Cool it, with a pinch of salt
Auteurs
Defay E.
Référence
Science, vol. 378, n° 6626, pp. 1275, 2022
Description
In salt Adding of when The countries water. on surface salt roads salt In is depresses with other of added. transforms ice harsh words, cubes How the winters, ice ice freezing much covered gets into putting colder? colder slush. point with kitchen salt reaches -10°C after a few seconds, whereas ice cubes of pure water remain at 0°C. Lilley and Prasher (1) revisited this cooling principle, and on page 1344 of this issue, they describe how to make it reversible. The idea behind this “ionocaloric” refrigeration is to take advantage of the large temperature change—and therefore the large heat absorption—obtained by melting a “special ice” when put in contact with a specific salt. The authors made this cooling process reversible to achieve an efficient cycle with potential wide applications in refrigeration. Ionocaloric refrigeration could be considered electrochemical cooling. The latter occurs in liquids containing mobile ions that can be displaced with an external voltage. However, the variation of temperature obtained with electrochemical cooling is limited to a fraction of degrees because there is no accompanying phase transition, such as melting ice (2). Triggering a phase transition with an external stimulus to induce cooling is the essence of caloric materials (3). Such materials could make cooling more efficient without requiring greenhouse gases, contrary to most refrigerators. Most gases used as refrigerants are hydro-fluorocarbons, which are much more potent greenhouse gases than carbon dioxide. Hence, magnetocaloric (4), electrocaloric (5), elastocaloric (6), and barocaloric (7) effects are temperature changes activated by the application of, respectively, a magnetic field, voltage, mechanical stress, and pressure. In the study by Lilley and Prasher, the ions of a salt trigger the melting of another material (called the solvent). Aptly, the authors called this the ionocaloric effect.
