Monolithic t ‐ZrO 2 Nanopowder through a ZrO(OH) 2 · x H 2 O Polymer Precursor
2004; Wiley; Volume: 87; Issue: 12 Linguagem: Inglês
10.1111/j.1151-2916.2004.tb07489.x
ISSN1551-2916
Autores Tópico(s)Catalysis and Oxidation Reactions
ResumoMonolithic t ‐ZrO 2 (tetragonal structure) nanopowder is synthesized with an amorphous ZrO(OH) 2 · x H 2 O polymer precursor. The H 2 O molecules impart the structure and promote reconstructive thermal decomposition of the structure to t ‐ZrO 2 nanoparticles on heating at temperatures as low as 200°C. A prevalent endothermic heat output in the dissociation process controls the local temperature in exothermic nucleation and growth of various groups of the reaction species so that it is self‐controlled in high‐energy nanoparticles. Crystallites are, on average, d = 8 nm diameter, and they have a high value of Gibbs free energy or lattice volume V o = 0.06770 nm 3 . The excess volume decreases to V o = 0.06705 nm 3 if the reaction temperature is increased to >200°C, i.e., approximately the bulk value of 0.06681 nm 3 ; there is a minor increase to d = 12 nm at 600°C. Many oxygen vacancies in the thin surface space‐charge layers seem to support the stability of small particles in this particular polymorph. A pure m ‐ZrO 2 (monoclinic structure) appears with d = 22 nm at temperature as low as 800°C. The results are analyzed using X‐ray diffractometry, microstructure, infrared spectroscopy, and thermal studies of the polymer precursor and derivative t ‐ZrO 2 nanoparticles.
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