Clarifying the kinetic glass transition

Daily experience shows that most liquids freeze into a crystalline solid when cooled. Elementary thermodynamics textbooks teach that this process is a first-order phase transition, taking place at a well defined, pressure-dependent temperature. However, some liquids, called “glassformers”, undergo a less common fate – as the viscous silica melt cools it gradually ceases to flow and rigidifies continuously into a disordered, amorphous solid: everyday bottle or window glass. There is no phase transition at a well defined temperature and the transformation depends on the thermal history of the material (such as the cooling rate of the quench). In fact many liquid materials undergo such a glass transition if the cooling rate is sufficiently high to bypass nucleation of the crystalline phase. For instance, certain metallic alloys, such as copper and silver or copper and magnesium, may be quenched into a glass if ultrafast cooling rates of 105Ks -1 or more are applied.