XPS Study of group IA carbonates

Abstract

The results of systematic XPS measurements of all alkali metal carbonates (Li, Na, K, Rb and Cs) are presented. The first set of experiments was performed with “as received” commercial carbonate powders under liquid nitrogen conditions using a precooling procedure. A second set of experiments was performed under similar experimental conditions after a preliminary grinding (mechanical activation) of the carbonates. In addition, Na2CO3 *1H2O, NaHCO3 and KHCO3 powders were studied. It was found that sample pre-cooling allows distinction between hydrocarbonates and carbonate hydrates. Storage in air leads to formation of hydrocarbonates at the surface of Li2CO3 and Na2CO3. This phenomenon being more pronounced in the former. In contrast, K2CO3 forms a hydrate with one H2O molecule. Rb2CO3 and Cs2CO3 have hydrocarbonates as well as hydrates at the surface and this is more pronounced for Cs2CO3. Grinding of the carbonates results in the formation of hydrocarbonates at the surface, the tendency to do so was found to increase down the group IA, namely, K<Rb≪Cs. For the most part, the hydrocarbonates formed were unstable in vacuum even under liquid nitrogen conditions. Chemical trends in C 1s and O 1s binding energies in carbonates and hydrocarbonates of the Group IA are discussed and related to the nature of the anion and alkali cation.