Presentation on theme: "Ionic lattice structures high melting and boiling points only conduct electricity when ions can move huge lattice of ions ions held together by attraction."— Presentation transcript:
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 lattices determined 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 Cs 2+ Cl -
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 +++ +++ +++ +++ +++ +++ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_ e_e_
Superconductors H. Kamerlingh Onnes liquified helium in 1908 investigated the low temperature resistivity of mercury resistance drops suddenly to zero at 4 K(-269 o C) - critical temperature
MaterialT-Critical Gallium1.1 K Aluminium1.2 K Indium3.4K Tin3.7K Mercury4.2K Lead7.2K Niobium9.3K Niobium-Tin7.9K LaBa 2 Cu 3 -oxide 30K YBa 2 Cu 3 -oxide 92 K TlBa 2 Cu 3 -oxide 125 K InSnBa 4 Tm 4 Cu 6 - 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 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 Photos courtesy Railway Technical Research Institute Left- guideway for the Yamanashi maglev test line in Japan. Right- how it works. 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 How it works. Guideway for the Yamanashi maglev test line in Japan.
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%)