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

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 mu m) was obtained from a methyl modified nanoparticulate SiO2 sol. The coatings were applied by dipping and were densified at 500 degrees C for 1 h. The fracture strength sigma(0) 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 sigma(0) = 24 MPa to 40 MPa (67% increase). The fracture strength increased to sigma(0) = 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 ill values of 4.1 and 4.2 for the TEOS and MTKS coating and 3.5 for double coating (uncoated glasses nz = 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. (C) 1999 Elsevier Science S.A. All rights reserved.