316不锈钢在硝酸嫁盐中的腐蚀行为研究
发布时间：2019-02-11 11:08
【摘要】：储热介质是太阳能热发电转化效率的核心,硝酸熔盐体系是太阳能热发电系统中一种较为成熟的传储热介质,其中Solar Salt(60%KNO3-40%NaN03)和HITECT(53%KN03-7%NaNO3-40%NaNO2)已经被广泛地应用于太阳能热发电站中。但由于硝酸熔盐在高温下仍具有腐蚀性且极易分解,因此储盐管道材料在熔融硝酸盐中的腐蚀成为太阳能热发电技术发展历程上的一个重要问题。材料在熔盐中的腐蚀主要表现为金属的活性溶解,而熔盐体系中的微量杂质和温度是腐蚀的主要推动力。材料在熔盐中的腐蚀本质上是一个电化学过程,故利用电化学技术监测材料的腐蚀过程,可获得腐蚀过程的动力学参数等信息。本文采用电化学监测技术研究316不锈钢在HITECT(53%KNO3-7%NaNO3-40%NaNO2)熔盐中的腐蚀行为,采用SEM/EDS观察了腐蚀产物的微观形貌和元素分布,利用XRD确定了腐蚀产物以及熔盐的相结构,分析了添加微量稀土元素、Cl-以及温度对腐蚀行为的影响。论文取得的主要结果如下:1.添加氧化钇可以降低316不锈钢的腐蚀速率,其腐蚀电流密度由9.47mA·cm-2分别降至7.13mA·cm-2和3.73mA·cm-2。电化学阻抗测试结果表明,316不锈钢在含稀土氧化物的三元硝酸盐中电荷转移电阻值升高,因此耐蚀性得以提高。2.Cl-会减缓三元硝酸盐的分解,显著提高不锈钢在三元硝酸盐中的腐蚀速率。极化曲线表明,其腐蚀电流密度由3.02mA·cm-2升至8.76mA·cm-2。电化学阻抗测试结果表明,316不锈钢在添加Cl-的三元硝酸盐中电荷转移电阻值降低,因而耐蚀性降低。3.温度升高使得316不锈钢的自腐蚀电流由2.02mA·cm-2升至8.09mA·cm-2和34.4 mA·cm-2。电化学阻抗谱测试结果表明,温度升高使得316不锈钢在三元硝酸盐中的转移电阻减小,说明温度升高会降低不锈钢在三元硝酸盐中的耐蚀性。从不锈钢腐蚀后的形貌和成分可以看出,不锈钢在三元硝酸熔盐中会发生选择性腐蚀,腐蚀层出现明显的元素富集区。温度升高会促进三元硝酸盐的分解,所以在保证太阳能储热蓄热正常的情况下,合理控制熔盐工作的温度,有助于降低材料在熔盐中的腐蚀及熔盐自身的分解。
[Abstract]:Heat storage medium is the core of conversion efficiency of solar thermal power generation. Nitric acid molten salt system is a more mature heat transfer medium in solar thermal power generation system. Solar Salt (60%KNO3-40%NaN03) and HITECT (53%KN03-7%NaNO3-40%NaNO2) have been widely used in solar thermal power plants. However, the corrosion of salt storage pipeline materials in molten nitrate has become an important problem in the development of solar thermal power generation technology because the nitric acid molten salt is still corrosive and easy to decompose at high temperature. The corrosion of materials in molten salt is mainly due to the active dissolution of metal, and the trace impurities and temperature in molten salt system are the main driving force of corrosion. The corrosion of materials in molten salt is essentially an electrochemical process, so the kinetic parameters of corrosion process can be obtained by using electrochemical technology to monitor the corrosion process of materials. The corrosion behavior of 316 stainless steel in HITECT (53%KNO3-7%NaNO3-40%NaNO2) molten salt was studied by electrochemical monitoring technique. The microstructure and elemental distribution of corrosion products were observed by SEM/EDS. The phase structure of corrosion product and molten salt was determined by XRD. The effect of adding trace rare earth elements, Cl- and temperature on corrosion behavior was analyzed. The main results are as follows: 1. The corrosion rate of 316 stainless steel can be reduced by adding yttrium oxide, and the corrosion current density of 316 stainless steel decreases from 9.47mA cm-2 to 7.13mA cm-2 and 3.73mA cm-2., respectively. The electrochemical impedance test showed that the charge transfer resistance of 316 stainless steel in the ternary nitrate containing rare earth oxides was increased, and the corrosion resistance of 316 stainless steel was improved. 2. The decomposition of nitrate was slowed down by Cl-. The corrosion rate of stainless steel in ternary nitrate was significantly increased. The polarization curve shows that the corrosion current density increases from 3.02mA cm-2 to 8.76mA cm-2.. The results of electrochemical impedance measurement show that the charge transfer resistance of 316 stainless steel decreases with the addition of Cl- in the ternary nitrate, thus the corrosion resistance of 316 stainless steel decreases. The temperature increases the corrosion current of 316 stainless steel from 2.02mA cm-2 to 8.09mA cm-2 and 34.4 mA cm-2.. The results of electrochemical impedance spectroscopy show that the transfer resistance of 316 stainless steel in the ternary nitrate decreases with the increase of temperature, which indicates that the corrosion resistance of 316 stainless steel in the ternary nitrate is decreased with the increase of temperature. It can be seen from the morphology and composition of stainless steel after corrosion that stainless steel can be selectively corroded in ternary nitric acid molten salt. The increase of temperature will promote the decomposition of ternary nitrate, so the reasonable control of the temperature of molten salt can reduce the corrosion of the material in molten salt and the decomposition of molten salt itself under the condition that the solar energy storage and heat storage is normal.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178
[Abstract]:Heat storage medium is the core of conversion efficiency of solar thermal power generation. Nitric acid molten salt system is a more mature heat transfer medium in solar thermal power generation system. Solar Salt (60%KNO3-40%NaN03) and HITECT (53%KN03-7%NaNO3-40%NaNO2) have been widely used in solar thermal power plants. However, the corrosion of salt storage pipeline materials in molten nitrate has become an important problem in the development of solar thermal power generation technology because the nitric acid molten salt is still corrosive and easy to decompose at high temperature. The corrosion of materials in molten salt is mainly due to the active dissolution of metal, and the trace impurities and temperature in molten salt system are the main driving force of corrosion. The corrosion of materials in molten salt is essentially an electrochemical process, so the kinetic parameters of corrosion process can be obtained by using electrochemical technology to monitor the corrosion process of materials. The corrosion behavior of 316 stainless steel in HITECT (53%KNO3-7%NaNO3-40%NaNO2) molten salt was studied by electrochemical monitoring technique. The microstructure and elemental distribution of corrosion products were observed by SEM/EDS. The phase structure of corrosion product and molten salt was determined by XRD. The effect of adding trace rare earth elements, Cl- and temperature on corrosion behavior was analyzed. The main results are as follows: 1. The corrosion rate of 316 stainless steel can be reduced by adding yttrium oxide, and the corrosion current density of 316 stainless steel decreases from 9.47mA cm-2 to 7.13mA cm-2 and 3.73mA cm-2., respectively. The electrochemical impedance test showed that the charge transfer resistance of 316 stainless steel in the ternary nitrate containing rare earth oxides was increased, and the corrosion resistance of 316 stainless steel was improved. 2. The decomposition of nitrate was slowed down by Cl-. The corrosion rate of stainless steel in ternary nitrate was significantly increased. The polarization curve shows that the corrosion current density increases from 3.02mA cm-2 to 8.76mA cm-2.. The results of electrochemical impedance measurement show that the charge transfer resistance of 316 stainless steel decreases with the addition of Cl- in the ternary nitrate, thus the corrosion resistance of 316 stainless steel decreases. The temperature increases the corrosion current of 316 stainless steel from 2.02mA cm-2 to 8.09mA cm-2 and 34.4 mA cm-2.. The results of electrochemical impedance spectroscopy show that the transfer resistance of 316 stainless steel in the ternary nitrate decreases with the increase of temperature, which indicates that the corrosion resistance of 316 stainless steel in the ternary nitrate is decreased with the increase of temperature. It can be seen from the morphology and composition of stainless steel after corrosion that stainless steel can be selectively corroded in ternary nitric acid molten salt. The increase of temperature will promote the decomposition of ternary nitrate, so the reasonable control of the temperature of molten salt can reduce the corrosion of the material in molten salt and the decomposition of molten salt itself under the condition that the solar energy storage and heat storage is normal.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178
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