Quality cathodes

The improved performance of the ZnCl2 cell is offset by the higher cost incurred through using a better quality cathode mix and more complex fabrication due to the requirement of more reliable seals. Since the improvement in performance out-matches the price differential between Leclanche and zinc chloride cells, there is an increasing tendency to phase out the classical Leclanche formulation in favour of the latter. The best zinc chloride cells, sometimes referred to as extra heavy duty (EHD), have at least twice the service life of even the best Leclanche cells. 

DoubleContact - Outotec. Outotec s DoubleContact intercell contact bar system is designed so that all electrodes have an electrical contact on each end. These electrical contacts are all line contacts. Outotec has claimed that the principal benefit of using the double contact system is a more even current distribution [4]. The basis of this design is that if there is a poor contact between an electrode and the contact bar, the electrode will still receive current from the contact on the other end of the electrode from the equalizer bar. Outotec claims that a more even current distribution is likely to reduce energy consumption and lead to better quality cathodes [4]. In this paper, the impact of the equalizer bars is not considered. This results in this system being considered as a simple dog-bone system. 

Fig. 3-6 Electrochemical depolarization after switching off the protection current as a function of the operating time of cathodic protection and the quality of the coating.

In planning cathodic protection, the specific resistivity of the water, the size of the surfaces to be protected and the required protection current densities have to be determined. The protection current density depends on the type and quality of the coating. Thermosetting resins (e.g., tar-epoxy resin coatings) are particularly effective and are mostly used today on coastal structures. They are chemically... 

Tanks for the transport of chemicals cannot usually be cathodically protected because of the danger of impurities contaminating the cargo. Particular emphasis is placed on the quality of the coating to avoid contamination by corrosion products. 

An alternative means of avoiding the hazard from fire is to bury the vessels or to employ the increasingly popular method of mounding. In either case, acknowledgment of the reduced hazard is indicated by the reduced separation distances (see Table 20.4). Since both burial and mounding preclude the possibility to monitor continuously the external condition of the vessels, very high-quality corrosion protection needs to be applied, often supplemented by cathodic protection, depending on soil conditions. 

High-voltage coating-testing equipment When cathodic protection is applied to a structure which has a protective coating, the current required is proportional to the bare metal area on the structure. Thus whenever a protective coating is applied it should be of good quality, with very few failures or pin holes in it, so that the cathodic-protection system may be economic. 

At normal current densities, about 96-98% of the cathodic current in a Watts solution is consumed in depositing nickel the remainder gives rise to discharge of hydrogen ions. The boric acid in the solution buffers the loss of acidity arising in this way, and improves the appearance and quality of the deposit. Although phosphides, acetates, citrates and tartrates have been used, boric acid is the usual buffer for nickel solutions. 

Vacuum arc can also be initiated by pulsed laser, as shown in Fig. 4 [15,16]. The target material is first vaporized into plasma by pulsed laser, and vacuum arc is subsequently initiated and more plasma is generated under the function of the electric field between the anode and the cathode (target). Since the arc is controllable, the surface quality might be evi-... 

The formation of colloidal sulfur occurring in the aqueous, either alkaline or acidic, solutions comprises a serious drawback for the deposits quality. Saloniemi et al. [206] attempted to circumvent this problem and to avoid also the use of a lead substrate needed in the case of anodic formation, by devising a cyclic electrochemical technique including alternate cathodic and anodic reactions. Their method was based on fast cycling of the substrate (TO/glass) potential in an alkaline (pH 8.5) solution of sodium sulfide, Pb(II), and EDTA, between two values with a symmetric triangle wave shape. At cathodic potentials, Pb(EDTA)2 reduced to Pb, and at anodic potentials Pb reoxidized and reacted with sulfide instead of EDTA or hydroxide ions. Films electrodeposited in the optimized potential region were stoichiometric and with a random polycrystalline RS structure. The authors noticed that cyclic deposition also occurs from an acidic solution, but the problem of colloidal sulfur formation remains. 

Buried Structures There has been no dramatic improvement in the protection of buried structures against MIC over the last several decades. Experience has been that coating systems, by themselves, do not provide adequate protection for a buried structure over the years for best results, a properly designed and maintained cathodic protection (CP) systemmust be used in conjunction with a protective coating (regardless of the quality of the coating, as applied) to control... 

An external magnetic field has also been used to confine the plasma [143]. An arrangement where electromagnets are located under the cathode is known as the controlled plasma magnetron method [144]. The diffusion of electrons to the walls is prevented by the magnetic field between cathode and anode. This results in an increase in electron density, and consequently in a faster decomposition of silane and a higher deposition rate. At a deposition rate of 1 nm/s, device quality material is obtained [144]. In addition, a mesh is located near the anode, and the anode can by biased externally, both in order to confine the plasma and in order to control ion bombardment. 

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