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 ri ng bending strength measurements. The samples were prepared by manual glass cutting and were coated with two different types of SiO2 coating: A TEOS c oating (thickness of about 100 nm) was obtained from sols synthesized by ac id catalysis of tetraethoxysilane and a MTKS coating (thickness of about 1 mu m) was obtained from a methyl modified nanoparticulate SiO2 sol. The coa tings 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 increase d 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 app lying MTKS or a double coating of TEOS followed by MTKS. The evaluation of these measurements using Weibull statistical analysis resulted in ill value s 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 conclusi on that the strengthening effect of the two different sol-gel systems is du e to a partial flaw healing and clamping of the crack sides. (C) 1999 Elsev ier Science S.A. All rights reserved.