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Let’s grow a solid
How solids grow
Put your own name here!
What is special about a solid?
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It keeps its shape.
A man-made object
A natural
object
2
Liquids
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Have no shape
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When solids get hot they melt
so atoms can move round freely.
to form a liquid
- like chocolate
on a hot day.
3
Solids remember
how they grew!
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We look at 2 ways that solids grow.
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and the types of solid formed.
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Water can form:
1.
frost and snowflakes – formed out of
2.
ice in icicles or on a pond – formed
the air
from water
4
1. Snowflakes and frost
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are very
irregular,
have many
points or
edges,
have lots of
space inside
them.
5
2.
Ice in icicles
Ice on a pond
It is transparent with
very flat surfaces
6
Water from the tap
and water from melted ice
Which is
which?
пЃ® Liquids do
not
remember.
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7
How do solids grow?
Why is it interesting
and useful to know?
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We make modern devices by growing
a solid atom-by-atom
п‚Ё to
give us the form that we want.
8
1
9
Snowflakes grow from vapour
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We have air with very
few water molecules in it.
Cold
surface
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When the water molecule
hits a cold surface it will
stick just where it lands
Molecule
– a new word?
A molecule of
water is the
tiniest particle
of water that
can exist and
still be water.
10
A computer can show this
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We use a simulation from Hong Kong
http://apricot.polyu.edu.hk/~lam/dla/dla.html
11
http://apricot.ap.polyu.edu.hk/dla/dla.html
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Growing a snowflake
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100 molecules
11 000 molecules
13
2
14
Ice from a puddle
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Why is
it
perfectly
flat?
15
Crystals
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When solids grow
the atoms add on
row by row to
form a layer.
Then another
layer grows on
top.
Then another -
A tiny natural crystal in a stone
16
How many layers of atoms in
this chunk of quartz crystal?
One layer is
very, very
thin.
пЃ® About 10000
layers make
the thickness
of paper.
пЃ® The crystal
has about 100
million layers
of atoms!
How big can a crystal grow? See
http://news.bbc.co.uk/1/hi/8466493.stm
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17
Growing a solid from liquid or a
solution
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An atom will join the solid only if
the conditions are exactly right.
If the solid is near to its melting
point the atoms can move around so
as to get a more perfect pattern.
We call this annealing.
18
Growing a solid atom by atom
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Send a beam of
atoms through a
vacuum and on to
a flat surface.
Keep the surface hot so that the atoms
can move around and find the best place
to settle.
19
What is the arrangement of
atoms?
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Each atom wants to be close to other
atoms.
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What pattern do we get?
We
see lines
пѓ crystals !
20
More atoms
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Can you
see a
pattern?
21
Lines
22
More lines
23
- in 3 directions
24
Bubble rafts show thisWe will make some soon.
25
How to make a bubble raft
Bowl
of
water
Add one spoonful
of detergent very
carefully
- stir gently.
Put in the yoghurt
pot - you will get
a stream of
bubbles.
The yoghurt pot is below the water surface and
above the bottom of the bowl.
Move your hand slowly from side to side to spread
the bubbles.
26
A bubble raft is a �solid’ layer
water.
on the surface of the
A bubble
raft grown
quickly.
27
What do we see ?
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The bubbles attract each other.
They all move a little so that a new bubble
goes in the best place.
The bubbles are attracted to the edge of
the container and to your fingers!
If a bubble bursts or the raft is disturbed
it will repair itself –
this is called annealing.
28
A bubble raft grown very slowly
пЃ® Can
you
see the
rows?
University of Cambridge
29
The bubbles are in rows
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In 3
directions
30
Who are the experts at
creating this order?
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Bees
п‚Ё
honeycomb
31
What else do we learn ?
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Bubbles are
made from air
and soapy water
BUT
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They do not look
like air, or water.
They do not
behave like air,
or water.
A foam dance!
32
What is special about bubbles?
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The soap films are very thin.
A thin film of water is very different from
water in a bucket or glass.
We have a very thin sandwich
air- water –air
33
Now back to solids
All crystalline solids have atoms in
layers like lots of bubble rafts.
пЃ® We can grow crystals from a
solution of salt in water.
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Special �sandwich’ crystals can be
grown, which have different atoms
in different layers.
34
Sandwich crystals can now be
grown layer by layer
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пЃ®
пЃ®
MBE (Molecular Beam Epitaxy)
п‚Ё 1 layer per second
п‚Ё 2,000,000 seconds for 1 mm
= 23 days for 1 mm
These special crystals are used
inп‚Ё LEDs
п‚Ё and-----
35
You use manufactured crystals
in – Computer
�chips’
Chips are in:
mobile phones
games consoles
laptops
MP3 players-36
What have we learned ?
•A solid remembers the way it is formed.
•A solid formed from vapour may be like a
snowflake.
•We get perfect solids from liquids and if the
solid is free to readjust, anneal.
•We grew a bubble raft on water and watched
it anneal.
•We saw that soap bubbles look very different
from water and air and behave differently too!
•We learned that modern devices depend on atomic
layer sandwiches.
37
Scientists do
amazing things!
There is lots to find out!
Keep asking questions!
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