Material Choices (OCR)

Material Properties

• Materials have unique characteristics that make them suitable for specific purposes.

  • Example: Metal is strong and durable, while plastic is flexible and lightweight.

• Some characteristics can be found in multiple materials.

  • Example: Both wood and metal can be strong, but wood is also flexible, while metal is typically rigid.

• Information about material properties helps in choosing the best material for a product.

  • Example: Comparing the strength-to-weight ratio of aluminum and steel to decide which is better for a bicycle frame.

Ceramics

• Ceramics are materials made from clay, which is hardened by heating.

  • Properties:

    • Hard: Resistant to scratching.

    • Strong in compression: Can withstand squeezing forces.

    • Weak in tension: Break easily when pulled or stretched.

    • Brittle: Snap rather than bend when stressed.

    • Opaque: Light cannot pass through.

Metals

• Metals are elements that readily lose electrons to form positive ions.

  • Properties:

    • Malleable: Can be shaped without breaking.

    • Ductile: Can be drawn into wires.

    • Good conductors of heat and electricity.

    • Strong in tension and compression: Resists both pulling and squeezing forces.

    • Stiff: Maintains shape under force.

    • Density: Varies between metals.

Polymers

• Polymers are large molecules made up of repeating smaller units called monomers.

  • Properties:

    • Poor conductors of heat and electricity.

    • Durable: Lasts a long time.

    • Low density: Lightweight.

    • Flexible: Can be bent without breaking (often).

    • Transparent or opaque: Light can pass through or not.

    • Soft: Can be easily scratched or dented.

    • Melting point: Varies depending on the type of polymer. Some soften when heated, while others remain solid.

Composite Materials

• A composite material is a combination of two or more materials with different properties.

• By combining these materials, the resulting composite often has superior properties to its individual components.

Components of a Composite Material

• Reinforcement

  • The material that provides strength and stiffness.

    • Examples include fibers (glass, carbon, aramid), particles, or whiskers.

• Matrix

  • The material that binds the reinforcement together. 

  • Common matrices include polymers (resins), metals, and ceramics.

Examples of Composite Materials

• Reinforced concrete

  • Concrete reinforced with steel rods or mesh. Combines the compressive strength of concrete with the tensile strength of steel.

• Fiber-reinforced plastics (FRP)

  • Plastics reinforced with fibers like glass, carbon, or aramid. Used in various applications due to their high strength-to-weight ratio.

• Wood

  • A natural composite of cellulose fibers embedded in a lignin matrix.

Advantages of Composite Materials

• Tailored properties

  • By selecting specific reinforcement and matrix materials, engineers can design composites with desired properties.

• High strength-to-weight ratio

  • Many composites are lighter and stronger than traditional materials.

• Corrosion resistance

  • Some composites, like fiberglass, are resistant to corrosion.

• Design flexibility

  • Composites can be molded into complex shapes.

Applications of Composite Materials

• Aerospace

  • Aircraft wings, fuselage, and components.

• Automotive

  • Car bodies, chassis, and engine components.

• Construction:

  • Reinforced concrete, prefabricated building panels.

• Sports equipment

  • Tennis rackets, golf clubs, bicycles.

• Marine industry

  • Boat hulls, masts, and sails.

Matching Properties to Use

• Property

  • A characteristic of a material that describes its behavior.

• Use

  • The application or purpose of a material.

    • Example:

      • Metal is strong and durable.

      • Metal is used to build bridges and cars because of its strength.

Table 1

• Mild steel has a lower tensile strength than aluminum, so it stretches more easily when forces are applied. It has a lower compressive strength.

• Tensile strength measures a material's ability to resist being pulled apart.

• Compressive strength measures a material's ability to resist being crushed.

• If mild steel has a lower tensile and compressive strength than aluminum, it would indeed stretch and crush more easily when subjected to forces.

Multiple Material Options

• Often, multiple materials can be suitable for a specific use. It's essential to evaluate the advantages and disadvantages of each option to make the best choice.

  • Example:

    • Use: Building a house

    • Material options: Wood, brick, concrete, steel

    • Evaluation: Consider factors like cost, insulation, durability, and aesthetics to choose the best material.

Key Considerations

• Required properties: What characteristics are essential for the product?

• Material availability: Is the material readily accessible and affordable?

• Processing methods: Can the material be easily shaped or formed into the desired product?

• Environmental impact: What is the material's impact on the environment during production and disposal?

• Cost: What is the overall cost of the material and its processing?

Alloys and Polymers

Alloys

• Alloy: A mixture of two or more elements, where at least one element is a metal.

  • Example: 

    • Brass is an alloy of copper and zinc.

• By understanding the properties of alloys, engineers and designers can select the most appropriate materials for specific applications, optimizing performance and efficiency.

Alloy Strength

• Increased strength

  • Combining metals often results in a stronger material.

    • Example: Brass is stronger than pure copper or zinc.

• Metal Lattice Structure

  • Pure metals have a regular arrangement of atoms (lattice).

  • When a force is applied, atoms can slide past each other, causing the metal to deform.

• Alloy Lattice Distortion

  • Adding different elements disrupts the regular lattice structure in an alloy.

  • This makes it more difficult for atoms to slide, increasing the material's strength.

    • Example: Brass's irregular structure due to copper and zinc atoms makes it stronger.

Alloy Steels

• Variety of steels

  • Iron combined with other metals creates different alloy steels with varying properties.

• Mild steel

  • Easily shaped for car body parts.

  • Susceptible to rust but can be protected by galvanizing and painting.

• Tool steel

  • Resistant to heat and wear, suitable for drill bits.

Uses of Alloys

• Alloys are created to enhance the properties of pure metals. 

• By combining different elements, we can produce materials with specific characteristics suitable for various applications.

Aluminum and Its Alloys

• Aluminum is a lightweight metal with excellent corrosion resistance due to a protective oxide layer.

• Aluminum foil for food packaging because it's malleable, non-reactive, and lightweight.

• Duralumin and magnalium

  • Stronger aluminum alloys with low density, ideal for aircraft components.

Copper and Brass

• Copper and brass excel in electrical conductivity and corrosion resistance.

  • Copper: Superior conductor, used in electrical wiring.

  • Brass: Stronger than copper, often used in plumbing and decorative items.

Gold

• Gold is a soft, malleable, and highly unreactive metal.

  • Use: Gold coatings on space helmets to reflect sunlight while maintaining visibility.

  • Gold alloys: Mixed with other metals for strength and durability in jewelry.

Addition Polymerization

• Poly(ethene): Used in plastic bags, plastic bottles, and other flexible plastic products.

• Poly(propene): Used in packaging, carpets, and plastic containers.

• Poly(chloroethene) (PVC): Used in pipes, window frames, and electrical insulation.

• Polytetrafluoroethene (PTFE): Known as Teflon, used in non-stick cookware and industrial applications.

Three stages of Addition

• Initiation:

  • Substance splits into two parts with unpaired electrons (free radicals).

  • Peroxides are often used as initiators.

  • Free radical bonds with a carbon atom in the monomer's double bond.

  • One electron from the free radical, one from the monomer's double bond form the new bond.

  • Remaining electron shifts to the other carbon, creating a new free radical.

• Propagation:

  • New free radical reacts with another monomer, adding two carbon atoms to the chain.

  • Process repeats to form long chains (thousands to millions of carbon atoms).

• Termination:

  • Two free radicals combine, forming a covalent bond and ending chain growth.

Properties of Addition Polymers

• Strong: Due to the long chains of carbon atoms.

• Insulators: Poor conductors of heat and electricity.

• Non-biodegradable: Take a long time to decompose in the environment.

Issues Related to Addition Polymers

• Environmental impact: Non-biodegradable plastics contribute to pollution.

• Dependence on fossil fuels: The production of alkenes from crude oil is a non-renewable resource.

Organic Molecules

• Functional Groups

  • These are specific groups of atoms within a molecule that determine its chemical properties and reactivity.

  • Examples include alcohols (-OH), carboxylic acids (-COOH), and amines (-NH2).

• Isomers

  • Molecules with the same molecular formula but different structural arrangements.

  • This leads to different properties and characteristics.

• Hydrocarbons

  • Organic compounds containing only carbon and hydrogen atoms.

  • Examples include alkanes, alkenes, and alkynes.

• Reaction Mechanism

  • The step-by-step process of how organic reactions occur.

  • Understanding mechanisms helps predict reaction products and optimize conditions.

• Stereoisomerism

  • Molecules with the same molecular formula and structural connectivity but different spatial arrangements.

  • This leads to different properties, such as optical activity.

• Giant Covalent Structures

  • Allotropes: Different structural forms of the same element (e.g., diamond, graphite, and fullerene for carbon).

  • Properties: Vary widely based on structure (e.g., diamond is extremely hard, while graphite is soft and slippery).

• Giant Ionic Lattices

  • Solubility: Many ionic compounds are soluble in water due to the attraction between water molecules and ions.

  • Crystal Structure: The arrangement of ions in a lattice often forms characteristic crystal shapes.

• Metallic Structures

  • Alloys: Mixtures of metals that often exhibit improved properties compared to pure metals.

  • Conductivity: Metals are also good conductors of heat due to the free movement of electrons.

• Intermolecular Forces

  • While not directly related to giant structures, understanding intermolecular forces (e.g., London dispersion forces, dipole-dipole interactions, hydrogen bonding) is crucial for explaining the properties of molecular substances.

Larger Molecules

Graphene

• Potential applications: Electronics, materials science, energy storage due to its exceptional conductivity and strength.

• Challenges: Mass production and stability in different environments.

Fullerenes

• Nanotubes: Potential applications in electronics, materials science, and medicine due to their high strength and conductivity.

• Buckyballs: Potential applications in medicine (drug delivery), electronics, and materials science.

Additional Concepts

• Carbon fibers: Another allotrope of carbon, used in reinforced composites due to their high strength-to-weight ratio.

• Graphene oxide: A derivative of graphene with oxygen-containing functional groups, used in various applications including water filtration and electronics.

Rusting and Corrosion

Factors Affecting Rusting

• Electrolytes: The presence of salts or acids can accelerate rusting by increasing the conductivity of the electrolyte solution.

• Temperature: Higher temperatures often increase the rate of chemical reactions, including rusting.

• Surface area: A larger surface area exposed to oxygen and water increases the rate of rusting.

Prevention of Rusting

• Coating: Applying paints, varnishes, or oils to create a barrier between the metal and the environment.

• Galvanization: Coating iron with a layer of zinc, which acts as a sacrificial anode.

• Alloying: Creating alloys with increased corrosion resistance (e.g., stainless steel).

Redox Reactions

• Oxidation states: Assigning oxidation numbers to elements to track electron transfer.

• Balancing redox equations: Using methods like the half-reaction method or the oxidation number method.

Disposal and Recycling

• Life-cycle assessment (LCA) is an analysis of a product's environmental impact.

  • Raw material extraction: Gathering resources from Earth's crust, atmosphere, oceans, or living organisms.

  • Manufacturing: Producing the product, often involving land use and waste generation.

  • Transport: Moving raw materials and finished products, consuming energy and potentially polluting.

  • Product use: The product's environmental impact during its lifespan.

  • Disposal: Managing the product at the end of its life through methods like landfill, incineration, recycling, or reuse.

• LCA is complex and involves making judgments. Disposal methods, for instance, have both pros (e.g., energy recovery from incineration) and cons (e.g., emissions).

  • Each LCA stage considers:

    • Raw material use (including water)

    • Energy consumption

    • Waste generation

• Raw Materials

  • Extracting raw materials impacts the environment by:

    • Depleting limited resources (e.g., ores, crude oil)

    • Damaging habitats through activities like quarrying, mining, or deforestation.

• Manufacture

  • Manufacturing affects the environment by:

    • Requiring land for factories

    • Generating polluting waste

• Transport

  • Product and raw material transportation consumes energy and produces pollutants.

  • The environmental impact depends on the transport method and distance.

• Use

  • A product's environmental impact during use varies.

    • Low impact: Wooden chair (unless cleaning or repair is needed)

    • High impact: Car

• Disposal

  • Common disposal methods:

    • Landfill: Contributes to land use.

    • Incineration: Releases waste gasses but can generate energy.

    • Recycling: Consumes energy and produces waste but conserves resources.

    • Reuse: Most environmentally friendly option, as it avoids disposal altogether.

  • Each disposal method has environmental consequences.

Recycling

Evaluating Recycling Viability

• Resource conservation: Balancing the use of finite resources (like crude oil, metal ores) with their preservation.

• Material availability: The quantity and accessibility of recyclable materials.

• Economic and practical considerations: Factors such as collection costs, sorting processes, and market demand.

• Impurity removal: The ability to purify recycled materials.

• Energy consumption: The energy required for transportation and processing.

• Environmental impact: The overall ecological consequences of the recycling process.

Recycling Metals

• Process:

  • Collection of used metal items.

  • Transportation to a recycling center.

  • Sorting and separation of different metals.

  • Melting and purification of metals.

  • Solidification into ingots for further use.

• Advantages:

  • Reduced need for mining and quarrying.

  • Decreased noise, dust, and traffic.

  • Preservation of natural habitats.

  • Extended lifespan of metal ores.

  • Lower energy consumption compared to ore extraction.

• Disadvantages:

  • Requires organization, labor, and fuel for collection and transportation.

  • Metal sorting can be challenging.

  • Additional transportation may be needed for metal processing.