| The decomposition of calcium carbonate spheres was investigated using 2 mm, 5 mm, and 7 mm diameter limestone particles in a large scale thermogravimetric analyzer at near isothermal temperatures. Experiments have been conducted in atmospheres of pure N{dollar}sb2,{dollar} 7% CO{dollar}sb2,{dollar} 14% CO{dollar}sb2,{dollar} and 21% CO{dollar}sb2{dollar} mixtures. Data were interpreted in terms of an apparent activation energy, E, and frequency factor, A, assuming a first-order reaction and an Arrhenius temperature dependency of the rate constant. Microscopic analysis showed that the decomposition reaction takes place on a definite boundary between the undecomposed carbonate and the layer of porous CaO and CaCO{dollar}sb3{dollar} formed outside it. This boundary moves towards the center of the particle, but the particle remains spherical in shape.; Porosimetry and surface area measurements of shaved layers of the partially decomposed product layer have indicated that decomposition follows a "grain model" for describing the conversion of the carbonate. A grain model will be discussed and methods used to analyze these results with respect to this model will be shown. A very interesting result of this research is that greater surface areas and more porous product are formed near the outer boundary of the decomposed solid. |
