Transition metals, alloys and corrosion

• Transition Metals

  • Most of the known metals are transition metals
  • They are very lustrous, hard, strong and good conductors of heat and electricity
  • They are highly dense metals and have very high melting points
  • They can have more than one oxidation state as they can lose a different number of electrons, depending on the chemical environment they are in
• Transition Metals Table

  • Cr
  • Mn
  • Fe
  • Co
  • Ni
  • Cu
• Compounds containing transition elements in different oxidation states

  Will have different properties and colours in aqueous solutions
• Transition metals themselves do not display a range of colours, it is the compounds they form that are colourful
• Catalysis

  • The transition elements are used extensively as catalysts
  • They do not take part in the reaction
  • Their catalytic characteristics stem from their ability to interchange between a range of oxidation states
• Common transition metal catalysts

  • Iron used in the Haber Process
  • Vanadium pentoxide (V2O5) used in the Contact Process to produce sulfuric acid
  • Nickel used in the hydrogenation of alkenes
• Transition metals in medicine and surgical applications

  • Titanium is useful as it is the only element that can bond with bones due to its high biocompatibility
• Corrosion is the destruction of materials by chemical substances in their environment which act on them over a period of time
• Corrosion caused by redox reactions

  1. The metal loses electrons and is oxidised

  2. The oxygen gains electrons and is reduced
• Rusting

  The corrosion of iron in the presence of water and oxygen from the air
• Corrosion and rusting are not the same process. Corrosion is the general term used to describe the degradation of metal surfaces. Rusting is the specific type of corrosion that happens only to iron.
• Barrier methods for preventing corrosion of metals

  • Paint
  • Oil
  • Grease
  • Plastic
• Galvanising

  Iron is coated with a layer of zinc to protect it from rusting
• Sacrificial corrosion

  A more reactive metal is intentionally allowed to corrode to protect a less reactive metal
• Electroplating

  1. The surface of one metal is coated with a layer of a different metal

  2. The anode is made from the pure metal used to coat

  3. The cathode is the object to be electroplated

  4. The electrolyte is an aqueous solution of a soluble salt of the pure metal at the anode
• Uses of electroplating

  • To make metals more resistant to corrosion or damage
  • To improve the appearance of metals
• Alloys

  Mixtures of metals where the metals are mixed together physically but are not chemically combined
• Alloys often have properties that can be very different to the metals they contain, for example they can have greater strength, hardness or resistance to corrosion or extreme temperatures
• Steel alloys

  Alloys of steel made by adding other metals such as chromium, manganese or nickel
• Steel alloys and their uses

  • Construction
  • Transport
  • Manufacturing
  • Other industries
• Aluminium alloys

  • Aluminium is mixed with copper, manganese and silicon for aircraft body production
  • Aluminium and magnesium (5%) make an alloy called magnalium which is used extensively in automobile and aircraft construction
• Uses of aluminium

  • Aircraft body production
  • Automobile and aircraft construction
• Copper alloys

  • Bronze (copper and tin)
  • Brass (70% copper, 30% zinc)
• Carats

  Used to express the purity of gold jewellery
• Pure gold with nothing else added is said to be 24 carat
• A 12 carat piece of gold jewellery contains 50% gold