Morphological and electronic characteristics of nanoalumina alone and in high-temperature (fumed) and low-temperature (mechanical) mixtures with nanosilica

Crystalline and electronic structures of nanoalumina alone and in different mixtures with nanosilica have been analyzed using X-ray diffraction (XRD) and ultrasoft X-ray emission spectroscopy (USXES). Narrowing of the OK α bands of crystalline alumina occurs with decreasing nanoparticle size. Electron transfer from oxygen to aluminum atoms due to Al–O bond breakage under irradiation leads to occupation of high-energy 3d level of Al. In nanoparticles, the Al–O bond strength and O–O interactions enhanced by Laplace (bubble) pressure lead to δ phase stabilizing if coherent-scattering region size (d CSR ) reaches 7 nm which is smaller than that for θ phase (d CSR  = 11–20 nm) of alumina and silica/alumina studied. The d CSR  values are in agreement with nanoparticle sizes calculated using self-consistent regularization method applied to nitrogen adsorption data.