Kinetics and Thermodynamics of Mineral Dissolution and Precipitation
Recent experimental work has been directed toward measuring the rates of reaction of minerals with aqueous solutions. The measurements are made by complementary techniques, including
- characterization of in-situ nano-topographical evolution of mineral surfaces in flowing solutions by digital holographic microscopy. The movie below shows the real-time development of an etch pit on a (104) surface of calcite when exposed to flowing deionized water.
- monitoring reaction rates in batch reactors and mixed flow reactors
- tracking changes in surface area and morphology by scanning electron microscopy (SEM) and nitrogen adsorption isotherms
We are also interested in relating microstructure characteristics of porous media to engineering properties such as stiffness, strength, viscoelastic response, and fluid permeability.
Sintering Kinetics and Mechanisms
Sintering of ceramic powders is a potential route to manufacturing in extreme or expeditionary environments such as remote regions of the Earth, on the Moon, or on Mars. To make sintering viable in these circumstances, the raw materials in these regions must be characterized and the sintering process must be tailored and optimized.
Recent work in our group has focused on understanding the mechanisms of densification and creep of Lunar regolith material. We use high-fidelity synthetic regolith powders, and we are investigating the influence of mineralogical composition and particle size distribution on the driving force and rate-controlling mechanisms of densification, coarsening, and creep.
The video below from our lab shows how the real-time shrinkage and deformation can be tracked with an optical heating microscope. The microscope captures projections of the specimen backlit by blue LED light as the sample is exposed to high temperatures. Continuous curves tracking volume as a function of time and temperature can be used to determine instantaneous rates of creep and deformation and how those rates depend on temperature and other environmental variables.
The specimen being studied in this video is a Lunar regolith powder designed to mimic the mineralogical composition in the highlands regions of the Moon. The plot shows how the specimen volume changes with temperature as it is heated at 5 K/min, and the right side of the video shows how the projections of two specimens change as the temperature increases.