The glassy substance is generally obtained by rapid cooling of the melt. When changing from the molten state to the glassy state, the viscosity increases sharply during the cooling process, and the particles can not be arranged regularly to form crystals, and the latent heat of crystallization is not released. Therefore, the glassy state A substance has a higher internal energy than a crystalline substance. Its energy is between the molten state and the crystalline state and belongs to the metastable state. From a mechanical point of view, glass is an unstable high-energy state. For example, there is a tendency to transition from a low-energy state, that is, there is a tendency to crystallize. Therefore, glass is a metastable solid material.