Comparative evaluation of freeze-dried and hot air-dried Spirulina Platensis extracts as green inhibitors for mild steel corrosion

Abstract

ABSTRACT Spirulina, a commercially farmed cyanobacteria, offers potential as a nontoxic corrosion inhibitor. However, traditional drying methods deteriorate its protective feature and this challenge must be overcome to enhance corrosive resistance. The present study compares the corrosive inhibitor performance of Spirulina extracts from freeze (SP1) and hot air drying (SP2). The electrochemical and microscopic techniques revealed that freeze-dried-derived Spirulina inhibited over 90% of corrosion through the chemisorption process where freeze-dried-derived Spirulina maximises the inhibitory compounds binding to steel. Polarisation measurements showed that SP1 provided higher inhibition efficiencies of over 93% at certain concentrations compared to around 88% for SP2. At the optimal concentration of 2 g/L, Rp values increased from 35.17 Ω/cm2 (uninhibited) to 531.3 Ω/cm2 for SP1 and 282.7 Ω/cm2 for SP2. Negative ΔGads values (−42.4 kJ/mol for SP2, −46.3 kJ/mol for SP1) and Langmuir isotherm fit indicated chemisorption-controlled adsorption. SEM/EDX showed SP1 and SP2 formed barrier layers inhibiting surface damage compared to blank steel. SP1 layer provided better protection. In short, through innovative applications of marine resources, greener corrosion management is enabled.