Mr. Rogers' IB Design Technology ObjectivesTimber - natural wood or composite (plywood, masonite, particle board)
- Describe the structure of natural timberUsed for making paper, rayon (artificial silk), photographic film (cellulose acetate), cigarette filters (cellulose acetate).
cellulose fibers: the light colored part of the grain structure.
Used for making masonite
lignin matrix: the dark colored part of the grain structure.
Outline the broad categories of trees and their related types of lumber.
conifer trees--softwoods: grow only in temperate regions.
deciduous trees--hardwoods: grow in both temperate and tropical regions.
List examples of composite timbers and discuss their properties and merits.
particle board (chipboard)
Outline criteria for the selection of timber for different structural and aesthetic design contexts.
Describe the reasons for treating or finishing wood.
reducing attack by organisms and chemicals,
modifying other properties.
Explain three differences in the selection of timbers for flooring if it were made of a hardwood, a softwood or a composite material.
ease of maintenance
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.)
Describe the physical structure of pure or alloyed metals.
crystaline--highly organized arrangements of atoms
composed of numerous grains--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.
Reheating a solid metal or alloy allows material to diffuse between neighbouring grains and the
grain structure to change. Slow cooling allows
larger grains to form; rapid cooling produces
smaller grains. Directional properties in the
structure may be achieved by selectively cooling
one area of the solid.
ceramics - earthenware, porcelain, stoneware, and glass
plastics - thermoplastics or thermosets
textile fibers - natural or synthetic
food - vegetable or animal origin
composites - fiber glass, carbon fiber