A Preliminary Study on the Protective Film Formation on Fr-Cr-X Alloys at High Temperature

Alloys of Fe-27Cr-39Ni, Fr-30Cr-6Zr and Fe-30Cr-6Ti have been exposed isothermally to an equilibrated gas mixture of 94.7% H2/1.3% H2S/4% H2O and 69.0% H2/1.0% H2S/30% H2O at 1143K. The reaction kinetics have been observed and related to the morphology and composition of the corrosion products to the sulphur and oxygen potentials in the gases and to appropriate thermodynamic phase stability diagrams. In the environments of low oxygen and high sulphur potentials, chromium rich sulfide scales develop on both Fe-27Cr-39Ni and Fe-30Cr-6Ti alloys which allow extensive corrosion for 7 hour test, while partially protective porous Cr2O3 layer develop on Fr-30Cr-6Zr alloy. In the environments of high oxygen and high sulphur potentials, dense and protective film (Cr2O3 of TiO2) develop on both Fe-30Cr-6Zr and Fe-30Cr-6Ti alloys while porous chromium rich sulfide scales develop on Fe-37Cr-39Ni alloy which can not protect the alloys from further attack