Try This!Which mechanical property is sought in each of the

following examples?

1. A plastic that keeps its shape even when twisted.

2. Wooden flooring that resists indentation by pointed objects, such as shoe heels.

3. A metal that stretches well to make wire.

4. A boat hull that resists shocks caused by running into shoals.

5. A material that bends easily, without breaking, to make gutters beneath a roof.

Degradation and Protection• Degradation: Decline in a material’s properties due to

the effects of the surrounding environment.

• Protection of a material: Application of a substance to a material to prevent or delay its degradation.

Categories of MaterialsThere are 2 categories of wood:1)Hardwood Deciduous trees2)Softwood Conifers

• Hardness, resilience, elastic• Low thermal and electrical conductivity• Light weight

Modified Wood

• Wood mixed with other substances (glue, plastics, preservatives)

Problems with Wood

• Decomposition (rotting)• Insect, fungi and microorganism infestations

These degradations reduce wood’s mechanical properties

Solutions:1) Varnishing, painting, protective coatings2) “Treated Wood” (more expensive)3) Can be coated with a basic substance (turns wood green)

CeramicsSolid material obtained from heating inorganic

matter containing oxides (compound containing oxygen).

*Often made from sand or clay*

• Low electrical conductivity• Hard• Resist heat• Fragile

Problems with Ceramics:

1) Acids and bases can degrade ceramics2) A sudden change in temperature can deteriorate the properties of ceramic

Metals and AlloysAlloys are metals mixed with other metals or non-metals

to make them more useful.

• Ductile• Malleable• Good conductors of heat and energy

Problems with metals and alloys:1) Rust

Solutions:- Coating with paint, grease, enamel...- Coating with other metals such as gold, chrome, zinc, etc.- “Quench hardening” and “Tempering” rapidly heating and

cooling them

PlasticsPlastics are made from fossil fuels.-Other substances can be added to plastics to obtain

specific properties-Poor conductors of heat and electricity

Thermoplastics• Become soft when heated and hard when cooled (can be recycled)

Thermosetting Plastics• Remains permanently hard (more resilient)

Problems and Solutions for Plastic Degradation:

1)Water absorption (use a waterproof coating)

2)Oxidation (add antioxidant materials to plastic)

3)UV rays (add pigment that absorbs UV rays)