E.I. Kauppinen

Multiply twinned C60 and C70 nanoparticles

Abstract Nanoparticles of C 60 and C 70 prepared by aerosol flow reactor method show a well developed morphology when produced at sufficiently high temperatures. Hexagonal plate shaped, icosahedral and decagonal particles of C 60 and C 70 are formed. Morphology and internal structure are studied by scanning and transmission electron microscopy. The plate-like particles are lamellar–twinned and grow preferentially on the side-faces by nucleation of new molecular layers along re-entrant corners. The decagonal multiply twinned nanoparticles are strained and show a distinct deviation from cubic symmetry. Some of the C 70 particles exhibit a modulated structure to accommodate the internal stress; this is possible because of the ellipsoidal shape of the C 70 molecule.

Aerosol Synthesis of Fullerene Nanocrystals in Controlled Flow Reactor Conditions

Fullerene nanocrystals in the size range 30–300 nm were produced starting from atomized droplets of C60 in toluene. The experiments were carried out under well-controlled conditions in a laminar flow reactor at temperatures of 20–600°C. Particle transformation and crystallization mechanisms of polydisperse and monodisperse (size classified) fullerene aerosol particles were studied. The results show that fullerene particles are roughly spherical having pores and voids at temperatures of 300°C and below. Particles are already crystalline and likely fine-grained at 20°C and they are polycrystalline at temperatures up to 300°C. At 400°C monodisperse particles evaporate almost completely due to their low mass concentration. Polydisperse particles are crystalline, but sometimes heavily faulted. At 500°C most of the particles are clearly faceted. In certain conditions, almost all particles are hexagonal platelets having planar defects parallel to large (111) faces. We suggest that at 500°C fullerene particles are partially vaporized forming residuals with lamellar defects such as twins and stacking faults, which promote crystal growth during synthesis. Subsequently fullerene vapor is condensed on faces with defects and hexagonal particles are grown by a re-entrant corner growth mechanism. At 600°C particles are single crystals, but they have a less distinct shape due to higher vaporization of fullerene. The final size and shape of the particles are mainly determined at the reactor outlet in the short time when the aerosol cools.

AHMED experiments on hygroscopic and inert aerosol behaviour in LWR containment conditions: experimental results

Abstract Hygroscopic NaOH, CsI, CsOH and inert Ag aerosol behaviour at different temperatures and relative humidities (RH) has been studied in a well instrumented and controlled vessel of 1.81 m3 total free volume. Homogeneous thermal-hydraulic conditions for aerosol measurement in the vessel were achieved. The aerosol number and mass concentration were measured continuously during the experiments using a Condensation Nucleus Counter and a Tapered Element Oscillating Microbalance. The particle size distribution and chemical composition in the test conditions were measured by Berner low pressure impactors. In the case of NaOH the half life of the aerosol mass concentration was more than four times longer at low RH (22%) as compared to high RH (96%). The half lives of the CsOH and CsI aerosols were only twice as long at low RH as compared to high RH. Thus at high RH (96–97%) the half lives of CsOH and CsI were twice as long as the half life for the NaOH aerosol. The faster decay of the NaOH aerosol is due to the smaller density decrease of NaOH during water condensation. CsOH particles grew rapidly to their equilibrium size at all humidities. The measured equilibrium size for CsOH aerosol agree well with the calculated particle size at different RHs. Experimental results were also compared with calculations obtained by severe accident computer codes. These calculated results will be presented in a later paper.

Analysis of size-fractionated coal combustion aerosols by PIXE and other analytical techniques

Abstract Particle-induced X-ray emission (PIXE) analysis, instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectrometry (ICP-MS) were used to study the chemical composition of size-fractionated in-stack fly-ash particles emitted during coal combustion. The samples were collected before the electrostatic precipitator at a gas temperature of 120°C during the combustion of Venezuelan coal in a 81 MW capacity circulating fluidized bed boiler. The sampling device consisted of a Berner low pressure impactor, which was operated with a cyclone precutter. The Nuclepore polycarbonate foils, which were used as collection surfaces in the low pressure impactor, were analyzed by the three techniques and the results of common elements were critically compared. The PIXE results were systematically lower than the INAA data and the percentage difference appeared to be stage-dependent, but virtually independent upon the element. The discrepancies are most likely due to bounce-off effects, particle reentrainment and other sampling artifacts, which may make that a fraction of the aerosol particles is deposited on the impaction foils outside the section analyzed by PIXE. However, by resorting to a “mixed internal standard” approach, accurate PIXE data are obtained. Also in the comparison between the ICP-MS and the INAA data significant discrepancies were observed. These are most likely due to incomplete dissolution of the particulate material and in particular of the alumino-silicate fly-ash matrix, during the acid digestion sample preparation step for ICP-MS. It is suggested that a comparison between ICP-MS data of acid digested samples and INAA can advantageously be used to provide speciation information on the various elements. Selected examples of size distributions are presented and briefly discussed.

Study of size-fractionated coal-combustion aerosols using instrumental neutron activation analysis

The chemical composition of aerosols emitted during coal combustion was studied as a function of particle size down to 0.01 μm. The aerosol collections were carried out in a 81 MW capacity boiler that burned Venezuelan coal in a circulating fluidized bed combustion chamber. The samples were analyzed with upstream of the electrostatic precipitator using a Berner low-pressure impactor, which was quipped with a cyclone pre-cutter to avoid overloading of the first impaction stages. The samples were analyzed by INAA for up to about 40 elements. The elemental concentrations in the particulate matter for each impaction stage were plotted as a function of stage number (particle size). For the elements Na, Al, K, Ca, Sc, Ti, V, Ga, La and Sm, the concentration variation was limited to a factor of 2 to 4, and the concentrations of these elements were lower for the initial and final impactor stages than for the intermediate particle sizes. The variations were also limited to a factor of 2–4 for Mn, Fe, As, Sb and Th, butall these elements showed increasing concentrations with decreasing particle size. Still other elements, such as Ni, Cr, Co, Za, W, Mo and the halogens, were highly enriched (up to 20–100 fold) in the fine particles when compared with the coarse particles.

In-stack particle size and composition transformations during circulating fluidized bed combustion of willow and forest residue

Abstract The in-stack transformations of the particle size and composition of the fly ash were studied experimentally during combustion of forest residue and willow in a 35 MW circulating fluidized bed co-generation plant. Samples of the in-stack fly ash were taken with 11-stage Berner low pressure impactors (BLPIs) at two locations in the flue gas stream, i.e., downstream of the circulating cyclone at a temperature of 810–850°C and downstream of the convective back pass at a temperature of 150–160°C. The mass size distribution of the fly ash was derived from weighing the BLPI substrate films. For obtaining the multielemental composition of the fly ash as a function of particle size, the BLPI films were analyzed by both particle-induced X-ray emission (PIXE) and instrumental neutron activation analysis (INAA).

Continuous method for pulverized coal combustion emission mass monitoring

Abstract A method for pulverized coal combustion aerosol mass concentration measurements with a dilution system and tapered element oscillating microbalance (TEOM) is introduced. The TEOM microbalance method gives continuous information about mass concentration variations in a minute scale time resolution. Particle upper size limit is chosen with a cyclone.

37 P 04 Aerosol assisted large area photoresist development method

Abstract A new method, aerosol assisted development (AAD), to utilize aerosol technology in optical lithography process, is presented. Aerosol droplets of selected liquid, formed in ultrasonic nebulizer, are deposited on a moving surface with a slit impactor. The constructed thin layer can be kept homogeneous even on large substrates. Development and also etching results of large area optical lithography may be improved by the method.