Microscopy and Quantitative Morphology of Aluminum Silicate Nanoparticles Grown on Organic Templates

Abstract

Biomimetic synthesis of ceramic materials is increasing in popularity because it offers many advantages. In this work, aluminum silicate nanoparticles were obtained on a self-assembled organic multilayer at near room temperature (30 < or = T < or = 50 degrees C) and at atmospheric pressure. Morphological and microanalytical characterization was carried out by means of transmission electron microscopy and subsequent image analysis. The roles of some process parameters such as template type, reactant concentration, [Al]:[Si] molar ratio, number of initiation steps (IS) of mineralization, and reaction time (rt) were assessed by comparing images, diffraction patterns, and EDX spectra. Generally, the Si-rich phase exhibited higher crystallinity, whereas the Al-rich phase was mostly amorphous. Crystal structure resulted with rt > or = 4 days for template-grown materials. Images of materials obtained at T = 50 degrees C, rt = 3 days, and 1 < or = IS < or = 4 were further analyzed by "spectrum enhancement," an algorithm based on the Fourier transform. Morphological indicators were extracted from suitably processed power spectral densities, a correlation matrix was formed, and multivariate statistics was carried out. Visual differences in nanoaggregate morphology were quantitatively translated. Materials were ranked by the spatial uniformity of nanoparticle distribution: the most uniform aggregates were those grown on templates by IS > or = 2. Univariate statistics validated the conclusion: the particles of those same materials had a narrower size distribution and sharper edges. This last property has been ascribed to crystalline structure, independently demonstrated by diffraction patterns.