Generation of nanoparticles from friction between railway brake disks and pads
- Generation of nanoparticles from friction between railway brake disks and pads
- 남궁형규; 김종범; 우상희; 박세찬; 김민혜; 김민수; 배귀남; 박덕신; 권순박
- friction; railway brake disk; nanoparticle; wear particle
- Issue Date
- Environmental science & technology
- VOL 50, NO 7, 3453-3461
- In this study, we measured the size distribution of particles ranging in size from 5.6 to 560 nm that were emitted between brake disks and pads under various braking conditions to observe and analyze changes to the resulting particle size distribution over braking time. A peak of 178–275 nm (200 nm peak) was observed in all braking conditions. However, the generation of spherical particles of a 10 nm range was observed only when the disk speed and brake force were above certain levels and intensified only when speed and brake force further increased. The total number concentration of ultrafine particles (no larger than 0.1 μm; PM0.1) generated was found to correlate with disk speed and brake force. Thus, the generation of nanoparticles resulting from disk speed and brake force was attributable primarily to increases in the contact surface temperature. The critical temperature for the generation of nanoparticles of a 10 nm range was found to be about 70 °C, which is the average temperature between the surface and the inside of the disk. If the speed or brake force was higher, that is, the temperature of the contact surface reached a certain level, evaporation and condensation took place. Vapor then left the friction surface, met with the air, and quickly cooled to form nanoparticles through nucleation. When the newly generated particles became highly concentrated, they grew through coagulation to form agglomerates or the vapor condensed directly onto the surface of existing particles of about 200 nm (formed by mechanical friction).
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