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

K12 Standards

Arizona Science Standards

High School

Physical Science

HS.P1

HS.P1U3.4

Corrosion

La corrosion est l'oxydation spontanée de métal en présence d'un oxydant, généralement de l'oxygène. C'est le même phénomène derrière la couleur bleu-vert de la Statue de la Liberté ou une ancre rouillée. Parfois, la corrosion est protectrice.Par exemple, le cuivre s'oxyde en présence d'oxygène, de dioxyde de carbone et d'eau, pour former du carbonate de cuivre basique, une couche protectrice bleu-vert et structurellement stable. D'autres types de corrosion sont préjudiciables. Par exemple, le fer s'oxyde en présence d'oxygène, d'eau, et des ions hydrogène, pour former des oxydes métalliques structurellement instables appelés rouille, qui s'écaille continuellement, exposant le métal sous-jacent à une nouvelle oxydation.La rouille est une réaction électrochimique spontanée. Les défauts de surface servent de régions anodiques où le fer, avec un potentiel d'électrode de 0, 44 volts, s'oxyde facilement en fer Les électrons migrent vers la région cathodique, où l'oxygène, avec un potentiel d'électrode de 1, 23 volts, est réduit en eau dans un environnement acide. Les ions hydrogène proviennent de la réaction atmosphérique entre le dioxyde de carbone et l'eau, formant de l'acide carbonique.Ensuite, les ions fer migrent vers la région cathodique via l'humidité de la surface et sont ensuite oxydés en fer hydrate d'oxyde, communément appelé rouille"La stoechiométrie de l'hydrate varie avec la quantité d'eau auquel le fer est exposé. La rouille est accélérée avec de l'humidité supplémentaire, des acides, et des électrolytes, qui améliorent le flux de charges, et la concentration d'ions H Les méthodes de prévention de la corrosion comprennent peindre la surface métallique pour éviter contact avec de l'eau et de l'oxygène ou usage d'alliages, une combinaison de plusieurs métaux. L'acier inoxydable est un alliage de fer contenant une petite quantité de chrome, qui se corrode pour former une couche d'oxyde non réactif à la surface protégeant le fer.Alternativement, la galvanisation est également utilisée. Ici, une vis de fer est recouverte d'une couche de métal plus facilement oxydé, comme le zinc, qui forme une couche protectrice d'oxyde de zinc protégeant le fer. Enfin, la protection cathodique contrôle la corrosion en convertissant le métal protégé en cathode.Les tuyaux de fer souterrains sont souvent connectés à un métal plus facilement oxydé, comme le zinc, où le zinc agit comme une anode sacrificielle étant oxydé, et le fer est la cathode protégée de la corrosion.

corrosion

La dégradation des métaux due aux processus électrochimiques naturels est connue sous le nom de corrosion. La formation de rouille sur le fer, le ternissement de l'argent et la patine bleu-vert qui se développe sur le cuivre sont des exemples de corrosion. La corrosion implique l'oxydation des métaux. Parfois, elle est protectrice, comme dans le cas de l'oxydation du cuivre ou de l'aluminium où une couche protectrice d'oxyde métallique ou de ses dérivés se forme à la surface, protégeant le métal sous-jacent de toute oxydation ultérieure. Dans d'autres cas, la corrosion endommage le métal, comme la rouille du fer. 
 Réaction redox indésirable : la rouille du fer 
 La rouille est due à l'exposition du fer à l'oxygène et à l'eau. La formation de rouille implique la création d'une cellule galvanique à la surface du fer, ce qui entraîne la production de fer(II). Les réactions redox concernées qui se produisent dans les régions anodiques (oxydation du fer) et cathodiques (réduction de l'oxygène) formées à la surface du fer sont les suivantes : 
 <img alt="Eq1" src="/files/ftp_upload/11440/11440_Equation_1.png" style="text-align: center; height: 150px;" />
 Le fer(II) réagit davantage avec l'air humide, formant un oxyde de fer(III) hydraté, qu'on appelle généralement rouille. 
 <img alt="Eq2" src="/files/ftp_upload/11440/11440_Equation_2.png" style="text-align: center; height: 50px;" />
 La stœchiométrie de l'hydrate varie en fonction de la quantité d'eau à laquelle le fer(II) est exposé, comme indiqué par l'utilisation de x dans la formule du composé. L'humidité, la présence d'acides et d'électrolytes augmente la vitesse de formation de la rouille. Contrairement à la patine sur le cuivre, la formation de la rouille ne crée pas de couche protectrice, et ainsi la corrosion du fer continue à mesure que la rouille s'écaille et expose à l'atmosphère du nouveau fer. 
 Prévention de la corrosion 
 Différentes méthodes peuvent être utilisées pour empêcher la corrosion. Une façon est de maintenir la surface métallique peinte pour éviter tout contact avec l'eau et l'oxygène. L'alliage des métaux, comme le mélange du fer avec de petites quantités de chrome dans l'acier inoxydable, est une autre méthode efficace pour empêcher la corrosion. Le chrome s'accumule près de la surface et subit une oxydation, ce qui par conséquent protège efficacement le fer de la corrosion. 
 Le fer et les autres métaux peuvent également être protégés de la corrosion par galvanisation, un procédé dans lequel le métal à protéger est recouvert d'une couche d'un métal plus facilement oxydé, généralement du zinc. Lorsque la couche de zinc est intacte, elle empêche l'air d'entrer en contact avec le fer sous-jacent et empêche ainsi la corrosion. Si la couche de zinc est percée par la corrosion ou l'abrasion mécanique, le fer peut toujours être protégé contre la corrosion par un procédé de protection cathodique, décrit dans le paragraphe suivant. 
 La protection cathodique utilise le principe de la conversion du métal à protéger à une cathode dans une réaction électrochimique. Pour ce faire, on connecte le métal protégé à un métal plus actif ou facilement oxydé comme le zinc ou le magnésium, connu sous le nom d'anode consommable. L'anode se corrode et est utilisée pour protéger le métal qui sert de cathode. La protection cathodique est le plus souvent utilisée dans les appareils ménagers tels que les chauffe-eau et les réservoirs souterrains de stockage d'eau. Il est important de noter que la protection cathodique peut être utilisée pour d'autres métaux que le fer. 
 Ce texte est adapté de<a href="https://openstax.org/books/chemistry-2e/pages/17-6-corrosion"> OpenStax, Chimie 2e, Chapitre 17.6 : Corrosion</a>.

La dégradation des métaux due à des processus électrochimiques naturels est connue sous le nom de corrosion. Formation de rouille sur le fer, ternissement de l’argent, et le bleu-vert ...

Education

Enseignement

JoVE Core

Chemistry

Chimie

Electrochemistry

Électrochimie

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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

balancing redox equations

Redox Reactions and Half-Reaction Balancing

Redox reactions involve electron transfer and changes in oxidation number. In electrochemistry, these reactions connect chemical changes with electrical energy. They also power technologies such as industrial metal processing and rechargeable batteries used in electric vehicles. Oxidation number is a way to track how an atom's electronic environment changes compared with the pure element, where the oxidation number is zero. For a simple ionic compound, the oxidation number matches the ion...

electromotive force

Cell Voltage and Electron Flow

Electric current is the flow of electric charge through a conducting medium or a solution. In wires, that charge is carried by electrons. In some solutions, ions can also move and carry charge. When electrons move through a wire, they produce an electric current. This idea connects to redox reactions, where electrons are lost and gained. In the spontaneous reaction between zinc and copper ions, zinc is oxidized to zinc ions. Copper ions are reduced to solid copper. Even so, this direct...

voltaic/galvanic cells

Galvanic Cells and Battery Reactions

Galvanic cells use spontaneous redox reactions to produce electric current. A common example is a disposable AA battery, which powers devices by turning chemical energy into electrical energy. Another example is a copper wire placed in silver nitrate solution, where the solution slowly turns bright blue and a grey solid forms on the wire. In the copper and silver reaction, copper is oxidized and silver ions are reduced. Copper forms cuprous ions, which give the solution its blue color. At the...

standard electrode potentials

Using Electrode Potentials to Predict Reactions

Electrode potentials help predict whether a redox reaction will happen on its own. A redox reaction involves electron transfer. In electrochemistry, the measured value is called cell potential or cell voltage. It shows the energy linked to charge transfer and is measured in volts, where 1 volt equals 1 joule per coulomb. A single half-cell cannot be measured by itself because electron transfer needs both a donor and a receiver. For that reason, scientists measure the difference between two...

cell potential and free energy

Redox Cell Potential, ΔG°, and K

Redox cell potential connects chemical energy, free energy change, and the equilibrium constant in an electrochemical cell. In these reactions, chemical energy is converted into electrical energy. That link helps predict whether a reaction is spontaneous and how far it may proceed. Thermodynamics is the study of how heat and other forms of energy are related. In an electrochemical cell, cell potential can also reflect oxidizing strength or reducing strength. A similar idea appears in acid-base...

the nernst equation

Cell Potential Under Changing Conditions

Cell potential changes when a redox reaction does not run at standard conditions. Standard cell potentials connect with standard free energy change, ΔG°, and the equilibrium constant K, but those relationships only hold at 1 M concentration, 298 K, and 1 atmosphere. A zinc(II) and tin(II) redox cell with E°cell = +0.291 V and ΔG° = −56.2 kJ is spontaneous under those standard conditions. As a cell discharges, the reactant concentration changes and the cell potential steadily drops. Many redox...

concentration cells

Cell Potential from Concentration Differences

Concentration cells are voltaic cells that use two almost identical half-cells. The half-cells use the same electrode and the same half-reaction. They differ only in the concentration of one redox species, so the cell potential depends on that concentration difference. In a concentration cell, the Nernst equation can be used to find the cell potential. For the zinc example shown, the calculated cell potential is positive. A positive cell potential means the overall reaction is spontaneous. <br...

batteries and fuel cells

Primary, Rechargeable Batteries and Fuel Cells

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 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

chemistry

JoVE Core Chimie anime les concepts de chimie générale en utilisant des leçons vidéo concises et faciles à comprendre. De plus, nos vidéos de scientifiques à l'action présentent des expériences de recherche, classiques ou insolites, effectuées dans des laboratoires modernes du monde entier.

Scientific Laws and Theories

Scientific Laws

In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. ...

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

The Quantum-Mechanical Model of an Atom

Shortly after de Broglie published his ideas that the electron in a hydrogen atom could be better thought of as being a circular standing wave instead of ...

Quantum Numbers

It is said that the energy of an electron in an atom is quantized; that is, it can be equal only to certain specific values and can jump from one energy ...

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

Develop and use models to explain the relationship of the structure of atoms to patterns and properties observed within the Periodic Table and describe how these models are revised with new evidence.

HS.P1U1.1

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ions and Ionic Charges

In ordinary chemical reactions, the nucleus &mdash; which contains the protons and neutrons of each atom and thus identifies the element &mdash; remains ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

ionic-compounds-formulas-and-nomenclature

Ionic Compounds: Formulas and Nomenclature

An element composed of atoms that readily lose electrons (a metal) can react with an element composed of atoms that readily gain electrons (a nonmetal) to ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

molecular-compounds-formulas-and-nomenclature

Molecular Compounds: Formulas and Nomenclature

Molecular compounds or covalent compounds result when atoms share electrons to form covalent bonds. Since there is no electron transfer, molecular ...

Polar Covalent Bonds

Covalent bonds are formed between two atoms when both have similar tendencies to attract electrons to themselves (i.e., when both atoms have identical or ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

Develop and use models for the transfer or sharing of electrons to predict the formation of ions, molecules, and compounds in both natural and synthetic processes.

HS.P1U1.2

Reaction Rate

The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time ...

Concentration and Rate Law

The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions ...

Temperature Dependence on Reaction Rate

The Collision Theory
Atoms, molecules, or ions must collide before they can react with each other. Atoms must be close together to form chemical bonds. ...

Reaction Mechanisms

Chemical reactions often occur in a stepwise fashion, involving two or more distinct reactions taking place in a sequence. A balanced equation indicates ...

Catalysis

The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed ...

Enzymes

Inside living organisms, enzymes act as catalysts for many biochemical reactions involved in cellular metabolism. The role of enzymes is to reduce the ...

determining-rate-laws-and-the-order-of-reaction

Determining Rate Laws and the Order of Reaction

Source: Laboratory of Dr. Neal Abrams &#8212; SUNY College of Environmental Science and Forestry
All chemical reactions have a specific rate defining the ...

Introduction to Catalysis

Source: Laboratory of Dr. Ryan Richards &#8212; Colorado School of Mines
Catalysis is among the most important fields of modern technology and presently ...

Ask questions, plan, and carry out investigations to explore the cause and effect relationship between reaction rate factors.

HS.P1U1.3

Biological Effects of Radiation

All radioactive nuclides emit high-energy particles or electromagnetic waves. When this radiation encounters living cells, it can cause heating, break ...

Dye-sensitized Solar Cells

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
Today&#39;s modern world requires the use of a large amount of energy. While ...

Batteries and Fuel Cells

A battery is a galvanic cell that is used as a source of electrical power for specific applications. Modern batteries exist in a multitude of forms to ...

Overview of Biomaterials

Biomaterials are materials engineered to interact favorably with biological organisms or molecules. These materials can be derived from or produced by an ...

biodistribution-of-nano-drug-carriers-applications-of-sem

Biodistribution of Nano-drug Carriers: Applications of SEM

Source:&#160;Peiman Shahbeigi-Roodposhti and Sina Shahbazmohamadi, Biomedical Engineering Department, University of Connecticut, Storrs, Connecticut
...

The degradation of metals due to natural electrochemical processes is known as corrosion. Rust formation on iron, tarnishing of silver, and the blue-green ...

Polymerization

Source: Vy M. Dong and Jan Riedel, Department of Chemistry, University of California, Irvine, CA
Polymers are made from macromolecules, which are composed ...

Obtain, evaluate, and communicate information about how the use of chemistry related technologies have had positive and negative ethical, social, economic, and/or political implications.

Rusting and Metal Protection

Description

Transcript

Tags

More videos by Standards