Interdiffusion study in the Pd–Pt system Varun A. Baheti • Raju Ravi • Aloke Paul Received: 16 February 2013 / Accepted: 9 March 2013 / Published online: 21 March 2013 Ó Springer Science+Business Media New York 2013 Abstract Interdiffusion, intrinsic, tracer and impurity diffusion coefficients are calculated in the Pd–Pt system. Interdiffusion coefficients are more or less insensitive to composition change. Activation energy varies in the range of 324–353 kJ/mol. Impurity diffusion coefficients calcu- lated in this study and available tracer diffusion coefficients in pure elements indicate that Pd has higher diffusion rate compared to Pt in pure Pd, whereas, both the elements have similar diffusion rates in Pt. Kirkendall marker experiments indicate that Pd has much higher diffusion rate in Pd3.5at.%Pt compared to Pt. 1 Introduction Pd–Pt alloys find use in many applications such as elec- trodes in automotive oxygen sensors [1], purification of hydrogen isotopes [2, 3] and hydrogen storage [2, 3]. Most of the physical and some mechanical properties could be explained based on the knowledge on diffusion. In many cases, products are developed with the help of interdiffu- sion process. In fact, Pd–Pt porous thin film electrode is being produced by interdiffusion between Pd/Pt bi-layer films for oxygen sensors [1]. Difference in mobilities of the species plays an important role on the formation of the electrode. Therefore, diffusion studies in this system are very important. To the best of our knowledge, only the tracer diffusion coefficients for the measurement of the self diffusion coefficients in pure elements are available in the literature. However, studies on interdiffusion are important to understand the factors influencing the diffusion of dif- ferent elements. This also helps to calculate variations in interdiffusion coefficients with the change in composition, the intrinsic, the tracer and the impurity diffusion coeffi- cients of the species. Therefore, the aim of this work is to conduct interdif- fusion studies in Pd–Pt system in the solid solution range. Diffusion couple experiments are conducted to calculate the variation of the interdiffusion coefficients with com- position. The variation of the activation energy with composition is calculated from the experiments conducted at different temperatures. Intrinsic and tracer diffusion coefficients are calculated at the Kirkendall marker plane. Indirectly estimated impurity diffusion coefficients are compared with the tracer diffusion coefficients of the species available in Pd and Pt. 2 Experimental procedure Diffusion couple technique was used to determine impor- tant diffusion parameters. 0.5 mm thick foils of Pd (99.95 wt%) and Pt (99.99 wt%) were used as starting materials for diffusion couples. Slices of approximately 5 mm 9 5 mm dimension were cut and prepared metallographically to obtain a flat and smooth surface. Following, these were cleaned ultrasonically in ethanol and dried in hot air. The couple halves were bonded by clamping in a special fixture with minimum required external pressure. Diffusion cou- ples were annealed in the temperature range of 1,150–1,300 °C(±5 °C) for 9–25 h in a calibrated tube furnace in high vacuum (*10 -4 Pa). Prior to annealing, more or less evenly distributed Y 2 O 3 particles (average size of 4.4 lm) were introduced at the contact interface as inert ‘Kirkendall’ markers. After the heat treatment, bonded V. A. Baheti  R. Ravi  A. Paul (&) Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India e-mail: aloke@materials.iisc.ernet.in 123 J Mater Sci: Mater Electron (2013) 24:2833–2838 DOI 10.1007/s10854-013-1179-1