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Microwave heating and dielectric diagnosis technique in a single-mode resonant cavity (1989)

Jow, Jinder ; Hawley, Martin C. ; Finzel, Mark C. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 60 (1989), S. 96-103

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ISSN: 1089-7623

Source: AIP Digital Archive

Topics: Physics , Electrical Engineering, Measurement and Control Technology

Notes: A single-mode microwave heating and dielectric measurement technique has been developed. The single- and swept-frequency methods were used to simultaneously heat the material and measure its complex permittivity in this single-mode technique. A cylindrical cavity and Nylon 66 rods were used in this study. The cavity was always resonated in the TM012-mode at 2.45 GHz. The measured changes in the resonant frequency and cavity Q factor of the cavity with and without the sample were related to complex permittivity of the sample using material-cavity perturbation. Temperature measurement was made using a fluoroptic thermometer. On-line measurements of complex permittivity and temperature were made during single- and swept-frequency microwave heating of the sample. Complex permittivity of Nylon 66 as a function of temperature using the single-frequency method was compared to that using the conventional swept-frequency method during microwave heating. It shows that dielectric measurements using the single- and swept-frequency methods are repeatable and consistent. However, the resolution in resonant frequency shifts and cavity Q factor measurements is higher in the single-frequency method. The measurement errors for permittivity and dielectric loss factor are less than ±4% and ±10% for the single-frequency method and less than ±5% and ±15% for the swept-frequency method. Therefore, the single-frequency method is more accurate than the swept-frequency method.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1140585

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Effect of stoichiometry and diffusion on an epoxy/amine reaction mechanism (1995)

Finzel, Mark C. ; Delong, John ; Hawley, Martin C.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 673-689

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ISSN: 0887-624X

Keywords: epoxy/amine mechanism ; crosslinking ; rate law ; diffusion limit ; kinetics ; Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: The bulk phase kinetics of an epoxy (DGEBA) /amine (DDS) thermoset have been studied using DSC, FTIR, and 13C-NMR. In the absence of catalyst, the reaction was found to involve a main exothermic reaction between epoxide and amine hydrogen and a side reaction between tertiary amine formed in the main reaction and epoxide. The main reaction was exothermic while the side reaction had no discernable exotherm. Etherification did not occur to any significant extent. Since only the main reaction is exothermic, DSC was very useful for studying the main reaction kinetics. FTIR was used for determining whether epoxide and amine hydrogen were consumed at different rates as a way of following the side reaction. An IR band previously unused by other investigators was used to monitor the amine hydrogen concentration. NMR confirmed the above mechanism by identifying the formation of a quaternary ammonium ion/alkoxide ion pair as a reaction product of tertiary amine and epoxide. This mechanism has been successfully fit to a rate law valid over the entire extent of reaction. The rate constant for the epoxy/amine addition reaction was found to depend on hydroxide concentration (extent), reaction temperature, and glass transition temperature and included contributions from uncatalyzed and autocatalyzed parts. The side reaction (quaternary ammonium ion formation) formed weak bonds which did not affect the overall system Tg. Both reactions were second order. The rate constants for the main reaction first increase with increasing extent due to autocatalysis by hydroxide before decreasing due to the diffusion limit caused by gelation and vitrification. © 1995 John Wiley & Sons, Inc.

Additional Material: 16 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/pola.1995.080330409

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Dielectric properties of a curing epoxy/amine system at microwave frequencies (1991)

Finzel, Mark C. ; Hawley, Martin C. ; Jow, Jinder

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 31 (1991), S. 1240-1244

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ISSN: 0032-3888

Keywords: Chemistry ; Chemical Engineering

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Dielectric data collected at 2.45 × 109 Hz has been analyzed using a mean relaxation time model over the temperature range 50 to 100°C and at extents of cure from 0 to 57% for a stoichiometric DER 332 (Dow)/DDS (Aldrich) mixture. The relaxation times thus obtained obey the Arrhenius law and tend to increase with the extent of cure. This corresponds to the more rigid nature of the molecular structure as the network forms and the dipolar relaxations become more inhibited. Decreases in the activation energy of the relaxation along with a widening of the relaxation time distribution imply that the relaxations involve ever shorter chain segments as the extent of cure increases.

Additional Material: 4 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/pen.760311614

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