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

腐食とは、酸化剤(通常は酸素)の存在下での金属の自発的な酸化です。それは、自由の女神や錆びた錨の青緑色の背後で同じ現象です。
一部の腐食は保護的です。例えば、銅は酸素、二酸化炭素、水の存在下で酸化し、青緑色で構造的に安定した保護層である塩基性炭酸銅を形成します。
その他の腐食は有害です。例えば、鉄は酸素イオン、水イオン、水素イオンの存在下で酸化し、錆と呼ばれる構造的に不安定な金属酸化物となり、それが連続的に剥がれ落ち、下にある金属をさらに酸化します。
錆びは自発的な電気化学反応です。表面の欠陥は、電極電位が-0.44ボルトの鉄が容易に酸化して鉄(II)になる陽極領域として機能します。
電子は陰極領域に向かって移動し、電極電位が+1.23ボルトの酸素は酸性環境で水に還元されます。水素イオンは、二酸化炭素と水の間の大気反応から来て、炭酸を形成します。
次に、鉄(II)イオンは表面の水分を介して陰極領域に移動し、さらに酸化されて酸化鉄(III)水和物、一般に「錆」として知られています。 水和物の化学量論は、鉄(II)がさらされる水の量によって異なります。
錆びは、追加の水分、酸、電解質によって加速され、電荷の流れとH +イオンの濃度を高めます。
腐食を防ぐ方法には、金属表面を塗装して水や酸素との接触を防ぐ方法や、複数の金属を組み合わせた合金の使用などがあります。ステンレス鋼は、少量のクロムを含む鉄の合金であり、クロムが腐食して鉄を保護する表面に非反応性の酸化物層を形成します。
あるいは、亜鉛メッキも使用されます。ここでは、鉄のネジは、亜鉛のような酸化しやすい金属の層でコーティングされており、これが鉄を保護する酸化亜鉛の保護層を形成します。
最後に、陰極防食は、保護されている金属を陰極に変換することにより、腐食を制御します。地下の鉄管は、亜鉛などの酸化しやすい金属に接続されていることが多く、亜鉛は酸化される犠牲陽極として機能し、鉄は腐食から保護された陰極です。

腐食

金属が自然の電気化学的プロセスによって劣化することを腐食といいます。鉄の錆び、銀の変色、銅の青緑色の錆などは腐食の一例です。腐食は、金属の酸化を伴う。銅やアルミニウムの酸化のように、表面に金属酸化物やその誘導体の保護層が形成され、下地の金属がさらに酸化されないよう保護される場合もあります。また、鉄の錆びのように、金属全体を破損させる場合もあります。
 好ましくない酸化還元反応の例: 鉄の錆び
 錆は、鉄が酸素や水にさらされることで生じます。錆が発生する理由は、鉄の表面にガルバニ電池が形成され、鉄（II）が生じるからです。鉄の表面に形成されたアノード（鉄の酸化）領域とカソード（酸素の還元）領域で起こる酸化還元反応には以下の通りです。
 <img alt="Eq1" src="/files/ftp_upload/11440/11440_Equation_1.png" style="text-align: center; height: 150px;" />
 この鉄(II)は、さらに湿度の高い空気と反応して、鉄(III)の酸化物の水和物を形成します。これが一般に「錆」と呼ばれるものです。
 <img alt="Eq2" src="/files/ftp_upload/11440/11440_Equation_2.png" style="text-align: center; height: 50px;" />
 水和水の量は、化合物の式にxが使われていることからもわかるように、鉄(II)がさらされる水の量によって変化します。水分、酸や電解質の存在は、錆の生成速度を高めます。銅の緑青とは異なり、錆が形成されても保護層は形成されないため、錆が剥がれ落ちて新鮮な鉄が大気にさらされると、鉄の腐食がさらに進行します。
 腐食の防止
 腐食を防ぐには様々な方法があります。一つの方法は、金属の表面を塗装して水や酸素との接触を避けることです。また、鉄に少量のクロムを混ぜたステンレスのように、金属を合金化することも有効な防食方法です。クロムは表面近くに集まり酸化被膜を形成するため、鉄を効果的に腐食から守ることができます。
 鉄やその他の金属は、亜鉛メッキによっても腐食を防ぐことができます。これは、保護すべき金属を、より酸化しやすい金属（通常は亜鉛）の層でコーティングするというものです。亜鉛層が無傷であれば、下地の鉄に空気が触れるのを防ぎ、腐食を防ぐことができます。亜鉛層が腐食や機械的な摩耗によって破損した場合でも、次で説明するカソード防食プロセスによって鉄を腐食から保護することができます。
 カソード防食は、防食対象の金属を電気化学反応でカソードに変えるという原理を利用しています。これは、保護される金属を、犠牲アノードと呼ばれる亜鉛やマグネシウムなどのより酸化されやすい金属と接合することで起こります。アノードは腐食し、カソードとして機能する金属を保護するために消費されます。カソード防食は、給湯器や地下貯水槽などの家庭用電化製品に最もよく使われています。重要なことは、カソード防食は鉄以外の金属にも使用できるということです。
 上記の文章は以下から引用しました。 <a href="https://openstax.org/books/chemistry-2e/pages/17-6-corrosion">OpenStax, Chemistry 2e, Chapter 17.6: Corrosion</a>.

自然の電気化学的プロセスによる金属の劣化は、腐食として知られています。鉄の錆の形成、銀の変色、そして青緑色...

Education

JoVE Core

Chemistry

化学

Electrochemistry

電気化学

KEY TERMS AND CONCEPTS

主要用語と概念

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

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 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

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