Review—Concentration Measurements In Molten Chloride Salts Using Electrochemical Methods

The electrochemical measurement of concentration in molten chloride salts is a valuable tool for the control of existing and potential industrial processes, recycling of precious materials and energy production. The electrochemical techniques commonly used to measure concentration and each techniques’ associated theory are discussed. Practices which improve measurement accuracy and precision are set forth. Exceptionally accurate and precise measurements published in the literature are evaluated based on their performance in specified concentration ranges. The strengths and weaknesses of the most accurate measurements are briefly explored. Chronopotentiometry (CP) and square wave voltammetry (SWV) are accurate and precise with low concentration measurements. SWV was accurate at low concentrations, even in multi-analyte mixtures. CP was accurate for only single analyte mixtures. Open-circuit potentiometry (OCP) is accurate and precise in single-analyte mixtures but yields large errors in multianalyte mixtures. Cyclic voltammetry (CV), chronoamperometry (CA) and normal pulse voltammetry (NPV) are accurate and precise across all concentration ranges. NPV is exceptionally well suited for measurements in melts with multiple electroactive species.

An Experimental Study on High Temperature Corrosion of TP347H Stainless Steel in Molten Chloride and Sulfate

The corrosion resistance of TP347H stainless steel was evaluated by measuring mass loss in molten salt at 500-650°C. The corrosion mechanism was characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The results show that the corrosion resistance of TP347H stainless steel increases with the increase of corrosion temperature. When the temperature is below 600°C, TP347H mainly generate low-stable FexOy, and the oxides such as Fe2O3, Fe3O4, Ni1.43Fe1.7O4 and NiFe2O4 are dissolved with the increase of temperature. NbO with higher stability is formed on the surface at 650 °C, which help Cr2O3 and NiO retain for a longer time. Mn-containing compounds on the surface further improve corrosion resistance of TP347H. The corrosion of TP347H stainless steel is mainly intergranular corrosion, and the temperature range of corrosion is consistent with the melting range of alkali metal chloride. Therefore, the molten alkali metal chloride plays a decisive role in the corrosion of TP347H stainless steel.