Solubility of oxygen in liquid sodium

JOURNAL

OF NUCLEAR

MATERIALS

28

(1968)

SOLUB~ITY

297-302.

OF OXYGEN IN LIQUID

H. BEISSWENGER In&&t

Neutronenphysik

fiir

The

solubility

of

oxygen

in

PUBLISHIN(X

CO., AMSTERDAM

SODIUM

and S. DORNER

md Reaktartechnik des Kernforschungszentrunas KarlsruiLe, Germany Received

determined

0 NORTH-HOLLAND

liquid

sodium

with a simplified amalgamation

21 July

was

method

1968

Dana quelques cas d’autres cours

de

leurs

etudes

auteurs ont trouve au

des

valeurs

beaucoup

plus

in the temperature range from 130 to 480 “C. A special

grandes pour la region inferieure de temperature

sampling technique has been developed which avoids

different de la formule &be

any

material

pouvait etre observbe en ee qui concerne nos propres

method the

resultats. La chaleur de dissolution Q du NaaO dans

contact

of

the

sodium

with

other

following filtration. By the amalgamation accuracy

has

consumption The

been

improved

considerably

temperature

saturation

and

le sodium Q=7.33

of

the

log ~=4.90&(1606/T),

(!Z’=abs.

temperature),

higher values of cs

range which differ from the

formula above. This deviation could not be observed The heat of solution

Q of NazO in

liquid

was

found

calculated

and

to

be

kcal/mole.

pro&de

temperatures

simplifie entre

130

a Bte determinee d’amalgamation et

480

“C.

a l’aide pour

Une

les

method%

filtration.

La

methode

de la

saturation c,

(T=temperature

eine

im Temperatur“C bestimmt.

besondere

Zur

Technik

der F&ration

riihrung

kommt.

mit

Das

zeichnet

weiterem

sich

durch

Die Temperaturabhangigkeit tration

Material

verwendete

in Be-

AmalgamationsGenauigkeit

und

aus. der Siittigungskonzen-

c, Iasst sieh dureh die Formel (T=abs.

im

unteren

Temperate), fanden andere

Temperaturbereioh

bedeutend

hohere cs-Werte, die von der obigen Formel abweichen.

temptiraturese prbsente sous h formule suivante

log c,=4.908-(1606/T),

1.

de

dabei

480

entwiokelt, mit der vermieden wird, dass das Natrium nach

Autoren

en mercure.

La dependanee de Ia concentration

wurde

und

darstellen. In einigen Untersuchungen

d’amalgamation

utilisee est caracterisee par sa precision et sa petite consommation

Probenahme

130

log c~=4.90&(1606~~),

qui Bvite Ie contact du sodium aver d’autres materiaux la

Amalgamationsverfahren

zwischen

geringen Quecksilberverbrauch

speciale fut mise en point pour la prise ~~ehantillo~ apres

einfachten beroich

verfahren

La solubilitti de I’oxygene d’un

elle prend la valeur

kcal/mole.

Die Lijslichkeit des Sauerstoffs wurde mit einem ver-

for our results. Q=7.33

ne

measured

range. Other authors found

markedly

in the lower temperature

sodium

liquide fut calculee;

qui

c, fohows the formula

in the whole temperature in same investigations

mercury

decreased.

dependence

concentration

the

plus haut. Get &art

Diese Abweichung nicht beobachtet

konnte werden.

bei uneeren Ergebnissen Die Ltisungswiirme Q des

NasO im fliissigen Na wurde berechnet; Q--7,33

abs.),

Introduction

sie betragt

kcal/Mol.

used. The logarithm of the saturation concentration plotted against reciprocal absolute tenlperature resulted in a straight line. However, in some works this straight line relationship held only in the higher temperature range. At lower temperature a change in the slope was observed. In a recent investigation Jahns and Weidman 5) found a straight line through the whole temperature range without break. In order to improve the present situation a further

The measurement of the soIubility of oxygen in liquid sodium has been the objective of several investigations I-5). In most of these works the solubility could be measured only in a small temperature range, with a single kind of apparatus. Broader temperature ranges required different apparatus. A comparison shows a considerable spread of the results, especially when more than one equipment was 297

H. BEISSWENGER

298

investigation

was attempted.

This experiment

was suggested because a considerable ment in the achieved 6).

analytical

AND S. DORNER

method

improvehad

been _Opcnmg

2.

sdrd

Experimental procedure

for

Idling

sodium

In order to obtain sodium saturated with oxygen, excess oxygen was added. This excess in the form

of NaaO was then removed

by

filtering. The filtered product was sodium saturated with oxygen at the filter temperature. For the sampling technique two types of experimental methods were used. They are described in the following sections. 2.1.

SODIUM FILTERING AND SAMPLINGIN GLASS VIALS

The apparatus used in the first method is shown in fig. 1. All parts of the apparatus are made of Pyrex glass. The container has connections for vacuum and nitrogen filling closed by a stopcock and provision for adding sodium. A glass filter is inserted and sealed into the lower portion of the apparatus. Sample vials are attached to the lower end. After drying the apparatus at 150 “C, sodium containing excess oxygen was added through the upper opening. The apparatus was then evacuated, and the container with the sodium and the filter were heated to the desired temperature to saturate the sodium with oxygen. The filter openings were small enough to prevent undesired flow of sodium through the filter during heating. When the desired temperature was reached, nitrogen pressure was applied to press it through the filter. After cooling the thin tube combining the vial with the filter was fused and drawn off. Because the glass apparatus was attacked by the sodium at a temperature above 300 “C, another apparatus, described below, was constructed in which a larger temperature range could be employed. 2.2.

SODIUM FILTERINGIN STAINLESS APPARATUS

AND

AMALGAMATION

In principle,

DIRECT

FILLING

STEEL IN

THE

VESSEL

the second

type

of apparatus

, n Sample

Fig. 1. Filtering apparatus. was similar

to the

first type,

however,

the

section of the apparatus heated for oxygen dissolution and the filter were made of stainless steel (fig. 2). Other sections of the apparatus kept at lower temperature remained of glass. In addition. an amalgamation vessel was made part of the apparatus. The sodium was filled in after the whole equipment was cleaned, and dried; then purified mercury was brought in to the amalgamation vessel. The sodium was heated to the desired temperature, then forced through the filter by nitrogen pressure. The sodium flowed directly into the amalgamation vessel without contacting either glass tube or stopcock. The filter temperature of the Na was limited

SOLUBILITY

OF OXYGEN

IN

LIQUID

299

SODIUM

NaaO. The amount of sodium in the remaining amalgam correcting

must be determined and used in the value obtained by titration. In

making this correction the sodium concentration of the remaining amalgam is assumed to be the same as that of the separated

amalgam.

This

method was described in detail by Kummerer and Dorner 6) at the IAEA Conference in

-Starnlrss-StrJ-Ftlte,

-Middle

Stopcock

.I

-

Copiltory

‘-Trlton

- stopcock

to

Fig. 2.

YDCUYrn

pump

Combined f%%ring and amalgam&ion apparatus.

because the reaction between the hot sodium and the mercury was so violent that the mercury began to evaporate. The maximum temperature for the Na was limited to 480 “C. 2.3.

EVALUATION

OF OXYGEN IN SODIUM

The first step is the dissolution of sodium sample in mercury. NazO is insoluble in Hg and remains on the surface of the mercury on the walls of the vessel. The Hg-Na alloy or amalgam is separated from the NazO by draining it off through the capillary below the amalgamation chamber. Then the NazO is dissolved in water, and the Na content is determined by titration. The amalgam cannot be completely separated from NaaO, a small amount remains with the

Cadaraehe 1963. The apparatus used consists mainly of an amalgamation vessel and a mercury supply vessel, connected by a capillary and a teflon stopcock. An evacuation connection to the mercury supply vessel, fitted with stopcock, is provided. The removable cover of the amalgamation vessel contains some cams on an inner surface which help to destroy the sample vial, as will be discussed below. All the parts of the apparatus are made of Pyrex glass including the stopcock, which are sufficiently tight without grease. In the second method (apparatus shown in fig. 2) the Na flows directly into the Hg. When a sufficient anlo~lnt of Na is brought* into the Hg vessel, the middle stopcock above is closed. After shaking to gather the drops at the wall, and cooling the stopcock below was opened and the amalgam drained down into the lower vessel. The NazO together with the remaining amalgam are treated as described in 6). 3.

Results Eleven experiments were performed

with the

separate sodium sample preparation and amalgamation apparatus (fig. 1) in the temperature range between 160 and 260 “C, and 18 experiments in the combined sodium sample preparation and amalgamation apparatus (fig. 2) in the temperature range between 130 and 480 “CL The most impo~ant values are shown in table 1. In fig. 3 the measured oxygen content is plotted on a logarithmic scale against the reciprocal absolute temperature. The values fall on a straight line within some spread. This straight line corresponds to the formula log cS= 4.908 - (1606/T),

100

10000

T--__,,w_. 200

300

400

500

600

.~_~_~

5000

-8 /

/

/

g//g q1

/n

a

P 0

/do

,8./a”

0

Filtered

in glass vials tt/trationl

0

Filtered

in fhe combmed

0

Filtered

in the combmed

0

j i

opparafus

0 ff/fraf/on)

mm

apparatus

d

a fName

IL,,.__--_ 3.0

2.5

Fig.

loooo c 5000

2000

‘-

3.

phofomefrje

evaiuat/onl

$

1 2.0

1.5

1.0

1OyT

OK

Measured values of the oxygen solubility in liquid sodium.

100

200

I

1

300

400

500

600

Temp OC

-

4 2 ,’

E

6

-_

-- -.~

!

--

,I

I-

30

Fig. 4.

Solubility

2.5

of oxygen

2.0

in liquid

sodium.

l

1. This work

A

2.S L. Walters

Q 3 H D Bogard

and

DLJ W/ii/urns

6

4 J D. Norden

and

K G.Bagley

B$ 5 0. N. Salmon

and

D

6. W Jahns

and

I”

7. A W Thorley

T J Cashmon

G Weldmann

:

15

Comparison

of the results by different authors.

-2

SOLUBILITY

OF

OXYGEN

IN

LIQUID

301

SODIUM

TABLE 1 Measured

oxygen

Temp.

cs (ppm)

T (“K)

(titration)

T

solubility

in liquid sodium

bpm)

cs

(flame-

Sampling

photometric)

403

6.5

413

9.9

423

12.9

combined

apparatus

433

20.4

combined

apparatus

434

23.1

glas vial

448

9.4

glas vial

452

17.4

glas vial

453

19.4

combined

460

28.2

glas vial

460

33.2

glas vial

460

12.8

glas vial

460

20.8

glas vial

473

20.6

combined

471

47.8

glas vial

477

39.5

glas vial

471

41.5

glas vial

494

31.0

523

54.3

523

54.5

533

68.2

573

116.4

combined

573

78.9

combined

apparatus

588

153.1

167.0

combined

apparatus

591

176.8

185.3

combined

apparatus

592

173.7

200.2

combined

apparatus

673

312.1

324.3

combined

apparatus apparatus

17.7

45.6 64.2

combined

apparatus

combined

apparatus

apparatus

apparatus

combined

apparatus

combined

apparatus

combined

apparatus

glas vial apparatus

673

334.7

combined

713

362.2

combined

apparatus

753

649.1

combined

apparatus

L

where cS is the oxygen content in ppm (wt) and T is the absolute temperature in “K. The spread of the measured values, in the temperature range below 200 “C, is about 5 10 ppm, in the upper temperature range about + 15 ppm. However, the accuracy of the average value should be better, and the straight line should not deviate more than f 3 ppm + 0.04 cSunless an unknown systematic error is involved.

4.

Heat of solution of NazO in liquid Na

In the case of low solubility dependence of the saturation

the temperature concentration cS

can be described lncs=

by:

(--Q/(RT))+C,

with Q= heat of solution (Cal/mole) ; R=gas constant, 1.986 (cal/mole. T = absolute temperature (OK) ; C = integration constant, or log c,= {-Q/(2.302

“K);

R))T-l+(C/2.302).

The heat of solution Q can be easily obtained from the experimental data when the saturation concentration cs is plotted in the logarithmic scale vs T-1. From fig. 3 we find the value of Q to be Q= 7335 Cal/mole.

302

5.

H.

BEISSWENGER

Discussion Our measured

values

are in rather

good

agreement with the values determined by Jahns

AND

S.

DORNER

temperature NaaO and solution.

to be above the melting point of additional heat is required for

Some authors

and Weidman 5). In fig. 4 all the values found

found

a break in the log cs

figure illustrates the spread of the values found

vs T-l line and considerably higher NasO values in the lower temperature range than

by

expected

by

different different

authors i-5) methods

are gathered.

and

also

shows

This the

by extrapolating

the values

of the

improvement in the experimental technique. In two successive reports Claxton 77s) has

higher temperature range. Our results indicate no break in t,he log cS vs T-1 plot; and from

compared the experimental results of the different authors and analysed t’hem by statistical methods. In addition he has treated the system as an “ideal solution”, and found the mathematical arrangement to correspond rather well with experimental data. An “ideal solution” exists when in the solution of a solid component in a liquid phase, only the heat of fusion of the solid component appears. This means that complete dissolution occurs at the melting point of the solid component. The mathematical formula in the case of the ideal solution is

a theoretical point of view, there is no indication of change in slope. It is also possible that higher oxygen values were obtained in the low temperature range because of oxygen contamination from moisture adsorbed on the vessel walls or from the atmosphere. This small amount of oxygen is not important at high cSvalues, but in the lower range it can be considerable. Perhaps it can cause the effect of the change in slope. Accordingly, the experimental results which give lower cS-values are more likely true than the other ones.

log ~~={-&/(2.303R)}(T-~-T,-l)> where T, is the melting temperature in “Ii. The correspondence found by Claxton with this arrangement and the experimental results appears to be a chance result, since the saturation concentration in wt y0 instead of the mole-ratio was used. It would be surprising if a system with components metallic Na and the oxide We have assumed “ideally”.

as different as NasO behaved that additional

heat would be needed for solution, and that an extrapolation of cs to complete solution would lead to a temperature higher than the melting point of NasO. If the straight line in fig. 3 is extrapolated to es= 106 ppm, we find the

References 1) S. L. Walters,

The effects of adding

oxygen

to

sodium flowing in a stainless-steel system, NP-1955 (MSA-TR-VI)

(1950)

2) A. D. Bogard and D. D. Williams, The solubility of sodium monoxide

in sodium, NRL-3865

3) J. D. Noden and K. &. Bagley,

(1951)

The solubility

of oxygen in sodium and sodium-potassium RDB(c)-TN-80

9

0.

alloy,

(1954)

N. Salmon and T. J. Cashman, The solubility

of sodium monoxide in liquid sodium

KAPL-

1653

(1956)

5,

W. Jahns and G. Weidmann,

Nukleonik

6)

189 S. Dorner and K. Kummerer,

Atomkernenergie

(1964)

9

167

7) K. T. Claxton, 8)

1 (1959)

(1965) 849 K. T. Claxton,

J. Nucl.

Energy,

J. Nucl. Energy

parts

A/B

21 (1967) 351

19