In Situ Bragg Coherent Diffraction Imaging Study of a Cement Phase Microcrystal during Hydration

Results of Bragg coherent diffraction imaging (BCDI) confirm that ion migration and consumption occur during hydration of calcium monoaluminate (CA). The chemical phase transformation promotes the hydration process and the formation of new hydrates. There is a potential for the formation of hydrates near where the active ions accumulate. BCDI has been used to study the in situ hydration process of CA over a 3 day period. The evolution of three-dimensional (3D) Bragg diffraction electron density, the “Bragg density”, and strain fields present on the nanoscale within the crystal was measured and visualized. Initial Bragg densities and strains in CA crystal derived from sintering evolve into various degrees during hydration. The variation of Bragg density within the crystal is attributed to the change of the degree of crystal ordering, which could occur through ion transfer during hydration. The observed strain, coming from the interfacial mismatch effect between high Bragg density and low Bragg density parts in the crystal, remained throughout the experiment. The first Bragg density change during the hydration process is due to a big loss of Bragg density as seen in the image amplitude but not its phase. This work provides new evidence supporting the through-solution reaction mechanism of CA

Ethylene Glycol and Its Mixtures with Water and Electrolytes: Thermodynamic and Transport Properties

A comprehensive thermodynamic model has been developed for calculating thermodynamic and transport properties of mixtures containing monoethylene glycol (MEG), water, and inorganic salts and gases. The model is based on the previously developed mixed-solvent electrolyte (MSE) framework, which has been designed for the simultaneous calculation of phase equilibria and speciation of electrolytes in aqueous, nonaqueous, and mixed solvents up to the saturation or pure solute limit. In the MSE framework, the standard-state properties of species are calculated from the Helgeson–Kirkham–Flowers equation of state, whereas the excess Gibbs energy includes a long-range electrostatic interaction term expressed by a Pitzer–Debye–Hückel equation, a virial coefficient-type term for interactions between ions and a short-range term for interactions involving neutral molecules. Model parameters have been established to reproduce the vapor pressures, solubilities of solids and gases, heat capacities, and densities for MEG + H₂O + solute systems, where the solute is one or more of the following components: NaCl, KCl, CaCl₂, Na₂SO₄, K₂SO₄, CaSO₄, BaSO₄, Na₂CO₃, K₂CO₃, NaHCO₃, KHCO₃, CaCO₃, HCl, CO₂, H₂S, and O₂. In particular, emphasis has been put on accurately representing the solubilities of mineral scales, which commonly appear in oil and gas environments. Additionally, the model predicts the pH of mixed-solvent solutions up to high MEG contents. On the basis of speciation obtained from the thermodynamic model, the electrical conductivity of the MEG + H₂O + NaCl + NaHCO₃ solutions is also calculated over wide ranges of solvent composition and salt concentration. Additionally, associated models have been established to compute the thermal conductivity, viscosity, and surface tension of aqueous MEG mixtures