Development of an External Pressure Balance Reference Electrode for Use in Supercritical Water Systems

开发用于超临界水系统的外部压力平衡参比电极

• 批准号: 14350377
• 负责人: HARA Nobuyoshi
• 金额: $ 10.94万
• 依托单位: TOHOKU UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2002
• 资助国家: 日本
• 起止时间: 2002 至 2004
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-14350377/
• 关键词: Supercritical water oxidation; Corrosion; External Pressure Balance Reference Electrode; Corrosion potential; Polarization curve; Ag-AgCl electrode; Hydrogen electrode; Subcritical water; 超臨界水酸化

Supercritical water oxidation (SCWO) is a promising method for decomposing hazardous organic wastes into harmless inorganic compounds in a high efficiency and a short time. However, SCWO reactors suffer from severe corrosion by hydrogen halide, nitrate, sulfate, and phosphate, which are formed during destruction of the wastes. Consequently, it is necessary to make clear corrosion mechanism in the SCWO environment and to establish the countermeasure to prevent corrosion. For this purpose, the development of electrochemical measurement is necessary. The objective of this study is to develop a new type of external pressure balanced reference electrode (EPBRE) for electrochemical measurement in supercritical water, to evaluate its performance, and to apply it to the measurement of anode polarization curves in supercritical water.A Ag/AgCl electrode was installed in a small pressure vessel at room temperature. The pressure of this external reference electrode was maintained at the same valu … More es as that of an autoclave at high temperature by pumping an internal solution (0.1M KCl) with a high-pressure pump. In this reference electrode system, liquid junction is set in the room temperature side, so that thermal liquid junction potential (TLJP) generates between the EPBRE and a test electrode in the high temperature side. In order to evaluate the value of TLJP, a Pt-hydrogen electrode (PHE) was first installed in the high temperature autoclave, and the potential difference between PHE and EPBRE electrodes was measured. 0.1M KCl, 0.05M Na_2SO_4, 1mM Na_2SO_4, pure water, 1mM HCl and 1mM NaOH were used for the test solution and TLJPs for the solutions were measured in the temperature range of 298〜773K. Thus evaluated TLJPs can be used to convert the measured potential into the potential referred to SHE. Anode polarization curves of SUS304 stainless steel were measured in the temperature range of 563-673K.It was found that there is little or no difference in the value of TLJP for 1mM Na_2SO_4 and 0.05M Na_2SO_4, indicating that the TLJP is independent of the concentration Na_2SO_4 over the range used in this experiment. The TLJP in 0.1 M KCl was approximately the same as that in Na_2SO_4. The change of TLJP with solution composition is small in neutral solutions used in this experiment. The anode polarization curves of SUS304 steel in 0.05M Na_2SO_4 solution showed four characteristic regions : active dissolution, passivity, transpassivity, and oxygen evolution. Starting potentials of transpassivity and oxygen evolution shifted to negative direction with increasing temperature. In supercritical 0.1M KCl solution at 673K, SUS304 steel was suffered from pitting. In the anode polarization curves of SUS304 steel at 673K, the starting potential of transpassive dissolution shifted to the positive direction with decreasing pH and at the same time the transpassive dissolution current density increased. Less

超临界水氧化（SCWO）是一种在短时间内将危险废物有机物分解为无害无机化合物的有前景的方法，但SCWO反应器会受到生成的卤化氢、硝酸盐、硫酸盐和磷酸盐的严重腐蚀。在进行测试的废物的过程中，有必要明确SCWO环境中的腐蚀机理并制定防止腐蚀的对策，为此，电化学测量的目标是必要的。本研究旨在开发一种用于超临界水电化学测量的新型外压平衡参比电极（EPBRE），评估其性能，并将其应用于超临界水阳极极化曲线的测量。在室温下安装在一个小型压力容器中，通过用泵泵送内部溶液 (0.1M KCl)，将外部参比电极的压力保持在与高温高压釜相同的值。在该参比电极系统中，液接界设置在室温侧，以便在EPBRE和高温侧的测试电极之间产生热液接界电势(TLJP)，以便评估该值。 TLJP首先在高温高压釜中安装Pt-氢电极(PHE)，测量PHE和EPBRE电极之间的电位差0.1M KCl、0.05M。测试溶液采用Na_2SO_4、1mM Na_2SO_4、纯水、1mM HCl和1mM NaOH，并在298〜773K温度范围内测量溶液的TLJP，因此评估的TLJP可用于将测量的电势转换为参考电势。在SHE温度范围内测量了SUS304不锈钢的阳极极化曲线。 563-673K。发现1mM Na_2SO_4和0.05M Na_2SO_4的TLJP值几乎没有差异，表明在本实验使用的范围内TLJP与Na_2SO_4的浓度无关。 KCl与Na_2SO_4中的TLJP大致相同，在所用的中性溶液中，TLJP随溶液组成的变化很小。实验中SUS304钢在0.05M Na_2SO_4溶液中的阳极极化曲线呈现出四个特征区域：活性溶解、钝化、透钝性和析氧，随着温度的升高，透钝性和析氧的起始电位向负方向移动。在673K的M KCl溶液中，SUS304钢出现点蚀。在673K的SUS304钢的阳极极化曲线中。 673K时，随着pH的降低，跨钝溶解的起始电位向正方向移动，同时跨钝溶解电流密度增加。