transitions in materials Flashcards
What are the atomic and microscopic scales?
A- To do with atomic bonding and crystallinity
M- To do with glass fibre composites, grain size or shape
What are metals?
Single elements and alloys Usually hard, opaque, lustrous Good conductors of heat and electricity Generally malleable Can be cast and amalgamated Eg. Stainless steel, gold, titanium
What is the metallic bond?
Lattice of bonded metal cations with a sea of electrons
Weaker than ionic and covalent
Why are metals lustrous?
Photon is absorbed
The electron moves from one orbital to another
Electrons go up to a higher energy level
As the electrons drop back down to a lower energy level, the photons are re-emitted
Why are metals malleable?
The layers of atoms slide over each other
What are the three metal transitions?
Solid>liquid>solid
Solid+liquid>solid
Solid>solid
What is a transition?
A reorganisation of the distribution of the atoms in a material
What are some ceramics and glasses?
Eg. Porcelain, perioglas, zirconia, lithium disilicate, hydroxyapatite
What are ceramics?
Inorganic, non-metallic compounds, usually crystalline in nature
Brittle, hard
High melting points
Weak tension, v high compressive strength
3D structure of covalent and ionic bonded compounds of a metal w non-metal
How are ceramics produced?
- Powder synthesis
- Preconsolidation processing (milling/grading/additives)
- Compaction/shape forming (produce “green body”)
- Drying
- Densification (sintering)
What are the three ceramic transitions?
Powder>sinter>solid
Solid>hot press>solid
Solid+liquid>solid
What are glasses?
Brittle, hard, non-crystalline solids
No long range atomic order
Supercooled liquid- nucleation has been avoided
Eg. Crystalline silica, amorphous silica, mixed oxide glass
How are glasses formed?
Melting, sol-gel techniques or vapour deposition
What are glass transitions?
Supercooling>no time to organise molecules>amorphous>glass
How might a green body be produced?
Dry pressing Isostatic pressing Slip casting Extrusion Tape casting Injection moulding
