Protection of Glass from Scratches: The Use of a Hard, Thin Coating to Minimize Damage

Abstract

Format

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Abstract

Used throughout human history, glass has recently been reconsidered as a major structural material as shown by the large window surfaces in use nowadays in vehicles and buildings. Its transparency hides a significant mechanical drawback, however: Brittleness, which arises from surface flaws. In times where reducing the weight and increasing the lifetime of structures is a growing concern, any strategy to increase the toughness of glass is of interest. Our study aims at coating glass surfaces with a hard, thin, transparent protective layer in order to minimize the density of surface flaws. A reverse micro-emulsion synthesis was used to produce a dispersion of colloidal silica nanoparticles (~30 nm in diameter) which were then deposited on a glass substrate by dip-coating. Thermal treatment was then used to remove any organic components, leading to the production of mono- and bilayer structures as observed via atomic force microscopy (AFM). Microindentation experiments revealed a lower elastic modulus in the coating versus the substrate, in spite of its fully inorganic nature. Scratch tests were then performed at increasing applied load using a custom-built sclerometer. The coating was found to delay the appearance of visually apparent scratches by reducing the degree of chipping observed during scratch development. Instead, such coatings exhibit a transition from ductile behavior directly to the abrasive regime classically observed in glass at high loads, avoiding the production of extended sub-surface cracks that normally give rise to visual damage.