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Abstract In pursuit of diamond nanoparticles, a capacitively-coupled radio frequency flow-through plasma reactor was operated with methane-argon gas mixtures. Signatures of the final product obtained microscopically and spectroscopically indicated that the product was an amorphous form of graphite. This result was consistent irrespective of combinations of the macroscopic reactor settings. To explain the observed synthesis output, measurements of C2and gas properties were carried out by laser-induced fluorescence and optical emission spectroscopy. Strikingly, the results indicated a strong gas temperature gradient of 100 K per mm from the center of the reactor to the wall. Based on additional plasma imaging, a model of hot constricted region (filamentation region) was then formulated. It illustrated that, while the hot constricted region was present, the bulk of the gas was not hot enough to facilitate diamondsp3formation: characterized by much lower reaction rates, when compared tosp2,sp3formation kinetics are expected to become exponentially slow. This result was further confirmed by experiments under identical conditions but with a H2/CH4mixture, where no output material was detected: if graphiticsp2formation was expected as the main output material from the methane feedstock, atomic hydrogen would then be expected to etch it awayin situ, such that the net production of thatsp2-hybridized solid material is nearly a zero. Finally, the crucial importance of gas heating was corroborated by replacing RF with microwave source whereby facilesp3production was attained with H2/CH4gas mixture.
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Thermal Shock Synthesis of Nanocatalyst by 3D‐Printed Miniaturized Reactors
Abstract High temperature synthesis and treatments are ubiquitous in chemical reactions and material manufacturing. However, conventional sintering furnaces are bulky and inefficient with a narrow temperature range (<1500 K) and slow heating rates (<100 K min−1), which are undesirable for many applications that require transient heating to produce ideal nanostructures. Herein, a 3D‐printed, miniaturized reactor featuring a dense micro‐grid design is developed to maximize the material contact and therefore acheive highly efficient and controllable heating. By 3D printing, a versatile, miniaturized reactor with microscale features can be constructed, which can reach a much wider temperature range (up to ≈3000 K) with ultrafast heating/cooling rates of ≈104K s−1. To demonstrate the utility of the design, rapid and batch synthesis of Ru nanoparticles supported in ordered mesoporous carbon is performed by transient heating (1500 K, 500 ms). The resulting ultrafine and uniform Ru nanoparticles (≈2 nm) can serve as a cathode in Li‐CO2batteries with good cycling stability. The miniaturized reactor, with versatile shape design and highly controllable heating capabilities, provides a platform for nanocatalyst synthesis with localized and ultrafast heating toward high temperatures that is otherwise challenging to achieve.
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- Award ID(s):
- 1635221
- PAR ID:
- 10456778
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 16
- Issue:
- 22
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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