Page 27 - Handbook of Thermal Analysis of Construction Materials

Section 2.0 - Classical Techniques 11

control the variations of the heating profile: frequency of the time-tempera-
ture oscillation; the amplitude of the oscillation; and the average, underly-
ing heating rate. Therefore, the application of the oscillating time-tempera-
ture wave to the heating ramp will have a great impact on the resulting heat
flow signal.
In dynamic DSC the temperature program is represented by: [39]

Eq. (4) T = bt + B • sin(wt)

where w = frequency
b = heating rate
B = amplitude of temperature program
Assuming a small temperature excursion and a linear response of
the rate of the kinetic process to temperature, Eq. (4) can be expressed as: [39]

Eq. (5) dQ/dt = C [b + Bw • cos(wt)] + f´´(T,t) + C • sin(wt)
p
where f´´(T,t) = is the underlying kinetic function after
subtraction of the sine wave modulation
C = amplitude of kinetic response to the sine
wave modulation

[b + Bw • cos(wt)] = measured dT/dt
Thus, as can be seen in Eq. (5), the heat flow signal will contain a
cyclic component which is dependent on amplitude of kinetic response (C),
amplitude of temperature (B), and frequency (w).
The periodic integration of the original dynamic DSC will result in
a deconvoluted DSC heat flow signal, which is equivalent to the heat flow
data obtained by traditional DSC. The subtraction of the C component
p
from the deconvoluted signal yields the kinetic component data. The C
p
component gives information on reversible thermal events, such as T g
while the kinetic component provides data on the irreversible aspects of
thermal transitions such as evaporation, decomposition, crystallization,
relaxation, or curing.
The new and unique capabilities of the dynamic technique include: [36]

• Improved resolution of closely occurring and overlapping
transitions.
• Increased sensitivity for low energy or subtle transitions.

• Heat capacity measurements (under low heating/cooling
rate conditions).