Potential sources of error in the use of FTIR to measure the level of oxidation in ultrahigh molecular weight polyethylene acetabular cups were evaluated using cups from a hip simulator wear study with and without artificial aging, as well as cups retrieved from clinically failed hip prostheses. Oxidation was measured as a function of depth below the bearing surface using transmission FTIR on microtomed sections of the cups. To account for the variation of the thickness of the microtomed sections, oxidation was plotted as the ratio of the absorbance of the carbonyl groups to the absorbance of a reference band at 2022 cm-1. Overnight soaking in hexane reduced the apparent levels of oxidation, presumably due to the extraction of absorbed contaminants. In cups with low to moderate levels of oxidation, the reference absorption was relatively independent of the level of oxidation and was linearly proportional to the thickness of the specimens, providing reproducible oxidation ratios. However, the scatter in the reference absorption and in the apparent oxidation ratio increased with increasing levels of oxidation and was greatest for the thickest (400 microm) microtomed sections. The profiles of the oxidation ratios for a given specimen that were plotted by the present study method could be numerically adjusted to coincide with the ratios plotted using the methods of two previous investigators, providing conversion factors that are useful for comparing results among the studies.
Herein, we describe the fabrication of LiCoO2 thin films by high-frequency (27.12 MHz) magnetron sputtering and investigate the effects of sputtering power and Ar/O2 ratio on their morphological and electrochemical properties. Films produced at higher sputtering powers and O2 proportions are shown to exhibit increased porosity and a greater number of surface active sites. The discharge capacity of the film prepared at a sputtering power of 180 W and an Ar/O2 ratio of 1/2 is determined as 22.894 μAh μm–1 cm–2 using half-cell electrochemical testing at 0.2 C for 20 charge–discharge cycles, and ∼90% of the 0.2 C discharge capacity is retained at 1.5 C. Finally, we compare films deposited at 27.12 MHz with those deposited at 13.56 MHz, showing that the former feature the advantages of higher deposition rate and increased surface porosity, which results in excellent electrochemical performance and good rate capability.
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