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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. Cs 2+. Cl -. Arrangement of ions in lattices. -ve (anion) larger - PowerPoint PPT Presentation
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Ionic lattice structures
• high melting and boiling points
• only conduct electricity when ions can move
• huge lattice of ions
• ions held together by attraction of opposite electrical charges
• brittle when hit hard
Arrangement of ions in latticesdetermined by the relative sizes of the 2 ions
-ve (anion) larger
than +ve (cation)
e.g. sodium chloride
-ve (anion) and +ve (cation) roughly the
same size e.g. caesium chloride
Cs2+
Cl-
Other lattice structures
Zinc blende (ZnS)
Rutile (TiO2)
Ionic latticesWhich 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 conductorsgood electrical conductors
• some resistance to electron flow at normal temperaturessome resistance to electron flow at normal temperatures
+ + +
+ + +
+ + +
+ + +
+ + +
+ + +
e_
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e_
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e_
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SuperconductorsH. Kamerlingh Onnes
• liquified helium in 1908
• investigated the low temperature resistivity of mercury
• resistance drops suddenly to zero at 4 K(-269oC) - critical temperature
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
Critical temperature for Superconductors
Theory of Superconductivity
In cooled metals, ions do not spring back so quickly
The two electrons effectively travel as a pair
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
Temporary local area of positive charge
A second electron is attracted to this area so follows the first electron through
Travelling as a pair, the electrons meet so little resistance that the metal can be considered to have zero resistance
Magnetic levitation
Superconductors are perfectly diamagnetic i.e. they
repel a magnetic field; this is called the Meissner
effect.
The Meissner Effect
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 superconductorsMaglev 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 superconductorsMaglev 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 superconductorsMaglev trains
How it works.
Guideway for the Yamanashi maglev test line in Japan.
Potential uses of superconductorsMagnetic 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%)
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