Metal Aerosols Research Articles

Measuring air borne nanoparticles for characterizing hyphenated RDD-SMPS-ICPMS instrumentation

Scanning Mobility Particle Sizer (SMPS) and Inductively Coupled Plasma Mass Spectrometry (ICPMS), complemented by a Rotating Disk Diluter (RDD) to a hyphenated RDD-SMPS-ICPMS measuring setup, allow online and simultaneous determination of size distribution and elemental composition of gas borne nanoparticles. This coupling strategy offers high flexibility in terms of dealing with different aerosols, loaded with metallic nanoparticles. The capabilities of such an instrument are demonstrated on uniformly composited metal aerosols, as well as an aerosol mixture containing smaller gold and larger silver nanoparticles. The size resolved ICPMS intensity curves correlate very well to the size distributions, determined by the coupled SMPS, and also to those from a non-modified reference SMPS instrument. Particulate iron, gold, and silver are detected with SMPS scan durations of a few minutes, and nanoparticles of different sizes and compositions are successfully distinguished. Sensitivity and limit of detection, related to particle number and mass concentration, are determined for several elements and particle diameters.

Occupational Risk And Health Status Of Workers In The Production Of Heat

Summary The health status of 1515 workers employed in heat production was investigated. The subjects studied were divided in four groups according to occupation and occupational risk factors: vibration, noise, dust, metal aerosols, overloading of the musculoskeletal and peripheral nervous system, and organic solvents. The control group included 152 administrative staff members. High prevalence of socially significant diseases – cardiovascular, endocrine and metabolic was detected in all the groups surveyed. The frequency of diseases of the cardiovascular system and the respiratory system was 2.7 times higher than that in the control group. Statistically reliable higher prevalence of lung diseases in the studied risk groups was found, especially in the group of welders and chemists: 45.3% и 17.4% respectively, as compared to 4.3% in the controls. These finding corresponded to the occupational risk. The following occupation diseases were diagnosed: pneumoconiosis in 26.6% and toxic pneumofibrosis in 5.1% of electric welders. As regards the group of chemists, toxic pneumofibrosis was found in 6.5%. toxic effects of irritants - in 6.5 %, and chronic intoxication with organic radicals - in 0.7 % of them. Occupational auditory neuritis was diagnosed in 1% of the turbine operators and crane operators. The relative share of workers with peripheral nervous system pathology (radiculopathies, polyneuropathies, distal sympathetic neuropathy, mononeuropathy) was reliably higher than that in the control group, and the frequency increased among the workers with more than ten years of service and older than 40.

Neurotoxicity following acute inhalation of aerosols generated during resistance spot weld-bonding of carbon steel

Welding generates complex metal aerosols, inhalation of which is linked to adverse health effects among welders. An important health concern of welding fume (WF) exposure is neurological dysfunction akin to Parkinson's disease (PD). Some applications in manufacturing industry employ a variant welding technology known as “weld-bonding” that utilizes resistance spot welding, in combination with adhesives, for metal-to-metal welding. The presence of adhesives raises additional concerns about worker exposure to potentially toxic components like Methyl Methacrylate, Bisphenol A and volatile organic compounds (VOCs). Here, we investigated the potential neurotoxicological effects of exposure to welding aerosols generated during weld-bonding. Male Sprague–Dawley rats were exposed (25 mg/m3 targeted concentration; 4 h/day × 13 days) by whole-body inhalation to filtered air or aerosols generated by either weld-bonding with sparking (high metal, low VOCs; HM) or without sparking (low metal; high VOCs; LM). Fumes generated under these conditions exhibited complex aerosols that contained both metal oxide particulates and VOCs. LM aerosols contained a greater fraction of VOCs than HM, which comprised largely metal particulates of ultrafine morphology. Short-term exposure to LM aerosols caused distinct changes in the levels of the neurotransmitters, dopamine (DA) and serotonin (5-HT), in various brain areas examined. LM aerosols also specifically decreased the mRNA expression of the olfactory marker protein (Omp) and tyrosine hydroxylase (Th) in the olfactory bulb. Consistent with the decrease in Th, LM also reduced the expression of dopamine transporter (Slc6a3; Dat), as well as, dopamine D2 receptor (Drd2) in the olfactory bulb. In contrast, HM aerosols induced the expression of Th and dopamine D5 receptor (Drd5) mRNAs, elicited neuroinflammation and blood–brain barrier-related changes in the olfactory bulb, but did not alter the expression of Omp. Our findings divulge the differential effects of LM and HM aerosols in the brain and suggest that exposure to weld-bonding aerosols can potentially elicit neurotoxicity following a short-term exposure. However, further investigations are warranted to determine if the aerosols generated by weld-bonding can contribute to persistent long-term neurological deficits and/or neurodegeneration.

Experimental study on the coexistent dual slagging in biomass-fired furnaces: Alkali- and silicate melt-induced slagging

The effects of silicon, aluminum, and potassium on alkali- and silicate melt-induced slagging are studied through the addition of aluminosilicate compounds and 30 biomasses to address the coexistent dual slagging during biomass combustion. For alkali-induced slagging mainly caused by alkali metal aerosols, the addition of aluminosilicate compounds, such as kaolin and SiO2, can remove approximately 80%, 40% to 60% of gaseous-K at 1273 and 1088K, respectively. Although SiO2 is more effective in removing gaseous-K, especially at 1088K (62.5%), it also exacerbates silicate melt-induced slagging because of its reaction with KCl and the formation of low-melting silicates. Hence, the use of SiO2 should be reconsidered. Initial deformation temperature (IDT) is used as the evaluation index for silicate melt-induced slagging. High IDT reduces the potential for silicate melt-induced slagging occurrence. IDT rises as Al2O3 and SiO2/K2O increase, but decreases as K2O, SiO2, SiO2/Al2O3, and (SiO2+K2O)/Al2O3 increase. The significant effects of the compounds on IDT follow this sequence: Al2O3>K2O>SiO2>SiO2/K2O>SiO2/Al2O3>(SiO2+K2O)/Al2O3. A set of criteria to evaluate the potential of silicate melt-induced slagging is proposed. The K2O–SiO2–Al2O3 ternary phase diagram is also constructed based on the ash properties of the 30 biomasses to reflect the true potential of silicate melt-induced slagging. It indicates that the K2O–SiO2–Al2O3 ternary diagram constructed based on pure K2O, SiO2, and Al2O3 underestimates the IDT of pure biomass. Results provide useful guidelines for biomass selection and slagging reduction.

Anti-agglomeration of spark discharge-generated aerosols via unipolar air ions

This paper reports the effect of air ions on the reduction of the agglomeration of metal aerosol particles generated from a homogeneous spark discharge. A carbon fiber ionizer was used to generate air ions near the spark channel formed between two metal electrodes. Once the air ions were generated, particles mixed with ions from the ionizer became charged by random collisions resulting from Brownian motion of the ions. Under the experimental conditions, the particle size right after the spark generation was about 4nm. Then, the size increased to 50nm, 1m downstream (residence time of 1.76s) of the spark channel due to Brownian agglomeration when there were no air ions injected. However, with the injection of air ions (ion concentration: particle concentration=10:1), the size of the particles was reduced to be around 10nm due to the repulsive force between unipolar charged particles with an average charge number of 0.39. In this study, the classical Brownian agglomeration theory for unipolar charged particles was combined with the moment method to predict the particle size distribution as a function of time. The theoretically determined particle size distribution was in good agreement with the size distribution measured using a scanning mobility particle sizer (SMPS) system.

Amorphous carbon encapsulation of metal aerosol nanoparticles for improved collection and prevention of oxidation

A technique to encapsulate silver nanoparticles in an amorphous carbon matrix to facilitate nanoparticle collection and limit nanoparticle oxidation is presented. A carbon source added to the metal salt precursor solution decomposes to generate amorphous carbon, which forms large aggregates that are efficiently collected by filtration. The carbon matrix can be removed by oxidation with hydrogen peroxide without damaging the silver nanoparticles within it. X‐ray diffraction showed no evidence of oxidation of encapsulated particles over a two‐week period, whereas bare particles showed oxidation after 1 day. Slight oxidation was observed following carbon removal, but no further oxidation was detected over a subsequent two‐week period. Carbon encapsulation improves nanoparticle collection efficiency, relative to direct collection of unagglomerated silver nanoparticles with membrane filters. The yield of metal nanoparticles is increased by a factor 1.5 to 3 using this approach. The encapsulating carbon itself forms dendritic nanostructures that may also be of interest. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4116–4123, 2013

Comparison of the DiSCmini Aerosol Monitor to a Handheld Condensation Particle Counter and a Scanning Mobility Particle Sizer for Submicrometer Sodium Chloride and Metal Aerosols

We evaluated the robust, lightweight DiSCmini (DM) aerosol monitor for its ability to measure the concentration and mean diameter of submicrometer aerosols. Tests were conducted with monodispersed and polydispersed aerosols composed of two particle types (sodium chloride [NaCl] and spark-generated metal particles, which simulate particles found in welding fume) at three different steady-state concentration ranges (Low, <103; Medium, 103–104; and High, >104 particles/cm3). Particle number concentration, lung deposited surface area (LDSA) concentration, and mean size measured with the DM were compared with those measured with reference instruments, a scanning mobility particle sizer (SMPS), and a handheld condensation particle counter (CPC). Particle number concentrations measured with the DM were within 16% of those measured by the CPC for polydispersed aerosols. Poorer agreement was observed for monodispersed aerosols (±35% for most tests and +101% for 300-nm NaCl). LDSA concentrations measured by the DM were 96% to 155% of those estimated with the SMPS. The geometric mean diameters measured with the DM were within 30% of those measured with the SMPS for monodispersed aerosols and within 25% for polydispersed aerosols (except for the case when the aerosol contained a substantial number of particles larger than 300 nm). The accuracy of the DM is reasonable for particles smaller than 300 nm, but caution should be exercised when particles larger than 300 nm are present. [Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resources: manufacturer-reported capabilities of instruments used, and information from the SMPS measurements for polydispersed test particles.]

Human Exposure to Particulate Matter and Their Risk Assessment over Delhi, India

Human exposure to particulate matter was determined in the urban environment of Delhi. Monitoring was done on an 8 h exposure basis. Samples were collected using an eight stages impactor (Marple Cascade Impactor) at five sites during December 2010 to March 2011. Fifteen samples were collected and each stage samples were analyzed gravimetrically and chemically (for metals). The maximum (2,118.45 μg/m3) exposure due to particulate matter (PM) was at Okhala, an industrial site and the minimum (490.17 μg/m3) in Jawaharlal Nehru University an educational Institute. Exposure due to metals (viz. Cu, Cd, Mn, Pb, Ni, Co) at the five locations was mostly dominated by Pb, Mn, Ni and least dominated by Cd,Cu and Co. Okhala was most polluted area and Jawaharlal Nehru University (forest area, out of industrial and commercial hub) the least. Pb, Ni, Co were dominant metal aerosols of Okhala, while Kaushambi, being fully residential area but located near waste site and national highway, was rich in Pb, Mn and Ni. Pb concentration exceeded government guideline.

Prevention of PCDD/Fs emission from a municipal wastewater sludge incinerator through enhanced control of copper aerosol

Municipal wastewater sludge incineration (MWSI) leads to products of incomplete combustion, including chlorinated species such as dioxins and furans (PCDD/Fs). Other pollutants, such as heavy metals (HM), are released too as a consequence of feed traces, which depend on the specific activities of each area. The main aim of this work is to determine whether the early separation of the potential catalysts on the PCDD/Fs formation –HM as copper or zinc– offers a promising way to prevent the emission of these trace pollutants, considering that the current end-of-pipe measures don’t ensure their stable emission. Experimental results cover the size distributed target metal contents along the incineration line. These results show a high concentration of copper in the most penetrating aerosol size range of the electrostatic precipitator (0.6 μm - 1.0 μm), and how low emission values of both, total and metallic aerosol (mass basis), are compatible with irregular and unexplained outliers of PCDD/Fs emission.

Experimental and theoretical investigations about the vaporization of laser-produced aerosols and individual particles inside inductively-coupled plasmas — Implications for the extraction efficiency of ions prior to mass spectrometry

Current quantification capabilities of laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) are known to be restricted by elemental fractionation as a result of LA-, transport-, and ICP-induced effects which, particularly, may provoke inaccuracies whenever calibration strategies on the basis of non-matrix matched standard materials are applied. The present study is dealing with the role of ICP in this complex scenario. Therefore, the vaporization process of laser-produced aerosols and subsequent diffusion losses occurring inside ICP sources were investigated using 2-D optical emission spectrometry (OES) and ICP-quadrupole (Q)MS of individual particles. For instance, Na- and Ca-specific OES of aerosols produced by LA of silicate glasses or metals revealed axial shifts in the onset and maximum position of atomic emission which were in the range of a few millimeters. The occurrence of these shifts was found to arise from composition-dependent particle/aerosol penetration depths, i.e. the displacement of axial vaporization starting points controlling the ion extraction efficiency through the ICP-MS vacuum interface due to a delayed, diffusion-driven expansion of oxidic vs. metallic aerosols. Furthermore, ICP-QMS of individual particles resulted in 1/e half-value signal durations of approximately 100μs, which complies with modeled values if OES maxima are assumed to coincide with positions of instantaneous vaporization and starting points for atomic diffusion. To prove phenomena observed for their consistency, in addition, “ab initio” as well as semi-empirical simulations of particle/aerosol penetration depths followed by diffusion-driven expansion was accomplished indicating differences of up to 15% in the relative ion extraction efficiency depending on whether analytes are supplied as metals or oxides. Implications of these findings on the accuracy achievable by state-of-the-art LA-ICP-MS systems are outlined.

Ultrasonic nebulization-sample introduction system for quantitative analysis of liquid samples by laser-induced breakdown spectroscopy

In this study, design and optimization studies of a sample introduction system based on ultrasonic nebulization of metal salts in aqueous environment for laser-induced breakdown spectroscopic detection were presented. The system consisted of an ultrasonic nebulizer connected to a tandem heater–condenser–membrane dryer unit that produces sub-micron size aerosols. Results indicate improvements in detection limits for some elements with the use of membrane dryer. Optimization studies were performed by systematical investigation of LIBS emission signal with respect to laser energy, carrier gas flow rate and detector timing parameters. Under optimized conditions, calibration graphs for Na, K, Mg, Ca, Cu, Al, Cr, Cd, Pb and Zn were constructed and detection limits were calculated. The applicability of the ultrasonic nebulization-LIBS system was tested on real water samples. This system establishes LIBS as an effective analytical tool for both qualitative and quantitative determination of metal aerosols in aqueous environments. This technique is sufficiently rapid to provide real-time monitoring of toxic metals.

Brief Analysis of the Simulative Plutonium Aerosol Source-Term in the Circumstance of High Explosive Detonation

The plutonium material in weapons grade nuclear device would be aerosolized and dispersed into the atmosphere if the device was involved in a high explosive detonation. It is significant to investigate the environmental and public hazard caused by the possible dispersion of plutonium. The original work is to determine the source terms of plutonium aerosol in certain nuclear accident scenario. In such scenario the inhalation of plutonium aerosols is the main human hazard source. Only the plutonium aerosols with aerodynamic diameter less than 10 μm are respirable and may ultimately lead to fatal human death. The field detonation test with plutonium by U.S. government is reviewed and the results indicate that for expected high explosive detonation scenario the plutonium source terms are 100 % aerosolization and 20 % respirable fraction. In order to find the aerosolized similarity of plutonium and several conventional metals, two detonation experiments in which the stannum foil and the vanadium powder are used as the replacement of plutonium respectively have been conducted by our group. After the detonation the metal aerosols are collected and analyzed. It has been found that the metallic powder is much easier to be aerosolized than the foil while the integrated aerosol source terms (respirable mass fractions) of stannum and vanadium are quite different with plutonium. Unlike the integrated aerosol data, the differential source terms (cumulative mass fractions via particle size) of the simulative samples are partially similar with plutonium.

Variations in time and space of trace metal aerosol concentrations in urban areas and their surroundings

Abstract. Using an unprecedentedly large geochemical database, we compare temporal and spatial variations in inhalable trace metal background concentrations in a major city (Barcelona, Spain) and at a nearby mountainous site (Montseny) affected by the urban plume. Both sites are contaminated by technogenic metals, with V, Pb, Cu, Zn, Mn, Sn, Bi, Sb and Cd all showing upper continental crust (UCC) normalised values &gt;1 in broadly increasing order. The highest metal concentrations usually occur during winter at Barcelona and summer in Montseny. This seasonal difference was especially marked at the remote mountain site in several elements such as Ti and Rare Earth Elements, which recorded campaign maxima, exceeding PM10 concentrations seen in Barcelona. The most common metals were Zn, Ti, Cu, Mn, Pb and V. Both V and Ni show highest concentrations in summer, and preferentially fractionate into the finest PM sizes (PM1/PM10 &gt; 0.5) especially in Barcelona, this being attributed to regionally dispersed contamination from fuel oil combustion point sources. Within the city, hourly metal concentrations are controlled either by traffic (rush hour double peak for Cu, Sb, Sn, Ba) or industrial plumes (morning peak of Ni, Mn, Cr generated outside the city overnight), whereas at Montseny metal concentrations rise during the morning to a single, prolonged afternoon peak as contaminated air transported by the sea breeze moves into the mountains. Our exceptional database, which includes hourly measurements of chemical concentrations, demonstrates in more detail than previous studies the spatial and temporal variability of urban pollution by trace metals in a given city. Technogenic metalliferous aerosols are commonly fine in size and therefore potentially bioavailable, emphasising the case for basing urban background PM characterisation not only on physical parameters such as mass but also on sample chemistry and with special emphasis on trace metal content.

Comparative microstructures and cytotoxicity assays for ballistic aerosols composed of micrometals and nanometals: respiratory health implications

Aerosol particulates collected on filters from ballistic penetration and erosion events for W–Ni–Co and W–Ni–Fe kinetic energy rod projectiles penetrating steel target plates were observed to be highly cytotoxic to human epithelial A549 lung cells in culture after 48 hours of exposure. The aerosol consisted of micron-sized Fe particulates and nanoparticulate aggregates consisting of W, Ni or W, Co, and some Fe, characterized by scanning electron microscopy and transmission electron microscopy, and using energy-dispersive (X-ray) spectrometry for elemental analysis and mapping. Cytotoxic assays of manufactured micron-sized and nanosized metal particulates of W, Ni, Fe, and Co demonstrated that, consistent with many studies in the literature, only the nanoparticulate elements demonstrated measurable cytotoxicity. These results suggest the potential for very severe, short-term, human toxicity, in particular to the respiratory system on inhaling ballistic aerosols.

Aerosol formation of Sea-Urchin-like nanostructures of carbon nanotubes on bimetallic nanocomposite particles

With the advantage of continuous production of pure carbon nanotubes (CNTs), a new simple aerosol process for the formation of CNTs was developed. A combination of conventional spray pyrolysis and thermal chemical vapor deposition enabled the formation unusual sea-urchin-like carbon nanostructures composed of multi-walled CNTs and metal composite nanoparticles. The CNTs formed were relatively untangled and uniform with a diameter of less than ~10 nm. The key to the formation of CNTs in this way was to create a substrate particle containing both a catalytic and non-catalytic component, which prevented coking. The density of the CNTs grown on the spherical metal nanoparticles could be controlled by perturbing the density of the metal catalysts (Fe) in the host non-catalytic metal particle matrix (Al). Mobility size measurement was identified as a useful technique to real-time characterization of either the catalytic formation of thin carbon layer or CNTs on the surface of the metal aerosol. These materials have shown unique properties in enhancing the thermal conductivity of fluids. Other potential advantages are that the as-produced material can be manipulated easily without the concern of high mobility of conventional nanowires, and then subsequently released at the desired time in an unagglomerated state.

Mitochondrial dysfunction and loss of Parkinson's disease-linked proteins contribute to neurotoxicity of manganese-containing welding fumes

Welding generates complex metal aerosols, inhalation of which is linked to adverse health effects among welders. An important health concern of welding fume (WF) exposure is neurological dysfunction akin to Parkinson's disease (PD), thought to be mediated by manganese (Mn) in the fumes. Also, there is a proposition that welding might accelerate the onset of PD. Our recent findings link the presence of Mn in the WF with dopaminergic neurotoxicity seen in rats exposed to manual metal arc-hard surfacing (MMA-HS) or gas metal arc-mild steel (GMA-MS) fumes. To elucidate the molecular mechanisms further, we investigated the association of PD-linked (Park) genes and mitochondrial function in causing dopaminergic abnormality. Repeated instillations of the two fumes at doses that mimic ∼1 to 5 yr of worker exposure resulted in selective brain accumulation of Mn. This accumulation caused impairment of mitochondrial function and loss of tyrosine hydroxylase (TH) protein, indicative of dopaminergic injury. A fascinating finding was the altered expression of Parkin (Park2), Uchl1 (Park5), and Dj1 (Park7) proteins in dopaminergic brain areas. A similar regimen of manganese chloride (MnCl(2)) also caused extensive loss of striatal TH, mitochondrial electron transport components, and Park proteins. As mutations in PARK genes have been linked to early-onset PD in humans, and because welding is implicated as a risk factor for parkinsonism, PARK genes might play a critical role in WF-mediated dopaminergic dysfunction. Whether these molecular alterations culminate in neurobehavioral and neuropathological deficits reminiscent of PD remains to be ascertained.

Effect of fireworks events on urban background trace metal aerosol concentrations: Is the cocktail worth the show?

We report on the effect of a major firework event on urban background atmospheric PM 2.5 chemistry, using 24-h data collected over 8 weeks at two sites in Girona, Spain. The firework pollution episode ( Sant Joan fiesta on 23rd June 2008) measured in city centre parkland increased local background PM 2.5 concentrations as follows: Sr (x86), K (x26), Ba (x11), Co (x9), Pb (x7), Cu (x5), Zn (x4), Bi (x4), Mg (x4), Rb (x4), Sb (x3), P (x3), Ga (x2), Mn (x2), As (x2), Ti (x2) and SO 4 2− (x2). Marked increases in these elements were also measured outside the park as the pollution cloud drifted over the city centre, and levels of some metals remained elevated above background for days after the event as a reservoir of metalliferous dust persisted within the urban area. Transient high-PM pollution episodes are a proven health hazard, made worse in the case of firework combustion because many of the elements released are both toxic and finely respirable, and because displays commonly take place in an already polluted urban atmosphere.

Physicochemical variations in atmospheric aerosols recorded at sea onboard the Atlantic–Mediterranean 2008 Scholar Ship cruise (Part II): Natural versus anthropogenic influences revealed by PM 10 trace element geochemistry

The geochemistry of PM 10 filter samples collected at sea during the Scholar Ship Atlantic–Mediterranean 2008 research cruise reveals a constantly changing compositional mix of pollutants into the marine atmosphere. Source apportionment modelling using Positive Matrix Factorization identifies North African desert dust, sea spray, secondary inorganic aerosols, metalliferous carbon, and V–Ni-bearing combustion particles as the main PM 10 factors/sources. The least contaminated samples show an upper continental crust composition (UCC)-normalised geochemistry influenced by seawater chemistry, with marked depletions in Rb, Th and the lighter lanthanoid elements, whereas the arrival of desert dust intrusions imposes a more upper crustal signature enriched in “geological” elements such as Si, Al, Ti, Rb, Li and Sc. Superimposed on these natural background aerosol loadings are anthropogenic metal aerosols (e.g. Cu, Zn, Pb, V, and Mn) which allow identification of pollution sources such as fossil fuel combustion, biomass burning, metalliferous industries, and urban–industrial ports. A particularly sensitive tracer is La/Ce, which rises in response to contamination from coastal FCC oil refineries. The Scholar Ship database allows us to recognise seaborne pollution sourced from NW Africa, the Cape Verde and Canary islands, and European cities and industrial complexes, plumes which in extreme cases can produce a downwind deterioration in marine air quality comparable to that seen in many cities, and can persist hundreds of kilometres from land.

Reducing Cr 6+ emissions from gas tungsten arc welding using a silica precursor

Hexavalent chromium (Cr 6+) emission from stainless steel welding operations poses a serious threat to worker safety and ambient air quality. In this study, tetraethyloxysilane (TEOS) was used as a silica precursor additive to welding shield gas during gas tungsten arc welding (GTAW) operations to determine the feasibility of using these chemicals for Cr 6+ exposure reduction. Fume aerosol samples were analyzed for Cr 6+ concentration using ion chromatography (IC) and for total Cr by inductively coupled plasma with atomic emission spectroscopy (ICP-AES). At high temperature, silica precursors are pyrolyzed to form amorphous silica (SiO 2) which can condense on the existing metal aerosols. The inert silica layer surrounding the aerosols can prevent further chromium oxidation by insulating chromium aerosols. Experimental results showed approximately 45% Cr 6+ reductions when 3.0% TEOS was added to the shield gas. Nitrate concentration also decreased by 53%, indicating that reactive oxygen species were also reduced. Transmission electron microscopy (TEM) images of collected fume aerosols showed SiO 2 coating on metal particles, verifying the proposed mechanism.

Microgravity compatible equipment for inert gas condensation of metals during parabolic flights

Agglomerates of nanosized metal particles can be deposited onto a variety of substrates using a custom-built, microgravity-compatible evaporation/condensation device. A metal aerosol with high solid loading is produced by rf-induction coil heating of a metal melt in a laminar inert gas flow. Valves and flow controllers operating in hypergravity and microgravity conditions allow powder samples to be prepared from such aerosols suppressing buoyancy and sedimentation effects. We present here the technical details for such a parabolic flight compatible metal aerosol source together with some initial results of nanoscale Ni agglomerates synthesized and deposited under microgravity conditions.