SCIART: Collaborative Research: Protection of Silver Objects from Corrosion using Atomic Layer Deposited Barrier Coatings

非技术描述 银制品的腐蚀，尤其是抛光银表面的腐蚀，对于全世界的艺术收藏来说是一个巨大的问题。由于主要博物馆中的物品通常都是独一无二的，因此保护方法和技术需要压倒性的证据来证明处理的有效性、对现有方法的改进以及可逆性。这项研究将使用一种称为“原子层沉积”（ALD）的非常强大的技术开发一种新型多层、多功能透明银阻挡涂层，该技术可以在原子水平上以精确的控制水平创建纳米厚的金属氧化物层。 由此产生的多层薄膜将被优化以降低银的腐蚀速率，同时符合艺术保护实践的严格标准。博物馆和大学的合作将产生一种有效、低成本的策略，以减少银器腐蚀，同时保留器物的外观和成分，而不妨碍未来的保护处理策略。 这些好处将通过出版物和演示与全球博物馆保护界分享。 技术细节 在这项工作中，用于保护银质艺术品的多层结构、多功能原子层沉积 (ALD) 薄膜被制造、表征和优化。银器变色是一个严重的问题，目前对世界各地博物馆收藏的无价艺术品造成了不可挽回的损害。 该方法基于 ALD：一种创新的热激活气相工艺，通过连续暴露于 2 种或多种气体反应物来诱导自限性化学吸附表面反应，从而合成纳米厚的固体薄膜，从而将氧化剂到达下层表面的速率降低几个数量级。探索多种成分和层结构以优化阻隔性能和光学透明度。通过反射光谱评估失去光泽，并使用 X 射线光电子能谱 (XPS) 测量一系列暴露后剥离氧化物后表面上的硫含量。 氧化剂通过薄膜的加速传输和银表面的反应，通过暴露于受控的高浓度 H2S 气氛中，并提高 ALD 涂层样品的温度来建立特征时间尺度，可能是几十年或更长时间。评估 ALD 金属氧化物涂层的可逆性，以确定银上金属氧化物薄层的沉积或去除是否会改变银表面的物理特性或化学成分。 通过沉积多层交替的铝和钛氧化物，可以防止氧化剂分子通过屏障涂层中的针孔直接撞击。 通过将铂埋层沉积到薄膜中，引入了新型氧化剂吸收功能。 银基材的图案化用于量化涂层对微观和宏观特征的光学特性的影响，并评估起始形貌在 ALD 氧化物沉积、去除过程中对艺术品表面形貌和成分稳定性的作用，以及对局部变色率的影响。 在沃尔特斯艺术博物馆和马里兰大学的合作中，研究生和本科生都接受了尖端 ALD 薄膜制造和表征技术以及博物馆保护实践方面的培训。

NONTECHNICAL DESCRIPTION The corrosion of silver artifacts, especially polished silver surfaces, is a monumental problem for art collections throughout the world. As objects in major museums are typically one of a kind, conservation methods and techniques require overwhelming evidence of treatment effectiveness, improvement over existing methods, and reversibility. This research will develop a novel multilayer, multifunctional transparent barrier coating for silver using a very powerful technique known as "atomic layer deposition" (ALD), which allows for the creation of nanometer thick layers of metal oxides with an exquisite level of control, literally at the atomic level. The resulting multilayer films will be optimized to reduce the rate of silver corrosion, while complying with the rigorous standards of art conservation practice. This museum and university partnership will result in an effective, low-cost strategy to reduce silver artifact corrosion, which also preserves artifact appearance and composition without precluding future conservation-treatment strategies. These benefits will be shared with the global museum conservation community through publications and presentations.TECHNICAL DETAILS In this work multilayer-structured, multifunctional atomic layer deposition (ALD) films for conservation of silver art objects are fabricated, characterized and optimized. Tarnishing of silver is a critical problem, presently producing irreparable damage to priceless art objects in museum collections throughout the world. The approach is based upon ALD: an innovative, thermally activated gas phase process for synthesizing nanometer-thick solid films by sequential exposure to 2 or more gas reactants to induce self-limited chemisorbed surface reactions, which reduces the rate of oxidant arrival at the underlying surface by orders of magnitude. Multiple compositions and layer structures are explored to optimize barrier performance and optical clarity. Tarnishing is evaluated via reflectance spectroscopy, and using x-ray photoelectrons spectroscopy (XPS) to measure the amount of sulfur on the surface subsequent to stripping the oxide after a series of exposures. Accelerated transport of oxidants through the film and reaction at the silver surface, using both exposure to atmospheres with controlled, elevated concentrations of H2S, and increasing the temperature of ALD coated samples are employed to establish the characteristic time scales, likely decades or longer. The reversibility of ALD metal oxide coatings is evaluated to determine if either the deposition or the removal of thin layers of metal oxides on silver changes the physical characteristics or chemical composition of the silver surface. The direct impingement of oxidant molecules through pinholes in barrier coatings is prevented by depositing multiple layers of alternating oxides of aluminum and titanium. Novel oxidant gettering functionality is introduced via deposition of buried layers of platinum into the films. Patterning of silver substrates is used to quantify the effect coatings have on the optical properties of micro and macro features and evaluation of the role of the starting topography on the topographical and compositional stability of the surfaces of art objects during ALD oxide deposition, removal, and on the local rate of tarnishing. Students at both the graduate and undergraduate level are trained in cutting-edge ALD film fabrication and characterization techniques, and in museum conservation practices in this collaboration between the Walters Art Museum and the University of Maryland.