Diffusion in single crystal of melilite: interdiffusion of Al + Al vs. Mg + Si
Diffusion in single crystal of melilite: interdiffusion of Al + Al vs. Mg + Si
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黄长石单晶中的扩散：Al Al 与 Mg Si 的相互扩散
DOI：
10.1007/s002690100212
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发表时间：
2001
影响因子：
1.4
通讯作者：
M. Morioka
中科院分区：
文献类型：
--
作者：
H. Nagasawa;Toshihiro Suzuki;Motoo Ito;M. Morioka
用耦合退火法测定了黄长石钙铝黄长石-奥镁黄长石体系中Al + Al与Mg + Si的互扩散系数。观察到的双退火样品的扩散系数变化约为2个数量级，显示出对钙铝黄长石-软铝黄长石组成的强烈依赖性：例如，在1350 °C下观察到的扩散系数在5 mol%软铝黄长石组成（Ak 5）时为3 × 10− 13 cm 2 s − 1，在Ak 80时增加到2 × 10− 11 cm 2 s − 1，然后在Ak 95时降低到1 × 10− 12 cm 2 s − 1。扩散系数-温度关系表明，对于富含钙铝黄长石的黄长石，扩散活化能约为420 kJ mol− 1。观察到的扩散系数-组成关系可以通过（1）扩散系数-熔化温度关系（弗林规则）和（2）局部电荷补偿的可行性的组合来解释，局部电荷补偿可能在中间化学组成中更容易保持。钙黄长石的高活化能值似乎对应于复杂的扩散机制。观察到的高度可变的扩散系数表明，钙铝黄长石晶体中的钙铝黄长石-铝黄长石环带的碳质陨石中的富Ca，Al包体可能提供了一个敏感的指示包体的热历史。
Interdiffusion coefficients of Al + Al vs. Mg + Si in the gehlenite–åkermanite system of melilite were determined by coupled annealing of synthesized end-member single crystals. The observed diffusion coefficients for a couple-annealed sample vary for about 2 orders of magnitude, showing strong dependence on the gehlenite–åkermanite composition: diffusion coefficient observed at 1350 °C, for example, is 3 × 10−13cm2s−1at 5 mol% åkermanite composition (Ak5), increases to 2 × 10−11cm2s−1at Ak80, and then decreases to 1 × 10−12cm2s−1at Ak95. The diffusion coefficient–temperature relation indicates high activation energy of diffusion of about 420 kJ mol−1for gehlenite-rich melilite. The observed diffusion coefficient–composition relation may be explained by a combination of (1) the diffusion coefficient–melting temperature relation (Flynn's rule) and (2) the feasibility of local charge compensation, which can possibly be maintained more easily in the intermediate chemical composition. The high activation energy value for gehlenitic melilite appears to correspond to the complex diffusion mechanism. The observed highly variable diffusion coefficients suggest that gehlenite–åkermanite zoning in the melilite crystals in Ca, Al-rich inclusions in the carbonaceous meteorites may provide a sensitive indicator for the thermal history of the inclusions.