Metals 1 - C5 Flashcards
What is a crystalline metal?
A material which is made up of small particles which are arranged regularly in a three dimensional structure over spaces many times the spaces between the particles.
What is a polycrystalline metal?
A material which is made up of small grains which border on ‘grain boundaries’ to other crystals of different dimensions.
What are grains?
The longitudinal arrangement or pattern of particles in a substance - crystalline.
What are grain boundaries/interface?
The boundary between where two grains, made up of tiny crystals, meet.
What is a lattice?
A regular three dimensional arrangement of particles over a large amount of space.
How do metallic bonds work, and how do they compare to intermolecular forces and covalent bonds?
Metals lose the outer electrons from their shells to become positively charged ions. The ions are held together by electrostatic forces with the delocalised electrons. Metallic bonds are much stronger than intermolecular forces, as metals are typically solid at room temperature with high melting and boiling points. However, covalent bonds are stronger.
Why are metals strong?
Metals are strong as they have strong electrostatic forces. This means a large amount of stress is required to break these bonds and cause failure in the metal.
Why are metals tough, ductile, and malleable?
Metals are tough because the bonds are non-directional. This means the metals can absorb large amounts of stress as the bonds deform. The layers can slide over each other in the lattice, so large amounts of stress are required for failure. Metals also do not experience large amounts of crack propagation due to the lattice structure. Where cracks propagate, stress is thousands of times greater at the bottom of the crack. As the lattice can slide, this spreads the area of the base. Therefore, stress is reduced. This makes metals malleable.
How do metals form?
If metals cool for a long period of time, they form perfect crystals. However, this is difficult to achieve. Metals often cool quicker, and form smaller crystals with more grain boundaries. The more grain boundaries there are in different orientations, the stronger the metal is, as these restrict the movement of lattices. However, this also makes metals more brittle.
How do metals deform?
Metals are elastic for strains around 0.1%, as ions pull apart a small amount as bonds pull them closer. Beyond this strain, bonds reach the elastic limit and ions start to deform plastically. The ions slide over each other and begin to deform plastically as they enter new permanent positions.
