Nanoparticles generated by combining hot wall and microwave plasma chemical vapor synthesis
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.134
Nanoparticles generated by combining hot wall and microwave plasma chemical vapor synthesis Alexander Levish* and Markus Winterer* *Nanoparticle Process Technology and CENIDE (Center for Nanointegration Duisburg-Essen), University of Duisburg-Essen, Lotharstr. 1, 47057 Duisburg, Germany
ABSTRACT
Controlling the oxidation state of iron and the crystal structure of iron containing compounds is the key to improved materials such as iron oxide nanoparticles for cancer treatment or heterogeneous catalysis. Iron oxides contain iron in different oxidation states and form different phases for one valence state (α-Fe3+2O2-3, β- Fe3+2O-32, etc.). Chemical vapor synthesis (CVS) allows the reproducible production of pure nanocrystals with narrow size distribution where particle formation and growth take place in the gas phase. Through the controlled variation of synthesis parameters CVS enables the synthesis of diverse iron oxide phases. In this study the energy for the CVS process is supplied by a hot wall furnace and a microwave plasma. The advantage of an plasma reactor as the first CVS stage is the fast and complete precursor decomposition at low temperatures. This results in a larger process window for the hot wall reactor in the second stage. The nanoparticles are examined regarding their structure, surface and valence by XRD and TEM.
INTRODUCTION Chemical vapor synthesis (CVS) allows reproducible synthesis of nanocrystalline nanoparticles with a narrow size distribution [1]. It also enables good control of synthesis parameters, which is the key requirement for phase pure synthesis of materials. Iron can form different (oxide) phases even at the same Fe/O ratios at different temperatures [2]. This chemical variability makes it is an interesting system for studying the redox mechanisms in gas phase synthesis of nanoparticles. Among all iron oxides low valence oxides are most interesting due to their nonstability and difficulty of their phase pure synthesis. Wustite, FeO, can be used as invasive and nonivasive body painting [3]. It is also known as food coloring pigment [3]. Magnetite, Fe 3O4, is used as contrast material for magnetic resonance imaging or cancer treatment [4,5]. Generally, the control over the oxidation state and morphology of iron is of a great industrial potential. EXPERIMENTAL For CVS of iron containing nanoparticles three different reactors are used. The first setup consists of a hot wall (HW) reactor according to figure 1, alternatively a
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microwave plasma (MWP) reactor (figure 2) and finally, the third setup comprises a serial combination of those modules (figure 3), which allows us to vary the temperature in the hot wall reactor with a known state after the microwave plasma reactor (MWP+H
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