L. Mendoza Zélis

Tool induced contamination of elemental powders during mechanical milling

Several metallic and semimetallic elements have been submitted to mechanical milling to investigate their contamination with chrome‐steel milling tools. Contamination was followed with 57Fe Mössbauer spectroscopy and X‐ray diffraction. The contamination yield, defined as the number of incorporated Fe moles per gram of sample, was found to be more simply related to the Poisson ratio than to the Young, shear or bulk moduli, or to the enthalpy of mixing of the Fe‐element couple.

Thermal mixing of Al-Fe multilayers

Al-Fe multilayers have been mixed by thermal treatment and their evolution followed by conversion electron Mössbauer spectroscopy. The initial and final states have been characterized by Rutherford backscattering spectrometry. The results are compared with those previously obtained in the ion beam mixing of similar systems.

The magnetic hyperfine field at140Ce in nickel

The hyperfine interaction of140Ce in nickel has been investigated by the time-differential perturbed-angular-correlation technique (TDPAC). The probe was produced by isotope separator implantation of the fission product140Xe, the β- decay chain of which finally populates excited states of140Ce.Different spin rotation spectra were observed before and after an 8 h annealing at 415°C. The analysis of the spectra led to the conclusion that the Ce ions were in the diamagnetic 4+ state. The dominant contributions to the hyperfine interaction are two different magnetic hyperfine fields: |Hhf1|=385±7 kOe and |Hhf2|=276±12 kOe.Hhf1 disappears after annealing. The fraction of nuclei which observeHhf2 is increased by the annealing procedure from 16% to 75%. It is assumed thatHhf1 is the hyperfine field of CeNi in an unperturbed substitutional site andHhf2 is attributed to Ce ions which have trapped a single vacancy.

Kinetic aspects of the solid hydrogenation– disproportionation–desorption–recombination process in Nd13.67Co15.74Al0.77Ga0.27Zr0.03Fe62.2B7.33 alloys

The hydrogenation–disproportionation–desorption–recombination process is known as a novel method for producing permanent magnets. The hydrogen driven reactions involved in this process are carefully studied here using Mossbauer effect, x-ray diffraction and scanning microscopy, in the Nd13.67Co15.74Al0.77Ga0.27Zr0.03Fe62.2B7.33 alloy. The temperature dependence of the hydrogenation disproportionation in the 119 kPa isochore line was obtained. Hydrogen absorption seems to occur in two steps: absorption from Nd at the grain boundaries followed by absorption from the Nd2Fe14B type phase. In order to determine the recombination kinetics, a typical mass of the alloy was submitted to disproportionation reaction at 800 °C under a hydrogen pressure of 119 kPa, followed by recombination, which was achieved by vacuum desorption at 800 °C and subsequent quenching to room temperature after various time intervals. It was found that the relative fraction of the Nd2(Fe,Co)14B phase, as obtained from the Mossbauer effect...

Mechanical alloying of Hf and Fe powders

Pure crystalline Hf and Fe powders were mixed and milled under an argon atmosphere. The evolution of the system with milling time was followed with Mössbauer effect spectroscopy and X-ray diffraction. The results indicate that in the first stages an amorphous Fe-rich alloy was gradually formed together with a solid solution of Hf in Fe beyond the solubility limit.