A novel dual mode X-band EPR resonator for rapid in situ microwave heating

Folli, Andrea; Choi, Heungjae; Barter, Michael; Harari, Jaafar; Richards, Emma; Slocombe, Daniel; Porch, Adrian; Murphy, D. M.

doi:10.1016/j.jmr.2019.106644

Cited by 7 publications

(12 citation statements)

References 23 publications

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“…New developments in microwave spectroscopy have been reviewed, including in dielectric measurements using cavity perturbation applied to the real-time measurement of ammonia storage in halide salts [71] and in metal-organic frameworks (MOFs) [72] for hydrogen storage applications. In microwave magnetic spectroscopy we have highlighted developments in electron paramagnetic resonance, with new methods using loop-gap resonators and dual mode cavities for simultaneous microwave heating [3], [80].…”

Section: Discussionmentioning

confidence: 99%

“…We develop bespoke cavities for X-band systems and have recently introduced a dual mode EPR cavity which allows simultaneous heating and EPR spectroscopy to be performed [3]. Chemical reactions can be perturbed away from thermodynamic equilibrium by imposing a rapid shock to the system, often by a temperature (T) jump, yielding non-equilibrium populations of reactive intermediate states.…”

Section: Microwave Spectroscopymentioning

confidence: 99%

“…Microwave science transcends traditional discipline boundaries and is still growing in relevance, continuously finding many new applications. In microwave chemistry, at low power, measurements using the microwave electric field have been able to sensitively measure changes in charge dynamics resulting from phenomena as varied as catalyst deactivation to adsorption of ammonia in zeolites [1], [2], whilst measurements with high frequency magnetic fields are commonly used in magnetic resonance imaging, nuclear magnetic resonance and electron paramagnetic resonance [3]. More recently, microwave magnetic field effects have been used to produce quantum images of current flow in graphene and even measure pulses in neurons [4], [5].…”

Section: Introductionmentioning

confidence: 99%

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Microwaves in Chemistry

Slocombe

Porch

2021

IEEE J. Microw.

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Section: Discussionmentioning

confidence: 99%

Section: Microwave Spectroscopymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microwaves in Chemistry

Slocombe

Porch

2021

IEEE J. Microw.

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“…Accurately determining the temperature of a sample heated via microwaves is challenging and alternative methods of determining temperature are being explored. The 6.1 GHz microwave heating system is described in detail in [17], but briefly comprises a low-power, solid state source (Keysight N5173B) with a power amplifier (Empower 1131-BBM5K8CGM) of saturated output power of 35 W and 10 W at 1 dB compression point. This amplifier is connected to the cavity heating port via a flexible coaxial cable.…”

Section: Resonator Design Considerationsmentioning

confidence: 99%

“…Furthermore, rapid heating can change not only the selectivity and product distribution of some reactions, but also provides a simple and effective means to study the dynamics and possible speciation of the reacting system itself, for example, via the application of a rapid temperature-jump (TJ) [14][15][16]. With this in mind, we recently introduced the concept of a dual mode "reactor-resonator" EPR cavity [17] that doubles up as an effective applicator for heating a sample but also allows for simultaneous EPR spectroscopy to be performed, simply by selection of two distinct resonant modes of different resonant frequencies.…”

Section: Introductionmentioning

confidence: 99%

Design Considerations of a Dual Mode X-Band EPR Resonator for Rapid In-Situ Microwave Heating

et al. 2022

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This paper describes the design considerations for a dual mode X-band continuous wave (CW) Electron Paramagnetic Resonance (EPR) cavity, for simultaneous EPR measurement and microwave heating of the same sample. An elliptical cavity geometry is chosen to split the degeneracy of the TM110 mode, allowing for a well resolved EPR signal with the TM110,a and TM110,b modes resonating at around 10 GHz and 9.5 GHz, respectively, the latter of which is used for EPR measurements. This geometry has the benefit that the TM010 mode used for microwave heating resonates at 6.1 GHz, below the cut off frequency of the X-band waveguide used for the EPR channel, providing effective isolation between the heating and EPR channels. The use of a pair of 9 µm thick copper clad laminates as the flat cavity walls allows for sufficient penetration of the modulation field (Bmod) into the cavity, as well as maintaining a high cavity Q factor (> 5700) for sensitive EPR measurements. Locating the heating port at an angle of 135° to the EPR port provides additional space for easier coupling adjustment and for larger sample access to be accommodated. The associated decrease of EPR signal strength is fully compensated for by using a 7.2 GHz low pass filter on the heating port. EPR spectra using 1.6 mm and 4.0 mm sample tubes are shown at room temperature (298 K) and 318 K for a standard Cu(acac)2 solution, demonstrating the effectiveness of this dual-mode EPR cavity for microwave heating during EPR detection.

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An in situ study of the thermal decomposition of 2,2′-azobis(2-methylpropionitrile) radical chemistry using a dual-mode EPR resonator

Magri

Barter²,

Fletcher-Charles³

et al. 2022

Res Chem Intermed

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A custom-built dual-mode EPR resonator was used to study the radical chemistry of AIBN thermal decomposition. This resonator enables both simultaneous in situ heating using microwaves and EPR measurements to be performed. The thermal decomposition of AIBN was compared following conventional heating methods and microwave-induced (or dielectric) heating methods. Under both heating conditions, the radicals formed and detected by EPR include the 2-cyano-2-propyl (CP●) and 2-cyano-2-propoxyl (CPO●) radicals. Under aerobic conditions, the observed relative distribution of these radicals as observed by EPR is similar following slow heating by conventional or dielectric methods. In both conditions, the kinetically favoured CPO● radicals and their adducts dominate the EPR spectra up to temperatures of approximately 80–90 °C. Under anaerobic conditions, the distribution can be altered as less CPO● is available. However, the observed results are notably different when rapid heating (primarily applied using a MW-induced T-jump) is applied. As the higher reaction temperatures are achieved on a faster timescale, none of the ST●-CPO adducts are actually visible in the EPR spectra. The more rapid and facile heating capabilities created by microwaves may therefore lead to the non-detection of radical intermediates compared to experiments performed using conventional heating methods.

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A novel dual mode X-band EPR resonator for rapid in situ microwave heating

Cited by 7 publications

References 23 publications

Microwaves in Chemistry

Microwaves in Chemistry

Design Considerations of a Dual Mode X-Band EPR Resonator for Rapid In-Situ Microwave Heating

An in situ study of the thermal decomposition of 2,2′-azobis(2-methylpropionitrile) radical chemistry using a dual-mode EPR resonator

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