Elsevier

Corrosion Science

Volume 52, Issue 2, February 2010, Pages 327-337
Corrosion Science

Indoor atmospheric corrosion of electronic materials in tropical-mountain environments

https://doi.org/10.1016/j.corsci.2009.09.019Get rights and content

Abstract

Indoor corrosion rate during one year exposure for carbon steel, copper, nickel, and tin was determined in three different atmospheres in Colombia. In addition, pollutants deposition rates and environmental parameters were also measured during indoor–outdoor conditions. The results show higher pollutant deposition in outdoor conditions, while inside metallic boxes the pollutant deposition significantly diminishes. No difference for relative humidity values was found between inside and outside measurements. For all samples, except nickel, the corrosion rate decrease with exposure time. The nature of corrosion products was found to be related to the exposure conditions.

Introduction

Atmospheric corrosion deals with the aggressiveness of environmental factors on metallic structures. Corrosion rates can vary dramatically between locations, being the pollutant deposition rate an important variable in the corrosion process [1]. There is a vast data and knowledge on outdoor atmospheric corrosion; leading to development of standards and classification systems [2]. Mendoza and Corvo [3] explored the variations of outdoor and indoor atmospheric corrosion for non-ferrous metals in a Cuban tropical environment. They found an interaction between chloride deposition rate and both rainfall (outdoors) and time of wetness (indoors). They concluded that these are the most significant variables influencing the corrosion process. In a similar way, Rocha et al. [4] performed experiments in a tropical environment located in Bolivia for ferrous and non-ferrous metals. In the case of steel, the results showed differences in the ISO classification. They found a C2 classification for outdoor category in contrast with an IC4 classification for indoor category; this is probably due to “Heat Trap” effect [4].

Indoor exposure studies have increased over the last decades, and great interest has grown regarding its influence in electronic material corrosion [5], [6], [7], [8], [9]. Indoor environments have a known effect on the performance of this type of materials, particularly regarding surface-related properties [10]. Metallic degradation can lead to equipment failures and even breakdowns in environments with a relatively low pollutant concentration. Takano and Mano [11] concluded that failures in electrical contacts and connectors were due to copper corrosion with the consequent formation of copper (I) oxide (Cu2O). Abbot [12] evaluated the effect of H2S, SO2, NO2 and Cl2 on contact electric materials, and it was found a synergic effect between SO2 and NO2 and atmospheric corrosion. Sulphidric acid have also been reported as a corrosion accelerator when is combined with NO2, particularly in the case of silver samples [13]. Likewise, other studies have shown that reliability of electronic equipment decreases due to contact corrosion [14], [15]. Frankenthal [16] evaluated the passivation and breakdown of electronic metals by factors such as moisture, contamination and applied voltage. Tidblad [17] performed statistical and superficial studies on the effect of acid deposition over metals used as electric contacts.

In Latin America, TROPICORR project (Tropical environment effect on degradation of electronic equipment) was involved in atmospheric corrosion studies seeking to explain the electronic materials behavior in tropical environments during long exposures. It also aimed to contribute establishing standard criteria applied to these specific conditions. In this paper, we reported the main results obtained during one year exposure in three atmospheric environments in Colombia. Rural environment representing unpolluted conditions was located in San Pedro town (outside Medellín, Antioquia); meanwhile urban and industrial atmospheres were located in the University of Antioquia campus (Northwest of Medellín) and Eafit University campus (Southwest of Medellín), respectively. The selection of the atmospheres location was based on previous studies [18].

Section snippets

Experimental

Metallic samples and pollutant collectors were located inside metallic boxes in three tropical atmospheres categorized as rural, urban and industrial environments. The classification was made according with the international standard ETS 300 019-1-0 [19]. Low carbon steel (SAE AISI C1019), silver, copper, tin, and nickel plates of 99.5% of purity were exposed by periods of 1, 3, 6, and 12 months. Corrosion rate was measured by both gain and mass loss techniques according to the ISO/TC156/WG4-N

Visual appearance

Fig. 1 exhibits the visual appearance of the samples after exposure. For each material, a photograph of the unexposed sample is presented. As a general point of view, samples exposed in the rural station presented just slight corrosion product formation on the surface. Carbon steel and nickel show corrosion products covering the surface during exposures in urban environment. Likewise, copper and tin samples exhibits surface darkening in this station. Also, nickel exhibits whitish corrosion

Conclusions

  • 1.

    Deposition rates of pollutants are lower inside the metallic boxes than outdoor, leading to a low corrosion rate for copper, carbon steel, tin and nickel. According to the ISO 9223 classification of time of wetness, urban and urban-industrial stations were classified as τ3, meanwhile the rural station corresponds to τ4. These results indicate that for indoor conditions, aggressiveness predictions by using TOW according to existing ISO standards are inaccurate.

  • 2.

    In the urban environment,

Acknowledgment

The authors thank to Programa de Sostenibilidad of the University of Antioquia for its financial support to this study.

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