7 Construction and Characterization of a Thermal Spray Coating Aerosol Generator

Thermal spray coating (TSC) is a surface treatment process whereby feedstock material is sprayed onto surfaces under pressure where it solidifies and forms a solid coating. In metal TSC processes, large quantities of aerosols, including fine and ultrafine metal particles are generated. However, exposure assessment for TSC is lacking. The goal of this study was to construct a TSC aerosol generation system and to characterize the physicochemical properties of aerosols generated during coating processes. A computer-controlled, automated electric arc wire-TSC aerosol generator system was built in an enclosed room, where a rotary motor rotates a metal feedstock pipe in circular and up-and-down directions to allow even deposition of coating material on the pipe surface. The characteristics of aerosolized particles during spray coating using a stainless-steel wire (PMET 720) showed that: 1) respirable mass concentrations ranged from 142–218 mg/m3 (3 spray shots with each shot of 1-sec during 20-min sampling), 2) diameter of peak particle number concentrations was between 360 nm and 400 nm, 3) mass median aerodynamic diameter determined by an impactor ranged from 290–370 nm, 4) particle morphology was observed to be diverse including chain-like agglomerates and spherical and cylinder-like shapes, and 5) metal composition was 80% iron, 17% chromium, and 3% manganese with trace amounts of nickel and copper. These findings are limited to one wire type and suggests the need for further investigations evaluating various parameters (e.g., wire/powder types, high/low energy, ventilation on/off) to obtain emission rates and recommend control measures.