|Mr. Rogers' IB Design Technology Objectives|
metals - ferrous (iron or iron alloys) or nonferrous
Draw and describe a metallic bond.
- positively charged nuclei in a sea of electrons
- outer electrons of metal atoms move freely in the metal's crystalline structure
bonding--positively charged nuclei and negatively charged cloud of free electrons are attracted.
Explain why metals are very good electrical and thermal conductors. (It's the movement of free electrons.)
one or more electrons in the outer shell are free to move
Describe the physical structure of pure or alloyed metals.
crystalline--highly organized arrangements of atoms
grain structure--small crystalline regions
Explain how grain size can be controlled and modified by the rate of cooling of the molten metal, or by heat treatment after solidification.
Rapid cooling or quenching: Small grain size, high tensile strength, high hardness
Slow cooling: Large grain size, greater malleability
Selective cooling: directional properties in the structure
Reheating or tempering: material diffuses between neighboring grains changing the grain structure