DISSOLUTION RATES AND ACTIVATION ENERGY FOR DISSOLUTION OF BRUCITE (001): A NEW METHOD BASED ON THE MICROTOPOGRAPHY OF CRYSTAL SURFACES

Abstract

Scanning Force Microscopy (SFM) was used to develop a method which can provide quantitative kinetic data of crystal growth and dissolution. Based on observations of single crystal faces in monolayer resolution, morphology and temperature dependent growth and dissolution rates can be obtained. From these kinetic data activation energies can be calculated and compared with existing theories. The experimental method works by extracting grown or dissolved terrace areas and step densities from image sequences taken at different temperatures. As an example, the method is applied for dissolution on the brucite (001) surface in acidic water (pH 2.7) within the temperature range of 21 to 35°C. At these conditions the dissolution rate depends nonlinearly on the step density and gives evidence for interstep interaction. The calculated activation energy for dissolution is 60 +/- 12 kJ mol-1. With this high activation energy, dissolution cannot be regarded as a transport-controlled process, and is therefore surface controlled.