Atmospheric corrosion effects of HNO3—Influence of concentration and air velocity on laboratory-exposed copper

A recently developed experimental set-up has been used to explore the atmospheric corrosion effects of nitric acid (HNO3) on copper, in particular the influence of concentration and air velocity. Characterization and quantification of the corrosion products on exposed samples were performed with Fourier transform infrared (FT-IR) microspectrocscopy, ion chromatography, X-ray diffraction (XRD), micro-balance and microscopy. At low air velocity (0.03 cm s−1) HNO3 deposition and weight gain of copper increased linearly with concentration up to 400 μg m−3 or 156 ppb. The influence of air velocity on corrosion of copper was tested within the range of 0.03–35.4 cm s−1. Although the air velocity in this study was significantly lower than typical outdoor wind values, a high HNO3 concentration of the air velocity of 35.4 cm s−1 resulted in a relatively high deposition velocity (Vd) of 0.9 cm s−1 on the metal surface and 1.2 cm s−1 on an ideal absorbent, which would imply a limiting deposition velocity on the copper surface (Vd,surf) of 3.6 cm s−1. Results obtained in this study emphasize the importance for future research on the corrosion effects of HNO3 on materials as very little has so far been done in this field.