Interfacial forces in calcite-fluid systems

The goal of this project has been to measure the forces that operate between surfaces of calcite (calcium carbonate), and between calcite and other materials, in fluids. This has major implications for the weathering and breakdown of rocks and how fluids move through calcite bearing rocks, as well as how we can design new materials made from calcium carbonate. I this project, we have shown that strong forces between calcite surfaces in water force them apart on the nanoscale, leading to reduced material strength. We have also found that these forces depend on the chemical composition of the fluid between the surfaces. We have established two new instruments in our laboratory, that we have used to measure forces between surfaces directly, and we are using them to measure forces between calcite surfaces that have been prepared in various ways. In the future, we will be looking specifically at the forces between rough and dynamic mineral surfaces.

When the distance between two solid surfaces is less than about a hundred nanometers, the physics of the interface become dominated by short- and long-range interfacial forces. These attractive or repulsive forces are important in numerous applications, a nd the present study will focus on their effect on subcritical crack propagation in brittle materials and the development of crystallization pressures in porous media. In particular, the proposed project aims to study the short-and long range interfacial forces that dominate in calcite-fluid-solid interfaces. Calcite is chosen because it is a relatively simple and well characterized material, and has numerous industrial, biological and geological applications. The main objective of the project is to devel op and use experimental methods for measuring force-displacement curves for interfaces of calcite against calcite, mica, silica or polymer, using a range of interfacial fluids. This will be achieved using a combination of atomic force microscopy and surfa ce force apparatus techniques. The results will be applied to the theoretical interpretation of recent experiments on subcritical crack growth in single calcite crystals, and to the development of crystallization pressure when a calcite crystal is growing in confinement inside a porous medium. Both of these processes are controlled by the transport and mechanics of a confined liquid film at the calcite interface.