Characterizing the effect of atomic layer deposited coatings for the prevention of glass alteration in museum collections
Phaneuf, Raymond J
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Glass alteration in museum collections poses a serious problem for museum conservators and collections managers. There are currently few options available to slow or stop the progression of glass alteration. This thesis work has focused on assessing the potential use of atomic layer deposited (ALD) amorphous metal oxide coatings on glass as a potential solution to this problem. A modified ASTM accelerated aging method was used to age the glass samples within a time frame that could be reasonably studied, and the spatially-averaged alteration responses of the glass types chosen for this thesis were determined. The effect of applied ALD coatings on the alteration experienced by glass samples that had been subjected to accelerated aging was assessed. It was found that while TiO2 ALD films did not have a significant effect on the degree of alteration experienced, Al2O3 ALD coatings resulted in a significant decrease in the alteration response measured. The success of these coatings was limited, however, by the presence of coating defects, which expand significantly on the surface of the glass samples as a result of the accelerated aging method used. These defects stem from both the formation of pinholes in the coating during the ALD process, and cracking or buckling of the coatings due to mismatches in the coefficients of thermal expansion between the glass and the coating. Methods of mitigation for the formation of these defects and resulting coating loss were investigated. In addition to the efficacy of the ALD coatings, the appropriateness of this method for the treatment of museum objects was assessed. This included investigations of the impact on the appearance of the object imparted by the coatings. Al2O3 ALD coatings were found to have a minimal effect on the perceived color of the glass samples. In addition, the reversibility of the treatment was examined, and it was found that Al2O3 ALD are able to be removed quickly and safely from glass sample surfaces using mild alkali etchant solutions.