Heat and Gas Diffusion in Comet Nuclei (pdf file 5.5 MB) - ISSI

224 Appendix B
B.4 Phase Transitions
Amorphous to Crystalline Water Ice:
The phase transition from amorphous to crystalline water ice is highly
exothermic, with a heat release during the transformation of 1620 J g-
mol −1 (Ghormley, 1968). An activation law, determined experimentally
by Schmitt et al. (1989), gives the crystallization time t cr as a function of
temperature
t cr = 9.54 × 10 −14 · e 5370/T [s] (B-11)
The energy released by the phase transition from amorphous to crystalline
ice, can be written as
Q tr = 1620 cdotN a−H 2 O
t cr
[Jm −3 s −1 ] (B-12)
where N a−H2 O is the number of g-moles of amorphous ice in the unit volume.