Fundamental Mechanisms for Mechanochemical Behaviors of Glass Surfaces - An Integrated Experimental and Computational Approach

非技术描述：玻璃的强度和耐磨性是许多消费品的重要性能，包括手机、显示器、汽车/航空航天车窗，以及玻璃的安全性。虽然几种强化工艺，如回火和离子交换，目前在工业上使用，但其科学基础并不完全被理解。这限制了玻璃强度和可靠性的进一步提高。玻璃的强度受制造和处理过程中产生的表面损伤以及玻璃成分的控制。该项目致力于更好地了解机械应力和表面化学(称为机械力化学)的组合效应的研究。这项研究的科学发现对玻璃制造商以及产品开发中的玻璃用户都有直接的好处。技术细节：硅酸盐玻璃表面在环境空气中的机械和机械力化学性能对碱性离子的淋溶及其与含水物种(羟基或水)的交换很敏感。这项研究假设界面剪切或机械变形导致水合物种周围的硅酸盐网络的局部扭曲，使得Si-O-Si网络的桥氧与水合物种之间的距离变得比导致Si-O-Si网络水解所需的临界长度更短。这一假说与玻璃科学中几个突出的重要问题有关，如应力诱导的钠离子输运和金属离子对玻璃网络的催化作用。虽然现有的应力腐蚀理论可以解释在外加拉应力下裂纹的扩展，但它不能完全解释承压水与玻璃接触时在压应力和剪应力下的化学反应。本项目采用密度泛函理论(DFT)和反应力场分子动力学(MD)模拟(ReaxFF)来研究关键假设和相关问题，并利用最先进的表面分析技术对理论计算结果进行了实验验证。该项目培养工程和材料科学方面的本科生和研究生，重点是玻璃及其强度。研究团队从代表性不足的群体中招募学生参与该项目。所有学生都从宾夕法尼亚州立大学材料研究所(MRI)和材料计算中心(MCC)的各种跨学科材料研究活动中受益。该团队向NanoHub和原子间模型知识库(OpenKim)网站提供计算数据，以便他们的用户可以为未来的力场开发和验证项目获取这些材料。ReaxFF和DFT模拟和表面分析结果的精选实例被整合到现有的两门研究生课程中。

NON-TECHNICAL DESCRIPTION: The strength and wear resistance of glass are important properties for many consumer products including mobile phones, displays, automotive/aerospace windows, and for the safety of glass, in general. Although several strengthening processes such as tempering and ion-exchange are currently used in industry, the scientific foundations are not all fully understood. This limits further improvements in glass strength and reliability. The strength of glass is controlled by surface damage created in manufacturing and handling, as well as by the composition of the glass. This project engages in research to better understand the combined effects of mechanical stress and surface chemistry (called mechanochemistry). The scientific findings of this research are directly beneficial to glass manufacturers as well as users of glass in product development. TECHNICAL DETAILS: Mechanical and mechanochemical properties of silicate glass surfaces in ambient air are sensitive to alkali ion leaching and its exchange with hydrous species (hydroxyl or water). This research hypothesizes that interfacial shear or mechanical deformation causes local distortion of the silicate network surrounding the hydrous species such that the distance between the bridging oxygen of the Si-O-Si network and the hydrous species becomes shorter than the critical length needed to induce hydrolysis of the Si-O-Si network. This hypothesis is relevant to several important questions that are outstanding in glass science such as stress-induced transport of sodium ions and the catalytic effects of metal ions on hydrolysis of glass network. While existing stress corrosion theory can explain crack growth under an applied tensile stress, it cannot fully explain the chemical reactivity of confined water in contact with glass under both compressive and shear stress. This project employs density functional theory (DFT) and molecular dynamics (MD) simulations with reactive force fields (ReaxFF) to study the key hypothesis and related questions, and theoretical calculation results are tested and validated experimentally using state-of-the-art surface analysis techniques. This project educates undergraduate and graduate students in the engineering and science of materials with a focus on glass and its strength. The research team recruits students from underrepresented groups to work on the project. All students benefit from participation activities associated with various interdisciplinary materials research activities at the Materials Research Institute (MRI) and Material Computation Center (MCC) at Penn State. The team offers computational data to the Nanohub and the Knowledgebase of Interatomic Models (OpenKim) websites, so that their user-base can access these materials for future force field development and validation projects. Selected examples of the ReaxFF and DFT simulations and surface analysis results are integrated in two existing graduate courses.