranda; SCHELLER, Thomas; http://lattes.cnpq.br/5712304485190137
This work describes the preparation, characterization e application of manganese oxides with layer structure like - birnessite with alkaline ions interlayer Na+ e K+. These structures are made of the octahedron MnO6 shared by edges and/or corners as basic building block, with oxidation states +2, +3 e +4, giving vacancies in the structure and a resulting negative charge neutralized by interlayer cations. The methods already known in literature to synthesize birnessite were: reduction (K, Na-birnessite) and sol - gel (Kbirnessite). Later, this layer structures synthesized were applied to the attainment of structures in tunnel: manganite, K-hollandite, and todorokite. From the synthetic methods, the most practical and efficient for the preparation of layer structures were chosen for study with the idea of making these compounds accessible to those interested in studying their different aspects. Some modifications were introduced into the original synthesizing route in order to adapt it to the possibilities and necessities of laboratory of geosciences, UFPA, as well as to overcome the problems which appeared during the experimental work.