Rest Of C6.1 Flashcards
What is corrosion
Reaction of a metal with substances in its surroundings
Only unreactive metals do not corrode
When iron and steel corrode this is rusting
What happens during rusting?
Redox reaction
Iron is oxidised to hydrated iron oxide
Iron + oxygen + water > hydrated iron oxide (orange brown rust)
Rusting continues until iron or steel is completely corroded
How can you investigate rusting?
1) set up three boiling tubes
2) first tube contains anhydrous calcium chloride which absorbs water vapour and keeps the nail dry
3) the second tube contains boiled water which does not contain dissolved oxygen and a bung which stops air getting back in
4) the nail in the tu is exposed to air and water
5) observe and record the appearance of the nails a few days later
How can you reduce rusting?
Stopping air and water reaching the surface of the metal:
- painting
- coating with oil, grease or plastic
- plating with zinc
- plating with tin
What is sacrificial protection?
Involves a metal that is more reactive than iron, such as magnesium or zinc
As long as the iron or steel object is in contact with is the more reactive metal corred first
Must be replaced once corroded
How does metal plating work?
Layer of metal plated onto an iron or serlo metal object prevents air and water reaching the iron or steel below
What is galvanising?
Dipping the meta, object in molten zinc
Once cooled and solidified the thin layer of zinc does two things:
1) stops air and water reaching the iron or steel
2) acts a sacrificial metal so the object is protected even if the zinc layer is damaged
What are ceramics?
Hard, non-metallic materials
Brick, china porcelain and glass
Contain metals and non-metals combined to form a giant ionic lattice or giant covalent structures
What are the properties of ceramics?
- high melting points
- hard and stiff but brittle
- poor conductors of electricity and heat
- mostly oxides so unreactive
How is glass made?
Melting sand and allowing it to cool and solidify
Has an irregular giant structure without crystals and is usually transparent
How are other ceramics made?
Clay is heated to very high temperatures and tiny crystals form joined together by glass
China and porcelain are usually coated in a g,are and reheated to form a smooth, hard and waterproof surface
What are the properties of aluminium, copper and steel for electrical cables?
Aluminium - 1.0 relative conductivity, 1.0 relative tensile strength, 2.7 density
Copper - 1.7 relative conductivity, 0.7nrelative tensile strength, 8.8 density
Steel - 0.6 relative conductivity, 2.6 relative tensile strength, 7.8 density
What are the properties of glass, porcelain and poly for insulators?
Glass - 1.0 electrical resistance, 1.0 relative tensile strength, 1.0 relative compressive strength
Porcelain - 0.4 ER, 0.02 TS, 7.0 CS
Poly - 0.03 ER, 0.01 TS, 0.04 CS
What are composite materials?
Made from two or more materials combined together with different properties
What is the polymer resin?
Fibres are embedded into resin
The fibres have a low density and high tensile strength but are brittle shears resin is hard wearing but not strong
The composite material is lightweight, strong and hard
Fibre glass consists of glass fibres in resin
What is concrete?
A composite material made aggregate, cement and sand
When water is added to this mixture chemical reactions happen that bind the ingredients together
High compressive strength but low tensile strength so steel rods can be embedded into concrete to get a composite material of steel-reinforced concrete which has high compressive strength and high tensile strength
What is plywood?
Composite material in which thin sheets of woods are glued together in layers
Resists bending in both directions so useful for floors and walls
What are the properties of the polymers poly(ethane), PET, ploy(propene)?
Poly(ethene) - cost 0.74 per kg, 15 tensile strength, 120C melting point, 85 maximum temperature
PET - 1.20, 78, 254, 70
Poly(propene) - 0.92, 35,176, 160
What is a life cycle assessment?
Analysis of the impact of making using and supposing a manufactured product
Includes:
- sustainability, use raw materials and energy
- environmental impact, safe products and pollution
- lifespan of the product and whether it can be recycled
- disposal, how easily the materials decompose
How can you use life cycle assessment data?
Allow to identify stages that could be improved or alternative materials that might for the same job
Why should we recycle materials?
Most products and materials will end up in landfill sites as waste which is not an efficient use of resources
Why is recycling important?
- conserves limited raw materials and energy resources
- reduces the release of harmful substances into the environment
- reducing waste
What are the factors that affect whether a material should be recycled or not?
- how easily the waste can be collected and sorted
- the amount and type of byproducts released by recycling
- cost of recycling compared to disposal in landfill or by incineration
- amount of energy involved at each stage
How are materials recycled?
Waste materials and products are collected and transported to a recycling plant
Materials need to be sorted
Sorted waste is the shredded or scrubbed into smaller pieces ready for processing
What happens during processing?
- metals are melted by heating and the molten metal poured into moulds to produce new block called ingots
- paper is mixed with water, cleaned and rolled and heated to make new paper
- glass is melted by heating and moulded into new glass objects
- polymers are melted and formed into new objects
