• PDF / 211,392 Bytes
• 5 Pages / 584.957 x 782.986 pts Page_size
• 17 Downloads / 224 Views

DOWNLOAD

REPORT

---

Silica-titania sub-close-packed single layers were deposited by spin coating titanium alkoxide sols containing inert 0.5 micrometer silica particles to study the process of reactive sintering more closely than has been done before. The sub-close-packed single layers were designed to achieve a coating density such that pairs or chains of silica particles were placed on the flat substrate and held together by the reactive titania thin films overlaid on the surface and in the neck regions of these essentially 2-D particle networks. Because of the low density of silica particles, all of the two-particle junctions and neck regions were aligned for geometrically direct viewing; as a result scanning electron microscopy was useful for observing the morphology of these neck regions. Image analysis was used to quantify the neck diameter for varying titania/silica precursor concentration ratios. Geometrical calculations that relate the change in neck volume to the neck radius are presented. Implications for design of reactive sintering systems are discussed. I. INTRODUCTION

Sintering is a process for fusing particles together to provide enhanced electric, mechanical or other materials performance characteristics. It depends on diffusion of material to form physical connection points and several mechanisms can be important: lattice diffusion, viscous flow, grain boundary diffusion, etc.1,2 Reactive sintering is used in cases where composite structures are desired and are being developed to provide processing at lower temperature where the kinetics of the matrix particle might not be rapid enough to form the requisite interparticle connections on their own. One of the potential applications of such low-temperature reactive sintering processes is in developing titania anodes for dye-sensitized solar cells (DSSCs) that use flexible substrates (where the substrate would be sensitive to otherwise higher treatment temperatures). We and other groups have used alkoxide reactive chemistries to prepare titania anodes by this method.3–5 Reactive sintering can also be used to build microstructures that are essentially parallel to structures that could come from sintering of previously synthesized core-shell particles. Multi-oxide materials with core-shell or composite structures have enormous scientific and technological value in materials science due to their unique and tailored properties.6–9 Silica-titania mixed oxides, in particular, have received a lot of attention in recent years because of their applications in photocatalysis.10–12 Methods to prepare silica-titania oxides include impregnation, precipitation, reverse micelle suspension and sol–gel techniques.13 One of a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.47 J. Mater. Res., Vol. 27, No. 8, Apr 28, 2012

the simplest methods, of course, is impregnating the nominally inert silica supporting structure with a solution of titanium alkoxide or tetrachloride precursor.14–16 We have adopted the silica-titania system for our model