title: Double freezing of (NH(4))(2)SO(4)/H(2)O droplets below the eutectic point and the crystallization of (NH(4))(2)SO(4) to the ferroelectric phase.
abstract: This paper presents the differential scanning calorimetry (DSC) results obtained from measurements of single droplets of different subeutectic concentrations (<40 wt % (NH4)2SO4) and diameters of 1-1.5 mm. The measurements show that despite the fact that the freezing of the droplets takes place below the eutectic temperature of Te ≈ 254.5 K, a phase separation into ice and a residual freeze-concentrated solution occurs. The residual solution is formed by the expulsion of NH4+ and SO42- ions from the ice lattice during the nucleation and growth of ice and may possess the eutectic concentration of 40 wt % (NH4)2SO4. On further cooling, the residual solution freezes to the eutectic solid mixture of ice/(NH4)2SO4 at a temperature that is either above or below the ferroelectric "Curie" temperature of Tc ≈ 223 K. If the freezing of the residual solution takes place below the Tc, then (NH4)2SO4 crystallizes directly into the ferroelectric phase.
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria.
authors.forename: A
authors.initials: A
authors.lastname: Bogdan
mesh_terms: D000645:Ammonium Sulfate / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D004574:Electromagnetic Fields; D005615:Freezing; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D000645:Ammonium Sulfate