HR: 0800h
AN: U11A-0004    [Abstracts]
TI: Control of the volumetric and viscosity ratios of iron-silicate emulsion on the core formation process
AU: Sato, M
AF: Graduate School of Natural Sciences and Technology, Kanazawa University, Kakuma, Kanazawa, 920-1192, Japan
AU: * Sumita, I
EM: sumita@hakusan.s.kanazawa-u.ac.jp
AF: Graduate School of Natural Sciences and Technology, Kanazawa University, Kakuma, Kanazawa, 920-1192, Japan
AB: In a vigorously convecting magma ocean, shearing motion would cause an iron-silicate emulsion to form. Iron or silicate droplets would eventually settle or rise to form the core and the mantle. Volumetric and viscosity ratios of the droplet to continuous phase can vary but how these control the phase separation process is not understood. Here we report on a series of experiments using an oil droplet in water or hydroxyethylcellulose solution (all Newtonian) to study how these ratios govern the gravitational phase separation process. First, we changed the volumetric fraction of oil. From tracking the boundary between the layer of solution and emulsion, we find that the initial phase separation rate depends strongly on oil fraction, and can be modelled by a buoyancy driven permeable flow using the Blake-Kozeny-Carman permeability formula. Next, we changed the droplet to continuous phase viscosity ratio (λ) and find that there are two distinct regimes with different styles of phase separation. Cases with λ < 100 are characterized by a sharp lower boundary and a vertically homogeneous mixture layer. On the other hand, cases with λ > 100 are characterized by a diffuse lower boundary and a large vertical gradient of composition resulting from efficient droplet coalescence. As a result, polyhedral foam structure develops at the top of the mixture layer which is slow to rupture and to transform into a uniform oil layer. We interpret these differences to arise from a faster coalescence rate relative to the separation rate at large λ, where the droplet deformation which inhibits coalescence becomes very small. We simultaneously measured electrical resistivity in order to monitor the temporal change of the mean composition in the mixture layer and found that the measurements were consistent with the visual observation. To summarize, we find that the separation rate is controlled by the permeable flow velocity, whereas the vertical compositional structure within the emulsion layer is controlled by the viscosity ratio. If the above viscosity ratio criterion can be applied to silicate-iron emulsion, the case where iron percolates through silicate droplets (λ >> 1) would yield a strongly stratified mantle, compared to the case where iron droplets sink (λ << 1). Future separation experiment using iron-silicate emulsion is needed to confirm this.
Sato, M. and Sumita, I., Experiments on gravitational phase separation of binary immiscible fluids, J. Fluid Mech., (in press)
DE: 5114 Permeability and porosity
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8125 Evolution of the Earth (0325)
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Union [U]
MN: 2007 Fall Meeting