An investigation of the absorption and the diffusion of gases in palladium metal and zirconium-iron alloy using fluorescent and Moss-bauer techniques

Date

1968

Journal Title

Journal ISSN

Volume Title

Publisher

Abstract

This work investigated the absorption and the diffusion of gases in palladium metal and zirconium-iron alloy using fluorescent and Mossbauer techniques. A hydrogen gas dis.charge experiment demonstrated silver activated ZnS and ZnCdS lumophors were caused to luminesce by the 4.76ev of energy released by each pair of hydrogen atoms recombining at the lumophor's surface. The sensitivity of the detectors required a minimum of 4.6X10[raised 6] atomic hydrogen recombinations/sec at the lumophor's surface. The lumophors were used to search for atomic hydrogen in a hydrogen gas stream after the gas had diffused through a palladium tube. The tube was heated from 90 to 500°C and the pressure on the entrance side varied from one to one and one-half atmospheres. No luminescence was observed indicating that the maximum fraction of atomic hydrogen present was 7.6 X10[raised -9]. The conclusion is that hydrogen desorbed as molecules from the metal surface.Two zirconium-iron alloys, each composed of 25 at.% Fe (.16.9 wt.%) and 75 at. % Zr (83.1 wt.%), were commercially prepared and were identical in all aspects except the duration of annealing. The alloy annealed for 12 hours was denoted A and a l/2"Xl/2" piece cut from A was denoted A-l; the alloy annealed for 6 hours was denoted B. X-ray analysis of A and B revealed that both were comprised of three intermetallic phases, viz., [proportional to] , a hexagonal close-packed structure, [rho] (Zr[lowered 4]Fe), and (Zr[lowered 2]Fe). The measurements also revealed that A possessed a larger amount of the [rho] phase but smaller amounts of the [proportional to] and [Phi] phases than B. This was attributed to the differences in the thermal histories of the two alloys. Comparison of Mossbauer measurements using A-l as an absorber at 4.2, 77, and 298°K with similar measurements or A and B at 298°K indicated each absorber had a fourteen line spectrum. Six of the total fourteen lines corresponded to the [rho] phase and represented a magnetic field H[lowered rho]=-330[plus minus]3 kOe. No appreciable quadrupole interaction or isomer shift relative to iron was observed. The spectra also revealed that the six lines characterizing the [rho] phase was much more intense for A and A-l than for B. Six more lines were deduced from a theoretical, calculated fit to the experimental data of A-l to correspond to the [Phi] phase. This subspectrum represented: a magnetic field H[lowered Phi]=-160±3 kOe, a vertical component of the electric field gradient tensor V[lowered zz]= 7.21X10[rasied 16]statvolts/cm[cubed], an asymmetry parameter [eta]=0.60, and an isomer shift [delta][lowered Phi]=0.0962±0.0392mm/sec. The remaining two lines comprised a quadrupole splitting and corresponded to the [proportional to] phase. The splitting energy [Delta]E[lowered Q]=4.32[plus minus]0.19X10[raised -8]ev and the isomer shift [delat][lowered proportional to]=0.34±0.08mm/sec. The spectra also showed that these two lines were much more intense in B than in A. It was also found that spectra of A-l taken two months after a spectrum of A exhibited peaks about 1.5 times more intense than A. This was attributed to the absorption of oxygen from the atmosphere by A-l. Upon absorption of 7.99 wt.% oxygen, A-l revealed a twenty six line spectrum. Measurements from 4.2 to 873°K were made and indicated a twenty six line spectrum. These lines corresponded to Fe[lowered 3]Olowered 4, Fe[lowered 2]O[lowered 3] (6), the [rho] phase (6), and the [proportional to] phase (2). The measurement at 873°K indicated an average field of -269 kOe. The spectrum at 298°K following the 873°k measurement indicated that only eight lines were present and corresponded to Fe[lowered 2]O[lowered 3] and the phase. Three possible areas of future research are discussed pertaining to the absorption of oxygen, the formation of Fe[lowered 3]O[lowered 4] , and the measurements of single phase alloys.

Description

Keywords

Citation