Paul Roth

Formation and properties of ZnO nano-particles from gas phase synthesis processes

ZnO nano-particles have been synthesized in low pressure flow reactors utilizing Zn(CH3)2 as precursor. Two different synthesis routes have been employed. A low pressure flame reactor and a microwave reactor were used for synthesis of ZnO particle in Zn(CH3)2 doped H2/O2/Ar flames and Zn(CH3)2 doped Ar/O2 plasmas, respectively. The particle formation process has been investigated in situ by a particle mass spectrometer. Also, sampled powders have been investigated ex situ by means of FT-IR, XRD, TEM, and UV-VIS. For both synthesis routes nanometer sized ZnO particles were found with particle diameters in the range between 4 to 8 nm. In cases of the flame reactor the results suggest a strong influence of water on the particle formation process.

Silicon Particle Formation by Pyrolysis of Silane in a Hot Wall Gasphase Reactor

The formation of silicon powder by pyrolysis of silane diluted in argon at different concentrations has been studied. A hot wall gas-phase reactor was used for the thermal decomposition of SiH 4 at 1000°C and atmospheric pressure. The composition, morphology, size, and shape of the particles produced has been studied utilizing electron microscopy, X-ray diffraction, infrared spectroscopy, and BET gas adsorption. Depending on the experimental conditions, agglomerates of polycrystalline, sintered particles have been obtained, which are composed of nanocrystallites of about 25 nm in size.

Soot particle sizing by LII during shock tubepyrolysis of C6H6

Abstract Time-resolved laser-induced incandescence (LII) and cw-laser extinction techniques have been used to size soot particles originating from benzene pyrolysis behind reflected shock waves. The LII-technique is based on fast heating of particles by a short laser pulse and on the subsequent time-resolved observation of the particle cooling, as measured by its thermal emission. Additionally, soot formation was measured by a cw-laser-extinction technique, which provides information about induction periods for soot formation and soot yield. Four groups of experiments with different benzene concentrations diluted in Ar were performed. For the experiments within each group the reaction temperature or the delay time interval between shock-induced heating of the mixture and the LII-laser pulse was varied. The analysis of the LII-data results in time-resolved growth curves for mean particle radii between 1 nm and 11 nm. Higher C6H6-concentrations lead to bigger particles. From the extinction data, high soot yields were found at longer reaction times. The induction periods measured agree with the range of values reported in previous studies.

Synthesis and characterization of nanowires formed by self-assembled iron particles

The formation of iron particles without and with carbon coating was studied in a hot wall flow reactor. The precursors ironpentacarbonyl (IPC, Fe(CO)5) and ethylene (C2H4) both diluted in N2 were used in a concentric tubular flow arrangement and were heated to temperatures between 570 and 1170?K at pressures between 50 and 500?mbar. In experiments without C2H4, either individual iron particles in the size range of or long iron chains composed of several hundreds of individual iron particles were found depending on the reaction conditions. In experiments with C2H4 addition, these particles or particle chains were covered by a thin carbon/carbide layer. The size of the primary particles was measured in situ by time-resolved laser-induced incandescence (TR-LII) and ex situ by rapid thermophoretic particle probing and TEM imaging.

Size analysis in low-pressure nanoparticle reactors: comparison of particle mass spectrometry with in situ probing transmission electron microscopy

Abstract The comparison of particle mass spectrometry (PMS) and transmission electron microscopy (TEM) as size determining techniques has been performed on nanosized particles produced in two different types of low-pressure gas-phase reactors. Results from PMS measurements are compared to image analysis carried out on particles in situ sampled on TEM grids either by non-intrusive molecular beam probing or by a high-speed sampling method. It has been shown that for flame generated Fe 2 O 3 nanoparticles the agreement between PMS measurement and TEM imaging is very good. ZnO particles, synthesized in a microwave plasma reactor show a similar good agreement for the respective analysis methods. To the contrary, the measured size of GeO 2 particles originating from a plasma process differs for the methods employed. PMS measurements yield smaller particles compared to TEM image analysis of molecular beam sampled particles which can be attributed to uncertainties in the physical properties of nano-GeO 2 particles.

Resonance absorption measurements of N, O, and H atoms in shock heated HCN/O2/Ar mixtures

Abstract Atomic resonance absorption spectroscopy (ARAS) was used to measure the concentrations of N, O, and H atoms behind reflected shock waves in HCN O 2 mixtures highly diluted in Ar. For the temperature range 2195 ≤ T ≤ 3390K at pressures of about 1.5–1.9 bar, the concentrations of the initial reactants varied between 25 and 200 ppm for HCN, and 50 and 1000 ppm for O2. Nearly 80 experiments were performed and compared with computer simulations based on a reaction model of 33 elementary reactions and selected rate coefficients. The rate coefficient of the reaction CN + O 2 → NCO + O (R3) was varied to match the measured and calculated concentration profiles. The determined rate coefficient of reaction R3 is found to be in good agreement with the result reported by Louge and Hanson in Int. J. Chem. Kin. 16: k 3 = 4.9 × 10 12 cm 3 mol -1 s -1 Using the rate coefficient data reported in the literature for the other reactions of the kinetic model, a percentage standard deviation of about ± 15 % was obtained from the experimental scatter observed for k3. However, a detailed uncertainty analysis conducted for two experiments led to error bars of about + 150% and −50% for the individual results of k3.

A Shock and Expansion Wave-driven Powder Disperser

The paper describes a method for dispersing small (micro- and milligram) quantities of dry powder using a shock and expansion wave technique. The batch-wise operating apparatus aerosolizes any particulate matter with primary particles down to the submicrometer size range. Depending on the initial pressure situation and on the powder mass to be dispersed, the degree of dispersion or the fraction of agglomerates can be adjusted in a wide range. For calibration purposes monodisperse aerosols can also be generated employing monosized powders. The operating characteristics of the device are presented.

Characteristics of Fe2O3 Nanoparticles from Doped Low-pressure H2/O2/Ar Flames

A burner stabilized premixed low-pressure flame has been used to generate iron-oxide (Fe2O3) nanoparticles with sizes in the range 7–20 nm. The H2/O2/Ar flames were doped with different amounts of iron-pentacarbonyl (Fe(CO)5) with concentrations in the range 524–2096 ppm. The influence of precursor concentration on composition, structure, morphology, and size have been studied utilizing transmission electron microscopy (TEM), X-ray powder diffraction (XRD), measurements of the specific surface area (BET), and infrared spectroscopy (FT-IR). The product particles consist of both, the γ- and the α-phase of Fe2O3. Average particle sizes were measured in the range 7.4–16 nm depending on precursor concentration and flame conditions.

Controlled formation and size-selected deposition of indium nanoparticles from a microwave flow reactor on semiconductor surfaces

Indium nanoparticles were synthesized in a microwave flow reactor by thermal decomposition of trimethylindium. The particles were extracted from the gas phase by molecular beam sampling, deflected in an electric field, and deposited on a semiconductor surface. The size of the deposited particles was selected by adjusting the deflection voltage. The geometric standard deviation of the size-selected particles was found to be smaller than 10%. The deposition method is compatible with epitaxial growth methods and enhances their potentials with nanoparticle technology.

Schadstoffreduzierung eines Dieselmotors mit Direkteinspritzung durch Einsatz von Fettsäure-Methylester

Aus der heutigen Sicht sind Dieselmotoren mit Direkteinspritzung unentbehrliche Fahrzeugantriebe, die zu einer deutlichen Verminderung des Brennstoffverbrauchs und damit der CO2-Emissionen beitragen. Zur Einhaltung der kunftigen gesetzlichen Grenzwerte Euro 4 und Euro 5 sind aber weitere Entwicklungsschritte zur Reduktion von NOx und Partikeln unbedingt notwendig. Die vorliegende an der Universitat Duisburg-Essen entstandene Arbeit macht einen Losungsvorschlag zur Reduzierung der gas- und partikelformigen Emissionen durch den Einsatz von Fettsaure-Methylester. Wegen der besonderen Komplexitat des Dieselmotors war es erforderlich, eine Vielzahl von Betriebsparametern zu variieren, um die Grenzen der Beeinflussung von Schadstoffemissionen zu ermitteln.