PH potential

Thermodynamic data (4) for selected manganese compounds is given ia Table 3 standard electrode potentials are given ia Table 4. A pH—potential diagram for aqueous manganese compounds at 25°C is shown ia Figure 1 (9). 

Figure 8.19 Transient pH, ( -potential and calcium ion concentration in an agitated reactor Jones etal., 1992a)...

Cron, C. J., Payer, J. H. and Staehle, R. W., Dissolution Behaviour of Fe-Fe3C Structures as a Function of pH, Potential and Anion an Electron Microscopic Study , Corrosion, 27, 1 (1971)... 

In contrast with the Pb-HjO system, it can be seen in Figure 4.13 that in the presence of SO " the corrosion zone in the region of low pH no longer exists, owing to the thermodynamic stability of PbSO. The Pb-HjO-COj system has been expressed in a similar pH/potential diagram in which account has been taken of insoluble carbonates and basic carbonates of lead. 

The predictions of the pH/potential diagram are generally fulfilled, but in very concentrated acid solutions, attack may diminish, owing to the relative insolubility of the relevant salt in the acid. Thus, lead nitrate, although soluble in water, has (owing to common ion effect) only slight solubility in concentrated nitric acid, and the corrosion rate is reduced. Similarly, lead chloride is less soluble in moderately concentrated hydrochloric acid than... 

Dissolution kinetics are influenced by pH, potential and the ions present in the test solution, and this forms the basis of selective metallographic etching techniques that have been used for some time . The potentiostat is often used to hold the potential of a multi-phase alloy constant at a level... 

The strength of acids and bases is measured on a pH (potential of hydrogen) scale pH = -logio [H+]... 

The (photo)electrochemical behavior of p-InSe single-crystal vdW surface was studied in 0.5 M H2SO4 and 1.0 M NaOH solutions, in relation to the effect of surface steps on the crystal [183]. The pH-potential diagram was constructed, in order to examine the thermodynamic stability of the InSe crystals (Fig. 5.12). The mechanism of photoelectrochemical hydrogen evolution in 0.5 M H2SO4 and the effect of Pt modification were discussed. A several hundred mV anodic shift of the photocurrent onset potential was observed by depositing Pt on the semiconductor electrode. 

Moorman, J.R. Yee, R Bjomsson, T. Starmer, CF. Grant, A.O. and Strauss, H.C. pKa does not predict pH potentiation of sodium ehannel blockade by lidocaine and W6211 in guinea pig ventricular myocardium. 

Vigorous intravenous hydration with dextrose 5% in water with half-normal saline at 3 L/m2 per day to maintain a urine output of 100 mL/m2 per hour or more is necessary, unless the patient presents with acute renal dysfunction. Alkalinization of the urine to a pH of 7.0 or more with 50 to 100 mEq/L of sodium bicarbonate has been used to promote uric acid solubility for excretion. This measure is controversial because xanthine and hypoxanthine are less soluble at alkaline pH, potentially leading to crystallization, especially during and after allopurinol therapy32 (see Fig. 96-6). Medications that increase serum... 

The results indicate that persistence of organosilicone surfactants in the parent molecule form will be limited on typical soil media and in aqueous environments. Reduced recovery was considered to be a result of abiotic degradation and/or strong sorption processes. Losses were most significant on solid media exhibiting extreme pH values and were also enhanced in the presence of clay substrates. Studies on clays indicated that pH, potential for intercalation and surface charges are important factors in the removal process. 

Fig. 8.1. Field ionization of a hydrogen atom (H). (a) close to a tungsten surface (W), (b) isolated. Conditions and symbols electric field 2 V A Pw image potential of W distorted by the field, Ph potential of the hydrogen atom distorted by the field, X work function, p Fermi level. Broken lines represent potentials in absence of the electric field. Adapted from Ref. [4] by permission. Verlag der Zeitschrift ftir Naturforschung, 1955.

It appears in this discussion that electrochemical parameters and not substrate properties are the main deciding factors in determining the texture of deposits. This is indeed so when a deposit s thickness is 1 pum or more. In case of thinner deposits, the substrate plays an important role as well (see the text above). Another nonelectrochem-ical factor may be the codeposition of particulate matter with some metal deposits. To summarize, we note that texture is influenced mostly by deposition current density, as it is itself a function of bath pH, potential, and other parameters. Not surprising, then, is the fact that in the case of physical vapor deposition (PVD), the deposition rate is the determining factor in setting the texture of the coating. 

Once one has a pH-potential diagram with lines drawn for the MB+ + ne M reaction and for the xA + mH+ + ne yD + zH2 reaction, all one has to do is to draw a line perpendicular to the pH axis at the particular value of pH corresponding to that of the solution (Fig. 12.10). If that line intersects the M"+ + ne M line at a more negative value of potential than the xA + mH+ + ne yD + zH20 line, then a simple conclusion follows. The M + + ne M reaction will tend to run spontaneously in the deelectronation direction and produce M + from M (i.e., dissolution), and the other reaction will tend to proceed spontaneously as an electronation reaction (and thus absorb electrons supplied during the deelectronation of the metal) if a path is provided for the electron flow from the sink for the deelectronation reaction to the source for the electronation reaction. The metal M will be said to tend to corrode spontaneously. 

When the hydrogen ion activity an+ is equal to the acidic function ki, i.e., when the pH is equal to — log ki, the latter quantity being represented by pki, the slope of the pH-potential curve is thus seen to be intermediate between 0.060 and 0.030. Such a slope corresponds, in general, to a point on the first bend of the curve in Fig. 84 the exact position for a slope of 0.045 is o btained by finding the point of intersection of the two lines of slope 0.060 and 0.030, as shown. At this point, therefore, the pH is equal to ph. 

The pH is thus equal to pfe when the slope of the pH-potential curve is midway between 0.030 and zero the value of pfc2 can be found by extending the lines of slopes 0.030 and zero until they intersect, as shown in Fig. 84. An examination of the pH-potential curve thus gives the values of the acidic dissociation functions for the particular hydroquinone as 7.9 and 10.6 for pA i and pA 2, respectively, at 30 . 

The case considered here is relatively simple, but more complex behavior is frequently encountered the reduced form may have more than two stages of acidic dissociation and in addition the oxidized form may exhibit one or more acidic dissociations. There is also the possibility of basic dissociation occurring, but this can be readily treated as equivalent to an acidic ionization (cf. p. 362). The method of treatment given above can, however, be applied to any case, no matter how complex, and the following general rules have been derived which facilitate the analysis of pH-potential curves for oxidation-reduction systems of constant stoichiometric composition. ... 

In the near future we anticipate further progress in ocean acidification as a result of increased atmospheric CO2 concentrations (Caldeira and Wickett, 2003) with sea surface pH potentially reaching as low as 7.8, a decrease of 0.5 pH units since the middle of the 20th century. More extensive periods of stratification and a spreading of oxygen-minimum zones in the world s oceans are also expected. Each of these processes is likely to impact on the oceanic N-cycle and the role cyanobacteria play within these systems. Specifically, these climate induced changes are likely to have significant effects on the composition of marine cyanobacterial communities and hence on the N dynamics they carry out. 

Pourbaix diagrams, or pH-potential diagrams, have been constructed to facilitate the prediction of the various phases (reactions and reaction products) that are stable in an aqueous electrochemical system at equilibrium. " Boundary lines in such diagrams divide the areas of stability for different phases and are derived from the use of Nemst equation... 

Table 4.4 gives the pH and the static mixed potential for each of the NH3 slurries as well as a prediction of the copper stability from the Cu-HjO and Cu-NHj-HjO pH-potential diagrams. 

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