Pressure solution at the molecular scale

Area of Science:

• Geochemistry
• Materials Science
• Crystallography

Background:

• Crystal dissolution is a fundamental process in geochemistry and materials science.
• Understanding dissolution mechanisms at the atomic level is crucial for predicting material behavior and geological processes.

Purpose of the Study:

• To investigate the topological evolution of gypsum crystal surfaces during dissolution.
• To elucidate the atomic mechanisms governing matter transfer from solid to liquid phases.
• To explore the role of tip-induced forces in dissolution, particularly pressure solution.

Main Methods:

• Utilized atomic force microscopy (AFM) to observe the dissolution of a gypsum single crystal.
• Studied the crystal's cleavage surface in a flowing undersaturated aqueous solution.
• Measured atomic step velocities under varying applied forces from the AFM tip.

Main Results:

• Observed that matter transfer occurs through the migration of atomic steps on the crystal surface.
• Found that step velocity is dependent on the force applied by the AFM tip.
• Identified distinct behaviors at high forces (corrosive wear) and low forces (<10 nN).
• Demonstrated that low-force step velocity follows the kinetic law of pressure solution.

Conclusions:

• Provided the first atomic-level evidence for the mechanism of pressure solution.
• Linked tip-induced pressure solution to the observed step velocity behavior at low forces.
• Highlighted the importance of atomic-scale investigations for understanding macroscopic geological phenomena.