Abstract
Scratch formation on glass surfaces is a ubiquitous phenomenon induced by plastic deformation, often accompanied by radial, lateral or median cracks with consequent chipping and brittle fracture caused during and after the event of dynamic abrasion instigated by shear stress by a harder material. This paper addresses the fundamental aspect of scratch formation on soda-lime-silica (SLS) glass surfaces. A constructive combination of surface-sensitive characterization tools, including field emission scanning electron microscopy (FESEM), laser scanning microscopy (LSM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and instrumented indentation technique (IIT), helped to investigate the structural cause of generation of visible scratches on SLS glass surfaces. The experimental results indicate that a silicate network possessing a mechanically weakening structural characteristic in terms of network connectivity confined to the region between 5 and 100 nm below the glass surface is likely to cause a destructive surface scratch eminently visible to the naked eye.
Highlights
Determination of the root cause of scratch formation on the soda-lime-silica glass surface was correlated to the network connectivity of the silicate structure
Nanoindentation was performed before the scratch test to investigate the surface hardness at a load of 10 mN; the results indicated a 10% enhancement in surface hardness restricted to a depth of about 300 nm below the surface of the heat-treated specimen
An elaborate investigation of the silicate structure was performed before scratch testing to determine the structural cause of the formation of scratches
Summary
The formation of a scratch is governed by the nature and live state of the SLS glass surface just before the event of scratching. The sub-Tg heat treated glass structure was found to be mechanically weaker in this region, called “intermediate zone”, owing to higher O Total/Si ratio This depth is critical to propagation of cracks from a surface flaw during a scratching event because the size of the cavities in the vicinity of crack tips is reported to be in the same range on the order of n anometers[31]. The surface scratch network on the untreated specimen seemed to contain more Q1 units (mechanically weakening entity), defined by a larger area under the shoulder peak at approximately 950 cm−1 (16.7%), relative to the H510 counterpart (only 1%), where the full width at half maxima (FWHM) was almost four times This corroborates the preceding observation of a lower variation in bond angle with depth from the heat-treated surface before scratching (stabilized initial network). The drawback associated with Raman spectroscopy is its inability for an accurate quantitative analysis, the area under the peaks can be compared within a particular spectrum to draw apparent interpretive conclusions
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