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PtSn

40 nm

PtSn

40 nm

Figure 65. (a) TEM micrograph of silica xerogel nanocomposite containing PtSn nanoclusters and (b) the corresponding XRD trace. Reprinted with permission from [607], J. P. Carpenter et al., Inorg. Chim. Acta 251, 151 (1996). © 1996, Elsevier Science.

90.0 NIGGLITE, SYN 25-614

Figure 65. (a) TEM micrograph of silica xerogel nanocomposite containing PtSn nanoclusters and (b) the corresponding XRD trace. Reprinted with permission from [607], J. P. Carpenter et al., Inorg. Chim. Acta 251, 151 (1996). © 1996, Elsevier Science.

The thermolytic conversion of molecular precursors to metal oxide-silica materials occurs in theoretical yields with a homogeneous distribution of silicon and the transition metal in the oxide matrix that can be attributed to the preservation of molecular-level homogeneity in the transition from precursor to ceramic material. The solid-state transformation gives relatively ordered porous structures, indicating that the precursor's crystalline lattice may function as a template to orient the condensation reactions in particular directions. The microstructure of the heat-treated ZrO2/SiO2 material shows a smooth silica matrix containing spherical ZrO2 particles that grow in size at higher temperatures (Fig. 67).

Roesky et al. have reported on the preparation and chemical properties of a large number of heterometallosiloxane compounds that represent an interesting class of model compounds and precursors to silica-based materials [608]. For example, Dhamelincourt et al. have used eight-membered titanium-containing halo-siloxane rings [(TiX2)2O4(SiBu2)2] (X = Cl, Br, I) (Scheme 31) as SSPs, prepared according to Scheme 31, to homogeneous TiO2/SiO2 material [310].

Figure 66. ORTEP view of the molecular structure of [Cu(OSi-(OBu)]4. Reprinted with permission from [299], K. W. Terry et al., Chem. Mater. 8, 274 (1996). © 1996, American Chemical Society.

One of the interesting findings of their study is the role of halogen atoms, in the precursor, in determining the phase of the resulting ceramic. For instance, the precursors containing chloride and iodide ligands produced silica mixed with anatase, whereas the bromide derivative yielded silica mixed with rutile [310].

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