Fracture toughnesses and surface energies of binary CaO- and MgO-phosphate glasses

The fracture of binary CaO- and MgO-phosphate glasses was studied by measuring the fracture toughnesses and calculating the resulting fracture surface energies. Application of the ionic potential concept yields a linear relationship describing both the normal - and the abnormal - structure glasses on the same surface energy/ionic potential plot. Trends are explained on the basis of the modifying cation to nonbridging oxygen bond density in the glass structure.