kam ganesan sandy hu lowell kwan kristie lau. introduction of transition temperature procedure ...

Kam GanesanSandy HuLowell KwanKristie 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 · YH2O▪ X is the compound▪ Y indicates the

molecules of water

Chemical Formula: Na2S2O35H2O

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: 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

Temperature of Sodium Thiosulpahte Pentahydrate

0

10

20

30

40

50

60

70

80

Time (s)

Tem

pera

ture

(˚C

)

Temperature of Sodium Thiosulphate Pentahydrate (311s - 1781s, 30 Second Intervals)

0

10

20

30

40

50

60

70

80

311

371

431

491

551

611

671

731

791

851

911

9711031

1091

1151

1211

1271

1331

1391

1451

1511

1571

1631

1691

1751

Time (s)

Te

mp

era

ture

(˚C

)

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

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 Tc (value of critical temperature varies for different materials)

Usually 20 K to less than 1 K (kelvins)

Behavior of heat capacity (cv, 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:

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:

o TYPE 1: soft

o TYPE 2: hard

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).

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

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.

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.

(Sn5In)Ba4Ca2Cu10Oy

HgBa2Ca2Cu3O8

Tl2Ba2CaCu2O6

Sn2Ba2(Tm0.5Ca0.5)Cu3O8+

Pb3Sr4Ca2Cu5O15+

Pb3Sr4Ca2Cu5O15 [left]

Sn2Ba2(Ca0.5Tm0.5)Cu3Ox [right]

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

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

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.

The Cooper pairs (coupled electrons) of a superconductor can tunnel through a thin insulating layer between two superconductors.

Superconducting magnets

Maglev Trains

MRI Imagers

Power Transmission

Electric Motors