# Ferric oxide : protective or not?

1. Apr 30, 2015

### mooncrater

1. The problem statement, all variables and given/known data
There are two lines in my textbook :
" Iron is passivated by strong oxidising agents like conc.$HNO_3,K_2Cr_2O_7$ due to the formation of a protective coat of $Fe_2O_3$."
And the other line says:
"Rusting occurs in the presence of $O_2,H_2O$ and $H^+$ resulting in the formation of $Fe_2O_3$ which is not protective and the corrosion continues"
Whats this? One line says that $Fe_2O_3$ is protective and other says it is not !

2. Relevant equations

3. The attempt at a solution
Can it be the reason that protective property of $Fe_2O_3$ is different for different conditions?

2. Apr 30, 2015

### Staff: Mentor

Apparently. Concentrated nitric acid is safely transported in steel tanks, as the iron from these tanks gets passivated and doesn't dissolve in the acid. Same steel will rust if put in sea water.