Solubility of nitrogen in liquid molybdenum

Scripta METALLURGICA

Vol. 8, pp. 289-292, 1974 Printed in the United States

SOLUBILITY

OF NITROGEN

Pergamon

Press,

Inc.

IN LIQUID HOLYBDEN~4

HOLGER DOMKE and MARTIN G. FROHBERG Institute of Metallurgy (General Metallurgy), Technical University, Berlin. (Received January 16, 1974)

Introduction Although

the solubility

of numerous

of nitrogen

invesTigationsl-13]

on its solubility

in liquid molybdenum.

bility at 2700 ° C first increases 150 Torr, appears

these results

According

with increasing

and then it decreases

unlikely.

in solid molybdenum

has been the subject

there is only one single reported

with further

work lq)

to this work I~) the solupressure increase

of nitrogen

up to

in pressure,

which

The aim of the present work has been to confirm or refute

by studying

once again the effect of pressure. Experimental

The experiments ring furnace.

were carried out in a ~00 KIiz- high vacuum-levitation

The leakage rate in the melting

Tort litre/sec

and The lowest achievable

maximum amount of molybdenum molybdenum rities

< 50 ppm). furnace

as purchased

(Fe~ i00 ppm,

chamber amounted

pressure

was 3 • 10 -6 Torr.

which could be levitated

was 6 grammes.

was 99,9+% pure with the foilowins

me!-

to 5 • 10 -5

amounts

The The

of impu-

C ~ 50 ppm, H L 10 ppm, N < I0 ppm~ other impurities

This molybdenum

was heated under high vacuum in a resistance

to 1900 ° C and held for one hour in order to reduce the impurity

con.

tent. Before each experiment

the melting

chamber was evacuated

After This it was filled with purified give the desired was levitated

pressure.

nitrogen

to 5

10 -6 Torr.

( > 99,£9 Vol.-%)

Before the main experiment

so as to

a piece of molybdenum

and heated To just below the melting point so as to bring down

further the oxy£en content

in the nitrogen.

This piece was then dropped and

a levitated

specimen was equilibrated

measurement

was carried out with the help of a sTandardized, optical~two-

colour pyrometer

and the pressure

with the atomosphere.

measurement

289

The temperature

with a membrane

vacuumeter.

I'90

SOLUBILITY OF NITROGEN IN LIQUID MOLYBDENUM

Vol. 8, No. 3

The experiments were cazTied out at 2650 ~ 20 ° C and within the pressure range of nitrogen of 50-500 Tort. After each experiment the specimen was quenched in a water-cooled copper crucible. Specimens from all the experiments were observed to be free from blow-holes which indicates a satisfactory cooling rate. The subsequent chemical analysis for nitrogen content was carried as described by C. Healy and A. Parker 15) . The reproducibility of the chemical analyses was good. out using Kjeldahl-method

Results and Discussion The results of the present investigations are shown in figure 1 where the w-t.% dissolved nitrogen is plotted against the square root of the nitrogen p~essure. This relationship is found to be linear and therefore abeys Sievez-~s law. Within the experimental pressure range (50-500 Tort) the following equation has been found to be valid:

wt. where

PN2

IN]

=

0.132

is in atomospheres.

0.12

~ 0.10

/

Z

z ,~

0.06

o

0.04.

//

,

14"

KO21MA I~'1"AI..

0.02.

~oo'c)

(P.~i & ('ro~, v') 2ig. I Solubility of nitrogen in molybdenum as a function of square root of its pressure The free energy change accompanying the solution reaction of nitrogen in liquid molybdenum at 2650 ° C

I N2

=

..rNl,

l.

Vol. 8, No.

3

SOLUBILITY OF NITROGEN

A G°

is ~iven by:

=

IN LIQUID MOLYBDENUM

11.75 ~ 0.05

291

Kcal

A comparison of The results f~om This work with Those of Kozima et a114) (see figure I) shows a desreemenT.

Our results show That

I) the solubility of nitrogen in liquid molybdenum is higher than That reported by l
(2620 ° C) as a function of square root. of nitrogen pres-

sure. These plots have been obtained by extrapolation of The data of various workers 4)-!3) . It can be seen from the figure solubility increase resulting from melting of molybdenum is about Tenfold. Conclusions The solubility of nitrogen in liquid molybdenum at 2650(~20 °) C has been found to increase linearly with the square root of nitrogen pressure in The experimental pressure range of 50-500 Tort. It is given by The following expression:

[N]

:

0.132

A£knowledEemen~s The authors are g~aTeful To the Deutsche Forschungsgemeinschaft cial support of This work.

for finan-

292

SOLUBILITY OF NITROGEN IN LIQUID MOLYBDENUM

Vol.

8 , No.

References I.

A.

Siever~s and H. Brining, Arch. EisenhOttenwes.

7, 641 (1933)

2.

A. Sieverts and G. Zapf, Z.Anorg.Allg. Chem. 229, 161 (1936)

3.

E. Martin, Arch. Eisenh~ttenwes.

4.

I.I. Zhukov, Ann.inst.anal.phys. Chim. 3, 14 (1926)

5.

F.S. Norton and A.L. Marshall, Trans. AIME 156, 351 (1944), in:

3, 407 (1929)

S. Dushman and J.M. Lafferty, Scientific Foundation of Vacuum Technique, p. 562, John Wiley, New York (1962). $.

R. Frauenfelder, J.Chem. Phys. 48, 3966 (1968)

7.

J.H. Evans and B.L. Eyre, Acta Her. 17, 1109 (1969)

8.

E. Fromm and H. Jehn, J.Less-Commin Metals 14, 474 (1968)

9.

E. Fromm and H. Jehn, Z.Metallk.

52, 373 (1971)

IO.

E. Fromm and H. Jehn, High Temp.-High Pres. 3, 553 (1971)

II.

E. Steinheil, Dissertation,

12.

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13.

G. H6rz and E. Steinheil, High Temp.-High Pres. 3, 565 (1971)

14.

Univ. Stuttgart (1970)

L.N. Kozima, A.V. Revjalin and A.H. Samarin, Dok.Akad. Nauk. SSSR,Chim. Techn. 184, 398, No. 2, (1969)

15.

C. Healy and A. Parker, AERE-R 649i - Rep., Harwell, Berkshire

(1970)

3