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GRN27 539
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OCT 30 1364
Por Oral Presentation at the
Alghath Conference on Analytical Chemistry in Nucleur Technology
Gatlinburg, Tennessee
October 6-8, 1964
THE RAPID DETERMINATION OF LOW CONCENTRATIONS OF OXYGEY AND
HYDROGEN IN ALKALI METALS BY A
MODIFIED AMALGAMATION TECHNIQUE
Gerrld Goldberg
Oak Ridge National Laboratory
Oak Ridge, Tennessee

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Research sponsored by the U. 8. Atomic Energy Commission' under contract
with the Union Carbide Corporation.
THE RAPID DETERMINATION OF LOW CONCENTRATIONS OF OXYGEN AND HYDROGEN
IN ALKALI METALS BY A MODIFIED AMALGAMATION TECHNIQUE
Gerald Goldberg
Pepkowitz and Judd were the first to report on the use of the amalgamation method
for the determination of oxygen in sodium.
In principle, successive additions of mercury,
and the draining of the resulting sodium amalgam, leave only the unreactive Na2O floating
on the sodium-free mercury. Water 18 then added to the residual Nazo and the resulting
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hydroxide solution 18 titrated with a standard acid to determine the stoichiometric amount
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of oxygen which 18 present.
The object of this work was to modify the amalgamation technique so that it would
be applicable to the routine determination of concentrations of oxygen of less than 50 ppen
in potassium and Nak, as well as in sodium. The apparatus was designed so as to be adapt-
able to several sampling techniques as well as to be operable with either an inert atmos-
phere or a vacuum. The reaction vessel in which the amalgamation is carried out was
designed so that it could be disconnected from the rest of the apparatus while under
vacuum. Due to this modification, complete removal of the alkali metal from the reaction
vessel can be hastened by manual shaking of the vessel during amalgamation. The standard
amalgamation method depends on the magnetic manipulation of a stirrer within the reaction
vessel to bring the mercury in contact with both the amalgam and the alkali metal that has
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splashed on the inner wall of the vessel.
The volume of mercury used during the course of
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an amalgamation was reduced significantly. The time required for an analysis was reduced
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from a period of several hours to less than one hour.
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Apparatus
Slide 1. The apparatus pictured is composed of two systems, a combination inert
gas pressure, vacuum system to the left of the three-way stopcock, and the reaction system
to the right of the stopcock. The vacuum system 18 composed of a liquid nitrogen cooled
trap, a mercury diffusion pump and a roughing pump. High purity helium, low in oxygen and
especially moisture content, 18 used as the inert gas.
The helium is passed through an
Anhydrone drying column and a liquid nitrogen cooled trap to remove any moisture that may
be present. The pressure regulator is a non-bleed type with a metal diaphragm. A by-pass
which connects the vacuum and the gas systems makes it possible to evacuate the helium
line from the gas cylinder to the three-way stopcock.
The reaction system is composed of the mercury reservoir and the reaction vessel.
An "O" ring joint is used in place of the more conventional ball joint as a connection
between the reaction vessel and the rest of the system to reduce the exposure of the mercury
to grease before it drains into the reaction vessel. The reaction vesse I 18 loaded with
sample within an inert atmosphere dry box and it is capped through the use of an "O" ring
seal rather than a tapered Joint to decrease further any contact of mercury with grease.
The unique feature of the apparatus 18 the fact that the amalgamation can be carried
out in vacuo while the reaction vessel 18 disconnected from the apparatus so that it may
be shaken to insure complete amalgamation. This modification decreases materially the
RESMI
number of extractions necessary to effect complete removal of the alkall metal from the
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vessel. The. ability to disconnect the reaction vessel from the apparatus simplifies the
subsequent dissolution and removal of the residual oxides as a small volume of solution.
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,
This, in turn, allows for greater precision in the subsequent titration of the solution
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with a standard acid.
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Slide 2. The apparatus pictured is used to carry out the titration of the solution
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which results from the dissolution of the residual alkali metal oxide to form the corres.
ponding hydroxide. Pictured are a standard pH meter, a Micro Metric Buret which uses a
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1-ml per inch syringe and 18 calibrated to 0.001 m2. and the titration cell.
The cell 16
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composed of a polyethylene cup made from a cut-down bottie, a rubber stopper, an inert
blanket-gas line, a standard combination electrode (Beckman No. 39142) and a small magnetic
stirring bar. The titration 18 carried out under an inert atmosphere to eliminate any coz
pick-up. The combination electrode aids in keeping the size of the beaker to a minimum.
Procedure
The sample 18 transferred to the reaction vessel within an inert atmosphere dry box.
The vessel 18 removed from the dry box and 18 connected to the apparatus;
The apparatus and the reaction vessel are then evacuated to a pressure of less than 1 micron
and 40 to
50 ml. of mercury are slowly added under vacuo to the vessel. (If samples of
.one
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potassium are being analyzed, heat 18 applied to the vessel until amalgamation occurs.)
.
The vessel is disconnected from the apparatus and 18 shaken to insure the complete amalga-
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mation of any alkali metal that has spattered on the wall of the vessel. The vessel is
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then connected to the apparatus and the apparatus and vessel are evacuated as before.
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In order to drain the amalgam from the reaction vessel, helium at 1 to 2 psig pressure
18 admitted to the evacuated reaction system by appropriate rotation of the three-way
stopcock. All but the last few ml'8. of amalgam are drained into a flask which contains
-4.
about 100 ml. of distilled water. The amalgamation and draining procedures are repeated
four times using 30 to 40 ml. additions of mercury. A total of five extractions 18 suffi-
cient for the analysis of up to 5 grams of sample. The final extraction may be examined
for alkali metal content by draining the mercury into a beaker which contains a few milli-
literu of water and a drop or two of phenolphthalein solution. If the solution should turn
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pink, still another extraction 18 necessary.
After the draining of the last mercury addition the reaction vessel is disconnected
from the apparatus. About 20 ml. of distilled water is added to the vessel, and the vessel
18 shaken in order to d18solve any residual oxide whic' may be present. The solution and
the remaining few ml's of mercury are drained into the titration cup through the hole in
• the rubber stopper in which the buret tip aloo enters the cup. The same procedure is
followed for two additional 10-ml. washings. (The blanket gas 11 flowing during the transfer
of the sample.) The hydroxide solution 18 then titrated with 0.100 N HCl and the change in
Po 18 plotted against the calibrated addition of the Hcl.
The change in slope of the
titration curve normally occurs around pH 7.
An alternative method which makes use of flame spectrophotometry may be substituted
for the titration. With this method the alkali metal oxide residue 18 dissolved and washed
from the reaction vessel with approximately 0.01 N HC1. The washings are transferred to a
volumetric flask and are diluted to volume. The sodium or potassium 18 then determined by
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flame spectrophotometry. In the case of Nak, the oxygen, as K20 and Nazo, would be
calculated separately, based on the amounts of potassium and sodium in the solution, and
1
the results would be combined.
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The weight of the sample is determined from the amalgam which is collected in the flask.
The hydroxide solution which resulted from the reaction of the alkali metal in the amalgam
with the water in the flask 18 titrated with a standard solution of Hc1 to a phenolphthalein
endpoint.
Results
For most analytical methods it 18 possible to prepare a set of standards and to
establish the reliability of the method based on the recovery of these standards. This is
not the case with the alkali metals. Under certain conditions, oxygen at varying concen-
trations may be added to the alkali metals, but one must first establish the concentration
of the oxygen which already exists in the metal.
This 18 best done by the determination of
the 6 erage value for a series of analysis on the same batch of metal. To this end a number
of ampoules of high-purity potassium were obtained from MSA Research Corporation. Each
ampoule contained from 5 to 6 grams of metal.
The analysis of a series of these ampoules
gave results in the range of from 8 ppm to 14 ppm of oxygen which 18 considered quite good
since each sample was a separate ampoule rather than a part of one ampoule.
Both K20 and KO2 of known purity were used as standards to check on the recovery of
XOARE
oxygen by this modified amalgamation procedure. Several ampoules of potassium were broken
and placed in separate reaction vessels within the drybox. Known amounts of the K20 and KO2
were also added separately to these reaction vessels. Between 95- and
covery of the
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oxygen added was achieved by flame spectrophotometric analysis of the solution of the residue
after amalgamation. Additional samples of K20 and KO2 were added to molten potassium con
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tained in columbium capsules within the drybox. These samples were cooled and then placed
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in reaction vessels. Again, recoveries were essentially 100% complete. Several attempts
were made to use mercuric oxide as a source of oxygen, but it was soon found that this
oxide is not as readily reduced by potassium as it 18 by Bodium.
Slide 3. A number of replicate samples of both potassium and NaK were analyzed in
a routine manner to further establish the reliability of the method. It was felt that
good precision would attest to reasonable accuracy. The potassium samples were routine loop
samples of varying oxide concentrations while the Nak samples were removed from drums which
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were at room temperature. The Nak samples were expected to contain very low concentrations
of oxide due to the limited solubility at this temperature,
Slide 4.
Several of the residues were examined for hydride and carbonate content. None was
found.
The first amalgamation was checked for off-gassing on several samples. No liberated
ts
gases were detected. Reaction conditions were al80 varied on some of the samples, such as,
the volume of mercury used for earn extraction, the settling times between drainings and
the number of extractions made per sample. Some of the residues were titrated, others were
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analyzed by flame spectrophotometry. Even with this variation of conditions the agreement
between replicate samples was quite good.
Approximately 1000 ppm of oxygen was added, as K20, to a sample of potassium. The
amalgam which resulted from the first addition of mercury was drained under vacun into a
molybdenum capsule. Mercury only was added to a second capsule.. A strip of zirconium
25
metal of known oxygen content was also placed in each of the capsules and the capsules were
· then sealed.
A gettering experiment was conducted at 8150°C. There was no siguificant
men
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differenco in oxygen pick-up notod on examination of tho zirconium strips by vacuum fusion
after the experiment. This experimont would tend to further substatiate the promise that
oxygen is not lost to the amalgam during amalagamation of the sample.
Slide Se Hore we 880 results obtained from the analysis of several samples of sodium.
Similar prcision has also boon attained at higher concentrations of oxygen. Those samples
were sections cut from different sodium loops. Notice the comparison with the results
obtained by the distillation method.
Conclusions
As a result of the data obtainod, it is felt that this method 18 both applicable and
reliable for the deteraination of oxygen in potassiwi and Nak. The applicability of the
amalgamation technique to the determination of oxygen in sodium has alroady been established.
Since the size of the sample to be analyzed is not limited, there should be no difficulty
in analyzing for oxygen in the order of 5 to 10 ppor.
Our initial approach to the detendination of bedragen was quite suple, Dowrated
water was added, under vacua, to the residuo which remained after
algumatian, Since the
akali motal hydride does not react with mercury, it would romin us a part of the residue
if at all present. The hydrogea which evolved from the reaction of the water oth the wall
metal hydride wus thea transfered to an evacuated suple bold and the amount was deterdaad
by gu chromatography. A correction could then be made for the ax gra rosult since ono purt
of hydrogen would be calculated erroneously u dght parts of oxygea. The porsibility of a
loss of hydrogen prior to the completion of the analgenation procedure did not become
evident untul meer
maples of Nak were malyzed to which hydrogen had boon added, art-
gassing during the first amalgamation was appareat imediataly. Recovery by water addition
was extremely low. Accordingly, the procedure was nodi fiod.
Procedure
Our new procedure is relatively simple. The first amalgamation is nfluxad for sovoru
minutos noithin the remotion vessel. The hydrogen which is evolved is transfered to an
onacuated sample bulb and 13 detordned by gas chromatography. The malgamation is carried
to completica for the subsequent detendation of oxygon on the sumo suple,
tr
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Apparatus
Since mercury and Max, us well us sodium, roact on contact, provision was made to
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prevent the loss of hydrogmn during the addition of the worcury to the reaction rossol.
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Slide be Pletured is a necondary, wall volume, wroury pourvoir which was added to the
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amalgamation apparatus. Prior to amalgamation this rosorvoir and the ruction vessel are
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evacuatod, Tho stopoock which io a part of the maction vooral in olosed and the reservoir
18 filled with moroury to the desired level. The stopoock 18 then opened and wild but the
the interested that its
last few cols of moroury are allowed to flow into the roaotian vossol bofore the stopcoak 10
av ...
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again closed. In this way a moroury soul to ostablished to koop any evolved gas from
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osoaping from the reaction vossol, Ball joints rather than "On ring joints are usod to
provido somo flexdbility to the connections, Subsequent additions of noroury way be made from
the main rosorvoir through the secondary roservoir with the stopoook lost opon.
Slido le Pictured 1. the apparatus uood to transfor gases from the maotion vessel to
the sample bulb. From right to lost wo s.. the reaction nsool, kator addition rinnel,
Anhydrono drying tubo, cold trap, Tooplor pump, and, atop tho Toopler pump, a sample bulb
made from a high vacuum stopoook. In the foreground 10 tho control box for the pump. Also
soos to tho manifold to which the apparatus and vacuum system are connected and the solenoido
which aro oporated from the control box, whon the gas has boon pumped to the sample bulb sido
of the pump, the controller makes it possible to bypao, the upper contact of the pump in order
to pump all of the gas into the sample bulb. The runnel and Anhydrano trap aro romoved whon
hydrogen evolved by refludng to transfored to the bulb.
Y
The apparatua io voraitile in that water or diluto acid may be added to the rosiduo to
Chook for the exdotence of ourbidos, carbonaton, cyanides and stable hydridos. Solectivo
separations may be made by the appropriato voo of other liquid nitrogon or a mixture of
dry ice and acotone as a coolant for the cold trap.
***PARA
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KTAS BUSC,*
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-20
Slide 8. Pictured is a schematic diagram of the Toepler pump controller. The pump
emwongwrth etwarrick,
cycle may be reversod at any time by the appropriate manipulation of the rotary switch or
it
the push button. The contacts of the pump are comected to socket P. The solenoids which
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are connected to both the pressure and vacuum systems necessary to the operation of the
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pump are connected to the controller at sockets P2, Pz. The pressure can be raised to ru
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the sample bulb to atmospheric pressure if necessary.
Results
slido %. Here we see some representative results of the recovery of hydrogon from
samples of Nak. An additional heating of the second amalgamation is nocessary at times in
order to achieve quantitative recovery at high concentrations, Hydrogen has also boen
recovered from hydroxide additions. We have been able to determine hydrogen in concentrations
as low as 5 micrgrams. The sensitivity of the method is enhanced by the fact that the
reaction apparatus can accomodato large samples, The rofwdng of the first amalgamation is
recommended even when hydrogen is not to be determined. In this way ara error in the
subsequent oxygon calculation which may be caused by residual hydrides is eliminated.
The amalgamation of a sample, including the transfer of the hydrogen, can be completed in
less than one and one-hall hours.
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DATE FILMED
12 / 14 /164








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LEGAL NOTICE

LE
This report was prepared as an account of Government sponsored work. Neither the United
States, nor the Commission, nor any person acting on behalf of the Commission:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
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B. Assumes any liabilities with respect to the use of, or for damages resulting from the
use of any information, apparatus, method, or process disclosed in this report.
As used in the above, "person acting on behalf of the Commission" includes any em-
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such employee or contractor of the Commission, or employee of such contractor prepares,
disseminates, or provides access to, any information pursuant to his employment or contract
with the Commission, or his employment with such contractor.
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END