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My highschool textbook tells me that sacrificial protection (more technically-cathodic protection) and electrolytic protection are different. I have searched high and low for an explanation of electrolytic protection, but I got nothing.

It describes the electrolytic protection, stating that the steel/iron structure is hooked up to an electrolytic (not electrochemical!) cell as the negative terminal (cathode) and the anode is an inert material (titanium, in the example).

Why does this work, if it does at all?

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  • $\begingroup$ Electrolytic protection and sacrificial protection are synonymous, in my opinion. It is obtained by applying a layer of zinc metal on a piece of iron exposed to rain. The iron piece will not get oxidized, because zinc will be oxidized before iron. $\endgroup$ – Maurice Feb 6 at 14:38
  • $\begingroup$ The world would be rather different without CP .Nat gas piped to homes, etc, would be rare. Many would not have water piped to homes ; many municipalites do not apply CP and hope for the best with their cast iron pipe , just replace as needed , the taxpayers will pay for it. Gasoline and plastics would be much more expensive because of transportation costs . I hoped a high school science text would not be so incompetent . But not surprised after looking at the local university chemistry. text. $\endgroup$ – blacksmith37 Feb 6 at 16:47
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I understand why a HS text might call it "electrolytic" , but in the real world it is called "cathodic protection" or CP. That is what to look for on the net. It is a multibillion dollar industry. Essentially all pipelines ( oil, gas, products, water , etc.) use it . A large majority off offshore steel structures ( oil platforms, ships, etc) use it. And many steel products are galvanized . There are two basic types ; sacrificial coatings and impressed current. Sacrificial coatings are represented by galvanized steel , also aluminum and cadmium coatings. Impressed current, CP is also two categories : Sacrificial anodes , usually aluminum ( which do not use rectifiers) , and inert anodes , usually titanium or graphite. These are buried in soils made more conductive with graphite powder (typically) and electrically connected to rectifiers which are then connected to the steel to be protected . The voltage is adjusted and monitored along the protected steel , eg. pipeline. Pipelines are coated with an electrically insulating coating to reduce the amount of current required to maintain a protective voltage , normally lower than - 0.65 V ( Cu - Cu SO4 half cell) Too low a voltage can cause hydrogen gas bubbles under the coating and hydrogen embrittlement of certain steels.There is also anodic protection but it has very specific limited applications. So, there is such a thing as "electrolytic" protection.

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  • $\begingroup$ This is it lads. Thank you good sir! $\endgroup$ – El Flea Feb 8 at 14:57
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As far as I know sacrificial protection refers to the protection of iron specifically, while electrolytic protection is for all metals.

The concept of electrolytic protection is that a valuable metal is connected with an invaluable and more reactive one to create an electrolytic cell. The invaluable is the anode as it is more reactive and it gets oxidized by the environment, while the less reactive valuable metal forms the cathod and is protected from oxidization.

A note : Electrochemical cells are cells that produce electricity and cells that electricity is applied to them. Electrolytic cells are cells that electricity is applied to them. So they are not exactly the same thing.

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