High Temperature Corrosion of Nickel in NaVO₃-V₂O₅Melts

Abstract

Many alloys used at high temperature in industrial processes are Ni-based and many others contain it in appreciable quantities, so it is of interest to evaluate the performance of pure nickel in order to determine the behavior of its alloys once the elements responsible for their protection have been depleted due to accelerated corrosion processes in the presence of vanadium-rich molten salts. Due to this, this work presents the study of Ni behavior in NaVO3-V2O5mixtures at different temperatures. The behavior of pure nickel was determined by both electrochemical and mass loss measurements. The results show that the aggressiveness of the vanadium salts is increased by increasing both the V2O5content and temperature. V2O5addition considerably increases the current densities of the anodic and cathodic reactions. The corrosion process of Ni is modified due to the presence of its corrosion products, and its presence increases the activation energy by at least one order of magnitude. Although nickel shows a high reactivity in vanadium-rich salts, its reaction products are highly stable and protect it from the corrosive medium because the corrosion reactions trap the vanadium and block the migration of nickel ions.

Rare Earth-Based Compounds as Inhibitors of Hot-Corrosion Induced by Vanadium Salts

“…Other proposals are based on the use of NiO, which is capable of reacting with vanadium salts, forming refractory compounds (Ni 3 V 2 O 8 ) with a higher melting point (1310 °C) than those obtained if Mg compounds are used as inhibitors [9,11]. These studies are consistent with those that indicate that metallic Ni shows a high resistance to corrosion by V salts due to the formation of a protective barrier of Ni 3 V 2 O 8 on its surface [14,15].…”

“…On the other hand, the mapping of Ni and O allows us to observe a superficial enrichment in Ni, as well as a lower density, as a corrosion product. Previous studies have shown that pure Ni shows good corrosion resistance in NaVO 3 at 900 °C [14], being able to develop a protective oxide (NiO) and highly stable corrosion products (Ni vanadates). Moreover, according to the element mapping, it is observed that the corrosion-product layer is formed by metal oxides and vanadates (of the alloy elements of the steel), and in a lower concentration by vanadium salts.…”

“…Lanthanum compounds decrease the aggressiveness of the melt because they neutralize the V due to the formation of lanthanum orthovanadate, which has a melting point greater than 1800 °C [34]. Additionally, it also increase the melt basicity and, therefore, the corrosivity of the vanadium salts decreases [5,6,14].…”

Performance of air plasma sprayed Cr3C2–25NiCr and NiCrMoNb coated X8CrNiMoVNb16–13 alloy subjected to high temperature corrosion environment

“…Simultaneously, VO 3 in equation (5) form V 2 O 5, and also some V 2 O 5 from the MS reacts with protective NiO and Cr 2 O 3 oxides to form Ni 3 V 2 O 8 and CrVO 4 oxides, respectively [31]. Porcayo-Calderon et al [35] stated that even at different temperatures (700 °C, 800 °C, and 900 °C), Ni element in the surface form Ni oxide layer, which is rich in Ni, V and O content and the same had been reported by other researchers [31]. These Ni layers are corroded by vanadium salt, but this corroded product acts as a barrier and prevents the infiltration of corrosion agents to the substrate.…”

Behavior of Ni20Cr Alloy in Molten Nitrate Salts

“…In general, the corrosion mechanism depends mainly on the type of anion in the molten salt, where those based on nitrates correspond to oxyanionic salts and the concentration of the oxide ion (O −2 ) defines the basicity of the melt. The importance of the basicity of the melt on the dissolution mechanism of the metallic surface and its protective layers has already been previously documented [21][22][23][24][25][26][27]. In the case of Solar Salt, in the molten state, it experiences the following decomposition reactions, and its reaction rate increases with increasing temperature [1,12,[28][29][30]:…”