The relationship between the rheology and phase equilibria of a picritic basalt from Kilauea Iki has been investigated at 1 atm along the QFM buffer. Between 1270 ø and 1180øC olivine and minor spinel are the only liquidus phases, and the melt volume decreases from 85 to 74 vol %. At the ol-sp-pc-cpx cotectic, melt is consumed more rapidly dropping to 47 vol % at 1139øC. The rheology of the magma is non-Newtonian, is characterized by time-dependent, pseudoplastic behavior, and is consistent with power law flow or Bingham pseudoplastic behavior. Non-Newtonian effects are most apparent when the crystal volume is greater than 25% and the shear rate is increasing. Once stirred, the magma approaches Newtonian rheology with decreasing shear rate. At 1170øC (approximately 25% suspended crystals) the apparent activation energy (calculated at unit shear rate) increases from 123 + 10 kcal mol-• to 452 + 21 kcal mol-X. When the change in liquid composition along the liquidus is included, the observed viscosities are in good agreement with those calculated from the Einstein-Roscoe equation for a serial size distribution of crystals. A quadratic fit to the shear stress-strain rate data yields a nonzero intercept indicative of a finite yield strength. The apparent yield strength increases with decreasing temperature reaching • 800 Pa at 1149øC. These extrapolated (and model dependent) values are in good agreement with those determined by other methods (Shaw et al., 1968' McBirney andMurase, 1984). The yield strengths can be fit by a power law expression, ao = 6500• b2'85, where ao is the yield strength and •b the crystal volume fraction. This expression recovers the yield strength estimates for other basalts, suggesting that it may be generally applicable to magmas in which the melt is of broadly basaltic composition. The magmas exhibit heating due to viscous dissipation during shearing. However, this effect is not large enough to produce the observed pseudoplasticity. We conclude that the non-Newtonian behavior in these magmas is due to reorientation of solids in the flow field and solid-solid interactions. We develop a model in which the time-dependent pseudoplasticity and yield strengths are produced by the relationship between solid phase contiguity (the fraction of solid internal surface area shared with other solids) and grain dispersive pressure due to shearing. Increased contiguity is related to increased apparent viscosities and yield strengths, while increased grain dispersive pressure due to shearing acts to diminish contiguity. Paper number 7B7035. 0148-0227/88/007B-7035505.00 cooled liquids (cf. Bockris and Lowe [1953, 1954], Bockris et al. [1955], Shaw [1963], Cukierrnan and Uhlmann [1973, 1974], Cranmer and Uhlmann [1981], and Urbain et al. [1982], among others). The variables investigated in these studies are temperature and bulk composition. Using these variables empirical models for the estimation of viscosity have been formulated [Shaw, 1972; Bottinga and Weill, 1972]. Other studies have concentrated upon th...
We have measured the dissolution rate of a simple five-component borosilicate glass (Na 2 0, CaO, A1 2 0 3 , B 2 0 3 , Si0 2 ) using a flow-through system. The experiments were designed to measure the dissolution rate constant over the interval pH 1 through pH 13 at 3 temperatures (250, 500 and 70 0 C). Dilute buffers were used to maintain a constant pH. Analyses of solutions and solid surfaces provided information that is used to develop a kinetic model for glass dissolution.Under all conditions we eventually observed linear dissolution kinetics. In strongly acidic solutions (pH 1 to pH 3) all components but Si were released in their stoichiometric proportions and a thick, Si-rich gel was formed. In mildly acidic to neutral solutions the gel was thinner and was both Si-and Al-rich, while the other components were released to solution in stoichiometric proportions. In mildly to strongly alkaline solutions all components were released to solution in stoichiometric proportions. By varying the flow rate at each pH we demonstrated a lack of transport control of the dissolution rate.The dissolution rates were found to be lowest at near-neutral pH and to increase at both low and high pH. A rate equation based on transition-state theory (TST) was used to calculate dissolution rate constants and reaction order with respect to pH over two pH intervals at each temperature. At 25 0 C between pH 1 and pH 7 based on the Si release rate the log rate constant for glass dissolution (g glass/m2od) was -0.77 and the order with respect to pH was -0.48. Between pH 7 and pH 13 the log rate constant for glass dissolution was -8.1 and the order with respect to pH was +0.51. The measured simple glass dissolution rate constants compare very well with constants estimated by fitting the same TST equation to experimental results obtained for SRL-165 glass and to dissolution rate estimates made for synthetic basaltic glasses.
The work presented in this report was supported by the Department of Energy (DOE) through the Nevada Operations Office (NVOO) as part of the Radionuclide Migration Program at the Nevada Test Site (NTS). The purpose of this program is to inves tigate the potential for underground migration of radionuclides in groundwater from the sites of underground nuclear explosions. Borg et al. have comprehensively reviewed this subject and have included an annotated bibliography (1). Levy (2) discusses in detail the specific aspects of an underground nuclear explosion which are relevant to radionuclide contamination of the ground water.The technology required to study the NTS groundwater problem is very similar to that required for studying the geo logic disposal of high-level vitrified nuclear reactor wastes.The energy crisis of the 1970's has emphasized the need for nuclear power and consequently there is considerable interest in developing an environmentally-acceptable means for disposing of the resultant nuclear wastes. deMarsily et al. (3) have discuss ed the feasibility for geologic disposal of nuclear wastes and have concluded that ion exchange with the rock surrounding the repository is the most important barrier between the waste and the biosphere. The Study Group on Nuclear Fuel Cycles and Waste Management of the American Physical Society (4) concluded that the management of nuclear waste was well within existing techno logy and that economic and political questions provided the greatest problems for nuclear energy use. They also state that hydrogeologic transport is the most likely route for contamina tion of the biosphere by a waste repository.Information on the interaction of radionuclides with ground water in deeply-buried, high-level, long-term "waste repositories" is available at only a few locations. One is the OKLO natural reactor in Gabon which has for over 1.7 billion years retained some of the radionuclides also present in nuclear wastes (5). Another is the Nevada Test Site, where radionuclides were first deposited underground on September 19, 1967 during the 1.7 kt 0-8412-0498-5/79/47-100-093$05.50/0
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