Grain growth kinetics of dolomite, magnesite and calcite: a comparative study
Grain growth kinetics of dolomite, magnesite and calcite: a comparative study
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DOI：
10.1007/s00269-010-0389-9
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发表时间：
2011-02
影响因子：
1.4
通讯作者：
N. E. Davis;N. E. Davis;J. Newman;P. B. Wheelock;P. B. Wheelock;A. Kronenberg
中科院分区：
文献类型：
--
作者：
N. E. Davis;N. E. Davis;J. Newman;P. B. Wheelock;P. B. Wheelock;A. Kronenberg
在温度T = 700-800°C、围压Pc = 300 MPa条件下，测定了化学计量白云石[CaMg（CO_3）_2]和菱镁矿（MgCO_3）的晶粒生长速率，并与方解石（CaCO_3）的生长速率进行了比较。通过热等静压（HIP）从高纯度粉末合成了三种碳酸盐的干燥、细粒聚集体;对于CaMg（CO 3）2、MgCO 3和CaCO 3，HIP合成的碳酸盐的初始平均晶粒尺寸分别为1.4、1.1和17 μm，孔隙率分别为2、28和0.04体积%。在随后的均衡退火过程中，所有碳酸盐的粒度粗化，平均值分别达到3.9，5.1和27 μm的CaMg（CO 3）2，MgCO 3和CaCO 3，在1周内。白云石的晶粒生长比菱镁矿或方解石的生长速率慢得多;假设三种碳酸盐的晶粒生长都是正常的，n = 3，则白云石在800°C时的速率常数K（0.55 × 10−5μm3/s）比菱镁矿小约30倍，比方解石小3个数量级。碳酸盐晶粒生长的变化可能受到阳离子组成和晶界处孔隙密度差异的影响，这些差异降低了晶界流动性。然而，粗化率最好的固溶体的程度相关; K是最大的方解石与广泛的镁取代钙，whileK是最小的白云石与可忽略的固溶体。次生相可能在白云石晶界处成核，这对碳酸盐岩的变形过程、流变学和反应动力学具有重要意义。
The rates of grain growth of stoichiometric dolomite [CaMg(CO3)2] and magnesite (MgCO3) have been measured at temperaturesTof 700–800°C at a confining pressurePcof 300 MPa, and compared with growth rates of calcite (CaCO3). Dry, fine-grained aggregates of the three carbonates were synthesized from high purity powders by hot isostatic pressing (HIP); initial mean grain sizes of HIP-synthesized carbonates were 1.4, 1.1, and 17 μm, respectively, for CaMg(CO3)2, MgCO3, and CaCO3, with porosities of 2, 28, and 0.04% by volume. Grain sizes of all carbonates coarsened during subsequent isostatic annealing, with mean values reaching 3.9, 5.1, and 27 μm for CaMg(CO3)2, MgCO3, and CaCO3, respectively, in 1 week. Grain growth of dolomite is much slower than the growth rates of magnesite or calcite; assuming normal grain growth andn= 3 for all three carbonates, the rate constantKfor dolomite (≃5 × 10−5μm3/s) atT= 800°C is less than that for magnesite by a factor of ~30 and less than that for calcite by three orders of magnitude. Variations in carbonate grain growth may be affected by differences in cation composition and densities of pores at grain boundaries that decrease grain boundary mobility. However, rates of coarsening correlate best with the extent of solid solution;Kis the largest for calcite with extensive Mg substitution for Ca, whileKis the smallest for dolomite with negligible solid solution. Secondary phases may nucleate at advancing dolomite grain boundaries, with implications for deformation processes, rheology, and reaction kinetics of carbonates.