Question

Isothermal crystallisation experiments on a lithium disilicate glass sample at 510 degree C gave the following results. By plotting a suitable graph, verify that the crystallisation process obeys the Johnson-Mehl-Avrami equation with a value of the Avrami exponent, n = 4, and determine the rate constant, k. What can you deduce about the mechanism of crystallisation and the morphology of the crystallites from this value of n?

Answer 1

a) we need to the plot of ln(ln(1/1-Y))) Vs ln(t). From the line obtain we calculate n and K

b)  the value of 4 can be said to have contributions from three dimensions of growth and one representing a constant nucleation rate. Alternative derivations exist where n has a different value.