钙熔盐电解中石墨阳极的破损机理及防护研究

【作者】 曾桂生；

【导师】 谢刚； 杨大锦；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2003， 硕士

【摘要】 为了提高钙生产企业的经济效益和加强其在市场中的竞争能力，钙生产企业必须通过各种渠道降低生产成本，也就是从各方面降低熔盐电解过程的生产原材料、辅料及能源等的消耗。石墨阳极在钙熔盐电解中是一项重要的消耗，它在钙熔熔盐电解过程中很容易破损，因而研究石墨阳极的破损机理及研究减少它的损耗具有一定的经济效益和实际意义。 本课题对石墨电极的损耗进行了分析，认为主要是化学损耗和机械损耗，尤其分析了它的氧化消耗动力学，探索了钙熔盐电解过程中的石墨阳极破损机理。理论上，钙熔盐电解过程中产生的Cl₂、HCl、CO₂及其熔盐电解质等对石墨阳极本身不会腐蚀，不可能使石墨阳极破损。通过SEM和电子探针分析，提出了钙熔盐电解过程石墨阳极的破损机理。认为石墨阳极的破损主要是由于石墨阳极中有比较多的孔隙，其中挥发进入石墨阳极表面孔隙的电解质吸水水解、脱水等过程发生膨胀，使周围的石墨颗粒应力不平衡而发生破损；其次是由于石墨阳极孔隙中活性高的石墨颗粒氧化。因此要延长石墨阳极的使用寿命，就必须消除石墨阳极中的孔隙和减少对电解质的吸附以及与氧气接触的机会，采取的有效措施是提高石墨阳极质量或对石墨阳极进行表面处理。本研究将主要集中在后一种方法，即在石墨阳极表面涂上一层比较薄的涂层材料。 在综合大量文献资料的基础上，综述了石墨阳极的抗氧化的方法，即主要有浸渍电极和涂层电极。对涂层的制备方法主要有包埋浸渗法、化学沉积法、等离子喷涂法、溶胶-凝胶法。对钙熔盐电解石墨阳极涂层材料的要求具有耐酸、碱、Cl₂等腐蚀，抗氧化，耐高温，能与C颗粒结合紧密，同时对钙熔盐电解不产生影响。 借助扫描电镜、X-射线衍射等分析技术，通过实验研究出了合适的涂层材料，即SiO₂、B₂O₃，加入水玻璃做为粘结剂。通过改进涂层制备工艺路线，发现涂层致密，涂层与石墨基体结合牢固。从本实验得出：涂层层制备工艺及控制涂层热处理的温度曲线非常重要的。 对涂层进行了XRD、SEM分析、氧化失重实验和热循环实验。实验结果表明该涂层在700-850℃下形成硼玻璃态，XRD实验表明物相的成分仍昆明理下人学硕l学位论文摘要然为BZO:.和5 102，BZO..的流动性能使之渗透到石墨电极的孔隙中，因此该硼玻璃涂层能对石墨基体起抗氧化作用。扫描电镜实验表明涂层能够渗透到石墨阳极孔隙中，玻璃态氧化防护层有效抑制了石墨基体的氧化反应，涂层表面致密无裂纹且附着力强，因而提高了基体的抗氧化能力。气种试样的氧化失重对比实验表明，无涂层的石墨阳极试样氧化失重严重，随着温度的升高，氧化速度加快，在确定温度下随着时间的延长，氧化损失不断增加。SIC涂层只能稍稍提高石墨试样的抗氧化能力，但是硼玻璃涂层比起无涂层的试样和有SIC涂层的试样，抗氧化能力显著提高，氧化失重和氧化速率随氧化时间变化很小。在温度分别为800℃和850℃进行了硼玻璃涂层热循环实验，样品具有极好的抗热冲击能力。实验结果表明该涂层是有效的。更多还原

【Abstract】 To elevate the economic benefit of the calcium enterprises and to strengthen the ability of competition in the marketing, the calcium enterprises must reduce the production costs by all the means, that is, decrease the loss of the raw and auxiliary materials and energy consumption and so on in the process of calcium molten salt electrolysis. Graphite anode is one of the important consumption in the process of calcium molten salt electrolysis, so it is important to research damage mechanism of the graphite anode and reduce its spoilage.The spoilage of the graphite electrode is analyzed in this thesis. It is thought that the chemical consumption and mechanical damage are the main factors. The oxidation kinetics of the graphite electrode is especially analyzed. The damage mechanism of the graphite anode in the calcium molten electrolysis process is investigated. In theory, The Cl2, HCl, CO2 produced in the calcium molten electrolysis process and the electrolyte can’t corrupt the graphite anode. With the analysis of SEM and electron probe, the destroying mechanism is put forward. The electrolyte volatilizes and condenses in the aperture in anode, then partly hydrolyzes and dewater, then the stress are produced by expansion in this process. The expansion stress is the dominant cause of the graphite anode damage, and the oxidation of the active graphite particles on the anode surface is subsidiary for the anode damage. The measures of prolonging the anode service life are to enhance the quality of the anode such as increasing the forming pressure in the preparation and surface treatment before application. So we can use the coating to deal with the surface of the graphite anode, that is, to smear a thin coating material on the surface of anode to fill in the holes and eliminate the contact between the active particles and the oxygen and the electrolyte. The protection coating can separate the graphite from the oxidization air to prevent from oxidization.An overview of current status of research graphite electrode to high temperature oxidation resistant is provided in this thesis. The main meansare impregnating and coating electrode, the methods of the preparation of the coating includes impregnation method, chemical vapor deposition, plasma spraying and the sol-gel method. The requirement of the coating materials of the graphite anode in the calcium molten electrolysis are that the coating used must resist the corrosion to Cl2, H2O and hydrochloric acid, while it has not affect on the calcium molten salt electrolysis, and that the price of the coating itself is low.The protection coating, which has be used on graphite anode of calcium molten salt electrolysis, is developed. The fitting coating materials are SiO2, B2O3 and soluble glass. It is found that the coating is compact without crack and with strongly adhesive. It also can be concluded that to control the temperature of the coating heat treatment is very important.The XRD, SEM analysis, the oxidation weigh loss and annealing circulation experiment with the coating are done. The results indicates the coating is morphology of boric glass which can permeate into the holes of the graphite anode and seal the cracks developed by the coating, and it is adhesive strongly to the graphite anode. It demonstrates that the coating had an excellent oxidation resistance characteristic. The contrast of the oxidation weight loss of three kinds of samples is done. The graphite anode sample without coating oxidizes severely. The oxidation rate is quick with the hoist of the temperature and the weight loss increased with the time pronging at certain temperature. The sample with SiC coating can only improve the anti-oxidation ability a little. The boric glass, however, can improve the anti-oxidation ability evidently, whose oxidation weight loss and rate are change slightly. The annealing circulation with the boric glass coating is done at 800C and 850C, and the results demonstrate the sample has a good impulsion ability. The results show the coating is effect更多还原