Resumo Pó precursor de mulita microfina de alta pureza de composição estequiométrica, 3Al2O3.2SiO2, foi sintetizado por rota sol-gel usando isopropóxido de alumínio e tetraetoxissilano. O pó precursor de mulita foi caracterizado por área de superfície BET, distribuição de tamanho de partícula, espectroscopia no infravermelho por transformada de Fourier, termogravimetria-análise térmica diferencial (TG-ATD), difração de raios X (DRX), microscopia eletrônica de varredura (MEV) e espectroscopia de raios X por dispersão de energia. A análise de fase do pó precursor e amostras calcinadas em diferentes temperaturas foi realizada por DRX. A cinética de cristalização não isotérmica do precursor de mulita foi estudada por TG-ATD em ar estático usando taxas de aquecimento de 5,0, 7,5, 10,0, 12,5 e 15 K.min-1. A morfologia dos grãos foi estudada por MEV. Os resultados mostraram que o pó precursor sintetizado de mulita possuía homogeneidade dos componentes Al e Si e o pó precursor amorfo foi convertido em cristal de mulita monofásico quando tratado termicamente a 970 °C. Com base nas equações de Flynn-Wall-Ozawa e Kissinger, a energia de ativação associada à cristalização da mulita foi determinada como 1189,8 e 1189,0 kJ.mol-1, respectivamente.

Abstract High-purity microfine mullite precursor powder of stoichiometric chemical composition, 3Al2O3.2SiO2, was synthesized through the sol-gel route using aluminum isopropoxide and tetraethyl orthosilicate. The derived mullite precursor powder was characterized by BET surface area, particle size distribution, Fourier-transform infrared spectroscopy, thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy. Phase analysis of the precursor powder and calcined samples at different temperatures was done by XRD. Non-isothermal crystallization kinetics of mullite precursor was studied by TG-DTA in static air using heating rates of 5.0, 7.5, 10.0, 12.5, and 15 K.min-1. Grain morphology was studied by SEM. The results showed that synthesized mullite precursor powder possessed homogeneity of Al and Si components, and the amorphous precursor powder was converted to monophasic mullite crystal when heat-treated at 970 °C. Based on Flynn-Wall-Ozawa and Kissinger equations, the activation energy associated with the crystallization of mullite was determined to be 1189.8 and 1189.0 kJ.mol-1, respectively.

Most molecular trees of trypanosomatids are based on point mutations within DNA sequences. In contrast, there are very few evolutionary studies considering DNA (re) arrangement as genetic characters. Waiting for the completion of the various parasite genome projects, first information may already be obtained from chromosome size-polymorphism, using the appropriate algorithms for data processing. Three illustrative models are presented here. First, the case of Leishmania (Viannia) braziliensis/L. (V.) peruviana is described. Thanks to a fast evolution rate (due essentially to amplification/deletion of tandemly repeated genes), molecular karyotyping seems particularly appropriate for studying recent evolutionary divergence, including eco-geographical diversification. Secondly, karyotype evolution is considered at the level of whole genus Leishmania. Despite the fast chromosome evolution rate, there is qualitative congruence with MLEE- and RAPD-based evolutionary hypotheses. Significant differences may be observed between major lineages, likely corresponding to major and less frequent rearrangements (fusion/fission, translocation). Thirdly, comparison is made with Trypanosoma cruzi. Again congruence is observed with other hypotheses and major lineages are delineated by significant chromosome rearrangements. The level of karyotype polymorphism within that "species" is similar to the one observed in "genus" Leishmania. The relativity of the species concept among these two groups of parasites is discussed.