Nick Shuttleworth - Physics MSci
Project Supervisor: Neal Skipper
The Viscosity of Metal Solutions: Are They Superfluids?
Project Outline
Project Aims
1. To design, build and calibrate at least one rotational type viscometer.
2. To determine the viscosity of Lithium-Ammonia solution over a range of
concentrations from 15MPM to 22MPM at ~240K (~-30C).
3. To establish a relationship between absolute temperature and viscosity for
Lithium-Ammonia solution at saturation.
Background – Lithium-Ammonia
The dissolution of lithium in ammonia occurs as purely charge based bonds form
between the lithium atoms and ammonia molecules. Solvated electrons form during
dissolution and their numbers increase with increasing concentration to saturation at
around 21 1 mole percent metal (MPM). At saturation the solution is a very good
conductor with a low density and is expected to have a very low viscosity. Viscosity
in metal-ammonia solutions decreases with increasing concentration and so the
viscosity value for saturated lithium-ammonia solution is almost certain to be below
the value of 0.135 cP (centipoise) for lithium-ammonia solution at 15MPM.
The below table2 is included for comparison.
Substance
Nitrogen at 77K
15MPM Lithium Ammonia Solution at 243K
Air at 271K
Water at 293K
Viscosity (cP)
0.0054
0.135
0.182
1.002
The below graph3 shows the results of previous measurements of the viscosities of
metal-ammonia solutions. It can be seen that the slopes of the curves for Na-NH3 and
K-NH3 decrease on approaching 15MPM and appear to tend to a limit but this is not
seen in the case of Li-NH3. No measurements of the viscosity of lithium-ammonia
solution have been made above 15MPM, hence the aim of this project: to fill in the
gap and discover whether it tends to a limit or zero.
1
Metal-Ammonia Solutions; J.J. Lagowski, M.J. Sienko; London Butterworths, 1970; page 248
The viscosity of Metal Solutions: Are they superfluids? Project Outline; J Bartlett UCL, 2003; page 2
3
Metal-Ammonia Solutions; J.J. Lagowski, M.J. Sienko; London Butterworths, 1970; page 250
2
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Background –Viscometers
Several types of viscometer exist, each with their specific strengths and weaknesses.
A summary4 is given below.
Type
Falling slug
Capillary
Vibrating type
Rotational
Principle
Measures rate of fall of a slug in a tube
filled with a viscous medium
Measures the back pressure required to
extrude material at a constant rate
Measures damping of a high frequency
probe applied to a probe [or wire]
Measures the torque required to rotate a
disk or cylinder in a viscous medium
Of the above, rotation based viscometers appear to be the most likely to give a
successful outcome to the project. Different types of viscometer will be researched
with specific attention being paid to ‘pure’ rotational and oscillating viscometers.
Future Work
Research into potential viscometer designs and materials, required instrumentation
and cooling methods will be carried out resulting in at least one built viscometer. The
viscometer(s) will be calibrated using fluids of well known low viscosity. A weak
solution of lithium-ammonia solution will be made up, tested and compared to
previously obtained values before proceeding to ‘new’ readings, as set out in the
‘Aims’ section, if it is deemed to be equal.
4
Viscometers and Their Use; H. J. Karam; Industrial and Engineering Chemistry, Vol 55 No. 2
February, 1963; page 39 - Excerpts
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Proposed Time Plan
3rd Oct
10th Oct
17th Oct
Week
1
2
3
24th Oct
4
31st Oct
5
7th Nov
6
14th Nov
7
21st Nov
28th Nov
5th Dec
12th Dec
8
9
10
11
19th Dec
26th Dec
2nd Jan
9th Jan
16th Jan
12
13
14
15
16
23rd Jan
30th Jan
6th Feb
13th Feb
20th Feb
27th Feb
6th Mar
13th Mar
17
18
19
20
21
22
23
24
20th Mar
25
Context Reading
4
He relevancy --- superfluids background
Risk Assessment --- Project Outline --- PROJECT
OUTLINE SUBMISSION (Oct 21) --- Lab safety
Investigate viscometer designs --- materials research (low
temp. and reactivity)--- Stirling Cooler/alternatives research
Calibration fluid research --- calibration methods
research/equations
Experimental methods research --- Learn to make up Li NH3
solutions
compatibility and accuracy issues looked at in detail ---torsion wire and other equipment research
Initial designs for viscometer and other equipment
Lab practicality test (if possible)
Draw up final viscometer design(s)
Submit final viscometer design(s) to workshop --- order
equipment
Break
Break
Examine Viscometer(s)
Progress Evaluation and Report
PROGRESS REPORT SUBMISSION (Jan 17) --Viscometer Calibration
Data Collection
Data Collection
Data Collection
Data Analysis
Data Analysis
Report Write-up
Report Write-up --- Presentation Creation
Presentation Creation --- PROJECT PRESENTATION
(Mar 14-17) --- Project Report write-up
Report Write-up --- PROJECT REPORT SUBMISSION
(Mar 24)
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