Name: rusting and metal protection
Uploaded: 2020-09-24T15:06:52.000Z
Duration: 2 min 49 s
Channel: JoVE

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Corrosion

La corrosión es la oxidación espontánea de un metal en presencia de un agente oxidante, generalmente oxígeno. Es el mismo fenómeno detrás del color azul verdoso de la Estatua de la Libertad o un ancla oxidada. Algo de corrosión ofrece protección.Por ejemplo, el cobre se oxida en presencia del oxígeno, dióxido de carbono y agua, para formar carbonato de cobre básico, una capa protectora azul verdosa y estructuralmente estable. Otra corrosión es perjudicial. Por ejemplo, el hierro se oxida en presencia de iones de oxígeno, agua e hidrógeno, en óxidos metálicos estructuralmente inestables llamados óxido"que continuamente se desprenden, exponiendo el metal subyacente a una mayor oxidación.La oxidación es una reacción electroquímica espontánea. Los defectos en la superficie sirven como regiones anódicas donde el hierro, con un potencial de electrodo de 0, 44 voltios, se oxida fácilmente en hierro Los electrones migran hacia la región catódica, donde el oxígeno, con un potencial de electrodo de 1, 23 voltios, se reduce a agua en un ambiente ácido. Los iones de hidrógeno provienen de la reacción atmosférica entre el dióxido de carbono y el agua, formando ácido carbónico.A continuación, los iones de hierro migran a la región catódica a través de la humedad de la superficie y se oxidan más en hidrato de óxido de hierro comúnmente conocido como óxido"La estequiometría del hidrato varía con la cantidad de agua a la que se expone el hierro La oxidación se acelera con la humedad, los ácidos y electrolitos adicionales, que mejoran el flujo de cargas y la concentración de iones H+Los métodos para prevenir la corrosión incluyen pintar la superficie del metal para evitar el contacto con el agua y el oxígeno o el uso de aleaciones, una combinación de metales múltiples. El acero inoxidable es una aleación de hierro que contiene una pequeña cantidad de cromo, que se corroe para formar una capa de óxido no reactivo en la superficie que protege el hierro. Como alternativa, también se utiliza la galvanización.Aquí, un tornillo de hierro se recubre con una capa de metal que se oxida más fácilmente, como el zinc, que forma una capa protectora de óxido de zinc que protege el hierro. Por último, la protección catódica controla la corrosión al convertir el metal protegido en el cátodo. Las tuberías de hierro subterráneas a menudo están conectadas a un metal que se oxida más fácilmente, como el zinc, donde el zinc actúa como un ánodo de sacrificio que se oxida, y el hierro es el cátodo protegido de la corrosión.

la corrosión

La degradación de metales debida a procesos electroquímicos naturales se conoce como corrosión. La formación de óxido en el hierro, el deslustre de la plata y la pátina verdeazúl que se desarrolla en el cobre son ejemplos de corrosión. La corrosión implica la oxidación de los metales. A veces es protectora, como la oxidación del cobre o el aluminio, en donde una capa protectora de óxido metálico o sus derivados se forma en la superficie, protegiendo el metal subyacente de la oxidación posterior. En otros casos, la corrosión daña el metal, como en la oxidación del hierro.
 Reacción redox indeseable: La oxidación del hierro
 La oxidación se produce debido a la exposición del hierro al oxígeno y al agua. La formación de óxido implica la creación de una celda galvánica en la superficie del hierro, lo que resulta en la generación de hierro (II). Las reacciones redox relevantes que ocurren en las regiones anódicas (oxidación del hierro) y catódicas (reducción del oxígeno) formadas en la superficie del hierro incluyen:
 <img alt="Eq1" src="/files/ftp_upload/11440/11440_Equation_1.png" style="text-align: center; height: 150px;" />
 El hierro (II) reacciona más adelante con el aire húmedo, formando un hidrato de óxido de hierro (III), comúnmente conocido como óxido.
 <img alt="Eq2" src="/files/ftp_upload/11440/11440_Equation_2.png" style="text-align: center; height: 50px;" />
 La estequiometría del hidrato varía con la cantidad de agua a la cual el hierro (II) está expuesto, como lo indica el uso de x en la fórmula compuesta. La humedad, la presencia de ácidos y electrolitos aumenta la tasa de formación de óxido. A diferencia de la pátina sobre el cobre, la formación de óxido no crea una capa protectora, por lo que la corrosión del hierro continúa a medida que el óxido se deshace y expone el hierro fresco a la atmósfera.
 Prevención de la corrosión
 Se pueden utilizar varios métodos para prevenir la corrosión. Una forma es mantener la superficie metálica pintada para evitar el contacto con el agua y el oxígeno. La aleación de metales, como la mezcla de hierro con pequeñas cantidades de cromo en acero inoxidable, es otro método eficaz para prevenir la corrosión. El cromo se acumula cerca de la superficie y es sometido a oxidación, por lo que protege eficazmente el hierro de la corrosión.
 El hierro y otros metales también pueden ser protegidos de la corrosión por galvanización, un proceso en el cual el metal a ser protegido está cubierto con una capa de un metal más fácilmente oxidado, generalmente zinc. Cuando la capa de zinc está intacta, evita que el aire entre en contacto con el hierro subyacente y, por tanto, evita la corrosión. Si la capa de zinc se rompe por corrosión o abrasión mecánica, el hierro puede estar protegido de la corrosión por un proceso de protección catódica, que se describe en el siguiente párrafo.
 La protección catódica utiliza el principio de convertir el metal que se va a proteger en un cátodo en una reacción electroquímica. Esto se consigue conectando el metal protegido a un metal más activo o fácilmente oxidado, como zinc o magnesio, conocido como ánodo de sacrificio. El ánodo se corroe y se utiliza para proteger el metal que sirve como cátodo. La protección catódica se utiliza más comúnmente en aparatos domésticos como calentadores de agua y tanques subterráneos de almacenamiento de agua. Es importante destacar que la protección catódica se puede utilizar para metales distintos del hierro.
 Este texto está adaptado de<a href="https://openstax.org/books/chemistry-2e/pages/17-6-corrosion"> OpenStax, Química 2e, Capítulo 17.6: Corrosión</a>.

La Corrosión

La degradación de los metales debido a procesos electroquímicos naturales se conoce como corrosión. Formación de óxido en el hierro, deslustre de la plata y el color azul verdoso ...

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rusting and metal protection

Corrosion is the natural breakdown of metals through electrochemical reactions. It can appear as rust on iron, tarnish on silver, or a blue-green patina on copper. In each case, the metal is oxidized. Some corrosion products can protect the surface, while others keep damaging the metal.

Rusting is the harmful type of corrosion seen in iron. It happens when iron is exposed to oxygen and water. A galvanic cell forms on the iron surface, and this drives oxidation at the anodic region and reduction of oxygen at the cathodic region. The iron(II) that forms then reacts with humid air to make iron(III) oxide hydrate, which is rust.

The amount of water in rust can vary, so its formula includes x to show changing stoichiometry. Moisture, acids, and electrolytes all speed up rust formation. Unlike the protective patina on copper, rust does not seal the metal. It flakes away and exposes fresh iron to air, so corrosion continues.

Metal corrosion can be slowed in several ways. One method is painting the surface so water and oxygen cannot reach it. Another is alloying, such as adding chromium to iron to make stainless steel. The chromium moves near the surface and oxidizes there, which helps protect the iron underneath.

Metals can also be protected by galvanization, where a layer of a more easily oxidized metal, usually zinc, coats the surface. If the zinc layer stays intact, it blocks air from the iron. If the coating is damaged, cathodic protection can still help. In that method, the protected metal is connected to a more active sacrificial anode, such as zinc or magnesium, which corrodes instead. This approach is used in water heaters and underground water storage tanks, and it can protect metals other than iron.

Rusting and Metal Protection

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concentration cells

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Batteries and fuel cells are galvanic cells that supply electrical power for many applications. They range from tiny button batteries in wristwatches to large systems that can provide backup energy to municipal power grids. Some are primary cells, which are single-use and cannot be recharged. Others are secondary cells, which use reversible reactions and can be charged again by an external power source. A common primary battery is the dry cell. It uses zinc as both the container and the anode,...

corrosion

Corrosion is the natural breakdown of metals through electrochemical reactions. It can appear as rust on iron, tarnish on silver, or a blue-green patina on copper. In each case, the metal is oxidized. Some corrosion products can protect the surface, while others keep damaging the metal. Rusting is the harmful type of corrosion seen in iron. It happens when iron is exposed to oxygen and water. A galvanic cell forms on the iron surface, and this drives oxidation at the anodic region and...

electrolysis

Electrolysis in Batteries and Metal Production

Electrolysis uses electrical energy to drive a nonspontaneous redox reaction. In a galvanic cell, a spontaneous redox reaction does electrical work on the surroundings by sending electrons through an external circuit. In electrolysis, an external circuit does work on the redox system by applying a voltage large enough to force the reaction in the opposite direction. This process is used in several real-world settings. Recharging a battery is one example, because an outside power source drives...

key terms and concepts

Learn how corrosion affects metals, why iron rusts, and how painting, stainless steel, galvanization, and cathodic protection help prevent damage.

Rusting and Metal Protection | JoVE K12

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Rusting and Metal Protection

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