Microwave-assisted hydrothermal synthesis of nanocrystalline zirconia

A simple, fast and energy efficient microwave-assisted hydrothermal method was developed for the preparation of nanocrystalline zirconia from commercially available ZrOCl2 8H2O and KOH. The synthesis was conducted at 180 degrees C for 20 min by two ways: direct decomposition of ZrOCl2 8H2O (sample Z), and precipitation of ZrOCl2 8H2O with KOH and dehydration of hydroxides (sample ZK). The as-synthesized powders were calcined at 500 degrees C, and all the resulting products were characterized by XRD, FE-SEM, HR-TEM and SAED. Both the assynthesized and calcined nanoparticles were highly crystalline. A single monoclinic phase was obtained for sample Z, while for sample ZK a tetragonal phase was achieved as the main phase with a minor fraction of monoclinic. The particles of the as-synthesized sample Z showed irregular and semi-hexagonal shapes, although they changed to spherical or ellipsoidal shapes during heat treatment. The particles of the sample ZK, both as-synthesized and calcined, exhibited nearly spherical or ellipsoidal shapes. The average crystallite size for the as-synthesized samples Z and ZK were 3.2 f 0.8 and 5.5 f 0.9 nm, respectively, while for the calcined ones the values were 8.5 f 1.2 and 7.6 f 1.2 nm, respectively. (c) 2025 The Author. Published by Elsevier Espana, S.L.U. on behalf of SECV. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/).