Water molecules in beryl and cordierite: high-temperature vibrational behavior, dehydration, and coordination to cations
Water molecules in beryl and cordierite: high-temperature vibrational behavior, dehydration, and coordination to cations
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DOI：
10.1007/s00269-011-0420-9
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发表时间：
2011-06-01
影响因子：
1.4
通讯作者：
Shinoda, K.
中科院分区：
文献类型：
--
作者：
Fukuda, J.;Shinoda, K.
典型的环硅酸盐、绿柱石和堇青石的天然样品包括在由开放腔形成的通道中的水和二氧化碳分子。通道中的水分子有两种形式，其区别在于它们是否与骨架外阳离子（II型）或不与骨架外阳离子（I型）配位。本文测量了绿柱石（100）面或堇青石（100）面和（010）面（cb面和ca面）在不同温度条件下的偏振红外光谱。主要谱带的光谱特征清楚地显示了I型和II型水分子在高温下的可区分行为，如下所示。在从室温到800 A摄氏度的温度范围内，快速脱水没有发生，II型水分子的谱带高度的下降小于I型水分子的谱带高度的下降，并且II型水分子的谱带位移更占主导地位。带高和带移的I/II型带的减少也不同绿柱石和堇青石，这是由于水分子固定在通道中的不同方式。在850 A ℃时脱水增强。绿柱石和堇青石的室温红外光谱均由850 A ℃淬灭，表明与Ⅰ型水分子有关的振动带消失后，与Ⅱ型水分子有关的振动带稳定。此外，观察到的II型带的频率变化，可能是因为II型水分子的配位状态的变化，以额外的框架阳离子的通道。
Natural samples of typical cyclosilicates beryl and cordierite include water and carbon dioxide molecules in channels formed by the open cavities. Water molecules in the channels have two forms that are distinguished by whether they coordinate to extra-framework cations (type II) or not (type I). We measured polarized infrared (IR) spectra for thin sections of the (100) plane of beryl or the (100) and (010) planes (cb and ca planes) of cordierite under various temperature conditions. The spectral features of major bands clearly showed the distinguishable behavior of types I and II water molecules under high temperature as follows. Over the temperature range from room temperature to 800A degrees C where rapid dehydration did not occur, the decrease in band heights for type II water molecules were smaller than those for type I, and band shifts were more predominant for type II water molecules. The decrease in band heights and band shifts of type I/II bands differed also for beryl and cordierite, which arises from the different ways in which water molecules are fixed in the channels. Dehydration was enhanced at 850A degrees C. The IR spectra at room temperature quenched from 850A degrees C both for beryl and cordierite showed that the vibrational bands related to type II water molecules were stable after those related to type I water molecules disappeared. In addition, frequency changes of type II bands were observed, possibly because of changes of coordination states of type II water molecules to extra-framework cations in the channels.