Corrosion-Resistant Bulk Amorphous Ni-Cr-Ta-Mo-Nb-5P Alloys in Concentrated Hydrochloric Acids

Abstract

Amorphous bulk Ni-Cr-Mo-22at%Ta-14at%Nb-P alloys resistant to concentrated hydrochloric acids was prepared by copper-mold casting. The amorphous alloys of single phase, such as (1- 4Cr)-1Mo-7P and (1-2.5)Cr-(1-2)Mo-4P alloys did not show detectable corrosion weight loss after immersion in 12 M HCl for 168 h. These alloys were spontaneously passive in concentrated hydrochloric acids due to presence of stable air- formed films, in which chromium was particularly rich in addition to enrichment of tantalum and niobium. The high corrosion resistance of the homogenous alloys of single phase was interpreted in terms of the presence of bi-layer structure film consisting of the outer stable triple oxyhydroxide, Cr1- xTaxNbyOzOH3+2x+2y-2z, and the inner MoO2 layer acting as the effective diffusion barrier.