Sixteen localities were involved in a broad study, resulting in the classification of the indoor corrosivity of metals considered in the ISO 11844 standard, especially lead. Recently, lead has been added to the standard as a metal specifically sensitive to volatile organic compounds such as acetic acid. Data on one-year exposure in museum depositories and exhibition spaces, archives, libraries, and churches show that the currently valid lead corrosivity categories are not correctly defined. The obtained data allowed for the proposal of new realistic ranges of indoor corrosivity categories for lead. The exposure program was also used to validate techniques for determining the corrosion degradation of metal coupons. Mass increase and mass loss techniques were supplemented with the galvanostatic reduction technique and the measurement of color changes. The study identified the limitations of the mass gain method. Not only is the galvanostatic reduction technique applicable for silver and copper coupons, but the build-up of reducible lead corrosion products depends on air corrosivity. CIELab color-change measurement has proven to be a simple and easy-to-apply method for monitoring the corrosivity of indoor atmospheres with regard to lead. A more reliable response is provided by the determination of color change after 3 months of exposure rather than after one year.
Air pollution in museums, libraries, churches, and other indoor environments of cultural heritage objects was studied since 1980s. For classification of corrosivity for such type of indoor environments the ISO 11844 series was developed in 2006. In 2020 the revision of this ISO 11844 series had been finished, where lead was included as standard specimen with high sensitivity to vapour organic acids. This paper gives results of exposure of lead standard coupons in museums and other similar indoor environments together with measurement of climatic parameters and air pollution to verify the new approach.
Indoors, volatile organic acids can play an important role in the degradation process of many materials. Considering this fact, metal corrosion coupons of copper, silver, lead, and zinc were exposed to different climatic conditions of 18 locations for 3, 12, and 30 months, and their corrosion rates were evaluated based on mass loss, as recommended by the ISO 11844 standard. The corrosion rates were compared with in situ colorimetric measurements to validate the colorimetry as a simple tool for estimating the corrosivity of an environment. The results have shown good correlation between the methods for two metals: silver and lead, confirming the possibility of non-destructive monitoring of their corrosion by measurement of color changes.
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