Dt Words #2

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  • Created by: Ishbel
  • Created on: 14-05-13 12:11
Atom
The smallest part of an element that can exist chemically.
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Molecule
Two or more atoms that are normally bonded together covalently.
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Alloy
mixture that contains at least one metal. This can be a mixture of metals or a mixture of metals and non-metals. An example of an alloy is brass, an alloy of copper and zinc.
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Composite
A mixture composed of two or more substances (materials) with one substance acting as the matrix or glue.
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Ionic
occur between a metal and a non metal; al
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Covalent
are formed when two nonmetals bond e.g plastics.
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Metallic Bond
This is often described as ‘a positively charged nuclei (ions) in a sea of electrons’.
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Timber Natural
Natural timber is timber that is used directly from the tree. Natural timber is a natural composite material comprising cellulose fibres in a lignin matrix.
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ThermoPlastics
can be melted and re-formed
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Thermosets
plastics (or thermosets, for short) can be heated and set only once.
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Density
The mass per unit volume of a material
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Electrical Resistivity
this is a measure of a material’s ability to conduct electricity. A material with a low resistivity will conduct electricity well.
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Thermal Conductivity
A measure of how fast heat is conducted through a slab of material with a given temperature difference across the slab
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Thermal Expansion
A measure of the degree of increase in dimensions when an object is heated. This can be measured by an increase in length, area or volume. The expansivity can be measured as the fractional increase in dimension per kelvin increase in temperature.
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Hardness
the resistance a material offers to penetration or scratching.
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Tensile Strength
The ability of a material to withstand pulling forces.
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Stiffness
The resistance of an elastic body to deflection by an applied force.
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Toughness
he ability of a material to resist the propagation of cracks. The opposite of brittleness.
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Ductility
The ability of a material to be drawn or extruded into a wire or other extended shape.
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Softwood
- 30 years to Mature - Less dense Celluose Fibres and lignin matrix - pine, cedar
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Hardwood
- Decidious - 100 years to mature - broad leaves and fruit bearing
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Plywood
composite timber. Each layer is 90 degrees parallel to the other
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Particle Board
Variety of thickness
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Hardwood Flooring
Durability - hard wearing and resistant to compressive forces. Ease of Maintenence - easily sanded and re-finished
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Softwood Floors
Durability - susceptable to compressive forces. Aesthetics - more warmer colours
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Explain how the movement of free electrons makes metals very good electrical and thermal conductors
Metals are positively-charged metal atom nuclei in a negatively-charged cloud/sea of outer free electrons; The free electrons are spread through the crystalline lattice and are mobile; The mobility of the sea of electrons contributes to the high elec
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Gradual cooling
a few crystals are formed - large grain size
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Rapid cooling
many crystals formed - small grain size.
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Reheating a solid metal
alloy allows the grain structure to re-align itself.
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Covalent Bond (Plastics)
In a covalent bond the outer electrons of some atoms come close enough to overlap and are shared between the nuclei, forming a covalent bond.
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The structure and Bonding of a thermoplastic
Thermoplastics are linear chain molecules, sometimes with side bonding of the molecules but with weak secondary bonds between the chains
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Describe the effect of a load on a thermoplastic.
up to elastic limit coiled chains are stretched; after elastic limit material is plastic – secondary bonds weaken and allow the molecular chains to flow over each other resulting in creep and flow of the thermoplastic material;
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Polypropylene
Light, hard, tough -impact resistant, good chemical resistance, can be sterilized, good resistance to work fatigue, good mechanically
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Polyethene
Good electrical insulator, tough- impact resistant, Stiff and hard, Can be sterilized, Soft/ Flexible, Good resistance to chemicals, durable
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Polyurethane
Formulations cover an extremely wide range of stiffness, hardness, and densities.
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Urea-formaldehyde,
Urea-formaldehyde resin's attributes include high tensile strength - strong, high surface hardness, and heat resistant. High brittleness so not tough or impact resistant. High stiffness.
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composition of glass
Glass is composed primarily of silicon dioxide (sand) together with some sodium oxide and calcium oxide (limestome)and small quantities of a few other chemicals.
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Describe a smart material
ne or more properties that can be dramatically altered,
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Describe a piezoelectric material
When a piezoelectric material is deformed, it gives off a small electrical discharge. When an electric current is passed through it, it increases in size (up to a 4% change in volume). They are widely used as sensors in different environments. Speci
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Describe shape memory alloys
SMA’s are metals that exhibit pseudo-elasticity and shape memory effect due to rearrangement of the molecules in the material.
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Other cards in this set

Card 2

Front

Molecule

Back

Two or more atoms that are normally bonded together covalently.

Card 3

Front

Alloy

Back

Preview of the front of card 3

Card 4

Front

Composite

Back

Preview of the front of card 4

Card 5

Front

Ionic

Back

Preview of the front of card 5
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