The vapor pressure of ytterbium in the pressure range of 40–4000 torr

248

JOURNAL OFTHE

Short

LESS-COMMON METALS

Communications

The vapor pressure of ytterbium

in the pressure range of 40-4000 torr

The vapor pressure of Yb was measured in an open “heat-pipe”. The method which has been described by the authors recently’ is briefly as follows. A tube closed at one end contains the test metal and argon at a certain pressure. The tube is heated in a vertical position by a RF furnace at the lower (closed) end. The heated part, enclosing the test metal, is brought to a temperature where the vapor pressure of the metal in the tube equals the argon pressure. At this point the vapor pushes the argon in the upper part of the tube and a zone of constant temperature is established in the lower part by the metal vapor; in fact there is a sharp change over in temperature between the metal vapor part and the argon. The pressure of the argon-measured at cold conditions-and the temperature in the hot zone give the corresponding data for vapor pressure and temperature of the test metal. This method works at vapor pressures TABLE

above 40 torr. I

VAPOR PRESSURE ___~ P (mm Hg):

OF Yb

T ("K):

42 1185

50 1205

60 1210

70 1225

80 1230

100 1250

120 1270

150 1290

200 1320

300 1360

P (mm Hg) : T (“I<) :

350 1385

520 ‘430

600 7440

740 1480

1125 1530

1470 1565

2205 1630

2950 1685

3670 1720

4430 1760

Yb lumps from Leytess,

N.Y.,

(purity 99.9%)

were used for the measurements

reported. The vapor pressure was measured in a tantalum (heat-pipe) results are given in Table I. The data follow a regression line given by log*

tube.

The

(tOr,.,=7.84-7E T (“K)

No previous experimental data were known to us. SAVAGE et al.2 measured the heat of sublimation at 394°C to be 3g.5+0.5 kcal/g.-at. This result does not differ very much from our value for the heat of evaporation which is 33.6 kcal/g.-at. at the boiling point (as derived from the slope of the regression line). NESMEYANOV3 calculated the boiling point from SAVAGE'S data and found 1660°K; which does not deviate too much from our value of 1482’K. J. BOHDANSKY H. E. J. SCHINS

Direct Conversion Group, CCR-Ewatom ISPRA, Varese (Italy)

H.E.J. SCHINS,]. Phys.Chem.,T~ (1967) 215. HUDSONANDF.H SPEDDING,J. Chem.Phys.,30 (1959) 221. 3 A. N. NESMEYANOV, Vapor Pressure of the Chemical Elements, Elsevier,Amsterdam,

I

J.BOHDANSKYAND

2 W.R. SAVAGE, D.E.

Received J.

March 23rd, 1967;

Less-Common

amended

Metals, 13 (1967) 248

April zznd, 1967

1963, p. 250.