Enhancement of fracture strength of cutted plate glass by the application of SiO2 sol-gel coatings

Abstract

The influence of SiO2 sol-gel coatings on the bending strength of soda lime plate glass samples has been investigated by 3 point bending and double ring bending strength measurements. The samples were prepared by manual glass cutting and were coated with two different types of SiO2 coating: A TEOS coating (thickness of about 100 nm) was obtained from sols synthesized by acid catalysis of tetraethoxysilane and a MTKS coating (thickness of about 1 µm) was obtained from a methyl modified nanoparticulate SiO2 sol. The coatings were applied by dipping and were densified at 500'°C for 1 h. The fracture strength σ0 of edge coated plate glass (60 x 25 x 3.8 mm), determined by 3 point bending test (according to EN 843-1), was increased after coating with TEOS from σ0 = 24 MPa to 40 MPa (67% increase). The fracture strength increased to σ0 = 56 MPa (133% increase) on applying MTKS or a double coating of TEOS followed by MTKS. The evaluation of these measurements using Weibull statistical analysis resulted in m values of 4.1 and 4.2 for the TEOS and MTKS coating and 3.5 for double coating (uncoated glasses m = 5.7), respectively. These results combined with high resolution secondary electron microscopy investigations led to the conclusion that the strengthening effect of the two different sol-gel systems is due to a partial flaw healing and clamping of the crack sides.