Navegando por Assunto "Mullita"

Agora exibindo 1 - 2 de 2

Acesso aberto (Open Access)
Caracterização mineralógica e geoquímica e estudo das transformações de fase do caulim duro da região do Rio Capim, Pará
(2003-12) CARNEIRO, Bruno Santana; ANGÉLICA, Rômulo Simões; SCHELLER, Thomas; CASTRO, Elton Anderson Santos de; NEVES, Roberto de Freitas
The Capim region (Pará State, northern Brazil) is the most important kaolin district in the Amazon region, with the largest Brazilian reserves of high whiteness kaolin for the paper coating industry. The main ore (soft kaolin horizon) is located at a depth of about 20 m, being covered by a hard, iron-rich kaolin level, also called flint or semi-flint kaolin, besides a sandy-clay overburden. The beneficiation of this kaolin produces large volumes of wastes, composed mainly of coarse-grained kaolinite, deposited in basins that occupy extensive areas. The main objective of this work is to carry out mineralogical and geochemical studies of the hard kaolin, and to evaluate its thermal transformations through calcination up to 1500 oC. The results show a mineralogical composition dominated kaolinite. The evaluated thermal transformations allows us to describe a series of chemical reactions from kaolinite to metakaolinite and further development of spinel, cristobalite and mullite. For the two analyzed samples, such transformations can start at different temperatures as a result of the different chemical compositions, mainly the iron contents.
Acesso aberto (Open Access)
Transformações térmicas e propriedades cerâmicas de resíduos de caulins das regiões do rio Capim e do rio Jari – Brasil
(Universidade Federal do Pará, 2006-03-23) MARTELI, Marlice Cruz; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607; NEVES, Roberto de Freitas; http://lattes.cnpq.br/9559386620588673
Mullite, Al6Si2O13, is a relatively rare mineral in nature, formed under exceptional conditions of high temperature and pressure, which can be used to synthesize this mineral. Mullite presents excellent mechanical resistance at high and normal temperatures; low thermal expansion coefficient; good chemical and thermal stability. Such characteristics explain the importance of mullite in traditional and advanced ceramics. This research proposes the development of a process to synthesize mullite using the wastes from kaolin processing industries located in the rio Jari (Monte Dourado-PA) and rio Capim (Ipixuna-PA) districts. Preliminary studies are made on the synthesized materials for application as base materials for grog and silicon-aluminum refractory bricks. The steps are: (a) mineralogical and chemical characterization, verifying the differences between the materials; (b) processing through calcinations of the wastes at increasing levels of temperature with 100 oC increments, ranging from 600 to 1500 oC, during 3 hours at each level, so mineralogical changes can be observed and; (c) the study of temperature and impurities effects through X-ray powder diffraction, scanning electron microscopy, green bodies cleavage, thin layer and polished section; and of ceramics properties, through green bodies retraction (shrinking). The results of this work indicate that detrites from kaolin industries at rio Jari and rio Capim are constituted mainly by kaolinite. The PR samples showed a higher level of structural order than the CR samples. The increase in calcination temperature favored agglomeration in both samples. A higher content of Fe in the CR samples influenced mullite formation, activation energy, and linear shrinking in sintering. Also, through to the results of the refractarity essays, both industrial waste samples showed that they can be used as starting materials for refractories and grog.