The position of gray tin in the tin-mercury system

THE

POSITION

OF GRAY

TIN

IN THE

P. H. VAN

TIN-MERCURY

SYSTEM*

LENT?

The determination of the solubility of gray tin and white tin in mercury at temperatures below 0°C is described. From these measurements, the phase-fields of gray tin could be added to our knoudcdge of the tin-mercury system. Gray tin can be in equilibrium with a solution of tin in mercury in the temperature range between -7.5 f l.O”C and -35.2 I_t 0.2”C. A mechanism is proposed for the transformation of white tin amalgams. LA

LOCALISATION

DE

L’ETAIN GRIS DANS ETAIN-MEBCURE

LE

DIAGRAMME

D’ETAT

L’auteur d&Gritla c~~~~&tion de la solubiliti de l’etain gris et de J’etain blanc dans Ie mercure aux tempbatures inferieures Q 0°C. Ses mesures permettent de determiner les domaines de phase de I’etain gris dans le diagramma d’etat Btain-mercure. L’etain gris peut etre en Bquilibreavec une solution d’etsin f 1,O”C et -35,2 f 0,2”C. L’auteur dans du mercure pour des temperatures comprises entre -75 propose une m&anisme de transformation des amalgames d’etain blanc. DIE

LAGE

VON

GRAUEM

ZINN

IM

SYSTEM

ZINN-QUECKSILBER

Die Bestimmung der Losliehkeit van grauem und w&BernZinn in Quecksilber bei Temperaturen unter 0°C wird beschrieben. Mach diesen ~essun~n konnten die Phasenfelder des grauen Zinns unserer Kenntnis des Systems Zinn-Quecksilber hinzugefiigt werdan. Graues Zinn ktannmit einer Losung von Zinn in Quecksiiber im Temparaturbereich zwischen -75 + 1,O”C und -35,2 f 0,2”C in Gloichgewicht &hen. Fur die Transformation von Amalgamen des w&J&nZinns wird ein Mechanismus vorgoschlegen.

INTRODUCTION

New interest has arisen in the tin-mercury after Ewald and Tufteo)

system,

succeeded in growing gray tin

single crystals from a solution of tin in mercury. Gray (a) tin is not included in the phase diagram given by Hansen(Q, a summary of all known investigations J’sn white

in

the

field

Heteren@), and

difference

of

when

gray

the

tin-n~er~ur.~

measuring

tin in mercury

between

the

of

at 0°C found

no

both modifications

and was not able to indicate

system.

solubility

in this respect

the position

of gray tin

in the diagram. According to Cohen and van Lieshout(

gray tin

is stable

below

132°C.

In the

phase

diagram

Fro. I. The tin-mercury phase diagram according to Hansen.

of

Below

Hansen (Fig. 1) three intermediate phases occur, of which two can exist at temperatures where gray tin is stable.

According

to the investigations

of Green’s),

reports-referring

indicated

by the formula

suggests

HgSnl, 9 although its tin content may vary from This phase is formed when about 88-94 at. y& white tin is brought into contact with mercury at temperatures above the melting point of mercury. * Received February 13, 1960.

VOL. 9, FEBRUARY

1961

phase

is

to

unpublished

results

of

Pry-

the occurrence

of still another

phase,

the

so called S-phase, which would be stable below 9O”C, in order to be able to explain thermal effects found at 90°C. No other investigator has ever confirmed these effects. Moreover, as we found that HgSn,, crystallizes from a solution of tin in mercury at room

1 Physical Laboratory of the National Defense Research Council of the Netherlands (R.V.G.-T.N.O.), The Hague. ACTA META LLURGICA,

intermediate

therch-the formula HgSn, for this phase; but others considered the formula HgSn or HgsSn more and Bornemann( Gayler also likely (Guertler”)

At higher mercury concentraphase is formed. This phase is

called the y-phase generally

a second

as can be concluded from the measurements The composition and crystal of van Heteren@). structure of this phase are unknown. Gaylex(‘n

with microscope and X-ray techniques, not more than 0.1 at.% mercury can dissolve in white (P) tin at room temperature. tions an intermediate

-34.6”C

stable,

temperature, we think phase is very unlikely.

125

that

the

existence

of this

ACTA

126

METALLURGICA,

VOL.

9, 1961

gray tin in the phase diagram 0 t 0 IO n + 0t

20 .u

from these measure-

ments.

van ~etefwl Gouy Joyner Ourmeasurements

EXPERIMENTAL

For

the

PROCEDURE

determinations

AND

of

the

RESULTS

solubilities

two

small glass tubes were used, each closed at one end with

a rubber

tube

and a pinch-cock,

other end with a rubber stop.

and at the

They were filled with

about 50 g mercury, purified by air oxidation and vacuum distillation. One tube was cooled to -40°C 0,. %

and then 0.5 g gray tin powder was added.

tin

was stored during 12 hr at -20°C.

FIG. 3. Mercury rich part of the tin-mercury phase

in the other tube about

dia.gram.

At low temperatures

the tin-mercury

system

was

investigated by van Heterenf3). His results are given in Fig. 2 together with points found by Joynercg) and Gouy(lO) in the vicinity points

of the liquidus

found by saturating 1 hr and analysing

of room at -18.8

temperature.

The

and 0°C have been

mercury with white tin during the solution. The solubilities

found in that way were 0.36 and 0.59 at.%, respectively. In another experiment mercury was saturated with white tin and with gray tin at 0°C during 5 hr. The solubilities found in that way were 0.62 and 0.60 at.‘+&, respectively. have been found

The other points

by van Heteren

in the slopes of cooling

in Fig. 2

from the changes

and heating

curves of amal-

gams with a well known composit#ion. From the measurements of van Heteren it appears that above -34.6% HgSn,a can be in equilibrium with a solution of tin in mercury.

This tube

To the mercury

0.5 g white tin powder was

added at room-temperature

(about 20°C).

It was kept

at this temperature, to exclude the presence of gray tin nuclei, (which may be present in the atmosphere) which

react

readily

at 20°C with

mercury,

under

formation of HgSn,,. The tubes with tin and mercury were suspended in a dewar-tube, filled with solid and liquid

of various

salt-water

eutectic

mixtures

(pre-

pared beforehand) and agitated intensely for 8 hr. After this the tubes were removed from the dewar, and by means of the pinch-cock solution

about

was drained and collected.

of the solution was determined

40 g of the

The tin content

by gravimetric

(as SnO,). The results are given in the following

analysis

table

and

have been plotted in Fig. 2. Here the two curves represent the liquidus curves of grsy tin and of BgSn1,.

Below this tempera-

TABLE

1

ture and above the mehing point of mercury (-38.9”C) the saturated solution is in equilibrium with HgSn,( 2). According to Ewald and Tufteo), HgSn,, crystallizes from above

a supersaturated about

-3O”C,

phase diagram.

solution

of tin in mercury

in agreement

However,

with the known

after 1 week at tempera-

tures in the range from -10”

to -3O”C,

vanished solution.

crystallized

and

gray

tin

From these observations

has

HgSn,,

has

from

the

we can conclude

that in

this temperature range gray tin can be in equilibrium with a solution of tin in mercury, but the nucleation

MaClz + Ho0 N&l+ Ha0 Na&03 + Hz0

- 33.6 1 0.242 0.243 0.243t 0.270 0.267 0.269 ~ 21.2 0.344 0.344 0.344 0.371 0.367 0.369 ~ 10.2 1 0.470 0.463 0.467) 0.4Q4 0.490 0.492

ZnSofffgH=o 2

--6.55 0.00 0.564 0.662 0.568 0.656 0.566 0.659~ ;0.561 0.656 0.559 0.656 0.560 0.656

THE

POSITION OF GRAY TIN TIN-MERCURY SYSTEM

As expected, in the temperature -10’ and -32.2”C the solubility

IN THE

range between of gray tin in

of gray tin is retarded to such extent, that HgSn,, crystallizes as a metastable phase. Thus the points

mercury is smaller than that of HgSn,,. At -6.5% the solubility of HgSnr, is the smaller one. From Fig. 2 it appears that the solubility of both phases is

measured by van Heteren in this temperature range represent metastable equilibria. In the course of investigations on the semiconductive properties of gray tin, we have determined the stable and metastable liquidus of the tin-mercury

the same at -7.5%. So this represents the temperature of the three-phases equilibrium: L-c&n-HgSn,,. At 0°C we found the same solubility for gray tin and with van Heteren), since HgSn,a (in agreement evidently gray tin at this temperature reacts with

system in the temperature range from 0” to -32.2%, by measuring the solubility of gray and white tin in mercury. We were able to indicate the position of

mercury to form HgSn,,. From the measurements at 0°C we may conclude that the equilibrium conditions arc reached in 8 hr.

VAN

Resulting

LENT:

GRAY

TIN

from a high or a low tin concentration,

IX

THE

SYSTEM

127

THE TRANSFORMATION CONTAINING A FEW PER

the

measured values agreed within 0.5 per cent. Their accuracy is fixed by the errors in the gravimetric

Sn-Hg

The

transformation

from

OF WHITE TIN CENT MERCURY

white

to

gray

tin

is

determinations. As the duplicates on the average differ less than 1 per cent from the measured values,

accompanied 20 per cent),

by a large volume expansion (about with the result that the gray tin falls

we estimate

into pieces.

Groen(12>5) showed

per cent.

the error in our measurements

The

equilibrium

error

in the

temperature

not more than at -6.5”C

of L-&-HgSn,,

&l.O”C,

at 10.5

determination

of

the

is certainly

but likely less, as we found

a definite difference between the solubility

of gray tin and HgSnlz. This result agrees with the observations and Tufte’l)

of Ewald

Mercury

which has a retarding influence on the transformation. As can be seen from the phase diagram, in the temperature range from -7.5” to -35.2”C transformation of of HgSn,,

In a recent article, Smith(ll)

describes the determina-

According

tion of the same three-phases

equilibrium temperature,

white tin at the transformation

method.

He found

-8.15

i

with our measurements.

also

e.g. lead,

a few per cent mercury,

agreement

crystal-

of mercury.

of other elements,

white tin, containing

a dilatometric

only HgSn,,

a small amount

suppresses the influence

pieces

that the tin

practically

O.l”C in excellent

-10°C

contains

that compact

provided

lizes from the mercury solution, and that above 1°C mercury reacts rapidly with gray tin to form HgSn,,.

using

that above

of gray tin can be obtained,

a mixture

be accompanied

by the liberation

to Fig.

of metastable

1, the mercury

HgSn,,.

transformation

(being

and white tin,) will of free mercury. reacts

with

the

front, under formation

But when all white tin at the

front

has reacted,

mercury

can be

However, no other points of the phase diagram were given by him. The values of the solubility of white

piled up to more or less extent. The mercury does not form a complete

tin at -18.8”C

to the transformation,

as tin can diffuse through

from the untransformed a result of the solubility

to the transformed part, as difference between the stable

with

and 0°C of van Heteren agree poorly

our results.

Probably

equilibrium

conditions

were not reached in his measurements. The temperature of the three-phases

equilibrium

L-crSn-IHgSn,(?)l(2) is given by the intersection of the liquidus curves of gray tin and HgSn,(?). This temperature is -35.2”C as follows from Fig. 2. As the slope of the liquidus

of gray tin is considerably

and the metastable accounts

phase.

for the coherence

hindrance

This mechanism

it

easily

of the gray tin and the

suppressing of the influence of the retarding elements, for these are solved in the mercury and do not play any active part in the transformation. Investigations in

steeper than that of HgSn,(?),

the error in the deter-

progress on the transformation

mination

will be given

submit evidence that this mechanism

actually occurs.

Details of this work will be published

in due time.

of this temperature

error in our solubility

determination.

by the

We estimated

this error to be not more than f0.2”C. As mercury is almost insoluble in gray tin and only to a very slight extent in white tin, mercury

will not

Smith’ll)

of white tin amalgams

also mentions the liberation

the transformation

of mercury at

front, but not the diffusion

of tin

through free mercury. He explains the suppressing of the influence of the retarding elements by supposing

have an appreciable influence on the transformation temperature of tin. Hence the temperature of the

that

three-phases equilibrium c&n-BSn-HgSn,, will be 13.2”C. The phase diagram, based on the temperatures

front to free mercury, present in cracks in the gray tin. No account is given for the coherence of the gray

of the three-phases

tin.

equilibria,

is drawn in Fig. 3.

the

atoms

will diffuse

at the transformation

ACKNOWLEDGMENTS

Thanks are due to Professor Dr. W. G. Burgers for his stimulating

interest and helpful comments,

to Miss J.

Kouwenhoven for assistance with the analysis and to the Chairman of the National Defense Research Council

of the Netherlands

permission

-100

bS’

0

I

IO

I

I

20

30

HQsn, I

40

50

*cc HgSn3+aS”

60

I

1

I

70

80

90

100

at %tin

FIG. 3.

The tin-mercury phase diagram the phase fields of gray tin.

extended

for his

REFERENCES

I”;

I

(R.V.O.-T.N.O.)

to publish this paper.

to

1. A. W. EWALD and 0. N. TUFTE, J. Appl. Phys. 29, 1007 (1958). 2. M. HANSEN, Constitution of binary ccZZoy,s.McGraw-Hill, New York (1958).

ACTA

128

METALLURGICA,

3. W. J. VAN HETEREN, Thesis, Amsterdam (1902); 2. Anorg. Chem. 42, 129 (1904). 4. E. COHEN and A. K. W. A. VAN LIESHOUT, 2. Phys. Chem.

173,1 (1953).

5. L. J. GROEN, Thesis, Delft, (1956). 6. M. L. V. GAYLER, J. Inst. Met. 60, 379 (1937). 7. W. GUERTLER, Handbuch rler Metallographie Bd. 1, S.719

VOL.

8. 9. 10. 11.

12.

9,

1961

Verlagsbuch-handlung Gebriider Bortaaeger, (1912). K. BORNEMANN, Metallurgic, Berlin 7, 108 (1909). R. A. JOYNER. J. Chem. Sot. 99, 1995 (1911). J. GOUY, J. Phys., Paris 4, 320 (1895). R. W. SMITH,Can&. J. Phys. 37, 1079 (1959). L. J. GROIN, Nature, Lord. 174, 1836 (1954).

Berlin