Atom

The smallest part of an element that can exist chemically.

MOLECULE 

Alloy

Composite: 

A mixture composed of two or more substances (materials) with one substance acting as the matrix or glue.

Describe a bond as a force of attraction between atoms.

1).  ionic bonds-non-metal and metal-gives electrons, therefore negatively charged.  opposite charges attract, therefore they are attracted.  they can conduct electricity through solvents when ions separate.  NA+CL

2).  covalent bonds-two non-metals bonded.  sharing electrons.  strong bonds.  two types: Molecular: weakly bonded e.g. water.  NEtwork covalent bonds: e.g. diamonds, tough element.  

3).  metallic bonds-formed between metals.  the free electrons make a glue to keep the metals together.  this makes the metal malleable and can conduct electricity (free electrons-vibrate-causes heat and kinetic energy). 

Charge: 

the quantity of unbalanced electricity in a body (either positive or negative) and constructed as an excess or deficiency of electrons and is measured in coloumbs

FIBRE : 

a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread with a length to thickness ratio of at least 80.  

man-made-plywood

natural wood: cherry/oak

ferrous metals: 

cutlery

non ferrous metals: coppy, brass, aluminium

thermoplastics: ice cube trays

Thermoset plastics: some plastic dishes

natural fibre: wool/cotton

Synthetic fibre: nylon socks

vegetable origin: carrots, apples

animal origin: fish/beef

glass: glass (cups)

earthenware:pottery 

porcelain: china dinner sets

Density- 

the mass per unit volume of a material (d=m/v)

e.g. high density=anchor, low density=foam

Electrical resistivity

-this is a measure of a material’s ability to conduct electricity.  A material with a low resistivity will conduct electricity well. 

e.g. low resistivity-wires in a cable, high resistivity-casing of a plug

Thermal conductivity

-a measure of how fast heat Is conducted through a slab of material with a given temperature difference across the slab.

e.g. high conductivity-glass, metal. low conductivity-bottle warmers, warm jackets.  

Thermal expansion (expansivity)

-a measure of the degree in dimensions when an object is heated.  This can be measured by an increase in length, area or volume.  This can be measured as the fractional increase in dimension per Kelvin increase in temperature

e.g. food (putting things in the oven), structures in hot climates (bridges)

Hardness-

the resistance of a material offers to penetration or scratching!

e.g. glass (you would prefer a glass to be resistant to scratching)

Toughness 

-the ability of a material to resist the propagation of cracks

e.g. concrete, metal structures. 

Plastic deformation-

Ductility-

the ability of a material to be drawn or extruded into a wire or other extended shape.

e.g. forming a shape that you want it to be (metal, plastic).

Stiffness

-the resistance of an elastic body to deflection by an applied force. 

e.g. scaffolding instead of metal (because of typhoons).  

Tensile strength-

the ability of a material to withstand pulling forces

e.g. high tensiles strength=fabric called Kevlar (for airplane tyres-strong).

1).  smell - designer must take into consideration the smell of the materials e.g. glue , or else it may repel customers from buying

Explain a design context where each of the characteristics is an important consideration.

Some of these properties are only relevant to food, while others can be applied to more than one material group. Although these properties activate people’s senses, responses to them vary from one individual to another, and they are difficult to quantify scientifically, unlike the other properties

Describe the structure of natural timber.

outline that timber can be classified according to the conditions needed for tree growth.

temperate forests = COOLER REGIONS

tropical forests= BETWEEN THE TROPIC OF CANCER AND CAPRICORN :) 

1).  wood=softer

2).  softwoods reproduce by cones

3).  have needles

e.g. pine, cedar, cypress

1).  wood=harder

2).  hardwoods reproduce by flowers

3).  have broad leaves

4).  dormant in winter 

5).  many lose leaves every autumn.

e.g. elm, maple, oak, beech

 Discuss the issues relating to the consideration of timber as a renewable resource.

1).  it takes a long time to mature-mohogany takes 100 years

2).  soil erosion-the roots of the tree hold the soil in.

3).  chopping down trees=less trees to remove green house gases=green house effect! 

4).  it destroys animal, insect and plant life ->extinction of species

composite timbers: 

Timber that has been reformed and glued to make products that have a variety of different properties

e.g. particle board

plywood

pinewood

Compare the characteristics of particle board, laminated woods (for example, plywood), pine wood (a softwood) and mahogany (a hardwood).

hard wood: mahogany (none/very little)-compressed fibres –costly, long time to grow-broad leaves

characteristics: grown in humid climates, not many grain lines on them.  

soft wood: pine (stripes)-cheap, less time to grow-grown in cold places. 

Outline criteria for the selection of timber for different structural and aesthetic design contexts.

building beams: its normally hidden so for aesthetics reasons, hardwood isnt needed, rough sawn pine is used normally.  

for flooring: hardwood.

furniture and childrens toys: painted or stained for aesthetics.

Describe the reasons for treating or finishing wood.

1).  to reduce splinters ->safety reasons

2).  reducing attack by organisms and chemicals

3).  enhancing aesthethics

4).  modifying other properties e.g. shape

Explain three differences in the selection of timbers for flooring if it were made of a hardwood, a softwood or a composite material.

hardwood: very durable e.g. esp in kicthens with high "traffic areas".  easy to clean, usually is dark in colour

soft wood: it is not durable and not hard.  it is easy to clean, usually light in colours - white/yellowy-gives the feeling of warmth :)

composites: highly durable, easy to clean, can be designed in colours of choice.

describe a metallic bond:

 [image]

Explain how the movement of free electrons makes metals very good electrical and thermal conductors.

metals exits as

crystals (pure or alloyed)

how metals solidify when they cool: 

1).  molten metal is cooled just below freezing temp.  crystals of a solid are formed when pure.

2).  all metals are solid at room temp (except mercury)

3).  a process of nucleation and growth achieves solidificaton

4).  DENDRITES grow out from the nuclei forming a tree-like structure in the direction of the fastest heat loss

1).  close packed hexagon: weak, poor strength

2).  face-centered cubic: ductile, good electrical conductors

3).  body-centered cubic:hard, tough

modification of grain size: 

the rate of cooling and the amount of impurities in the molten metal will affect grain size:

1).  gradual cooling = large grain size

2).  rapid cooling=small grain size

3).  reheating a solid metal/ alloy allows the grain structure to re-allign itself.

4).  directional cooling in a structure is achieved by selectively cooling one area of a solid.  

hardening: 

tempering: 

hardening ferrous products by heating it up for a second time and then cooling it with oil.  

 The object of tempering is to decrease hardness and increase toughness to produce the desired combination of mechanical properties. 

normalising -remember Massage example- anjali! :) : 

planishing: 

Producing a smooth surface finish on metal by rapid succession of blows delivered by highly polished dies or by a hammer designed for the purpose, or by rolling in a planishing mill. 

annealing: 

case-hardening: 

plastic deformation:

occurs when a force PERMANENTLY deforms a material even after the force is removed.

Explain how metals work-harden after being plastically deformed.

an alloy is a metal compound produced by combining a metal with one or more other elements to change its properties: 

1).  change melting point

2).  increase strength/hardness/ductility

3).  change colour (brass to copper)

4).  change electrical and thermal properties

super alloys: 

list two design criteria for super alloys: 

1).  Creep is the tendency of a metal (or material) to slowly move or deform permanently due to the long term exposure of stress that are below the yield strength or ultimate strength of the metal. Creep is more severe when metals are subjected to near the melting point heat for long periods of time.

2).  Oxidation resistance is the ability of a material to resist the direct and indirect attack of oxygen (oxidation). 

aircraft turbines

space vehicles

submarines

nuclear reactors

Describe a covalent bond.

plastics: 

made up of long chains of molecules : "macromolecules" -links in chains are covalent bonds.  strong and primary bonds.  

secondary bonds are bonds that are made with the next chain -becomes weaker (allowing plastics to be formed/moulded).  

1).  Durable, safe (smooth, easy to get rid of sharp edges, doesn’t shatter),

2).  waterproof, multiproof,

3).  lightweight,

4).  easy to clean,

5).  transparent,

6).  cheap, moulding (economical-no extra bits wasted), 7).  poor conductor,

8).  colour, doesn’t rust or damage with weather, 9).  recycleable. 

1).  thermoplastics

2).  thermosets

1).  Weak bonds

2).  shapes can be made by heat (constantly can be reused to shape).  <-more environmentally friendly (can be reused)

thermosets:

 [image]

1).  strong bonds

2).  stays as a solid, no matter if heated because their primary bonds are very strong so the chains cannot flex.  

used for: making heat appliances.  

1).  lime

2).  soda

3).  sand

4).  ash

Sand, limestone, sodium carbonate-heat them to 1500 celcius.  After that it is either moulded or blown.  

1).  they add scrap glass to it = less sand and less of other ingredients used.  

2).  it is recycled and sterilized instead of melting down and adding costs-using heat and electricity-unefficient.  

1).  reflective

2).  good conductor of heat 

3).  sand

4).  transparent

5).  fragile

6).  brittle

7).  hard

8).  liquid or solid

9).  multipurpose

10).  harmful 

11).  poor conductor of electricity

12).  doesnt react

13).  crystal glass-sparkles

14).  its not porous (moist doesn't go out of it) 

boron + soda glass 

produces heat/ sturdy glass

toughened glass/tempered glass: SHATTERS into tiny fragments but no sharp shards are produced when shattered.  easy to break but safe :) 

2).  Laminated glass: safety glass that holds together when shattered due to a thin layer of material - mostly plastic- between the two layers.  it prevents cracks from growing and it can be made bullet proof.  :)   

1).  reproduces plate glass

2).  glass flooring 

3).  bricks

4).  aestheticalling pleasing

5).  thermal conductor

6).  hard.

Describe the matrix composition of composites.

refers to how composite materials are formed together.  the separate materials then when combined, reinforce each other making it stronger and a much more useful material.  

this is where one material acts as a glue "matrix" holding the other material in place 

e.g. fibreglass.  

smart materials have one or more properties that can be altered.  

e.g. 1).  viscosity

2).  volume

3). conductivity

the property that can be altered influences the application of the smart material.

1).  piezoelectric materials

2).  magneto-rheostatic materials

3).  electro-rheostatic materials

4).  shape memory alloy