Pulsed laser annealing of carbon black

Laser heating was used to study the rates and trajectories of carbon black during the earliest stages of annealing. A commercial carbon black, Regal 250 (R250 Cabot Corporation) was heated with a Q-switched Nd:YAG laser and a continuous wave CO₂ laser. Structural transformations were observed with transmission electron microscopy. Micrographs were processed with in-house codes for the purpose of extracting distributions of fringe length, tortuosity (curvature), and number of lamellae per stack. Time-temperature-histories with nanosecond temporal resolution and temperature reproducibility within tens of degrees Celsius were determined by spectrally resolving the laser induced incandescence signal and applying multi-wavelength pyrometry. The Nd:YAG laser fluences include: 25, 50, 100, 200, 300, and 550 mJ/cm². The maximum observed temperature ranged from 2400 °C to the C₂ sublimation temperature of 4180 °C. The CO₂ laser was used to collect a series of isothermal (2600 °C) heat treatments versus time (100 ms–20 s). Laser heated samples are compared against R250 annealed in a furnace at 2600 °C. The material transformation trajectory of Nd:YAG laser heated R250 was different than the traditional furnace heating. The traditional furnace annealing pathway is followed for CO₂ laser heating as based upon equivalent end structures.