Dynamic and topographic observation of calcite dissolution using enhanced in-situ phase-shift interferometry

The dissolution rate of calcite in water with and without .ow was measured using enhanced phaseshift interferometry (PSI). This technique uses a white light source instead of laser light to shorten the coherent wave-length providing quick and precise measurements of mineral dissolution and growth over relatively short time scales (several tens of minutes). Phase shift interferometry is non-invasive technique that allows surface observation at the molecular level in water as well as direct, simultaneous measurement of step velocity and the behavior of crystal surfaces during dissolution. The theoretical PSI resolution in the vertical direction in water is 0.78 nm; however the practical detection limit of the calcite dissolution experiments was 4.2 nm due to the effects of external and internal inferences such as apparatus drift, air drag, etc. The calcite dissolution rate at zero water flow was estimated from the retreat velocity as 0.0494 nm/s, which corresponds to flux rate of 1.33E-10 mol/cm²/s. This is around the lower limit of previously published data obtained mainly by powder experiments. The dissolution rates for different vicinal slopes of the surface were also measured. These rates were well-correlated with the vicinal slopes in accordance with BCF theory indicating that there is a mutual interaction between neighboring growth/dissolution steps via diffusion, consistent with previously published AFM measurements. The effect of topographical features on the microscopic dissolution behavior was clearly observed during the PSI measurements. The dissolution velocity at the isolated step in pure water was obtained as 2.8 nm/s by fitting the experimental data. Thus, it is possible to examine and determine global calcite dissolution rates using the topographical measurements determined from PSI experiments.