Investigation on ice nucleation / hydratecrystallization by aqueous solution of ammonium sulfate

Abstract

A brief review has been presented on how the study of ice nucleation in the atmosphere as well as laboratory has evolved during the past fifty odd years. In recent years, sulfates and nitrates are identified to constitute a significant fraction of aerosols. So, aqueous solution of Ammonium Sulfate is used as a seeding agent for ice nucleation in a laboratory scale cold room. Ice nucleation is studied over the range of −20.6°C to 0°C. The variation of crystal concentration with temperature has a sharp peak at −18.2°C, but there are also two other smaller peaks at −12.7°C and −1.7°C. Incidentally, −18.2°C coincides with the eutectic temperature of Ammonium Sulfate and water mixture. The aqueous solution of Ammonium Sulfate has the ability to form hydrate crystal on the positive side of 0°C up to +5.3°C. The hydrate nature of the crystal is confirmed after carrying out different supporting experiments. Hydrate crystals are grown in an incubator within the above temperature range. Energy Dispersive X-rays (EDX) analysis shows the presence of sulphur and oxygen. X-ray Diffraction (XRD) analysis establishes the presence of ammonium sulfate as well as hydrated form in the grown crystal. Lastly, 1H-NMR study confirms the presence of Ammonium Sulfate and water in the grown crystal.