Abstract
Corrosion behavior of nickel in concentrated NaOH solutions at high temperatures in the presence of pressurized oxygen has been investigated in relation to a proposed process for waste PET to be chemically recycled. Under 5 MPa of oxygen, nickel became less corrosion-resistant as the concentration of NaOH increased at 423 K, forming Ni(OH)_2 on its surface. At 473 K, the amount of corrosion took maximum at 10 mol kg^<-1> (m) of NaOH. The corrosion product changed from Ni(OH)_2 to NiO at 30 m and the weight loss decreased. At 523, corrosion product was NiO at every concentration of NaOH but it was rather coarse below 10 m, whereas it turned dense at 30 m, decreasing the amount of corrosion. NiO layer on nickel formed in air at high temperature prior to exposure to NaOH solution also worked as a corrosion barrier. Several materials such as inconel and hasteloy were also tested and inconel was found to be most resistant against corrosion.
