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Show Systems Control Corp. cascade impactor, providing on-line size classification of all particles having an aerodynamic diameter greater than 0.1 ~m. Particles smaller than 0.1 ~m were collected on a backup filter. 2. deposition of a portion of the supermicron particles on a deposit collection probe. This probe utilizes variable diameter (0.05 in. - 0.125 in.) uncooled mullite tubes, oriented perpendicular to the gas flow, and inserted into the hot particle-laden flow. The supermicron particles are inertially impacted on the tube surfaces at velocities of 1-5 mis, and the amount collected is dependent both on the particle stickiness and aerodynamic impaction efficiency. The capture efficiency is determined from the ratio of the mass of deposit on the substrate to the mass of the particles that passed through the projected area of the substrate tubes. RESULTS AND DISCUSSION Predicted Oxidation Behavior During pyrite oxidation, the duration of the melt phase is important because of its implications for deposition. If a liquid film is present on the surface of an impacting particle, a significant portion of its initial kinetic energy would be lost upon impact via viscous dissipation. This dissipation process minimizes particle rebound and significantly increases its deposition or sticking efficiency.11 Examining the transformations of excluded 45 ~m pyrite particles for typical pulverized coal combustion conditions (1450 K, 5 percent 02) shows that the predominant steps are pyrrhotite oxidation and magnetite crystallization (Figure 3). Note that the fractional time for which a melt state is present constitutes more than 80 percent of the total time for conversion to solid magnetite. The duration of the entire oxidation step is found to be approximately proportional to the square of the particle diameter, as a result of the domination of boundary layer diffusional processes. This clearly indicates that the absolute duration of the me l t phase will be substantially increased for larger particles. If a transforming 7 |