Morphology and chemical composition
Figure 7 shows TEM images of fine particles emitted during
welding, which were collected in copper grids. The same
particles were also subjected to chemical analysis by EDS,
and the obtained spectra are presented in Figure 8.
The obtained TEM images show mainly aggregates of very
fine particulates of spherical shape, characteristic of molten
metal emissions. These particles seem to be amorphous,
having individual sizes lower than 10 nm or not higher than
100 nm. The shape and morphology of ultrafine particles
emitted does not significantly vary with the gas mixture used.
Nevertheless, the aggregation type seems to be somewhat
different, as particles generated with the gas mixture Ar+ 8%
CO2 are, usually, more dispersed, as shown in Figure 7
(bottom, right).
Regarding the number of particles per cubic centimeter of
air, Lee et al. (2007) found numbers of particles per cubic
centimeter ranging from 1.69105 to 2.06106 in arc
welding performed in conventional booths with a background
concentration of 9.08103, Stephenson et al. (2003) measured
around 2105/cm3 during arc welding of carbon steel, and
Hovde & Rayner (2007) measured number of particles per
cubic centimeter ranging from 9800 using 16V and 82 800
using 24V, during arc welding of carbon steel; while Buonanno
et al. (2011) measured concentrations ranging from 2105 to
8105/cm3. Therefore, the number of particles measured in
this study is somewhat lower but still of the same magnitude
range of the numbers measured in the mentioned previous
studies. It is important to point out that these values are
essential to be able to characterize the exposure at specified
distances from sources that tend to be higher, on an order of
magnitude, when referring to worker exposure.