Föreläsning 1 - materialgrupper Flashcards
What are the main material groups?
Metals, ceramics, polymers, and composites
What determines the structure of a material?
How atoms, molecules, and phases are arranged.
- Electron structure
- Crystal structure
* Crystal = ordered structure
* Amorphous = unordered structure
- Microstructure: how crystals and constituents are ordered.
Which kinds of atomic bonds are there?
- Covalent bonds:
- Strong
- Directional
- Ceramics, polymers - Metallic bonds:
- Strong
- Free electrons => electric and thermal conduction
- Metals - Ionic bonds:
- Strong
- Bonding between ions
- Ceramics - Van der Waal, hydrogen, polar bonds:
- Weak
- Between polymer chains
Describe the structure and properties of ceramics
- Non-organic, chemical compound between metal- and non-metal.
Examples: Al_2O_3, O_3, SiC, SiO_2
Cement, concrete, brick, porcelain, glass, technical ceramics
Structure:
- Mostly crystalline
- Covalent- or ion bonds
- Exception: glass is amorphous
- Glass Softens between 800 - 1200 degrees Celsius
Properties:
- High melting temp
- Chemically stable
- High stiffness and hardness
- Brittle
- Electric and thermally insulating
Manufacturing:
- Ceramic materials are made from different minerals
- Clay or powder
- Shaped to the form of the product
- Sintered at around 2/3 of the melting temp
Describe the structure and properties of metals
Common metals:
- Steel
- Aluminium
- Cu, Mg, Ti, Ni
They usually come as alloys:
- Steel = Fe + C
- Bronze = Cu + Sn
- Brass = Cu + Zn
Crystalline structures
Properties:
- Medium to high melting temps
- Electrically and thermally conductive
- High stiffness
- High strength (hardness)
- Not brittle
- High density
- Can be cast
- Can be formed by plasticity: rolling, pressing…
- Can be machined: drilling, milling, turning…
Describe the structure and properties of polymers (plastics)
- Organic material consisting of macro molecules
- Made of oil, but also other organic raw materials
- Plastics = polymers + additives
Properties:
- Low operating temp
- Relatively low stiffness and yield limit
- Low density
- Electrically inuslating
- Easy to form
Name three types of polymers and their different properties
Thermoplastics:
- Long polymer chains
- Weak bond between chains
- Can be formed by heat
- Recyclable
Thermosettings:
- Network of molecules
- Covalent bonds
- Can not be formed by heat
- Not recylable
Rubber (elastomers):
- Sparsely connected network
- Can not be formed by heat
- Not recyclable
Describe the structure and properties of composites
- Combination of two or more materials, e.g. polymer and carbon fiber
- Fibers: carbon, glass, aramid
- Long or short fibers, particles
Other examples:
- Concrete = cement and rock
- Cemented carbide = Co and WC
Name the four kinds of forming methods
- Primary forming
- Secondary forming
- Joining
- Surface treatment
What kinds of material properties are there?
- General properties
- Mechanical properties
- Electrical, magnetical and optical properties
- Thermal properties
- Chemical properties
- Environmental properties
What are the general properties?
- Price
- price/kg
- price/volume
- price/performance
Density:
* kg/volume
What are the mechanical properties?
- Stiffness
- How much a material deforms at a certain load
- Yield strength
- At what load (stress) a material is permanently deformed.
- Fracture toughness
- At what load a material breaks
What are the electric, magnetic and optical properties?
- Electric conduction
- Electric insulation
- Maganetism
- Transparent, reflexing, colour
interaction between light and electrons in the material
What are the thermal properties?
- Melting temp
- Min and max operating temp.
- Thermal conduction
- Specific heat capacity
- Thermal expansion
What are the chemical properties?
- Corrosion
- Oxidation
- Other reactions
- Poisonous
