Heat of Sublimation of CaO

Studies on the mechanism of atom formation in graphite furnace atomic absorption spectrometry

“…This conclusion is supported by observations by Aggett and Sprott (14) that the appearance temperature for atomization of aluminum is the same from both a carbon and a tantalum atomizer. A reasonable interpretation of the results is based on the following reaction: A1203(b) (67) and the bond energies of A10(g) (66,68) and 0^, is 221 kcal mol-1, in good agreement with the observed Ea value. When most of the Al203(8) has vaporized, thereby depleting the supply of Al203(g), A10<g) becomes the dominant precursor of Al(g).…”

“…Since carbon reduction of CaO(s) is not favorable at 1900 K (Table I), it must be concluded that Ca(g> is formed by thermal dissociation of CaO. The heat of vaporization of CaO is 147 ± 15 kcal mol-1 (66), and as a result CaO(g), compared to the gaseous products of its dissociation, is a minor gas phase species in equilibrium with CaO(s) (63). As found in the cases of the oxides of Zn, Cd, Mg, and Mn, it is to be expected that, under these conditions, the atomization energy of CaO should correspond to the negative of the heat of formation of CaO<s) from the elements in their standard states at 1900 K, i.e., CaO(S) -* Ca<g) + 1/202(g); AH{900 = 188 kcal mol-1.…”