Sacrificial protection

It follows from the above that, for an anode material to offer sacrificial protection, it must have an open-circuit potential that is more negative than that of the structure itself (the cathode). The extent of protection experienced by the cathode will depend on the potential it achieves. This is dependent on the electrochemical properties of the anode which in turn are governed by its composition and the environment to which it is exposed. 

Aluminium does provide a protective barrier to corrosive attack on steel but its ability to provide sacrificial protection is limited. The use of Al-Zn... 

Primers containing 93-95% zinc dust by weight in non-saponifiable media provide sacrificial protection to clean steel (see Section 14.3). 

Environment Reduce kinetics of cathodic reaction Lower potential of metal Cathodic inhibition Reduce a , reduce O2 concentration or concentration of oxidising species lower temperature, velocity agitation Cathodically protect by sacrificial anodes or impressed current sacrificially protect by coatings, e.g. Zn, Al or Cd on steel Formation of calcareous scales in waters due to increase in pH additions of poisons (As, Bi, Sb) and organic inhibitors to acids... 

In order to realize the precise control of core/shell structures of small bimetallic nanoparticles, some problems have to be overcome. For example, one problem is that the oxidation of the preformed metal core often takes place by the metal ions for making the shell when the metal ions have a high-redox potential, and large islands of shell metal are produced on the preformed metal core. Therefore, we previously developed a so-called hydrogen-sacrificial protective strategy to prepare the bimetallic nanoparticles in the size range 1.5-5.5nm with controllable core/shell structures [132]. The strategy can be extended to other systems of bi- or multimetallic nanoparticles. 

Having introduced matters pertaining to the electrochemical series earlier, it is only relevant that an appraisal is given on some of its applications. The coverage hereunder describes different examples which include aspects of spontaneity of a galvanic cell reaction, feasibility of different species for reaction, criterion of choice of electrodes to form galvanic cells, sacrificial protection, cementation, concentration and tempera lure effects on emf of electrochemical cells, clues on chemical reaction, caution notes on the use of electrochemical series, and finally determination of equilibrium constants and solubility products. 

Sacrificial protection may be described typically through the cell of the type presented below ... 

Set up a zinc/iron cell to demonstrate sacrificial protection. Analyse the cell reactions as above. R... 

Corrosion is a major problem of ships as iron corrodes easily. However, magnesium corrodes more easily than iron. Therefore, a bar of magnesium is attached to the side of a ship. The magnesium bar, instead of the exposed part of the ship, corrodes. This is called sacrificial protection as magnesium is sacrificed to protect the ship. When it is completely corroded, the magnesium bar is replaced. Zinc can also be used for the same purpose. 

Various reasons have been put forward as to why the spore is less sensitive to H202 than the vegetative cell. In the spore, the DNA is covered by the so-called small acid-soluble proteins (SASP) instead of water which makes it relatively inaccessible to oxidative damage as these SASPs may provide compaction besides sacrificial protection (e.g., Setlow 1994,1995 Setlow and Setlow 1993). 

Lead powder. The oil-suspension of metalhc lead powder is used in the preparation of protective primers for steelwork where it is normally present as the sole pigment. Lead pigments act as a barrier and provide a degree of sacrificial protection similar to that of zinc dust. 

The principle of cathodic or sacrificial protection is founded in the natural potential differentials between different metals. Zinc anodes are intentionally placed in electrical contact with steel structures so that, as they corrode, the steel is protected. In other systems, a current may be applied to the structure to be protected so as to cause the current to flow to an artificial anode. 

Figure 10 Hydrogen-sacrificial protective strategy for the preparation of bimetallic nanoparticles with a core/shell structure. (Reprinted with permission from Ref. 130. Copyright 1997 American Chemical Society.)... 

Metals and activity series crossword. 1. Displaces silver but not lead. 2. Honorary metal in many versions of the activity series. 3. Unreactive metal, a salt of which is used in the chloride test. 4. Most abundant transition metal in Earth s crust. 5. This metal forms a nitrate which is hard to decompose. 6. Metal used in sacrificial protection of iron from corrosion. 7. First member of Group lA element. 8. This metal does not react with water, but reacts with acid. (Taken from Metals and the reactivity series, InfoChem, issue no. 23, September 1993. Reprinted with permission of Education in Chemistry.)... 

It is not practical to galvanize large objects, such as a ships or pipes. Instead a block of a reactive metal, such as magnesium (or zinc), is attached to the large object and, again, preferentially loses electrons to oxygen. This method of protecting the metal is known as sacrificial protection. 

SACRIFICIAL PROTECTION - Reduction of corrosion of a metal in an electrolyte by galvanically coupling it to a more anodic metal. A form of cathode protection. 

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