The corrosion behaviour of three refractory diborides (TiB2, ZrB2 and HfB2) have been compared in acid solutions containing different anions, that is chlorides, sulphates, oxalates citrates and fluorides. TiB2 corrosion is sensitive to both the presence of Ti-complexing anions and, particularly, the solution pH. In fact, at pH 1 this diboride suffers the strongest corrosion attack. ZrB2 and HfB2 exhibit quite similar corrosion behaviour. The protectiveness of their surface oxide films increases as the stability of the complexes formed by hafnium and zirconium with the aggressive anions decreases. An interesting exception in the corrosion behaviour of all diborides is observed in citrate solution as citrate anion forms quite stable Ti(IV)-, Zr(IV)-, Hf(IV)-complexes, but markedly inhibits the diboride corrosion process, even at pH 1. Fourier Transform Infra Red (FTIR) spectroscopy is used to investigate this discrepancy.
Corrosion behaviour of three refractory diborides in aqueous solutions
MONTICELLI, Cecilia;ZUCCHI, Fabrizio;DAL COLLE, Maurizio
2008
Abstract
The corrosion behaviour of three refractory diborides (TiB2, ZrB2 and HfB2) have been compared in acid solutions containing different anions, that is chlorides, sulphates, oxalates citrates and fluorides. TiB2 corrosion is sensitive to both the presence of Ti-complexing anions and, particularly, the solution pH. In fact, at pH 1 this diboride suffers the strongest corrosion attack. ZrB2 and HfB2 exhibit quite similar corrosion behaviour. The protectiveness of their surface oxide films increases as the stability of the complexes formed by hafnium and zirconium with the aggressive anions decreases. An interesting exception in the corrosion behaviour of all diborides is observed in citrate solution as citrate anion forms quite stable Ti(IV)-, Zr(IV)-, Hf(IV)-complexes, but markedly inhibits the diboride corrosion process, even at pH 1. Fourier Transform Infra Red (FTIR) spectroscopy is used to investigate this discrepancy.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
