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Sol-Gel Synthesis and Structural Characterization of Nano-Composite Powder: NiAl2O4:SiO2

P. Muralidharan, I. Prakash, M. Venkateswarlu and N. Satyanarayana
Pondicherry University, IN

Keywords: sol-gel, NAS, XRD, FTIR, nanocomposite

Nano-composites are important class of materials because of many of their physical and chemical properties show particle size dependence. Nano-structured metal (Zn, Mg, Ca) aluminate, with spinel structure, dispersed in SiO2 glassy matrix materials are found to exhibit improved properties such as great thermal stability, hardness, etc. and thus, gained interesting importance in the technological applications like optical, refectories, high alumina cement oxidation catalysts, etc. The preparation of such materials can be obtained by controlling both the size and polydispersity of the particles in the host matrix through special synthesis methods like sol-gel, solid state reaction, etc. Recently, wide varieties of glass or glass-ceramic monoliths, nano-structured powders, etc. are synthesized through sol-gel technique, since it has the advantages of low temperature processing, high chemical homogeneity, and purity, etc. Hence, the above mentioned advantages focused our attention to synthesize nano-crystals of spinel structure NiAl2O4 dispersed in SiO2 glassy matrix through insitu reaction sol-gel method and characterize by XRD and FTIR. Nano-composite of NiAl2O4 / SiO2 glassy matrix were prepared by insitu reaction sol-gel process using precursor chemicals of tetraethylorthosilicate (TEOS), Al(NO3)3.9H2O and NiNO3. Fig. 1 shows flow chart for preparing NiO - Al2O3 - SiO2 (NAS) xerogel through sol-gel process. The precursors were mixed, according to their respective molecular weight percentages, using the following chemical composition formula 5% NiO 6% Al2O3 89% SiO2. The ratio of water to TEOS is maintained as 16: 1. The solution was stirred for 2 hrs at 338 K and then allowed to form gel at same temperature. The xerogel was heat treated at 338, 673, 873, 1073, 1123 and 1163 K for two hours at each temperature and are characterized by XRD and FTIR. The nucleation of NiAl2O4 crystals appeared at 1073 K and further heated to 1163 K for the growth of the crystals. Fig. 2 shows the X-ray diffraction of the NAS samples heat treated at different temperatures 338, 673, 873, 1073, 1123 and 1163 K. The peak free pattern confirmed amorphous nature of the sample below 1073K. The sample heated at 1073 K and above showed the characteristic peaks confirmed crystalline NiAl2O4 phase in the SiO2 amorphous matrix. Fig. 3 shows FTIR spectra of NAS sample heat treated at different temperatures 338, 673, 1073 and 1123 K. In fig. 3, the samples heated at different temperatures showed characteristic changes in the band positions confirm the formation NAS structure. Detailed results will be presented and discussed.

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