Pore formation in glass–ceramics: Influence of the stress energy distribution

In glass–ceramics, the density difference between the new, semi-crystalline system, and the ambient phase requires a deformation of the grains. However, the first stage of surface induced crystallization is the creation of rigid shell, opposing the shrinkage. Therefore, an important stress appears inside the grain. If the average density of the new system is higher than that of the ambient phase, a tensile stress is generated. In the opposite case, a compressive stress is developed. As soon as the system is neither pure elastic body nor pure plastic one, the concentration of the stress energy depends on the distance from the interface. We describe theoretically the distribution profile of the stress energy. Depending on the stress attenuation parameter and the grain size, there are two solutions. The first one predicts a maximum in the middle of the grain. According to the second, there are two maxima close to the crystal/glass interface. This explains the appearance of cabbage like crystals or of crystalline grains with a pore in the center.