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see also: Thermal
Simulations,
Algorithm
of Thermal Simulations,
Application
Zoalene
During the curing of epoxy
resin a large amount of heat is generated: approximately 350
J/g. Under adiabatic conditions and a thermal capacity Cp of
2 J/gK the heat generation results in a temperature jump of
175¡C. Because the decomposition of epoxy resins starts at
230¡C, the start temperature (for the adiabatic case) must
be lower than 55¡C.
In the following sample, the curing kinetics are determined
for a composite containing epoxy resin and a filler. On the
basis of kinetics analysis and of caloric data as heat
capacity, heat conductivity over the course of temperature
is calculated for specific conditions, especially the
thermal coupling at ambient temperature.
The goal of this work is the check of maximum temperature
which is achieved for the specific conditions.
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Conditions of
DSC measurements
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Instrument:
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NETZSCH
DSC 204
PhoenixÆ
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Heating
rates/(K/min):
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1, 2,5, 5,
10
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Sample
mass/mg:
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4 .. 5
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Atmosphere:
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N2
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Crucible:
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Aluminum,
pierced
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Kinetic analysis of DSC measurements
Using a triple-step model,
a useful fit-quality is achieved.
Kinetic parameters of the best model
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lg
A1/s^-1:
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10.69
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E1/(kJ/mol)
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94.85
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React.ord
1:
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1.36
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lg
A2/(kJ/mol):
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6.04
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E2/(kJ/mol)
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72.49
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React.ord
2:
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0.91
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lg
A3/(kJ/mol):
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8.82
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E3/(kJ/mol)
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91.62
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lg Kcat
3:
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0.70
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FollReact.
1:
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4.50E-02
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FollReact.
2:
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0.776
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Area 1
..4/(J/g):
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-287.0
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Simulation of self-heating
On the basis of results of
kinetic analysis and conditions of reactor, the simulation
is performed.
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Conditions of
simulation
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Reactor
type:
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cylinder
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Diameter/cm:
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40
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Transfer
Coeff/(W/cm^2K):
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1.36E-3
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Start
temperature/¡C
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56
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Cp/(J/gK):
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1.89
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Density/(g/cm^3):
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1.28
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Heat
conductivity/(W/cmK):
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0.0025
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Temperature vs. time at
different distances from the center.
The self-heating starts
very slowly. In the center the curing reaction is finished
first. Now the heat is transferred more to the cold border.
Because the curing reaction at the border starts from a
higher temperature value, here the maximum temperature is
located.
In order to achieve a full curing after a time of 12 hrs the
ambient temperature is increased to 140 ¡C.
3D-plot of
self-heating
In the 3D plot the general
behavior is more clearly depicted. The maximum near the
border and the general decrease of temperature after full
curing is visible.
This picture demonstrates the problems which are combined
with the curing reaction of a large body: the behavior in
the center is very close to the behavior of an adiabatic
system. The jump in temperature is approximately Delta T =
Heat/Cp. Unexpectedly, the critical position is near the
border.
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