Al-Foam Case Study

The production stages of mixing and compaction to produce the green compact (sugar-Al powder compact) were exactly the same as in the case of producing pure Al-foams [10,11]. Nevertheless the stages of dissolution and sintering had to be properly adjusted for achieving the carbon coating on the Al-foam. In this case the crystalline raw cane sugar was partially removed from the green compact by water leaching at room temperature. About 70% wt. of the sugar in the green compact was dissolved in water. When the percentage of the dissolved sugar exceeded 70% wt. inadequate or discontinuous carbon coating on the Al-foam was observed. When the percentage of the dissolved sugar was less than 60% wt. then partial collapse of the foam structure was

The decomposition temperature of raw cane sugar was crucial for determining the exact heating cycle. Therefore, thermogravimetric analysis and differential thermal analysis were used (TG-DTA) to determine the decomposition temperature of raw cane sugar along with the chemical reactions as well as the physicochemical transformations that took place during the heating stage. Twenty four (24) gr of raw cane sugar were used, whilst thermal analysis was performed under inert argon atmosphere for a temperature range from25 to 700°C employing a heating rate of 10 oC /

The minimum at 190oC on the DTA curve indicated the endothermic effect of the melting of the sugar. The TG curve shows that the weight of the sugar did not change up to the melting point. During the sugar melting the process of caramelization began. Initially the decomposition of sugar (disaccharide) to fructose and glucose monosaccharides (by removal of water molecules) occurs. Subsequently, the formation of caramel takes place [19,20]. After the melting process of sugar, its decomposition initiated and two reaction stages were distinguished. The first decomposition stage began after melting (210oC) and terminated at 340oC. The weight loss during this stage reached about 60%. In this stage the decomposition of monosaccharides was accompanied with the formation of gaseous brown coloring matter. The second stage consisted of the decomposition of the gaseous products from 340οC to 400οC. This phase was accompanied by several endothermic reactions which were attributed to reactions between the gaseous products. The TG analysis indicated that the pyrolysis to carbonaceous materials was practically completed at around 400oC, leaving a remaining mass percentage of 18%, which was composed of various forms of