On the use of Pd filters on proton conducting SOFC ceramics

Ceramic proton conductors are materials which conduct protons under an applied electric field and permit the construction of a SOFC in analogy to the oxygen ion conductor 8YSZ. Such protonic ceramic fuel cells have been labelled PCFCs to distinguish them from the standard SOFCs. PCFCs have several advantages when compared with standard SOFCs. First, there is no water contamination of the fuel gas. Second, the protonic conductivity may be higher in the intermediate temperature range (550 to 700 °C). Also, the activation energy for proton migration is much lower than that of oxygen ion conduction. In addition, internal reforming is also possible permitting the use of natural gas. An intriguing possibility is the use of palladium filters on the fuel side which only permit the diffusion of protons to the filter-electrolyte interface. This may reduce undesirable mixing of the fuel and the oxygen on either side of the electrolyte. In this work, it is shown that the entry of protons from the Pd into the ceramic conductor is straightforward. Prototype test PCFCs are shown to operate as required. To test the Pd - ceramic proton conductor system a study was undertaken using Pd tubes which were coated with thin layers of the proton conducting ceramics. When flushing the tube insides with hydrogen and exposing the outsides to air, Nernst voltages of such electrochemical cells could be recorded as a function of temperature. The present rather preliminary work, however, was hampered by leakage of the thin film HTPC's. Thus, the theoretical Nernst voltages were not attained. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

On the theory of Boson peak in glasses

A universal mechanism of the Boson peak formation in glasses is proposed. The mechanism is based on the concept of interacting quasilocal oscillators. Even in the case of weak interaction, the low-frequency spectrum becomes unstable. Due to anharmonicity, the system undergoes a transition into a new stable configuration. As a result, below some characteristic frequency ω_c, proportional to the typical strength of interaction, the renormalized density of states becomes a universal function of ω with a Boson peak feature; i.e., the reduced density of states g(ω)/ω² has a maximum at a frequency ω_b?ω_c. We derive an analytic form of this function.     

Phonon density of states of single-wall carbon nanotubes

The vibrational density of states of single-wall carbon nanotubes (SWNT) was obtained from inelastic neutron scattering data from 0 to 225 meV. The spectrum is similar to that of graphite above 40 meV, while intratube features are clearly observed at 22 and 36 meV. An unusual energy dependence below 10 meV is assigned to contributions from intertube modes in the 2D triangular lattice of SWNT bundles, and from intertube coupling to intratube excitations. Good agreement between experiment and a calculated density of states for the SWNT lattice is found over the entire energy range.     

Bestimmung von Rutheniumspuren mit Dithizon Mittels substöchiometrischer Isotopenverdünnungsanalyse

Hexachlororuthenat (III) and the ruthenylion (RuO²⁺) react with dithizone on heating in weak acid water—ethanol solution. The complexes formed can be extracted into chloroform. Based on this reaction, a reproducible, selective determination of ruthenium (20 ppb) is achieved by means of substoichiometric isotope dilution analysis, using¹⁰⁶Ru.     

Phase transitions in metal-hydrogen interstitial alloys by temperature dependent photoacoustic measurements

Phase transitions in metal hydrogen interstitial alloys were investigated by means of the temperature dependent photoacoustic technique. First as well as second order phase transitions were observed. The results are discussed on the basis of the Rosencwaig-Gersho and Korpiun-Tilgner models. We show that the method can be used to study phase diagrams and to gain information on the thermal parameters of the materials involved.     

Zur tribochemischen Umsetzung von Gold und CO2 mit Hilfe radioaktiver Markierung

The formation of carbon and Au₂O₃ under the conditions of mechanical working of Au in a CO₂ atmosphere has been proved by radiochemical and infrared measurements. The free enthalpy of this reaction (90 kcal/g-atom) exceeds the sublimation heat of the Au (72 kcal/g-Atom) and is an example of the high excess energy due to mechanical working. It is concluded that the chemical bonds of the CO₂ molecule are ruptured and the gold atoms are ionized in the triboplasma formed by the mechanical treatment.