Polythermal Study of the Systems M(ClO4)2-H2O (M2+ = Mg2+, Ca2+, Sr2+, Ba2+)

Abstract

The solubility polytherms in the systems for which the cryoscopic data are lacking were measured. The structural models of the electrolyte solutions were discussed on the basis of the solubility polytherms.

A revised Pitzer model for low-temperature soluble salt assemblages at the Phoenix site, Mars

“…In NaClO 4 solutions, FPDs measured by Hennings et al (2013) and Freeth (1924) sometimes differ from our measurements by up to six degrees at the same molality. In Ca(ClO 4 ) 2 solutions, the data of Pestova et al (2005) is scattered above and below our dataset by an average of about one degree. The data of Dobrynina et al (1984) is also consistent with our dataset at low molality, but differs significantly from both our study and Pestova et al (2005) above $6 mol kg À1 .…”

“…Our equilibrium method of measuring FPD and solubility is in contrast to dynamic methods (e.g. Pestova et al, 2005), in which the temperature is raised or lowered until the solid phase dissolves or precipitates. To prevent the salt solutions from corroding the copper, the interior of the reaction vessel (75 cm 3 volume) was lined with polyethylene.…”

“…Furthermore, there are disagreements between different low-temperature datasets. Dobrynina et al (1980) and Pestova et al (2005) have measured the Mg(ClO 4 ) 2 eutectic at 205 K, whereas Stillman andGrimm (2011) andToner et al (2014a) have measured the eutectic at 216 K. Similarly, Dobrynina et al (1984) and Pestova et al (2005) disagree on both the eutectic and salt solubilities in Ca(ClO 4 ) 2 solutions. With respect to mixtures of perchlorate salts, no experimental data is available below 298.15 K.…”

“…FPDs at lower temperatures have been primarily determined using dynamic methods, in which the temperature is raised or lowered at a constant rate until ice either precipitates or melts completely (e.g. Dobrynina et al, 1980;Pestova et al, 2005). However, dynamic methods may give inaccurate FPDs at low temperatures due to slow reaction kinetics (Toner et al, 2014a).…”

Laboratory investigation of perchlorate deliquescence at the surface of Mars with a Raman scattering lidar

“…While this previous work on microscopic samples demonstrated that perchlorate deliquescence should be thermodynamically favored under certain Martian conditions, other experimental results have indicated that the process is not rapid enough to allow for a substantial amount of bulk deliquescence during the Martian diurnal cycle [Fischer et al, 2014]. There also exists some question as to the exact nature of the eutectic temperature of the magnesium perchlorate-water system with previously measured freezing point depressions ranging from À68°C [Pestova et al, 2005] to À57°C [Stillman and Grimm, 2011]. It has even been suggested that magnesium perchlorate brines could remain as a supercooled liquid throughout the entirety of the coldest Martian nights [Toner et al, 2014b].…”