Synthesis and Characterization of α-Al2O3 by Sol-Gel Process and Development of Zn-Al2O3 Composites by Powder Metallurgy Route

Abstract

In the present study α-Al2O3 powders of nanometric size were successfully synthesized by sol-gel method using two different precursors, one using aluminium chloride(AlCl3),ethanol(C2H5OH) and ammonia(NH3) followed by calcination at 1200oC for 2 h in a furnace, and the second process using aluminium nitrate (Al(NO3)3), malic acid (C4H6O5) and polyvinylpyrrolidone, PVP ((C6H9NO)n) followed by heat treating at 1250°C for 2 h. The alumina formed were analysed by X-ray diffraction (XRD) and particle size analysis to characterize the powders in terms of their crystallinity and their crystallite size. Further characterizations of particles were carried out using scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) techniques. It was found that much finer particle size of α-Al2O3 could be achieved when Al(NO3)3 was used as a precursor. The decrease in size accompanied by an increase in aspect ratio makes it an ideal reinforcing agent for high strength composites and results in its highly superior properties. The present study also involved the development of Zn-Al2O3 composites by reinforcing the Zn-matrix with α-Al2O3 as reinforcement. α-Al2O3 is very attractive due to their unique combination of excellent mechanical properties and high thermal stability which makes them an ideal reinforcing agent for high strength composites. Zn-Al2O3 composites were developed containing 50 and 60 vol.% α-Al2O3 by an ex-situ process that includes blending commercially available Zn and α-Al2O3 powders together in required compositions followed by compaction at 300 MPa and heat treatment at 500oC for 2 h. The Zn-Al2O3 composites fabricated were analysed by using optical microscopy, SEM and EDX. Mechanical properties like wear resistance and hardness of the composites were analysed to find out the effect of the addition of α-Al2O3 in the Zn-matrix. It was found that addition Al2O3 to Zn matrix improved the hardness as well as the wear resistance of Zn