Enhanced BaZrO₃ mechanosynthesis by the use of metastable ZrO₂ precursors

Abstract

The current work assesses the impact of structural differences between stable and metastable ZrO2 precursors on the mechanochemical preparation of BaZrO3. Monoclinic (m-ZrO2) and tetragonal (t-ZrO2) zirconia polymorphs were prepared without stabilizing additives by slow alkaline precipitation. High-energy milling of the individual ZrO2 precursors induced different partial transformations in each case. The as-synthesized m-ZrO2 powders showed partial conversion to the tetragonal polymorph on mechanical activation, reaching about 10% t-ZrO2 after 420 min accompanied by increases in strain. In contrast, the as synthesized t-ZrO2 powders underwent the inverse transformation to the monoclinic phase, producing about 50% m-ZrO2 after 120 min with the liberation of strain. The t-ZrO2 precursor was shown to exhibit the higher reactivity with barium peroxide, yielding significantly earlier formation of barium zirconate under room-temperature mechanosynthesis. The progress of the mechanochemical formation of BaZrO3 has been discussed with respect to the differing behaviour of the ZrO2 precursors upon mechanical activation and associated thermodynamic perspectives.

Development of Nano-tetragonal Zirconia-Incorporated Ni–P Coatings for High Corrosion Resistance

“…They were: (1) at 2h values 30.59°and 30.80°with relative intensities of 100.00% and 84.90%, (2) at 2h values 50.69°a nd 51.09°with relative intensities of 75.58% and 58.92%, respectively. These observations revealed the formation of nano-tetragonal zirconia by the preparation process in accordance with the reports of Sherafat and Antunes [58]. The average crystallite size of the nano-tetragonal zirconia was calculated using Scherrer equation.…”

Site Redistribution, Partial Frozen-in Defect Chemistry, and Electrical Properties of Ba1–x(Zr,Pr)O3−δ

“…The formation of BaZr 1– y Pr y O 3−δ (0 ≤ y ≤ 0.2) and Ba 0.95 Zr 0.8 Pr 0.2 O 3−δ compositions was performed by high-energy milling of stoichiometric amounts of ZrO 2 (TOSOH,TZ-0), Pr 6 O 11 (Aldrich, >99.9%), and BaO 2 (Riedel-de-Häen, 95% purity) powders. Substitution of the commonly used barium carbonate by a less stable peroxide precursor allows thermodynamic conditions for room-temperature mechanosynthesis, , thus minimizing risks of uncontrolled barium losses during calcination at high temperature. Milling experiments were carried out at room temperature in air, as described elsewhere. , Powder samples were collected at regular periods of time for analysis by X-ray diffraction (XRD) using a Rigaku Geigerflex diffractometer (Cu Kα radiation, scan rate 3°·s –1 ) in order to inspect the progression of the mechanochemical reaction.…”

Modeling of electrical conductivity in the proton conductor Ba0.85K0.15ZrO3−δ

“…Here ZrO 2 is in metastable tetragonal form prepared by slow alkaline precipitation, as described in a previous publication by the current authors [20]. Mechanosynthesis was carried out in a planetary ball mill, (Retsch PM200), in air, at 650 rpm, using tetragonal zirconia vials (Retsch) and balls with diameters of 5 and 10 mm (Tosoh Co.).…”

“…Mechanosynthesis was carried out in a planetary ball mill, (Retsch PM200), in air, at 650 rpm, using tetragonal zirconia vials (Retsch) and balls with diameters of 5 and 10 mm (Tosoh Co.). Further information on this technique can be found in references [20,21]. The ball to powder ratio was fixed at 10:1.…”