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

Korozyon, bir oksitleyici ajan, genellikle oksijen varlığında metalin kendiliğinden oksidasyonudur. Özgürlük Anıtı'nın mavi-yeşil renginin veya paslı bir çapanın ardındaki aynı fenomendir. Korozyonun bir kısmı koruyucudur.Örneğin, bakır, mavi-yeşil ve yapısal olarak kararlı bir koruyucu tabaka olan bazik bakır karbonat oluşturmak için oksijen, karbon dioksit ve su varlığında oksitlenir. Diğer korozyonlar ise zararlıdır. Örneğin, demir oksijen, su ve hidrojen iyonlarının varlığında oksitlenir ve pas adı verilen yapısal olarak kararsız metal oksitlere sürekli olarak pul pul dökülür ve alttaki metali daha fazla oksidasyona maruz bırakır.Paslanma, kendiliğinden oluşan bir elektrokimyasal reaksiyondur. Yüzeydeki kusurlar, 0, 44 Volt elektrot potansiyeline sahip demirin, demire kolayca oksitlendiği anodik bölgeler olarak görev yapar. Elektronlar, 1, 23 Voltluk elektrot potansiyeline sahip oksijenin asidik bir ortamda suya indirgendiği katodik bölgeye doğru hareket eder.Hidrojen iyonları, karbonik asit oluşturan karbondioksit ve su arasındaki atmosferik reaksiyondan gelir. Daha sonra, demir iyonları yüzey nemi yoluyla katodik bölgeye göç eder ve genellikle pas'olarak bilinen demir oksit hidrata oksitlenir. Hidratların stokiyometrisi, demirin maruz kaldığı su miktarına göre değişir.Paslanma, yüklerin akışını ve H+iyonlarının konsantrasyonunu artıran ek nem, asitler ve elektrolitlerle hızlandırılır. Korozyonu önleme yöntemleri arasında su ve oksijen ile teması önlemek için metal yüzeyin boyanması veya birden fazla metalin bir kombinasyonu olan alaşımların kullanılması yer alır. Paslanmaz çelik, demiri koruyan yüzeyde reaktif olmayan bir oksit tabakası oluşturmak için aşınan, az miktarda krom içeren bir demir alaşımıdır.Alternatif olarak galvaniz de kullanılır. Burada bir demir vida, demiri koruyan koruyucu bir çinko oksit tabakası oluşturan çinko gibi daha kolay oksitlenen bir metal tabakasıyla kaplanır. Son olarak, katodik koruma, korunan metali katoda dönüştürerek korozyonu kontrol eder.Yeraltı demir boruları genellikle çinko gibi daha kolay oksitlenen bir metale bağlanır;burada çinko, oksitlenen kurban anot görevi görür ve demir, korozyondan korunan katottur.

korozyon

Doğal elektrokimyasal işlemlere bağlı metallerin bozulması korozyon olarak bilinir. Demir üzerinde pas oluşumu, gümüşün kararması ve bakır üzerinde gelişen mavi-yeşil patina korozyon örnekleridir. Korozyon, metallerin oksidasyonunu içerir. Bazen bakır veya alüminyumun oksidasyonu gibi koruyucudur, burada yüzeyde koruyucu bir metal oksit tabakası veya türevleri oluşur ve altta yatan metali daha fazla oksidasyondan korur. Diğer durumlarda, korozyon, demirin paslanması gibi metale zarar verir.
 
 İstenmeyen Redoks Reaksiyonu: Demirin Paslanması
 
 Paslanma, demirin oksijene ve suya maruz kalması nedeniyle oluşur. Pas oluşumu, demir yüzeyinde bir galvanik hücrenin oluşturulmasını içerir ve bu da demir(II) oluşumuna neden olur. Demir yüzeyinde oluşan anodik (demirin oksidasyonu) ve katodik (oksijenin azaltılması) bölgelerde meydana gelen ilgili redoks reaksiyonları şunları içerir:
 
 <img alt="Eq1" src="/files/ftp_upload/11440/11440_Equation_1.png" style="text-align: center; height: 150px;" />
 
 Demir(II) ayrıca nemli hava ile reaksiyona girerek, yaygın olarak pas olarak bilinen bir demir (III) oksit hidrat oluşturur.
 
 <img alt="Eq2" src="/files/ftp_upload/11440/11440_Equation_2.png" style="text-align: center; height: 50px;" />
 
 Hidratın stokiyometrisi, bileşik formülde x kullanımı ile belirtildiği gibi, demirin(II) maruz kaldığı su miktarına göre değişir. Nem, asitlerin ve elektrolitlerin varlığı pas oluşum hızını arttırır. Bakır üzerindeki patinadan farklı olarak, pas oluşumu koruyucu bir tabaka oluşturmaz ve bu nedenle pas pul pul dökülürken demirin korozyonu devam eder ve taze demiri atmosfere maruz bırakır.
 
 Korozyonun Önlenmesi
 
 Korozyonu önlemek için çeşitli yöntemler kullanılabilir. Bir yol, su ve oksijen ile temastan kaçınmak için metal yüzeyi boyalı tutmaktır. Metallerin alaşımlanması, demirin paslanmaz çelikte az miktarda krom ile karıştırılması gibi, korozyonu önlemek için etkili bir yöntemdir. Krom yüzeye yakın toplanır ve oksidasyona uğrar, böylece demiri korozyondan etkili bir şekilde korur.
 
 Demir ve diğer metaller de, korunacak metalin daha kolay oksitlenmiş bir metal, genellikle çinko tabakası ile kaplandığı bir işlem olan galvanizleme ile korozyondan korunabilir. Çinko tabakası sağlam olduğunda, havanın alttaki demirle temas etmesini önler ve böylece korozyonu önler. Çinko tabakası korozyon veya mekanik aşınma ile bozulursa, demir yine de bir sonraki paragrafta açıklanan bir katodik koruma işlemiyle korozyondan korunabilir.
 
 Katodik koruma, elektrokimyasal reaksiyonda korunacak metali bir katoda dönüştürme prensibini kullanır. Bu, korunan metali, kurban anot olarak bilinen çinko veya magnezyum gibi daha aktif veya kolayca oksitlenmiş bir metale bağlayarak elde edilir. Anot korozyona uğrar ve katot olarak hizmet eden metali korumak için kullanılır. Katodik koruma en çok su ısıtıcıları ve yeraltı su depolama tankları gibi ev aletlerinde kullanılır. Önemli olarak, katodik koruma sadece demir dışındaki metaller için kullanılabilir.
 
 Bu metin bu kaynaktan uyarlanmıştır: <a href="https://openstax.org/books/chemistry-2e/pages/17-6-corrosion">OpenStax, Chemistry 2e, Chapter 17.6: Corrosion</a>.

Korozyon

Doğal elektrokimyasal süreçler nedeniyle metallerin bozunması korozyon olarak bilinir. Demirde pas oluşumu, gümüşün kararması ve mavi-yeşil ...

Education

JoVE Core

Chemistry

Kimya

Electrochemistry

Elektrokimya

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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...

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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...

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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...

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Redox Cell Potential, ΔG°, and K

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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

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Rusting and Metal Protection

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