A STUDY OF THE DISSOLUTION OF Zr-O ALLOYS IN HYDROFLUORIC ACID

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1962

OSTI ID:4659671

Custead, W G

An investigation was made to ascertain and explain, if possible, the effect of oxygen in the metal on the kinetics and electrochemistry of the reaction of zirconium in hydrofluoric acid solutions. The effect of oxygen on the dissolution rates, activation energies, and dissolution potentials, and the difference effect for zirconium in hydrofluoric acid and hydrofluoric- hydrochloric acid mixtures were determined. The dissolution rates of the alloys were determined in a hydrofluoric acid range of 0.10 to 0.50N and a temperature range of 10 to 50 deg C. The alloy-HF reaction rate decreased with increasing oxygen content. The reaction was first order with respect to the un-ionized HF concentration over the range studied and the reaction order was independent of oxygen content. The activation energy for the reaction increased as the oxygen cortent increased (i.e., from 4.1 plus or minus 0.1 kcal/mole for 1.52% oxygen to 5.2 plus or minus 0.2 kcal/mole for 6.97% oxygen). Additions of hydrochloric acid caused the rates of dissolution of both zirconium and the alloys in hydrofluoric acid to increase greatly whereas the order of the reaction and the activation energies were not altered. The dissolution potentials of the alloys were determined in hydrofluoric acid solutions at 25 deg C. Difference effect measurements on the alloys showed that: anodic currents have a very strong influence on the dissolution reaction, the difference effect is directly proportional to the current density and independent of the hydrofluoric acid concentration but the proportionality constant increases slightiy with oxygen content, hydrochloric acid additions result in an increase in the proportionality constant which relates the difference effect to the current density, there is no noticeable temperature dependency on the proportionality constant in the range 10 to 50 deg C, and anodic currents cause a slight increase in the activation energy of the dissolution reaction. The results of this investigation strongly suggested that the slow step in the dissolution process is the diffusion of un- ionized HF through effective diffusion layers to the metal surface. It was shown that the experimental results could be correlated with the diffusion rate theory supplemented with Langmuir's adsorption theory. A reaction mechanism for the dissolution process was proposed. It was postulated that oxygen in the metal does not effect the hypothesized mechanism; the free or unbound zirconium of the alloy matrix reacted as if there were no oxygen present. (Dissertation Abstr.)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-17-037245
• OSTI ID: 4659671
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ADSORPTION
ANODES
CHEMICAL REACTIONS
CHEMISTRY
CURRENTS
DIFFUSION
ELECTROCHEMISTRY
HYDROCHLORIC ACID
HYDROFLUORIC ACID
OXYGEN
OXYGEN COMPOUNDS
REACTION KINETICS
SOLUBILITY
SOLUTIONS
THERMODYNAMICS
VELOCITY
ZIRCONIUM
ZIRCONIUM ALLOYS