Kinetic Analysis and Characterization of Epoxy Resins ... - FedOA

Introduction 51
materials that have dielectric loss factors in the middle of the conductivity range,
as illustrated in Figure 1.17.
Figure 1.17: Relationship between the dielectric loss factor and ability to
absorb microwave power for some common materials.
In contrast, conventional heating transfers heat most efficiently to materials with
high conductivity.
Although equations 1.20 and 1.21 are useful for assessing the effect of electrical
properties on microwave power absorption, material processing is much more complex.
The dielectric properties are dependent on the mobility of the dipoles within
the structure, and therefore the dielectric properties are functions of temperature,
frequency, and, for reacting systems, degree of reaction. Therefore, the ability of
the material to absorb energy changes during processing. For example, at room
temperature silicon carbide (SiC) has a loss factor of 1,71 at 2,45 GHz. The loss
factor at 695 ◦ C for the same frequency is 27,99 [13].
The phase shift of current in electrical circuits is analogous to how energy is
dissipated in dielectric materials. As mentioned before, dipole polarization lags
behind the electric field due to internal forces in the material. The phase shift,
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