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

Abstract

In part I of this work, it was found that titanium (Ti) wire encapsulated within mechanically milled alumina powder and sintered at 13501C forms potentially useful microcavities due to the consolidation of Kirkendall porosity. Here a series of samples sintered at 13501C in the range 0-24 h has shown the remarkable way in which these cavities form. The cavity has already started in samples quenched from the top of the heating ramp (0 min at 13501C). It is surrounded by a diffusion zone B300 lm in diameter, which does not change size throughout the firing process although the contents change markedly. The diffusion zone microstructure is initially complex with phase sequence TiO 2 / Al 2 O 3 /TiO 2 1Al 2 O 3 /Al 2 TiO 5 . Microstructure evolution may be summarized as outward growth of the cavity accompanied by inward growth of the Al 2 TiO 5 resulting in a B190-lm-diameter cavity surrounded by a 50-lm-thick layer of Al 2 TiO 5 . The formation of the cavity and surrounding microstructure is discussed although some features, such as the nucleation of Al 2 TiO 5 in the part of the diffusion zone furthest from the Ti source and the ring of Al 2 O 3 , which persists in between Ti-rich parts of the diffusion zone are still poorly understood.

Microcavity Formation in Alumina Using Ti Templates I: Formation Conditions

“…This view is reinforced by similarities with samples made using Al 2 O 3 milled using steel media but sintered for less time. Those results are presented in an accompanying paper 23 . Adjustments to the sintering time or temperature may be all that is required to allow the Ti to completely diffuse to form a more complete microcavity in alumina milled in ZrO 2 media.…”

“…Under the conditions used in this work, the combination of Ti and Al 2 O 3 gives the most promising results. The mechanism and kinetics of cavity formation is investigated in greater detail in a companion paper 23 …”

On the Enhanced Solute Content, Shape, Defect Microstructures, and Optical Properties of Ti-Doped γ-Al2O3 Nanocondensates

“…Regarding to the Kirkendall effect on solute expulsion, cation interdiffusion in close-packed oxides was known to cause microcavities such as in the alumina−Ti diffusion couples , and mesopores such as in nonstoichiometric nickel−cobalt oxide via the oxyexsolution and Kirkendall effects . It is not clear whether the { hkl }-specific etch pits have anything to do with Kirkendall pores due to Ti−Al interdiffusion through a close-packed oxygen sublattice.…”