Colour evolution of the oxide layer formed on the Au-25Fe AND Au-24.5Fe-0.5Co

Authors

DOI:

https://doi.org/10.17533/udea.redin.n78a08

Keywords:

Magnetite, oxide layer, coloured gold alloys, colour theory

Abstract


The colour theory proposed by Heavens in 1991 has been applied to calculate the thickness of magnetite thin layers, Fe3 O4 , which were obtained by heat treatment at 250 °C in a gold alloy (Au-24.5Fe-0.5Co). The reflectance spectra obtained from the polished samples with different oxidation (and colour) degrees were used to calculate the real part of the refraction index and the (imaginary) extinction coefficients of both the metallic substrate (n2 , k2 ) and the magnetite layer (n1 =2.42, k1 ). The a+bλ+cλ2 form was taken adjusting parameters between experimental and theoretical curves. The fitting of the data resulted in deviations between 2 and 10% for thicknesses in the range of 0 nm (only substrate) and 65 nm (dark blue colour). By means of a mathematic model and following the Heavens’ theory, the thickness of each layer has been predicted with high precision, using the spectral reflectance. Consequently, we propose that by using this methodology, the values of the extinction coefficients of the oxide species can be easily obtained, and the thicknesses of the oxide layers can be predicted. The magnetite thickness values found in this study fall into the interval reported in the literature for first-order interference in steels, from light-yellow (~46 nm) to blue (~72 nm).

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Author Biographies

Sandra Milena Restrepo-Arcila, Universidad de Antioquia

Departamento de Matemáticas, Facultad de Ingeniería, Docente de cátedra

Alejandro Iván Echavarría-Velásquez, Universidad de Antioquia

Profesor Departamento de Ingeniería de Materiales

Facultad de Ingeniería

Marco Antonio Giraldo-Cadavid, Universidad de Antioquia

Profesor Instituto de física, Facultad de Ciencias Exactas y Naturales

Jorge Andrés Calderón-Gutierrez, Universidad de Antioquia

Profesor Departamento de Ingeniería de Materiales, Facultad de Ingeniería

Héctor Darío Sánchez-Londoño, Universidad de Antioquia

Profesor Departamento de Ingeniería de Materiales, Facultad de Ingeniería

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Published

2016-03-18

How to Cite

Restrepo-Arcila, S. M., Echavarría-Velásquez, A. I., Giraldo-Cadavid, M. A., Calderón-Gutierrez, J. A., & Sánchez-Londoño, H. D. (2016). Colour evolution of the oxide layer formed on the Au-25Fe AND Au-24.5Fe-0.5Co. Revista Facultad De Ingeniería Universidad De Antioquia, (78), 62–68. https://doi.org/10.17533/udea.redin.n78a08