Combined impact of confinement and solute on freezing is greater than the sum of the parts
Combined impact of confinement and solute on freezing is greater than the sum of the parts lead image
Though the effects of confinement on the freezing of pure water are known, water in confined spaces like soils is rarely pure, and the impact of solutes on freezing is not well understood. Because the interplay between the two parameters can have large geophysical effects, Ginot et al. compared the freezing behavior of water in confined, porous regions with various salt (KCl) concentrations to understand their combined effects.
The authors found confinement and the presence of salt work synergistically to lower the water’s freezing temperature. These combined effects are over an order of magnitude larger than the impact of confinement alone, and much larger than the sum of the two individual contributions.
“We were surprised to see such a strong synergy between the two effects,” said author Sylvain Deville. “We were expecting to observe a synergy – this was the goal of the study – but the magnitude of the effects we observed is really striking.”
As larger pores begin to freeze, the ice expels the salt into smaller pores, increasing the salt concentration there and causing further delays in freezing. This can lead to a large mushy layer in the soil, where ice and water coexist. Because even a small amount of salt can have a large impact on the freezing, it is critical to consider these effects, as they can impact soil’s strength and permeability, lead to variations in salt concentration that are detrimental to local plant life and microbial activity, and impact cryo-tolerance of construction materials.
“The exciting part is that these results could be helpful to understand many solidification patterns that we still have a hard time to explain today, in particular in soils freezing,” Deville said.
Source: “Solute strongly impacts freezing under confinement,” by Félix Ginot, Théo Lenavetier, Dmytro Dedovets, and Sylvain Deville, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0008925 .
