Calcium silicate hydrate-in-situ development of the silicate structure followed by infrared spectroscopy

In the current study, the development of the silicate structure of synthetic calcium silicate hydrates with different calcium contents was followed by in-situ infrared (IR) spectroscopy and correlated to the in-situ phase development evaluated by X-ray diffraction (XRD). A baseline correction method initially developed for X-ray diffractograms was successfully adapted for the complex background of the fingerprint region in in-situ IR, which significantly contributed to signal quality and reproducibility. The development of separate silicate infrared bands could be monitored over 24 h of reaction. These bands could be assigned to oligomeric and dimeric species based on their time and stoichiometry-dependent development. It was clearly shown that the main peak of the dimeric silicate species was overlooked in the literature. The correlation of time-dependent events to in-situ XRD revealed that changes in the unit cell of calcium silicate hydrate are related to silicate polymerization. The results were compared to Si-29-MAS-NMR, which highlighted the benefits of in-situ IR spectroscopy.

Automated summary

This study used in-situ infrared spectroscopy and X-ray diffraction to investigate the structural development of synthetic calcium silicate hydrates with different calcium contents. A baseline correction method initially developed for X-ray diffractograms was successfully adapted for in-situ IR, leading to improved signal quality and reproducibility. The separate silicate infrared bands were monitored over 24 hours, showing the development of oligomeric and dimeric species and revealing insights into the correlation between silicate polymerization and unit cell changes in calcium silicate hydrate. Comparisons with Si-29-MAS-NMR highlighted the advantages of in-situ IR spectroscopy.