(Color online) (a) A schematic drawing of the mechanical impact (or pulse laser ignition) experimental setup to investigate the dynamic fracture of metal strips and combustion of fragments in controlled environments. The method utilizes a BB gun (or an IR pulse laser), a high-speed camera, and a three-position laser velocimeter. (b) A composite image of the high-speed camera records (recorded at 8000 fps), showing the space-time trajectory of burning particles ejected from a metal strip by a pulsed laser ignition. The discontinuous segments indicate the different frame image. Note that the particle speed decreases with time because of the drag force behind small particles, from which the particle size, size distribution, and burn time can be obtained (see the text).
(Color online) (a) The particle size distribution of mechanically initiated metal particles, showing a mean particle size of 3.1 μm in diameter. (b) The EDS spectrum of post-burnt particle suggesting the chemical composition roughly corresponding to ZrO2 and HfO2. The SEM picture of a particle is shown in the inset, showing a core/shell structure of the burnt particle.
(Color online) (a) The spectral sensitivity of the CCD overlaid with the blackbody radiance curves at 4000, 3000, and 2000 K. The present single-channel spectro-pyrometer employs a narrow beam path filter (Δλ = 70 nm) centered at 650 nm (the vertical purple hatched area). (b) The time-resolved temperature of burning single particle of a 3.4 μm diameter metal particle (DM) and the emissivity ɛ = 1, plotted in comparison with the temperatures using metal oxide particle diameter (DMO) and ɛ = 0.8 (upper green line) and 0.9 (lower red line). The temperature profile shows the burst temperature of ∼4100 K and a subtle temperature jump during the cooling period likely arising from solidification of molten ZrO2 or cubic to tetragonal phase transition of solid ZrO2. (c) A composite image of mechanically initiated single particle, recorded at the rate of 54 000 fps, along the space-time trajectory, showing a variation in light intensity at 650 nm (Δλ = 70 nm). The time resolution is 18/19 μs alternately. The time for burst temperature (TB) and micro-flash near the end of combustion are indicated. Also, see (b) for the temperature evolution.
(Color online) (a) The burst temperature TB plotted as a function of the metal particle diameter DM, showing a linear decrease of TB with increasing DM. (b) The burn times of mechanical impact generated particles (upper blue line and diamond symbols) and thermal laser-ablation particles (lower red line and dot symbol), plotted as a function of DM, following the power law dependences.
(Color online) (a) The temperature burn rate plotted as a function of metal particle size, which decreases with increasing the metal particle diameter (a) Comparison of mass burn rates of Zr (lower red line and black diamond symbols) and Al particles (upper green line and green dot symbols) plotted as a function of metal particle diameter.
Article metrics loading...
Full text loading...