THERMODYNAMIC MODELLING OF THE CORROSION PROCESS OF Fe–Cr–NiALLOYS IN ASULFATE-BEARING AGGRESSIVE MEDIUM: DEVELOPMENT OF AN OPTIMAL COMPOSITION BASED ON THE NERNST EQUATION AND POURBAIX DIAGRAMS

Thispaperpresentsathermodynamicmodel ofthecorrosionprocessoftheFe–(0–20%)Cr–(0–10%)Nialloysystemin anaggressiveliquidmedium containing10–50 g/LH2SO4, 1–6 g/LCu2+ andFe3+ ions, characteristicofthehydrometallurgicaldivisionofAlmalykMMC JSC. Thescientificproblemaddressedis thatpurelyexperimentaloptimizationofcorrosion-resistantcoatingcompositionsis time-andresource-intensive, whichmotivatesatheoreticallypredictivethermodynamicapproach. Pourbaixdiagramswereconstructedoverthetemperaturerange25–70 °Con thebasisoftheNernstequationandtheGibbs–Helmholtzformula. TheinfluenceofCrandNicontenton thecorrosionratewasevaluatedusingthepolarization-resistance(Stern–Geary) method. Accordingto theresults, Fe+18%Cr+6%Niwasidentifiedas theoptimal composition(Vcorr= 0.011 mm/year). Thescientificnoveltyofthestudyliesin theintegratedthermodynamic–electrochemicalmodellingframeworkdevelopedspecificallyforasulfatemedium containingsimultaneousCu2+ andFe3+ oxidizers, acombinationnotpreviouslytreatedjointlyin thereviewedliterature. Thefindingsofferapracticallyapplicablebasisforselectingcorrosion-resistantsteelgradesandcoatingsforhydrometallurgicalequipment.