A kinetic study of the exsolution of pentlandite (Ni,Fe)9S8from the monosulfide solid solution (Fe,Ni)S
A kinetic study of the exsolution of pentlandite (Ni,Fe)9S8from the monosulfide solid solution (Fe,Ni)S
复制标题
一硫化物固溶体(Fe,Ni)S中镍黄铁矿(Ni,Fe)9S8的溶出动力学研究
DOI：
10.2138/am-2004-0106
复制
发表时间：
2004
影响因子：
3.1
通讯作者：
A. Studer
中科院分区：
文献类型：
--
作者：
B. Etschmann;A. Pring;A. Putnis;B. Grguric;A. Studer
摘要利用一系列退火/淬火和原位冷却中子衍射实验研究了镍黄铁矿从单硫化物固溶体中出溶的动力学。通过退火/淬火技术检查了五种mss组合物，所述退火/淬火技术覆盖组合物范围Fe 0.9Ni 0.1S至Fe 0.65Ni 0.35S，并且使用423和773 K之间的退火温度持续1小时至5个月。对Fe_（0.9）Ni_（0.1）S ~ Fe_（0.7）Ni_（0.3）S范围内的四种合金成分进行了原位冷却实验。将这些固溶体的样品加热至973 K，然后在24 h内以50 K的步骤冷却至373 K。出溶的程度进行了监测Rietveld相分析，使用粉末中子衍射数据。退火/淬火实验确定，镍黄铁矿从高于573 K的mss的初始出溶是非常迅速的，并且在退火的1小时内有效地完成。然而，mss/磁黄铁矿组合物保持富镍（17原子%的镍）5个月后退火，表明在低温下的组成重新调整发生在很长一段时间。在573 K以下，出溶速度较慢，速率常数在6 × 10 -6 ~ 1 × 10-5/s之间，在473 ~ 423 K之间镍黄铁矿从mss Fe_（0.5）Ni_（0.2）S中出溶的活化能为5 kJ/mol。原位冷却实验表明，在冷却过程中，出溶开始的温度从Fe 0.7Ni 0.3S的873 K降低到Fe 0.9Ni 0.1S的823 K，在598 ~ 548 K的温度范围内，出溶在实验的时间尺度上有效地停止。用Avrami模型（y = 1 - exp（-kntn））对动力学数据进行了分析，发现出溶的初始速率随Ni含量的增加而增加，从Fe 0.9Ni 0.3S的2 × 10 - 6 Zs增加到Fe 0.7Ni 0.3S的4 × 10-5/s。高Ni含量和高M：S比有助于形核速率，表明形核发生在Mss晶体内的S空位而不是晶界处。的Avrami几何常数n的值在脱溶冷却后变化，表明在反应过程中的生长机制的三种可能的变化。讨论了杂质和硫逸度对反应速率的影响。镍黄铁矿从磁黄铁矿中出溶的速率常数估计比本文报道的要慢4 ~ 5个数量级，但在地质时间尺度上仍然非常快。高金属流动性持续在这个系统中在低温下，甚至在室温下，和纹理和成分观察到的性质是一个非常低的温度（<100 ℃）平衡的组合在地质时间尺度的结果。
Abstract The kinetics of the exsolution of pentlandite from the monosulfide solid solution (mss) have been investigated using a series of anneal/quench and in situ cooling neutron diffraction experiments. Five mss compositions were examined by anneal/quench techniques covering the composition range Fe0.9Ni0.1S to Fe0.65Ni0.35S and using annealing temperatures between 423 and 773 K for periods from I h to 5 months. In situ cooling experiments were performed on four mss compositions in the range Fe0.9Ni0.1S to Fe0.7Ni0.3S. The samples of these solid solutions were heated to 973 K, and then cooled to 373 K in steps of 50 K over a 24 h period. The extent of exsolution was monitored by Rietveld phase analysis using powder neutron diffraction data. The anneal/quench experiments established that initial exsolution of pentlandite from mss above 573 K is very rapid and is effectively complete within 1 h of annealing. However, the mss/pyrrhotite compositions remained Ni rich (17 at% Ni) after 5 months annealing, indicating that compositional readjustment at low-temperatures occurs over long periods. Below 573 K, exsolution is less rapid with rate constants in the range 6 × 1O-6 to 1 × 10-5/s and the activation energy for exsolution of pentlandite from mss Fe0.5Ni0.2S between 473 and 423 K is 5 kJ/mol. The in situ cooling experiments showed that the temperature at which exsolution commences upon cooling decreases from 873 K for Fe0.7Ni0.3S to 823 K for Fe0.9Ni0.1S and that exsolution effectively ceased on the time scale of the experiments at temperatures between 598 and 548 K. The kinetic data were analyzed using the Avrami model where y = 1 - exp(-kntn) and the initial rates of exsolution were found to increase with Ni content from 2 × 1O-6Zs for Fe0.9Ni0.3S to 4 × 10-5/s for Fe0.7Ni0.3S. Both high Ni content and high M: S ratio served to facilitate nucleation rate, indicating that nucleation occurs at S vacancies within mss crystals rather than at grain boundaries. Values of the Avrami geometric constant n vary during exsolution upon cooling indicating three possible changes in the growth mechanism during the reaction. The roles of impurities and S fugacity on reaction rates are discussed. The rate constants for exsolution of pentlandite from mss/pyrrhotite in nature are estimated to be 4 or 5 orders of magnitude slower than those reported here, still very rapid on a geological time scale. High metal mobility persists in this system at low temperatures, even at room temperature, and the textures and compositions observed in nature are a consequence of very low-temperature (<100 0C) equilibration of assemblages over geological time scales.