Microcavity Formation in Alumina Using Ti Templates I: Formation Conditions

Abstract

It has been found that fully enclosed microcavities can be engineered within Al2O3 ceramics using 125 μm diameter Ti wires as templates. A high‐energy milling pretreatment of the alumina causes diffusion of the Ti into the surrounding alumina leaving all of the Kirkendall porosity consolidated into a central cavity. Control experiments using unmilled alumina confirm the necessity of the milling procedure and experiments with different milling media have excluded incidental doping by milling induced contamination as a primary driver of cavity formation. The internal microcavities produced here may lead to new applications in small scale instrumentation and implantable therapeutic devices.

Microcavity Formation in Alumina Using Ti Templates II: Mechanism and Kinetics

“…When 125 μm Ti wires are embedded within mechanically milled alumina and sintered at 1350°C, cylindrical microcavities templated on the original Ti wire develop. The phases in the area surrounding the microcavity have been shown above and in earlier work 1 to be TiO 2 (rutile), Al 2 O 3 (corundum) and Al 2 TiO 5 (pseudobrookite). Cavity development goes through several stages and appears to reach a stable state after approximately 8 h. From the results herein, we may reconstruct the formation of the microcavities as a series of (overlapping) steps.…”

“…1 despite the boundary between rings 2 and 3 becoming quite diffuse. This maintenance of good contact between the oxidized Ti and its surroundings is essential for cavity formation as may be verified by the absence of a central cavity in samples prepared using unmilled alumina 1 …”

“…1 show the elemental composition (excluding oxygen) of two of the surrounding rings (rings 3 and 5). The phase identification conducted previously 1 indicated that each of the metals is in its highest oxidation state. The inner two rings (1 and 2) show only TiO 2 in the EDS spectra whereas the darker ring appears porous and as indicted in the upper spectrum is predominantly Al 2 O 3 although some TiO 2 or Al 2 TiO 5 is present.…”

“…The sample preparation methodology is described in detail in Goodshaw et al 1 and only a condensed version is given here. Alumina powder (corundum structure, 99.9%, Aldrich Pty.…”

“…In part I, the discovery of a method for producing fully or partly enclosed microcavities within a fired alumina body was reported 1 . Titanium (Ti) wires embedded within high‐energy milling pretreated alumina powders and fired at 1350°C for 4 h were found to diffuse into the surrounding alumina leaving a microcavity templated on the wire.…”