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Show A problem with particle coagulation was frequently observed while developing the separation methods. At times the top fraction would transform from an opaque suspension to a clear liquid phase containing rapidly-settling visible aggregates. A series of coagulation experiments were conducted using various liquid phases including isopropyl alcohol, ethyl alcohol / water mixtures with HC1 or N a O H added to adjust pH, and with dilute detergent solutions (to simulate improperly rinsed glassware). The conditions separating stable particle suspensions from rapid coagulation were not conclusively determined. However, coagulation could be avoided by keeping the concentration of the suspension very dilute. Concentrations below 0.01 -0.05 m g of soot per ml liquid did not coagulate overnight, and concentrations as high as 0.1 m g of soot per ml were usually stable long enough to perform separations. This established the quantities of starting fly ash and ethyl alcohol used for the separations. Properties of Refined Fractions Yield of the refined soot and char products from the bulk sample separation method typically represented less than 1 0 % recovery of the starting material. The remainder was in the intermediate washing which were discared. Multiple batches were run to generate the necessary amount of sample needed for analysis. Initially, there was an expectation that the amount of soot could be correlated with the surface area per mass of fly ash. Table 5 shows the B E T surface area for selected samples. Both the soot and char fractions from different fuels and combustion conditions show a wide range of surface area. The low surface area of the C K char fraction is consistent with the char annealing reported by Hurt. [9] Unsworth et al. reported using the presence of multiple peaks in the oxidation rate during constant heating rate T G A to distinguish soot, vitrinite char and inertinite char in samples collected from a flat flame burner. [23, 24] Samples of laboratory and power plant fly ash, both as-collected and fractionated, were analyzed by T G A to see if this would provide an alternative method to quantify soot and char in mixtures. Table 6 shows preliminary T G A data for selected samples. As expected, the Char and Soot 12 September 4, 1998 |