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

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Results and Discussion 158 A remarkable increase of the thermal profile in term of heating rate and absolute temperature values has been noticed, as illustrated in Figure 3.45. Figure 3.45: Comparison of the thermal profiles between the epoxy system incorporating 2 p.h.r. of an organic sensitizer with the same resin free from additives. However this investigation is still in progress and there is again a range of uncertainty of about 10 ◦ C. In fact the sensitizing effect of this organic compound is so strong, that also a little variation of its percentage can determine a not negligible difference of the thermal profile of the epoxy mixture. In any case the effect of this substance as microwave sensitizer has been observed also by other authors [36, 37], but they have reported only a modicum temperature enhancement. The electromagnetic energy absorbed by the mixture containing this sensitizer is very great. In fact under microwave radiation not only the epoxy group, but also the specific polar group of this organic sensitizer rotate around their electric centre, following the oscillation of the EM field. In this way the kinetic rotational energy is converted to heat and therefore the temperature of the whole mixture strongly increases. 158
Results and Discussion 159 This effect operates both during the initial dielectric heating of the epoxy mixture and after the following activation of the curing reaction. Probably using 2 p.h.r. of this organic sensitizer the complete conversion of the epoxy system can be achieved in a shorter time or alternatively with a lower radiations power, in both the cases with a considerable energy saving. 3.8.2 Metallic Nanopowders The influence of another type of sensitizer has been studied. Nickel nanopowders have been chosen, because they can improve the microwave absorption. In fact they sensitive to the oscillating EM field, due to their ferromagnetic properties [38]. However these metallic nanopowders increase also the thermal conductivity of the epoxy mixture and therefore improve the energy dissipation, during both the initial dielectric heating and the following exothermic curing reaction. For this reason the sensitizing effect is partially downsized. Instead of the organic sensitizer, the nickel nanopowders do not interfere with the curing reaction. In fact they do not possess functional groups able to interact with the reagents of the epoxy mixture. A 20 p.h.r. quantity has been identified as the most suitable amount for the temperature raising. The formulation of the epoxy mixture, used in these experiments is reported in Table 3.31. The mixture containing 20 p.h.r. of nickel nanopowder has been prepared as illustrated in the section 2.1.3 on page 54. It has been microwave cured using the operative conditions listed in Table 3.30 and the temperature of sample has been recorded by datalogger. Figure 3.46 shows a comparison of thermal profiles followed by the epoxy mixture free from additives and by the same system incorporating the nickel nanopowders. 159
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UNIVERSITA’ DEGLI STUDI DI NAPOLI
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3 I thank all the lecturers of PhD
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5 Microwaves are electromagnetic ra
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CONTENTS 7 1.8.1 DielectricProperti
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CONTENTS 9 4 Conclusions and Outloo
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LIST OF TABLES 11 3.2 Average value
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List of Figures 1.1 Diglycidylether
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LIST OF FIGURES 15 2.23 Onset tempe
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LIST OF FIGURES 17 3.38 Comparison
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Introduction 19 cannot be melted an
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Introduction 21 • bismaleimides;
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Introduction 23 cold solders, casti
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Introduction 25 Average Properties
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Introduction 27 In Figure 1.4 n can
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Introduction 29 ducts and it genera
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Introduction 31 tween current-carry
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Introduction 33 that describe the p
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Introduction 35 1.3.5 Lorentz Force
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Introduction 37 Figure 1.11: Electr
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Introduction 39 Even microwaves can
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Introduction 41 production requirem
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Introduction 43 fect of the electro
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Introduction 45 following different
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Introduction 47 Debye equations bas
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Introduction 49 Although these mode
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Introduction 51 materials that have
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Chapter 2 Experimental In this chap
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Experimental 55 Characteristic Note
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Experimental 57 If the oven is used
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Experimental 59 In monomodal applic
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Experimental 61 Figure 2.5: Right s
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Experimental 63 Figure 2.8: Front v
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Experimental 65 regardless of the a
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Experimental 67 • The number of t
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Experimental 69 Figure 2.11: Surfac
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Experimental 71 Figure 2.12: Repeti
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Experimental 73 From the Figure 2.1
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Experimental 75 in the centre of th
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Experimental 77 not read the water
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Experimental 79 Test number 1 2 3 4
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Experimental 81 Figure 2.19: Plot o
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Experimental 83 2.5 Datalogger This
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Experimental 85 same reason a wood
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Experimental 87 Material Behaviour
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Experimental 89 in function of the
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Experimental 91 2.6.3 Influence of
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Chapter 3 Results and Discussion Th
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Results and Discussion 95 There is
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Results and Discussion 97 Figure 3.
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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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Page 163 and 164: Conclusions and Outlook 163 degree
Page 165 and 166: Appendix A A Brief History of Micro
Page 167 and 168: A Brief History of Microwave Oven 1
Page 169 and 170: Bibliography [1] W. Callister, “M
Page 171 and 172: BIBLIOGRAPHY 171 [19] P. I. Karkana
Page 173: BIBLIOGRAPHY 173 [34] K. D. V. Pras
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Kinetic Analysis and Characterization of Epoxy Resins ... - FedOA

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