高温高压下水热体系中黄铁矿-金原电池的腐蚀电化学原位测量研究

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	高温高压下水热体系中黄铁矿-金原电池的腐蚀电化学原位测量研究
其他题名	In Situ Electrochemical Study on Pyrite-Gold Galvanic Cell in Hydrothermal Systems at High Temperature and High Pressure
	周丽
	2006-12-26
学位授予单位	中国科学院地球化学研究所
学位授予地点	地球化学研究所
学位名称	博士
关键词	高温高压水热体系黄铁矿金导电性矿物原电池腐蚀电流开路电压腐蚀电化学
摘要	水流体-导电性矿物相互作用是自然界中水流体-固体相互作用的重要组成部分，是许多矿床形成和演化的核心过程。迄今为止，绝大多数地质和地球化学家们对导电性矿物在水流体中的溶解机制普遍存在模糊的认识，认为水流体中导电性矿物的溶解和定位是一种简单的化学溶解和沉淀或简单的氧化溶解和还原定位过程，而实质上导电性矿物（组合）在水流体中的溶解是一种由电极电位差驱使下的类似于金属腐蚀的复杂电化学过程。当具有不同电极电位的矿物在溶液中相互接触，就会形成短路原电池发生电化学腐蚀。其中，电极电位低的矿物作为原电池的阳极，其溶解会加剧，而电极电位高的矿物作为原电池的阴极，其溶解会受到抑制。鉴于前人对水流体-导电性矿物相互作用的腐蚀原电池反应机理的模糊认识，本论文工作基于腐蚀原电池观点对高温高压条件下NaCl水流体体系中黄铁矿与金之间的原电池反应进行了研究。在本工作中，作者与所在的研究小组一道，首先自行研制了一套可用于高温高压水热体系中导电性矿物腐蚀电化学原位测量的高压釜反应装置。该装置主体部件选用在高温高压下具有高强度、抗腐蚀等优良性能的工业纯钛制成。在该装置中，通过将热电偶直接插入高压釜釜腔内，成功地实现了釜内流体温度的准确测量和精确控制。对高压釜不同部位的测温结果表明，沿高压釜的径向与轴向均存在显著的温度梯度，其中釜塞保护锥体处的温度比釜内流体的温度低约8℃，釜外壁中心处与釜内的温度差约10℃；对400℃保温条件下釜内流体温度的直接测量表明，釜内温度波动小于0.5℃。在该装置中，通过将脆性导电性矿物制作成锥形电极，采用耐高温无机绝缘材料制作密封部件，利用锥体自紧式密封技术，成功地解决了脆性电极和电极引线的高压密封与高温绝缘问题；通过引入另一根辅助性的矿物电极引线，成功地解决了原位监测实验过程中矿物电极与引线接触处是否进水的难题，确保了实验的可信度。可行性试验结果表明，该方法不仅可用于高温高压下水流体-导电性矿物，而且可广泛用于水流体-金属间相互作用的腐蚀电化学原位测量研究。利用上述自行研制的腐蚀电化学实验装置，本工作对高温高压（250-400℃；10-35 MPa）NaCl水流体体系中黄铁矿-自然金原电池的热力学和动力学进行了实验研究。原位测量结果表明：（1）黄铁矿-金原电池的腐蚀电流变化与其开路电压的变化一致；（2）汽-液平衡条件下，黄铁矿-金原电池的开路电压和腐蚀电流在液相中比在汽相中要大；（3）在温度为400 C、压力远离临界点的过热蒸气和超临界区域，压力在实验研究的范围内（10-35 MPa）对黄铁矿-金原电池的开路电压和腐蚀电流均无显著的影响，随压力的增加两者仅略有增大，但当温度压力跨越临界点时，包括温压从汽-液平衡曲线同时进入超临界区以及温度恒定在400 C、压力跨越临界点时，黄铁矿-金原电池的开路电压和腐蚀电流在临界点附近均发生突变。（4）在本工作中实验的温度、压力和水流体体系条件下，由黄铁矿与金构成的原电池在大多数情况下黄铁矿为阳极，因此在原电池短路时黄铁矿在水流体中发生氧化溶解，而金则为阴极，在原电池短路时金的溶解受到保护，仅在个别狭窄的温度压力范围内情况才相反。上述原位测量结果与电极表面水流体的性质以及黄铁矿和金的能带结构密切相关，运用混合电位理论、Butler-Volmer方程以及半导体电化学的波动能级模型对实验结果能进行很好的解释。
其他摘要	The interactions between electrically conductive minerals and aqueous fluids are important portions of aqueous fluid-solid interactions in nature, which play an important role in the formation and evolution of ore deposits. To date, the mechanism of the dissolution and precipitation of electrically conductive minerals in aqueous fluids has not been well understood by most geologists and geochemists. Usually they consider that an electrically conductive mineral is dissolved and precipitated by a simple mechanism similar to that of a non-conductive mineral or through simple oxidative and reductive processes. However, the dissolution of electrically conductive minerals in aqueous fluids is essentially a complicated electrochemical corrosion process driven by electrochemical potential difference, like the corrosion of metals. For example, galvanic corrosion may occur when two sulfide minerals with different potentials contact each other in solution. The mineral with lower potential acts as an anode and its oxidation is intensified, whereas the mineral with higher potential as a cathode and protected. It is on the basis of the viewpoint of corrosion galvanic cell that this paper carried out the experimental studies on both the dissolution thermodynamics and kinetics of pyrite-gold couple in NaCl hydrothermal system at high temperature and high pressure. In this work, we first designed and manufactured a new type of autoclave , which could be widely used to in situ measure the corrosion electrochemical processes of electrically conductive minerals in high-temperature and high-pressure hydrothermal systems. The main parts of the new equipment were made of pure titanium with high strength and perfect anti-corrosion properties at high-temperature and high-pressure conditions. In this equipment, the reliable measurement and accurate control of the fluid temperature in the autoclave were achieved by directly installing the thermocouple at the center of autoclave cell. During the 400℃ maintaining process, for example, the fluctuation of the fluid temperature in the autoclave could be controlled less than 0.5℃. Results of the temperature measurements for different parts of the autoclave indicated that there existed remarkable temperature gradients along both the axial and radial directions of the autoclave. The temperature of the steel cone in the plug of the autoclave and the temperature at the center of the outer wall of the autoclave were approximately 8℃ and 10℃ lower than that of the fluids in the autoclave, respectively. To solve the problems of high-pressure sealing and high-temperature insulating of both the brittle mineral electrode and lead wires, the brittle mineral was manufactured into a cone, the seal accessories were made of heat-resistant inorganic insulation materials, and the cone self-sealing technique was employed. By using a nickel wire as assistant lead of the mineral electrode, we successfully realized the in situ monitoring of the leakage of water from autoclave cell into the contact surface of lead wire with the mineral electrode and effectively guaranteed the reliability of our experiments. Our feasibility tests indicated that the in situ electrochemical measurement system developed in this work was applicable not only to the study of the interactions between aqueous fluids and electrically conductive minerals, but also to the investigation of the electrochemical corrosion processes of metals in aqueous fluids at high temperature and high pressure. Using the above technique, we in situ measured both the thermodynamic and kinetic behaviors of pyrite-gold galvanic cell in NaCl hydrothermal systems at high temperature and high pressure (250-400℃; 10-35 MPa). The main results are as follows: (1) Variations of the corrosion current of the pyrite-gold galvanic cell were consistent with the changes of its open-circuit voltage; (2) Under vapor/liquid equilibrium conditions, both the open-circuit voltage and the corrosion current of pyrite-gold galvanic cell in liquid were higher than those in vapor; (3) In super-heated vapor region and supercritical region of NaCl-H2O diagram, the influences of pressure at constant temperature of 400 C on the open-circuit voltage and the corrosion current of pyrite-gold galvanic cell were not remarkable, with both the parameters only slightly increasing with pressure. But near the critical temperature and/or pressure of the aqueous fluids, both the open-circuit voltage and corrosion current of pyrite-gold galvanic cell changed drastically with temperature and/or pressure, no matter the temperature and pressure reached the critical point simultaneously along the vapor-liquid equilibrium curve of NaCl-H2O diagram, or only the pressure reached the critical pressure at constant temperature of 400 C; (4) Under the experimental conditions of this work, the pyrite acted in general as an anode and its oxidative dissolution in the fluids was enhanced when coupled with gold, while the gold acted as the cathode, whose dissolution was protected. Only in several narrow temperature and pressure ranges, was the situation opposite. The theoretical analysis in the present work demonstrated that the above measured electrochemical behavior of pyrite-gold galvanic cell closely related to the properties of the fluid on the electrode surface and to the energy-band structures of pyrite and gold electrodes Moreover, the above experimental results could be well explained by the mixed potential theory and Butler-Volmer equation in solution electrochemistry and the fluctuating energy level model in semiconductor electrochemistry.
页数	83
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3204
专题	研究生_研究生_学位论文地球深部物质与流体作用地球化学研究室
推荐引用方式 GB/T 7714	周丽. 高温高压下水热体系中黄铁矿-金原电池的腐蚀电化学原位测量研究[D]. 地球化学研究所. 中国科学院地球化学研究所,2006.

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