topic 5 - transition metals, alloys and corrosion Flashcards
where are transition metals found
in the middle of the periodic table
typical properties of transition metals (4)
- high melting point (apart from mercury)
- high density
- make good catalysts (eg iron is used in the haber process)
- form colourful compounds
what colour compounds do Fe^2+ ions form
light green
what colour compounds do Cu^2+ ions form
blue
what colour compounds do Fe^3+ ions form
orange/brown
alloy
a mixture of metals / the addition of another element to a metal
why are alloys stronger
they contain different elements with different sized atoms making it difficult for layer to slide over each other
steels
alloys of iron
used more often than pure iron
how is steel made
small amount of carbon are added to iron
other metals are added to make alloy steels
general differences steel vs iron (2)
- steels are harder than iron
- iron is more likely to rust than steel
3 types of steel
low carbon steel
high carbon steel
stainless steel
low carbon steel (make-up and properties)
0.1-0.3% carbon
malleable
high carbon steel (make-up and properties)
0.22-2.5% carbon
very strong, brittle and inflexible
stainless steel (properties)
corrosion resistant
strong
copper alloy examples
bronze
brass
bronze (makeup)
copper + tin = bronze
bronze (properties and uses)
bronze is much harder than copper
made into medals, statues and decorative ornaments
brass (makeup)
copper + zinc = brass
brass (properties and uses)
brass is more malleable than bronze
used in situations where less friction is needed such as water taps and door fittings
gold alloys (makeup and uses)
zinc, copper and silver used to strengthen the very soft and malleable gold
used to make jewellery
aluminium alloy example
magnalium
aluminium alloys (properties and uses)
low density and stronger than regular aluminium
used to make aircraft
magnalium (makeup)
aluminium + magnesium = magnalium
low magnesium content magnalium (properties and uses)
light strong and corrodes less easily than pure aluminium
used for cars and aeroplanes
high magnesium content magnalium (properties and uses)
more reactive, burns brightly and is more stable than magnesium
used for fireworks
corrosion
a process where something is slowly damaged or destroyed by a chemical process
rusting
the corrosion of iron
what is corrosion (reaction)
corrosion is caused by redox reactions
metals corrode in the presence of water and oxygen
metal is oxidised
oxygen is reduced
how to prevent rusting (what are you blocking)
coating iron with a barrier to keep out oxygen or water or both
how can you prevent rusting (techniques)
painting
oiling or greasing (especially on moving parts)
sacrificial protection
sacrificial protection
placing a more reactive metal with iron so it is corroded instead
galvanisation
an example of sacrificial protection where a coat of zinc is placed on an iron object
often done to corrugated iron roofing
electroplating
coating the surface of a metal with another metal using electrolysis
what should the cathode, anode and electrolyte be in electroplating
cathode - the object to be electroplated
anode - bar of metal being used as plating
electrolyte - solution containing metal ions of the plating metal
2 examples of when we use electroplating
we electroplate household items such as cutlery/cooking utensils to stop corrosion (protective metals used are unreactive and don’t corrode easily)
jewellery and decorative items may be electroplated gold or silver to make them look shiny
what happens in terms of movement of ions in electroplating
metal ions from electrolyte move to the cathode, where they are reduced and the metal is deposited on the object
the anode keeps the metal ions ‘topped up’
