1
Darren Steele
Mentor: Jim Spencer
Synthesis of Samarium Cobalt Nanoblades
Introduction:
As particle accelerator technology takes on smaller dimensions such as those
found in photonic crystal fibers (PCF’s) it is imperative that all of the major supporting
components of a traditional accelerator be brought down to the same scale. One of the
key components to any accelerator is the magnets used for altering the charged particles’
trajectories. For conventional accelerators, electromagnets are employed, but at the
micron scale a new technology must be implemented. In 2008 researchers at Northeastern
University and Sandia National Laboratory published a paper that announced a new
method to synthesize samarium cobalt nanoblades with dimensions on the order of 100
nm which is composed of recyclable and environmentally friendly materials.1 SmCo
alloy is a rare-earth–transition-metal (RE-TM) permanent magnetic material, which is
characterized by having a sufficiently high Curie temperature, a high magnetization, and
a high magnetocrystalline anisotropy. The first two of these properties are provided
predominantly by the sublattice of the 3d element Cobalt, while the third is due mainly to
the rare-earth samarium, sublattice.2 If such material could be produced to be air-stable,
the material would presumably possess the bulk material’s ability to withstand high
temperatures, radiation and magnetic fields, hence would be capable of being
implemented into new accelerator concepts such as the PCF’s for testing. See Figure 1
for the conventional unit cells of SmCo5 and Sm2Co17.2 Note that the SmCo5 phase takes
on a hexagonal close-packed structure.
2
Figure 1: Samarium cobalt alloy phases. SmCo5 is on the right.
The previously introduced method proposed one year ago is a method classic to
nanoparticle synthesis and commonly referred to as the polyol process. Salts, in this case
Sm(NO3)3·6H2O and Co(NO3)2·6H2O, are placed in a polyol medium, specifically
tetraethylene glycol, which serves three functions. It dissolves the salts as a solvent,
releasing metal ions into solution, acts as a stabilizing ligand, and acts as a reducing
agent, which refers to its ability to reduce metal ions into atoms by providing electrons
through its own oxidation to lower the ions’ positive charge to neutral.3 The metal atoms
group together forming nuclei composed of the most stable lattice structures, which by
mixing the proper stoichiometric amounts, could be SmCo5, Sm2Co17 or others. The
nuclei germinate into final nanoparticles whose shapes and size depend on the many
parameters of the process of their creation. PVP is added to prevent aggregation of
nanoparticles and to provide a means of protection from oxidation. It will be attempted to
synthesize SmCo5 as it is the simpler of the two SmCo high performance permanent
magnetic phases found in Figure 1. The chemical synthesis will involve small yields on
3
the order of tenths of a gram and take place at the Geballe Laboratory of Advanced
Materials (GLAM). The product of each synthesis will be characterized individually via
standard XRD and SEM techniques at the Stanford Nanocharacterization Laboratory
(SNL) in order to analyze the effects of varying parameters on crystal phase purity,
nanoparticle shapes and size distributions. It would be necessary to measure the magnetic
properties of the particles to assess their value in future particle accelerator applications.
Chemicals:
-99.9% purity Sm(NO3)3·6H2O
-98% purity Co(NO3)2·6H2O
-Tetraethylene glycol
-Polyvinylpyrrolidone (PVP), Average molecular weight: 10,000 g/mol
-200 proof HPLC grade ethanol
-Hexane
Materials:
-500 mL three neck flask
-100 mL graduated cylinder
-100 mL beaker
-Condenser
-Rubber septum
-Thermocouple glass adaptor
-Magnetic stir bar
-Heating mantle with thermostat control and thermocouple
-Glass vials
-50 mL centrifuge vial
-Micro spatula
-Micro pipette
-Glass joint grease
-Liquid nitrogen
Safety Considerations:
When working in a wet chemical lab it is imperative to wear proper personal
protection equipment (PPE). For the purposes of this experiment, nitrile gloves, complete
coverage safety goggles and a lab coat are to be worn and maintained at the experimental
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site. MSDS information reports none of the listed chemicals have serious acute toxicity
concerns. Review Table 1 for experimental hazard descriptions and hazard controls.
Table 1: Experimental Hazards and Controls
Hazard
Hazard Description
Probability/Severity
Control
Chemical exposure to
skin
Irritation or chemical
absorption through
skin. Acute and chronic
risks found in MSDS.
High probability of skin
contact/ Low severity of
direct external exposure.
Chemical exposure to
eyes
Irritation or blindness.
Specific descriptions
found in MSDS.
Chemical exposure by
inhalation of ingestion
Specific effects depend
on dose and given in
MSDS. Chronic
toxicity effects are
noted but not fully
evaluated for both
metal nitrates.
Moderate probability of
eye contact/ Moderate to
high severity from eye
contact
Moderate probability/
Low to moderate severity
Utilization of proper
PPE. Nitrile gloves and
lab coat. Store unused
reagents in respective
chemical cabinets and
chemical waste in
designated waste
containers.
Utilization of proper
PPE. Complete closure
safety goggles.
Direct exposure to
liquid nitrogen
Contact of liquid
nitrogen by skin or
clothes may result in
severe burns and
permanent tissue
damage.
Low probability/ Low to
high severity depending
on circumstance.
Contact of heating
mantle or hot glass
Moderate burns may
result from contacting
heated objects.
Low probability/ Low
severity.
Ignition of samarium
cobalt alloy or
tetraethylene glycol
during reaction phase.
Heating up to 300°C
provides conditions for
combustion of SmCo
metal and glycol vapor,
if oxygen gas and an
ignition source are
present in reaction
vessel.
Low probability/
Moderate severity
Condensation of
oxygen in Schenk line
trap
Liquid oxygen is
extremely dangerous
and reacts violently
with organic
compounds. If it
collects in trap and then
evaporates, it may
result in Schenk line
manifold explosion.
Moderate probability/
Moderate to high
severity depending on
concentrations of organic
compounds in cold trap.
Dry chemicals and
liquids should be
handled in fume hood
as much as possible,
storage containers
should be closed after
use, and all spills
should be cleaned up
immediately.
Store liquid nitrogen
out of immediate work
area in properly
labeled dewar and
utilize standard liquid
nitrogen PPE including
cryogenic gloves and
safety goggles during
transfer.
Maintain knowledge of
where heated objects
are located and allow
hot glass to return to
room temperature
touching glass with
back of hand prior to
handling.
Allow for several
vacuum-nitrogen
cycles prior to heating.
Close fume hood
during reaction in the
unlikely event that a
systematic failure
results in combustion.
Ensure no flames or
source of sparks are
present in fume hood
during reaction.
When shutting down
Schlenk line manifold,
remove liquid nitrogen
from trap and allow
glass to return to room
temperature prior to
shutting off vacuum
pump.
Hazard Risk with
control implemented
Very low.
Very low.
Very low.
Moderately low.
Very low.
Moderately low.
Very low.
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Methods:
Weigh 0.15 g of samarium nitrate hexahydrate, 0.48 g of cobalt nitrate
hexahydrate, and 0.83 g of PVP in a 200 mL three-neck-round-bottom flask. (Note: If
only smaller flasks are available, downsize reagent quantities while maintaining 1:5
molar ratio of samarium to cobalt precursor). Add 100 mL of tetraethylene glycol. Total
metal ion concentration should be approximately 0.02 M. Place rubber septum on one of
the two side necks. Add magnetic stir bar into flask and place thermocouple along with
greased glass plug adaptor into the remaining side neck. (Note: The glass adaptor may
need to be wrapped in teflon tape to ensure no leakage) After ensuring heating mantle
and thermostat control are plugged in to wall outlet, place flask in mantle. The proposed
synthesis will deviate from the original by being conducted using a Schlenk line
technique as opposed to the more laborious glove box method. A typical double manifold
Schlenk line may be seen in Figure 2.
Figure 2: Schlenk line double manifold apparatus.4
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Provide adequate fresh grease to designated Schlenk line joint and attach
condenser. Grease condenser joint and attach flask. Ensure that the Schlenk line,
condenser, flask and mantle assembly is secure, open vacuum line stopcock, turn on
vacuum pump and after two minutes submerge the Schlenk line’s low-temperature trap in
liquid nitrogen. (Important: Transfer liquid nitrogen from storage dewar into a transfer
container, then pour into an adequate thermos which will submerge the trap to at least
two-thirds of its length). Set thermostat control to 100°C but do not begin heating. Open
dry nitrogen gas valve and adjust flow rate until a steady flow is observed at the bubbler.
Close stopclock for fifteen seconds and reopen to allow vacuum. Repeat vacuum-refill
cycle two more times and close stopcock such that the reaction vessel is exposed to
positive pressure nitrogen gas. Note that the fraction of air remaining in a flask after n
vacuum-refill cycles is given by the expression (f)n where f is the fraction of original
atmosphere in the flask after one cycle.5 Begin heating. Heat solution for one hour and
observe for signs of black residue. If no product appears, allow another half an hour of
heating. If still no solids, raise temperature.
Upon observation of reasonable product, turn thermostat control to room
temperature, open stopcock to restore vacuum, remove liquid nitrogen containing
thermos and vent vacuum line to allow liquid caught in trap to thaw to be properly
disposed in designated waste containers.6 Once the system has returned to room
temperature, turn off vacuum pump and close nitrogen gas valve. Feel that the reaction
vessel has indeed cooled by pressing the back of the hand against the glass and remove
the vessel from the Schlenk line. If the solids settle to the bottom, remove sufficient
liquid such that solids may be transferred along with a maximum of approximately 50 mL
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of liquid to a centrifuge vial; otherwise transfer entire contents to multiple centrifuge
vials to prevent loss of product. Place vial(s) in centrifuge and after solids are packed
well, remove remaining liquid into beaker for proper disposal. Rinse solids with ethanol
and repeat centrifuge process. Transfer solids to storage vial (25 ml) and disperse in
hexane. Label vial with contents and a number to be recorded along with reaction
conditions for distinction purposes. Repeat procedure for higher temperatures up to
300°C, longer times, different order of addition of reagents, and varying PVP to nitrate
ratio to determine optimal parameters for desired nanoparticle shapes and sizes.7 Each
reaction product should be placed in separate hexane filled vials and stored together on
designated storage rack. Employ powder x-ray diffraction (XRD) if available and
scanning electron microscope (SEM) techniques to verify structural composition and
nanoparticle geometry and distributions. Specific procedure for such techniques will
depend on specific instruments located at the SNL. Obtain size and shape distribution and
measure magnetic properties of particles.
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References:
1.
C. N. Chinnasamy, J. Y. Huang, L. H. Lewis, B. Latha, C. Vittoria, and V. G. Harris,
Appl. Phys. Lett. 93, 032505 (2008).
2.
Pfeiler, W. Alloy Physics: A Comprehensive Reference, 1st ed., Wiley: New York,
2007; pp 878-879.
3.
R.S. Ningthoujam, N.S. Gajbhiye, and Sachil Sharma, J. Phys. 72, 3 (2009); p 577.
4.
Shriver, D.F.; Drezdzon, M.A. The Manipulation of Air-Sensitive Compounds, 2nd ed.,
Wiley: New York, 1986.
5.
Girolami, G. S.; Rauchfuss, T.B.; Angelici, R.J. Synthesis and Technique in Inorganic
Chemistry, 3rd ed., University Science Books: Sausalito, CA, 1999; p 173.
6.
Kubiak, C.P. Kubiak Lab Manual. http://kubiak.ucsd.edu/manual/schlenktech.php
(accessed July 21, 2009).
7.
A. Slistan-Grijalva et al., Materials Research Bulletin, 43, (2008); p 91.