"Sulfation behavior was measured at 1000 and 1200ÀC for eight calcium oxide sorbents which were well characterized in terms of particle size, pore structure, and specific surface area. Sulfation results were compared with predictions of a simple mathematical model which applied the measured sorbent characteristics. The comparisons, intended to provide direction for model development, suggest need for model improvement in areas such as global kinetics at short times, and accountability for changes in structure due to sintering during sulfation. Subsequently, the effects of the high temperatures on the surface areas of the sorbents in the absence of sulfation were also determined. Surface areas were marginally higher for the larger sorbents after 1000ÀC injection; but, in general, no correlation between particle size and surface area loss could be found. Surface area decay was shown to be very rapid in the first 200 ms, and subsequently very slow. Differences between carbonate and hydrate sorbents' reactivities were investigated using aerodynamically size-classified materials: hydrates were found more reactive on an equal prereactor size basis. Also, no thermal comminution of the hydrate particles was noted within the high temperature environment. Thus, the superiority of hydrates on a common prefiring size basis cannot be explained in terms of their fragmentation into smaller particles upon firing."