Transcript Ionic lattice structures

Ionic lattice structures
• high melting and boiling points
• brittle when hit hard
• ions held together by attraction of opposite electrical charges
• huge lattice of ions
• only conduct electricity when ions can move
Arrangement of ions in lattices
determined by the relative sizes of the 2 ions
-ve (anion) larger
-ve (anion) and +ve (cation) roughly the
than +ve (cation)
same size e.g. caesium chloride
e.g. sodium chloride
Cs2+
Cl-
Other lattice structures
Zinc blende (ZnS)
Rutile (TiO2)
Ionic lattices
Which type of structure, CsCl or NaCl, are the following likely to have?
1. Lithium fluoride
2. Calcium sulphide
3. Potassium fluoride
4. Iron (II) oxide
Metals
• good electrical conductors
• some resistance to electron flow at normal temperatures
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Superconductors
H. Kamerlingh Onnes
• liquified helium in 1908
• investigated the low temperature resistivity of mercury
• resistance drops suddenly to zero at 4 K(-269oC) - critical temperature
Critical temperature for Superconductors
Material
T-Critical
Gallium
1.1 K
Aluminium
1.2 K
Indium
3.4K
Tin
3.7K
Mercury
4.2K
Lead
7.2K
Niobium
9.3K
Niobium-Tin
7.9K
LaBa2Cu3-oxide
30K
YBa2Cu3-oxide
92 K
TlBa2Cu3-oxide
125 K
InSnBa4Tm4Cu6- oxide
150 K
Theory of Superconductivity
Metal ions in lattice vibrate as
if attached by stiff springs
Positive ions are attracted
to passing electrons
Ions quickly spring back after electrons have passed
In cooled metals, ions do not spring back so quickly
Temporary local area of positive charge
A second electron is attracted to this area so follows the first electron
through
The two electrons effectively travel as a pair
Travelling as a pair, the electrons meet so little resistance that the
metal can be considered to have zero resistance
The Meissner Effect
Superconductors are perfectly diamagnetic i.e. they
repel a magnetic field; this is called the Meissner
effect.
Magnetic levitation
More levitation!
Potential uses of superconductors
Transport
 Maglev trains (Paris to Rome in just over 2 hours!)
 Frictionless bearings increasing efficiency of electrical motors and
generators in electric-powered transport
 Smaller, lighter gyros in spacecraft and satellites
Potential uses of superconductors
Maglev trains
Maglev- Magnetic levitation trains
which float over a guideway
replacing steel wheels and tracks.
Frictionless so can travel up to
500km/h (310mph) – viable option
replacing aircraft for some
journeys.
China- Shanghai transrapid shuttles 19
miles from Pudong airport to Longyang
train station in 8 min flat at 430 km/h
Potential uses of superconductors
Maglev trains
http://video.google.com/videoplay?docid=6261317600045015385
Main components to the Japanese system are:
 A large electrical power source (a/c current)
 Metal coils lining a guideway or track
 Large guidance magnets attached to the train underside
The magnetic field created by the electrified superconducting coils in the
guideway walls and the track combine to levitate it 1-10cm.
Potential uses of superconductors
Maglev trains
Guideway for the Yamanashi
maglev test line in Japan.
How it works.
Potential uses of superconductors
Magnetic Resonance Imaging (MRI) - non-invasive imaging of parts of body
Uses a superconducting electromagnet to
produce a magnetic field x10,000 stronger
than the earth’s
The electromagnet wire is made from a
superconducting Niobium-titanium alloy is
cooled by liquid helium (4K).
Machines cost around
£500,000 and have
high running costs
but most large
hospitals in the UK
have one.
Potential uses of superconductors
Power transmission - reduce energy lost as heat (currently up to 10%)