ISSN:
1551-2916
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Controlled-geometry cavities, initially ≈20 μm × 20 μm × 0.5 μm, were introduced into 〈inlineGraphic alt="inline image" href="urn:x-wiley:00027820:JACE00604:JACE_00604_mu9" location="equation/JACE_00604_mu9.gif"/〉 -plane titanium-doped (≈210 ppma;≈500 wt. ppm) sapphire substrates using photolithographic methods, and subsequently internalized by diffusion bonding. The samples were annealed in air for prolonged periods at 1600° and 1800°C to convert the titanium to the 4+ state and to allow the pore shapes to adjust. Pores with an equivalent spherical radius of ≈3.6 μm reached a quasi-equilibrium shape within 160 h at 1600°C and within 48 h at 1800°C. The Wulff shape was determined using optical microscopy, scanning electron microscopy, and atomic force microscopy. The Wulff shape of Ti4+-doped alumina includes well-defined c(0001), 〈inlineGraphic alt="inline image" href="urn:x-wiley:00027820:JACE00604:JACE_00604_mu10" location="equation/JACE_00604_mu10.gif"/〉 , and 〈inlineGraphic alt="inline image" href="urn:x-wiley:00027820:JACE00604:JACE_00604_mu11" location="equation/JACE_00604_mu11.gif"/〉 facets and smoothly curved sections. The 〈inlineGraphic alt="inline image" href="urn:x-wiley:00027820:JACE00604:JACE_00604_mu12" location="equation/JACE_00604_mu12.gif"/〉 and a 〈inlineGraphic alt="inline image" href="urn:x-wiley:00027820:JACE00604:JACE_00604_mu13" location="equation/JACE_00604_mu13.gif"/〉 facets, which are components of the Wulff shape of undoped sapphire, are not discernable. In contrast to undoped alumina, for which the r-plane has the lowest energy, the c-plane is the lowest energy plane in Ti4+-doped alumina. The surface energy sequence of the stable c, r, and p surfaces differs from that in undoped alumina. The Wulff shape varies with temperature. Samples equilibrated at 1800°C were re-annealed at 1600°C. Pore shape changes were reversible, indicating that the observed pore shapes were close to the equilibrium (Wulff) shape.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1551-2916.2005.00604.x
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