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Table 1 – Simplified Avrami exponent interpretation Avrami exponent
1 < n < 2 2 < n < 3 3 < n < 4
one can calculate t1/2 Figure 1):
Growth geometry One-dimensional, rod-like Two-dimensional, disc-like Three-dimensional, spherulitic (6) using Eq. [6] (also see
where: X(T) is fraction crystallized at temperature T ΔHC
is overall heat of crystallization dHC/dT is enthalpy of crystallization during
infinitesimal temperature range dT T0
is temperature at initial crystallization
T is temperature during crystallization T∞
complete.
Eq. (4) can be related to Eq. (1) by using Eq. (5) to convert the temperature-dependent data to time-dependent data and fit using the Avrami equation:
(5)
where: t is time T0
is temperature when crystallization is
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is temperature at crystallization onset
T is temperature during crystallization process β is cooling rate (°C/min). For this experiment, t0
is obtained by defining
it at some point of conversion—arbitrarily 1% or X(t) = 0.01 (Eq. [1]). Once t0
is established, the
linear form of the Avrami equation (Eq. [3]) is utilized to plot log(–ln(1 – X(t)) versus log t. Eq. [3] is a linear equation of the form of y = mx + b, but often the crystallization data is linear in a narrow range and different crystallization regimes are apparent. A good starting point is between the limits of X(t) = 0.2 and X(t) = 0.8. This will often yield a straight line of slope n and intercept log k. From the Avrami parameters,
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