Advanced synchrotron X-ray-based characterization of hydrated magnesium carbonates complemented by Raman spectroscopy

The emissions of carbon dioxide (CO2) is a major concern for the world. Cement industry contributes a significant part of it, more particularly, Portland cement is the main contributor. The thesis work focuses on characterizing hydrated magnesium carbonate (HMC) cements that can capture carbon and store permanently. In this work, HMC is formed from the reaction of magnesium hydroxide (mineral name: brucite) with sodium bicarbonate (NaHCO3) in water. Magnesium acetate (MgAc) was used as ligand separately in addition to water to check how different aqueous solutions affect the formation and conversion of HMCs. The reaction products were characterized by synchrotron X-ray based spectromicroscopy (STXM-XANES), synchrotron X-ray diffraction (SXRD), and lab-based Raman spectroscopy. The results reported the formation of various HMC phases like nesquehonite, dypingite, etc. Without MgAc, nesquehonite converted to eitelite and with MgAc, into acetate-containing giorgiosite (ACG). ACG is a relatively new phase that incorporates MgAc into its structure. Moreover, in absence of MgAc, some brucite was left unreacted even after 28 days of reaction, while with MgAc it reacted completely. The STXM-XANES study shows how polarization of X-ray beam affects the XANES spectra, while SXRD helps to identify early precipitation of ACG just after 1 day of reaction. Overall, this work contributes to the advancement of carbon-negative HMC cement and opens new pathways towards more sustainable materials for construction industry.