1. CHAPTER 16
Solids and Liquids
16.3 Metals and Alloys

2. Macroscopic physical properties ultimately come from the microscopic world of molecules and chemistry

3. Physical properties Electrical conductivity Density Hardness
Elasticity
Transparency
Strength
Electrical conductivity
The ability for electrical current to flow through a material
Example:
Copper and aluminum are excellent conductors, but glass, rubber, and plastic are insulators

4. Physical properties Thermal conductivity Density Hardness Elasticity
Transparency
Strength
Electrical conductivity
Thermal conductivity
The ability for heat to flow through a material
Example:
Metals are good heat conductors; rubber and plastics are moderate heat conductors

5. Physical properties Electrical conductivity Thermal conductivity
Density
Hardness
Elasticity
Transparency
Strength
Electrical conductivity
Thermal conductivity
Metals are good conductors of electricity and heat

6. Physical properties Electrical conductivity Thermal conductivity Why?
Density
Hardness
Elasticity
Transparency
Strength
Electrical conductivity
Thermal conductivity
Why?
Metals are good conductors of electricity and heat

7. Metallic bonding
In Chapter 15 we saw that a copper wire is capable of carrying an electrical current thanks to electrons that are free to move around.

8. Solo (unbonded) metal atom
Metallic bonding
Metals have low ionization energies; valence electrons are not strongly bound to their parent atoms.
Solo (unbonded) metal atom
A metal is like a fixed lattice of positive ions in a sea of free electrons

9. Metallic bonding Electrons are small, light, and therefore fast
They can carry energy quickly Thermal conductivity
They can carry charges quickly Electrical conductivity

10. Conductivity Thermal conductivity 1 cm 2oC 1oC 1 W of heat
How many watts (W) of heat would flow through a 1 cm of material if there were a difference of 1oC between opposite sides
1 cm
2oC
1oC
1 W of heat

11. Conductivity Thermal conductivity Electrical conductivity 1 cm 2oC 1oC
How many watts (W) of heat would flow through a 1 cm of material if there were a difference of 1oC between opposite sides
Electrical conductivity
How many amperes (A) of electrical current would flow through a 1 cm of material if there were a difference of 1 volt (V) between opposite sides
1 cm
2oC
1oC
1 W of heat
1 cm
1 V
0 V
1 A of current

12. Conductivity
metals
nonmetals
Note how different the conductivity values are between metal and nonmetals

13. Copper (Cu) is a pure metal

14. Alloys
Bronze is a metal too, but you won’t find it in the periodic table

15. Alloys
Bronze is a homogeneous mixture (a solution!) of two pure elements: copper and tin
Bronze is a metal too, but you won’t find it in the periodic table

16. Some alloys Bronze 6061 Aluminum Brass Steel copper and tin
coins, tools, bells, statues
6061 Aluminum
96%–98% Al, 1% Mg, 0.5%–1% Si
bicycle frames, aircraft, boats
Brass
copper and zinc
musical instruments, plumbing
Steel
iron and carbon
buildings, bridges

17. a binary alloy Bronze Brass Steel copper and tin copper and zinc
iron and carbon
alloying elements
binary alloy: an alloy made up of only two different elements.

18. Bronze 6061 Aluminum copper and tin 96%–98% Al, 1% Mg, 0.5%–1% Si
A complex alloy is made up of three or more alloying elements

19. Properties of alloys
Copper and tin melted together create bronze, but bronze is stronger than both copper and tin!
Alloys often have better physical properties than any of their constituent pure elements

20. Properties of alloys
Pure iron is naturally very soft. Adding less than 1% carbon can create incredibly strong steel

21. Properties of alloys
The latest military aircraft are made of complex alloys of titanium (Ti), vanadium (V) and zirconium (Zr) in very specific proportions.

22. This also changes how an alloy melts or freezes.
Binary phase diagrams
Sterling silver
contains 12 atoms of copper for every 88 atoms of silver
Cu: 12% by atoms
Cu: 7.5% by mass
Fitting two different atoms into a crystal lattice changes the crystal structure.
This also changes how an alloy melts or freezes.

23. Binary phase diagrams This alloy is a liquid above 779oC
Silver–copper phase equilibrium diagram
This alloy is a liquid above 779oC

24. Binary phase diagrams Melting points:
Silver–copper phase equilibrium diagram
Melting points:
Pure silver: 991oC
Pure copper: 1,085oC
Ag-Cu alloy
(39% Cu): 779oC

25. binary phase diagram: a graph showing the phase of an alloy at different temperatures and compositions.
eutectic point: the temperature and composition where an alloy’s melting point is the lowest.

26. Alloys are solid solutions of elements with new properties and melting points.
Free electrons can carry charge and heat very fast.
Metals are good electrical and thermal conductor.