CHAPTER 16 Solids and Liquids 16.3 Metals and Alloys

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

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

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

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

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

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.

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

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

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

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

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

Copper (Cu) is a pure metal

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

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

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

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.

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

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

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

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

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.

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

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

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.

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.