Chemistry of Materials PDF

# Chemistry of Materials ## Tema 1: Enlace en los Materiales Properties of materials depend on: - The geometric arrangement of the atoms - The different types of interactions between the atoms ### **Ionic** - Transfer of electrons from electropositive atoms to electronegative atoms - Electrost...

# Chemistry of Materials ## Tema 1: Enlace en los Materiales Properties of materials depend on: - The geometric arrangement of the atoms - The different types of interactions between the atoms ### **Ionic** - Transfer of electrons from electropositive atoms to electronegative atoms - Electrostatic bond (non-metal + metal) - High bond energy, high melting point, hardness - One atom donates its valence electron(s) to another atom. *Examples*: Cements, concretes, rocks, plaster, limes, bricks. ### **Covalent** - Sharing of electrons between pairs of atoms (non-metal + non-metal) ### **Metallic** - Sharing of delocalized electrons between all the atoms in a metallic crystal (metal + metal) ## Tema 4: Corrosion - Treatments Materials degrade due to: - **Fatigue**: Usage and application - **Corrosion**: Interaction of metals with the surrounding environment, causing a chemical change deteriorating its properties. - **Corrosion**: A combination of both fatigue and corrosion. ### **Corrosion** - **Fe + O2 → Iron oxide (FeO2)** - Increased aggression of atmospheres and technological advancements lead to a faster deterioration due to corrosion. - Corrosion is accelerated by fluids causing the breakage of pipes. **Examples**: - **Corrosion Cavitation**: Vapor bubbles that form in the liquid due to pressure changes are collapsed near the metal surfaces, which causes physical and chemical damage to the material. - **Corrosion Visible/Invisible**: Corrosion can also occur inside the material and is not visible on the surface. (pipes, cables, etc.) - **All materials corrode**, but some corrode more than others. The corrosion mechanisms are not the same and depend on the material. ### **Metallic Corrosion** - **Air**: Yellow discoloration (silver), green spots (copper, bronze (Sn+Cu)) - **Water**: Gray/green spots (copper), Gray/various colors (lead), black spots (Pb) ### **Ceramic Corrosion** - **Atmosphere (humidity)**: Discoloration and weakening (cement), discoloration (sandstone) - **Water**: erosion (limestone), moss, lichens, bacteria (granite) ### **Plastic Corrosion** - It takes years for biodegradable polyethylene to corrode. - It can also discolor/swell due to the cycles of cold-heat, exposure to sunlight, and brake fluids. ### **Sunlight** - Decomposes materials (typically plastics) through photochemistry. - Temperature deforms and weakens the material, and discolors them. ## Porque se corroen los materiales?: - Materials found in nature are corroded and mixed with various substances. It takes energy to obtain pure materials. Materials corrode and return to their natural state, releasing energy. - There is a cancellation of the processing of materials, and the subsequent formation of new materials. The harder it is to extract a metal, the more susceptible it is to corrosion. ##Ejemplos en Materiales de Construccion: - **Chlorides**: CO2 + Oxygen in hardened concrete. They penetrate dissolved in water and distribute through the network of pores in the concrete. - **CO2** reacts with a component of hardened cement (Ca(OH2)), forming CaCO3 and lowering the pH, which corrodes and modifies the properties of the cement. - **Sulfates(SO2)** in hardened concrete: Mg+Ca2+ (substitution): MgSO4+Ca(OH)2 → Mg(OH)2 - **Etringita**: Crystals in the form of needles, causing an increase in the volume of the concrete and consequent cracking. - **Corrosion of Metals**: Caused by the atmosphere and rain, some metals corrode more than others - **Degradation of polymers**: Caused by heat, solar radiation, and water ## Protection against Corrosion: 1. **Choose the adequate material**: Depending on the function and the environment where it is used (Ex: titanium instead of iron for a structure.) 2. **Design the material appropriately**: Prevent the formation of galvanic cells. Two metals with very different corrosion behaviors will behave differently (ex: steel will oxidize before other materials in these cells.) * **Make the surface area of the metal that oxidizes much larger than the surface area of the stainless steel**. * **Avoid cracks in assembled or joined materials.** **Welding and adhesive joints** are better than rivets/bolts in these cases. * **Mechanical joining** is more prone to corrosion (storing corrosive materials). (mechanics = bolts) (welding = welding) (adhesives = glues) 3. **Using Protective Methods**: a) **Coatings**: Permanent and act as barriers against corrosion. - **Paint**: Polymers - **Nickel plating**: Metallic - **Anodizing**: Metal oxides b) **Cathodic Protection**: The material to be protected is connected to another material that corrodes faster (sacrificial anode, usually Mg or Zn). * This is a widely used method to protect buried pipes (Ex. Steel pipe 3mm. Without protection: 2.5 years. With protection: 250 years). c) **Inhibitors**: Substances added to the medium in small concentrations that decrease the rate of corrosion. They form a protective layer on the surface of materials. They provide temporary protection. # Polymers - **Substances (usually organic)** of natural/artificial origin with a high molecular weight. - **Formed** by the union of low molecular weight molecules called **monomers**. - The number of monomers in a polymer can reach **thousands or millions**. ## Polymerization: - The process where a monomer converts into a polymer. *Example*: Vinyl chloride → Polyvinyl chloride ## Degree of Polymerization: - The number of units that repeat in a chain. - In real polymers, the number is not equal for all chains, so we talk about an average degree of polymerization (difficult process). ## Physical Properties: - **Low melting point (Tm)** - **Thermal and electrical insulators** - **High expansion coefficients** (change their dimensions in freeze/heat cycles) ## Mechanical Properties: - **More ductile than metals** - **Poor tensile strength and low tenacity** ## Chemical Properties: - **Stable against aggressive media** (more or less unstable against UV light and heat) ## Types of Polymers: - **Homopolymers:** All monomers that compose the polymer are the same. - **Copolymers:** Formed by two or more different monomers. The arrangement of the monomers in the chain influences the properties. ## Structures of Polymers: - **Linear:** The same type of bond repeats linearly (thermoplastics). They lack lateral branches. - **Branched:** Lateral chains join the main chain. Higher branch degree means the polymer is stronger and more viscous (thermoplastics). - **Cross-linked:** Bonds are formed between neighboring chains (thermosets (very cross-linked) and elastomers (slightly cross-linked)). Stronger and more rigid. ## Mechanical and Thermal Properties: - **Thermoplastics:** Chains are more or less linear (but can have some branching). They are flexible due to Van-der-Waals interactions. They can be melted without decomposition, and you can apply repeated cold/hot cycles without degrading the polymer. - **Thermosets:** Chains are very cross-linked by covalent bonds. They are strong and brittle. They harden when heating. - **Elastomers:** Chains are very flexible with some cross-linking. They deform elastically without permanent change in shape. They return to their initial shape when the deforming force is removed. They are elastic. ## Orientation of Chains in Space - **Amorphous**: Disordered (thermosets, thermoplastics, elastomers) - **Crystalline**: Ordered (ONLY thermoplastics to a certain degree) - **Semicrystalline**: Contains disordered parts and ordered parts (spherulites in an amorphous matrix). ## Degree of Crystallinity and Properties: - As the degree of crystallinity increases: - Density - Rigidity - Resistance (normal and thermal) - If the polymer is transparent in the amorphous state, it turns opaque in the semicrystalline state. - Values of properties like crystallinity degree, density, elastic modulus, and melting temperature rise when the density of polyethylene (PE) is high. ## Glass Transition Temperature (Tg) - Temperature at which a polymer solidifies as an amorphous solid and acquires a glassy structure. - When the temperature drops below Tg, the polymer becomes brittle. - If Tg is high, the polymer exhibits a rubbery characteristic. ## Polymers in Construction - Insulation - Carpentry - Floor coverings - Roofing - Solar panels - Acoustic and safety panels - Pipes - Electrical insulation # Ceramics - Compounds formed by metallic and non-metallic elements with **predominantly ionic bonding** and high melting temperatures. - They are commonly **brittle**, **hard**, and have **low tenacity and ductility**. - They are **sensitive to abrupt temperature changes** (thermal shock). - They are **crystalline at an atomic level**, but they can be produced in a non-crystalline state using specific techniques (glass). - **Thermal and electrical insulators**. - They include a wide variety of compounds: - Porcelain - Bricks - Glass - Cement ## Ceramic Structures: - **Completely or partially** ionic compounds formed by metal cations and non-metal anions. - They exhibit complex crystalline structures. - They present stable structures when **cations (anions) are completely surrounded by anions (cations)**. ## Traditional Ceramics: - **Bricks, cements, tiles, and silicates**. - **Silicates**: The essential components of rocks, and therefore the Earth's crust. - Composed of silicon, oxygen, and other metals. - **Silica**. The most commonly called compound of silicon and oxygen: Silicon dioxide (S1O2). It is a spatially ordered compound, forming quartz and its different forms. - **Alumina**. Aluminum oxide (Al₂O₃). ## New Ceramics: - A special kind of ceramic formed by compounds such as: - Aluminum oxide (Al2O3). - Silicon carbide (SiC). - Silicon nitride (Si3N4). - Its properties can be modified by the addition of other elements. - They are expensive and manufactured in laboratories - They have high mechanical and melting point properties. ## Amorphous Ceramics (Glass) - **Basic Unit**: Silicon dioxide (SiO4). - They have a very high melting point and are viscous. - They have **modifiers (fluxes) to reduce their viscosity**. - They are traditional ceramics but are manufactured differently. ## Products of Glass and its Additives: - **Additives**: Specific modifiers that depend on the glass application. | Product | SiO2 | Na2O | CaO | Al2O3 | MgO | K2O | PbO | B2O3 | Others | |---|---|---|---|---|---|---|---|---|---| | Soda-lime glass | 71 | 14 | 13 | 2 | | | | | | | Window glass | 72 | 15 | 8 | 1 | | 4 | | | | | Glass for containers | 72| 13 | 10 | 2 | | | 1 | | | | Glass for bulbs | 73 | 17 | 5 | 1 | | | 4 | | | | Laboratory glass | 74 | 17 | 4 | 1 | | | 2 | | | | Vycor | 96 | 1 | 3 | | | | | | | | Pyrex | 81 | 4 | 2 | | | | | 13 | | | Glass-E (fibers) | 54 | 1 | 17 | 15 | 4 | | | 9 | | | Glass-S (fibers) | 64 | | | 26 | 10 | | | | | | Optical glass | 67 | 8 | | | | | 12 | 12 | | | Boron glass | 67 | | | | | | 12 | 12 | | | Lead glass | 46 | | | | | | 45 | | ZnO | ## Conventional Concrete: - A composite material made of: - **Aggregates**: Granular material with high mechanical and chemical resistance (sand, gravel, crushed stone). - **Binder**: Cement (CaO, SiO2, Al2O3, Fe2O3, and other compounds), acts as a binder when mixed with water. - **Water**: The activator for the reaction of the binder. - **Aggregates + Binder + Water = Setting (reaction)** ## Features of Conventional Concrete: - **Strength**. Cement's strength depends on the amount of binder present, the type of aggregates, and their ratios. - **The product (aggregate)** is obtained through the calcination (high temperature decomposition) of limestone and clay. It's used in the production of cement. - **Cement**: The result of mixing clinker, gypsum, and additives (to modify the viscosity or setting time). The amount of each component determines the final use of the cement. ## Polymer Concrete: - Conventional concrete where part or all the cement has been substituted by polymers to improve its mechanical and physical properties. - Most used polymers: polystyrene, epoxy, polyester, and polymethyl methacrylate. ## Properties of Polymer Concrete: - **Excellent mechanical resistance** in tension and compression - **Lightweight element production** - **High resistance to corrosive materials** and UV radiation. - **Low permeability** and good resistance to water. - **Higher resistance** to freeze/thaw cycles than conventional concrete, which is porous. - **Almost null water absorption**. - **Good surface stability** and no porosity. - It avoids the risk of fermentation and bacterial development. - **High dimensional stability** - **Good absorption of vibrations** - **Easy to apply color** - **High resistance to impact**. # Metals and Alloys - **Metallic bonding** (metal + metal) and **crystal structure** - **High electrical and thermal conductivity** due to the mobility of electrons. - **High plasticity** (permanent deformation) - **Bright** (reflect light) - **High alloyability**. ## Irons and Steels - **Transition metal**. - Transition metal's crystal structure depends on temperature (T). * **25°C → BCC Ferrite (α)** * **912°C → FCC Austenite (γ)** (higher temperature) * **1394°C → BCC Ferrite(δ)** (higher temperature) * **1538°C → liquid** - **Iron-Carbon System (Steels and Cast Irons)**: * **Carbon**: Interstitial solute in iron * **Iron** has a low solubility of carbon (maximum: 0.022% at 727 °C) * **Cementite** forms as the solubility limit is exceeded. * Cementite is **hard, brittle**, and reinforces the strength of some steels. - **Steel:** Iron + Carbon (in small quantities) - **Carbon**: Occupies interstitial sites in the crystal lattice of the iron metal (octahedral interstitial site). - **Steel:** Fe + C (< 2.1%) - **Cast Iron:** Fe + C (2.1% - 6.7%). Carbon is dissolved in smaller quantities. - **When C > 6.7%,** Fe + C → Fe3C (cementite, brittle and hard). ## Heat Treatments: - Heating and cooling metal/alloy under specific conditions of time and cooling/heating rate (FCC). - **Annealing**: Heating to a specific temperature (800-950°C) and slow cooling in a furnace. - The steel loses hardness and gains ductility, and removes internal stresses - The slower the cooling, the more the material loses its hardness. - **Normalizing**: Heating to 800-950°C and cooling in air. The cooling process is faster than in annealing. - It produces steel with better mechanical resistance. - **Tempering**: Heating to a higher temperature (900-950°C), to obtain an austenitic structure. It involves fast cooling in water, oil, gas, etc., down to near room temperature, to achieve a martensitic structure. - It produces high hardness steels. ## Hardenability: - It's used to describe a metal's ability to harden to a certain depth, by martensite formation. ## Jominy Test: - To determine the hardenability of a steel. 1. An austenitized sample is heated to a specific temperature for a specific time. 2. One end of the sample is quenched with a water jet with a specific velocity and temperature. 3. After cooling, the hardness of the sample is measured at different points along the sample. 4. A hardness curve of the sample is produced against the distance from the quenched end. ## Thermo-chemical surface treatments: - They modify the surface of a metal alloy to increase its hardness. - **Carburizing and Nitriding**: A steel with low carbon content is exposed to a carbon-rich or nitrogen-rich atmosphere to enrich the surface with these elements. It produces a hard and resistant layer. The depth of the layer depends on the temperature and the duration of the treatment. - **Carburizing**: Increases the carbon content of the metal surface. - **Nitriding**: It provides a similar hardening effect. The steel is exposed to a nitrogen-rich gas atmosphere. - **Cementation**: MxCn, generate carbides - **Nitriding**: MxNy, generate nitrides (C, N are absorbed from ammonia gas and produce carbides and nitrides, respectively, on the surface). This is a **surface reaction and does not involve melting**. # Alloys - **Ferrous**: Based on iron (Fe). - **Non-ferrous**: Not based on iron (Fe). ## Ferrous Alloys (based on Fe): - **Iron** is the main component. - They are the most widely used alloys (especially steels). - **Disadvantages**: - High density - They are very susceptible to corrosion (they degrade readily in the presence of oxygen and humidity). ## Steels: - Iron-Carbon alloys (C < 1.4%). - They are classified by carbon content (C). - **Low Carbon Steels:** - C < 0.25%. - They are soft and not very resistant. - Ductile and tenace. - **Medium Carbon Steels:** - 0.25% < C < 0.6%. - They are more resistant and less ductile and tenance. - **High Carbon Steels:** - C > 0.6% - 2.4%. - They exhibit higher resistance and have less ductility and tenacity. ## High alloy steel or stainless steel - Fe, C, chromium (Cr>11%) , and other elements such as nickel (Ni) and molybdenum (Mo). - They are highly corrosion-resistant due to the presence of chromium (Cr). - They have a lower melting point than regular steel. - **Cast Iron:** - %C > 2.1% - %Si > 0.5% - 3%. - They are less mechanically resistant than steel. ## Non-ferrous Alloys (where the main component is not iron): - **Copper Alloys:** - **Good thermal and electrical conductor** (conducts heat and electrical current well). - **Corrosion resistant** (less susceptible to oxidation than iron, especially in the presence of oxygen and humidity). - **Ductile** (easily deformed plastically). - **Brass:** Cu+Zn (<40%) - **Bronze:** Cu+Sn (<12%) - **Monel:** Cu+Ni (solid solubility total. High resistance and excellent mechanical properties). ## Aluminum Alloys: - **High thermal and electrical conductivity** (conducts heat and electricity well). - **Ductile** (highly plastic). - **Corrosion resistant** (especially due to self-passivation). - **Disadvantages**: * Low melting temperature (600°C). * Low elastic modulus (lacks good mechanical resistance). ## Main Alloys: - **Aluminum + magnesium (Mg), titanium (Ti), Lithium (Li):** Very lightweight alloys. - **High specific resistance**. - **Low weight but high resistance** (good mechanical resistance). - It is becoming a strong competitor to steel in many structural applications (because it is easier to shape). - **Properties**: - **Low density** (2.7 g/cm3 compared to 7.8 g/cm3 for steel). - **High corrosion resistance** (self-passivation) (steel + Cr is expensive). - They can **withstand structural damage** in stressful situations, even when the structure is already damaged. - **High fatigue resistance** with cyclic loads. ## Superalloys: -(Ni, Co, Ti). - They have exceptional mechanical properties at high temperatures. - They can operate at temperatures close to the melting temperature. - **Good resistance** to corrosion in extreme environments - **Difficult to manufacture** due to their high cost. - **Used for applications that require high performance** in stressful conditions. - Blades in superalloy titanium. ## Widely used alloys in construction: - **Steel**: Reinforcement in concrete because of its excellent mechanical properties. - **Corrugated steel**: Good plasticity deformation (less brittle). - **Aluminum**: Windows, roofs, walls, and roofs. It is a good material to ensure energy efficiency. **Properties**: - **Good thermal insulation** (good thermal insulation for buildings). - **Recyclable** (sustainability). - **Resistant to corrosion**. - **Suitable for electrical wiring**, plumbing, and HVAC (Heating, Ventilation, and Air-Conditioning) due to its excellent conductivity. - **Titanium**: - **Lightweight** - **Extremely corrosion-resistant** - **Low thermal expansion coefficient** (half that of stainless steel). - Used in heating and cooling systems, pipes, and as interior and exterior cladding. ==End of OCR for page 16==