Abstract

The previous survey of the French CaRPE project has shown a lack of information and showed the interest to assess the residual exposure to particles from plasma spray operation. This paper presents the results of various sampling operations and emission analyses of plasma spraying equipment from the workstation outside the thermal spray booth to the filtration system outlet. For this test campaign; the measurements were carried out on the one hand with continuous measuring devices (concentration in number; size distribution); and on the other hand with samplers ensuring sampling over a given period ("spot" measurement); at different points; i.e.; on the thermal plasma spraying process; at the level of the channelled discharge; upstream and downstream of the filtration system; on the operator; close to the access door to the booth; in the ambient air. The metallic micrometric powder was transformed into particles of much smaller size. The particle number concentration was particularly high in the booth with 600particle/cm3; for a size ranged from 0.5 to 20µm. For submicron particles; the concentration reached 107particle/cm3 but decreased significantly at the outlet of the filter system. The results show the existence of two families of particles; i.e.; the "nanometric background" and the micron-sized particles. The nanometric background corresponded to the presence of very small particles; which covered the surface of the sampling grids. Their density was considerably higher for the grids taken upstream of the dust collection system; i.e.; the entire grid was covered. These particles were in an oxidized state. It can be seen that this "nanometric background" was weakly or strongly aggregated in a "filamentary" form. These aggregates were made up of spherical nanometric particles of 5 to 10nm. The rare micron particles were weakly oxidized. Very great vigilance is therefore recommended in order to protect the operator; since we must remember that we are in the presence of a very high concentration of nanostructured metallic particles.

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