Reduction and reoxidation kinetics of Ni-based solid oxide fuel cell ͑SOFC͒ anodes were investigated over a range of temperatures between 600 and 800°C. Dense ͑no open porosity͒ two-phase NiO + YSZ ͑yttria-stabilized zirconia͒ samples, with and without small amounts of oxide additives ͑CaO, MgO, TiO 2 ͒, were fabricated and then reduced in a hydrogen-containing environment. The time dependence of the reduced layer thickness at various temperatures was measured. Reoxidation studies were conducted on fully reduced anodes that were subsequently reoxidized in air over a temperature range between 650 and 800°C. A simple theoretical model was developed to describe the kinetics of reduction and reoxidation based on two series kinetic steps: diffusion and interface reaction. It was observed that the reduction kinetics was linear ͑interface-controlled͒, while the reoxidation kinetics was nearly parabolic ͑diffusion-controlled͒. Also, the kinetics of reduction was thermally activated with an activation energy of ϳ95 kJ/mol. By contrast, over the temperature range investigated, the kinetics of reoxidation was essentially independent of temperature. The interface control of the reduction process implies that gas-phase diffusion through porous Ni + YSZ, formed upon reduction of NiO to Ni, is considerably faster than the kinetics of the actual reduction reaction occurring at the interface separating the pristine and the reduced regions. By contrast, diffusion control of the reoxidation process was attributed to slow, gaseous diffusion on account of the very small amount of porosity that remains when Ni reoxidizes to NiO, developed presumably due to a slight shape change of Ni particles that may occur at high temperatures. Doping the anodes with stable oxides, such as CaO and MgO, significantly reduced both the reduction and reoxidation kinetics of Ni-based anodes.

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Damage to hard bearing surfaces of total joint replacement components typically includes both thin discrete scratches and broader areas of more diffuse scraping. Traditional surface metrology parameters such as average roughness (R a) or peak asperity height (R p) are not well suited to quantifying those counterface damage features in a manner allowing their incorporation into models predictive of polyethylene wear. A diffused lighting technique, which had been previously developed to visualize these microscopic damage features on a global implant level, also allows damaged regions to be automatically segmented. These global-level segmentations in turn provide a basis for performing high-resolution optical profilometry (OP) areal scans, to quantify the microscopic-level damage features. Algorithms are here reported by means of which those imaged damage features can be encoded for input into finite element (FE) wear simulations. A series of retrieved clinically failed implant femoral heads analyzed in this manner exhibited a wide range of numbers and severity of damage features. Illustrative results from corresponding polyethylene wear computations are also presented.