Potassium-hydrated silicate solution unfreezable down to 190 K.
The freezing point of pure water is expected to be about 163 K in the absence of hydrogen bonds for water molecules and no rotation of water molecules. In anticipation of freezing point depression by breaking of the hydrogen bonds and formation of irrotational bonds with OH groups, a potassium-hydrated silicate solution was prepared. From thermal and ultrasonic analyses, we found that the silicate solution has a eutectic point of around 190 K in the SiO2-KOH-H2O system. The differential scanning calorimetric (DSC) analysis showed a sharp exothermal peak of 45.7 J/g with the freezing point of 232 K. The FT-IR difference spectrum indicated that the solution is constructed of silanol structure with OH groups and siloxane linkage with (Si-O-Si) bonds. The former is derived from hydration of water in the presence of potassium, while the latter makes the structure stable by being irrotationally bound for hydration shells, by analogy with the C-O bonds in protein with non-frozen water molecules. The formation of the solution unfreezable down to 190 K might be due to both hydration and structural anchor effects.
Fukuhara
Mikio
M
Institute for Materials Research, Tohoku University, Aoba, Sendai 980-8577, Japan. a80010@tungaloy
Kokuta
Akiyoshi
A
D002152:Calorimetry, Differential Scanning; D005615:Freezing; D006878:Hydroxides / Q000032:analysis; D010100:Oxygen / Q000032:analysis; D011188:Potassium / Q000032:analysis*; D017640:Silicates / Q000032:analysis*; D013696:Temperature
D006878:Hydroxides; D017640:Silicates; D011188:Potassium; D010100:Oxygen