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ABSTRACT. Welding fume contains ele-ments that, in their pure forms, can be haz-ardous to worker health if inhaled or ingested. Therefore, the chemical compo-sition of welding fume must be examinedwhen considering fume toxicity. Variouschemical analysis techniques are pre-sented and their applicability to airborneparticles is described. Knowledge of parti-cle size is important because a given char-acterization technique only provides accu-rate data for a specific size range. For thepurpose of comparison and illustration,this paper uses several characterizationtechniques to analyze the chemistry ofmild steel welding fume. X-ray diffraction(XRD) shows that mild steel gas metal arcwelding (GMAW) fume is predominantlymagnetite while the mild steel shieldedmetal arc welding (SMAW) fume containsboth a mixed alkali fluoride phase and aFe-Mn oxide spinel phase. Energy disper-sive spectrometry (EDS) was found to bean effective technique for evaluating theelemental composition of welding fume,and the results of the elemental analysesof a few welding fumes are reported.

Introduction

Although it is almost impossible toconsume enough iron oxide to cause atoxic effect (Ref. 1), steels contain alloyingelements that, in their pure forms as foundin other industries, could be hazardous toworker health if inhaled or ingested. Allsteels contain manganese while stainlesssteels also contain chromium and nickel.Although essential for health in small

doses, pure manganese is a neurotoxinthat can cause manganese poisoning inlarge doses. Chromium and nickel can becarcinogenic. Welders are exposed tothese elements if they inhale weldingfume. Welding fume consists of metaloxide particles that form during welding.These particles are small enough to be-come and remain airborne and are easilyinhaled.

Chromium, nickel, and manganese arenot found as pure elements in weldingfume. They are present as impure com-pounds, which do not present the sametoxic risk as pure elements. The oxidationstate of chromium and manganese also af-fects their toxicity. Trivalent chromium isinert, whereas hexavalent chromium canbe carcinogenic. There is evidence that theoxidation state of welding fume man-ganese is less toxic than that used to setmanganese exposure limits (Ref. 2).Therefore both the elemental and chemi-cal composition of welding fume must beconsidered when assessing fume toxicity.

Information about the chemistry ofmild steel welding fume can be used tocompare the predicted toxicity of weldingfume to that of elements found in other in-dustries. It can also be used as an exampleof the methods used to study particlechemistry in general.

When analyzing airborne particles like

those in welding fume, the most importantfactor to consider is particle size. This isbecause a given characterization tech-nique only provides accurate data for aspecific size range. Many previous studiesof particle chemistry do not take this factinto account when reporting chemicalcomposition, and thus some of these stud-ies present misleading conclusions. Thishas been fairly common in welding fumeliterature, particularly with regard to stud-ies involving energy dispersive spec-troscopy with scanning electron micro-scopes (SEM-EDS). For example, it isinaccurate to report compositional gradi-ents measured with SEM-EDS acrossfume particles that are smaller than half amicrometer, because the SEM beam pen-etrates and samples the volume of suchsmall particles rather than just their sur-face. Welding fume particles range in sizefrom 0.005 to 20 µm, although less than10–30% (depending on the weldingprocess) of the fume mass is larger than 1µm (Ref. 3). Therefore, it is important tocarefully consider the techniques for ana-lyzing welding fume.

Methods

Chemical Analysis of Particles

Table 1 lists the various analysis tech-niques that can be used to characterizewelding fume (and other particulate mat-ter). The information provided and theparticle size ranges for which these tech-niques are applicable vary considerably.For further details, Refs. 2 and 4–6 containreviews of the various techniques used tochemically characterize particles.

In practice, there are two types of ele-mental characterization techniques: thosethat measure proportional to the atomicnumber and those that measure propor-tional to the atomic mass. The former pro-

SUPPLEMENT TO THE WELDING JOURNAL, JUNE 2005Sponsored by the American Welding Society and the Welding Research Council

Chemical Analysis of Welding Fume Particles

Airborne particle size is the most important factor in determining the accuracy of amethod for chemical analysis

BY N. T. JENKINS AND T. W. EAGAR

KEY WORDS

ChromiumFume AnalysisHealthManganeseNickelParticle SizeToxicologyWelding Fume

NEIL T. JENKINS, Ph.D., is with Martinos Center for Biomedical Imaging, MassachusettsGeneral Hospital, Charlestown, Mass.,rood@alum.mit.edu. THOMAS W. EAGAR, Sc.D., P. E., is with Department of Materials Science and Engineering, Massachusetts Instituteof Technology, Cambridge, Mass., tweagar@mit.edu.

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duce data easily transformed intomolar/atomic fractions, whereas the lattercreate data reported as weight percent-ages. If one has reliable values for each el-ement present in the specimen being ana-lyzed, then one can convert from atomicfraction to weight percent and back. How-ever, no analysis technique is able to mea-sure every element with the same accu-racy, so inconsistencies exist whencomparing the results of different tech-

niques. When this happens, conversionbetween weight and atomic percentages isonly approximate, because the entire massis not equally characterized. Therefore,the elemental data from multiple tech-

niques cannot be compared, except withinthe two major groupings presented herein.

The techniques that report mass in-

Fig. 1 — Welding fume collection chamber.

Fig. 2 — Transmission electron micrograph offume created from 2%O2-Ar-shielded gas metalarc welding with 0.045-in. mild steel ER70S-3 wireat 30 V and ~200 A. Fig. 3 — Transmission electron micrograph of

fume created from shielded metal arc welding with0.094-in. mild steel E7018-A electrode at 70 A.

Table 1 — Chemical Composition and Size Characterization Techniques for Particles

Characterization Method Size Range (mm) Detection Limit Notes(NA = not applicable)

Particle Size DistributionImpactors (various types) 0.1–20 NA Size distribution by mass chemically analyze size groupsElectric aerosol analyzer (EAA) and 0.01–1 NA Size distribution by number

differential mobility particle sizerAerodynamic particle sizer 0.1–25 NA Size distribution by numberScanning electron microscope (SEM); 0.5–50 NA Particle sizes can be measured from micrographs

high resolution (HRSEM) 0.002–1Electron probe microanalysis (EPMA) 0.5–50 NA Particle sizes can be measured from micrographsTransmission electron microscope (TEM) 0.001–1 NA Particle sizes can be measured from micrographsLight microscopy 1–400 NA

Elemental CompositionX-ray fluorescence spectrometry (XRF) bulk 100 ppm Atomic numbers >10 very fastNeutron activation analysis (NAA) bulk 0.01% Atomic numbers >10, requires nuclear reactorOptical emission spectrometry bulk 1–10 ppm Atomic numbers >10

and mass spectrometryAtomic absorption spectrometry (AAS) bulk 10 ppmEnergy-dispersive spectrometry with 1–50 0.1% Atomic numbers >10

SEM (SEM-EDS)Wavelength-dispersive spectrometry 1–50 0.1% Atomic numbers >4

with EPMA (EPMA-WDS)Energy-dispersive spectrometry with 0.01–0.5 0.1% Atomic numbers >5

TEM (TEM-EDS) scanning TEM can map element distribution at nm resolutionProton-induced X-ray emission >5 0.1% Atomic numbers >10

spectrometry (PIXE)Laser microprobe mass spectrometry >1 10 ppm All elements

(LAMMS)Secondary ion mass spectrometry (SIMS) >5 10 ppm Light element capableAuger electron spectrometry (AES) >0.1 0.1% Atomic numbers >3 lower sample must be conductiveX-ray-induced photo-electron spectrometry >5 0.1% Surface composition (3–5 nm deep)

(XPS or ESCA) contamination error common

Chemical SpeciationX-ray diffraction (XRD) bulk NA Only of crystalline material; particles must be >0.05 mm

or they will seem amorphousX-ray-induced photoelectron spectrometry bulk NA Need appropriate standards

(XPS or ESCA) Collect on noninteracting filterSelected area electron diffraction with TEM ~0.3 NA Only of crystalline material

(TEM-SAED)

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stead of molar quantity are also those withthe more frequent inaccuracies in report-ing data. For example, iron and aluminumcannot be determined with great accuracywith inductively coupled plasma massspectrometry (ICPMS) when in high con-centrations (greater than 5 wt-%). Thebags used to contain the sample duringneutron-activated analysis (NAA) oftencontain aluminum, which distorts theanalysis of that element. The acids used todissolve material for emission spectrome-try/spectroscopy often cannot dissolveeverything, so such analyses are often in-complete. The accuracy of X-ray fluores-cence spectrometry (XRF) and neutronactivation analysis (NAA) is dependent onthe standards used to calibrate the mea-surements. Therefore each of these meth-ods has limitations.

When energy-dispersive spectrometry(EDS) is used with transmission electronmicroscopy (TEM), the resolution of themicroanalysis should be considered. Be-cause of electron interactions with the ma-terial (i.e., beam broadening), the spatialresolution decreases with increasingatomic number. Thus, it may not be possi-ble to measure the change in compositionin a very small area. However, the thinnerthe sample analyzed, the less beam broad-ening will occur. For a review of the limi-tations involved in electron microscopy,see Ref. 7.

These weaknesses are in addition tothe inability of nearly all techniques to ac-curately analyze any elements lighter thansodium. Even when a method can analyzeelements as light as carbon, problems likewater condensation on the filament (as intransmission electron microscopy) or sur-face contamination with carbon dioxide

(as with X-ray-induced photoelectronspectrometry) can obscure the presence ofelements such as oxygen or fluorine. High-powered electron beams can also breakdown organic contaminants, causing a filmof carbon to deposit that obscures thesample. Because welding fume alwayscontains oxygen, lack of informationabout oxygen concentration makes it im-possible to determine the entiremolar/mass quantity of the fume.

Therefore the most convenient way toanalyze welding fume is by the molar frac-tion of the metal cations. Since energy dis-persive spectrometry (EDS) and X-ray-induced photoelectron spectrometry(XPS) report data in this form, these tech-niques are well suited for welding fumeanalysis, especially when one considersthe respective size limitations with respectto ultrafine particles.

Since welding fume can be collected asa powder, it is easily prepared as a bulkmaterial, e.g., for X-ray diffraction (XRD)analysis; it only becomes difficult to pre-pare if one wishes to analyze individualdiscrete particles, although for transmis-sion electron microscopy, the small sizesaid sample preparation enormously incomparison with samples that must bethinned by ion sputtering and similarprocesses.

Therefore, there are many studiesusing X-ray diffraction and electron mi-croscopy to analyze welding fume parti-cles (Refs. 8–17). There are also severalthat use surface characterization tech-niques, mostly XPS (Refs. 18–24). Thereare a few that use multiple techniques(Refs. 2, 25–30) for a complete weldingfume analysis.

For the purpose of comparison and il-

lustration, this paper uses several charac-terization techniques to analyze the chem-istry of mild steel welding fume. These in-clude inductively coupled massspectroscopy (ICPMS), X-ray fluores-cence spectrometry (XRF), neutron acti-vation analysis (NAA), X-ray-inducedphoto-electron spectrometry (XPS), X-ray diffraction (XRD), and energy disper-sive spectrometry with scanning and trans-mission electron microscopy (SEM-EDS,TEM-EDS).

Fume Collection

The fume for this study was collected ina chamber (Fig. 1) designed by Prof. GaelUlrich and coworkers at the University of

Fig. 4 — Transmission electron micrograph offume created from self-shielded flux cored arcwelding with 0.045-in. mild steel E71T-GS wire at30 V and ~170 A.

Fig. 5 — X-ray diffraction spectrum of fume created from 2%O2-Ar-shielded gas metal arc welding with 0.045-in. mild steel ER70S-3 wire at 30V and ~200 A.

Fig. 6 — X-ray diffraction spectrum of fume created from shielded metalarc welding with 0.094-in. mild steel E7018-A electrode at 70 A.

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New Hampshire. The design is publishedin a thesis and a paper (Refs. 31, 32) inwhich an excellent critique of fume collec-tion methods can also be found.

A weld was laid on a cylindrical pipeabout 25 cm (10 in.) in diameter and 30cm (12 in.) long. The pipe rotated insidea chamber that moved horizontallyaround the pipe. An arc welding gun wasinserted into the chamber through a holeso that a weld bead could be laid on thepipe forming a spiral as the pipe rotatedand as the chamber moved transversely.The power source was a primary invertermachine current-rated at 500 A/40 V at100% duty cycle.

Negative pressure was applied to thechamber so that fume could be collectedwhile the pipe was welded, and shortlythereafter. This pulled the fume out of thechamber at a rate of ~2 L/min (4 ft3/h)through filters (0.2 µm Corning [Nucleo-pore] PC filter, 37 mm diameter) sta-tioned approximately 30 cm (12 in.) abovethe arc. The fume was then removed fromthe filters for analysis. Table 2 lists thewelding parameters used.

Results and Discussion

Figures 2–4 show TEM images of weld-ing fume agglomerates. Tables 3–6 andFigs. 5 and 6 contain chemical data fromwelding fumes collected from mild steelelectrodes using shielded metal arc weld-ing (SMAW), gas metal arc welding(GMAW), and flux cored arc welding(FCAW).

The results from various chemicalcharacterization techniques can be com-pared. Despite the extremely differentresolution of the two types of electron mi-croscopy as shown in Table 4, and despitethe much larger sampling of particles inSEM-EDS, the compositions reported byTEM-EDS and SEM-EDS are very simi-lar for both GMAW and SMAW fumes.

X-ray-induced photoelectron spec-trometry (XPS) reports quite a differentcomposition. There are two possible rea-sons. XPS probes only the top fewnanometers of the surface of the analyzedmaterial. So, as previous research on weld-ing fume with XPS has reported, the sur-face of the individual fume particles may

be enriched in the more volatile elements,like manganese or the alkali metals, form-ing core-shell particle morphologies(Refs. 18–24). This would be supported bythe presence of multiple phases as re-ported by the XRD. However, although itis possible that the surface of weldingfume particles is enriched in certain ele-ments, it is doubtful that XPS can detectthis phenomenon in nanoparticles. Asnoted in Table 1, XPS is only effective an-alyzing the surfaces of individual particleslarger than 5 µm. When it is used to ana-lyze the bulk chemistry of particles thatcan be as small as 5 nm, it is not clear whatsurface XPS is analyzing, because the XPSbeam could be interacting with multipleparticles. Therefore XPS is not a reliableanalysis technique for the bulk or surfacechemistry of ultrafine particles. It does,however, provide data on chemical bondsthat can be used to determine the valencestates of the elements it detects.

Another possibility for the differencein composition is that XPS analysis maypreferentially report the composition oflarge particles, those near 5 µm in diame-ter. It is possible that liquid weld slagforms micrometer-sized spatter droplets,or “microspatter,” more readily than liq-uid metal does (Ref. 3). Slag microspattercontains more manganese and silicon thanmicrospatter formed from liquid metal.The larger particles in welding fumewould therefore have a composition morelike that reported by XPS than by EDS.This theory could be tested by separatingfume in size groups and analyzing sepa-rately with XPS or other analytical techniques.

Table 2 — Parameters for Welding Fume Generation

Welding Parameter Condition

Welding Travel Speed ~16 mm/s (14 in./min)Contact Tip to Work Distance ~19 mm (0.75 in.)Electrode Angle ~10 degree drag angleWire Diameter 0.094 in. (2.4 mm) (SMAW) or

0.045 in. (1.2 mm) (GMAW, FCAW)Shielding Gas Flow Rate unshielded (SMAW, FCAW) or

16.5 L/min (35 CFH) (GMAW)Shielding Gas Composition unshielded (SMAW, FCAW) or

Ar–2% O2 (GMAW)Work Piece Composition A500 carbon steelElectrode Designations E7018-A (SMAW)

ER70S-3 (GMAW)E71T-GS (FCAW)

Wire Feed Speed (wfs) notedVoltage positive electrode; magnitude notedCurrent steady; magnitude noted

Table 3 — Composition of GMAW and FCAWWire Used To Create Welding Fume

wt-% ER70S-3 E71T-GSGMAW FCAW

mild steel mild steel

Fe 98.04 91.69Cr 0.046 0.190Ni 0.038 0.028Cu 0.160 0.002Co 0.000 0.001Mn 1.162 0.731Si 0.551 0.270Al 0.000 3.143Ti 0.000 0.001Zr 0.000 0.000Mo 0.005 0.002K 0.000 0.025Na 0.000 0.007Ca 0.000 0.340Mg 0.000 0.941Ba 0.000 2.463O 0.000 0.160F 0.000 <0.001CL 0.000 0.001

Measured with emission spectrometry and inert gas fusion.

Table 4 — Composition of the Metal Cations in Bulk Welding Fume with Techniques Based onAtomic Numbers

Mole Fraction of Cations Only SEM-EDS TEM-EDS(a) XPS

2% O2 Ar-shielded GMAW with 0.045-in. mild steel ER70S-3 wire at 30 V, ~200 AFe 0.877 0.887 0.767Mn 0.098 0.104 0.233Si 0.025 0.008 <0.01SMAW with 0.094-in. mild steel E7018-A electrode at 70AFe 0.270 0.280 <0.01Mn 0.099 0.103 0.052Si 0.095 0.057 0.131K 0.276 0.295 0.575Ca 0.251 0.252 0.241Na 0.011 0.013 <0.01

(a) Compositional average of 3 fume agglomeratesAlthough not listed, oxygen is present in all fume, and fluorine is present in SMAW fume.

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Thus, of the three analysis techniquesreported in Table 4, it is probable thatSEM-EDS and TEM-EDS provide themost accurate measure of the mole frac-tion of the elements in the fume.

The atomic-mass-based analysis tech-niques listed in Table 5 yielded a fairlybroad set of data. It should again be em-phasized that these data cannot be com-pared with the previously discussed datafrom atomic-number-based analysis tech-niques. As noted, without data for each el-ement present in the fume (and, as noted,the data for oxygen and other anions areusually lacking) one cannot convert be-tween molar fraction and weight percent.Secondly, the weight percent reportedhere represents the total fume, not just themetal cations, as in Table 4. Also, thesemethods can be imprecise because of cal-ibration sensitivities. Nevertheless, thevalues for manganese from reports byother researchers (Refs. 33–35) vary be-tween 1 and 15 wt-% of the total weldingfume, hence, the data presented hereinare believed to be typical.

From the XRD spectra, it is clear thatthe GMAW fume is predominately mag-netite (an oxide spinel phase dominatedby iron, but which can contain manganeseimpurities), while the SMAW fume con-tains both a complex alkali-alkali earthfluoride phase and an oxide spinel phasecontaining a mixture of manganese andiron. This agrees with previous XRD stud-ies of welding fume (Refs. 8–17). Voitke-vich (Ref. 23) used X-ray photoelectronspectroscopy (XPS) and X-ray diffraction(XRD), while Minni et al. (Ref. 24) usedelectron spectroscopy to study weldingfume. They concluded that Mn2+, orMn3+, as opposed to Mn4+, are the mostprobable oxidation states of manganese in

welding fume. This also agrees with theXRD data presented herein. Manganesein welding fume is present as part of thespinel phase. Such phases contain metalions (e.g., predominately iron mixed withthe manganese) that are +2 or +3.

The amorphous fraction reported byX-ray diffraction may be generated bysmall nanoparticles in the welding fumebecause all the atoms in particles smallerthan 50 nm are essentially on the surface,and therefore cannot form standard crys-tal lattices. Such particles are essentiallyamorphous.

Previous X-ray diffraction studies havereported many phases in welding fumeand have suggested that each single fumeparticle contained three or more phases.This is obviously not the case for ultrafineparticles; a particle less than a micrometerin diameter cannot contain many phasesbecause its small volume will homogenizevery rapidly. In addition, because it is dif-ficult for XRD to detect crystals that aresmaller than 50 nm, a particle would haveto be at least half a micrometer to containmultiple detectable phases. Most weldingfume particles are smaller than that.Transmission electron microscopy showsthat fume can be heterogeneous withmany phases contained individually inseparate particles (Ref. 3). Therefore, ifXRD reports that there are five phases,this means that there are at least five dif-ferent types of particles, not that there isone particle that has each of the fivephases contained in an extremely smallvolume. It is possible that large particles(greater than 100 nm) that have coalescedor sintered from smaller particles maycontain multiple phases (Ref. 36). It is alsopossible that some large particles have acore-shell morphology with a metal oxidecore and a slag exterior; this may be thecase with the SMAW fume (Ref. 3). How-ever, it is doubtful there are particles withmore than two phases present.

The analyses presented herein did nottake different particle sizes into account;therefore, the results represent the bulkonly (with the exception of TEM-EDS,where the reported composition repre-

sents a very small sample of individualfume particles). There may be a change inchemistry with particle size that is not de-tected by an analysis that averages overmany particles simultaneously. This is im-portant for inhalation toxicology, becauseparticles of different sizes are inhaled dif-ferently (Ref. 37). If the chemistry varieswith particle size, the reported bulk chem-istry may not be an accurate average of allparticles, because some analytical tech-niques may sample data more stronglyfrom certain particle size groups than others.

Because of the size-related complica-tions of chemically analyzing weldingfume particles that range from a fewnanometers to a few micrometers (Ref.38), a better procedure would be to sepa-rate welding fume into size groups and toanalyze the size groups separately. Thiscan be done with a cascade impactor (Ref.39), with stages separating fume intogroups of particles. A suggested groupingwould separate particles smaller than 0.1µm from those 0.1 to 0.5 µm, those 0.5 to1 µm, and those larger than 1 µm.

There are five reasons for this sug-gested grouping. First, most impactorscannot distinguish between particlessmaller than 0.1 µm (Table 1). Second, theparticles that deposit in the alveolar pas-sages of the lung when inhaled are pre-dominantly smaller than 0.1 µm, while theinhaled particles that deposit in the noseand throat are generally larger than 1 mi-crometer (Ref. 40). Separating these sizegroups aids inhalation toxicology analysis.Third, analysis techniques tend to have anupper or lower boundary of 0.5 µm (Table1). Fourth, separating it into four groupsinstead of two helps prevent overloadingon the impactor stages. Fifth, airborneparticles smaller than 0.1 µm are formedthrough vapor condensation, while air-borne particles larger than 1 micrometerare created through liquid droplet ejec-tion. Particles from 0.5 to 1 µm are a mix-ture of the two types of particles (Ref. 3).These formation paths strongly influencethe particle chemistry, so it is important toseparate them and to analyze both types of

Table 5 — Composition by Weight of BulkWelding Fume with Techniques Based onAtomic Masses

wt-% ICPMS(a) XRF NAA

2% O2 Ar-shielded GMAW with 0.045-in.mild steel ER70S-3 wire at 30 V, ~200AFe 37.8 55.0 NAMn 8.8 12.8 NASi NA NA NACu 0.9 1.1 NASelf-shielded FCAW with 0.045-in. mild steelE71T-GS wire at 30 V, ~170AFe 18.1 23.7 32.4Mn 0.5 2.7 1.6Ba NA NA 9.8Mg NA NA 8.8Al 56.3 NA (b)

(a)% SMAW fume undissolved in acid: 25(b) aluminum present strongly but obscured by aluminum insample bag.NA = not analyzed because of experimental difficulties.Oxygen and fluorine were also not analyzed and are notlisted here because they are anions.

Table 6 — X-ray Diffraction of Mild Steel GMAW and SMAW Fume

Chemical Approximate ApproximatePhases Crystalline Amorphous

Detected Amount of Amount ofSample(%) Sample (%)

GMAW Fe3O4 (spinel) 64 36(ER70S-3, 30 V 300 in./min

SMAW (K, Na, Ca, Mn) F2 (fluoride) 71 29(E7018-A 3/32 in., 70A) MnFe2O4 (spinel)

See Figs. 5 and 6 for X-ray diffraction spectra

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particles with multiple techniques.The smallest two groups can be ana-

lyzed with transmission electron mi-croscopy, energy dispersive spectrometry,and electron diffraction. The largest twocan be analyzed with scanning electronmicroscopy, energy dispersive spectrome-try, and X-ray diffraction. Each size groupshould also be digested in acid and ana-lyzed with emission spectroscopy. Caremust be taken to dissolve all of the fumein the acid; otherwise, the results will notbe valid.

Conclusions

Various chemical analysis techniquesare presented in this paper and their ap-plicability to welding fume particles is dis-cussed. The range in their size complicatesthe analysis of airborne particles like thosein welding fume. Particle size is the great-est factor when determining the utility ofan analytical method. If this is not takeninto account, erroneous conclusions canbe easily made.

There are the two groups of elementalcharacterization techniques: those that re-port molar quantities and those that re-port atomic mass. The elemental datafrom various analytical techniques cannotbe easily compared, except within thesetwo groups. There seem to be fewer com-plications with the molar analytical tech-niques. Because of this and because oxy-gen analysis of small particles is difficult,the most convenient way to analyze the el-emental composition of welding fume(which is comprised of oxides and halides)is by the molar fraction of the metalcations. This is most easily done withSEM-EDS and TEM-EDS.

Other techniques used on weldingfume by previous researchers such as XPS,AES, XRF, and PIXE, yield data that areproblematic to analyze. However, XRD iswell suited for determining the phasecomposition of welding fume.

It was shown that mild steel GMAWfume is predominately magnetite in whichthe cations are approximately 10% Mn.Mild steel SMAW fume contains both acomplex alkali-alkali earth fluoride phaseand an oxide spinel phase. The metalcation fraction of that fume was approxi-mately 27% Fe, 10% Mn, 10% S, 28% K,25% Ca.

The analyses presented herein did nottake different particle sizes into account;therefore, these results represent the bulkonly. However, it has been shown thatfume can be heterogeneous with manyphases contained individually in separateparticles. It would prove useful to separatewelding fume into size groups and to ana-lyze the size groups separately. This can bedone with a cascade impactor, with stages

separating fume into groups of particles.The smallest groups can be analyzed withtransmission electron microscopy, energydispersive spectrometry, and electron dif-fraction. The largest groups can be ana-lyzed with scanning electron microscopy,energy dispersive spectrometry, and X-raydiffraction. All groups can be analyzed byspectrometry of acid-digested fume. Inthis way, welding fume chemistry wouldbest be characterized by size and by bulk(which would be a simple mass-weightedaverage of the chemistry of the sizegroups). This would aid in determining thetoxicity of welding fume inhalation andshed light into how welding fume forms.

Acknowledgments

The funding for this project was pro-vided by a grant from the U.S. Navy, Of-fice of Naval Research. Dr. NicholasLawryk of the National Institute of Occu-pational Health and Safety provided theXRF analysis of the welding fume, Dr. Krishna Murthy of the Harvard School ofPublic Health performed the ICPMS.Libby Shaw, Joseph Adario, MichaelAmes, Donald Galler, and Dr. AnthonyGarrett-Reed of Massachusetts Instituteof Technology assisted with XPS, XRD,NAA, SEM, and TEM, respectively.

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