Precursor concentration, variation

As the corrosion rate, inclusive of local-cell corrosion, of a metal is related to electrode potential, usually by means of the Tafel equation and, of course, Faraday s second law of electrolysis, a necessary precursor to corrosion rate calculation is the assessment of electrode potential distribution on each metal in a system. In the absence of significant concentration variations in the electrolyte, a condition certainly satisfied in most practical sea-water systems, the exact prediction of electrode potential distribution at a given time involves the solution of the Laplace equation for the electrostatic potential (P) in the electrolyte at the position given by the three spatial coordinates (x, y, z). 

For catalytic application it is necessary to incorporate hetero-atoms into the silica framework. Several samples have been synthesised using different aluminia precursors. The metal content was determined by X-ray fluorescence analysis, UV-VIS spectra, IR spectra and solid state NMR spectroscopy, respectively. X-ray fluorescence analysis provides information about the metal content of the samples. By variation of the metallic precursor concentration the metal content of the product could be enhanced up to 10 % w/w. 

The textural properties of the hybrid materials are also strongly dependent upon the hydrolysis conditions and the nature of the linker. After hydrolysis in a homogeneous medium, nitrogen adsorption and TEM measurements indicate the formation of non-porous solids with BET specific surface areas lower than 7 m except for 2g. Variation of the precursor concentration does not strongly affect these values. In contrast, hydrolysis under microemulsion conditions leads to a significant increase in the specific surface areas, mainly in the case of the flexible alkylene linker (Table 3.2.5). 

Figure 13-4. Deposition rate variations versus precursor concentration in the atomized solution, for aerosolr-gel deposited Si02 films (a), and MTPS-based hybrid orgmic/inorgmic Si02 films (b). The deposition rate is defined as the ratio of the film thickness, measured after soT-gel transformation, to the aerosol sweeping tune (deposition time). Films were deposited using a horizontalflow (a) and a vertical flow reactor (b).

Concentration of precursor The variation of the concentration may have a significant influence on features of the fermentation process, in particular the on incorporation (Inc), the dilution factor (Dil) and the mass yield of the metabolite. 

Two models have been proposed to explain the variation of the size of the particles with the precursor concentration and with the size of the aqueous droplets. The first is based on the La Mer diagram [16,17], which has been proposed to explain the precipitation in an aqueous medium and thus is not specific to the microemulsion. This diagram (Fig. 2) illustrates the variation of the concentration with time during a precipitation reaction and is based on the principle that the nucleation is the limiting step in the precipitation reaction. In the first step, the concentration increases continuously with increasing time. As the concentration reaches the critical supersaturation value, nucleation occurs. This leads to a decrease of the concentration. Between the concentrations and CIm the nucleation occurs. Later, the decrease of the concentration is due to the growth of the particles by dif-... 

Two of the many products of ethylene radiolysis—methane and propane—show no or only negligible variation with field strength. Methane is produced by a molecular elimination process, as evidenced by the inability of oxygen or nitric oxide to quench its formation even when these additives are present in 65 mole % concentration (34). Propane is completely eliminated by trace amounts of the above scavengers, suggesting methyl and ethyl radicals as precursors ... 

Variation of the content of impurities in the different CNT preparations [21] offers additional challenges in the accurate and consistent assessment of CNT toxicity. As-produced CNTs generally contain high amounts of catalytic metal particles, such as iron and nickel, used as precursors in their synthesis. The cytotoxicity of high concentrations of these metals is well known [35, 36], mainly due to oxidative stress and induction of inflammatory processes generated by catalytic reactions at the metal particle surface [37]. Another very important contaminant is amorphous carbon, which exhibits comparable biological effects to carbon black or relevant ambient air particles. 

There has been considerable variation in the choice of base used. In most cases, hot, concentrated potassium hydroxide gives good results, but sometimes potassium hydroxide in aqueous DMSO, potassium f-butoxide in DMSO or NaH in DMSO is more satisfactory (80TL585). The tercyclic oxetane (50), however, was not formed from the hydroxy-cyclic sulfate precursor under any of these conditions, but use of the amidine base (49) at room temperature produced it in 46% yield (81JOC3144). 

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