XPS Study on the Stability and Transformation of Hydrate and Carbonate Phases within MgO Systems.

MgO cements have great potential for carbon sequestration as they have the ability to carbonate and gain strength over time. The hydration of reactive MgO occurs at a similar rate as ordinary Portland cement (PC) and forms brucite (Mg(OH)₂, magnesium hydroxide), which reacts with CO₂ to form a range of hydrated magnesium carbonates (HMCs). However, the formation of HMCs within the MgO-CO₂-H₂O system depends on many factors, such as the temperature and CO₂ concentration, among others, which play an important role in determining the rate and degree of carbonation, the type and stability of the produced HMCs and the associated strength development. It is critical to understand the stability and transformation pathway of HMCs, which are assessed here through the use of X-ray photoelectron spectroscopy (XPS). The effects of the CO₂ concentration (in air or 10% CO₂), exposure to high temperatures (up to 300 °C) and curing period (one or seven days) are reported. Observed changes in the binding energy (BE) indicate the formation of different components and the transformation of the hydrated carbonates from one form to another, which will influence the final performance of the carbonated blends.