Thermogravimetric analysis of Ontario limestones and dolomites I. Calcination, surface area, and porosity

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Abstract
The calcination of natural Ontario limestones and dolomites in a flow of 100 cm3/min of nitrogen at 745 °C required from 0.43 ± 0.03 to 0.35 ± 0.05 min/mg of 100 mesh samples, respectively. The nitrogen adsorption isotherm at 77 °K for all the calcined samples belonged to the type II isotherm of the B.D.D.T. classification. There was hardly any hysteresis between the adsorption and desorption branches which implied that most of the pores were relatively large in agreement with independent measurements of the most probable pore diameter by an Aminco mercury intrusion porosimeter (~ 0.1 μ). The B.E.T. surface areas ranged from 13.6 to 34.2 m2/g of oxide calcined at 745 °C. The surface area decreased rapidly with increasing calcination temperature. At 1090 °C the surface area was less than 1 m2/g. The surface area was also related to percentage calcination, percentage calcium oxide in the sample, and size of the sample. A sample of pure magnesium carbonate calcined at 565 °C had an inordinately large surface area of 174 m2/g; pure calcium carbonate calcined at 745 °C, 15.2 m2/g. Using a model of non-intersecting cylindrical or square capillaries for the pore configurations, one could calculate the surface area, porosity, and bulk density of the calcined samples with satisfactory agreement.

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