The segregation behaviour of a Pt90Rh10 alloy studied with a three-dimensional atom-probe

The surface and the bulk composition of Pt90Rh10 alloy samples were analyzed by a three-dimensional optical atom probe in ultra high vacuum. Measurements on these particular alloys on (012) and (133) oriented specimens show a weak Rh segregation at annealing temperatures between 800 and 1200 K. At higher temperatures the segregation behaviour of Rh decreases and above 1500 K almost bulk composition is observed. These results can be explained satisfactorily with the aid of the classical broken bond model, at lower temperatures the lower sublimation energy of Rh compared to Pt is a driving force for Rh segregation and at higher temperatures the entropy of mixing favours the Rh solution in the bulk. To evaluate the influence of adsorbates on the segregation behaviour of Rh annealing treatments were accomplished in the presence of oxygen.