Using Our Resources Flashcards
Corrosion
Caused by chemical reactions between metal and substance in environment
Affect strength and appearance
Form of rusting
What is needed for rusting?
Both air and water for iron to rust
Preventing rusting
Paint Oil or grease Plastic Less reactive metal More reactive metal
Zinc in rusting
Protects iron Iron is galvanised Zinc is more reactive than iron Zinc has stronger tendency to form positive ions by giving away electrojs Zinc loses electrons = oxidised Zinc is sacrificed to protect iron
Magnesium or aluminium in rusting
Used instead of zinc in harsher conditions
Usually if in contact with sea water
What’s an alloy?
Mixture of metals
Copper alloys
Bronze = tine and copper = statues Brass = zinc and copper = Hard and workable
Aluminium alloys
Low density
Alloyed with side range of other elements
Lightweight
Armour plating on tanks
Gold alloys
Harder when alloyed
Gold usually alloyed with copper
Jewellery
Varying proportions of 2 metals gives different shades
Steels
Iron and carbon
Carbon steels
Removing most carbon from iron = using blast furnace
Carbon content decreases = cheapest steels made
High carbon = strong and brittle
Low carbon = soft and easily shaped, not as strong and less likely to shatter
Alloy Steels
Steels = expensive, contain high percentage of metals
Nickel steel alloys = bridges, resistant to stretching, operates well under hot conditions
Chromium-nickel steels = stainless steel, hard, strong, resistant to corrosion, cooking utensils and cutlery
Stainless steels = chemical industry, make vessels, expensive, withstand high temperatures and pressures
What do the properties of polymers depend on?
Monomers used to make it
Conditions chosen to carry out reaction
What are the 2 types of polyethenes
HD and LD
high density and low density
LD polyethene
Very pressures and trace of oxygen, ethene forms LD polyethene
Polymer chains randomly branched and cannot pack closely together = so have low density
HD polyethene
Using catalyst at 50*C and raised pressure Makes straighter polyethene chains Pack closely together High density High softening temperature Stronger than LD
How do you classify polymers?
What happens to them when they are heated
Thermosoftening Polymers
Soften easily
Re-set when cool down
Made up of individual polymer chains that are tangled together
Thermosetting Polymers
Do not melt when heated
Strong covalent bonds which form “cross inks” between chains
Thermosoftening Chains forces
Weal forces between chains Heat = weak intermolecular forces broken Polymer becomes soft Polymer cools down = intermolecular forces bring polymer molecules back together Polymer remoulded
Thermosetting chains for forces
Monomers make covalent bonds between polymer chains
When heated to shape them
Bonds strong so stop polymer softening
Covalent “cross-links” between chains do not allow them to separate
Polymer char’s at high temperatures
Glass
Sand, limestone, sodium carbonate Raw materials heated to 1500*C Metals react to form molten glass Cools down turns solid Particles don't form regular pattern Molten glass frozen OR use glass making mixture
Ceramics
Electrical insulators, resistant to chemical attack
Made by moulding wet clay into desires shaped then heating
Clay contain compounds of metals and non-metals = ionic bonding and covalent
Ions and atoms arranged in giant structures
Clay is wet, water molecules get between layers fired
Water driven out and strong bonds form = changing properties
High temp makes it hard
Brittle because when hit ions repel each other away, cracking
Examples of composites
Wood = plywood, thin sheets of wood glues together, plywood resists splitting along grain (MDF) made of woodchips, shavings or sawdust Concrete = cement, sand and gravel mixed with water, hard, strong, resist bending
