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

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 calcu lated and compared with existing theories. The experimental method wor ks by extracting grown or dissolved terrace areas and step densities f rom image sequences taken at different temperatures. As an example, th e method is applied for dissolution on the brucite (001) surface in ac idic water (pH 2.7) within the temperature range of 21 to 35 degrees C . At these conditions the dissolution rate depends nonlinearly on the step density and gives evidence for interstep interaction. The calcula ted activation energy for dissolution is 60 +/- 12 kJ mol(-1). With th is high activation energy, dissolution cannot be regarded as a transpo rt-controlled process, and is therefore surface controlled.