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At first sight there seems to be no rationale for the chemical properties of aluminium, that, although its reactions with oxygen can be violent, the metal is stable to atmospheric oxidation. The fi...rst part of this programme is about the chemistry of aluminium and its oxide, in an attempt to discover reasons for the apparent paradox in aluminium chemistry. Prof. Haynes introduces the programme Dr. Johnson demonstrates the reaction of aluminium with air, with oxidising, acids, in bombs as an explosive intenslfier, and with iron oxide in the thermit reaction. Dr. Mason demonstrates the reaction of aluminium with chlorine and the immediate reaction of the product with the atmosphere Dr. Johnson demonstrates the decomposition of aluminium nitrate to the oxide and Illustrates the electrolytic extraction of aluminium from its ore. Finally he shows the reaction with air and oxidising acids again, but this time the aluminium 'surface is rubbed with mercury to break down the protective oxide layer. PART 2 - In the unit, metal structure is discussed in terns of the packing of atoms into layers and layers into crystal structures. In the programme, the behaviour of atoms in layers is demonstrated, using a bubble raft to simulate the properties of metal samples in three different states. The first of these is the metal grown as a single crystal, the second, the more common polyerystalline state, and finally, the metal alloyed with another to toughen it. Dr. Johnson concludes by demonstrating the face-centered cubic, bodycentered cubic and hexagonal packing of layers of atoms into their respective crystal structures. This demonstration forms an essential part of the exposition of this topic in the unit.
Metadata describing this Open University video programme
Item code: S25-; 03
First transmission date: 19-02-1972
Published: 1972
Rights Statement:
Restrictions on use:
Duration: 00:21:55
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Producer: David Jackson
Contributors: Len Haynes; David Johnson; Joan Mason
Publisher: BBC Open University
Keyword(s): Aluminium oxide; Atomic layers; Bubble raft; Chemical properties of aluminium; Decomposition; Electrolytic extraction; Explosives
Footage description: Len Haynes, with a large periodic table, introduces the programme. David Johnson compares pieces of iron and aluminium sheeting after several days exposure to the atmosphere. The iron shows considerable corrosion. Shot of the statue of Eros (made of aluminium) in Piccadilly Circus. Johnson next places aluminium foil into a tube containing nitric acid. No reaction can be seen. Film shots of WW2 bombs being dropped from an aircraft. Johnson with an empty bomb case explains that these often contained aluminium powder which inflamed spontaneously on contact with air and intensified the blast. Johnson next mixes iron oxide with aluminium granules in a bowl and ignites the mixture. A violent reaction results in which iron is separated from the other product, aluminium oxide. This reaction is the basis of the thermit process. The thermit reaction equation is shown on the screen. Johnson introduces Joan Mason. Mason demonstrates the reaction of aluminium with chlorine. She heats aluminium foil in a stream of chlorine gas forming aluminium chloride in the process. Mason then reacts this with ammonia vapour. Johnson heats a test tube containing aluminium nitrate. A dark gas, nitrogen dioxide, is given off. The other product of the reaction is aluminium oxide. Johnson shows a piece of bauxite containing aluminium oxide. Film shots show the industrial aluminium production process from bauxite as the raw material to the final alumimium ingot. Commentary by Johnson explains the process. Johnson with an ingot of aluminium explains why it is often so resistant to oxidation. Johnson performs two experiments to demonstrate the reactivity of aluminium when its protective oxide film is removed. He soaks two pieces of aluminium foil in mercuric nitrate then exposes one to the air and places the other in nitric acid. The nitric acid reaction is violent and the other, although not violent, is quite marked. Len Haynes introduces the second part of the programme which deals with the crystal structure of metals. Film shots of a bubble raft analogue demonstrate how atoms packed together in layers behave. Commentary by David Johnson. Film shots of a copper rod which was grown as a single crystal. The rod is bent with very little pressure because layers of atoms slip over one another easily. Micrograph of a polycrystalline piece of copper. Film shots of the bubble raft show what happens at crystal boundaries where dislocation are stopped. Shots of a polycrystalline copper rod being bent. This time it is much more difficult. Shots of the bubble raft with simulated atoms of tin added. This demonstrates another way in which the flow of dislocation is limited. Shots of a copper-tin alloy (bronze) rod being bent. This time it is very difficult. David Johnson uses molecular ball models to demonstrate the two close packed metallic structures, hexagonal and face centred cubic. He points out similarities and differences.
Master spool number: 6LT/70253
Production number: 00521_2163
Videofinder number: 1771
Available to public: no