Ionic species leaching

Release of tetracycUne hydrochloride from PCL fibers was evaluated as a means of controlled administration to periodontal pockets (69). Only small amounts of the drug were released rapidly in vitro or in vivo, and poly(ethylene-co-vinyl acetate) gave superior results. Because Fickian diffusion of an ionic hydrochloride salt in a UpophiUc polymer is unlikely, and because PCL and EVA have essentially identical Fickian permeabilities, we attribute this result to leaching of the charged salt by a mechanism similar to release of proteins from EVA (73). Poly-e-caprolactone pellets have been found unsuitable for the release of methylene blue, another ionic species (74,75). In this case, blending PCL with polyvinyl alcohol (75% hydrolyzed) increased the release rate. 

Fu et al. 02 reported enhanced OSC with Au addition to ceria based on the CO pulsing technique. They were also unable to discern the active state of Au, as both metallic and ionic species were present in XPS measurements after calcination at 400 °C. In a later report, the authors403 removed metallic Au particles by extraction with a 2%NaCN solution and observed that the lightoff curves remained unchanged, with activation energies being virtually identical for the leached materials relative to the materials prior to leaching, 47.8 kJ/mol for deposition-precipitation method... 

During production, ds-diaminedichloroplatinum is released, which could leach through soil. Abiotic or biotic processes can convert this to an ionic species, which could enhance its adsorption to soil, cis-Diaminedichloroplatinum will slowly convert to lra s-diaminedichloroplatinum in water. This form will remain dissolved unless it precipitates to the sediment or is adsorbed to suspended particulates. 

It was also undertaken to identify the ionic species of Pu present. Because of the extreme dilution of the ions (tracer) 1t was not possible to use conventional methods of identification (absorption spectra etc.). On the other hand it was necessary to use this extremely diluted solution because, as pointed out earlier, it most nearly simulates the natural situation. Extremely minute amounts of radionuclides may be leached from a source and somehow find their way through the pores of rocks. 

Anodic passivation of steel surfaces can be efficiently achieved by metal chromates. Chromates of Intermediate solubility (e.g., zinc chromate and strontium chromate) allow a compromise between mobility in the film and leaching from the film to be achieved. Chromates inhibit corrosion in aqueous systems by formation of a passivating oxide film. The effectiveness of chromate inhibitors in aqueous systems depends on the concentration of other ionic species in solution, for example, chloride. Synthetic resin composition can also significantly influence the effectiveness of chromate pigments. The effect appears to be related to the polarity of the resin (20) chromate pigments appear to be less effective in resins of low polarity. 

Lead enters surface water from atmospheric fallout, run-off, or wastewater. Little lead is transferred from natural minerals or leached from soil. Pb ", the stable ionic species of lead, forms complexes of low solubility with major anions in the natural environment such as the hydroxide, carbonate, sulfide, and sulfate ions, which limit solubility. Organolead complexes are formed with humic materials, which maintain lead in a bound form even at low pH. Lead is effectively removed from the water column to the sediment by adsorption to organic matter and clay minerals, precipitation as insoluble salt (the carbonate, sulfate, or sulfide) and reaction with hydrous iron, aluminum, and manganese oxides. Lead does not appear to bioconcentrate significantly in fish but does in some shellfish such as mussels. When released to the atmosphere, lead will generally occur as particulate matter and will be subject to gravitational settling. Transformation to oxides and carbonates may also occur. 

This technique has been illustrated by considerations on the movement of ions in hydrated concrete [32], In this way, the leaching of ionic species and eventually statements concerning the service time of concrete can be obtained. 

The ability of SO2/O2 mixtures to oxidise iron and various other ionic species is well known (5), and a similar process for the reoxidation of ferrous ions during the leaching of copper sulphide minerals has been recently published (6). 

When placed in a physiological medium, bioactive glasses leach Na ions and subsequently also K, 81 +, and SiOH species. These ionic species are replaced with H3O+ ions from the... 

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