Characterizing the Effectiveness of Atomic Layer Deposited Coatings for the Prevention of Glass Disease

Abstract

Glass disease, the broad term used to describe the process by which historic glass objects degrade, presents a particularly challenging problem for museum curators and conservators. This challenge stems from both an imprecise understanding of how glass disease progresses and a lack of treatment options to slow or stop it. This work is a joint investigation by the University of Maryland, Department of Materials Science and Engineering and the Smithsonian Institution, Museum Conservation Institute that is aimed at both testing and building upon recent findings by the glass science community about the chemistry and kinetics of glass disease, and proposing a potential treatment option.Conventional museum practice for glass conservation is often based upon untested assumptions; as an example, a common suggestion is that the progression of object degradation due to glass disease stems from a loss of water, i.e., that "drying out" is the cause of the cracking and opacification often observed [1]. In contrast, recent work from glass science literature [2,3], as well as our own results, suggest that the opposite is, in fact, responsible for the onset and progression of glass disease. We have observed early stages of glass disease on samples that have been continuously submerged in aqueous solutions. These results indicate that effective preservation strategies must focus on preventing water from contacting the surface of the glass.We are able to prevent the direct contact of water with the surface of glass objects through the application of a highly impermeable coating using Atomic Layer Deposition (ALD). ALD is a technique that was developed for use in microelectronics and allows for the buildup of an amorphous oxide film, one atom layer at a time. In previous work, our group has shown that ALD coatings can prevent tarnishing by acting as a diffusion barrier between silver objects and atmospheric corrosive species [4]. Benefits of this technique include atomic level uniformity of the coating regardless of object's topography, ease of removal using mild alkali solutions, and minimal impact on the object's appearance.Early results have been obtained by comparing the structural evolution of the near-surface region of glass samples with and without ALD coatings after a series of accelerated aging/aqueous acidic immersion experiments as observed in light microscopy, and the chemical changes that occur during the ion exchange reaction that drives the process as determined via x-ray microanalysis. A significant finding in our studies is that crack formation nucleates at the interface between the corrosion layer and the underlying pristine glass, and not at the sample surface as has sometimes been previously assumed [ Fig.1]. Scanning electron microscopy-based energy dispersive x-ray spectroscopy (SEM-EDS) analysis showed migration of sodium ions in the glass matrix due to acid attack. We have found direct evidence for the depletion of sodium around the cracks in the corroded gel layer, as well as precipitate products both in t...

Glass alteration in 19th century glass photographic plates: Potential role in gelatin delamination

“…Even under accelerated aging conditions in a laboratory, glass alteration research most often relies on nanoscale analysis or inductively coupled plasma–mass spectrometry techniques to detect and study the progression of glass alteration, as it is seldom advanced enough for the alteration layer to be easily visible using SEM–EDS imaging techniques 28,29 . Museum objects, such as these glass photographic plates, provide a unique opportunity to both visualize, document, and study the development of glass alteration as it has naturally occurred over time.…”

“…Even under accelerated aging conditions in a laboratory, glass alteration research most often relies on nanoscale analysis or inductively coupled plasma-mass spectrometry techniques to detect and study the progression of glass alteration, as it is seldom advanced enough for the alteration layer to be easily visible using SEM-EDS imaging techniques. 28,29 Museum objects, such as these glass photographic plates, provide a unique opportunity to both visualize, document, and study the development of glass alteration as it has naturally occurred over time. Previous work on alteration observed in glass storage vials in biological specimen collections under aqueous conditions at the Smithsonian and a study at the Library of Congress on the early 19th century glass flutes revealed a similar naturally formed depleted alteration layer by SEM.…”

Glass alteration in atmospheric conditions: crossing perspectives from cultural heritage, glass industry, and nuclear waste management

“…Other invasive conservation approaches implying a minimal amount of deposited chemicals have been attempted, with the purpose of stabilizing the hydrated layer with respect to the silicate network hydrolysis (such as in refs. 39,40 ). In this latter approach, the industrial methods consisting of spraying zinc salt solutions on the surface of flat glass 41 have been tested on synthetic unstable glasses subjected to accelerated ageing in climatic chambers.…”