CCI Newsletter, No. 32, November 2003

Science of Conservation: Cyclohexylamine: An Unwanted Museum Visitor

by Marie-Claude Corbeil, Senior Conservation Scientist, and Kate Helwig, Conservation Scientist, Analytical Research Laboratory

Conservators at Glenbow Museum in Calgary, Alberta, recently noticed that crystals were forming on artifacts both on display and in storage, and as different as the leather case of a tape recorder, a sandstone sculpture, a contemporary painting, a wooden barrel, a wooden crate and a stoneware jug. Even after brushing the crystals off the artifacts, they would soon reappear on objects.

To determine the nature and source of these mysterious crystals, small samples were removed from the artifacts and sent to CCI for analysis. Microdiffractometry showed that the crystals were composed of cyclohexylammonium chloride, C₆H₁₃N•AHCl.

Our research showed that cyclohexylamine, a vapour phase inhibitor (VPI) often used in steam generation and distribution systems required for heating or humidification to protect the ferrous components of these systems from corrosion,^1,2 could be the culprit. It, along with other VPIs such as morpholine and diethylaminoethanol, was determined to be used in the museum's steam humidification system.

The artifacts on which the cyclohexylamine crystallized must have been acidic, as is no doubt the case for the artifact shown here. As for the source of chlorides, required for the salt to form, it may have been from the artifacts themselves or external pollutants. Cyclohexylamine is a stronger base than morpholine (and probably also stronger than diethylaminoethanol), which means that of the three VPIs, cyclohexylamine will react first with any acid. This explains why only the cyclohexylamine salt formed on the objects.

Although VPIs help prevent corrosion of metals, this example shows that they can react with other types of material in an unexpected and undesirable way. Glenbow Museum staff are taking measures to address the problem now that the source is known.

1. Malaiyandi, M., G.H. Thomas, and M.E. Meek. "Sampling and Analysis of Some Corrosion Inhibiting Amines in Steam Condensates." Journal of Environmental Science and Health, Part A, Environmental Science and Engineering 14, 7 (1979): pp. 609–627.
2. Malaiyandi, M., and M.J. Goddard. "Development of Analytical Methodology and a Report on Collaborative Study on the Determination of Morpholine, Cyclohexylamine, and Diethylaminoethanol in Aqueous Samples by Direct Aqueous Injection Gas Chromatography." Journal of Testing and Evaluation 18, 2 (1990): pp. 87–97.