Studies into the corrosion of brass in an indoor museum environment

Abstract

Cultural heritage is the product of and testament to past traditions and intellectual achievements, of which collections of historic scientific instruments provide the most significant of records in the history of science field. This work presents the results of studies into the atmospheric corrosion of brass, one of the main metal components of these instruments, in their own museum storage space, which is an indoor environment typical of a museum in a tropical clime. The studies, which lasted 300 days, were done on strips of brass with a similar composition to that of the instrument parts. They included preliminary tests, an environmental exposure test and an accelerated test (alternate immersion), which was adapted from the methodology proposed by M. Pourbaix. Overall, it was possible to simulate an acceleration of the real atmospheric corrosion process using adapted alternate immersion test. The results obtained by scanning electron microscopy (SEM) and x- ray diffraction (XRD) showed that the first oxidation product formed was cuprite, and that the process was very slow. It was not possible to identify any sulfur compounds, though the SEM analyses showed the presence of this element on the surface of the strips. The results of the Rutherford backscattering spectroscopy (RBS) and SEM analyses suggested that, based on the thickness of the layers of corrosion products formed, there was a relationship between the time scales of the alternate immersion and atmospheric exposure tests, whereby each 30 days of accelerated test corresponded to approximately 300 days of exposure to the environment under study.