Kinetics of the high- to low-density amorphous water transition

In situ neutron diffraction experiments have been carried out to study the kinetics of the transformation of high-density amorphous (HDA) water into its low-density amorphous state at temperatures 87 K less than or equal to T less than or equal to 110 K. It is found that three different stages are comprised in this transformation, namely an annealing process of the high-density matrix followed by a first-order-like transition into a low-density state, which can be further annealed at higher temperatures T less than or equal to 127 K. The annealing kinetics of the HDA state follows the logarithm of time as found in other systems showing polyamorphism. According to the theory of transformation by nucleation and growth the apparent first-order transition follows an Avrami-Kolmogorov behaviour. An energy barrier DeltaE approximate to 33 kJ mol(-1) is estimated from the temperature dependence of this transition.