Determining Transition Temperatures of Hydrates FINAL ... - vinstan

winkwellmadeΠολεοδομικά Έργα

15 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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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)

(1) solid

another phase
= evolution/absorption of heat


this temperature
= transition temperature



Hydrates



Seeding & Supercooling



Crystallization



Applications






(2) Superconductivity

loss of electrical resistance



this temperature =
transition temperature



Zero resistance


-

Type I


-

Type II



Quantum effect



Meissner effect



Applications


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
.


20mL Sodium Thiosulphate
Pentahydrate



temperature
, until hydrate
evaporates



air jacket




cooled to ~40
°
C (i.e. supercool)



seed crystal added



temperature



crystallization occurs



temperature stabilizes


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
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
Time (s)
Temperature (˚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
971
1031
1091
1151
1211
1271
1331
1391
1451
1511
1571
1631
1691
1751
Time (s)
Temperature (˚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



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:




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.


(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]



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