Sacrificial anode

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short definition

a sacrificial anode is an anode, which becomes “sacrificed “by construction the protection by metal parts. Together with the metal parts which can be protected it forms an intended, controlled local cell.

simplified function mode and sample applications

around metals in very aggressiveTo protect environments against corrosion, like e.g. , One connects the endangered metal to fuel depots, underground pipes or oil drilling rigs electrically leading with a metal, which can be oxidized more easily and in accordance with the electro-chemical electromotive series is more unedler. For iron for example the base metals aluminum , zinc or magnesium comein question. These base metals become stabilization and/or. for optimal protection current yield in addition-alloys further metals. The alloys are in a standard (DIN and/or. VG) fixed.

For the same reason zinc or aluminium anodes is attached at boats and ships, which are in the seawater on the way. On rivers andLakes are often used magnesium anodes. The unedlere zinc and/or. Aluminum or magnesium gives electrons at acceptors over the iron (e.g. Oxygen) in the sea water off, the anode alloy goes into solution. The anode procedure of the galvanic cell - the oxidation - takes place thus at the anode material.Separates on (sacrificial anode), the iron remains slow unangegriffen.

A further application is the cathodic corrosion protection with memory. The steel tanks interiorcoated with enamel gotten with the time of tears and can do in these places through-rust which a new acquisition to the consequence have could. Around thata magnesium sacrificial anode will avoid into the memory screwed, which goes in place of the steel into solution. This anode uses itself and must be replaced occasionally by a new. One wants to avoid the exchange offers itself for the compensation a foreign current anode in such a way, thosethen only more with the plug socket to be connected must and permanent corrosion protection offers.

more detailed function mode by the example of a Zinkannode of a sea-going boat/ship

the periodic system of the elements assigns a place to each metal. One compares two different metals with one another (e.g. Zinc and iron), is always one of it (here that zinc) the inferior and (here the iron) the metal with higher order.

Are located the two metals more ineinender in contact, for example, by not affecting in in vein isolated, because an article made of the metal manufactured(the zinc anode), brightly and without each surface treatment on the other article (e.g. then one „iron trunk “) and comes then still another electrolyte is screwed in addition (here sea water) gives the inferior metal over a time axis in an electron exchange with the metal with higher order its molecules to thatElectrolyte off, until the inferior metal was loosened completely in the electrolyte.

Now are manufactured ship - and bottom structures not from pure iron, but from a steel alloy. In addition, alloys are permitted over molsche computations in with higher order and inferior to divide and also in relationset for the pure metals.

That leads to it that the sacrificial anodes function also at alloys, however often from the manufacturers very exactly computed alloys represents. Regards one for example a boat with a out sea water-firm aluminum manufactured trunk (aluminum stands under zinc and sea water-firmAluminum is an alloy, then a zinc anode at the trunk would cause that the expensive trunk of the cheap anode is sacrificed. It becomes still more difficult, if the boat propellers -/screw drive has. Often the wave is, those from the transmission to the propeller is enough from steel manufactured.Stevenrohr, which is place, in which the drive shaft breaks through the trunk from the inside outward, often from a brass alloy manufactured. The propeller or the marine propeller can be manufactured from aluminum, bronze or steel. And all these expensive components are to remain. ToBoat/ship to distributing sacrificial anodes is an electrolytic destruction, which prevent corrosion.

In addition it comes that the electrolyte is differently aggressive. With ships and boats the Salzgehalt determines the Agressivität electrolytes. And the Salzgehalt is in so-called „fresh water districts “, thus in inland waters another, than in oneDead end beside sea, like the Baltic Sea, or in the middle on high lake in the central Atlantic.

Opferannoden in the boat and shipbuilding are computed therefore by the shipyards or also the manufacturers of the components (the engines, the propeller, etc.) in every detail on the final material composition and the final intended purpose.

Work on []

Durability at vessels

usually such sacrificial anodes must be changed once in each season (or with the change of the operational area). And the anode no wear should show, should one on error tracing go with so a change. Because always one dissolves at boats and ships something.And if it is not the sacrificial anode, then something different one, somewhere at the vessel, where it can become correctly expensive. Something by the electrolyte in any case is dissolved. Or like the proverb reads: „The electrolyte eats its bread. So or so.)

error tracing

ifa sacrificial anode to vessel (which was in the water) not dissolves, has that always one of four reasons:

electrically isolated mounting

the sacrificial anode and the metal, which applies to protect it, affect each other only isolated, for example, because the Unterwasserschiffa steel boat was only painted and then only the trunk anode was applied, which was to work now against the color and not the metal of the trunk (which does not function naturally). Or there is an isolation because the sacrificial anode against the metal which can be protected does not rest. Orweil die Opferanode mehrere, miteinander verbundene Metalle schützen soll, von denen eines isoliert gegen ein anderes montiert wurde, ohne dass danach eine Verkabelung stattfand, welche die Metalle gegeneinander „erdete“.

falsche Metalle

Die Legierung der Opferanode ist nicht minderwertiger, als diethe article, for example, which can be protected, by screwing a zinc anode to an aluminum trunk, or a cheap reproduction anode instead of the chemically through-composed anode of the original manufacturer to a complex alloy of a drive system.

wrong anode for the electrolyte

magnesium anodes at a steel trunk on invery salzhaltigem water do not function, because magnesium is elektrylotisch inferior, as sodium chloride already loosened in the water (salt). Zinc anodes at a steel trunk in inland waters function more badly than magnesium anodes, but function.

electrically isolated anode

who its Unterwasserschiff paints, after the trunk anodeat the trunk and the anode was attached thereby does not leave blank, does not isoloiert the anode against the electrolyte. That applies also to every other sacrificial anode, all the same where attached. It must be bright, in order to be able to function.


in the classical antiquity one already worked metalson lake, although within the range of the Unterwasserschiffes only with copper plates, in order to protect the wood trunk from the destruction by the so-called „[ship drilling worm]] “. With the fact one stated that one was not allowed to use iron nails for the attachment of the copper plates at the trunk, because these, like one at that time, „the wood said makes ill “. One observed completely exactly that the iron nails separated from the wood and went then with the copper plates on depth. Basic knowledge was missing still, but one could eliminate the problem nevertheless, by one the copper plates with copper nails to the wood trunkstruck. One did not need sacrificial anodes (and one knew not).

In the detail the iron nail had gone as the metal inferior opposite the copper plates into dissolution. Sometime sea water (together with zoo and Phytoplankton ) could by developing columns into the Nagellöcher penetrate and these to destroy begin.And the iron nail was so far dissolved sometime that it was not held completely from the Nagelloch most awkward, or however the copper plate no more by a head of the nail at the trunk and then only the headless nail stump in the wood stayed.

Only in 19. Century, as steam enginesand propellers made of metal for the drive of the ships ensured, constantly came metals with sea water into contact. The phenomenon of the iron nails, which fell the copper plates to the victim, was sufficiently well-known. One experimented with different metals, in order to protect the drive systems. Over test stages in individual shipyardsone did not come outside.

In 20. Century changed everything. The elements were examined, the structure of the atoms seemed admit, ships out „iron “were built. The sacrificial anode was to be described suddenly in function and building method from each specialist to and designed and found starting from center20. Century a general spreading in the boat and shipbuilding.

See also: Rust (corrosion)


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