In situ time-lapse synchrotron radiation X-ray diffraction of silver corrosion

Abstract

Several heritage systems have been studied using state-of-the-art synchrotron techniques. The cultural heritage value of silver is documented in museum collections across the globe. However, the silver surface is not as chemically stable as that of other precious metals, and is susceptible to corrosion by atmospheric gases. It is therefore of special interest to clarify these surface reactions by using in situ, time-lapse chemical and structural analysis in controlled ambients in order to develop strategies to reduce or even prevent the atmospheric attacks. In order to study the initial corrosion processes of silver in the presence of corrosive gases in situ time-lapse X-ray diffraction experiments were performed on the XMaS beamline at the European Synchrotron Radiation Facility, Grenoble. Highly pure silver samples were weathered with synthetic air containing 500 ppb of both H₂S and ozone, at relative humidity (RH) levels, and XRD patterns were tracked every 10 min over a total weathering time of 24 h. The time-lapse Synchrotron Radiation (SR)-XRD data show that pure silver exposed to those atmospheres starts to form crystalline corrosion products after only 10 minutes. Silver sulfates, silver oxides, intermediates and mixed species are formed on the sample surface over the duration of the experiment. The data collected using a newly combined environmental cell/gas flow set up introduces a set of highly useful tools for scientists who wish to study time-lapse gaseous corrosion at ambient temperature and pressure.