Development of a thermal spray coating aerosol generator and inhalation exposure system

Thermal spray coating involves spraying a product that is melted by extremely high temperatures and then applied under pressure under pressure onto a surface. Large amounts of a complex metal aerosol (e.g., Fe, Cr, Ni, Zn) are formed during the process, presenting a potentially serious risk to the operator. Information about the health effects associated with exposure to these aerosols is lacking. Even less is known about the chemical and physical properties of these aerosols. The goal was to develop and test an automated thermal spray coating aerosol generator and inhalation exposure system that would simulate workplace exposures. An electric arc wire- thermal spray coating aerosol generator and exposure system was designed and separated into two areas: (A) an enclosed room where the spray coating occurs; (B) an exposure chamber with different measurement devices and controllers. The physicochemical properties of aerosols generated during electric arc wire- thermal spray coating using five different consumable wires were examined. The generated particles regardless of composition were poorly soluble, complex metal oxides and mostly arranged as chain-like agglomerates and similar in size distribution as determined by MOUDI and ELPI. To allow for continuous, sequential spray coating during a 4-hr exposure period, a motor rotated the metal pipe to be coated in a circular and up-and-down direction. In a pilot animal study, male Sprague-Dawley rats were exposed to aerosols (25 mg/m3 x 4 hr/d x 9 d) generated from electric arc wire- thermal spray coating using a stainless-steel PMET720 consumable wire. The targeted exposure chamber concentration was achieved and maintained during a 4-hr period. At 1 d after exposure, lung injury and inflammation were significantly elevated in the group exposed to the thermal spray coating aerosol compared to the air control group. A thermal spray coating inhalation system was designed and constructed that will generate continuous metal spray coating aerosols at a targeted concentration for extended periods of time without interruption for future animal exposure studies.