Jeffrey W. Fergus

Lithium Ion Battery Anode Aging Mechanisms

Degradation mechanisms such as lithium plating, growth of the passivated surface film layer on the electrodes and loss of both recyclable lithium ions and electrode material adversely affect the longevity of the lithium ion battery. The anode electrode is very vulnerable to these degradation mechanisms. In this paper, the most common aging mechanisms occurring at the anode during the operation of the lithium battery, as well as some approaches for minimizing the degradation are reviewed.

Review of the effect of alloy composition on the growth rates of scales formed during oxidation of gamma titanium aluminide alloys

One of the important properties in the development of gamma titanium aluminides for high-temperature applications is oxidation resistance. The scales formed during the oxidation of titanium aluminides are generally complex and the specific scale morphology can be strongly influenced by relatively small amounts of alloying additions. This paper includes a compilation of reported oxidation rates for a wide variety of titanium aluminide alloys. This compilation provides a basis for evaluating the variation in oxidation rates among similar alloys as well as reviewing the effect of various alloying additions on the oxidation behavior of gamma titanium aluminum alloys.

Doping and defect association in oxides for use in oxygen sensors

Oxygen sensors provide valuable information for improving the efficiency of, and thus reducing harmful emissions from, combustion processes, such as in internal combustion engines. Oxide materials can be used in different ways to generate an oxygen partial pressure dependent output. The type of sensor in which a particular oxide is used depends on the ionic and electronic defects in the oxide, which can be, to some extent, controlled by doping. In this paper, the issues in selection of an oxide for use in resistive-type, potentiometric-type and amperometric-type oxygen sensors are reviewed. Prototypical examples of materials, specifically titania and zirconia, commonly used in these sensors are discussed to illustrate the effects of doping and defect interaction on the electrolytic and transport properties of oxide materials for use in oxygen sensors.

The application of solid fluoride electrolytes in chemical sensors

Abstract The potential of chemical sensors for improving the quality control and efficiency of industrial processes has resulted in considerable research activity in the development of chemical sensors. Due to the combination of good ionic conductivity with low electronic conductivity, a number of solid metal fluorides are excellent electrolytes and thus have been used in chemical sensors for numerous applications ranging from room temperature oxygen gas sensors to sensors for use in the processing of molten metals. The most studied metal fluorides are those which form the cubic fluorite crystal structure, such as CaF2 and PbF2. However, recent research activity has shown that fluorides which form other crystal structures, such as tysonite (e.g. LaF3) and rutile (e.g. MgF2), have promising applications in chemical sensors. In this paper, the application of solid fluoride electrolytes in chemical sensors will be reviewed.

Attachment of Listeria monocytogenes to an Austenitic Stainless Steel after Welding and Accelerated Corrosion Treatments

Austenitic stainless steels, widely used in food processing, undergo microstructural changes during welding, resulting in three distinctive zones: weld metal, heat-affected zone, and base metal. This research was conducted to determine the attachment of Listeria monocytogenes in these three zones before and after exposure to a corrosive environment. All experiments were done with tungsten inert gas welding of type 304 stainless steel. The four welding treatments were large or small beads with high or low heat. After welding, all surfaces were polished to an equivalent surface finish. A 10-microl droplet of an L. monocytogenes suspension was placed on the test surfaces. After 3 h at 23 degrees C, the surfaces were washed and prepared for scanning electron microscopy, which was used to determine attachment of L. monocytogenes by counting cells remaining on each test surface. In general, bacteria were randomly distributed on each surface type. However, differences in surface area of inoculum due to differences in interfacial energy (as manifested by the contact angle) were apparent and required normalization of bacterial count data. There were no differences (P > 0.05) in numbers of bacteria on the three surface zones. However, after exposure to the corrosive medium, numbers of bacteria on the three zones were higher (P < 0.05) than those on the corresponding zones of noncorroded surfaces. For the corroded surfaces, bacterial counts on the base metal were lower (P < 0.05) than those on heat-affected and weld zones.

Structure and Conductivity of Tetragonal and Rhombohedral Lanthanum Oxyfluoride Compounds

Lanthanum oxyfluoride compounds can form on the electrodes of LaF 3 -based oxygen sensors, so transport through these compounds can affect sensor performance. At high temperatures, lanthanum oxyfluoride forms a cubic fluorite structure, which orders into either a tetragonal or rhombohedral structure during cooling. In this paper, results on the structure and conductivity of lanthanum oxyfluoride (LaO 1 x F 1+2x ) compounds with different ordered structures (tetragonal and rhomhohedral) and compositions (x = 0-0.75) are reported. X-ray powder diffraction results indicate that the value of x in tetragonal LaO 1-x F 1+2x ranges from 0 to 0.43. Impedance spectroscopy results indicate that the minimum conductivity occurs near the stoichiometric LaOF composition (i.e., x = 0), where the fewest anion point defects are present.

The Effect of Transition-Metal Doping on Chromium Deposition at Pt/YSZ Cathode Interfaces

Understanding compositional effects, especially at solid oxide fuel cell operating conditions, is important for the selection of materials that minimize the impact of chromium deposition. In this study, the effect of yttria-stabilized zirconia (YSZ) doping on Cr deposition at a Pt electrode/YSZ electrolyte interface was investigated. A comparison between undoped and doped YSZ electrolyte surfaces after cathodic polarization in moist air at 800 degrees C in the presence of chromia indicated that the presence of Mn, Co, or Fe in the electrolyte significantly promotes Cr deposition at the electrode/electrolyte interface. Electron microscopy of the Co-doped YSZ electrolyte surface after cathodic polarization for 10-45 h clearly showed that with Co doping, the deposition of Cr occurs preferentially at YSZ grain boundaries. Impedance spectroscopy results showed that chromium deposition led to a decrease in resistance with Mn- and Fe-doped YSZ electrolyte, which was attributed to the increase in the three-phase boundary length. However, this beneficial effect of Cr deposition was not observed with Co doping, which may be related to the preferential deposition of chromia at the YSZ grain boundary, resulting in fewer Cr deposits at the cathode/electrolyte interface

Sensors for monitoring the quality of molten aluminum during casting

The quality of a cast product depends directly on the quality of the molten metal from which the product is cast. Techniques for determining melt quality often require the laboratory analysis of samples taken from the molten metal. In addition to reducing processing efficiency, delays associated with this laboratory analysis can lead to uncertainties because the melt conditions can change during holding at high temperatures. On-line monitoring of the melt quality provides more rapid feedback for improved process control. In this article, techniques for monitoring the important aspects of melt quality, specifically chemical composition, gas content, and inclusion content, are reviewed.

Crystal chemistry of neodymium oxyfluoride

Crystallography data reported in the literature for neodymium oxyfluoride has been summarized and analyzed. This analysis shows good agreement among most of the reported results, along with some inconsistent results. Neodymium oxyfluoride forms three crystal structures, all of which are derived from the cubic fluorite structure. There are two forms of stoichiometric NdOF, cubic and rhombohedral. The third crystal structure, tetragonal, forms when excess fluorine, relative to NdOF, is present and has a range of stoichiometry.

Transition Metal Spinel Oxide Coatings for Reducing Chromium Poisoning in SOFCs

The promising metallic alloys for use as interconnects in solid oxide fuel cells form a protective chromia scale during operation. Although chromia has desirable transport properties it can be oxidized to a vapor species, which, after long operation times, can lead to chromia deposition on the cathode and degrade fuel cell performance. One approach to minimizing this chromium poisoning is to apply a ceramic coating to the alloy.