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Molecules 2015, 20(12), 21672-21680; doi:10.3390/molecules201219793

Microwave-Assisted Superheating and/or Microwave-Specific Superboiling (Nucleation-Limited Boiling) of Liquids Occurs under Certain Conditions but is Mitigated by Stirring

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA
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Authors to whom correspondence should be addressed.
Academic Editors: Marilena Radoiu, Jean-Jacques Vanden Eynde and Annie Mayence
Received: 28 October 2015 / Revised: 17 November 2015 / Accepted: 20 November 2015 / Published: 4 December 2015
(This article belongs to the Special Issue Microwave-Assisted Organic Synthesis)
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Abstract

Temporary superheating and sustained nucleation-limited “superboiling” of unstirred liquids above the normal atmospheric boiling point have been documented during microwave heating. These phenomena are reliably observed under prescribed conditions, although the duration (of superheating) and magnitude (of superheating and superboiling) vary according to system parameters such as volume of the liquid and the size and shape of the vessel. Both phenomena are mitigated by rapid stirring with an appropriate stir bar and/or with the addition of boiling chips, which provide nucleation sites to support the phase-change from liquid to gas. With proper experimental design and especially proper stirring, the measured temperature of typical organic reaction mixtures heated at reflux will be close to the normal boiling point temperature of the solvent, whether heated using microwave radiation or conventional convective heat transfer. These observations are important to take into consideration when comparing reaction rates under conventional and microwave heating. View Full-Text
Keywords: superheating; microwave; reflux; temperature; boiling point superheating; microwave; reflux; temperature; boiling point
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Ferrari, A.; Hunt, J.; Stiegman, A.; Dudley, G.B. Microwave-Assisted Superheating and/or Microwave-Specific Superboiling (Nucleation-Limited Boiling) of Liquids Occurs under Certain Conditions but is Mitigated by Stirring. Molecules 2015, 20, 21672-21680.

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