Magnetic properties of Ho2Fe17-xMnx - Influence of Mn substitution
The structural and magnetic properties of Ho2Fe17−xMnx (x=0−5) have been investigated by x-ray diffraction, Mossbauer spectroscopy and DC magnetization measurements (0-5 T) over the temperature range 4.5–350 K. Similar to other ferrimagnetic R2Fe17−xMnx systems, the unit cell volume generally increases with Mn content other than for low Mn values where a slight maximum is detected around x ~ 0.5. The nature of the magnetic phase transitions around TC is shown by Arrot plot analysis to be second order for all samples. The Curie temperature remains essentially unchanged for Mn contents up to x=1.0 (TC = 336 K for x=0.0, TC = 338 K for x=1.0) before decreasing steadily with further increase in Mn content (TC = 209 K for x=5). The 57Fe hyperfine interaction parameters have been determined from variable temperature Mossbauer spectra.
Atomistic simulation for ordered Ho3Fe29−xCrx and disordered Ho2Fe17 intermetallic compounds
The structural properties of intermetallic Ho3Fe29−xCrx have been studied by using ab initio pair potentials obtained by the lattice inversion method. Calculated results show that in Ho3Fe29−xCrx, the order of site preference is 4g(Fe6), 4i(Fe3) and 4i(Fe2), and the calculated lattice constants coincide quite well with experimental values. The evolution process from ordered Ho3Fe29 to disordered Ho2Fe17 (Th2Ni17-type) is evaluated. The structural properties of the disordered Ho2Fe17 compound, including lattice constants and X-ray diffraction have been calculated, and the lattice constants are in good agreement with experiments.
Stability of planar PEMFC in Printed Circuit Board technology
Abstract The use of planar PEMFCs in printed circuit board (PCB) technology with a thickness of less than 3.5 mm are presented. This planar design consists of an open cathode side which allows a completely passive, self-breathing operation of the fuel cell. Power densities of 100 mW/cm 2 at 500 mV with hydrogen as a fuel were achieved. A steady operation with this type of fuel cell was demonstrated over a week without any cell flooding. Since the electrical conducting elements of PCBs usually are made of copper, corrosion in the wet environment of a PEMFC is expected. Thus, a significant degradation in performance of fuel cells made of plain copper PCBs was seen in long-term operation. In order to avoid corrosion, the copper layer has to be coated. Fuel cells in PCB design with diverse coatings were tested in long-term operations up to 1000 h under load. Moreover, corrosion currents have been determined by the use of potentiodynamic scans. Promising coatings are electroplated Cr and Ni and a combination of Ni/Au.