Potential determining

Fig. V-3. Schematic representation of (a) the Stem layer (b) the potential-determining ions at an oxide interface (c) the potential-determining and Stem layers together.

The f potential of silver iodide can be varied over the range 75 mV, by varying the Ag or 1 concentration again demonstrating that varying the concentration of potential-determining ions can reverse the sign of the f potential. 

These effects can be illustrated more quantitatively. The drop in the magnitude of the potential of mica with increasing salt is illustrated in Fig. V-7 here yp is reduced in the immobile layer by ion adsorption and specific ion effects are evident. In Fig. V-8, the pH is potential determining and alters the electrophoretic mobility. Carbon blacks are industrially important materials having various acid-base surface impurities depending on their source and heat treatment. 

Material Potential-Determining Ion Point of Zero Charge... 

Table XI-1 (from Ref. 166) lists the potential-determining ion and its concentration giving zero charge on the mineral. There is a large family of minerals for which hydrogen (or hydroxide) ion is potential determining—oxides, silicates, phosphates, carbonates, and so on. For these, adsorption of surfactant ions is highly pH-dependent. An example is shown in Fig. XI-14. This type of behavior has important applications in flotation and is discussed further in Section XIII-4.

In addition to the collector, polyvalent ions may show sufficiently strong adsorption on oxide, sulfide, and other minerals to act as potential-determining ions (see Ref. 98). Judicious addition of various salts, then, as well as pH control, can permit a considerable amount of selectivity. 

Electroless plating rates ate affected by the rate of reduction of the dissolved reducing agent and the dissolved metal ion which diffuse to the catalytic surface of the object being plated. When an initial continuous metal film is deposited, the whole surface is at one potential determined by the mixed potential of the system (17). The current density is the same everywhere on the surface as long as flow and diffusion are unrestricted so the metal... 

A.STM.B764, Std. Methodfor Simultaneous Thickness and Electrochemical Potential determination of Individual Eayers in Multi-layer Mickel deposit (STEP test), American Society for Testing and Materials, Philadelphia, Pa., 1986. 

Although the [100] data are quite limited, the shear deformation potential determined is the only measurement for this valley in germanium. At atmospheric pressure and small strains the (100) valley minimum is well above the (111) valley minima and not accessible for measurement. In the present... 

The results for the chemical potential determination are collected in Table 1 [172]. The nonreactive parts of the system contain a single-component hard-sphere fluid and the excess chemical potential is evaluated by using the test particle method. Evidently, the quantity should agree well with the value from the Carnahan-Starling equation of state [113]... 

Emission spectra have been recorded for four aryl-substituted isoindoles rmder conditions of electrochemical stimulation. Electrochemiluminescence, which was easily visible in daylight, was measured at a concentration of 2-10 mM of emitter in V jV-dimethylformamide with platinum electrodes. Emission spectra due to electrochemi-luminescence and to fluorescence were found to be identical, and quantum yields for fluorescence were obtained by irradiation with a calibrated Hght source. Values are given in Table X. As with peak potentials determined by cyclic voltammetry, the results of luminescence studies are interpreted in terms of radical ion intermediates. ... 

In 3% sodium chloride solution at 60°C the austenitic irons again show superior characteristics to the ferritic. The breakdown potentials determined in this environment, which provide a relative measure of the resistance to attack in neutral chloride solutions, are generally more noble for the austenitic irons than for the ferritic (Table 3.47). This indicates that the austenitic irons should show better corrosion resistance in such environments. 

At the start the cathode is invariably a metal different from that to be deposited. Frequently, the aim is to coat a base metal with a more noble one, but it may not be possible to do this in one step. When a metal is immersed in a plating bath it will corrode unless its potential is sufficiently low to suppress its ionisation. Fortunately, a low rate of corrosion is tolerable for a brief initial period. There are cases where even when a cathode is being plated at a high cathodic (nett) current density, the substrate continues to corrode rapidly because the potential (determined by the metal deposited) is too high. No satisfactory coating forms if the substrate dissolves at a high rate concurrently with electrodeposition. This problem can be overcome by one or more of the following procedures ... 

It must be emphasised that standard electrode potential values relate to an equilibrium condition between the metal electrode and the solution. Potentials determined under, or calculated for, such conditions are often referred to as reversible electrode potentials , and it must be remembered that the Nernst equation is only strictly applicable under such conditions. 

Standard potentials are determined with full consideration of activity effects, and are really limiting values. They are rarely, if ever, observed directly in a potentiometric measurement. In practice, measured potentials determined under defined concentration conditions (formal potentials) are very useful for predicting the possibilities of redox processes. Further details are given in Section 10.90. 

If a controlled-potential determination is to be carried out, additional equipment will be required, namely an electronic voltmeter, a potentiostat and a reference electrode. The latter is most commonly a saturated calomel electrode, the construction of which is described in Chapter 14. 

Some examples of controlled cathode potential determinations are shown in Table 12.3. 

The SAH water potential determines many aspects of their behavior in the soil. The processes of water redistribution in the soil, its transport to the plant roots, and assimilation follow the osmotic laws and are regulated by the thermodynamic potential. 

Pitting potential, determination of, 258 Pit-patent formation, flow chart to compute, 298 Platinum Clavilier, 135... 

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