Dissolution Processes at Step Edges of Calcite in Water Investigated by High-Speed Frequency Modulation Atomic Force Microscopy and Simulation

Crystal clear imaging on the atomic scale

19 December 2017

Rapid, atomic-level imaging of calcium crystals dissolving in water has revealed the nanoscale changes taking place at their edge.

Calcite (CaCO₃) is an abundant mineral in the Earth’s crust, and its largest carbon reservoir, but our understanding of how calcite grows and dissolves in water, thereby absorbing or releasing carbon, is limited by the low resolution and speeds of imaging techniques.

To take a closer look, an international team including researchers from Kanazawa University developed a high-speed frequency modulation atomic force microscope (AFM). An AFM contains a tiny probe that ‘feels’ the surface of an object and generates a three-dimensional image. One frame is recorded per second — fifty times faster than conventional frequency modulation AFM.

The group used this technique to examine the molecular changes at the surface of calcite crystals in water, and observed a previously unseen phase in the form of a layer of calcium hydroxide (Ca(OH)₂) a few nanometres thick.

Understanding how calcite dissolves in water could improve models of the global carbon cycle, and clarify the potential for this mineral to absorb atmospheric carbon.

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References

1. Nano Letters 17, 4083−4089 (2017). doi: 10.1021/acs.nanolett.7b00757