PNNL

Abstract

Understanding of crystalline carbonate composition requires reliable models of the fundamental controls on metastable intermediate phase composition. Here we use small-angle X-ray scattering (SAXS), X-ray pair distribution function (PDF), thermogravimetric analysis (TGA), inductively coupled plasma mass-spectrometry (ICP-MS), and transmission electron microscopy (TEM) to determine the composition-dependent density of an amorphous Ca Sr carbonate (ACSC) solid solution and use the measurements to evaluate ab initio molecular dynamics (AIMD) generated models. Experiments indicate co-correlated Sr and water contents that preserve a continuous additive volume, suggesting that water in ACSC is structural and the carbonate anion radius is significantly smaller compared to crystalline carbonates. Measured densities are ?ACC = 2.195 ± 0.034 g/cm3 and ?ASC = 2.971 ± 0.034 g/cm3. At low water content, n, AIMD models are in good agreement with experiments, but predict changes in coordination at higher n that are not observed in experiment.