%0 Journal Article
%T Core-and-shell nature of St ber silica particles
%A Leite Carlos A. P.
%A Souza Elizabeth F. de
%A Galembeck Fernando
%J Journal of the Brazilian Chemical Society
%D 2001
%I Sociedade Brasileira de Qu¨Şmica, SBQ
%X Two different samples of monodisperse St ber silica particles were examined in the analytical transmission electron microscope, using different imaging modes: bright-field, dark-field, energy-loss and elemental distribution maps. The particles (effective diameters = 141 and 36 nm) are formed by domains of variable O/Si ratio, which is consistent with a variable degree of hydration, and they coexist with particles with a high O/Si ratio measuring a few nanometers only, which appear dispersed in the picture background. Bright-field and energy-loss images of the larger particles show a core-and-shell morphology, and the shells have a higher amount of high-O/Si domains as well as contaminating carbon compounds. On the other hand, the smaller particles (effective diameter = 36 nm) are also formed by distinct domains, but their morphology is neither spherical or core-and-shell. The mechanisms for particle formation presented in the literature are discussed, considering the present findings.
%K colloidal silica
%K transmission electron microscopy
%K energy-filtered imaging
%K silica particle microchemistry
%U http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532001000400013