Terry Cole

Performance and impedance studies of thin, porous molybdenum and tungsten electrodes for the alkali metal thermoelectric converter

Columnar, porous, magnetron-sputtered molybdenum and tungsten films show optinum performance as AMTEC electrodes at thicknesses less than 1.0 μm when used with molybdenum or nickel current collector grids. Power densities of 0.40 W cm−2 for 0.5 μm molybdenum films at 1200 K and 0.35 W cm−2 for 0.5 μm tungsten films at 1180 K were obtained at electrode maturity after 40–90 h. Sheet resistances of magnetron sputter deposited films on sodium beta″-alumina solid electrolyte (BASE) substrates were found to increase very steeply as thickness is decreased below about 0.3–0.4 μm. The a.c. impedance data for these electrodes have been interpreted in terms of contributions from the bulk BASE and the porous electrode/BASE interface. Voltage profiles of operating electrodes show that the total electrode area, of electrodes with thickness <2.0 μm, is not utilized efficiently unless a fairly fine (∼1×1mm) current collector grid is employed.

EPR Spectrum of Solid Nitrogen Afterglow at 4.2°K

Because the Rayleigh afterglow induced in nitrogen is of undoubted importance to physics, chemistry, and astrophysics, as well as in studies of the earths atmosphere, it seemed of primary interest to determine whether thermally condensed activated nitrogen would yield an electron paramagnetic resonance (EPR) spectrum. We have recently observed intense EPR spectra in the afterglow solidified at 4.2°K, and they plainly indicate the presence of atomic nitrogen.

High‐field 23Na magnetic resonance studies in beta‐alumina

A study of the 23Na magnetic resonance spectrum (1/2– −1/2 transition) at high magnetic field, 63.4 kG, in a single crystal of beta‐alumina is reported. A comparison of the high‐field rotation spectra obtained at room temperature with previous results obtained in lower magnetic fields allows the extraction of the 23Na chemical shift tensor, the first such tensor measured for an alkali atom. The three principal values for the sodium chemical shift tensor were equal within the experimental error of ±3 or 4 ppm. Linewidth measurements at the high field confirm the suggestions of lifetime broadening of room temperature lines and indicate that by 150 °K second‐order quadrupole broadening controls the linewidth. Measurements at low temperatures produce complex spectra which are interpreted to indicate that motional averaging of the sodium environments is still taking place at 77 °K.