It is important to note that for th

It is important to note that for the monolithic samples prepared via cold sintering, the bands associated with Si-O-Si shifted to lower wavenumbers (especially the one around 475 cm−1 moving to ~ 410 cm−1). Certainly, further studies are required to establish the exact mechanism causing such result, yet we still can speculate. The shift might be correlated with depolymerization caused by the sodium ions originating from NaOH solution [14].It was shown for soda lime glasses that the Si-O-Si band around 1050 cm−1 was very sensitive to structural changes and increasing the non-bridging oxygen (NBO) content could result in the IR shift. Such a matter seems to be the case here that with the increasein processing pressure, temperature and especially the NaOH concentration, the amount of NBO was enhanced (assuming no other contributions, and all Na+ is exchanged into the glass structure, then the NBO fraction is calculated to increase from 0.241 with no additive to 0.246 at 5M and 0.254 at 15M for the cold sintered specimens, calculations done based on the starting glass composition and change in the NaOH density within 5-15 M), and thus the formation of a probable gel aided sintering. A similar slight shift of the broad band to higher 2θ angles can be seen from the differences in between the XRD patterns (Fig. 1(b)) of the raw powder and cold sintered glass bodies. There are no measurable crystalline phases, suggesting that the samples maintained their amorphous state after CSP at all processing conditions studied.