The Low-Imperature XRD Analysis: A Study On Ice Structures

As discussed above, during DSC analysis two types of FFW and NFW were observed in PS, PT, and MA samples. The low-temperature XRD technique was used in this study to define the boundary between the FFW and NFW in PS, PT, and MA samples more accurately. Dowell and co-workers [29] and Shallcross and Carpenter [30] have reported the low-temperature XRD studies on ice structures. The low-temperature XRD analysis has been used by the authors to study the properties of water in low-rank coals [16, 26].
The low-temperature XRD analysis was carried out on PS, PT, and MA samples with different water contents in the ranges of 33.23-53.99%, 25.41-60.17%, and 23.01-68.36%, respectively. The XRD patterns are shown in Fig. 8. The XRD patterns of PS samples
8b also showed two major phases of H2O and SiO2. During DSC analysis of PT, one exothermic peak (FFW) was observed in samples containing 30.58% to 59.81% water, and no phase transition was detected in samples with water content lower than 30.58% (Fig. 1b). During XRD analysis of PT (Fig. 8b), ice crystals were observed in samples containing 60.17-26.53% water. However, no ice crystals were detected in samples with water contents lower than 26.53%. The XRD patterns of MA in Fig. 8c showed three major phases of H2O, SiO2, and Al2(Si2O5)(OH)4 in samples with different water contents. During DSC analysis of MA, one exothermic peak (FFW) was observed in samples with 34.10-72.8% water content, and no peaks were observed in samples with water contents below 34.10% (Fig. 1b). During XRD analysis of MA (Fig. 8c), ice crystals were observed in samples with water contents in the range of 24.08-68.36%. However, no ice crystals were observed in samples with water contents below 24.08%. These results indicated that MA sample had higher amount of FFW compared with PS, and PT samples. This can be attributed to smooth morphology of MA particles and lack of pores on the surface of the particles. Therefore, in MA samples water was mainly present as FFW (intraparticle water and surface adsorption
However, no freezable bonded-water was detected in biomass samples. FTIR analysis and sessile drop contact angle measurements indicated that MA sample was more hydrophilic compared to PS and PT samples due to higher concentration of oxygen-containing functional groups. A shift in the position of FFW peak was observed in MA during DSC analysis due to stronger hydrophilicity of microalgae compared with PS and PT samples. The freezing enthalpies of FFW in biomass samples were in the range of 319.04-297.7 kJ/kg and were in good agreement with the enthalpy of bulk water. Low-temperature XRD analysis was used to define the boundary between the FFW and NFW and indicated that more FFW was present in MA compared with PS and