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Thermal and structural characterization of the ZrO2−x(OH)2xto ZrO2 transition

Published online by Cambridge University Press:  31 January 2011

E Torres-GarciÁa ,
A. Peláiz-Barranco ,
C. Vázquez-Ramos  and
G. A. Fuentes
E Torres-GarciÁa*
Affiliation:
Area de IngenieriÁa QuiÁmica, Universidad A. Metropolitana-Iztapalapa, 09340 Me’xico, D.F., México, and Facultad de QuiÁmica, Instituto de Materiales y Reactivos, Universidad de La Habana, Zapata y G, Vedado, Habana 10400, Cuba
A. Peláiz-Barranco
Affiliation:
Facultad de FiÁsica, Instituto de Materiales y Reactivos, Universidad de La Habana, San Lázaro y L, Vedado, Habana 10400, Cuba
C. Vázquez-Ramos
Affiliation:
Instituto de InvestigacioÁn en Materiales, Universidad Nacional A. de México, México D.F. 04510, México
G. A. Fuentes*
Affiliation:
Area de IngenieriÁa QuiÁmica, Universidad A. Metropolitana-Iztapalapa, 09340 México, D.F., México
*
a)Address all correspondence to this author.[email protected],[email protected],[email protected]
a)Address all correspondence to this author.[email protected],[email protected],[email protected]
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Abstract

The exothermic process that occurs around 700 K during calcination of ZrO2−x(OH)2x, associated with the crystallization of the low-temperature tetragonal metastable phase of ZrO2, was analyzed using x-ray diffraction, high-resolution thermogravimetric analysis (TGA), nitrogen adsorption, and modulated differential scanning calorimetry (MDSC). High-resolution TGA allowed us to determine the water loss, resulting from condensation of OH− groups. The amount was 0.137 wt% in our case, equivalent to 1.7 × 10−2 mol of H2O/mol of ZrO2. That corresponds to about one −OH group per nm2 being lost in that process. By using MDSC we determined that the change in enthalpy (∆Hglobal = −15.49 kJ/mol of ZrO2) was the result of two parallel contributions. One of them was reversible and endothermic (∆Hrev = 0.11 kJ/mol of ZrO2), whereas the other was irreversible and exothermic (∆Hirrev = −15.60 kJ/mol of ZrO2). The variability and magnitude of the exotherm, as well as the fact that the accompanying weight loss is so small, are consistent with a mechanism involving the formation of tetragonal nuclei, rather than global crystallization, and hence depend on the number of nuclei so formed.

Type
Articles
Information
Journal of Materials Research , Volume 16 , Issue 8 , August 2001 , pp. 2209 - 2212
Copyright
Copyright © Materials Research Society 2001

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