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Robert H. McCallister 《Contributions to Mineralogy and Petrology》1978,65(3):327-331
The coarsening kinetics of exsolution lamellae have been determined for an initial composition of 0.541 CaMgSi2O6–0.459 Mg2Si2O6 (Di54.1) at 1300 °, 1200 ° and 1100 ° C. Portions of this material were annealed for varying lengths of time, and the average wavelength () was obtained from measurements made by utilizing transmission electron microscopy (TEM). All experiments were conducted within the (001) coherent spinodal for this system (McCallister and Yund, 1977), and the lamellae are coherent up to and including the largest wavelength observed, 1054 Å.At all three temperatures mentioned previously the data are consistent with the following relationship:
The activation energy for the process, as determined from the respective kinetic constants (k), is 99±2 Kcal/mol. This value is similar to that found for Ca self diffusion in pseudo-wollastonite and wollastonite, and suggests the possibility that the diffusion of Ca may be controlling the rate of coarsening.A comparison of exsolution microstructures in the synthetic samples with those observed in clinopyroxenes found in kimberlites and with similar Ca/Ca + Mg indicates that the latter cooled rapidly to the effective quench temperature. 相似文献
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Evaluation of soil top-cover systems to minimize infiltration into a sanitary landfill: A case study
The design of a top-cover system is a very important aspect of the closure of sanitary landfills. Soil material properties, sequencing, and vegetation are critical to top-cover design. To date, very few field investigations have been undertaken to determine the effectiveness of these designs. Results from a field investigation of top-covers proposed for an active landfill site in south Florida are reported here. Measurements were made of each component of the water balance equation: S = [P +I] – [ET +R +Q] whereS, P, I, ET, R, andQ represent water storage, rainfall, irrigation, evapotranspiration, surface runoff, and deep seepage, respectively. Deep seepage, determined using soil water tensiometers, is the amount of water infiltrating the landfill top-cover and is therefore the upper limit of potential leachate generation.Results indicate that the locally available rock tailings (carbonate silt) is an effective topliner component of the top-cover system. The results of the field investigation also showed that the EPA water balance model used to estimate infiltration during landfill design was greater than the actual field measurements. 相似文献
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The position of the titanomagnetite subsolidus stability field boundaries, within the Fe-Ti-O ternary, above 1,000° C, has been calculated from chemical equilibrium considerations, using experimental data for the calibrated buffers of end member compositions. The relationship between chemical composition and intrinsic oxygen fugacity, within the single phase spinel field, has been investigated with a Frenkel cation point defect model. With this calculation scheme, conditions for departure from strict metal-oxygen stoichiometry to stable cation rich or deficient phases can be predicted.
相似文献4.
A tripartite earthquake response spectrum exhibits peak values of acceleration, velocity, and displacement in concert, each as a function of natural frequency of vibration. Because cokriging is a regionalized variable technique for multiple variable estimation, it was employed to jointly estimate peak values of acceleration, velocity, and displacement through a frequency discretization process. The objective of this application was to develop a technique for estimation of response spectra at uninstrumented locations. Because magnitudes of the three response variables differed, these data were normalized prior to cokriging. This process simply involved dividing each type of variable by its maximum value for a given frequency; hence, values of each type of variable ranged between zero and one. This allowed better accuracy in developing cross-variograms. Cokriging proved to be an efficient and accurate technique to use for the estimation of tripartite response spectra. 相似文献
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R. Aragon R. H. McCallister H. R. Harrison 《Contributions to Mineralogy and Petrology》1984,85(2):174-185
Interdiffusion couple experiments were performed with titanomagnetite single crystals at 1,000°C, 1,100° C and 1,200° C in various buffered atmospheres. The dependence of the interdiffusion coefficient on oxygen fugacity, composition and temperature was interpreted in terms of point defect structure. Estimates of the cation tracer diffusivities indicate that Fe migrates via a point defect mechanism, involving mixed tetrahedral-octahedral site jumps, with an activation energy of 33 Kcal/mole; whereas Ti migration is one to two orders of magnitude slower, is restricted to octahedral sites and has an activation energy of 60 Kcal/mole. 相似文献
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Robert H. McCallister Gordon L. Nord Jr. 《Contributions to Mineralogy and Petrology》1981,78(2):118-125
Twenty-six subcalcic diopside megacrysts (Ca/(Ca+ Mg)) = 0.280–0.349, containing approximately 10 mol% jadeite, from 15 kimberlite bodies in South Africa, Botswana, Tanzania, and Lesotho, have been characterized by electron microprobe analysis, X-ray-precession photography, and transmission electron microscopy. Significant exsolution of pigeonite was observed only in those samples for which Ca/(Ca+Mg)0.320. The exsolution microstructure consists of coherent (001) lamellae with wavelengths ranging from 20 to 31 nm and compositional differences between the hosts and lamellae ranging from 10 to 30 mol% wollastonite. These observations suggest that the exsolution reaction mechanism was spinodal decomposition and that the megacrysts have been quenched at various stages of completion of the decomposition process.Annealing experiments in evacuated SiO2 glass tubes at 1,150° C for 128 hours failed to homogenize microstructure, whereas, at 5 kbar and 1,150° C for only 7.25 hours, the two lattices were homogenized. This pressure effect suggests that spinodal decomposition in the kimberlitic subcalcic diopside megacrysts can only occur at depths less than 15 km; the cause of the effect may be the jadeite component in the pyroxene. Apparent quench temperatures for the exsolution process in the megacrysts range from 1,250° C to 990° C, suggesting that decomposition must have commenced at temperatures of more than 1,000° C.These P–T limits lead to the conclusion that, in those kimberlites where spinodal decomposition has occurred in subcalcic diopside megacrysts, such decomposition occurred at shallow levels (<15 km) and, at the present erosion level, temperatures must have been greater than 1,000° C. 相似文献
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