Steele potential

In summary, preliminary studies indicate that plasma spray coatings show great potential for improving the bondability of steel. Potential drawbacks include the requirement for relatively expensive plasma spray equipment and the necessity to keep the substfate temperature below that which would lead to undesirable metallurgical changes. 

Steel Potential C (V) Potential E (V) Critical current density D (mA/cm... 

Cathodic Current Densities for Protecting Steel Examples of current density requirements for the protection of steel (to achieve a steel potential of —0-8 V vs. Ag/AgCl/seawater) are given in Tables 10.13 and 10.14. It should be realised that the current demand of a structure will be influenced by, inter alia, temperature, degree of aeration, flow rate, protective scales, burial status, presence of bacteria and salinity. 

To represent the elasticity and dispersion forces of the surface, an approach similar to that of Eqs. (3) and (4) can be taken. The waU molecules can be assumed to be smeared out. And after performing the necessary integration over the surface and over layers of molecules within the surface, a 10-4 or 9-3 version of the potential can be obtained [54,55], Discrete representation of a hexagonal lattice of wall molecules is also possible by the Steele potential [56], The potential is essentially one dimensional, depending on the distance from the wall, but with periodic variations according to lateral displacement from the lattice molecules. Such a representation, however, has not been developed in the cylindrical pore... 

The influence of HjOj concentration on stainless steel potential was determined by exposing a coupon to known concentrations of HjOj in aerated river water and measuring and pH. After correcting for a -60 mV/pH unit change due to slight acidification from the added HjOj, E followed the relationship ... 

It is often beneficial to define a coordinate Rti that describes the center of mass of the top layer. There are three common ways to set up the top layer. (1) The positions of top layer atoms r are confined to (lattice) sites rW)o, which are connected rigidly to the top layer. (2) The top layer atoms are coupled elastically to sites rra 0 fixed relative to the top layer, e.g., with springs of stiffness k. (3) An effective potential, such as a Steele potential Vs34 is applied between embedded atoms and the top layer. Specific advantages and disadvantages are associated with each method. Approach (1) may be the one that is most easily coded, (2) allows one to thermostat the outermost layer in an effective manner, whereas (3) is probably cheapest in terms of CPU time. 

What would the steel potential have been if measured by a Cu/CuS04 reference electrode ... 

The gas-solid interaction for an adsorbate molecule with a pore wall is taken as the well-known Steele potential for graphite [16] ... 

Another mean-field potential, which is often used, is obtained by areal integration over the first layer of a semi-infinite graphite substrate and volume integration over all others. This gives the well-known (10-4-3) Steele potential [15],... 

Equation (11.7) is the fluid-solid interaction energy for either atoms such as noble gases or IC-LJ molecules. For a polyatomic molecule with M centers of LJ type, the solid—fluid interaction energy can be determined the same way as we have presented earlier for fluid—fluid interaction. The interaction potential energy between a site a of the molecule i and the homogeneous flat solid substrate is calculated by the same 10-4-3 Steele potential [26, 27] ... 

Note that the solid-fluid potential energy in the above integrand is a function of H (e.g., the 10-4-3 Steele potential). 

This technique requires the permanent application of a small direct current to protect the steel. It can also lead to repassivation of the reinforcement if it lowers the steel potential below the repassivation potential (Section 7.3). Provided it is applied properly, cathodic protection is able to stop corrosion for any level of chloride con-... 

Circulation of current between the anode and the reinforcement has several consequences. Besides lowering of the steel potential (which was discussed in Section 7.5), chemical reactions on the surface of the reinforcement and ionic migration within the concrete take place. 

Figure 20.3c shows the effect of application of cathodic protection on carbonated concrete. The applied cathodic current density, even if it brings about only a small lowering of the steel potential, can produce enough alkalinity to restore the pH to values higher than 12 on the reinforcement surface and thus promote passivation. The effectiveness of cathodic protection in carbonated concrete was studied with specimens with alkaline concrete, carbonated concrete and carbonated concrete with 0.4% chloride by cement mass that were tested at current densities of 10, 5, and 2 mA/m (of steel surface) [45]. Carbonated concrete specimens polarised at 10 mA/m showed that, although initially protection was not achieved since the four-hour decay was slightly lower than 100 mV, after about four months of polarization, the protection criterion was fulfilled and higher values, in the range 200-300 mV of the four-hour potential decay were measured (Figure 20.6). The same results were obtained on carbonated and slightly chloride-contaminated concrete.

The problem of hydrogen embrittlement and prestressing steel has been discussed in Section 7.8 for cathodic protection, and Section 7.11.5 for realkalization. The realkalization process applies 20-50 V DC between the anode and the steel. It must therefore send the steel potential well beyond the level needed for hydrogen evolution. 

Haney, E. G. (1981). The zinc-steel potential reversal in cathodic protection. Corrosion 81 Conf., Toronto, NACE, preprint, 15 pp. 

FIG. 8—Typical electrochemically monitored etching curve for zinc/aluminum aiioy coatings on steel. Potential regions are labeled to indicate the dissolution occurring within each region [47],... 

Steel potentially contains °Co. Bear that in mind if steel plays any part in the construction - framework, top plate, base plate and sample holders. Pre-1950s steel is best, if obtainable. 

Alloy Potential (V) vs. AgjAgCl in Seawater Bare Steel Potential (V) Anode Capacity a A.h/Kg)... 

The graphitic surfaces were modeled using the Steele potential in the slit pore geometry. 

Grand canonical Monte Carlo simulations were performed to calculate individual adsorption isotheims in carbon sUt pores. The interactions potential, (/,/ of a fluid molecule at a distance z fiom a single solid wall is described by the 10-4-3 Steele potential [10] ... 

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