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 Materials There are 2 categories of wood: 1)Hardwood  Deciduous trees 2)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 coatings 2)“Treated Wood” (more expensive) 3)Can be coated with a basic substance (turns wood green)

Ceramics Solid 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 ceramics 2) A sudden change in temperature can deteriorate the properties of ceramic

Metals and Alloys Alloys 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

Plastics Plastics 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)