Corrosión y Degradación de Materiales

Corrosion - Treatments

• Materials degrade due to use, application, and corrosion (or a combination of both).
• Corrosion is the interaction of metals with their surroundings, leading to chemical changes and property deterioration.
• Iron + Oxygen = Iron Oxide (FeO₂). Atmospheric and technological advancements make corrosion more severe and result in significant losses.
• Corrosion speeds up with fluids, leading to pipe failures.
• Corrosion-Cavitation: Vapor bubbles in a liquid, due to pressure changes, form and collapse near metal surfaces, causing physical and chemical damage to the material.
• Corrosion can occur internally, making it invisible on the surface (e.g., pipes, cables).
• Different metals corrode in various ways. Corrosion susceptibility depends on the material.

Corrosion Examples

• Metals: Discoloration varies depending on the liquid (e.g., yellow (silver), green (copper/bronze)). Air: discoloration (yellow - silver, green - copper/bronze), water: discoloration (gray/green - copper, gray/various hues - lead), and black (lead).
• Ceramics: discoloration, erosion, and the presence of organisms (bacteria, molds).
• Atmosphere: (humidity): discoloration and weakening (cement), discoloration (sandstone).
• Water: Erosion (limestone), moss, lichen, and bacteria (granite).
• Plastics: Decolorization/swelling may take time, but is affected by temperature cycles, sunlight exposure, and liquid exposure.

Why Materials Corrode

• Naturally occurring materials are often already mixed with other substances. Obtaining pure materials requires energy. Corrosion returns the material to its natural state, releasing energy.
• Processes involved in treating and shaping materials can be disrupted by corrosion, which makes the materials more susceptible to further degradation.

Material Construction Examples

• Chlorides: CO₂ + Oxygen in reinforced concrete. Chlorides dissolve in water and permeate concrete pores. CO₂ reacts with concrete compounds (Ca(OH)₂) forming CaCO₃, which lowers pH and damages the properties of the cement.
• Sulfates: (SO₄²⁻) in concrete. Substitution of Mg²⁺/Ca²⁺ leads to MgSO₄ and Ca(OH)₂ formation, generating Mg(OH)₂ crystals, causing concrete cracking due to volume increase.
• Metal Corrosion: Caused by atmosphere, rain, and other conditions, varying in severity among different metals.
• Polymer Degradation: Caused by heat, radiation, and water.

Corrosion Protection

• Material Selection: Choosing the right material for the intended application (e.g., titanium instead of iron for a structure).
• Design: Preventing galvanic cells (contact of dissimilar metals), and proper material joining techniques are vital (e.g., welding, adhesives are more corrosion-resistant than riveting).

Methods of Protection

• Coatings: (Permanent) act as barriers against corrosion (e.g., paints, plating with nickel).
• Cathodic Protection: Using a more reactive metal to protect the material. The reactive metal gets consumed to protect the material of interest (e.g., zinc coating protects steel).
• Inhibitors: Substances added to the environment in small quantities to slow down the corrosion process by creating protective layers on the material’s surface.

Polymers

• Organic substances of natural or synthetic origin with high molecular weights. Polymers are formed through the linking of smaller molecules called monomers.
• Polymerization: The process of creating a polymer from monomers.
• Degree of Polymerization: The number of repeating units in a polymer chain.

Polymer Properties

• Physical Properties: Often have low melting temperatures, are thermal and electrical insulators, and have high coefficients of expansion.
• Mechanical Properties: Typically display lower strength and ductility compared to metals.
• Chemical Properties: Generally stable in aggressive environments.

Polymer Structures

• Linear: Consist of a single chain with repeating monomers. (Thermoplastics)
• Branched: Possess side chains attached to the main chain. (Thermoplastics)
• Cross-linked: Monomers are linked together to form a network. (Thermosets)
• Network: A network of cross-linked polymer chains. (Thermosets)

Ceramic Properties

• Physical Properties: High melting points, excellent thermal and electrical insulation, but brittle and hard.
• Chemical Properties: Resistant to chemical attack, but can be sensitive to thermal shock (rapid temperature changes).

Ceramic Structures

• Ceramics are compounds composed of metallic and nonmetallic elements. They are typically ionic or covalent.
• They form stable lattices when cations and anions are appropriately positioned

Traditional Ceramics

• Silicates, silica, and alumina are often used in ceramics.
• Silicon dioxide (silica) is the primary constituent in many types of rock in the earth's crust.
• Alumina (aluminum oxide): commonly used in refractories (heat-resistant materials) and other high-temperature applications.
• New Ceramics (e.g. aluminum oxide, silicon carbide): designed for specific applications due to their high mechanical strength and high melting point.

Glass/Glass Products

• Often made up of silica (SiO2), soda (Na₂O) and lime (CaO), and other additives.
• Properties depend on the chemical composition.

Concrete

• Mixture of aggregates, cement, and water.
• Cement reacts with water to form a solid material binding the aggregates (stone, sand, gravel) together.

Polymer Concrete

• Concrete reinforced with polymers.
• Polymer concrete enhances the material's properties such as flexibility, resistance to aggressive environments, and other similar traits

Metals and Alloys

• Metallic Bonding:
• Electrical Conductivity:
• Heat Conductivity:
• Plasticity: The ability to be deformed permanently without fracture.
• Alloying: The process of combining different metals or a metal with a nonmetal substance to produce an alloy.

Ferrous Alloys (e.g., Steel)

• Primarily iron, but containing carbon.
• Steel - Iron with carbon, used for various structural applications.
• Other alloys (e.g., cast iron).

Non-ferrous Alloys (e.g., Aluminum)

• Aluminum - Good strength, lightweight and conductive.
• Other alloys (e.g., copper alloys, like bronze and brass).

Steel Treatment Techniques

• Annealing: Heat treatment to soften steel.
• Normalizing: Heat treatment to improve uniformity of microstructure.
• Hardening: Heat treatment to increase hardness.
• Tempering: Heat treatment to reduce brittleness after hardening.
• Case Hardening (Surface Hardening): Enhancing only the surface area of a component, making it stronger and resistant to wear. For example, nitriding, carburizing (increasing the carbon content).

High-Alloy Steels (e.g., Stainless Steel)

• High Cr content for superior corrosion resistance.
• Alloying elements (e.g., nickel and molybdenum).

Non-ferrous Alloy Examples

• Alloys of copper (e.g., brass, bronze, nickel, etc.)
• Alloys of aluminum.
• Titanium alloys.

Heat Treatment Testing

• Jominy Test: Used to assess the hardenability of steel specimens. A specimen is heated and quenched at one end, and the hardness is measured at different locations along the length of the component.

Este cuestionario aborda diversos tipos de corrosión y su relación con diferentes materiales, así como la degradación de polímeros y cerámicos. A través de preguntas específicas, se evaluará tu conocimiento sobre los procesos de corrosión, polimerización y las condiciones que afectan la durabilidad de estos materiales. ¡Pon a prueba tus conocimientos y aprende más sobre la ciencia de los materiales!