2.9 Determination of the Sensitivity of Metals to Corrosion by Atmospheric Pollutants: Aldehydes and Carboxylic Acids

The Getty Conservation Institute

Mary Striegel
Dusan Stulik
Period of Activity: 2/90 to 7/91

Project Abstract
Corrosion problems resulting from low levels of pollutants have been found in museum display and storage areas. Compounds such as acetaldehyde, acetic acid, formaldehyde, and formic acid, and volatile organic compounds evolved from coatings, adhesives, and sealants used in museums, can cause corrosion of metals. Particularly susceptible are lead alloys and lead-containing copper alloys. Hydrogen sulfide and other sulfur-containing gases react with silver objects to produce tarnish.

To evaluate the quantitative aspects of this problem, information on the relation between the extent of metallic corrosion and pollutant exposure is required, and from this came estimates of maximum acceptable pollutant concentrations in museums. This information specified the need for installation of air purification devices, modification of air-handling equipment, or replacement of air-polluting construction materials.

The objective of this study was to determine the corrosion sensitivity of lead, copper, silver, their alloys, shells, and ceramic tiles to pollutants found in museums. The investigation focused on measurements of corrosion rates of these materials as functions of pollutant exposure time. If possible, corrosion products will be identified to provide information on reaction mechanisms. The results of ongoing surveys conducted by GCI to determine acidic and aldehydic pollutant levels in various museums will be used to guide selection of test conditions.

The project consisted of three phases: (1) preliminary studies to establish sample preparation and gas-handling techniques and to determine gross corrosion rates; (2) developmental tests to determine the efficiency of various corrosion rate measurement techniques with emphasis placed on in situ studies; (3) investigation of corrosion rates at museum concentration levels. Initial studies in phase 1 were performed on lead, lead-tin, and copper-lead alloys in the presence of the lower organic acids and aldehydes.

Primary Publications
Taketomo, A. G., "Corrosion Bibliography," In-house annotated bibliography, The Getty Conservation Institute, 1987.

ABSTRACT-Literature on those aspects of corrosion in which the GCI may develop research projects has been collected. These include:

a.) environmental causes and mechanisms of corrosion;
b.) measurement techniques for corrosion;
c.) conservation problems related to corrosion conservation problems related to corrosion; (especially to bronze objects);
d.) corrosion inhibitors and
e.) protective coatings.

Articles may be cited in more than one section, however, this will be indicated. Abstracts were usually written by the original abstractor, but may have been edited extensively to meet the Getty Conservation Institute research interests. Unless otherwise noted, the language of the original articles is English.

Striegel, M. F., "The Effects of Low Concentrations of Gas Phase Formaldehyde on Some Inorganic Materials Found in Museums," Paper presented to the American Institute for Conservation of Historic and Artistic Works, Albuquerque, New Mexico, June 3, 1991. Also, Postprint of the Object Specialty Group, American Institute for Conservation of Historic and Artistic Works, Vol. 1, 1991, Albuquerque, New Mexico, pp. 1-12.

ABSTRACT-This paper presents the preliminary findings of a study on the potential damage of formaldehyde air pollution on inorganic materials similar to those found in museum collections. Glasses, ceramic glazes, shells, and metals were exposed to 1200 parts per billion (ppb) concentrations of gas phase formaldehyde for 30, 60, and 100 day time intervals. Damage to materials was evaluated on the basis of changes in visual appearance after exposure to formaldehyde. Evidence of surface changes was documented using optical microscopy, scanning electron microscopy, and color measurement.