Diffusivity oxygen fugacity

Point defects and diffusion diffusivity and oxygen fugacity... 

Ryerson F.J., Durham W.B., Cherniak D.J., and Lanford W.A. (1989) Oxygen diffusion in olivine effect of oxygen fugacity and implications for creep. /. Geophys. Res. 94, 4105-4118. 

The measurement of diffusion rates as functions of various activities, in particular oxygen fugacity, is extremely important to clarifying the diffusion mechanisms and aid in extrapolation. The work of Ryerson et al. (1989) is the only geochemical example of such type of work. Questions of concern include under what conditions does the /02-dependence occur, and what does it tell us about the main mechanism of O2 transport (e.g. permeation versus diffusion, network versus molecular oxygen diffusion etc.). 

The activation energy was probably an apparent one which was a combination of the effects of the lattice diffusion of Ar atoms, with trapping in point-defect vacancies. There were no discernible differences in Ar diffusion in different crystallographic directions, and the diffusivity did not vary as a function of the intrinsic oxygen fugacity of the experimental vessel. 

Farver J.R. and Yund R.A. (1990) The effect of hydrogen, oxygen, and water fugacity on oxygen diffusion in alkali feldspar. Geochim. Cosmochim. Acta 54, 2953-2964. 

Oxygen diffusion in quartz dependence on temperature and water fugacity. Chem. Geol. 90, 55-70. 

Edwards K. J. and Valley J. W. (1998) Oxygen isotope diffusion and zoning in diopside the importance of water fugacity during cooling. Geochim. Cosmochim. Acta 62, 2265-2277. 

The fate of chemicals in the environment depends not only on processes taking place within compartments, but also by chemical partitioning between compartments. For example, there may be exchange of chemicals between air and water or soil. Movement from the water or soil into the air is accomplished by volatilization and evaporation of volatile or semivolatile compounds. Movement of chemicals from the air to water or soil is accomplished by deposition or diffusion into the water. Chemicals can also move from water to soil or sediment and vice versa. If a solid chemical in the soil or sediment dissolves into the water, this is called dissolution , while the opposite is called precipitation . If a chemical dissolved in water attaches to a soil or sediment particle, this is called adsorption , while the opposite is called desorption . The fugacity of a chemical, that is, its tendency to remain within a compartment, is affected by the properties of that chemical, as well as the chemical and physical properties of the environments such as temperature, pFF, and amount of oxygen in water and soil. Wind or water currents, wave action, water turbulence, or disturbance of soil or sediment (through the action of air or water currents, animals, or human activities) may also affect partitioning of chemicals. 

Farver JR (1994) Oxygen self-diffusion in calcite Dependence on temperature and water fugacity. Earth Planet Sci Lett 121 575-587... 

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