Computer simulations conducted at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) could help scientists make sense of a recently observed and puzzling wrinkle in one of nature’s most important chemical processes. It turns out that calcium carbonate—the ubiquitous compound that is a major component of seashells, limestone, concrete, antacids and myriad other naturally and industrially produced substances—may momentarily exist in liquid form as it crystallizes from solution.
Calcium carbonate is a huge player in the planet’s carbon cycle, so any new insight into how it behaves is potentially big news. The prediction of a dense liquid phase during the conversion of calcium carbonate to a solid could help scientists understand the response of marine organisms to changes in seawater chemistry due to rising atmospheric CO2 levels. It could also help them predict the extent to which geological formations can act as carbon storage reservoirs, among other examples.
The research may also reconcile some confounding experimental observations. For more than a century, scientists believed that crystals nucleate from solution by overcoming an energy barrier. But recent studies of calcium carbonate revealed the presence of nanoscopic clusters which, under certain conditions, appear to circumvent the barrier by following an alternative aggregation-based crystallization pathway.
The Berkeley Lab-led team used molecular dynamics simulations to study the onset of calcium carbonate formation. The simulations predict that in sufficiently supersaturated calcium carbonate solutions, nanoscale dense liquid droplets can spontaneously form. These droplets then coalesce to form an amorphous solid prior to crystallization.
The findings support the aggregation-based mechanism of calcium carbonate formation. They also indicate that the presence of the nanoscale phase is consistent with a process called liquid-liquid separation, which is well known in alloys and polymers, but unexpected for salt solutions.
This story is reprinted from material from the Berkeley Lab, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.