Electrochemical nucleation and growth of black and white chromium deposits onto stainless steel surfaces

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2010-09, Vol.647 (2), p.128-132
• Main Authors: Aguilar-Sánchez, M., Palomar-Pardavé, M., Romero-Romo, M., Ramírez-Silva, M.T., Barrera, E., Scharifker, B.R.
• Format: Article
• Language: English
• Subjects: Chemistry; Chromium; Current transients; Electrochemistry; Electrodeposition; Exact sciences and technology; General and physical chemistry; Nitrate reduction; Nucleation; Study of interfaces
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2010.06.012

Chromium electrodeposition onto a stainless steel substrate from 0.62 M CrO 3 aqueous solution containing, 0.05 M BaCO 3 and 0.01 M H 2SiF 6 was evaluated in the absence (i) and presence (ii) of 0.02 M KNO 3. Chromium electrodeposited from the electrolytic bath (i) was white-gray colored, whereas deposition from bath (ii) formed a black-colored surface. SEM-WDX and XPS analysis of the steel surfaces covered with these two deposits revealed different features for black and white chromium films. While white-Cr film was mainly composed by Cr(OH) 3, the black-Cr film comprised Cr 2O 3. The white-Cr deposit appeared as a smooth film while the black deposit consisted of numerous dispersed, nano-sized clusters. Analysis of potentiostatic current density transients ( j– t curves) recorded in these systems according with the theoretical model proposed by M. Palomar–Pardavé, B.R. Scharifker, E.M. Arce, M. Romero–Romo, Electrochim. Acta, 50 (2005) 4736, indicates that formation of white-Cr deposit was carried out by multiple nucleation of Cr(OH) 3 centers with three-dimensional growth limited by mass transfer of ( Cr 2 O 7 ) 2 - ions. On the other hand, black-Cr deposit electrocrystallization involved the formation of Cr 2O 3 nuclei growing at a rate limited by the mass transfer of ( Cr 2 O 7 ) 2 - ions, with simultaneous reduction of nitrates on their surfaces.