Selective dry oxidation of the ordered Pt–11.1 at.% V alloy surface evidenced by in situ temperature-controlled X-ray diffraction

A temperature-controlled X-ray diffraction study of the cold-rolled Pt–11.1 at.% V alloy was undertaken to gain better insight into the incomplete transformation of the metastable cubic disordered phase into the tetragonal ordered Pt8V phase, earlier reported by Nxumalo and Lang [11]. This study has revealed a complex behaviour of the alloy when is annealed in primary vacuum. Upon heating above 450 °C, an ordering of vanadium atoms in the Pt–11.1 at.% V alloy leads to the appearance of a tetragonal Pt8V phase. Concomitantly, vanadium atoms at the surface of the ordered alloy are slowly oxidized into V2O3 Corundum type phase by the low oxygen partial pressure existing in primary vacuum. This segregation of vanadium oxide onto the surface depleting the subsurface region in vanadium, an almost pure Pt cubic phase grows at the V2O3-ordered Pt8V alloy interface with increasing the temperature. This investigation also shows that an external selective oxidation of the cold-rolled Pt–11.1 at.% V alloy takes place when is annealed in flowing argon atmosphere.

Figure optionsDownload as PowerPoint slideHighlights
► Use of in situ temperature-controlled X-ray diffraction to provide key information in understanding the incomplete ordering of vanadium in the cold-rolled Pt–11.1 at.% V annealed in primary vacuum or in argon.
► When the ordered Pt8V phase appears, an oxidation of vanadium atoms at the surface of the alloy occurs.
► A depletion in vanadium of the subsurface region of the alloy is evidenced by the growth of an almost pure Pt cubic phase at the vanadium oxide–Pt8V interface.
► The incomplete transformation of the cold-rolled Pt–11.1 at.% V alloy originates from the external selective oxidation of vanadium.