Experimental evidence for interaction of water vapor and platinum crucibles at high temperatures : Implications for volatiles from igneous rocks and minerals
Experimental evidence for interaction of water vapor and platinum crucibles at high temperatures : Implications for volatiles from igneous rocks and minerals
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DOI：
10.1016/j.gca.2011.12.020
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发表时间：
2012-04-15
影响因子：
5
通讯作者：
Aubaud, Cyril
中科院分区：
文献类型：
--
作者：
Clog, Matthieu;Cartigny, Pierre;Aubaud, Cyril
从火成岩和矿物中提取水通常是通过感应加热沉积样品的铂合金坩埚来实现的。在这里，我们表明，水和Pt-10%Rh坩埚之间的化学相互作用发生在高温下。已知量的水与保持在高温（900-1300 ℃）下的Pt坩埚反应5-10分钟，然后回收。实验表明，在反应过程中，平均有20%的水流失到坩埚中，剩余水的同位素组成发生了高达千分之二十五的变化。只有20-50%的损失的水可以通过在1300摄氏度下重新加热坩埚来回收。在坩埚上使用相同的标准水进行重复实验显示，同位素位移仅减少至千分之2。这与Pt-10%Rh坩埚的记忆效应是相容的。我们建议，大量（至少几十μ mol）的水仍然被困在坩埚和部分同位素交换之间的捕获和引入的水影响随后的同位素组成的注入水。我们的结论是，应避免使用铂合金，作为坩埚或箔，从岩石或矿物中提取水。这项研究中强调的相互作用揭示了以前对几个地幔样品的不一致观测。在没有使用金属坩埚的情况下，对14个玄武岩样品进行了重新分析，结果显示，相对于以前的研究，氢的同位素组成富集了10-20份氘。上地幔的同位素组成接近于千分之-60，而不是之前假设的千分之-80。(C)2011爱思唯尔有限公司保留所有权利。
The extraction of water from igneous rocks and minerals is classically achieved by induction heating of a platinum alloy crucible where the sample has been deposited. Here, we show that chemical interaction between water and Pt-10% Rh crucibles occurs at high temperature. Known amounts of water were reacted with a Pt crucible held at high temperatures (900-1300 degrees C) for 5-10 min and then recovered. The experiments show that on average 20% of the water was lost to the crucible during the reaction, and that the isotopic composition of the remaining water was shifted by up to 25 parts per thousand. Only 20-50% of the lost water was recoverable by re-heating the crucible at 1300 degrees C. Repeated experiments using the same standard water on the crucible showed a decrease of the isotopic shift to only 2 parts per thousand. This is compatible with a memory effect of the Pt-10% Rh crucible. We propose that a large amount (at least several tens of mu mol) of water remains trapped in the crucible and that partial isotopic exchange between trapped and introduced water affects subsequent isotopic composition of injected water. We conclude that the use of Pt alloys, as crucibles or foils, to extract water from rocks or minerals should be avoided. The interaction highlighted in this study shed light on previously inconsistent observations made on several mantle-derived samples. Fourteen basaltic samples were also re-analyzed without using a metal crucible and show isotopic compositions of hydrogen enriched by 10-20 parts per thousand in deuterium relative to previous studies. The isotopic composition of the upper mantle is closer to -60 parts per thousand, rather than -80 parts per thousand as postulated earlier. (C) 2011 Elsevier Ltd. All rights reserved.