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Chemistry for Sustainable Development

2014 year, number 4

Thermal Decomposition of Solid Substances as a Method to Obtain Nanocrystalline Structurally Ordered Media

1Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch, Russian Academy of Sciences, Ul. Kutateladze 18, Novosibirsk 630128 (Russia)
2Novosibirsk State University, Ul. Pirogova 2, Novosibirsk 630090 (Russia)
Keywords: thermal decomposition, pseudomorphosis, nanocrystalline structurally ordered media, supercrystal, small-angle X-ray scattering
Pages: 333–343


For one reactions class of thermal decomposition of the type of crystallohydrate dehydration, decompositions of carbonates, hydroxides and other compounds, we managed to go the entire way – from the starting reagent to the final morphology of the solid product. Possible phase formation mechanisms for this type of processes were considered. A general algorithm that allows theoretically predicting the size and shape of the particles of final product was proposed. The product of thermal decomposition is a porous compact formation that conserves the geometric dimensions and shape of the starting precursor particle (pseudomorphosis). There is a fraction of emptiness inside pseudomorphosis, equal to the difference between the molar volumes of the starting reagent and product. Pseudomorphosis consists of oriented product nanocrystals equally sized and shape interconnected, that is, represents a structured system. It was demonstrated experimentally that pseudomorph obtained by dehydration of CuSO4 x 5H2O monocrystal behaves analogously to liquid crystals as an optically anisotropic medium, i. e., possess birefringence. This is the evidence of the ordered locations of particles composing it. It was established that the spatial distribution of the intensity of small-angle X-ray scattering from pseudomorphosis obtained by dehydration of CuSO4 x 5H2O monocrystal (performed at the synchrotron radiation source of INP, SB RAS, applying a two-coordinate detector) possessed angular anisotropy. Based on the received data, the sizes of the rod-shaped particles were assessed: thickness (~8 nm), length (~100 nm) and their location in pseudomorphosis.