In this paper the non-isothermal devitrification of a glass of composi
tion CaO . 0.1P(2)O(5) . 0.9SiO(2) has been studied. Comparison with l
iterature data about the glass CaO . SiO2 enables discussion of the in
fluence of the equimolar substitution of P2O5 for SiO2. The crystal gr
owth activation energy is E(c) = 128 +/- 14 Kcalmol(-1) and is lower t
han that for CaO . SiO2. The experimental results suggest that this ef
fect can be linked to an analogous compositional effect on the viscous
how activation energy. A surface nucleation mechanism is operative as
in the case of the parent glass CaO . SiO2. However the nucleation ra
tes would be reduced as a result of the need for diffusion in the non-
stoichiometric glass.