The most dramatic disagreement that exists between the science and the experiment in ion exchange strengthening of an alkali-containing silicate glass is that the magnitude of surface compression developed after ion exchange is a factor of three to five lower than that expected on the basis of molar volume difference. CGR-sponsored research undertook to explore the possibility that the ion-exchanged glass layers had physical properties significantly different from those of the melted glasses corresponding to the local mixed-alkali composition. Density, Young's modulus, Poisson's ratio, thermal expansion coefficient and network dilation coefficient of a sodium ion-exchanged lithium aluminosilicate glass have been measured in sequentially sectioned layers, or using progressive ion exchange experiments and finite element stress analysis.
