Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Physical Chemistry → Electrochemistry ↓


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Corrosion is a natural process in which metals degrade as they react with their environment. The process is electrochemical, meaning it involves the movement of electrons between the metal and its surrounding environment. Corrosion weakens the metal structure and is a significant concern in sectors ranging from construction to transportation.

Understanding corrosion

To understand rust, consider a simple iron nail exposed to air and moisture. This nail will slowly rust over time. Rusting is a common form of corrosion, in which iron reacts with oxygen and water vapor to form iron oxide, a reddish-brown compound. The basic reaction for rusting of iron is as follows:

4Fe + 3O 2 + 6H 2 O → 4Fe(OH) 3

This reaction shows that iron reacts with oxygen in the presence of water to form hydrated iron(III) oxide, commonly called rust.

Electrochemical nature of corrosion

Corrosion is an electrochemical process that generally involves the flow of electrons from a metal to a nonmetal in a chemical cell. During this process, two half-reactions occur at different locations on the metal surface, which can be understood as anodic and cathodic reactions.

Anodic reaction

The anodic reaction involves the oxidation of the metal. In the case of iron, the anodic reaction can be represented as follows:

Fe → Fe 2+ + 2e -

In this reaction, iron atoms lose electrons to form iron ions. These electrons are released into the surrounding environment, leaving the surrounding area negatively charged.

Cathodic reaction

At the cathodic site, reduction occurs, usually involving a non-metallic element. For example, in the presence of atmospheric oxygen, the electrons released by the anodic reaction can reduce oxygen at the cathodic site:

O 2 + 4H 2 O + 4e - → 4OH -

In this reduction reaction, oxygen is converted into hydroxide ions, OH -, which can further react with iron ions to form rust.

Mechanism of corrosion

The corrosion process involves a complex series of electrochemical reactions. Both anodic and cathodic reactions can occur at microscopic sites distributed across the metal surface. The spatial separation of these processes is important, as it creates conditions that maintain the flow of electrons.

For further clarification, consider the following diagram, which shows the basic flow of electrons in a corrosion cell:

Anode Cathode E - Fe2+ → Fe2 + + 2e− O 2 + 4H 2 O + 4e - → 4OH -

In this view, the anode (in green) is the site of metal dissolution, while the cathode (in orange) is where reduction occurs. Electrons, driven by the electrochemical potential difference, flow from the anode to the cathode. This flow sustains the overall corrosion process.

Types of corrosion

Corrosion can present itself in a variety of forms, each of which is affected by different environmental conditions and material properties. Understanding these types helps to reduce and effectively prevent corrosion.

Uniform corrosion

Uniform corrosion occurs evenly across the exposed surface of the metal. This is the most common form of corrosion and is often the easiest to predict and manage. For example, the gradual rusting of an iron fence is a case of uniform corrosion.

Galvanic corrosion

Galvanic corrosion occurs when two different metals, in electrical contact, come into contact with an electrolyte. The less noble metal (anode) corrodes faster while the more noble metal (cathode) corrodes slower. An example of this type is the corrosion seen at the junction of steel and copper pipes.

Pitting corrosion

Pitting corrosion involves localized attack in the form of tiny holes or pits on the metal surface. This type is particularly damaging because it can cause failure with little overall metal loss. It is common in stainless steels exposed to chloride environments.

Crevice corrosion

Crevice corrosion occurs in confined spaces where stable solution is present. Tight joints, overlaps and surface deposits are classic sites for this type of corrosion, which often affects stainless steel and aluminum alloys.

Intergranular corrosion

Inter-granular corrosion attacks the grain boundaries of metals. It can occur in stainless steel that is improperly heated, causing the precipitate of chromium carbides that eliminate chromium from surrounding grains, making them susceptible to corrosion.

Stress corrosion cracking (SCC)

SCC is the growth of cracks in corrosive environments, which are exacerbated by tensile stress. It is a dangerous form as it can cause unexpected and sudden failures of the material. Stainless steels are particularly susceptible to SCC in chloride environments.

Corrosion control methods

Understanding the mechanisms and types of corrosion allows the development of effective control strategies. Many methods have been designed to reduce or prevent corrosion in various applications.

Material selection

A primary way to control corrosion is to select materials that are naturally resistant to corrosive environments. Stainless steel and non-metallic materials such as plastics and ceramics are chosen for their corrosion-resistant properties.

Protective coatings

Applying protective coatings such as paint or plating to metal surfaces protects them from direct exposure to corrosive environments. These coatings create a physical barrier that slows down oxidation processes.

Cathodic protection

Cathodic protection techniques involve making a metal the cathode of an electrochemical cell by connecting it to a corroding "sacrificial" anode. A common example is connecting zinc anodes to steel structures immersed in water.

Environmental control

By controlling environmental factors such as humidity, temperature and exposure to corrosive agents, corrosion can be slowed down to a great extent. For example, humidity control is important in the storage and packaging of metal products.

Conclusion

Corrosion is an inevitable natural process that affects metals through various electrochemical reactions. The complexity of corrosion mechanisms requires a deep understanding of both the material and the environment. By applying scientific principles, designing appropriate structures and employing preventive techniques, the effects of corrosion can be minimized, ensuring the safety, longevity and functionality of metal systems.


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