Closure to “Discussion of ‘High Temperature Oxidation of Two Zirconium-Tin Alloys’ [M. W. Mallett and W. M. Albrecht (pp. 407–414)]”

Abstract

The oxygen consumed is used up in two processes: (a) solution in the metal, and (b) forination of an oxide fihn. Have the authors any estimate, either experimental or from diffusion calculations, of the amount used in each process? ~I. W. MALLETT AND W. M. ALBRECHT: Calculations based upon diffusion data indicate that about 0.5 1.5% of the total amount of oxygen consumed by a reacted specimen was used up in the diffusion process. Normal variations in rate data are greater than this. In the proposed mechanism, solution of oxygen must occur. However, not all of the dissolved oxygen diffuses into the metal core since much of it is incorporated into the advancing oxide fihn by further oxidation.

On the Defect Structure of ZrO[sub 2] and HfO[sub 2]

“…If intrinsic ionization (Eq. [4]) predominates, the electrical conductivity is independent of oxygen pressure and the concentration of electrons (or electron holes) is given by [e-] = K41/2 [5] 2. If intrinsic ionization is negligible, the electrical conductivity is determined by Eq.…”

“…For HfO2 it is proposed that when the conductivity due to the coupled transport becomes too small, the conductivity due to intrinsic ionization will predominate and the conductivity will become essentially independent of oxygen pressure (Eq. [5]). This behavior is observed for HfOe at Poe < 10-B-10-s atm.…”

“…This is partly due to a lack of knowledge of the relative importance of and interplay between oxygen dissolution in the metal and oxide (ZrO2) formation (1). From various studies (1)(2)(3)(4)(5)(6)(7)(8)(9) it is reasonable to conclude that the ZrO2 layer has a protective effect and that a transport of ions through the scale at least partially determines the rate of oxidation of zirconium.…”

“…From the literature it does not appear that the defect structure of ZrO2 is known. In interpretations of the oxidation mechanism of zirconium this is commonly assumed to involve oxygen vacancies and a corresponding n-type conductivity (4)(5)(6)(7)(8)(9). However, recent studies by Rudolph (10) have shown that the electrical conductivity of ZrO2 is proportional to about Po21/5.'…”

Chemical Engineering Division Quarterly Report for April, May, June 1.56

“…Large temperature gradients existed along the condenser, and it was concluded that the heating was not uniform. Resistance heating was substituted in the last four tests (l6 through 19) in an attempt to provide uniform temperature control. Uniform heating of the condenser was observed up to the time of distillation.…”