Choosing materials - SC26 Flashcards
What are ceramics?
range of durable compounds that change very little when heated
what are the properties of ceramics?
chemically unreactive, hard and stiff, brittle, poor electrical and thermal conductors, high melting points
what is the structure of ceramics
giant structures with many covalent or ionic bonds
what are types of clay ceramics?
brick, porcelain and china
how are clay ceramics formed?
clay is heated to a very high temperature and tiny crystals form and join together
how are porcelain and china formed from clay?
after crystals form and join together, they are dipped in a glaze and heated strongly again
how is glass made?
by melting sand then allowing it to cool and solidify
why are glass and clay ceramics similar?
they both have giant structures which means they have the similar properties
What in the structure of glass differs from that of clay ceramic, what is the end result?
atoms in glass are not arranged in a regular way to form crystals so glass is transparent instead of opaque
describe the steps in the float process for modern window glass?
molten glass is poyred onto a bath of moletn tin where it spreads out on the surface. The flat layer of glass is drawn away and cooled in a continuous process
why are polymers a good choice for material?
they can be moulded into complex shapes - they are chemically unreactive and strong
why would polymers not be a good choice of material?
poor electrical and thermal conductors
What is rigid PVC good for?
underground pipes and window frames
how can PVC be made softer?
using plasticisers
what is flexible PVC used for?
indoor water pipes and waterproof flooring
what are the properties of metals?
strong, hard, shiny, high melting points, good electrical and thermal conductors. malleable
what do different metal elements mix together to form?
alloys
how do alloys differ from metals?
stronger
what does electroplating metal with unreactive metal allow?
improve appearance or resistance to corrosion
what is a composite material?
mixture of 2 or more materials, combined to produce a material with improved properties
What is true about the materials used in composite materials?
they have contrasting properties, are visable in the composite materal and can often be seperated out by physical seperation methods
how is contrete made?
mixing cement, sand, aggregate and water together.
what happens as contrete sets hard?
chemical recations happen that bond the solid components together. The sand and aggregate form the reinforcement of the concrete
what is the reinforcement in concrete bonded together by? what does this form
by cement which forms the matrix
what is tensile strength?
resist being stretched
why are glass fibres good as a reinforcement?
low density and high tensile strength
what is compressive strength a measure of?
how well a material resists being squashed
what is concrete strong / weak in?
strong in compression, weak in tension
what is concrete suitable for?
road surfaces and foundations
What material reinforces contrete, what is the effect?
steel bars are strong in tension and so the contrete resists cracking better than concrete alone (contrete now strong in tension and compression)
why is steel-reinforced concrete better than regular?
strong in tension and compression, less dense + cheaper than steel alone
what is wood composed of as a natural composite material?
cellulose fibres in a matrix of ploymer called lignin
When is wood stronger?
along the grain rather than across the grain
How is plywood constructed?
odd numbers of thin sheets of wood, each glued at right angles to the sheet below
What is wood’s tensile strength along the grain?
80
what is wood’s tensile strength across the grain?
4
what is plywood’s tensile strength?
25-40
