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

קורוזיה היא החמצון הספונטני של מתכת בנוכחות סוכן חמצון, בדרך כלל חמצן. זו אותה תופעה האחראית לצבעו הכחול-ירקרק של פסל החירות או של עוגן חלוד. חלק מתהליכי הקורוזיה מגנים על חומר.לדוגמה, כשנחושת מתחמצנת בנוכחות חמצן, פחמן דו-חמצני ומים, היא יוצרת נחושת פחמתית, שכבה כחולה ירוקה המספקת הגנה מבנית יציבה. תהליכי קורוזיה אחרים מזיקים. לדוגמה, ברזל מתחמצן בנוכחות יוני חמצן, מים ויוני מימן ויוצר תחמוצת מתכת בלתי יציבה מבחינה מבנית הנקראת חלודה, הנוטה להתקלף ולחשוף את המתכת שתחתיה לחמצון נוסף.חלודה היא תגובה אלקטרוכימית ספונטנית. פגמים על פני השטח משמשים כאזורי האנודה שבהם ברזל, עם פוטנציאל אלקטרודה של מינוס 0.44 וולט, מתחמצן בקלות לברזל האלקטרונים נודדים לעבר האזור הקתודי, שבו חמצן, בעל פוטנציאל אלקטרודה של פלוס 1.23 וולט, מחוזר למים בסביבה חומצית. יוני המימן מגיעים מהתגובה האטמוספרית בין פחמן דו חמצני לבין מים, היוצרים חומצה פחמנית.לאחר מכן יוני ברזל הנודדים לאזור הקתודי דרך הלחות שמעל פני השטח, מחומצנים עוד להידראט התחמוצת ברזל מימן הנקראת חלודה"הסטויכומטריה של ההידראט משתנה בהתאם לכמות המים שהברזל חשוף לו. החלדה מואצת עם תוספת לחות, חומצות ואלקטרוליטים, המחזקים את זרימת המטענים וכן את ריכוז יוני H+שיטות למניעת חלודה כוללות צביעת פני השטח של המתכת למניעת מגע עם מים וחמצן או שימוש בסגסוגות, שילוב של מתכות מרובות. פלדת אל-חלד היא סגסוגת של ברזל המכילה כמות קטנה של כרום, העובר קורוזיה ויוצר שכבת תחמוצת לא מגיבה על פני השטח, המגנה על הברזל.לחלופין, נעשה שימוש גם בגלוון. כאן מברג מברזל מצופה בשכבה המתחמצנת בקלות רבה יותר כמו אבץ, היוצרת שכבה מגנה של תחמוצת אבץ, השומרת על הברזל. לבסוף, הגנה קתודית מגנה מפני קורוזיה באמצעות המרה של המתכת המוגנת לקתודה.צינורות תת-קרקעיים מברזל מחוברים לעיתים קרובות למתכת המתחמצנת בקלות רבה יותר כמו אבץ, כשהאבץ מוקרב כאנודה מתחמצנת והברזל הוא הקתודה, המוגנת מחלודה.

קורוזיה

<div style="direction:rtl">

הרס של מתכות כתוצאה מתהליכים אלקטרוכימיים טבעיים מכונה קורוזיה. היווצרות חלודה על ברזל, הכתמה של כסף והפטינה הכחולה-ירוקה המתפתחת על נחושת הם דוגמאות לקורוזיה. קורוזיה כרוכה בחמצון של מתכות. לפעמים זה מגן, כמו חמצון של נחושת או אלומיניום, שבו שכבת הגנה של תחמוצת מתכת או נגזרותיה נוצרת על פני השטח, המגנה על המתכת הבסיסית מפני חמצון נוסף. במקרים אחרים, קורוזיה פוגעת במתכת, כמו החלודה של ברזל. 

תגובת חמצון-חיזור לא רצויה: החלודה של הברזל 

חלודה מתרחשת עקב חשיפה של ברזל לחמצן ומים. היווצרות חלודה כרוכה ביצירת תא גלווני על פני השטח של ברזל, מה שמביא ליצירת ברזל(II). תגובות חמצון-חיזור הרלוונטיות המתרחשות באזורים האנודיים (חימצון ברזל) והקתודיים (חיזור חמצן) הנוצרים על פני הברזל כוללים: 
<img alt="Eq1" src="/files/ftp_upload/11440/11440_Equation_1.png" style="text-align: center; height: 150px;"> 

הברזל(II) מגיב עוד יותר עם אוויר לח, ויוצר תחמוצת ברזל לחה(III), הידועה בכינויה חלודה. 
<img alt="Eq2" src="/files/ftp_upload/11440/11440_Equation_2.png" style="text-align: center; height: 50px;"> 


הסטוכיומטריה של הלחות משתנה בהתאם לכמות המים שאליה נחשף ברזל(II), כפי שמצוין על ידי השימוש ב-x בנוסחת התרכובת. לחות, נוכחות של חומצות ואלקטרוליטים מגבירה את קצב היווצרות החלודה. בניגוד לפטינה על נחושת, היווצרות החלודה אינה יוצרת שכבת הגנה, וכך נמשכת קורוזיה של הברזל כשהחלודה מתקלפת וחושפת ברזל טרי לאטמוספירה.

מניעת קורוזיה 

ניתן להשתמש בשיטות שונות למניעת קורוזיה. דרך אחת היא לשמור על משטח המתכת צבוע כדי למנוע מגע עם מים וחמצן. סגסוגת מתכות, כמו ערבוב ברזל עם כמויות קטנות של כרום בנירוסטה, היא שיטה יעילה נוספת למניעת קורוזיה. הכרום נאסף ליד פני השטח ועובר חמצון, ובכך מגן ביעילות על הברזל מפני קורוזיה. 

ניתן גם להגן על ברזל ומתכות אחרות מפני קורוזיה על ידי גלוון, תהליך שבו המתכת שיש להגן מצופה בשכבה של מתכת מתחמצנת בקלות רבה יותר, בדרך כלל אבץ. כאשר שכבת האבץ שלמה, היא מונעת מגע של אוויר עם הברזל הבסיסי ובכך מונעת קורוזיה. אם שכבת האבץ נפרצה על ידי קורוזיה או שחיקה מכנית, הברזל עדיין עשוי להיות מוגן מפני קורוזיה על ידי תהליך הגנה קתודי , המתואר בפסקה הבאה. 

הגנה קתודית מנצלת את העיקרון של המרת המתכת להגנה לקתודה בתגובה אלקטרוכימית. זה מושג על ידי חיבור המתכת המוגנת למתכת פעילה יותר או מתחמצנת בקלות כמו אבץ או מגנזיום, המכונה אנודת ההקרבה. אנודה קורוזיה ומתרגלת בהגנה על המתכת המשמשת כקתודה. הגנה קתודית משמשת לרוב במכשירי חשמל ביתיים כגון מחממי מים ומיכלי אגירת מים תת קרקעיים. חשוב לציין, ניתן להשתמש בהגנה קתודית למתכות שאינן רק ברזל. 

טקסט זה מותאם מ<a href="https://openstax.org/books/chemistry-2e/pages/17-6-corrosion">OpenStax, Chemistry 2e, Chapter 17.6: Corrosion</a>.</div>

השפלה של מתכות עקב תהליכים אלקטרוכימיים טבעיים ידוע בשם קורוזיה. היווצרות חלודה על ברזל, השחרת כסף, וכחול-ירוק ...

Education

JoVE Core

Chemistry

כימיה

אחד

Electrochemistry

אלקטרוכימיה

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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 Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

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