Volatilization of sodium from silicate melt spheres and its application to the formation of chondrules |
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| Authors: | Akira Tsuchiyama Hiroko Nagahara Ikuo Kushiro |
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| Institution: | Geological Institute, University of Tokyo, Hongo, Tokyo, 113, Japan |
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| Abstract: | The rates of volatilization of Na from liquid spheres of chondrule compositions have been determined as functions of time, temperature, partial pressure of oxygen, and sizes of the spheres. The Na2O content in the sphere is uniform in each run. but it decreases with time of the run, indicating that the rate of diffusion of Na in the liquid is greater than that of volatilization, and that the latter is the rate-controlling process. The rate of sodium volatilization becomes greater with increasing temperature and with decreasing PO2 and size of the spheres. The relation of the Na2O content in the liquid sphere with time and its size indicate that the amount of Na2O volatilized from the liquid spheres within unit time is proportional to the surface area of the spheres and the concentration of Na2O in the liquid. From these relations, the rate of volatilization of sodium can be obtained at constant temperature and Po2. The rate of volatilization of sodium satisfies the Arrhenius relation within the temperature range from about 1450–1600 C at 10?9,2 atm pO2; the activation energy for the sodium volatilization is approximately 100 kcal-mole?1. The rate is also approximately proportional to within the range of pO2 from 10?10.2 to 10?5.0 atm at about 1500° C. Based on the present results and the Na2O contents in chondrules. it is suggested that they experienced an instant heating with maximum temperature of 1400–2200° C followed by an immediate cooling. |
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