Potentiometric determination of the gibbs energies of formation of SrZrO 3 and BaZrO 3
- PDF / 685,827 Bytes
- 7 Pages / 603.28 x 783.28 pts Page_size
- 12 Downloads / 254 Views
I.
INTRODUCTION
T H E R E is current interest in oxides with perovskite structure that exhibit ionic conduction.t l] Recent electrochemical measurements by the authors indicate that both pure and doped SrZrO3 and SrHfO3 are good oxide-ion conductors that can be used as sensors for oxygen in liquid metals. Because of the new prominence of alkalineearth zirconates and hafnates as solid electrolytes, systematic studies have been conducted on their free energies of formation. This article reports measurements on SrZrO 3 and BaZrO 3. A study on CaZrO3 is published elsewhere, t2] The thermodynamic information is useful for assessing potential interactions of these materials with liquid metals, support materials, and auxiliary electrodes. Both strontium and barium zirconates are formed in the fuel pins of nuclear reactors under normal operating conditions of temperature and oxygen chemical potential. I3j The fission products, strontium and zirconium, react with oxygen in UO2_+~ or (U, Pu)O2• fuel to form the zirconate. They are also formed by the reaction of K.T. JACOB, Chairman and Professor, Materials Research Center, and Professor, Department of Metallurgy, is with Indian Institute of Science, Bangalore 560012, India. Y. WASEDA, Director, Institute for Advanced Materials Processing, is with Tohoku University, Sendai 980, Japan. Manuscript submitted August 1, 1994.
METALLURGICAL AND MATERIALSTRANSACTIONS B
strontium and barium with oxidized ZIRCALOY* clad*ZIRCALOY is a trademark of Westinghouse Electric Company, Pittsburgh, PA.
ding. t4j High-temperature thermodynamic properties of the compounds are therefore needed for the evaluation of fuel-fission product interactions and are relevant to nuclear technology. The low-temperature heat capacities of SrZrO3 and B a Z r O 3 have been measured in the temperature range 51 to 296 K by King and Weller.tS] The standard entropies calculated from the measurements are as follows: S~29S.15K(SrZrO3) = 115.0 (+2) J K -1 mol -l S~98.15K(BaZrO3) = 124.7 (---2) J K -l mol-' Levitskii et al.[6] have measured high-temperature enthalpy increments of SrZrO3 and BaZrO3 from 300 to 1650 K by drop calorimetry. Nagarajan et al. tTJ have reported enthalpy increments for SrZlO 3 and BaZrO3 from 1030 to 1687 K, using high-temperature differential calorimetry. Drop calorimetry has been used by Fomichev et al. 18] for measurements on SrZrO3 from 526 to 2318 K and by Cordfunke and Konings t9j on BaZrO3 from 407 to 775 K. L'vova and Fedos'ev tl~ have determined the enthalpies of reaction of ACO3 (A = Sr, Ba) and ZrO2 in a bomb calorimeter, carbon black being used as the
VOLUME 26B, AUGUST 1995--775
initiating substance. Corrections were applied for incomplete reaction and combustion of carbon black. From the enthalpy changes for reactions of the type A G O 3 (s) + Z r O 2 (s) ----->A Z I O 3 (s) + C O 2 (g)
It, 02, SrO + SrF2JCaF2JSrZrO3 [2]
in the temperature range 1180 to 1360 K. In a strict sense, the reference electrode containing pure SrO is not stable in contact with CaF2, which was us
Data Loading...
