Spectroelectrochemical Study of Stainless Steel Corrosion in NaCl-KCl Melt

Abstract

High-temperature spectroelectrochemestry was applied to study corrosion of various types of stainless steel in molten salts. The electronic absorption spectra of products of anodic dissolution of stainless steel major components (iron, chromium, nickel, molybdenum, manganese, titanium) were measured in NaCl-KCl melt at 750 0 C. The effectiveness and limitations of applying spectroscopic method for studying alloys corrosion was demonstrated on example of anodic dissolution of AISI 316L, 316Ti and 321 austenitic steels. The major corrosion products of steels are iron, manganese and chromium species. Prolongation of anodic dissolution leads to increasing chromium-to-iron ratio in the melt. Titanium in steels forms very stable carbonitride species that aren't dissolved during anodic oxidation.

Corrosion of Nickel-Chromium-Molybdenum Based Alloy in Chloride Melts Containing Transition Metal Ions

“…Thus, as a result of formation of new excessive phases, the continuous γ-solid solution Ni-Cr-Mo is transformed into a three-phase system -grain of alloy | depleted in molybdenum zone | excessive phase. As the interaction process of multicomponent steels and alloys with molten chloride has an electrochemical nature (4,8,9), the depletion by the electropositive molybdenum zone will act as a anode of formed microgalvanic pairs in the obtained three-phase system during the contact with electrolyte. The most electronegative elements of anode zone formed galvanic element (such as chromium and manganese) will be etched from this region (Figure 3).…”

“…The described influence is caused by unavoidable high temperature exposure in contact with molten salts for a prolonged period of time. Previously our group showed that the main reason of intergranular corrosion in molten chlorides is the sensitization effect resulting in formation of excessive carbide phases at the grain boundaries (9). The formation of heterophase structure leads to appearance of microgalvanic pairs and acceleration of corrosion processes.…”

“…The cations of melt, impurities in electrolytes or oxidizing components of gas atmosphere can act as typical oxidizing agents. A detailed research of austenitic steel corrosion in NaCl-KCl based melts revealed the noticeable influence of thermal processing of steel materials on their corrosion resistance that may lead to interganular destruction of the metal (8,9). The described influence is caused by unavoidable high temperature exposure in contact with molten salts for a prolonged period of time.…”

Molten Salt Reactor Engineering Study for Off-Gas Management

“…Combining spectroscopy with electrochemistry in spectroelectrochemistry is particularly valuable for the interrogation and control of conditions present in the salt. Spectroelectrochemistry has been used in molten salt systems for both its ability to determine speciation and for controlling the oxidation states of specific species within these systems (Nagai et al, 2005;Polovov et al, 2007;Volkovich et al, 2007;Polovov et al, 2008;Abramov et al, 2010;Nagai et al, 2011;Park et al, 2011;Nagai et al, 2013;Schroll et al, 2016). Corrosion products such as Cr, Fe, Ni, Mo, Ti, and Mn have been studied using spectroelectrochemical methods (Volkovich et al, 2007;Abramov et al, 2010).…”

Corrosion of Ferritic and Ferritic-Martensitic Steels in NaCl-KCl-VCl2 Melts

“…The absence of titanium in the surface layer can be explained by the formation of inclusions of titanium carbide and carbonitride in the bulk of steel. It was shown that such compounds do not dissolve in contact with the electrolyte but can transfer to the melt as solid particles in a result of spalling (21). The determined kinetic dependencies of sample weight change and corrosion rate for 08Kh17T in molten NaCl-KCl-VCl 2 salt at 750 0 C are presented in Figures 2 and 3, respectively.…”