In situ XRD characterization of hydrogen desorption from electrochemically deposited Pd coating L. Borgese,P. Zanola,E. Bontempi,D. Rossi, L. E. Depero ACA and OCCA 2010 Abstract One of the main problems in electrochem- ical Pd deposition of coatings is the hydrogen desorp- tion thatcauses microcracking phenomena. With the aim of understanding the structural changes due to the hydrogen desorption, the kinetics of the phase trans- formation from hydride to metallic structure has been followed by in situ X-ray diffraction (XRD) experi- ments. The structural evolution of samples obtained by two different electrochemical baths has been com- pared. It was found that the solubility and the desorption kinetics of hydrogen are significantly influ- enced by the presence of structural defects.Residual stresseshave been evaluated forboth samplesby means of 2D X-ray diffraction (XRD 2 ). The presence of amine complexes in the bath seems to contribute to reducing the crystalline dimension of the Pd-phase, and the differences between the specific volumes of a and b phases is reduced for nanostructured coatings. Keywords X-ray diffraction, Palladium, Electrochemistry, Coatings,Residual stress Introduction The electrodeposition technique is widely applied for surface finishing and microfabrication, increasing the interestin structuralproperties of such deposits. For electricalcontacts, electrochemically deposited palla- dium coatings are still a possible alternative to gold and silver deposits,because oftheir excellentresistance and solderability. 1,2 However, in view of its white bright gold-like appearance, the mostattractive application of palla- dium coatings is for jewelry and fashion accessories. 3 One of the main problems for electrodeposited Pd in theseapplicationsis surfacemicrocrackingdue to desorption of the unavoidable co-deposited hydrogen: indeed, if the deposition efficiency is <100%, hydrogen is produced and diffuses into the face-centered cubic (fcc) Pd metal structure and solid solution of palladium hydride PdH x is deposited. 2,3 The high solubility and mobility of hydrogen 4,5 cause phase transformations and volume changes that may compromise the func- tional and aesthetical properties of the coatings. 2,3,6,7 Palladium has a fcc structurewith a = 3.889 A ˚ . When hydrogen is dissolved in the structure, the so- called a-phase is formed and the structure parameter a increases linearly to 3.893 A ˚ when H/Pd atomic ratio is 0.03. Above this concentration,the secondphase appears with a lattice constant of 4.025 A ˚ . Both phases coexist until a composition of PdH 0.58 , when the alpha phase disappears. 2,3,8,9 Since the b-phase isunstable atstandard condi- tions, 2 b fi a transformation occurs, releasing hydro- gen. Because ofthe volume contraction, this phase transformation causes coating stresses and structural defects, usually relieved by surface microcracking. Of course, this phenomenoncompromisesthe applicationsin decorative industriesbecause ofthe low quality of products. The aim of the paper is to discuss structural and microstructural changes of Pd electrochemical depos- ited coatings by following the hydrogen desorption at standard conditions by means of in situ X-ray diffrac- tion (XRD) experiments. In particular,the kinetics of the hydrogen desorption process will be followed and L. Borgese,P. Zanola,E. Bontempi (&), L. E. Depero INSTM and Chemistry for Technology Laboratory, Universita ` degli Studi di Brescia, Via Branze 38, 25123 Brescia, Italy e-mail:elza.bontempi@ing.unibs.it D. Rossi Coventya S.r.L Auromet Division, via Chiusa 1, 51031 Agliana (PT), Italy J. Coat.Technol.Res.,7 (6) 691–695, 2010 DOI 10.1007/s11998-010-9253-6 691