Alumina reduction by laser ablation using a continuous-wave CO₂ laser toward lunar resource utilization

Aiming at development of a new method of alumina reduction that is useful for ore mined from the moon, experiments of alumina reduction using CW laser ablation were conducted with a kW-class CW CO₂ laser with 400–2000 W power. After a laser beam was focused on a sintered alumina rod, the surface was heated to a temperature necessary for ablation of alumina. Ambient pressure in the test chamber was controlled by supplying Ar gas at 0–0.30 atm, 0.50 atm and 1.0 atm initially, with gas evacuated using a rotary vacuum pump. Under those conditions, an ablation plume was ejected continuously from the sintered alumina rod surface, which was not observed in vacuum. Ambient pressure was increased to 0.40 atm, 0.65 atm, and 1.2 atm. Moreover, emission spectra from the ablation plume were measured; Al I line spectra were detected. Results show that alumina reduction occurred without reducing stores. The equilibrium temperature varied with ambient pressure and laser intensity: 3100–3700 K. Molar reduction of 9.7% and energy conversion efficiency of 0.64% were achieved. Further improvement of the molar reduction percentage can be achieved using increased laser intensity and ambient pressure.