Lokale In situ-Raman-Analyse der Gas- und Feststoffphase zum Verständnis des katalytischen Wachstumsprozesses von Kohlenstoff-Nanoröhren
Zusammenfassung der Projektergebnisse
Within the scope of the second project period, an in situ Raman spectroscopy setup for the analysis of the emergent solid phase has been developed, optimized and integrated to the available setup established during the first funding period, in order to simultaneously monitor the parameters of interest of the solid and gas phases during the formation and growth of carbon nanotubes (CNTs) in a cold wall reactor for catalytic chemical vapor deposition (CCVD). For this purpose, modifications in the reactor construction with respect to an additional optical access and an alternative for feeding the fresh gas flow were also necessary. Furthermore, a substitute for the catalyst preparation method presented in the first funding period had to be established, since the former catalyst MOCVD-precursors were not accessible anymore. In order to attain a reliable quantitative interpretation of the measured data, an improved numerical approach for spectra evaluation has been implemented in a MATLAB routine, so that by in situ monitoring the CCVD process, both comprehensive qualitative and quantitative analyses could be carried out. Ex situ measurement techniques, like Raman spectroscopy and Scanning electron microscopy (SEM) have been applied to analyze the substrates after the CCVD process in order to validate the outcome of the in situ investigations. On the basis of the real-time in situ Raman spectra of the emerging solid phase, the moment of nucleation or first signal detection, the time-range of the CNT growth as well as the end of the deposition due to catalyst deactivation could be monitored through the appearance and development of the characteristic D and G Raman bands for carbon materials. Thus, by qualitatively monitoring the nanocarbon formation and growth, the CCVD process can be better understood, controlled and optimized at least with regard to one relevant parameter, which is the deposition time. By means of the improved numerical approach for spectra evaluation, the D/G ratio, which is a reliable parameter to assess the defect and disorder content of the growing nanostructures, could be estimated as a function of the reaction time. The Raman spectroscopy setup for the gas phase analysis exhibits a very high detection sensitivity and together with the numerical approach for spectra evaluation, result in very accurate and precise results at the rather unfavorable environment for Raman measurements. Acetylene conversion as well as the accompanying thermal effects in the gas phase could be monitored in situ during the deposition process. Correlation was found between the acetylene conversion and the quality of the resulting CNTs. Thus, it is possible to assess the catalytic activity departing from both in situ solid and gas phase parameters, offering therewith new possibilities for process fundamental research and process optimization towards a CNT-tailored production.
Projektbezogene Publikationen (Auswahl)
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"In situ monitoring of the acetylene decomposition and gas temperature at reaction conditions for the deposition of carbon nanotubes using linear Raman scattering", Optics Express 18, 18223-18228 (2010)
K. Reinhold-López, A. Braeuer, N. Popovska, and A. Leipertz
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“In situ optical monitoring of the solution concentration influence on supercritical particle precipitation”, Journal of Supercritical Fluids 55, 282-290 (2010)
S. Dowy, A. Braeuer, K. Reinhold-López, and A. Leipertz
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“Catalytic growth of carbon nanotubes on zeolite supported iron, ruthenium and iron/ruthenium nanoparticles by chemical vapor deposition in a fluidized bed reactor”, Powder Technology 207, 17–25 (2011)
N. Popovska, K. Danova, I. Jipa, and U. Zenneck
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"Flow field characterization in a vertically oriented cold wall CCVD reactor by particle image velocimetry", Chemical Engineering Journal 184, 315-325 (2012)
K. Reinhold-López, A. Braeuer, A. Schmitt, N. Popovska-Leipertz, and A. Leipertz
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"In situ Raman monitoring of the solid and gas phases during the formation and growth of carbon nanotubes inside a cold wall CCVD reactor", Carbon 78, 164-180 (2014)
K. Reinhold-López, A. Braeuer, B. Romann, N. Popovska-Leipertz, and A. Leipertz
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„In-situ Raman monitoring of the formation and growth of carbon nanotubes via chemical vapour deposition” (7th World Congress on Particle Technology, Beijing, China, May 18 – 22, 2014, Abstract No. 757), Procedia Engineering 102, 190 – 200 (2015)
K. Reinhold-Lopez, A. Braeuer, B. Romann, N. Popovska-Leipertz, und A. Leipertz
