01 - Introduction & Basics

Classify the materials into material groups and give examples

What’s the difference between ferrous and non-ferrous materials?

• ferrous materials: contain iron Fe as main element

• Non-ferrous: can contain iron Fe but not as the primary element

What’s the density limit between light & heavy metals?

4.5 g/cm3

What are the most important ferrous materials?

Iron & steel (fer & acier)

What’s the definition of cast iron?

Group of iron alloys with high proportion of carbon (>2%) and silicon (1.5%)

What’s steel? (Acier)

Iron-carbon alloy that contains less that 2.06% of carbon (by mass)

What are the properties of metals?

• high electrical conductivity

• High thermal conductivity

• Ductility (formability)

• Metallic gloss (mirror finish)

For what reasons do we use non-ferrous metals?

• corrosion resistance

• High-temperature strength

• Scaling resistance (entartrage? Couche d’oxyde)

• Low density (light)

• Electrical properties

What are the reasons metals have their particular properties?

• cohesion of atoms by metallic bonds (atoms held together, electrons shared among many atoms)

• Periodic arrangement of the atoms (crystal lattice)

• electrons moving freely in the lattice —> electrical & thermal conductivity

Classify materials according to their use & explain what are the different categories

Construction/structural materials: used for their structural properties, buildings & constructions

Functional materials: respond to external stimuli (light, heat, electricity…)

What can we say about “The optimal material”?

THE optimal material doesn’t exist, but there is a material that is optimal for a specific application

What are the different factors to consider when selecting a material?

Why do materials (in general) have different properties?

Properties depend on:

• the type of atomic bonds

• The atoms arrangement

What are the 2 categories of atomic bonds? What types of atomic bonds are there in each?

• primary chemical bonds

  • ionic bonds (e- are transferred)

  • Covalent bonds (e- are shared)

  • Metallic bonds (e- are delocalised, free to move)

• Secondary bonds (van der Waals)

  • Dipole formation

  • Hydrogen bonds

What are the 3 different types of arrangement of the atoms/molecules?

• amorphous: randomly arranged, without a repeating pattern

• Crystalline: arranged in repeating, periodic pattern (crystal lattice)

• Crystalline ordered: same as crystalline + the individual crystalline grains are aligned in a specific orientation

Describe the metallic bond

• occurs between metal atoms

• All atoms “share” e- that are delocalised and free to move (electron gas model/ sea of e-)

• No preferred direction in the bonding

• Metallic crystals are closely packed (maximises the #of atoms that can fit into a given space)

Describe the behavior of atoms according to the bonding forces & the distance between atoms

When atoms bond, their e- rearrange to lower the overall energy of the system & become more stable

The nucleus of the atoms repel each other (+/+) and electrons as well (-/-) —> repulsive forces

Nucleus and e- attract each others —> attractive forces

At equilibrium distance r0, attractive & repulsive forces balance/cancel out & and the system is stable (net force = 0)

What’s the formula of the bonding energy?

E,be = E,isolated - E,bonded

Difference between the energy of an isolated atom, and its energy when bonded

What are the different scales of metals (name & value)?

• Macroscopic scale (cm)

• Microscopic scale

  • Grain scale (micrometer)

  • Atom scale (nanometer)

What’s a crystal lattice & how does it form?

Regular, repeating arrangement of atoms in 3D space

Formed when attractive & repulsive forces balance (equilibrium position of atoms)

What’s the unit cell of a crystal lattice?

Smallest repeating unit that creates the lattice when repeated in 3 directions.

Fundamental “building block” of lattice

defines the geometry and symmetry of the lattice

ALWAYS in 3D

What are the 4 most common cubic lattices?

Which ones are closest sphere packing models?

• primitive cubic lattice

• Face centered cubic lattice (fcc)

• Body centered cubic lattice (bcc)

• Hexagonal close packing (hcp)

Closest sphere packing models: fcc, bcc, hcp (atoms are the closest possible)

What’s the problem with the primitive cubic lattice?

Atoms are not optimally arranged

They can easily move (with a small force) to a more stable position

What’s the advantage of a stable arrangement?

The height (vertical distance between atoms layers) is reduced

Improved packing density

Closer = stronger bonds = more stable

What’s an octahedral plane?

Plane where atoms are arranged the most closely together (maximises contact between atoms)

Draw a face centered cubic unit cell.

What proportion of the volume is occupied by atoms?

What’s the sequence of octahedral planes?

74%

(highest packing density for equally sized spheres)

Sequence: ABC ABC ABC

(each new layer fits into the gals of the previous layer but never in the same gaps as the previous or next layer)

Draw a body centered cubic unit cell.

What’s the packing density? (Volume occupied by atoms)

68% packing density

Draw a hexagonal close packing unit cell.

What’s the packing density?

What’s the stacking sequence of octahedral planes?

74%

(highest packing density for equally sized spheres)

AB AB AB

What’s the coordination number?

What is it for fcc? Bcc?

Number of nearest neighbor atoms surrounding a central atom in a crystal lattice

• fcc: 12

• bcc: 8