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

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Introduction 50 as an equivalent conductance [12]. If the electric field is assumed to be uniform throughout the volume, the following simplified equation for power, P , absorbed per unit volume can be obtained from equation 1.19: P=2π f ɛ II E 2 (1.20) As energy is absorbed within the material, the electric field decreases as a function of the distance from the surface of the material. Therefore, equation 1.20 is valid for only very thin materials. The penetration depth is defined as the distance from the sample surface where the absorbed power is 1/e of the absorbed power at the surface. Beyond this depth, volumetric heating due to microwave energy is negligible. Assuming the dielectric constant of free space is ɛ 0 , the penetration depth is given by the following equation [7]: d= c ɛ 0 2 π f ɛ II (1.21) The penetration depth and knowledge of how the electric field decreases from the surface are particularly important in processing thick materials. If the penetration depth of the microwave is much less than the thickness of the material only the surface is heated. The rest of the sample is heated through conduction. Equation 1.21 shows the dependence of the penetration depth on the frequency of operation. Equations 1.20 and 1.21 give an insight as to which dielectric materials are suitable for microwave processing. Materials with a high conductance and low capacitance (such as metals) have high dielectric loss factors. As the dielectric loss factor gets very large, the penetration depth approaches zero. Materials with this dielectric behavior are considered reflectors. Materials with low dielectric loss factors have a very large penetration depth. As a result, very little of the energy is absorbed in the material, and the material is transparent to microwave energy. Because of this behavior, microwaves transfer energy most effectively to 50
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, 51
Page 1 and 2: UNIVERSITA’ DEGLI STUDI DI NAPOLI
Page 3 and 4: 3 I thank all the lecturers of PhD
Page 5 and 6: 5 Microwaves are electromagnetic ra
Page 7 and 8: CONTENTS 7 1.8.1 DielectricProperti
Page 9 and 10: CONTENTS 9 4 Conclusions and Outloo
Page 11 and 12: LIST OF TABLES 11 3.2 Average value
Page 13 and 14: List of Figures 1.1 Diglycidylether
Page 15 and 16: LIST OF FIGURES 15 2.23 Onset tempe
Page 17 and 18: LIST OF FIGURES 17 3.38 Comparison
Page 19 and 20: Introduction 19 cannot be melted an
Page 21 and 22: Introduction 21 • bismaleimides;
Page 23 and 24: Introduction 23 cold solders, casti
Page 25 and 26: Introduction 25 Average Properties
Page 27 and 28: Introduction 27 In Figure 1.4 n can
Page 29 and 30: Introduction 29 ducts and it genera
Page 31 and 32: Introduction 31 tween current-carry
Page 33 and 34: Introduction 33 that describe the p
Page 35 and 36: Introduction 35 1.3.5 Lorentz Force
Page 37 and 38: Introduction 37 Figure 1.11: Electr
Page 39 and 40: Introduction 39 Even microwaves can
Page 41 and 42: Introduction 41 production requirem
Page 43 and 44: Introduction 43 fect of the electro
Page 45 and 46: Introduction 45 following different
Page 47 and 48: Introduction 47 Debye equations bas
Page 49: Introduction 49 Although these mode
Page 53 and 54: Chapter 2 Experimental In this chap
Page 55 and 56: Experimental 55 Characteristic Note
Page 57 and 58: Experimental 57 If the oven is used
Page 59 and 60: Experimental 59 In monomodal applic
Page 61 and 62: Experimental 61 Figure 2.5: Right s
Page 63 and 64: Experimental 63 Figure 2.8: Front v
Page 65 and 66: Experimental 65 regardless of the a
Page 67 and 68: Experimental 67 • The number of t
Page 69 and 70: Experimental 69 Figure 2.11: Surfac
Page 71 and 72: Experimental 71 Figure 2.12: Repeti
Page 73 and 74: Experimental 73 From the Figure 2.1
Page 75 and 76: Experimental 75 in the centre of th
Page 77 and 78: Experimental 77 not read the water
Page 79 and 80: Experimental 79 Test number 1 2 3 4
Page 81 and 82: Experimental 81 Figure 2.19: Plot o
Page 83 and 84: Experimental 83 2.5 Datalogger This
Page 85 and 86: Experimental 85 same reason a wood
Page 87 and 88: Experimental 87 Material Behaviour
Page 89 and 90: Experimental 89 in function of the
Page 91 and 92: Experimental 91 2.6.3 Influence of
Page 93 and 94: Chapter 3 Results and Discussion Th
Page 95 and 96: Results and Discussion 95 There is
Page 97 and 98: Results and Discussion 97 Figure 3.
Page 99 and 100: Results and Discussion 99 Parameter
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Results and Discussion 101 After pr
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Results and Discussion 103 of insta
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Results and Discussion 105 1. Mecha
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Results and Discussion 107 where k
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Results and Discussion 109 Kinetic
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Results and Discussion 111 Figure 3
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Results and Discussion 113 3.3 Comp
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Results and Discussion 115 pedestal
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Results and Discussion 117 Tables 3
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Results and Discussion 123 t MW [s]
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Results and Discussion 125 simulate
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Results and Discussion 129 t DSC [s
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Results and Discussion 133 Using th
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Results and Discussion 135 forward
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Results and Discussion 141 than the
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Results and Discussion 143 Since ev
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Results and Discussion 145 ditions.
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Results and Discussion 147 3.23 and
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Results and Discussion 149 The T g
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Results and Discussion 151 3.6.1 St
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Results and Discussion 153 Flexural
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Results and Discussion 155 3.7.2 FT
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Results and Discussion 157 identifi
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Results and Discussion 159 This eff
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Results and Discussion 161 Also in
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Conclusions and Outlook 163 degree
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Appendix A A Brief History of Micro
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A Brief History of Microwave Oven 1
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Bibliography [1] W. Callister, “M
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BIBLIOGRAPHY 171 [19] P. I. Karkana
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BIBLIOGRAPHY 173 [34] K. D. V. Pras
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