Influence of sodium nitrate on the phases formed in the MgO-Al2O3-SiO2-H2O system

The incorporation of sodium and aluminium in magnesium silicate hydrate phases (M-S-H), possible binding cement, was investigated. Magnesium alumino containing (M-A-S-H N samples) were synthesized batch experiments with NaNO3 ~ 100 mmol/L at Mg/Si ratios equal to 0.8 1.2, Al/Si 0, 0.1 0.2, equilibrated 20 50 °C. Thermogravimetric analysis (TGA), X-rays diffraction (XRD), 29Si MAS NMR data showed that M-A-S-H formed, a similar structure as M-S-H. 27Al 23 Na only little sorbed, while possibly incorporated both tetrahedral octahedral sites M-A-S-H. We found evidence the presence nitrate led formation hydrotalcite-like phase probably NO3? trace hydrated alumino-silicate sodium: N-A-S-H gel. These minor limited uptake by M-S-H higher Al contents (Al/Si = 0.2).