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Fractal quantification of aluminum pitting corrosion induced by humid tropical climate

 

Cuantificación fractal de la corrosión de aluminio por picaduras inducida por el clima tropical húmedo

 

L. Veleva, A. García-González*, and G. Pérez

 

Departamento de Física Aplicada, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Unidad-Mérida, Antigua carretera Mérida-Progreso Km.6, C.P. 97310, Mérida, Yucatán, México. *Corresponding author. E-mail: alcionegarcia@yahoo.com.mx

 

Received 4 of February 2012
Accepted 11 of November 2012

 

Abstract

During three annual exposure periods, aluminum samples of wire, used for transmission of high voltage electricity, were exposed at outdoor atmospheric marine-coastal and rural environments, located in the humid tropical climate of Yucatan Peninsula, in the Mexican gulf. In atmospheric conditions the naturally formed aluminum oxide layer can be destroyed by the presence of chlorides, causing pitting localized corrosion attack, difficult for evaluation. The concepts of fractal geometry and self-similarity were used in this study for evaluation of the pitting corrosion as a function of time, making a statistics of the frequency of appearance of pits versus the area occupied by them. The data showed that the distribution of the pits follows a power law. The exponent of self-similarity varied between 1.7-1.9 and it is relatively stable with the progress of corrosion progress. The progress of pits in area and frequency is more pronounced in time in the marine-coastal atmosphere, compared to pitting developed in rural-urban one. The concepts of fractal geometry and self-similarity can quantify the extent of localized corrosion with time, as nondestructive form and rapid method.

Keywords: aluminum, fractal quantification, atmospheric corrosion, pitting corrosion, self-similarity.

 

Resumen

Durante tres años, se expusieron muestras de alambre de aluminio (usadas para el transporte de electricidad de alto voltaje), en dos diferentes atmósferas, en una marina-costera y la otra rural-urbana, en el clima tropical húmedo de la península de Yucatán, en el golfo de México. En estas condiciones de exposición, la capa de óxido natural del aluminio puede ser destruida en presencia de cloruros, causando picaduras localizadas por el ataque corrosivo, lo que dificulta su análisis. Los conceptos de geometría de fractales y auto-similaridad se utilizaron para la evaluación de la corrosión por picadura en función del tiempo, haciendo una estadística de la frecuencia de aparición de picaduras contra el área superficial ocupada por estas. Los datos muestran que la distribución de picaduras sigue una ley de potencias. El exponente de auto-similaridad varió entre 1.7-1.9 y es relativamente estable con el avance de la corrosión. El aumento del tamaño del área de las picaduras y en frecuencia, es más pronunciado con el tiempo en la atmósfera marina-costera, en comparación con la rural-urbana. Los conceptos de geometría de fractales y auto-similaridad pueden predecir la extensión de la corrosión localizada de aluminio con el tiempo, de una forma no destructiva y rápida.

Palabras clave: aluminio, cuantificación fractal, corrosión atmosférica, corrosión por picadura, auto-similaridad.

 

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