Interfacial Electrical Resistance Research Articles

Oxygen Transport in the SOFC Cathode

The impedance of the La0.75Sr0.2MnO3-cathode/electrolyte interface for cathodes with different porosity is measured. The impedance spectra are fitted using a developed model of the oxygen transport at this interface. After the measurements, the cathode is removed from the electrolyte. The contact area and the three-phase boundary length (TPBL) at the interface are estimated from SEM images of the electrolyte surface. The dependence of the interfacial electrical resistance on the microstructure is discussed. It is shown that the bulk diffusion of oxygen vacancies at the interface at 950°C is high enough to use the whole La0.75Sr0.2MnO3/YSZ contact area F for the oxygen transport into the electrolyte for microstructures with 2F/TPBL ≤ 2 μm. The impact of the surface diffusion of oxygen species on polarization resistance at operation temperatures <900°C is discussed. The polarization resistance and the morphology of composite cathodes made from La0.75Sr0.2MnO3/YSZ and yttria- or scandia-stabilized zirconia powders (3YSZ, 8YSZ, 10ScSZ) are investigated by impedance spectroscopy at 800–950°C. The polarization (interfacial) resistance decreases gradually with addition of electrolyte powder in the uLSM cathode material independent of the electrolyte powder used. The interfacial resistance of the uLSM/3YSZ, uLSM/8YSZ, and uLSM/10ScSZ composite cathodes is almost the same. The interaction between uLSM and doped zirconia particles is discussed on the basis of the interfacial resistance, activation energies, and high-frequency impedance.

Diffusion controlled oxygen transport and stability at the perovskite/electrolyte interface

The impedance of the La 0.8Sr 0.2MnO 3 (LSM) cathode/electrolyte interface for cathodes with different porosity was measured. The impedance spectra were fitted using the developed model of the oxygen transport at the La 0.8Sr 0.2MnO 3 cathode/electrolyte interface. Following these measurements, the cathode was removed from the electrolyte. The contact area F and the three-phase boundary length (TPBL) at the interface were estimated from SEM micrographs of the electrolyte surface. The dependence of the interfacial electrical resistance on the microstructure is discussed. It is shown that the bulk diffusion of the oxygen vacancies at the interface at 950 °C is high enough to use the whole La 0.8Sr 0.2MnO 3/YSZ contact area F for the oxygen transport into the electrolyte for microstructures with 2 F/TPBL≤2 μm.

Influence of particulate Al 2O 3 addition on interfacial microstructure and electrical sheet resistance of thick film metallized aluminum nitride substrates

Submicrometer-sized Al 2O 3 powders were three-roll mixed with RuO 2-based resistor paste (Shoei R-2310) in varying weight ratios (5–20 wt.%), followed by thick-film printing the mixtures onto AlN substrates and fired over 850°C in ambient air. Observation of the interfacial microstructure reveals that the addition of Al 2O 3 reduced the formation of interfacial pores pronouncedly; whilst, the film changed toward a porous structure as the powder loading approaches toward 20 wt.%. The electrical resistance of the film was found to increase exponentially with the Al 2O 3 fraction. A critical threshold for the resistance increase was at ∼10 wt.% of the Al 2O 3 fraction.

Transient liquid phase sintering composites: Polymer adhesives with metallurgical bonds

Conductive composites composed of a metallurgically alloyed web with an interpenetrating polymer network have been developed. The metal and polymer networks are simultaneously formed in situ. Bulk as well as interface electrical connections are metallurgically alloyed providing stable conduction. Conventional solder paste dispensing and processing equipment can be utilized. Preliminary analysis of electrical, mechanical and reliability characteristics have been performed. The bulk and interfacial electrical resistance is comparable to solder compounds. Test vehicles pass drop testing with a variety of lead configurations and surface finishes. Electrical characteristics remain consistent both during and following humidity exposure and thermal cycling.

Fabrication of cathode for solid oxide fuel cells using flame assisted vapour deposition technique

Thick films of lanthanum strontium manganese oxide, La 1 − x Sr x MnO 3 (LSM), cathode material for solid oxide fuel cells, was deposited using the flame assisted vapour deposition method, a simple and cost-effective technique. The surface morphology and microstructure of porous cathode films were analysed using scanning electron microscopy. X-ray diffraction indicated the presence of a desirable lanthanum strontium manganese oxide phase at the deposition temperature of 710 °C. The interfacial resistance between the electrode and electrolyte was measured by an AC impedance method. The interfacial electrical resistance was measured to be comparable with existing literature. In addition, the effect of deposition temperatures on the film's microstructure was discussed.

Fundamentals of stick-slip

Simultaneous measurements of momentary friction and electrical resistance using the hoop apparatus have resulted in new insights into the behavior of the ubiquitous thin interfacial films at contact spots. The experimental focus of the present paper is the amplitude of the stick-slip motion of a multifiber slider as a function of the humidity, speed and applied load. The stick-slip amplitude is found to increase with increasing relative humidity and contact spot size, respectively, and to decrease with increasing substrate speed. Furthermore, the interfacial electrical resistance spikes at the beginnings of slip episodes and shows an unexpected hysteresis during stick-slip cycling. The data suggest a two-component model, including (i) an approximate double molecular layer of adsorbed water between the contact spots and (ii) menisci at the periphery of the contact spots at high humidities. Together with the general analysis presented in appendix A, this model presents a framework for the understanding and control of stick-slip in sliding systems.

Teaming measurements of the coefficient of friction and of contact resistance as a tool for the investigation of sliding interfaces

A new apparatus is described which measures the momentary co-efficient of friction and the interfacial electrical resistance of a sample sliding in a rotating hoop under the combined action of friction and gravity. The apparatus is housed under a bell-jar and thus can be used in various ambient atmospheres or vacuum. Preliminary measurements made on a brass sample and on a Ag-graphite sample (75 wt.% Ag), sliding on α-brass, are discussed in terms of the surface film resistivity and number of contact spots as a function of normal force.

Friction, Wear, and Interfacial Electrical Resistance. Part I: The Hoop Apparatus

An apparatus has been developed for the gathering of data from which, through suitable analysis, detailed information on the momentary condition of a sliding interface may be obtained. The information includes the number of the contact spots, the electrical resistivity of the interfacial film, and the flash temperature at the contact spots. The apparatus provides for the continuous simultaneous recording of the coefficient of friction and of the interfacial electrical resistance of a slider in stick-slip motion at constant load and controllable average speed, and/or of the interfacial resistance of a slider at constant speed under controllable load. Loads between 0.3 and 10N and speeds up to 0.15m/s may be selected, in a variety of atmospheres and ambient pressures, as the apparatus is enclosed in a bell jar. It consists of a rotating cylindrical metal hoop inside of which a metal slider moves under the forces of friction and gravity, giving stick-slip behavior full play, and a slider in fixed position subjected to controllable, hydrostatically applied loads. The entire apparatus can be used with a controlled atmosphere or vacuum. The motion of the stick-slip slider, from which the coefficient of friction is inferred, is recorded on one pen of a three-pen strip-chart recorder and the electrical contact resistances between the two sliders and the hoop on the other two pens. The dependence of contact resistance on load, obtainable from the fixed slider without removing the bell jar, permits a determination of the number of contact spots provided the constriction resistance is not negligibly small compared to the film resistance. Deliberate changes of the contact spot temperature can be made by adjusting the current through the slider/hoop interfaces.

High Vacuum Adhesion Test Apparatus

A vacuum apparatus is described to measure the interfacial adhesion of uniaxially loaded metal surfaces. Integral abrasion and ion beam bombardment devices for removing surface contaminant films in vacuum prior to interfacial contact are contained in the system. Measurements of the tensile force to rupture contact weldments in copper showed that the adhesion strength varied with the effectiveness of surface oxide removal and with the applied compressive contact stress and corresponding deformation strain. The interfacial electrical contact resistance was observed to decrease substantially with increasing adhesion.