TY  - JOUR
A1  - Hoffmann, Andreas
A1  - Rohrbach, Felix
A1  - Uhl, Matthias
A1  - Ceblin, Maximilian
A1  - Bauer, Thomas
A1  - Mallah, Marcel
A1  - Jacob, Timo
A1  - Heuermann, Holger
A1  - Kuehne, Alexander J. C.
T1  - Atmospheric pressure plasma-jet treatment of polyacrylonitrile-nonwovens—Stabilization and roll-to-roll processing
JF  - Journal of Applied Polymer Science
N2  - Carbon nanofiber nonwovens represent a powerful class of materials with prospective application in filtration technology or as electrodes with high surface area in batteries, fuel cells, and supercapacitors. While new precursor-to-carbon conversion processes have been explored to overcome productivity restrictions for carbon fiber tows, alternatives for the two-step thermal conversion of polyacrylonitrile precursors into carbon fiber nonwovens are absent. In this work, we develop a continuous roll-to-roll stabilization process using an atmospheric pressure microwave plasma jet. We explore the influence of various plasma-jet parameters on the morphology of the nonwoven and compare the stabilized nonwoven to thermally stabilized samples using scanning electron microscopy, differential scanning calorimetry, and infrared spectroscopy. We show that stabilization with a non-equilibrium plasma-jet can be twice as productive as the conventional thermal stabilization in a convection furnace, while producing electrodes of comparable electrochemical performance.
KW  - batteries and fuel cells
KW  - electrospinning
KW  - fibers
KW  - irradiation
KW  - porous materials
Y1  - 2022
U6  - http://dx.doi.org/10.1002/app.52887
SN  - 0021-8995 (Print)
SN  - 1097-4628 (Online)
N1  - Weitere Informationen: Bundesministerium für Bildung und Forschung, Fördernummer: 13XP5036E. Deutsche Forschungsgemeinschaft, Fördernummern: 390874152, 441209207, 327886311
VL  - 139
IS  - 37
SP  - 1
EP  - 9
PB  - Wiley
ER  - 
TY  - JOUR
A1  - Hoffmann, Andreas
A1  - Uhl, Matthias
A1  - Ceblin, Maximilian
A1  - Rohrbach, Felix
A1  - Bansmann, Joachim
A1  - Mallah, Marcel
A1  - Heuermann, Holger
A1  - Jacob, Timo
A1  - Kuehne, Alexander J.C.
T1  - Atmospheric pressure plasma-jet treatment of PAN-nonwovens—carbonization of nanofiber electrodes
JF  - C - Journal of Carbon Research
N2  - Carbon nanofibers are produced from dielectric polymer precursors such as polyacrylonitrile (PAN). Carbonized nanofiber nonwovens show high surface area and good electrical conductivity, rendering these fiber materials interesting for application as electrodes in batteries, fuel cells, and supercapacitors. However, thermal processing is slow and costly, which is why new processing techniques have been explored for carbon fiber tows. Alternatives for the conversion of PAN-precursors into carbon fiber nonwovens are scarce. Here, we utilize an atmospheric pressure plasma jet to conduct carbonization of stabilized PAN nanofiber nonwovens. We explore the influence of various processing parameters on the conductivity and degree of carbonization of the converted nanofiber material. The precursor fibers are converted by plasma-jet treatment to carbon fiber nonwovens within seconds, by which they develop a rough surface making subsequent surface activation processes obsolete. The resulting carbon nanofiber nonwovens are applied as supercapacitor electrodes and examined by cyclic voltammetry and impedance spectroscopy. Nonwovens that are carbonized within 60 s show capacitances of up to 5 F g⁻¹.
Y1  - 2022
U6  - http://dx.doi.org/10.3390/c8030033
SN  - 2311-5629
N1  - This article belongs to the Collection "Nanoporous Carbon Materials for Advanced Technological Applications"
VL  - 8
IS  - 3
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Schopp, Christoph
A1  - Rohrbach, Felix
A1  - Langer, Luc
A1  - Heuermann, Holger
T1  - Detection of welding wire length by active S11 measurement
JF  - IEEE Transactions on Plasma Science
N2  - A novel method to determine the extruded length of a metallic wire for a directed energy deposition (DED) process using a microwave (MW) plasma jet with a straight-through wire feed is presented. The method is based on the relative comparison of the measured frequency response obtained by the large-signal scattering parameter (Hot-S) technique. In the practical working range, repeatability of less than 6% for a nonactive plasma and 9% for the active plasma state is found. Measurements are conducted with a focus on a simple solution to decrease the processing time and reduce the integration time of the process into the existing hardware. It is shown that monitoring a single frequency for magnitude and phase changes is sufficient to achieve good accuracy. A combination of different measurement values to determine the length is possible. The applicability to different diameter of the same material is shown as well as a contact detection of the wire and metallic substrate.
KW  - Circuit simulation
KW  - Hot S-parameter
KW  - Modeling
KW  - Plasma
KW  - Plasma diagnostics
Y1  - 2024
U6  - http://dx.doi.org/10.1109/TPS.2024.3356659
SN  - 0093-3813 (Print)
SN  - 1939-9375 (Online)
IS  - Early Access
SP  - 1
EP  - 6
PB  - IEEE
ER  -