Definitions Flashcards
Blast Furnace Process
Blast furnace = steel structure lined with firebricks.
Ore + coke + limestone are charged into furnace.
Coke = fuel.
Chemical reaction reduces iron oxide to iron.
Blast of hot air blown through nozzles to increase quantity of iron.
Limestone = flux (takes no part in reaction - absorbs bulk of impurities and forms slag).
Iron + slag fall to bottom of furnace and are tapped from different ports.
Extraction + Production of Aluminium
Extracted from BAUXITE.
Alumina first purified.
Then dissolved in molten cryolite.
Product is electrolysed to produce aluminium.
Polymer Synthesis
Plastics derived from petrochemicals.
x2 Methods for forming large monomers = addition polymerisation + condensation polymerisation.
Addition Polymerisation
PE, PP, PS, PVC, PTFE
Monomers join together.
No loss of atoms from molecules.
SPECIFIC polymer chain lengths produced.
Condensation Polymerisation
PA, UP, PU
Monomers join together.
Elimination of atoms or group of atoms.
Variety of chain lengths produced.
Ionic Bonding
Pair of elements. One with a loose electron, one with an electron gap.
Ions bond together due to attraction of opposite charges.
Covalent bonding
Bonding based on sharing of electrons between atoms.
Strong.
Lack of free mobile electrons.
Poor conductors of heat and electricity.
Van der Waals Bonding
Secondary bonding.
Molecules that are neutral or have no charge.
Molecules = dielectric diopoles.
Charges in molecules unevenly distributed.
Hydrogen Bonding
Intermolecular.
Permanent diopole attraction.
Metallic Bonding
Free roaming electrons shared by positive ions.
High electrical conductivity.
Amorphous
Materials in which atoms and molecules are not arranged in any order.
Crystalline
Materials that have atoms and molecules arranged in a specific order.
Body Centre Cubic (BCC)
Chromium
Molybdenum
Tungsten
Iron
R=(a✔️3)/4
Volume of atoms=24/3(pir^3)
Volume of lattice cell = a^3
Face-centred Cubic (FCC)
Aluminium Copper Lead Nickel Gold
R=(a✔️2)/4
V=44/3(pir^3)
Volume of lattice cell = a^3
Hexagonal-close-packed
Beryllium
Magnesium
Zinc
Titanium
Packing Factor
Volume of atoms/Volume of lattice cell
Point Defects
Vacancies = atoms missing at lattice points. Interstices = surplus atoms lodge into spaces.
Line Defects
Extra plane of atoms within a crystal structure.
Originate during crystallisation.
When shears stress applied, stress builds up until bond breaks and dislocation moves.
Planar Defects
Surface = defect because of different bonding to bulk of material.
Stacking faults = occur when stacking of atoms is disrupted.
Grain boundaries: Molten metal solidifies, crystals form. Each crystal = atoms aligned. When atoms touch boundaries are formed.
Extraction of Iron
Main ores = haematite, magnetite, limonite.
Iron extracted using smelting in blast furnace, Bessemer process, open heart process and electric arc furnace process.
Screw Dislocation
Slip direction = parallel to defect line.
Volume defects
Defects that occupy a volume.
Branched Polymers
Have side chains attached to chain molecule.
Branching cause by impurities of presence of monomers with reactive groups.
Cross-linked polymers
Two or more chains joined together by side chains.
Cause by chemical reactions.
Eg. Vulcanised rubber, thermosetting plastics.
Thermoplastics
Van der Waals force.
Amorphous or semi crystalline.
Flexible - molecular rotation.
More crystallinity = greater stiffness.
Amorphous Thermoplastics
ABS, PMMA, PC, PS, PVC
Lower shrinkage
Good surface finish
Easier to deform
Inferior resistance
Semi Crystalline Thermoplastics
PA, PE, PP, PET
Better chemical resistance
Good wear resistance
Higher creep
More variable shrinkage
Thermosets
Epoxy Resins, MF, UF
Cross linked molecular structures using covalent bonds.
Weaker at high temps.
Thermal transitions
Tm = melting point
Tg= glass transition temp. (Temp. at which polymer chains can vibrate)
Solid solution
Solid solution formed when solute added to solvent without having changing the crystal lattice.
No new structure formed.
Constitution (alloy)
Phases present
Weight fraction of each phase
Composition of each phase
Liquidus line
Line above which only liquid phase exists. Below the SOLIDUS line only the solid phase exists. SOLVUS line indicates limit of solid solubility in diagram.
Eutectic
An isothermal reaction in which one LIQUID phase freezes to form two or more SOLID phases.
Eutectoid
One SOLID solution changes into TWO OTHER SOLID PHASES.
Strain/work hardening
Strengthening of material so that higher stresses are required to deform it plastically.
Occurs due to crossing of paths of gliding dislocations. Gliding dislocations meeting grain boundaries = prevent motion.
Precipitation/age hardening
Improves strength by introduction of small particles.
Used in alloys.
Alloy heated to temp where second phase is completely soluble. Alloy rapidly quenched.
