Costandy S. Saba

Oxidative stability and degradation mechanism of a cyclotriphosphazene lubricant.

Chromatographic and spectroscopic techniques were used to investigate the degradation products from bulk oxidative and thermal stability testing of a substituted tricyclophosphazene high-temperature lubricant. Analytical investigation into the degraded lubricant revealed oligomerization to be the dominant mode of degradation, resulting in most of the observed viscosity increases. GC/MS, FT-IR, and (31)P NMR data confirmed the existence of a cyclotetramer structure in the degraded fluid, while GPC analysis indicated the possibility of a much smaller amount of higher oligomers. The poor reproducibility observed for the oxidation results is likely due to the influence of trace contaminants or the relative degree of retention of ionizable volatile products that could act as oligomerization catalysts.

Determination of Wear Metals in Aircraft Lubricating Oils by Atomic Absorption Spectrophotometry Using a Graphite Furnace Atomizer

Atomic absorption spectrophotometry equipped with a graphite furnace atomizer has proven to be a very effective technique for determining iron, copper, aluminum, magnesium, and other critical wear metals in lubricating oils. Oil samples are diluted 1:4 with kerosene, and 0.5–20 μL can be analyzed by direct injection into the furnace. Analytical conditions have been established for 10 wear metals. Working curves, times, and temperatures for drying, ashing, and atomizing cycles have been determined. Precision of analysis was determined for standards (dissolved) and samples containing metallic particles (undissolved). The RSDs for 10 runs of 3 ppm Fe, 1 ppm Cu, and 1 ppm Al were 10.0, 4.0, and 3.9 percent, respectively. Metal powders of Fe, Cu, and Al having maximum sizes of 5, 10, and 20–30 μm were analyzed and precisions determined. Comparative analytical results were obtained for Fe particles of 1, 3, 5, 8, 10, 12, and 20–30 μm with the use of various spectrometric techniques. The graphite furnace was shown to be superior to ICP, DCP, flame AA, and rotating disk AES. In the analysis of used oil samples, the graphite furnace gave better precision and analyzability for Fe and Cu than the other instruments considered.

Temperature-resolved molecular emission spectroscopy: an analytical technique for solid materials.

Temperature-resolved molecular emission spectroscopy is described as a thermal analysis method for the analysis of solids and liquids. The technique uses an electrically heated graphite cup to decompose and/or vaporize the sample. The vapors are carried by a stream of argon into a cool hydrogen diffusion flame. Both the quantity and the nature of the decomposed species can be determined. The technique is particularly useful for the determination of sulfur, phosphorus, or nitrogen. Calibration curves for sulfur show the expected parabolic shape, and those for phosphorus are linear. The detection limit for elemental sulfur was determined to be approximately 50 ng. The evolution of sulfur is shown to be related to the decomposition temperature which is characteristic of the sulfur-containing species. Reproducibility of the decomposition temperatures is typically ±2%.