In recent years MgO-based cements have been proposed as promising alternative to traditional CaO-based cements, with the aim of both reducing the CO¬2 emissions associated with the production of Portland cement and developing sustainable materials to be used in the field of radioactive waste disposal.1 In fact, MgO-based cements were found to be more suitable for immobilization of nuclear or metal-containing waste, owing to their lower pH and corrosiveness compared to Portland cement.2 The binder properties of MgO-based cements are due to the Magnesium Silicate Hydrate (M-S-H) phase, an amorphous phase formed by the simultaneous hydration of a source of magnesium (typically highly reactive MgO) and a source of silica. The structure of M-S-H, from the sub-nanometric to the micrometric scale, and the hydration mechanisms behind its formation have recently been object of intense research.3-4 However, a full comprehension of these features and of their correlations with the mechanical properties of the final material is still lacking. In this work the multi-scale structural properties of novel MgO-based cements were investigated by means of solid-state NMR (SSNMR) spectroscopy and 1H NMR relaxometry. In particular, materials obtained by hydration of a 1:1 molar mixture of MgO and fumed silica (MgO/SiO2) and mixed formulations containing different amounts of MgO/SiO2 and Portland cement were studied. High-resolution SSNMR experiments for the observation of 1H, 29Si and 27Al nuclei, carried out on samples lyophilized at different times of hydration were exploited to obtain information on the nature and structure, at the sub-nanometric scale, of the formed phases. On the other hand, 1H T1 Fast Field Cycling (FFC) experiments and measurements of 1H T2 relaxation times, performed directly on the cement pastes, allowed us to monitor the state of water in the pastes, providing insights into the evolution of the porous structure with the hydration time. In order to achieve a deeper and more complete understanding, NMR results were compared and integrated with those obtained by X-Ray Diffraction (XRD), thermogravimetry (TGA), IR spectroscopy, Scanning Electron Microscopy (SEM) and calorimetric techniques. This work was financially supported by MIUR (FIR2013 Project RBFR132WSM). References (1) Walling, S. A.; Provis, J. L. Chem. Rev. 2016, 116, 4170-4204. (2) Zhang, T.; Vandeperre, L. J.; Cheeseman, C. Bottom-up Design of a Cement for Nuclear Waste Encapsulation. In Ceramic Materials for Energy Applications; John Wiley & Sons, Inc.: New York, 2011; pp 41- 49. (3) Chiang, W.-S.; Ferraro, G.; Fratini, E.; Ridi, F.; Yeh, Y.-Q.; Jeng, U.-S.; Chen, S.-H.; Baglioni, P. J. Mater. Chem. A 2014, 2, 12991-12998. (4) Tonelli, M.; Martini, F.; Calucci, L.; Fratini, E.; Geppi, M.; Ridi, F.; Borsacchi, S.; Baglioni, P. Dalton Trans. 2016, 45, 3294-3304.
Multi-scale structural investigation of alternative MgO-based cements by solid-state NMR spectroscopy and NMR relaxometry
F Martini;M GEPPI;L CALUCCI;S BORSACCHI
2018
Abstract
In recent years MgO-based cements have been proposed as promising alternative to traditional CaO-based cements, with the aim of both reducing the CO¬2 emissions associated with the production of Portland cement and developing sustainable materials to be used in the field of radioactive waste disposal.1 In fact, MgO-based cements were found to be more suitable for immobilization of nuclear or metal-containing waste, owing to their lower pH and corrosiveness compared to Portland cement.2 The binder properties of MgO-based cements are due to the Magnesium Silicate Hydrate (M-S-H) phase, an amorphous phase formed by the simultaneous hydration of a source of magnesium (typically highly reactive MgO) and a source of silica. The structure of M-S-H, from the sub-nanometric to the micrometric scale, and the hydration mechanisms behind its formation have recently been object of intense research.3-4 However, a full comprehension of these features and of their correlations with the mechanical properties of the final material is still lacking. In this work the multi-scale structural properties of novel MgO-based cements were investigated by means of solid-state NMR (SSNMR) spectroscopy and 1H NMR relaxometry. In particular, materials obtained by hydration of a 1:1 molar mixture of MgO and fumed silica (MgO/SiO2) and mixed formulations containing different amounts of MgO/SiO2 and Portland cement were studied. High-resolution SSNMR experiments for the observation of 1H, 29Si and 27Al nuclei, carried out on samples lyophilized at different times of hydration were exploited to obtain information on the nature and structure, at the sub-nanometric scale, of the formed phases. On the other hand, 1H T1 Fast Field Cycling (FFC) experiments and measurements of 1H T2 relaxation times, performed directly on the cement pastes, allowed us to monitor the state of water in the pastes, providing insights into the evolution of the porous structure with the hydration time. In order to achieve a deeper and more complete understanding, NMR results were compared and integrated with those obtained by X-Ray Diffraction (XRD), thermogravimetry (TGA), IR spectroscopy, Scanning Electron Microscopy (SEM) and calorimetric techniques. This work was financially supported by MIUR (FIR2013 Project RBFR132WSM). References (1) Walling, S. A.; Provis, J. L. Chem. Rev. 2016, 116, 4170-4204. (2) Zhang, T.; Vandeperre, L. J.; Cheeseman, C. Bottom-up Design of a Cement for Nuclear Waste Encapsulation. In Ceramic Materials for Energy Applications; John Wiley & Sons, Inc.: New York, 2011; pp 41- 49. (3) Chiang, W.-S.; Ferraro, G.; Fratini, E.; Ridi, F.; Yeh, Y.-Q.; Jeng, U.-S.; Chen, S.-H.; Baglioni, P. J. Mater. Chem. A 2014, 2, 12991-12998. (4) Tonelli, M.; Martini, F.; Calucci, L.; Fratini, E.; Geppi, M.; Ridi, F.; Borsacchi, S.; Baglioni, P. Dalton Trans. 2016, 45, 3294-3304.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
