Transformations in aluminum oxyhydroxide under powerful short-pulse microwave radiation

Modification of a material based on Al oxyhydroxide (boehmite/γ-Al2O3) with metal Al fragments (nanoparticles, clusters) has been achieved by the treatment of the material under powerful short-pulse microwave radiation (pulse duration 20 ns, pulse repetition 25 Hz, power density 8 kW/cm2, frequency 2.85 GHz, amplitude of the electric strength component ~2.5·106 V/m). The Al oxyhydroxide was precipitated from a mixture of AlCl3 with ammonia solution and heated at 250 °C for 4 hours. The prepared sample was of predominant amorphous structure, the overall water content (adsorbed, bound, structured) amounted to 15 wt.% in average. The microwave irradiation of the samples (1-3 min) resulted in formation of Al fragments smaller than 100 nm within the solid matrix. Formation of metal Al in the irradiated samples was detected by means of thermal analysis, X-ray diffraction, and transmission electron microscopy. The average content of Al in irradiated samples amounted to ~1.5 wt.%. A rational explanation of the observed metallization effect has been suggested.