Other
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........11g&link_type=abstract
Thesis (PHD). BROWN UNIVERSITY , Source DAI-B 58/06, p. 2929, Dec 1997, 138 pages.
Other
Albite, Forsterite, Enstatite
Scientific paper
The congruent melting kinetics of Amelia albite were experimentally determined at 1125o C,/ 1150o C,/ 1175o C, and 1200o C. It was determined that congruent melting is a heterogeneous process. Melting is initiated at external surfaces and cleavage planes. Melting kinetics of albite are best described using a normal growth model. Congruent melting of albite was found to be interface controlled, and rates of melting are directly proportional to the amount of superheat, and inversely proportional to viscosity. Comparison of the results obtained here with previous studies of melting kinetics on other materials (oxides and silicates) finds that the normal growth model can be used to predict melting rates within an order of magnitude. The normal growth model was used to predict congruent melting rates of forsterite and enstatite as well as other minerals which may have been present in the chondrule forming region of the solar nebula. Constraints on the peak temperatures of chondrule formation are thus obtained. Specifically, chondrules containing relict grains of forsteritic olivine and enstatitic pyroxene could not have been heated above 1901o C and 1577o C, respectively, for more than a few seconds. Reanalyses of Na-Al-rich chondrule glasses by EPMA have found that previous EPMA work resulted in loss of Na from the activated volume due to migration in an electrical potential gradient. The Na-Al-rich chondrules have Na/Al ratios of unity, suggesting that they did not lose alkalis during flash heating. Experiments reproduced the chondrule glasses and determined the formational constraints of these chondrules. Specifically, the chondrules needed to have been cooled at low rates (<6o C/hr) at the lower temperature end of chondrule formation.
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