Kinetic study of the oxidation and reduction of praseodymium oxides: (1/7) Pr/sub 7/O/sub 12/ + (1/7 - x/2) 0/sub 2/ reversible PrO/sub 2-x/

Journal Article · Sat Mar 14 23:00:00 EST 1981 · J. Solid State Chem.; (United States)

DOI:https://doi.org/10.1016/0022-4596(81)90008-6· OSTI ID:6469492

Inaba, H; Lin, S H; Eyring, L

Kinetic and thermodynamic studies between the ordered iota (n = 7 in Pr/sub n/O/sub 2n-2/) and the disordered ..cap alpha.. (PrO/sub 2-x/) phases have been carried out as a function of oxygen pressure at 655, 675, 695, and 715/sup 0/C using a sample of small single crystals. The existence of a reproducible hysteresis loop, which depends on the temperature and pressure, having an inflection point around a composition PrO/sub 1/ /sub 75/ is shown. The inflection point is interpreted as a phase of n = 8 in Pr/sub n/O/sub 2n-2/ (eta) coherently intergrown with n = 7, 9, and 10, giving an average composition of PrO/sub 1/ /sub 75/. In order to interpret the kinetic data, various theoretical models were examined, for example, oxygen diffusion, a phase-boundary reaction control, or nucleation and growth. None of these models, however, is capable of correlating the experimental data. It was found that a plot of the reaction rate versus the ambient oxygen pressure extrapolates linearly to a finite pressure at zero rate, as was previously observed in the oxidation reaction between the eta and zeta phases of the same system. The model developed for the oxidation reaction between the eta and zeta phases has been modified by taking into account the intermediate phases around PrO/sub 1/ /sub 75/, through which the reaction passes. The modified rate law has two reaction constants: the rate constant from the reactant transforming to the intermediate phase (k/sub 1/) and for the transformation from the intermediate to the product phase (k/sub 2/). The fit to the experimental curve is satisfactory for both the oxidation and reduction reaction. From the temperature dependence of the observed rate constants, the activation energy for the oxidation and reduction was determined to be 75.0 and 60.9 kcal/mole, respectively.

• Research Organization: Arizona State Unvi., Tempe
• OSTI ID: 6469492
• Journal Information: J. Solid State Chem.; (United States), Journal Name: J. Solid State Chem.; (United States) Vol. 37:1; ISSN JSSCB
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
ELEMENTS
KINETICS
NONMETALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PRASEODYMIUM COMPOUNDS
PRASEODYMIUM OXIDES
PRESSURE DEPENDENCE
RARE EARTH COMPOUNDS
REACTION KINETICS
REDOX REACTIONS