Kam Ganesan Sandy Hu Lowell Kwan Kristie Lau

 Introduction of Transition Temperature  Procedure  Seeding  Supercooling  Observations  Conclusion of Data  Sources of Experimental Error  Discussion  Transition Temperature (II)

 Compounds with water in formula  Does not indicate a wet substance  In the formula:  X · YH 2 O ▪ X is the compound ▪ Y indicates the molecules of water

 Chemical Formula:  Na 2 S 2 O 3 5H 2 O  also sodium hyposulfite  Molar mass = 179 gmol -1  colourless crystalline compound  variety of uses  photographic processing  antidote to cyanide poisoning  slightly toxic and harmful to skin

 Retort stand  Test tube clamp  Ring clamp  Wire gauze  Bunsen burner  Flint lighter  Beaker tongs  Thermometer  Boiling tube  20 g of Sodium Thiosulphate Pentahydrate  Scoopula  1 L beaker  Safety Goggles  Computer (with software)  150 mL of water  Temperature probe  Electronic Scale

 Set up retort stand with all necessary equipment  Measurement and add all substances  Attach and set up temperature probe to the computer and prepare LoggerPro program Above: Setup of experiment.

Above: Sodium thiosulphate in crystallized form

 Lowering temperature below freezing point  Supercooled substance will crystallize rapidly when seed crystal is added Above: Melted sodium thiosulphate pentahydrate cooling in the air jacket.

 one crystal of a substance is added to solution of substance solution  acts as basis for the intermolecular interactions to form upon  Expedites crystallization

 Seeding at super cooled state causing evolution of heat  rapid crystallization  transition temperature approximately 47.6˚C  close to the theoretical transitional temperature, approx. 48˚C  fairly accurate results  99.17% accuracy

 Contamination  Capabilities of LoggerPro  Time Lapse of 5 seconds lost  Judging change of state  Condensation

 Discussion  Transition Temperatures  Endothermic Versus Exothermic  Practical Uses and Application  Modifications to the Experiment  Transition Temperature (II)  Transition Temperature of Glass  Superconductivity

 change from one solid phase to another  found to be when temperature stays constant after crystal added  It is therefore when 2 states exist in equilibrium in a substance

 Endothermic: absorbs heat  Exothermic: releases heat  Compound was heated until it changes state, then it is cooled  Crystal is then added to supercooled liquid  Was our experiment ENDO or EXO (If wrong, try again)?

 Sodium thiosulphate crystal acts as a seed crystal speeding up crystallization process  Compound releases heat (EXOthermic) when crystal is added  Temperature of compound rapidly rises  Seed crystal allows intermolecular forces to react and collide (increase speed of recrystallization)

 Temperature changes include steady fall as liquid cools  Once crystal is added to supercooled liquid, temperature rapidly rises as crystallization takes place

 Water bath  Use of temperature probes and LoggerPro  Super cooling  Air jacket  Seeding and Crystallization

 Better computer software  Ensuring uniformity in heating substance  Determination of liquid state Above: The thermometer probe, stirring rod and substance are crammed in a small space.

 Temperature at which amorphous solid becomes brittle when cooled and malleable when heated  Transitions temperatures apply to polymers or glass  Kinetic energy

Superconductivity Zero Resistance Type I Type II Meissner Effect Magnetic Levitation Quantum Effects Applications

SUPERCONDUCTORS

 Varying physical properties:  Heat capacity  Critical temperature  Critical field  Critical current density  Properties that stay the same:  All superconductors have exactly ZERO resistance

NORMAL  Electric resistant  Current is a “fluid of electrons” moving across heavy ionic lattice  Electrons constantly collide with ions in lattice  During collision, energy carried by the current is absorbed by the lattice and converted to heat → vibrational kinetic energy of lattice ions SUPER  Zero resistance  Electronic fluid cannot be resolved in individual electrons  Instead, it consists of electrons known as Cooper Pairs:  attractive force between electrons from the exchange of phonons  Due to QM, the energy spectrum of this Copper pair fluid has an energy gap (limited energy ΔE that must be supplied in order to excite the fluid)  If ΔE is larger than thermal energy of lattice fluid will not be scattered by the lattice

 occurs when temperature T is lowered below critical temperature T c (value of critical temperature varies for different materials)  Usually 20 K to less than 1 K (kelvins)  Behavior of heat capacity (c v, blue) and resistivity (ρ, green) at the superconducting phase transition

 If the voltage = zero, the resistance is zero (sample is in superconducting state).  The simplest method to measure electrical resistance of a sample is:  Place in electrical circuit in series with current source I  Measure resulting voltage V  The resistance is given by Ohm’s law:

2 CLASSES OF SUPERCONDUCTORS  The Meissner effect breaks down when the applied magnetic field is too large.  Superconductors can be divided into two classes according to how this breakdown occurs: oTYPE 1: soft oTYPE 2: hard

TYPE 1  Consists of superconducting metals and metalloids.  Characterized as the "soft" superconductors.  Require the coldest temperatures to become superconductive.  Obtains intermediate state.  They exhibit sharp transition to a superconducting state.  Has "perfect" diamagnetism (ability to repel a magnetic field completely).

TYPE 1 EXAMPLES  Lead (Pb)  Mercury (Hg)  Tin (Sn)  Aluminium (Al)  Zinc (Zn)  Beryllium (Be)  Platinum (Pt)

TYPE 1-BCS THEORY  BCS Theory is used to explain this phenomenon  It states: When sufficiently cooled, electrons form "Cooper Pairs" enabling them to flow unimpeded by molecular obstacles such as vibrating nuclei.

TYPE 2  Consists of metallic compounds and alloys.  Characterized as “hard" superconductors  Difference from Type 1: transition from a normal to a superconducting state is gradual across a region of "mixed state" behavior.  Mixed state: do not change suddenly from having resistance to having none (has a range of temperatures where there is a mixed state).  Not perfect diamagnets; they allow some penetration of a magnetic field.

TYPE 2 Examples  (Sn 5 In)Ba 4 Ca 2 Cu 10 O y  HgBa 2 Ca 2 Cu 3 O 8  Tl 2 Ba 2 CaCu 2 O 6  Sn 2 Ba 2 (Tm 0.5 Ca 0.5 )Cu 3 O 8+  Pb 3 Sr 4 Ca 2 Cu 5 O 15+ Pb 3 Sr 4 Ca 2 Cu 5 O 15 [left] Sn 2 Ba 2 (Ca 0.5 Tm 0.5 )Cu 3 O x [right]

Meissner Effect  When a superconductor is placed in a weak external magnetic field H, it penetrates the super conductor a very small distance λ, called the London penetration depth  This decays exponentially to 0 within the bulk of the material

 The Meissner Effect is the expulsion of a magnetic field from a superconductor

London Equation  The Meissner effect was explained by the brothers Fritz and Heinz London, who showed that the electromagnetic free energy in a superconductor is minimized provided:  H = magnetic field  Λ= London penetration depth

A magnet levitating above a superconductor, cooled by liquid nitrogen. When temperature of superconductor in a weak magnetic field is cooled below the transition temperature… Magnetic Levitation

Explanation  Surface currents arise generating a magnetic field which yields a 0 net magnetic field within the superconductor.  These currents do not decay in time, implying 0 electrical resistance.  Called persistent currents, they only flow within a depth equal to the penetration depth.  For most superconductors, the penetration depth is on the order of 100 nm.

 Superconductivity: a quantum phenomenon, thus several quantum effects arise.  1961: flux quantization discovered - the fact that the magnetic flux through a superconducting ring is an integer multiple of a flux quantum.flux quantization  The Cooper pairs (coupled electrons) of a superconductor can tunnel through a thin insulating layer between two superconductors.Cooper pairs

 Superconducting magnets  Maglev Trains  MRI Imagers  Power Transmission  Electric Motors