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Atmospheric corrosion effects of HNO3—method development and results on laboratory-exposed copper
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.ORCID iD: 0000-0002-9453-1333
2005 (English)In: Atmospheric Environment, ISSN 1352-2310, Vol. 39, no 38, 7362-7373 p.Article in journal (Refereed) Published
Abstract [en]

The effects of the atmospheric pollutant nitric acid (HNO3) on materials compared to other corrosive gases, e.g. sulphur dioxide (SO2), nitrogen dioxide (NO2) or ozone (O-3), have so far received little or no attention. The high sticking coefficient of HNO3 makes this gas one of the most difficult gases to work with. A new apparatus has now successfully been developed for studying the atmospheric corrosion effects of HNO3 Oil materials. HNO3 concentration measurements up to 1080 mu g m(-3) (420 ppb) were performed by dissolving the gas in water and analysing the nitrate concentration with ion chromatography (IC). Small changes in relative humidity (RH) largely affect the concentration of this pollutant in the exposure chamber and the high sticking coefficient of this gas on copper and quartz glass has been shown. The quartz glass surface, however, became saturated after a certain time of exposure and at 82% RH, the number of monolayers on the surface was estimated to be 10-13. Initial results of copper samples exposed to HNO3 show that at 63% RH and 25 degrees C, the deposition of HNO3 on copper is slightly lower than on a perfect absorber. The loss of HNO3 during exposure of the samples showed good agreement with the amount of nitrates dissolved from surfaces of the samples after exposure. FT-I R, XRD and IC analyses of copper exposed to HNO3 and mass loss and mass gain analyses confirmed cuprite (Cu2O) and the basic copper nitrate, gerhardtite, as the main corrosion products. Deposition, as well as the corrosion effect, of HNO3 on copper appeared to be greater than that of any of the other above-mentioned pollutants.

Place, publisher, year, edition, pages
2005. Vol. 39, no 38, 7362-7373 p.
Keyword [en]
nitric acid, relative humidity, gerhardtite deposition, material degradation
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-6441DOI: 10.1016/j.atmosenv.2005.09.022ISI: 000233671700015ScopusID: 2-s2.0-27544481257OAI: diva2:11156
QC 20100831Available from: 2006-11-29 Created: 2006-11-29 Last updated: 2010-08-31Bibliographically approved
In thesis
1. HNO3-Induced Atmospheric Corrosion of Copper, Zinc and Carbon Steel
Open this publication in new window or tab >>HNO3-Induced Atmospheric Corrosion of Copper, Zinc and Carbon Steel
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The role of nitric acid (HNO3) on the atmospheric corrosion of metals has so far received little or no attention. However, the last decades of decreasing sulphur dioxide (SO2) levels and unchanged HNO3 levels in many industrialized countries have resulted in an increased interest in possible HNO3-induced atmospheric corrosion effects. In this study a new method was developed for studying the corrosion effects of HNO3 on metals at well-defined laboratory exposure conditions. The method has enabled studies to be performed on the influence of individual exposure parameters, namely HNO3-concentration, air velocity, temperature and relative humidity, as well as comparisons with newly generated field exposure data.

The corrosion rate and deposition rate of HNO3 on copper was shown to follow a linear increase with HNO3 concentration. The deposition velocity (Vd) of HNO3 increased up to an air velocity of 11.8 cm s-1. Only at a higher air velocity (35.4 cm s-1) the Vd on copper was lower than the Vd on an ideal absorbent, implying the Vd of HNO3 at lower air velocities to be mass-transport limited.

Within the investigated temperature range of 15 to 35 ºC only a minor decrease in the HNO3-induced copper corrosion rate could be observed. The effect of relative humidity (RH) was more evident. Already at 20 % RH a significant corrosion rate could be measured and at 65 % RH the Vd of HNO3 on copper, zinc and carbon steel reached maximum and nearly ideal absorption conditions.

During identical exposure conditions in HNO3-containing atmosphere, the corrosion rate of carbon steel was nearly three times higher than that of copper and zinc. The HNO3-induced corrosion effect of copper, zinc and steel turned out to be significantly higher than that induced by SO2 alone or in combination with either NO2 or O3. This is mainly attributed to the much higher water solubility and reactivity of HNO3 compared to SO2, NO2 and O3. Relative to SO2, zinc exhibits the highest sensitivity to HNO3, followed by copper, and carbon steel with the lowest sensitivity.

Extrapolation of laboratory data to an assumed average outdoor wind velocity of 3.6 m s-1 enabled a good comparison with field data. Despite the fact that ambient SO2 levels are still much higher than HNO3 levels, the results show that HNO3 plays a significant role for the atmospheric corrosion of copper and zinc, but not for carbon steel. The results generated within this doctoral study emphasize the importance of further research on the influence of HNO3 on degradation of other materials, e.g. stone and glass, as well as of other metals.

Place, publisher, year, edition, pages
Stockholm: Kemi, 2006
Nitric acid, deposition velocity, mass transport, air velocity, relative humidity
National Category
Chemical Sciences
urn:nbn:se:kth:diva-4194 (URN)91-7178-483-7 (ISBN)
Public defence
2006-12-08, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Available from: 2006-11-29 Created: 2006-11-29

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