Abstract
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 degrees 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 gamma- and alpha-phases to pure gamma phase and finally, at a temperature of 1000 degrees C and above, a single-gamma-Al2O3 phase appears with the increase in crystallinity as the temperature increases. The particle sizes are closely related to gamma-Al2O3 to alpha-Al2O3 phase transformation.