Study On The Mechanism Of Mechanochemical Wear Of Soda-Lime Glass

Owing to its superior chemical and physical properties, soda-lime-silica (SLS) glass has been widely used in architecture, solar energy as well as precision engineering, etc. Due to the water molecules and mechanical vibration in the environment, the tribology phenomena such as friction and wear are one of the critical roles to limit its application. The typical surface precisions of SLS glass, such as chemical-mechanical polishing, contain lots of friction and wear issues. In addition, due to the surface tribology issues, the lifetime of solar energy substrate wear of SLS glass was only ～30% of expected value. The wear of SLS glass is also the main issue for the reduction lifetime of for architecture applications. However, the friction and wear of SLS glass is very lacking. Thus, in order to reveal the mechanochemical wear mechanisms of SLS glass, it is necessary to study the mechanisms of the mechanochemical process at SLS glass surface. The mechanochemical research of SLS glass will not only help understand and control the material damage and removal of SLS glass, but also enrich the nanotribology theory.In present thesis, the mechanochemical wear behaviors of SLS glass surface were intensively investigated. Firstly, upon a ball-on-flat tribometer, the macro-wear behaviors of SLS glass surface are investigated by studying the effect of sodium ion leaching and exchange, and the effects of counter-surface reactivity. Then, using an atomic force microscopy (AFM), the mechanochemical wear of SLS glass at nanoscale is revealed. Then, the effects of sodium concentration on the tribological properties of SLS glass were studied. Based on these systematical investigations, the main conclusion could be summarized as following:(1) The effect of sodium ion (Na+) leaching and exchange with water-related species on the macro-wear of SLS glass was discovered and the related mechanism was proposed.In humid air, SLS glass exhibited superior wear resistance as relative humidity (RH) increased, while other glasses without leachable sodium ions, such as fused quartz, borosilicate glass and barium-boroaluminosilicate glass exhibited poor wear resistance as the RH increased. It was also found that the wear of SLS glass in acid conditions was lower than that in pure water. It was proposed that Na+ ions at SLS glass surface in humid condition could leach out and exchange with hydronium ion (H3O+), result in the compressive stress at SLS glass surface, which was considered as the main mechanism for the superior wear resistance of SLS glass surface at higher RH conditions.(2) The effects of counter-surface reactivity on the macro-wear of SLS glass surface were revealed, and the related mechanisms were proposed.In dry environment, the wear behaviors at SLS glass interface were dominated by mechanical wear, creating a rough and deep wear track. However, in humid environments, the wear behaviors at SLS glass interface was dominated by mechanochemical wear, ball materials with higher hardness got worn off through tribochemical reactions, while the tribochemical wear of SLS glass was slight. It was demonstrated that if the chemical reactivity of counter-surface was close to the SLS glass, the tribochemical wear of SLS glass would occur more readily.(3) The mechanical wear and chemical wear behavior of SLS glass at nanoscale were revealed and its correlation of macro wear and nanowear were proposed.By controlling the humidity, applied load and counter-surface, three wear modes of SLS glass at nanoscale, namely mechanical wear, stress-corrosion and tribochemical wear are investigated. When the SLS glass substrate was rubbed with a chemically-inert diamond tip in an inert environment (vacuum), the surface wear behavior of SLS glass were dominated by mechanical wear. It was found that hillock-like protrusion was formed at the glass surface under lower contact load conditions, while surface material removal occurred under higher load conditions. When the SLS glass substrate was rubbed with a chemically-inert diamond tip in the presence of reactive gas (humid air), the surface wear behavior of SLS glass were dominated by stress-corrosion wear. When the SLS glass substrate was rubbed with a chemically-reactive silica surface in the presence of reactive gas (humid air), the surface wear behavior of SLS glass were dominated by tribochemical wear. It was also demonstrated that the discrepancy between macrowear and nanowear may due to the multi asperity contact at macroscale, the wear debris at sliding interface may also play some roles.(4) A novel approach for controlling tribological properties of SLS glass was proposed.Upon thermal poling process, the concentration of Na+ ions at SLS glass surface could be depleted or gradiented at the anode and cathode side respectively. When the Na+ ions were depleted at the anode side of SLS glass surface, the nanohardness and modulus, as well as nanoscratch resistance of glass surface decreased. The tribochemical wear of Na+-depleted glass increased as the RH increased. On the other hand, when the Na+ ions were gradiented at the cathode side of SLS glass surface, the nanohardness, modulus and nanoscratch resistance of glass surface increased slightly, the tribochemical wear of Na+-gradiented surface were suppressed at high RH conditions.Overall, based on these systematical investigations of mechanochemical wear of SLS glass are extensively studied in present thesis. The research results will not only help extent the lifetime of SLS glass and reveal the mechanism of material removal at microscale, but also enrich the nanotribology theory.