Aluminato de lítio : síntese e caracterização morfológica, textural e estrutural

Abstract

In this work LiAlO2 powders have been synthesized by two different methods: sol-gel and coprecipitation, changing the concentration of reactants and drying process. In the sol-gel process was employed a Al/Li molar ratio equal to 1:1 with controlled drying of the material (SOLLi sample). In the samples synthesized by coprecipitation were employed Al/Li molar ratios equal to 1:1, 1:4 and 1:7. The precipitate were dried (COPLi-1 and COPLi-2 samples) and freeze-dried (COPLi-3 and COPLi-4 samples). After drying all samples were calcined at different temperatures and characterized structurally, texturally and morphologically. On the structural characterization of the samples, it was noted that the -LiAlO2 and -LiAlO2 phases were obtained in the two synthesis processes. The -LiAlO2 phase was observed only for COPLi-1 and COPLi-2 samples. The NaNO3 phase was detected in COPLi-2, COPLi-3 and COPLi-4 samples at 550 ºC by X-ray diffraction due to the LiNO3 excess employed in the synthesis. The LiAl2(OH)7.2H2O and Li2Al2O4.xH2O phases were observed only to samples synthesized by coprecipitation and the LiAl5O8 phase was not detected by DRX in the COPLi-3 and COPLi-4 samples. However, FTIR analysis indicated the presence of this phase in both samples. Thermal analysis results indicated events associated with loss of water molecules, LiAl2(OH)7.2H2O, NaNO3 and -LiAlO2 decomposition in addition to Li2Al2O4.xH2O phase crystallization for samples synthesized by coprecipitation. For SOLLi sample, there was events associated to loss of water molecules, pyrolysis of organic waste and LiAl5O8 phase formation. Results of Al/Li molar ratio were close to the stoichiometric for SOLLi sample calcined at 550 and 750 ºC. However, at 550 ºC only peaks of -LiAlO2 phase were observed by DRX and at 750 ºC a mixture of -LiAlO2 and -LiAlO2 phases was obtained. Values closer to the stoichiometric were also observed in the COPLi-4 sample calcined at 950 and 1150 ºC where the Li loss is more critical. In both temperatures the -LiAlO2 phase was observed with high purity indicating the feasibility of the method to obtain such phase. In the textural characterization, it was obtained values of specific surface area comparable to those reported in the literature except for SOLLi and COPLi-2 samples calcined at 1150 ºC where there was high compression of the particles preventing gas adsorption analysis. The morphological characterization of the samples revealed morphologies such as: nanoflakes, microsheets and rods. The nanoflakes were considered as primary particles forming microsheets and rods (secondary particles). It was also observed secondary particles called agglomerate or aggregates of nanoflakes in addition to agglomerates of microsheets