PubMed · 15633823
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Ginny Jorgensen, Charles John Palenik. 2004. Preparing instruments for sterilization.. https://pubmed.ncbi.nlm.nih.gov/15633823/
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This study investigated the surface characterizations and corrosion resistance of as-received commercial nickel-titanium (NiTi) dental orthodontic archwires from different manufacturers using a cyclic potentiodynamic test in artificial saliva with various acidities. An atomic force microscope was used to evaluate the surface topography of the NiTi wires. The surface chemical analysis of the passive film on the NiTi wires was characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy. A scanning electron microscope, together with an energy-dispersive spectrometer, was used to analyze the surface characterizations of the NiTi wires before and after the corrosion tests. Two-way analysis of variance was used to analyze the corrosion-resistance parameters with the factors of wire manufacturer and solution pH. The results showed that the surface structure of the passive film on the tested NiTi wires were identical, containing mainly TiO2, with small amounts of NiO. A different surface topography was observed on the NiTi wires from various manufacturers. The corrosion tests showed that both the wire manufacturer and solution pH had a statistically significant influence on the corrosion potential, corrosion rate, passive current, breakdown potential, and crevice-corrosion susceptibility. The difference in the corrosion resistance among these NiTi dental orthodontic archwires did not correspond with the surface roughness and pre-existing defects.
Recent strategies to reduce elevated nitrate concentrations employ metallic Fe0 as a reductant. Secondary products of Fe0 corrosion include magnetite (Fe3O4), green rust [Fe6(OH)12SO4], and wüstite [FeO(s)]. To our knowledge, no studies have been reported on the reactivity of NO3- with FeO(s). This project was initiated to evaluate the reactivity of FeO(s) with NO3- under abiotic conditions. Stirred batch reactions were performed in an anaerobic chamber over a range of pH values (5.45, 6.45, and 7.45), initial FeO(s) concentrations (1, 5, and 10 g L(-1)), initial NO3- concentrations (1, 10, and 15 mM), and temperatures (3, 21, 31, and 41 degrees C) for kinetic and thermodynamic determinations. Suspensions were periodically removed and filtered to measure dissolved nitrogen and iron species. Solid phases were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Nitrate reduction by FeO was rapid and characterized by nearly stoichiometric conversion of NO3- to NH4+. Transient NO2- formation also occurred. The XRD and SEM results indicated the formation of Fe3O4 as a reaction product of the heterogeneous redox reaction. Kinetics of NO3- reduction suggested a rate equation of the type: -d[NO3-]/dt = k[FeO]0.57[H]0.22[NO3-]1.12 where k = 3.46 x 10(-3) +/- 0.38 x 10(-3) M(-1) s(-1), at 25 degrees C. Arrhenius and Eyring plots indicate that the reaction is surface chemical-controlled and proceeds by an associative mechanism involving a step where both NO3- and FeO(s) bind together in an intermediate complex.
We investigated the spatial distribution and speciation of Pb in the weathering crust and soil surrounding corroding metallic Pb bullets in a shooting range soil. The soil had a neutral pH, loamy texture, and was highly contaminated with Pb, with total Pb concentrations in the surface soil up to 68 000 mg kg(-1). Undisturbed soil samples containing corroding bullets were collected and embedded in resin, and polished sections were prepared for micro-X-ray fluorescence (micro-XRF) elemental mapping and micro-X-ray absorption near edge structure (micro-XANES) spectroscopy. Bullet weathering crust material was separated from the metallic Pb cores and analyzed by powder X-ray diffraction analysis. Our results show a steep decrease in total Pb concentrations from the bullet weathering crust into the surrounding soil matrix. The weathering crust consisted of a mixture of litharge [alpha-PbO], hydrocerussite [Pb3(CO3)2-(OH)2], and cerussite [PbCO3], with litharge dominating near the metallic Pb core and cerussite dominating in the outer crust, which is in contact with the soil matrix. On the basis of these results and thermodynamic considerations, we propose that the transition of Pb species after oxidation of Pb(O) to Pb(II) follows the sequence litharge --> hydrocerussite --> cerussite. Consequently, the solubility of cerussite limits the activity of Pb2+ in the soil solution in contact with weathering bullets to < or =1.28 x 10(-6) at pH 7, assuming that the CO2 partial pressure (PCO2) in the soil is equal or larger than in the atmosphere (PCO2 > or = 0.000 35 atm).