Clathrates

1. Clathrates

2. Clathrates Cage-like frameworks of metals with other metals occupying the cavities of the cages.

3. Clathrates These can be synthesized by mixing finely divided quantities of the metals in the correct proportions and careful heating and cooling.

8. 5 membered rings

9. 5 membered rings 5 + 6 membered rings

14. Clathrates of this type have useful thermal and semiconductor properties.

15. Clathrates of this type have useful thermal and semiconductor properties. A good semiconductor that has poor thermal conductivity is useful for making a thermo-electric device.

16. Thermo-electric cooler

17. Holes and electrons carry energy electrically. Thermo-electric cooler

18. Holes and electrons carry energy electrically. Electrical energy is converted to heat. Thermo-electric cooler

19. Holes and electrons carry energy electrically. Electrical energy is converted to heat. Poor thermal conductivity of semiconductor keeps heat from returning to cooling site. Thermo-electric cooler

20. Ceramics and glass

21. quartz

22. Each O bonds to 2 Si quartz

23. Each O bonds to 2 Si Each Si bonds to 4 O quartz

24. Each O bonds to 2 Si Each Si bonds to 4 O quartz SiO2

25. Glass Na2O.CaO.(SiO2)6

26. Glass Na2O.CaO.(SiO2)6 Approximate formula

27. Quartz: crystalline, long-range order

28. glass: short-range order but not crystalline

29. glass: short-range order but not crystalline All Si bound to 4 O

30. glass: short-range order but not crystalline All Si bound to 4 O Many O are ‘terminal’

31. glass: short-range order but not crystalline All Si bound to 4 O Many O are ‘terminal’

32. glass: short-range order but not crystalline All Si bound to 4 O Many O are ‘terminal’ Ratio of O/Si Is > 2.

33. glass: short-range order but not crystalline All Si bound to 4 O Many O are ‘terminal’ Ratio of O/Si Is > 2. SixOy cluster is anionic

34. glass: short-range order but not crystalline Na+ and Ca2+ balance charge of anion SixOy cluster is anionic

35. Properties of glass vs. quartz.

36. Properties of glass vs. quartz. Glass has a lower melting point

37. Properties of glass vs. quartz. Glass has a lower melting point Glass is softer Glass does not crystallize – this makes it easier to shape it as it cools to a solid form.

38. Special glasses:

39. Special glasses: Borosilicate glass

40. Borosilicate glass Replace some of the Si sites with B

41. Borosilicate glasses have lower coefficients of expansion than soda-lime glasses.

42. Borosilicate glasses have lower coefficients of expansion than soda-lime glasses. Most materials expand when heated.

43. Most materials expand when heated. The coefficient of expansion is a factor, which when multiplied by the temperature change, gives the amount a material will expand or contract.

44. Since glasses are quite brittle, they are less likely to break when the temperature changes if they have a relatively low coefficient of expansion.

45. Borosilicate glasses have higher melting points than soda-lime glasses.

46. Borosilicate glasses have higher melting points than soda-lime glasses. Soda-lime glasses can be melted using a flame generated from methane and air.

47. Borosilicate glasses have higher melting points than soda-lime glasses. Soda-lime glasses can be melted using a flame generated from methane and air. It is necessary to use a methane/oxygen flame to work borosilicate glass.

48. Cements:

49. Cements: Portland cement is a specifically formulated powder.

50. Cements: Portland cement is a specifically formulated powder. When mixed with the proper amount of water it first forms a slurry which flows and can be formed.