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