| 1. |
- Elmquist, Lennart, 1967-, et al.
(författare)
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On the relation between primary and eutectic solidification structures in gray iron
- 2012
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Konferensbidrag (refereegranskat)abstract
- The solidification of hypoeutectic gray cast iron starts with the nucleation of primary austenite crystals. Before graphite is nucleated, and the eutectic structure is formed, these crystals start to grow as columnar or equiaxed dendrites. However, very little is known about these dendrites, and especially how they influence the subsequent eutectic structure. Besides, it has previously been shown that the primary solidification structure influences the formation of defects. Shrinkage porosity was found between the dendrites, in the grain boundaries, and the formation of the primary solidification structure was found to influence problems related to metal expansion penetration. Therefore a better understanding about the formation of this structure is of importance. In this work, different inoculants and their influence on the formation of the micro- and macrostructures has been investigated. The inoculants considered are commercially used inoculants, i.e. inoculants used in the foundries, as well as different iron powders. The addition of iron powder is used to promote the primary solidification structure. It is shown that the nucleation of the dendrites is influenced by the amount of iron powder. Secondary dendrite arm spacing is a quantitative measurement in the microstructure related to these dendrites, which in turn depends on the solidification time. Eutectic cell size, on the other hand, is found to depend on secondary dendrite arm spacing. It is shown how the addition of inoculants influences both primary and eutectic solidification structures, and how they are related to each other.
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| 2. |
- Escalera, Edwin, et al.
(författare)
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Thermal treatment and phase formation in kaolinite and illite based clays from tropical regions of Bolivia
- 2012
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Ingår i: 6th EEIGM International Conference Advanced Materials Research. - Bristol : IOP Publishing Ltd.
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Konferensbidrag (refereegranskat)abstract
- The aim of this study was to compare the thermal behaviour of clays containing illite and kaolinite in various proportions. The clays contained small amounts of K and Fe, which act as fluxing agents. In order to investigate the phase formations during heating, the samples were examined in a differential scanning calorimeter at temperatures up to 1300°C. The thermal expansion of the samples was determined by dilatometer measurements from room temperature up to 1150°C. Phases were identified using x-ray diffraction and scanning electron microscopy. In all samples, most of the kaolinite was transformed into metakaolinite during heating up to 650°C, while illite remained unchanged up to 950°C. There was no influence of K and Fe on dehydroxylation. Metakaolinite formed at temperatures above 950°C leading to a Si-Al spinel. Furthermore, mullite was formed in the temperature interval 1050-1150°C. In this temperature range, the mechanism of mullite formation depended on the amount of K and Fe in the samples, changing the temperature of formation of mullite. It was observed by x-ray diffraction that most of the illite was transformed into a Si-Al spinel phase at 1050°C, and during further heating transformed into mullite. An increased amount of illite in the clays slightly decreased the melting temperature. The dilatometer measurements showed expansion and shrinkage for the dehydroxylation and spinel-phase formation, respectively.
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