Quantification of surface reactivity using rate spectra

• Applicant: Privatdozent Dr. Cornelius Fischer
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262215751

The ability to predict dissolution rates is critical for modern questions in Geoscience. The current approach uses a material constant for rate calculations. However, experimental results show a rate variability of up to three orders of magnitude under identical chemical conditions. Additionally, the rate variability shows no Gaussian distribution. A mean rate (or rate constant) computed from such a distribution contains little predictive significance. As a consequence, the current approach to calculate and predict rates is not appropriate and the application of current predictions is risky. At present, the only alternative to the current approach is the concept of rate spectra. A rate spectrum is the frequency distribution of all contributions to the overall rate. The integral of the spectrum quantifies the total rate at a given time. Consequently, rate spectra are able to quantify both the total rate as well as their variability. Thus, they also provide the proper basis for rate prediction. The components of the rate spectra are not yet understand mechanistically. Their variability cannot yet be explained. Thus further research is needed to analyze and understand rate spectra in depth. We propose the analysis of rate spectra over time using a representative system. We choose calcite single crystals, because this mineral phase is often found at the Earth s surface, and chemical reactions involving calcite are very important in these environments. The proposed investigations combine experimental approaches and computer simulation calculations. We will also use complimentary methods of surface analysis and kinetic Monte Carlo (kMC) simulations to analyze rate spectra over a large range of the length scale. From these analyses we anticipate deeper insight into the problem of upscaling of reaction rates.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Andreas Lüttge