Microbial induced corrosion in Zn-Ni-Cu and Zn-Ni-Cu-TiB2 coated mild steel

Abstract

Zn-Ni-Cu and Zn-Ni-Cu-TiB 2 coatings were coated on a mild steel substrate utilizing a high-velocity oxy-fuel (HVOF) thermal spray process. A field emission scanning electron microscope (FESEM) was used to examine the microstructural characteristics of both coated and uncoated mild steel samples. Immersion tests following ASTM G-31, ASTM G1-03, standards were performed in Escherichia Coli (E-Coli) bacteria medium for 28 days (672 hrs), the weight loss of uncoated mild steel specimen was 982.5 mg, for Zn-Ni-Cu coated mild steel it was 116.5 mg, and for Zn-Ni-Cu-TiB 2 coated mild steel it was 115.1 mg. The uncoated mild steel specimen showed well-developed bacterial colonies on the surface and floating colonies of bacteria were observed in the medium solution. The coatings performed well and limited the growth of bacteria. Very few colonies of bacteria could be seen in both coated sample mediums. The presence of Zn and Cu prevented the bacterial attachment with coated surface and hence prevented the underlying substrate from being corroded substantially. Tafel polarization and electrochemical impedance spectroscopy (EIS) in Escherichia Coli (E-Coli) medium confirmed that coated samples were more corrosion resistant than uncoated mild steel specimens because the corrosion potential (Ecorr) values of both coated samples were higher than uncoated mild steel suggesting better anodic protection. The corrosion current density (Icorr) of both coated samples (Zn-Ni-Cu and Zn-Ni-Cu-TiB 2 ) were lower than uncoated mild steel specimens also inferring better performance of a coating in microbial induced corrosive environments.