The Pennsylvania State University The Graduate School College of Engineering UNDERSTANDING SHEAR-INDUCED HYDROLYSIS REACTIONS ON SODA LIME SILICA GLASS SURFACE A Dissertation in Chemical Engineering by Jiawei Luo 2018 Jiawei Luo Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy May 2018 The dissertation of Jiawei Luo was reviewed and approved* by the following: Seong H. Kim Professor of Chemical Engineering and Materials Science Dissertation Advisor Chair of Committee Carlo G. Pantano Distinguished Professor of Materials Science and Engineering Dissertation Coadvisor Manish Kumar Associate Professor of Chemical Engineering Associate Professor of Biomedical Engineering Associate Professor of Civil and Environmental Engineering Kristen Fichthorn Merrell Fenske Professor of Chemical Engineering Professor of Physics Head of the Department Graduate Program *Signatures are on file in the Graduate School iii ABSTRACT Soda lime silica (SLS) glass is the most widely used glass materials in terms of mass in windows, bottles & containers, etc. One of the biggest challenge for SLS glass is its brittleness or propensity to be damaged at ambient conditions. One important reason is that cracks propagation on the SLS glass surface can be significantly accelerated by tensile stress induced corrosion reactions of amorphous silicate network, which breaks the Si-O-Si bonds to form two silanol groups, known as stress corrosion effect. It has also been found that stress corrosion reactions are faster with the increase of relative humidity (RH). The propagation of cracks will eventually lead to the failure of SLS glass. However, very little is known on the reactions between glass and water in the environment induced by interfacial shear, which results in the removal of SLS glass. Recently, it has been observed that SLS glass shows unique response to interfacial shear in humid conditions through a ball-on-flat wear test. For most of the commercial flat glasses, including silica, borosilicate glasses, boroaluminosilicate glasses and aluminosilicate glasses, the amount of wear will increase as the humidity level increases. Only SLS glass shows wear resistance at high relative humidity. It is found that shear-induced hydrolysis reactions take place on SLS glass surface for medium and low RH conditions. Then this shear-induced hydrolysis reaction must be “suppressed” or have similar reaction rates of its reverse reactions (condensation + + of silanols) at high RH. One hypothesis is that Na /H + H2O exchange could take place at high RH, which creates surface residual compressive stress at the meantime. Compressive stress which could lower the effective tensile stress on glass surface, is believed to stabilize or hinder the propagation of cracks. Then the amount of wear could also be lowered if the applied stress is not large enough to induce hydrolysis reactions. To test this hypothesis and explore the factors that govern the shear-induced reactions on SLS glass surface, effects of different structural units, surface mechanical properties and iv + + compressive stress, Na /H + H2O exchange are investigated in this dissertation. It should be noted that these factors cannot be easily isolated. Therefore, multiple different treatments need to be performed to modify the surface chemical structures of SLS glass. These surface treatments include hydrothermal reactions, leaching in acid solution, thermal poling in controlled environment, ion-exchange with KNO3. The governing factors are determined through correlating the changes in surface chemical structure, mechanical properties with the wear behavior. It is found that surface mechanical properties, compressive stress created by ion-exchange process and + + alteration layers created by Na /H + H2O exchange are not responsible for SLS glass’s unique wear behavior at high RH. These conclusions has been demonstrated by analyzing the chemical structure and mechanical properties of modified SLS surface by hydrothermal treatment, Na+/K+& Na+/Ag+ exchange, thermal poling treatment and leaching in acid solutions. While no specific mechanism has been identified, mobile Na+ cations and silicate network structure are suggested to be the dominating factors. Another contribution of this dissertation is the improved understanding of amorphous silicate network of glass surfaces which plays vital roles in shear induced reactions. Several novel approaches based on non-destructive spectroscopy have been developed to describe the wide distribution of structural parameters of silicate network. With the assist of molecular dynamics (MD) simulation, the weighted mean of Si-O bond length is in linear relationship with the weighted mean of Si-O-Si asymmetric stretch absorbance. Then a new mathematical algorithm has been developed to extract absorbance of Si-O-Si asymmetric stretch from specular reflectance infrared spectra. By utilizing the selection rule of sum frequency generation (SFG) spectroscopy, O-HO distribution in the subsurface of SLS glass has been roughly identified, which is in good agreement with theoretical prediction. Speciation of hydrous species (ratio of SiOH/H2O) can be determined through a new algorithm based on attenuated total reflectance infrared (ATR-IR) spectroscopy and H depth profile. v A new hypothesis on the unique wear behavior based on the current findings is proposed: shear induced hydrolysis and condensation reactions are in dynamic equilibrium in the presence of Na+. Existence of Na+ can lower the activation energy barrier, especially for condensation reactions. At high RH, Na+ can migrate through the adsorbed water layers and moved to the silanol sites to “catalyze” condensation reactions. To prove this hypothesis, MD simulation with reactive force fields as well as experimental work are required. vi TABLE OF CONTENTS List of Figures .......................................................................................................................... x List of Tables ........................................................................................................................... xix Publications .............................................................................................................................. xx Preface… ................................................................................................................................. xxii Acknowledgements .................................................................................................................. xxiii Chapter 1 Introduction ............................................................................................................. 1 Motivation ........................................................................................................................ 1 Understand shear-induced hydrolysis reactions of SLS glass at high RH by controlling and analyzing the surface chemical structure and mechanical properties .................................................................................................................. 3 Background and literature review .................................................................................... 5 Unique surface chemical structure of SLS glass ...................................................... 5 Stress-induced reactions between SLS glass surface and H2O (g) in the environment ...................................................................................................... 10 Chapter 2 Summary of employing specular reflectance infrared (SR-IR) spectroscopy, attenuated total reflectance infrared (ATR-IR) spectroscopy, environmental-control indentation and wear tests to analyze the surface structure and mechanical properties of SLS glass ..................................................................................................................... 20 Overview .......................................................................................................................... 20 Applying SR-IR and ATR-IR to analyze the structure of Si-O-Si network and hydrous species in the surface region of SLS glass .................................................. 21 Differences of SR-IR and ATR-IR in analyzing glass materials ............................. 21 Obtaining surface Si-O-Si structure with SR-IR and hydrous species with ATR- IR ...................................................................................................................... 24 Friction and wear test for glasses under applied tensile stress ......................................... 31 Cleaning procedure prior friction and wear test ....................................................... 31 Characterization of wear track with optical profilometry ........................................ 32 Holder design for wear test of glass under applied tensile stress ............................. 33 Labview software development for crack initiation load analysis of glass materials with Hertzian indentation ......................................................................................... 34 Environmental controlled Vickers indentation ................................................................ 37 Chapter 3 Hydrothermal reactions of soda lime silica glass – revealing subsurface damage and alteration of mechanical properties and chemical structure of glass surfaces ............................................................................................................................ 40 Overview .........................................................................................................................