光谱学与光谱分析, 2023, 43 (4): 1205, 网络出版: 2023-05-03  

方解石高温相变实验研究

Experimental Study on High-Temperature Phase Transformation of Calcite
作者单位
1 北京经济管理职业学院珠宝与艺术设计学院, 北京 100102
2 中国地质大学(北京)珠宝学院, 北京 100083
3 浙江地矿科技有限公司, 浙江 杭州 310000
摘要
作为常见碳酸盐矿物, 方解石形成于多种地质环境, 在地球上广泛分布, 在地球深部随着温度压力的改变可转变为不同的相态, 其在不同的温压条件下的物理化学性质对于研究地球深部碳循环可具有一定的指示意义。 由于方解石在1 164 K附近发生分解, 目前关于方解石在高温下的相变研究还相对较少, 尤其是CaCO3-Ⅰ到CaCO3-Ⅳ的相变, 需要更多的实验数据加以佐证。 在通CO2气氛条件下, 采用高温Raman(298~1 323 K)和高温XRD(298~1 223 K)实验技术对方解石在不同温度条件下的行为进行了研究。 高温Raman实验发现: 随着温度的升高, 拉曼峰逐渐向低频率方向移动, 峰的半高宽随之增加, 峰强基本呈现逐渐降低的趋势; 随着温度的升高, 276 cm-1峰向低频方向移动, 当温度升高至973 K时, 该峰频率出现反常行为, 移向高频265 cm-1, 在1 023~1 223 K范围内频率基本保持在265 cm-1不变, 温度升高至1 248 K时, 再次移向高频266 cm-1, 并在1 248~1 298 K范围保持不变; 706和1 430 cm-1谱峰频移在1 223 K附近也发生了同样的异常行为; 谱峰频移的异常现象推测与CaCO3-Ⅰ到CaCO3-Ⅳ、 CaCO3-Ⅴ相变相关, 与相关报道的相变温度点十分接近。 高温XRD实验发现: 随着温度的升高, 一些衍射峰移向高角度, 一些衍射峰移向低角度, 部分相邻的衍射峰发生合并并逐步分离的现象; 衍射峰(211)在1 123~1 173 K 附近消失, 推测与CaCO3-Ⅰ到CaCO3-Ⅴ的相变相关; 方解石a轴呈现出负热膨胀, c轴呈现出正热膨胀; 通过热膨胀方程对CaCO3-Ⅰ在不同温度下的晶胞参数进行拟合, 获得a轴方向在常温下的热膨胀系数α0(a)为-0.60(2)×10-5/K, c轴方向在常温下的热膨胀系数α0(c)为2.42(4)×10-5/K, 体积V在常温下的热膨胀系数α0(V)为1.21(2)×10-5/K; 然而1 000 K附近XRD图谱没有发生明显的改变, 即未发现CaCO3-Ⅳ的存在。
Abstract
As a common carbonate mineral, calcite is formed in various geological environments and is widely distributed on the earth. It can change into different phase states with the temperature and pressure change in the deep earth. Its physicochemical properties under different conditions can be of certain guiding significance for understanding the deep carbon cycle of the earth. Due to the decomposition of calcite near 1 164 K, there are relatively few studies on the phase transition of calcite at high temperatures, especially the phase transition from CaCO3-Ⅰ to CaCO3-Ⅳ, which needs more experimental data. In this study, the behavior of calcite at different temperatures was studied by high-temperature Raman (298~1 323 K) and XRD (298~1 223 K) under the CO2 gas stream. High-temperature Raman experiment shows that, with the increase in temperature, the Raman peak obviously moves to the low frequency, the half-height width of the peak gradually increases, and the peak intensity decreases. The Raman shift of 276 cm-1 gradually moves to the lower frequency with increasing temperature. When the temperature rises to 973 K, the Raman shift appears abnormal behavior and moves to 265 cm-1. The frequency remains unchanged in the range of 1 023~1 223 K. When the temperature rises to 1 248 K, it moves to 266 cm-1 and remains unchanged between 1 248 and 1 298 K. Th Raman shift of 706 and 1 430 cm-1 also behavior abnormally near 1 223 K. The abnormal temperature of the Raman shift is speculated to be related to the phase transition of CaCO3-Ⅳ to CaCO3-Ⅴ, which is very close to the phase transition temperature reported by previous research. High-temperature XRD experiments indicate that, with the increase in temperature, some diffraction peaks move to a lower angle, some diffraction peaks move to a high angle, and some adjacent diffraction peaks merge and gradually separate. The peak (211) disappears near 1 123~1 173 K, which is speculated to be related to the phase transition from CaCO3-Ⅰ to CaCO3-Ⅴ. The a-axis of calcite shows negative thermal expansion, and the c-axis shows positive thermal expansion. The thermal expansion equation fitted the cell parameters at different temperatures, and the thermal expansion coefficientα0(a) is -0.60(2)×10-5/K, α0(c) is 2.42(4)×10-5/K, and α0(V) is 1.21(2)×10-5/K. However, there was no obvious change in the XRD pattern near 1 000 K. That is, no CaCO3-Ⅳ was found.

王美丽, 施光海, 张晓晖, 杨泽钰, 邢瑛梅. 方解石高温相变实验研究[J]. 光谱学与光谱分析, 2023, 43(4): 1205. WANG Mei-li, SHI Guang-hai, ZHANG Xiao-hui, YANG Ze-yu, XING Ying-mei. Experimental Study on High-Temperature Phase Transformation of Calcite[J]. Spectroscopy and Spectral Analysis, 2023, 43(4): 1205.

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