Phase transformation and structural characterization studies of aluminum oxide (Al₂O₃) nanoparticles synthesized using an elegant pulsed laser ablation in liquids technique

Pulsed laser ablation in liquid (PLAL) is an emerging technique for synthesis of pure metal and metal-oxide nanoparticles. The advantages of PLAL over the conventional chemical methods are the lower cost, high purity, stability of produced nanoparticles and do not need a vacuum chamber. In this work, we applied PLAL technique to synthesize high purity nano crystalline Al₂O₃ particles. The nanocrystalline Al₂O₃ powder obtained was further subjected to heat treatment in the temperature range of 600-1200 °C to investigate the phase transformation of the obtained Al₂O₃ nanopowder. A Q-switch Nd:YAG laser beam of 532 nm wavelength having 5 ns pulse width, laser fluence of 450 mJ/cm² and 10 Hz frequency was employed as an excitation source. The synthesized nano crystalline phases of Al₂O₃ nanoparticles were investigated using various advanced analytical techniques like X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), energy dispersive X-ray Spectroscopy (EDS), transmission electron microscopy (TEM), selective area electron diffraction (SAED), Fourier transform infrared spectroscopy (FT-IR) and gravimetric analyses (TGA and DSC). SEM and FE-SEM techniques were adopted to investigate the morphological structure of Al₂O₃ of bulk parent material and the nanocrystalline Al₂O₃ powder obtained after laser ablation in de-ionized water without any further heat treatment (as-prepared Al₂O₃) respectively. With these analytical techniques, we observed the identification of three steps on the phase transformation of Al₂O₃ i.e., from the mixture of γ- and α-phases to pure γ phase and finally, at a temperature of 1000 °C and above, a single-α-Al₂O₃ phase appears with the increase in crystallinity as the temperature increases. The particle sizes are closely related to γ-Al₂O₃ to α-Al₂O₃ phase transformation.