charcoal and C denotes fixed carbon. Reaction (2) represents the liberation of water from the cement during the The rate of reaction between iron oxides and heating of the pellet. charcoal, agglomerated together as pellets, hasThe thermal decomposition of charcoal is an endothermic been correlated with the swelling of the pellets and reaction. It starts in the temperature range 573-773 K. The with the morphology of the iron formed. The products of such a reaction induce reactions ( 4)-( 6). experimental techniques employed wereThe products of these reactions cause the gasification of thermogravimetric analysis, X-ray diffraction the reducing agent, reactions ( 7) and ( 8), which generates analysis, and microscopic examination of partially reducing gas (CO and H 2 ). reduced pellets. The experiments were performed Therefore, the reduction of a self-reducing pellet involves in the temperature range 1223-1423 K. The two types of reaction: conditions that favour the growing of iron in the (i) direct reaction (solid-solid) between iron oxide and form of whiskers, and hence lead to catastrophic carbon and swelling, have been determined.I&S/1400 (ii) a sequence of gas-solid reactions. As the solid-solid reaction is very slow compared with the

The steps Fe203+Fe304,

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An investigation into the effects of processing variables on the microsegregation of directionally cast samples of Cu-8 wt pct Sn alloys is presented. The samples were previously obtained in four different experimental conditions, which brought about different types of dendritic growth. Each sample had a cylindrical shape and was sectioned into transversal slices whose degree of microsegregation was measured by microprobe analyses and by quantitative metalography. A decrease in microsegregation along the longitudinal axis toward the cast sample surface was observed. This behavior was simulated by using a comprehensive microsegregation mathematical model and detailed thermal history of samples. Columnar and equiaxed regions of cylindrical samples were seen to have different levels of microsegregation, which might be the result of differences in interdendritic distances (ID), as shown by experimental evidence. It was also noticed that solute profiles calculated by a mathematical model and those obtained by microprobe analyses showed a better agreement if local dendrite arm spacing was considered in the calculations rather than an average spacing.

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