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Materials and their uses

Materials and their uses. Structure of Materials. The specification states;. Materials behave as they do because of their structure; the way their atoms and molecules fit together You need to know; - how the internal structure of a material influences the way it behaves

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Materials and their uses

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  1. Materials and their uses Structure of Materials

  2. The specification states; Materials behave as they do because of their structure; the way their atoms and molecules fit together You need to know; - how the internal structure of a material influences the way it behaves - ways in which properties materials can be modified by altering the structure of the material

  3. Using Materials

  4. Materials Salt -ionic Copper - metallic Diamond - covalent

  5. Why choose the three materials? • salt • copper • diamond Materials behave as they do because of their structure; the way their atoms and molecules fit together

  6. Properties of Materials We have known many of the properties of materials for thousands of years • Metals are shiny, they have a high melting point, they are malleable, ductile, they are insoluble and they conduct electricity* • Salt is an ionic compound. It is crystalline, it is soluble in water, has a high melting point and it conducts electricity in solution* • Diamonds are covalent. They are crystalline, they have a high melting point, they are insoluble and they do not conduct electricity* *All later discoveries

  7. Why? • We know how materials behave – their properties • The next question is why? • An important development in our scientific knowledge pointed to the answer i.e. The understanding that electricity is a flow of charged particles The flow of charge is called the current and it is the rate at which electric charges pass though a conductor. The charged particle can be either positive or negative.

  8. Conducting electricity Two types of materials that we know conduct electricity are • Metals • Salt (in solution or molten) The search to find their ‘charged particles’ eventually led to an understanding of the structure and properties of materials

  9. Structure of the Atom The bigger the orbit – the higher the energy Electrons can move between energy levels. To move up they must take in energy (incoming radiation) / when moving down they give out energy as electromagnetic radiation

  10. Metals Metals conduct electricity • They have charged particles which are free to move The understanding that electricity is a flow of charged particles

  11. Metallic Bonding Each atom loses control of its outer shell electron resulting in a lattice of positive ions surrounded by a ‘sea’ of electrons

  12. Metallic bonding is the result of strong electrostatic attraction between the positive core and the negative ‘sea’ of electrons The strength of the bond gives metals their high melting point The melting point of gold is 1064oC

  13. Crystals in metals Metals have a crystalline structure which is not usually visible When the metal first solidified from the molten state, millions of tiny crystals grow The longer the metals takes to cool, the larger the crystals

  14. Grains • When the molten metal solidifies, different regions crystallise at the same time • The crystalline areas are known as ‘grains’ • Eventually growing grains meet at grain boundaries • At these boundaries there are can be atoms which do not fit into the crystal structure dislocation

  15. Metals objects are formed by casting • Molten metal is pored into a mould and allowed to cool • As the metal cools small crystals (grains) appear • The crystals grow until they form a solid mass of small crystals • The objects formed from the casting process have dislocations

  16. Properties of metals • Hard but malleable and ductile – metals can be hammered into sheets or drawn into wires because blocks of atoms or grains can slip or roll over one another. • This movement is helped by the • presence of dislocations

  17. If a small stress is put onto the metal, the layers of atoms will start to roll over each other. If the stress is released again, they will fall back to their original positions. Under these circumstances, the metal is said to be elastic. • If a larger stress is put on, the atoms roll over each other into a new position, and the metal is permanently changed.

  18. Conduct electricity because the delocalised electrons are free to move to move around the structure • Are shiny because as light shines on the metal the electrons absorb energy and jump temporarily to a higher energy. When the electron falls back to its lower level the extra energy is emitted

  19. The energy is emitted as light and as different metal elements have different separations in the electron orbits they emit different quantities of energy

  20. Flame tests Lithium Red Sodium Yellow Potassium Lilac Calcium Brick red Barium Green

  21. Flame tests Aurora Borealis

  22. Cold Working Metals can be ‘cold –worked’ – forced into new shapes at a low temperature This creates more dislocations in the crystals The more dislocations a metal has, the more they get in the way of each other The metal becomes stronger but less ductile – more brittle

  23. Annealing • Annealing is a treatment used to restore softness and ductility to metals • The metal is put in a furnace to soften the metal • It is then allowed to cool slowly so that new crystals form and there are fewer dislocations

  24. Alloying – mixing elements one of which is a metals • a. Prevent rust(corrosion) Chromium and nickel are added to iron to form stainless steel. The chromium can form an oxide layer that can prevent iron from oxidising (rust). Suitable for make cutlery, sinks etc.b. To make it harder Carbon is added to Iron to form steel. Steel is very hard, however brittle also. Suitable for making bridges, car bodies, pipes etc.

  25. Aluminium is very light but very malleable. When it is added to copper and magnesium, it forms duralumin which is very hard, withstands corrosion and lightweight. It is strong but light enough to make an airplane body. c. To improve the appearance A normal metal usually gets dull when it exposed to air, water and uv light over a long time. To create an attractive surface and look, metals such as nickel and chromium are added. Nickel is added to copper to form an alloy used to make coins attractive and shiny

  26. Salt Salt conducts electricity when it is dissolved in water Chlorine 35Cl 17 The understanding that electricity is a flow of charged particles There must be charged particles which are free to move

  27. An atom has no charge: number of positive protons = number of negative electrons When sodium loses an electron it becomes a charged particle/ a positive ion When chlorine gains an electron it becomes a charged particle/ a negative ion

  28. Sodium chloride crystal

  29. Ionic Bonding As with metals the strong electrostatic attraction between the positive and negative ions results in ionic compounds having a high melting point (salt melts at 808oC) Ionic compounds conduct because when they are dissolved in water they separate into positive and negative ions (the charged particles) which move to the positive and negative terminals

  30. Carbon • Carbon is all around us • It’s in proteins, fats, carbohydrates • It makes up 20% of the human body • We use it to symbolise love and commitment and to write on paper • It is the main component in fossil fuels • It is a key ingredient in the emerging field of nanotechnology

  31. Diamond • Diamond does not conduct electricity Diamond consists of atoms of carbon bonded together to form a material with a very high melting point It has no free charged particles An uncut diamond

  32. Bonding in diamond Carbon atoms are bonded by sharing electrons in a covalent bond • Covalent bonds form when outer shell electrons are attracted to the nuclei of more than one atom • Both nuclei attract the electrons equally so keeping them held tightly together

  33. Giant Covalent Bonding Repeating crystal lattice High melting point due to strength of covalent bonds (3550oC) Cannot conduct electricity as it has no free charged particles

  34. Graphite Like diamond graphite has strong covalent carbon to carbon bonds and a high melting point (3720OC) Graphite conducts electricity The bonds between the covalently bonded sheets of carbon are weak bonds and the electrons are easily attracted to a positive terminal

  35. Fullerenes C60 Buckyball ‘Buckyball’ Carbon nanotube Discovered in 1985 Fullerenes are a type of carbon made up of ‘cages’ or tubes of at least 60 atoms of carbon

  36. Fullerenes are highly stable chemically and have a variety of unusual properties. • Chemists have been able to add branches of other molecules to them, place atoms inside of them, and stretch them into rods and tubes. Fullerenes can be made to be magnetic, act as superconductors, serve as a lubricant, or absorb light. Current work on the fullerene is largely theoretical and experimental. Recent research has suggested many uses for fullerenes, including medical applications, superconductors, and fibre-optics.

  37. Polymers The largest group of covalent compounds are polymers Polymers are long carbon chains sometimes with different functional groups added and all held together by covalent bonds The bonding in a polymer chain is strong covalent bonding The bonding between chains can create either thermsoftening plastics or thermosetting plastics

  38. Polymer Monomer polyester polytetrafluorethylene polyvinylchloride

  39. Thermoplastics • In thermosoftening plastics like poly(ethene) the bonding is like ethane except there are lots of carbon atoms linked together to form long chains. They are moderately strong materials but tend to soften on heating and are not usually very soluble in solvents. Can be recycled A thermosoftening plastic (thermoplastic) Weak bonds between chains

  40. Thermoplastics Polyethene, polypropene,polyvinylchloride, polytetrafluoroethylene

  41. These can be heated enough to be reshaped. This stretches the cross links. When cooled in the stretched state they stay stretched and retain the new shape • If reheated the • chains are free • to slide back to their • original shape

  42. Fibres nylon Hydrogen Bonding Hydrogen bonding is a result of the electrostatic attraction between hydrogen and oxygen due their different electronegativities

  43. Thermoset plastics • Thermosetting plastic structures like melamine have strong 3D covalent bond network they do not dissolve in any solvents and do not soften on heating and are much stronger than thermoplastics They do not lend themselves to recycling like thermosoftening plastics which can be melted and re-moulded. A thermosetting plastic Covalent bonds between chains)

  44. Thermosets Bakelite, melamine resin, epoxy, urea formaldehyde

  45. Both thermoplastics and thermoset plastics can be strong, tough, rigid and stable towards chemical attack • Bonds between atoms are strong covalent bonds so they do not conduct electricity • Bonds between chains are weak intermolecular bonds • When plastics melt or dissolve it is the intermolecular forces that are broken so the different parts can slide past one another

  46. Uses of thermosets

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