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:
The crystallization of ordered (Zr,Ti)2O4 from the oxides succeeded for the first time, at 800°–1200°C and 13–20 kbar, using either ammonium carbonate or copper oxide as flux. The composition of the ordered phase, coexisting with either zirconia or rutile, is pressure–temperature dependent, ranging from XTi= 0.60 to 0.68. Its reproducibility and reversibility suggest the ordered compound crystallized at/near thermodynamic equilibrium. The presence of flux permits the equilibration of phase assemblages well below 1200°C, a region previously inaccessible for equilibrium experiments in the ZrO2–TiO2 system due to sluggish kinetics. Thus we were able to determine the ZrO2–TiO2 phase diagram at 20 kbar at temperatures as low as 800°C. In contrast, room-pressure experiments did not result in the spontaneous nucleation of ordered (Zr,Ti)2O4 from the oxides, and seeds were required to initiate growth. The flux-aided synthesis of ordered (Zr,Ti)2O4 from the oxides, at constant temperature and in its stability field, has the following advantages over previous crystallization attempts, which consisted of slow cooling of the disordered polymorph through the ordering transition. The ordered compound forms at equilibrium, therefore permitting phase equilibrium studies and thermodynamic interpretation. Large grain sizes facilitate quantitative analysis of the composition with electron microscopy. Microcracks and ZrO2 exsolution, reported from samples cooled through the transition, can be avoided. The composition and the ordering state of the ordered compound can be controlled with pressure and temperature. Using the flux-based synthesis method, well-crystallized samples can now be obtained for future crystal structure refinements, calorimetric and dielectric measurements, or investigations into the phase transition.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1151-2916.2004.tb06360.x
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