Protection of Glass from Scratches: The Use of a Hard, Thin Coating to Minimize Damage
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Protection of Glass from Scratches: The Use of a Hard, Thin Coating to Minimize Damage Ronan Tartivel1,2, Emmanuelle Reynaud2, Fabien Grasset3, Jean-Christophe Sangleboeuf1, and Tanguy Rouxel1 1 LARMAUR FRE CNRS 2717, Universite de Rennes 1, Campus de Beaulieu, Rennes, 35042 Cedex, France 2 Mechanical Engineering/Nanomanufacturing Center of Excellence, UMass Lowell, One University Avenue, Lowell, MA, 01854 3 Sciences chimiaues de Rennes UMR-CNRS 6226, Universite de Rennes 1, Campus de Beaulieu, Rennes, 35042 Cedex, France, Metropolitan 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 inorganice nature. Scratch tests were then performed at increasing applied load using a custom-built sclerometer (Fig. 1). 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.
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Figure 1. Scratch test patterns for a 0 to 2.5 N loading frame. a- Soda-Lime-Silicate glass (substrate) annealed 15 min at 350°C, b- Nanoparticle-based coating on the same substrate.
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