The effect of operating conditions during plating on the electrochemical behavior and morphology of trivalent solution-derived chromium coatings
El efecto de las condiciones de funcionamiento durante el cultivo sobre el comportamiento electroquímico y la morfología de los recubrimientos de cromo trivalentes derivados de solución
O.J. Suarez1, J.J. Olaya1* and S. Rodil2
1 Universidad Nacional de Colombia, Bogotá, Colombia. Ciudad universitaria edificio de posgrado de materiales. Bogotá-Colombia. *Corresponding author. E-mail: jjolaya@unal.edu.co
]]> 2 Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, México D.F.-México.
Received 28 of February of 2012
Accepted 17 of January of 2013
Abstract
Trivalent electrolyte-based chromium plating represents an alternative for the major problems associated with traditional hexavalent plating. Response surface methodology was chosen in this work for designing experiments. Chromium coatings were obtained from trivalent solutions in a chloride-based bath using different operating conditions. Three concentrations (0.19, 0.38 and 0.57 mol L-1 as Cr(III) ), three pH (2.0, 3.0 and 4.0) and temperature (25°C, 32°C, 40 oC) was varied during the experiments. Scanning electron microscopy and energy dispersive X-ray analysis were used for examining the coatings surface morphology and composition; the coulometric method was used for thickness measurement and potentiodynamic and impedance tests on 3% NaCl were made on a three-eletrode cell for studying chromium film electrochemical behavior. Large differences in morphology, thickness and corrosion resistance were observed, mainly due to variations in chromium concentration and pH solution. Crack; patterns were observed on films obtained at high pH values independently of process temperature.
Keywords: trivalent chromium, plating, microstructure, corrosion, electrochemical impedance.
Resumen
]]> Los electrolitos basados en el cromo trivalente presentan una alternativa a los problemas asociados con los recubrimientos tradicionales basados en cromo hexavalente. En este trabajo se empleó un diseño de experimentos de superficie de respuesta para observar el efecto de las variables. Los recubrimientos de cromo se obtuvieron a partir de soluciones de cloruro de cromo modificando las condiciones de electro deposición. Tres concentraciones (0.19, 0.38 y 0.57 mol L-1 de Cr(III)), tres valores de pH (2.0, 3.0 y 4.0) y tres temperaturas (25°C, 32°C y 40 oC) se variaron durante los experimentos. La morfología y composición de los recubrimientos se analizó por medio de microscopía electrónica de barrido y la sonda de análisis de dispersión de rayos X acoplada al microscopio; el espesor de los mismos se midió por titulación coulombimétrica y el comportamiento electroquímico a la corrosión se estudió por medio de polarización potenciodinámica y espectroscopía de impedancia electroquímica en NaCl 3%. Se observaron grandes diferencias en la morfología, espesor y resistencia a la corrosión debido principalmente a la variación en la concentración de cromo y al pH de la solución. Se observaron patrones de agrietamiento cuando el depósito se obtuvo a altos valores de pH independientemente de la temperatura del electrolito.Palabras clave: cromo trivalente, electro plateado, microestructura, corrosión, impedancia electroquímica.
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Acknowledgements
División de Investigación Universidad Nacional de Colombia, project 202010010654, Red de Macrouniversidades de América Latina y el Caribe, CONACYT projects P45833 and DGAPA IN102907 and ALFACROM LTDA.
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