Effects of hydration on thermal expansion of forsterite, wadsleyite, and ringwoodite at ambient pressure
Effects of hydration on thermal expansion of forsterite, wadsleyite, and ringwoodite at ambient pressure
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DOI：
10.2138/am.2009.3122
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发表时间：
2008-12
影响因子：
3.1
通讯作者：
Y. Ye;Richard A. Schwering;J. Smyth
中科院分区：
文献类型：
--
作者：
Y. Ye;Richard A. Schwering;J. Smyth
摘要：利用单晶 X 射线衍射测量了镁橄榄石、硅锰矿、尖角橄榄石及其含水形式在环境压力下，温度从低至 133 K 至高至 919 K 的热膨胀系数。采用 ln(V/V0) 与 T 的二阶多项式拟合，导出了 α = a1 × T + a0 形式的膨胀系数。无水硅锰矿的单晶持续温度高达 859 K。观察到含水镁橄榄石在 919 K 时脱水，而含水硅锰矿在 655 K 时开始脱水。0.20 wt% 的尖角橄榄石晶体在 911 K 时分解，并且观察到含有 0.74 和 2.4 wt% H2O 的两个尖角橄榄石样品以不可逆的方式分解。晶胞分别在 808 K 和 606 K 膨胀。从室温到高温，无水镁橄榄石和含水镁橄榄石的平均热体积膨胀系数分别为36.4(5)和38.1(9)×10-6 K-1；无水和含水硅锰矿分别为 28.5(5) 和 35.8(8) × 10-6 K-1；对于含有 0.2、0.74 和 2.4 wt% H2O 的尖角橄榄石样品，分别为 30.6(9)、35.2(15) 和 34.9(7) × 10-6 K-1。因此，镁橄榄石、瓦兹利石和尖角橄榄石在其含水形式中均具有比其无水形式更大的热膨胀系数。
Abstract Single-crystal X-ray diffraction has been used to measure the thermal expansion coefficients of forsterite, wadsleyite, ringwoodite, and their hydrous forms at ambient pressure, from temperatures as low as 133 K to as high as 919 K. Second-order polynomial fitting to ln(V/V0) vs. T was applied to derive the expansion coefficients in the form of α = a1 × T + a0. The single crystal of anhydrous wadsleyite persisted up to 859 K. Hydrous forsterite was observed to dehydrate at 919 K, whereas hydrous wadsleyite started to dehydrate at 655 K. The crystal of ringwoodite with 0.20 wt% broke down at 911 K, and the two ringwoodite samples with 0.74 and 2.4 wt% H2O, were observed to break down with an irreversible unit-cell expansion at 808 and 606 K, respectively. From room temperature to high temperatures in this study, the mean thermal volume expansion coefficients are 36.4(5) and 38.1(9) × 10-6 K-1, respectively, for anhydrous and hydrous forsterite; 28.5(5) and 35.8(8) × 10-6 K-1, respectively, for the anhydrous and hydrous wadsleyite; 30.6(9), 35.2(15), and 34.9(7) × 10-6 K-1 for the samples of ringwoodite with 0.2, 0.74, and 2.4 wt% H2O, respectively. Thus, forsterite, wadsleyite, and ringwoodite all have larger thermal expansion coefficients in their hydrous forms than in their anhydrous forms.