SC26 - Bulk and Surface Properties of Matter Including Nanoparticles Flashcards
SC26a - What are ceramics?
A range of durable compounds that change very little when heated
SC26a - What are the properties of ceramics?
- Chemically unreactive hard and stiff brittle
- Poor electrical and thermal conductors
- High melting points
These properties are due to their giant ionic/covalent structures with strong bonds
SC26a - What are three examples of clay ceramics?
- Bricks
- Porcelain
- China
SC26a - How are clay ceramics created?
- When clay is heated to high temperatures, tiny crystals form and join together.
- Bricks are decorated by adding a coloured substance before heating, or by moulding in patterns.
- Porcelain and china are dipped into a ‘glaze’ and heated strongly.
- This makes them hard, waterproof and smooth.
SC26a - How is glass created?
Melting sand and then allowing it to cool and then solidify
SC26a - What are the similarities and differences between glass and clay ceramics?
- They both have similar properties because they both have giant structures
- But, the atoms in glass aren’t arranged in a regular pattern to form crystals and so glass is transparent rather than opaque
SC26a - How is modern window glass created?
The float process:
- Molten glass is poured onto a bath of molten tin.
- As it spreads out, it is drawn away and cooled in a continuous process
SC26a - What are polymers?
Polymers are substances with high relative formula masses as they are formed by joining many monomers (smaller molecules) together
SC26a - What are some general properties of polymers?
Properties depend on structure and chemical composition, but generally:
- Can be moulded into complex shapes
- Strong
- Chemically unreactive
- Poor electrical and thermal conductors
SC26a - How can PVC be made softer?
By using plasticisers in its manufacturing.
This makes it more flexible
SC26a - What are some properties of metals?
- Strong
- Hard
- Shiny
- High melting points
- Good electrical and thermal conductors
- Malleable
SC26a - How can metals be made stronger?
Alloying: Mixing the metal with one or more other elements
SC26a - Why may a metal be electroplated?
- To improve resistance to corrosion
- To improve appearance
SC26b - What is a composite material?
A material that is made up of two or more materials, combined to make a material with improved properties
SC26b - How do the individual materials in a composite material relate to each other?
- They often have contrasting properties
- They can be separated out by physical means
SC26b - What are the reinforcement and the matrix?
- The reinforcement is what you are binding together
- The matrix is how you hold them together
(reinforcement is straw and matrix is the glue)
SC26b - What is the difference between tensile and compressive strength?
- Tensile: Resistance when stretched
- Compressive: Resistance when squashed
SC26b - What is wood a composite material of?
Cellulose fibres in a matrix of a polymer called lignin
SC26b - How does the strength of wood differ depending on how you cut it?
It is stronger along the grains (parallel to lines of lignin) than across the grain (perpendicular to lines of lignin)
SC26b - How is plywood strong from all angles?
It has an odd number of sheets of wood glued in right angles to the sheet below so that you are always cutting across and along the grain simultaneously
SC26b - What is pykrite a composite of?
Reinforcement of ice in a matrix of wood pulp
SC26b - What is concrete a composite of?
Reinforcement of sand and aggregate (small stones/gravel) in a matrix of cement (and water to help it set)
SC26b - What is fibreglass a composite of, and why is it useful?
- Reinforcement of thin glass in a matrix of resin polymer.
- Glass fibres are brittle but with low density and high tensile strength
- Resin is hardwearing but not strong.
- Combining them makes fibreglass low density, strong and hardwearing
SC26b - Why may concrete be reinforced with steel?
- Concrete has a low tensile strength but high compressive strength
- Steel is very dense and more expensive than concrete
- Reinforced with steel it will have high tensile and compressive strength and also be cheaper and less dense than steel alone
SC26c - What are bulk materials (give examples)
Materials consisting of a large number of atoms e.g:
Lumps and powder
SC26c - What are nanoparticles?
Particles consisting of just a few hundred atoms
SC26c - Compare the size of a nanoparticle to that of an atom and that of a cell
Atom: 0.1nm
Nanoparticle: 1-100nm
Bacterium cell: 1000nm
SC26c - How are nanoparticles formed?
They largely occur naturally, but can be formed through manufacturing processes
SC26c - What does it mean if a substance is nanoparticulate?
It consists of nanoparticles
SC26c - What properties of nanoparticles make them useful?
- Their small size
- Their large Surface area : Volume ratio
SC26c - What is nanoparticulate titanium dioxide used for and why?
- It is used for (almost invisible) sunscreen
- Titanium dioxide absorbs harmful UV radiation
- When nanoparticulate, it is small enough to be transparent
SC26c - How do stain resistant clothes work?
- Nanoparticles on the clothes fibres have a really large Surface area : Volume ratio
- This makes them useful as chemical catalysts
- They catalyse the breakdown of stains, cleaning the clothes
SC26c - What are the dangers of nanoparticles?
- Their small size allows them to be breathed in or passed through cell-surface membranes
- Their large SA:V allows them to catalyse harmful reactions and carry toxic substances
SC26c - Why are the risks of nanoparticles not fully known?
Nanoparticulate materials haven’t been in use for very long
