Rosie Grayburn

Towards a new method for coating heritage lead

BackgroundEthanolic solutions of long-chain carboxylic acids can be applied to lead metal substrates to form a coating of lead carboxylate which provides protection against atmospheric pollutants.Results and conclusionsIn this paper we describe the optimal inhibitor concentration for the coating on lead. Electrochemical impedance data taken before and after immersion in media modelling oak emitted volatile organic compounds (VOCs) polluted atmospheres show that coating effectiveness decreases after exposure, but the effect is lessened if longer chain carboxylates are used.

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

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.

Evaluation of an X-ray-excited optical microscope for chemical imaging of metal and other surfaces.

The application of a modular system for the nondestructive chemical imaging of metal and other surfaces is described using heritage metals as an example. The custom-built X-ray-excited optical luminescence (XEOL) microscope, XEOM 1, images the chemical state and short-range atomic order of the top 200 nm of both amorphous and crystalline surfaces. A broad X-ray beam is used to illuminate large areas (up to 4 mm(2)) of the sample, and the resulting XEOL emission is collected simultaneously for each pixel by a charge-coupled device sensor to form an image. The input X-ray energy is incremented across a range typical for the X-ray absorption near-edge structure (XANES) and an image collected for each increment. The use of large-footprint beams combined with parallel detection allows the power density to be kept low and facilitates complete nondestructive XANES mapping on a reasonable time scale. In this study the microscope was evaluated by imaging copper surfaces with well-defined patterns of different corrosion products (cuprite Cu2O and nantokite CuCl). The images obtained show chemical contrast, and filtering the XEOL light allowed different corrosion products to be imaged separately. Absorption spectra extracted from software-selected regions of interest exhibit characteristic XANES fingerprints for the compounds present. Moreover, when the X-ray absorption edge positions were extracted from each spectrum, an oxidation state map of the sample could be compiled. The results show that this method allows one to obtain nondestructive and noninvasive information at the micrometer scale while using full-field imaging.

SR-XRD in situ monitoring of copper-IUD corrosion in simulated uterine fluid using a portable spectroelectrochemical cell

The objective of this work is to study the initial corrosion of copper in the presence of gold when placed in simulated uterine fluid in order to better understand the evolution of active components of copper-IUDs. In order to carry out this study, a portable cell was designed to partially simulate the uterine environment and provide a way of tracking the chemical changes occurring in the samples in situ within a controlled environment over a long period of time using synchrotron spectroelectrochemistry. The dynamically forming crystalline corrosion products are determined in situ for a range of copper-gold surface ratios over the course of a 10-day experiment in the cell. It is concluded that the insoluble deposits forming over this time are not the origin of the anticonception mechanism.

Further advances in lead carboxylate coatings: coating unprimed heritage lead

Further to the previously published work in this journal “Towards a new coating for heritage lead”, a coating has been trialled with samples replicating aged lead artefacts. Lead was corroded in an oak environment to simulate storage or display in a wooden case then coated with ethanolic solutions of tetradecanoic and octadecanoic acid. X-ray diffraction and electrochemical impedance data suggests an better-quality coating is formed leading to improved corrosion resistance.Graphical abstractPerformance and appearance of corroded coupons: coated and uncoated