Chemical Melting of Ice: Effect of Solution Freezing Point on the Melting Rate

Abstract

Icy roads in wintertime present a hazard for road users. It is therefore desirable to maintain bare roads. To achieve this, deicing chemicals are typically applied. One important property of the chemicals that are used is how fast they can melt ice. Understanding what affects the melting rate, however, is limited. An experiment was therefore designed to study how the driving force for the melting—the chemical potential difference between ice and solution—affects the chemical melting rate of ice. In this study, the driving force was represented by the solution freezing points. The experiment was performed at −5°C (23°F) by using the solutions of four chemicals: sodium chloride, magnesium chloride, and calcium chloride, as well as potassium formate. These four solutions were mixed to have four freezing points. They were −10°C (14°F), −18°C (−0.4°F), −30°C (−22°F); and the eutectic temperature of each chemical. The results showed that there was a clear correlation between solution freezing point and how fast the solution could melt ice. The solutions with the lowest freezing point melted ice four to five times faster than the solutions with the highest freezing point. The importance of solution freezing point was attributed to its direct relation to the solution chemical potential, with a low freezing point giving a large driving force for the phase change. In addition, it was found that the type of chemical plays a role on the melting rate of ice. The fastest melting chemical (potassium formate) melted ice 45% faster than the slowest melting chemical (magnesium chloride), which is attributed to potassium formate having a higher ion mobility. A higher ion mobility allows a faster transport of solute to the ice–solution interface.

Effect of Prewetting Brines and Mixing on Ice-Melting Rate of Salt at Cold Temperatures: New Tracer Dilution Method

“…Under static conditions, the rate of chemical ice melting will quickly slow and be limited by the rate of the diffusion of the deicer to the ice surface. Wåhlin and Klein-Paste recently demonstrated experimentally that the ice-melting rates of different brines depend directly on the diffusion rates of the ions under static conditions (18). Thus, physical mixing (such as was done in these experiments or which will occur in the field from traffic action) can greatly increase the ice-melting rate of prewetted salt by providing an additional convective mechanism to facilitate the transport of deicer ions to the ice surface and therefore increase the ice-melting rate.…”

Evaluating Performance of Alternative Deicers for Winter Road Maintenance: Deicing and Corrosivity

“…NaCl and KFo were also found to exhibit same results. Two pairs were not far off one another, but it was seen that NaCl and KFo both happened to have more ice melted in comparison to the solutions freezing point (Wåhlin et al, 2016).…”

“…Gerbino The findings from the paper showed that potassium acetate and calcium chloride had the best performance at every temperature consistently and the sodium chloride performed the worst consistently except for the beet juice mixes. Wåhlin et al (2016) completed a series of ice melting tests in a similar setup to that listed in SHRP 205.4. However, for their tests there were major changes in a few aspects of the tests such as sample geometry, solution amount, and environment.…”

“…In more recent years we have seen a plethora of new laboratory experiments conducted in the area. Wåhlin et al (2016) completed a study determining what affects melting rate.…”

“…The experiment was performed at -5 °C and the results showed that there was a direct correlation between a sample's freezing point and how fast they could melt the ice. It was also determined that solutions with a higher ion mobility have faster melting due to their ability to transport the solute faster (Wåhlin, 2016). Fay and Shi (2011) also completed laboratory experiments to test the ice melting efficiency of multiple alternative deicers.…”