Bio-oil is a new liquid fuel but very acidic. In this study, bio-oil pyrolyzed from rice husk and two bio-oil/diesel emulsions with bio-oil concentrations of 10 wt% and 30 wt% were prepared. Tests were carried out to determine their corrosion properties to four metals of aluminum, brass, mild steel and stainless steel at different temperatures. Weight loss of the metals immersed in the oil samples was recorded. The chemical states of the elements on metal surface were analyzed by X-ray photoelectron spectroscopy (XPS). The results indicated that mild steel was the least resistant to corrosion, followed by aluminum, while brass exhibited slight weight loss. The weight loss rates would be greatly enhanced at elevated temperatures. Stainless steel was not affected under any conditions. After corrosion, increased organic deposits were formed on aluminum and brass, but not on stainless steel. Mild steel was covered with many loosely attached corrosion materials which were easy to be removed by washing and wiping. Significant metal loss was detected on surface of aluminum and mild steel. Zinc was etched away from brass surface, while metallic copper was oxidized to Cu2O. Increased Cr2O3 and NiO were presented on surface of stainless steel to form a compact passive protection film. The two emulsions were less corrosive than the bio-oil. This was due to the protection effect of diesel. Diesel was the continuous phase in the emulsions and thus could limit the contact area between bio-oil and metals.
