Effect of sol-gel thin coatings on the fracture strength of glass

The effect of ZrO2-3 mol% Y2O3 sol-gel thin coatings on the fracture of soda-lime glass is investigated. For this purpose, a recently developed strength measurement procedure-based on making a brittle material flex on top of a soft substrate by applying a load with a spherical indenter to the top surface of the system-is used. Results suggest significant variation of both the average fracture strength and the Weibull modulus on coated glass slides. It is suggested that the origin of such variations can be attributed to a certain chemical degradation of the glass during the coating process. This chemical attack produces a highly homogeneous flaw population on the glass surface which governs its fracture behavior. Implications of this work for the practical use of coated glass layers are discussed.