Cathode effect

The cathodic effectiveness of the passive steel in cement mortar can be seen in Fig. 5-13. The cell current is measured between a mortar-coated DN 100 pipe section and an uncoated steel ring 16 mm broad as anode. It can be clearly seen that the cell current immediately falls and after 100 days goes toward zero. The same result is obtained by removing the specimens and aerating the mortar coating and repeating the experiment with the same components [51]. 

Enamel coatings are used for the internal protection of storage tanks that in most cases have built-in components (e.g., fittings with exits, probes, temperature detectors) that usually exhibit cathodic effectivity. These constitute a considerable danger of pitting corrosion at small pores in the enamel. Corrosion protection is achieved by additional cathodic protection which neutralizes the effectiveness of the cathodic objects. 

The anode is usually soluble, and is made from a high purity form of the metal being deposited, or occasionally from an alloy. A soluble anode is often the cheapest and most convenient means of replacing the metal reduced at the cathode. Effective anode corrosion is important, and different examples present a variety of types of dissolution. 

Neutron imaging Two-dimensional H20 (liquid) Relatively high resolution technique, real-time data, applicable to typical fuel cell designs Need a powerful neutron source, very difficult to separate anode/cathode effects... 

A corrosion-inhibiting admixture is a chemical compound which, when added in small concentrations to concrete or mortar, effectively checks or retards corrosion. These admixtures can be grouped into three broad classes, anodic, cathodic and mixed, depending on whether they interfere with the corrosion reaction preferentially at the anodic or cathodic sites or whether both are involved [48], Six types of mechanisms, viz. anodic (oxidizing passivators), anodic (non-oxidizing passivators), cathodic, precipitation (anodic and cathodic effects), oxygen... 

By combining the information from Erg. 2 with that obtained from the cathodic effect shown in Fig. 1, the efficiency of ft.q2 photoproduction ( tH202) via the electroreduction of photogenerated oxygen can be estimated. H2°2 can be defined as the ratio between the H202 generation ratr-w —ding to [2] and the... 

Cheng, H., Scott, K. and Christensen, P. A. (2004d) Influence of reactor design on electrochemical hydrodehalogenation of 2, 4-dibromophenol in a paraffin oil - cathode effect. Environ. Sci. 

Electrorefining — Electrolytic process aimed at the purification of a metal (M). Impure metal anodes are elec-trochemically dissolved in a suitable electrolyte (solution of a M salt) to form ions of the desired element, which are reduced at the cathodes, effecting a selective deposition of M with high purity. Depending on its nature, the anode impurities are left as anodic slimes (collected from the bottom of the electrolytic cell) or as ions in the electrolyte (continuously bled to a purification circuit). This performance can be easily understood by noting that the elements with higher reduction potential than M will not undergo oxidation and thus are re-... 

The hollow-cathode plume (HCP) [137] makes rather different use of the hollow-cathode effect. The hollow-cathode base is a sample disc with a 1-2 mm orifice. By choosing appropriate gas pressures and discharge currents, the energetic plume is ejected through the orifice. A constricted hollow-cathode discharge localized in the narrow orifice creates intense sputter action on the surface of the disc and causes direct transport of the atoms into the plume for excitation — and ionization, if required. 

This decrease may not occur in the case of structures subjected to wetting/ drying cycles or in conditions where oxygen consumed at the surface of the passive steel is replaced. This may happen in hollow piles of offshore structures, as depicted in Figure 8.2. Similar conditions may arise in tuimels buried or submersed in chloride-containing environments. Rebars on the inside of hoUow (air-filled) structures may be effective cathodes with noble potentials. They increase the potential of rebars closer to the seawater side of the cross section, stimulating corrosion initiation at lower chloride contents than without additional cathodic effects. Subsequently they may increase the corrosion rate at the anodes by consuming the electrons produced. The final corrosion rate will be a function of the ratio between anodic and cathodic areas, which is influenced by the concrete resistivity. 

Water is produced at the cathode/membrane interface, and it must be transported to the anode and cathode flow channels to be removed. At present, we do not have a direct measurement of the water activity in the membrane (the partial pressure of water in the membrane, p> embrane do know the water content in the effluent streams. The experimental data may be integrated from the known initial water content (after the water injection) to the steady state current and partial pressures of water. Integration of Eq. (3.4) gives the steady state membrane water content for known water partial pressure at the anode and cathode. Effective mass transfer coefficients for water from the cathode/membrane interface to the cathode gas flow channel and from the cathode/membrane interface to the... 

One of the examples, the so-called cathode effect in A1 electrolysis, has been reported in 1966 [28]. This typical blockade phenomenon occurs at A1 cathode at very high current densities of about tens A cm . This effect shows itself in sharp increase of ohmic resistance at the cathode followed by arc or glow discharge. The early explanation suggested the formation of a layer of gaseous sodium. In our opinion, formation of dielectric solid film accounts better for this phenomenon. 

Liu Y, Ji C, Gu W, Baker DR, Jome J, Gasteiger HA (2010) Proton conduction in PEM fuel cell cathodes effects of electrode thickness and ionomer equivalent weight. J Electrochem Soc 157(8) B1154-B1162... 

Chromium poisoning of the porous composite cathode. Effect of cathode thickness and current density. 

Electrochemical Reactor Design and Configurations, Table 3 Parameters for the model polarization curves of Fig. 3. The same value of fS was used for the anode and cathode. Effects of reactant conversion have been neglected in ji... 

Fleig J, Maier J (2004) The polarization of mixed conducting SOFC cathodes Effects of surface reaction coefficient, ionic conductivity and geometry. J Eur Ceram Soc 24 1343... 

The delay observed in the oxidation process when the polymer was previously polarized at high cathodic potentials for long periods of time, reported as a memory effect by Villeret and Nechtschein [298], was partially quantified by Odin [293,294,299]. A complete description of these cathodic effects was provided by Otero and Grande [300-2], based on an electrochemical model of conformational relaxation. 

Konysheva E, Mertens J, Penkalla H, Singheiser L, Hilpert K (2007) Chromium poisoning of the porous composite cathode effect of cathode thickness and current density. J Electrochem Soc 154(12) B1252-B1264... 

The potential values listed can change by a considerable margin if a biofilm with a high level of cathodic effectiveness forms on the metal surface at normal ambient temperature within 1-4 weeks. If chlorine is added to the seawater to prevent fouling, the reduction of the hypochlorite ions produced to chloride ions raises the potential by a considerable amount. Raising the temperature to about 25-30 C above average seawater temperature, which would prevent formation of the biofilm, reduced the potential accordingly. 

So, in order to create a system stable to corrosion and to decrease the rate of corrosion, it is necessary to find a way to promote the cathodic effectiveness (for example as it is in this specific case of investigations, carried out by us, to modify the steel surface with Ce02-Ce2Q3... 

In water with a pH near 7.0, a low concentration of chlorides, silicates, and phosphates cause passivation of steel when oxygen is present hence, they behave as anodic inhibitors. Another anodic characteristic is that corrosion is localized in the form of pitting when insufficient amounts of phosphate or silicate are added to saline water. However, both sUicates and phosphates from deposits on steel increase cathodic polarization. Thus, their action appears to be mixed, i.e., a combination of both anodic and cathodic effects. 

The great maj ority of PTR-MS experiments carried out to date have employed a DC hollow cathode electrical discharge as the means of generating ions. Before considering the details of this ion source as it is applied to PTR-MS, some background information on electrical discharges and the hollow cathode effect will be given. 

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