Thursday, Sept 24, 09 - APS-3A

HW: Check Quia for review and summary questions

5-min quiz on ideas from crystal structure of metals lab.
Went over Quiz

Content Objectives:
Students will be able to
1. Explain how the rate of cooling affects crystal growth
2. Describe with pictures, defects in metals
3. Explain how defects can affect properties of metals

BB Boards - 1 per 2 people
Showed defects: vacancies and line defects
Showed grains - regular groupings of BBs (models of atoms)
Had students sketch pictures of defects and grains in their notes.

BB board worked great on overhead

Handed out 6" pieces of metal wire, 1 per 4 students. Told students NOT to touch them.
Group nominated one student to bend the wire, and then bend back. It did not get straight showing that it was harder to bend, stronger.

Bending introduced defects. The slip planes could not move through the defects as well making the metal less ductile and stronger.

Showed intro to Conan the Barbarian - where they make the sword. Talked about the various scenes: heating to change crystal structure to make easier to shape, hammering to introduce carbon to make steel and also pound out impurities, bellows to add air to get a hotter flame, quenching to make hard, annealing to make strong and flexible.

Used BB boards to model rapid cooling (small or no grains) and slow cooling (large crystals). Showed pictures of Chihuahua Giant Crystals, Giant's Causeway basalt columns, basalt columns in Columbia River Gorge. Discussed rate of crystal formation and size.

Talked about cooling lava that contained different materials with different temperatures at which they solidity. Used analogy of room mates moving into a room. First to move in gets more space. First crystals to form are larger.

Students worked in groups of 4. One returned BB boards and wires. One got a microscope, showed how to handle it. One got goggles. Students set up microscopes at lowest setting. I handed out slides with Phenyl Salicylate. Student with goggles heated to melting with barbecue lighter. I went around and placed seed crystal on slide so students could watch crystal formation. I asked them to see what happened when grain boundaries ran into each other and also check the shape of the crystals (rhombic).