A New Low-Brittleness Glass in the Soda-Lime-Silica Glass Family

In the soda-lime-silica glass family, the effect of each constituent of the composition on the brittleness was first investigated. Vickers indentation was employed to estimate the brittleness (ratio of harness ( H ) to fracture toughness ( K _c)) by measuring the C / a ratios (where C and a are the characteristic crack and indentation diagonal lengths, respectively). It was observed that a higher silica content and a lower lime content helped to lower the brittleness. Substitution of potash and magnesia for soda and calcia, respectively, was effective in lowering the brittleness. From these results, a higher molar volume was found to be a key factor for reducing the brittleness. A new low-brittleness glass was then developed with a brittleness as low as 5.1 µm^-1/2 as compared with the brittleness of 7.1 µm^-1/2 for commercial soda-lime-silica glass. The crack initiation load ( P *), measured by the Vickers indentation method, for this new low-brittleness glass was almost 10 times as high as P * of commercial soda-lime-silica glass. The new glass shows lower hardness and higher fracture toughness than the commercial soda-lime-silica glass.