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- ItemReview on quality assurance along the CFRP value chain - Non-destructive testing of fabrics, preforms and CFRP by HF radio wave techniques(Amsterdam [u.a.] : Elsevier, 2015) Heuer, H.; Schulze, M.; Pooch, M.; Gäbler, S.; Nocke, A.; Bardl, G.; Cherif, Ch.; Klein, M.; Kupke, R.; Vetter, R.; Lenz, F.; Kliem, M.; Bülow, C.; Goyvaerts, J.; Mayer, T.; Petrenz, S.Eddy current testing is well established for non-destructive testing of electrical conductive materials [1]. The development of radio frequency (RF) eddy current technology with frequency ranges up to 100 MHz made it possible to extend the classical fields of application even towards less conductive materials like CFRP [2][3](Table 2). It turns out that RF eddy current technology on CFRP generates a growing number of valuable information for comprehensive material diagnostic. Both permittivity and conductivity of CFRP influence the complex impedance measured with RF eddy current devices. The electrical conductivity contains information about fiber texture like orientations, gaps or undulations in a multilayered material. The permittivity characterization influenced by dielectric properties allows the determination of local curing defects on CFRP e.g. hot spots, thermal impacts or polymer degradation. An explanation for that effect is seen in the measurement frequency range and the capacitive structure of the carbon rovings. Using radio wave frequencies for testing, the effect of displacement currents cannot be neglected anymore. The capacitive structures formed by the carbon rovings is supposed to further strengthen the dielectric influences on eddy current measurement signal [3]. This report gives an overview of several realized applications and should be understood as a general introduction of CFRP testing by HF Radio Wave techniques.
- ItemCellulose-carbon nanotube composite aerogels as novel thermoelectric materials(Amsterdam [u.a.] : Elsevier, 2018) Gnanaseelan, Minoj; Chen, Yian; Luo, Jinji; Krause, Beate; Pionteck, Jürgen; Pötschke, Petra; Qu, HaisongThermoelectric materials based on cellulose/carbon nanotube (CNT) nanocomposites have been developed by a facile approach and the effects of amount (2–10 wt%) and types of CNTs (single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs)) on the morphology (films and aerogels) and the thermoelectric properties of the nanocomposites have been investigated. Composite films based on SWCNTs showed significantly higher electrical conductivity (5 S/cm at 10 wt%) and Seebeck coefficient (47.2 μV/K at 10 wt%) compared to those based on MWCNTs (0.9 S/cm and 11 μV/K, respectively). Lyophilization, leading to development of aerogels with sub-micron sized pores, decreased the electrical conductivity for both types by one order of magnitude, but did not affect the Seebeck coefficient of MWCNT based nanocomposites. For SWCNT containing aerogels, higher Seebeck coefficients than for films were measured at 3 and 4 wt% but significantly lower values at higher loadings. CNT addition increased the thermal conductivity from 0.06 to 0.12 W/(m∙K) in the films, whereas the lyophilization significantly reduced it towards values between 0.01 and 0.09 W/(m∙K) for the aerogels. The maximum Seebeck coefficient, power factor, and ZT observed in this study are 49 μV/K for aerogels with 3 wt% SWCNTs, 1.1 μW/(m∙K2) for composite films with 10 wt% SWCNTs, and 7.4 × 10−4 for films with 8 wt% SWCNTs, respectively.
- ItemLiquid assisted plasma enhanced chemical vapour deposition with a non-thermal plasma jet at atmospheric pressure(Amsterdam [u.a.] : Elsevier, 2016) Schäfer, Jan; Fricke, Katja; Mika, Filip; Pokorná, Zuzana; Zajíčková, Lenka; Foest, RüdigerThe present study introduces a process for the synthesis of functional films onto substrates directly from the liquid phase. The reported method is based on the initialization of the synthesis by means of an atmospheric pressure plasma jet operating with argon above a thin liquid film of the starting material. The process is demonstrated by the formation of a thin, solid SiOx film from siloxane-based liquid precursors. Changes in the chemical properties of the precursor were studied in-situ during the polymerization process on the diamond crystal by using Fourier transform infrared spectroscopy The elemental composition of the SiOxCy films was analyzed by X-ray photoelectron spectroscopy (XPS). Furthermore, XPS was applied to study the effect of post-annealing processes on the composition of the films. The obtained deposits exhibit a low concentration of carbon groups. The amount of hydroxyl groups and interstitial water can be reduced significantly by post-process annealing of the films.