Chromium-containing silica materials

Chromium-containing silica samples were obtained from soluble sodium silica te solutions in the presence of different chromium nitrate concentrations. Precipitation was carried out in ethanolic media. Gel precipitate was dried by liophylization and samples measured by transmission electron microscopy (TEM), X-ray energy-dispersive spectrometer. X-ray mapping, X-ray photoemi ssion spectroscopy (XPS), and particle size analysis. Spherical chromium co ntaining silica particles with 3.5% and 4.8% (at.%) of chromium were obtain ed. Particle size analysis results showed that with increased addition of c hromium in sodium silicate solutions produces agglomerates whose sires rang e from 1 to 0.2 mu m. Chromium mapping and XPS results show that chromium o xide is preferentially segregated on particle surfaces. Chromium oxide was detected on particle surface with a binding energy of 576.77 +/- 0.05 eV as obtained from XPS analysis. During the hydrolysis and condensation process es chromium oxide precipitates on the silica surface and it affects the sil ica chain size. (C) 2000 Elsevier Science B.V. All rights reserved.