Di-phasic xerogel-derived composites, such as SiO2AgCl, SiO2-AIPO4, SiO2-CePO4, SiO2 -Nd2O3, SiO2-CdS, SiO2CrPO4, SiO2-BaSO4 and SiO2-PbCrO4 have been characterized in detail by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) techniques. The SiO2-AgCl photochromic composites with small amounts of AgCl did not show any crystallinity either by XRD or by SAED. Thin edges of these SiO2-AgCl composites did not reveal discrete AgCl particles because these are too small to be resolved even by TEM and are expected to be in the range 1.5 to 2.5 nm in size based on the pore size of silica gel. A few large AgCI-Ag particles precipitated on the outside of silica gel were, however, detected by TEM-SAED in silica gels with higher concentrations of AgCl. The SiO2-AIPO4 and SiO2-Nd2O3 composites are noncrystalline and did not show any periodic structure by TEM and SAED. Heat treatments to 400 or 600° C did not crystallize the AIPO4 or Nd2O3 phases. On the other hand, SiO2-CePO4 and SiO2-CdS composites showed lath-like particles of CePO4 and irregular particles of presumably CdS on the surfaces of silica gels. The SiO2-BaSO4 and SiO2-PbCrO4 composites showed crystals of BaSO4 and PbCrO4 which are too large to be incorporated in the silica gel pores. These results show that the size and crystallinity of a second phase within silica gels can be controlled by the appropriate manipulation of the different parameters, and to do so is an important advantage for this new class of diphasic nanoscale composite xerogel materials.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials
- Materials Science(all)