Experimental study of laser irradiated graphite oxidation using IFTS

Abstract

Graphite oxidation is investigated at varying porosity and laser irradiance, resulting in surface temperatures of 1500–3100 K. Samples are irradiated using a 1.07 µm fiber laser at irradiances of 1000 and 3600 W/cm2 in dry air environment (20% O2, < 1% H2O) at atmospheric pressure, producing a buoyant flow. Combustion plumes are analyzed using a midwave (MW) imaging Fourier transform spectrometer (IFTS) at 2 cm−1 spectral resolution, 0.5 mm/pixel spatial resolution, and data cube rates of 1 Hz. Spectral signatures from CO and CO2 are predominant in the 1800–2500 cm−1 spectral region. A radiative transfer model is used to infer species concentration and temperature from the hyperspectral data, resulting in 2D characterization of the reacting boundary layer. Plume temperatures of up to 2500 K are observed. CO and CO2 populations are correlated with surface temperature, with a general trend of [CO]/[CO2]=10exp(−5,200/Ts). A simplified model incorporating diffusion transport and surface kinetics is presented to assess the relative strengths of the S1) 2C+O2⇒2CO, S2) C+CO2⇒2CO, and S3) C+O2⇒CO2 surface oxidation mechanisms. The role of kinetic and transport mechanisms is discussed.