Summary
Ammonium chloride (NH4Cl) is considered an acidic salt because it is formed from a strong acid (HCl) and a weak base (NH3). Aqueous solutions containing NH4Cl tend to be acidic if there is not excess ammonia or a stronger base available in the system. Corrosion by concentrated aqueous solutions of NH4Cl can be very rapid, approaching that of aqueous HCl (i.e., greater than 25 mm/y [1000 mpy] on carbon steel). Dilute solutions of NH4Cl (< 1000 ppmw) are low-corrosive, but corrosion rates increase significantly with increasing NH4Cl concentration. Corrosion rates increase when oxygen is present (especially at lower temperatures), and decrease somewhat in the presence of H2S.