Zirconium Sites Research Articles

Hydrogen sorption properties of non-stoichiometric ZrMn 2-based systems

Hydrogen sorption by several non-stoichiometric ZrMn 2-based alloys was studied at pressures up to 50 atm and over a temperature range from 23 to about 200°C. The dissociation pressure of the hydrides is raised by a factor of 500–1000 for ZrMn 2T 0.8 or ZrMn 2T 1.2 (T ≡; transition element or Cu) as the host material compared with that for ZrMn 2 as the host material. Among the hydrides studied, ZrMn 2Co 0.8-H exhibited the highest value for the plateau pressure. Measurements of the experimental densities of the non-stoichiometric host materials show good agreement with the substitutional model in which manganese and/or T partially replace zirconium at the zirconium sites. The hydrides have remarkably low heats of formation and entropies of 12–19 kJ (mol H 2) −1 and 50–80 J (mol H 2) −1 K −1 respectively. The hydrogen absorption or desorption is extremely rapid, e.g. 90% of the hydrogen was released or absorbed in about 1 min. The hydrides studied exhibit features which strongly suggest that they have technological potential.

The hyperstoichiometric ZrMn1 + xFe1 + y− H2 system I: Hydrogen storage characteristics

The ZrMn 1 + x Fe 1 + y −H 2 systems with x, y = 0.11-0.53 and x + y ⩽ 0.64 were studied as a function of composition, temperature (0–200 °C) and hydrogen dissociation pressure (0.01–50 atm). The hyperstoichiometric manganese and iron appear to substitute at the zirconium sites with a net effect of raising the vapor pressure of their hydrides to 500–1500 times that of ZrMn 2 hydride. The ZrMn 1.27Fe 1.58 alloy does not absorb measurable quantities of hydrogen, presumably because of the very high vapor pressure of its hypothetical hydride. The hydrides of ZrMn 1.22Fe 1.11 and ZrMn 1.11Fe 1.22 alloys have dissociation pressures in the range of 1–2 atm at room temperature. The hydrogen capacities of these alloys are quite high, e.g. about 185 cm 3 g −1. Enthalpies and entropies of dehydrogenation, obtained from a van't Hoff plot of ln p H 2 versus 1/ T, are very low, being 9.8–13.4 kJ (mol H 2) −1 and 42–53 J (mol H 2) −1 K −1 respectively. The kinetics of hydrogen absorption and desorption are extremely fast.

Hyperfine magnetic fields at181Ta nuclei in ZrZn2containing Ti and Hf

The hyperfine magnetic field at 181Ta nuclei at the zirconium sites in ferromagnetic ZrZn2 was measured by the method of time-differential perturbed angular correlations at 4.2K. The value obtained was -17.3+or-0.3 kOe. The field was also measured as a function of the concentration of hafnium and titanium substituting at the zirconium sites and compared with magnetization measurements on the same samples. The rate of change of hyperfine field with concentration is not as great as that of the magnetization.

The effect of fast-neutron irradiation on Zr4Al3

The effect of fast-neutron radiation on the structure of Zr4Al3 has been studied using X-ray diffractometry. The changes in line intensity are explained by the disordering caused by the replacement of 0.5 atom in zirconium sites by aluminum. The anisotropic changes in the size of the unit cell can be partially explained by the geometrical changes produced by the disordering of atoms of unequal size.

Electron paramagnetic resonance or rare earth ions in calcia stabilized zirconia: Gd3+and Yb3+

The paramagnetic resonance spectra of Gd3+ and Yb3+ in annealed single crystals of calcia stabilized zirconia have been investigated in the X band. In both cases, sites of almost cubic symmetry with a weak axial deformation, the principal axis of which is directed along a (100) direction, were observed. Hyperfine structure for the two odd isotopes was resolved with A171=2701+or-10 MHz and A173=738+or-10 MHz. The authors results support the conclusions of Carter and Roth concerning the existence of a disorder-order transformation of calcia stabilized zirconia by annealing at 1000 degrees C, and confirm the ordered arrangement they proposed for the O2- ions around the zirconium sites. The atomic arrangement and the presence of Ca2+ ions and oxygen vacancies near the defects can account for the anomalous linewidths observed.