Michael C. H. McKubre

ac Impedance spectroscopy of the anodic film on zirconium in neutral solution

The frequency dependence of the impedance of the anodic film on Zr has been determined using ac impedance spectroscopy. This technique has been used to provide an in situ monitor of the thickness and resistance of the film during formation. The data suggest that the film can be modelled adequately by a parallel RC combination, with an additional series resistance corresponding to the solution resistance. A better fit was obtained using a constant phase element circuit, with a phase angle varying from 84° for thin films to 90° for thicker films. If φ = 84°, the thickness measured by a standard capacitance bridge would be expected to vary by a factor of 1.66 over a frequency range of 0.5–1000 Hz. The inverse of the capacitance (from fits to the parallel RC circuit) was observed to increase linearly with anodic charge for all solutions and charging rates used in this work. The efficiency of film formation calculated from this data was < 100% for charging rates of 0.05 and 0.5 mA cm−2, while it was close to 100% for a charging rate of 5 mA cm−2, in borate and phosphate solutions. The efficiency exceeded 100% in sulphate solution at the high charging rate, presumably due to incorporation of sulphate ions from the electrolyte. The parallel resistence of the anodic film on Zr increased with open circuit exposure time, while the capacitance was unchanged, suggesting that the film is becoming more defect-free, but not thickening during the open circuit exposure. The air-formed film on Zr after the HF etch was about 5 nm in thickness.

Impedance Measurements in Electrochemical Systems

The application of relaxation techniques1 and steady state sinusoidal modulation (“ac impedance,” “ac polarography”) methods2–7 for the investigation of electrochemical phenomena has expanded rapidly over the past two decades. The various methods have been used to ascertain reaction mechanisms, particularly those for electrode processes involving organic reactants, and for the measurement of kinetic parameters (transfer coefficients, exchange current densities, heterogeneous rate constants, etc.). The techniques have also proved valuable for the investigation of metal dissolution and passivation phenomena. A review of the application of these techniques in corrosion science was recently published by Macdonald and McKubre.7 The principal advantage of the frequency domain sinusoidal modulation techniques is that processes which exhibit a wide range of relaxation times are accessible in a single experiment. It is important to note, however, that the time domain “relaxation” or “transient” techniques and the frequency domain methods in principle yield the same information and that both can be used to define the interfacial impedance.

NEW PHYSICAL EFFECTS IN METAL DEUTERIDES

Following the initial claims of 1989, the body of research on anomalous effects in metal deuterides has grown to include thousands of papers on a wide spectrum of topics. DoE, to facilitate their review of this set of research, has asked for the preparation of the following summary. The entire body of research is not addressed. Rather, a subset of research from two areas is presented: selected issues associated with excess heat production in deuterated metals, and a brief discussion of some aspects of nuclear emissions from deuterated metals.

Isothermal flow calorimetric investigations of the D/Pd and H/Pd systems

Abstract Isothermal calorimetric studies of the D/Pd and H/Pd systems have been carried out at high deuterium (hydrogen) loadings (i.e. [D(H)]/[Pd] > 0.9) at approximately 30°C. Under these conditions, the generation of “excess power” was observed in a series of deuterium-based experiments, but not in a hydrogen-based experiment. The results of these experiments enable several (tentative) conclusions to be reached concerning the conditions necessary for the reproducible observation of this anomalous thermal effect.

Temperature coefficient of resistivity at compositions approaching PdH

Abstract Measurements have been made of the temperature coefficient of resistivity, λ , versus hydrogen concentration, H/Pd, at very high concentrations in the Pd–H system. Unusually high hydrogen compositions were achieved using an electrochemical loading procedure which allowed stable Pd–H systems to be obtained. It is well known that increasing the H/Pd concentrations leads to three different phases ( α , α + β , β ), respectively, in the Pd–H system; the β phase is thought to end in an asymptotic limit. Possible evidence that a new phase ( γ ) exists, bordering the β phase at compositions H/Pd > 0.9 is reported and discussed.

Search for 3He and 4He in Arata-Style Palladium Cathodes II: Evidence for Tritium Production

Abstract Measurements have been made of 3He, 4He, and 3H in a sample containing 2.7% of the gas from the interior of an Arata-style hollow palladium electrode charged with ~5 g Pd-black that had undergone electrolysis in D2O as a cathode for 90 days and then as an anode for a further 83 days. There is no evidence for the much larger amounts of 4He observed by Arata and Zhang in similar experiments. However, a very large concentration has been found of 3He, 2.3 ± 0.5 × 1012 atoms/cm3 standard temperature and pressure that apparently can all be attributed to the decay of tritium produced during electrolysis. No direct production of 3He can be specified, a result that is also different from the conclusions of Arata and Zhang. The 3He and tritium measurements and the results of a gas analysis using a Finnigan-type mass spectrometer show that at the end of the anodic electrolysis, the electrode void contained 5.8 ± 0.7 × 1013 atoms tritium in the gas phase as HT, DT, and T2, and 1.7 ± 0.3 × 1015 atoms tritium in the aqueous phase as HTO, DTO, and T2O. At this stage, the gas phase pressure was ~18.8 atm in a free volume of 0.6 cm3, and the total mass of water was ~5.7 mg. The gas phase tritium value is viewed as a lower limit for gaseous tritium produced inside the electrode because some of that tritium must have been removed into the D2O electrolyte during the anodic episode. The 3He and 4He measurements were also made in the two samples of the Pd-black and in sections cut from the walls of both Pd electrodes. The H2O electrolyzed samples did not show any evidence of unusually high 3He and/or 4He, but all the D2O electrolyzed samples showed clear evidence of 3He from tritium decay. A stepwise temperature heating experiment performed with a 24.9-mg sample of the D2O Pd-black showed that the diffusion process for 3He can be described by an equation of the form D = D0 exp(-U/kT) with an activation energy U of 1.1 eV. It is also apparent that the 3He from tritium is quantitatively retained in the Pd-black at room temperature.

Electrochemical measurements on metal oxide electrodes—II. Impedance measurements on Nb-doped single crystal TiO2

Abstract Mott—Schottky plots were measured on single crystal Nb-doped TiO 2 in aqueous buffer solutions and KCl electrolytes of concentration between 1 M and 10 −4 M KCl. The influence of surface pretreatment, nature of the dopant and solution conductivity on the Mott—Schottky plots was examined. The surface pretreatment was found to affect the frequency dispersion of the Mott—Schottky plots. Analyses of published data and results from the present study suggest that the point of zero charge of differently doped TiO 2 samples influences the flatband potential. The impedance measurements in KCl electrolytes showed that the flatband potential of single crystal Nb-doped TiO 2 could be determined in low conductivity electrolytes such as 10 −3 M KCl.

A new look at low-energy nuclear reaction (LENR) research: a response to Shanahan

In his criticisms of the review article on LENR by Krivit and Marwan, Shanahan has raised a number of issues in the areas of calorimetry, heat after death, elemental transmutation, energetic particle detection using CR-39, and the temporal correlation between heat and helium-4. These issues are addressed by the researchers who conducted the original work discussed in the Krivit and Marwan (K&M) review paper.

The effect of ultrasound on the electrochemical loading of hydrogen in palladium

Although the application of ultrasound for the control and modulation of various chemical processes is a subject of continued interest [l], there is surprisingly little discus- sion in the recent literature of the effects of ultrasound on fundamental electrochemical processes. In early systematic studies of the hydrogen evolution reaction under acidic conditions [2,3], it was observed that, on a platinum elec- trode, the overvoltage for hydrogen evolution decreased by up to 30mV on the application of ultrasound, and that this decrease was largely independent of current density in the approximate range l-100 mA cm-‘, i.e. the Tafel slope was largely unaffected under these conditions. On removal of the ultrasound, the original polarization was regained only on continued electrolysis for up to 1 h. These results refer to electrolytes which had been pre-electrolysed for 10 to 20h. With more extensive pre-electrolysis (36h), the results were generally similar; however, the polarization decrease on the application of ultrasound was smaller (by a factor of two) under comparable conditions, and the origi- nal polarization was recovered rapidly on cessation of irradiation. On the application of ultrasound to a nickel electrode evolving hydrogen, the same general phe- nomenon was observed, i.e. a decrease in overvoltage without a significant change in Tafel slope [3]. For these experiments, the acoustic frequency was 3OOkHz and the ;icoustic intensity was estimated to be approximately I Wcmw2 of electrode area.

The Electrochemical Impedance of the Na/S Cell I . Experiments and Results

We have carried out a number of experiments to characterize some electrochemical properties of a Na/S cell. They were: measurements of the cell EMF, cell voltage and current on charge and discharge, both at constant current and with stepped currents; cell impedance from 0.5 mHz to 10 kHz; and measurements of the relaxation of the open-circuit voltage. At the onset of the single phase region in the sulfur electrode, the cell impedance from 5 to 0.5 mHz rises to a maximum due to the onset of a diffusion controlled process. The measurements of cell voltage and current confirm this experimental result