March, 1961
THERMODYNAMIC PROPERTIES OF GASEOUS RUTHENIUM CHLORIDES
517
ordination number of four as well as an oxidation This suggests that PdClz forms a closed structure number of two. or a very long chain polymer in the liquid state. Oranskaya and Mikhailova6 reported vaporThe vapor pressure data yield some additional qualitative information about the liquid state of pressure data measured by the transpiration the system. The heat of the reaction method over the range 610 to 757". If we take into account that they considered PdC12, rather 1/5PdsClio(g) = PdCln(g) than PdsCl,o, to be the vapor species, their data is about 58 kcal./mole; this is very close to the 62 roughly agree with ours. Their temperatures kcal./mole heat required for the evaporation of the were not high enough to permit observation of the monomer from the liquid and is much larger than effect of change in liquid composition on vapor the 4 kcal./mole PdClz value required for the evapo- pressure. ration of the pentamer. Thus, the bonding beAcknowledgments.-The authors are indebted tween PdC12 units in the pentamer is qualitatively to R. C. Jensen, &I. C. Garrison and R. E. Inyard equal in strength to their bonding to the liquid. for performing some of the experimental work.
THERMODYNAMIC PROPERTIES OF GASEOUS RUTHENIUI11: CNI,ORIDES AT HIGH TEMPERATURE' BY WAYNEE. BELL,M. C. GARRISON AND ULRICH MERTEN John J a y Hopkins Laboratory for Pure and Applied Science, General Atomic Division of General Dynamics Corporation, S a n Diego, California Received September 86, 1060
The thermodynamic properties of the gaseous ruthenium chlorides have been studied over the range 650 to 1500" and at chlorine pressures from 0.1 to 1.5 atm. The effect of chlorine pressure on vapor pressure indicates that the important vapor species are RuCll and RuCb. Over RuC13(s)a t a chlorine pressure of 1 atm., RuCL(g) is the principal species, reaching a maximum partial pressure of 0.065 atm. at 853O-the temperature at which RuCb(s) decomposes. Above 853", where Ru(s) is the stable condensed phase, the partial pressure of RuCla(g) decreases with increasing temperature, and RuC&(g) becomes the principal species. A t 1500°, the partial pressure of RuCls(g) in equilibrium with Ru(s) and 1-atm. Clz is 0.16 atm. Thermodynamic quantities were determined for the reactiona and species studied.
Introduction Several investigators2 have observed the volatility of ruthenium chloride in the region 600 to 800". Shchukarev, Kolbin and Ryabov3 reported vapor pressures measured over the range 575 to 727" and assumed RuCL to be the vapor species. Recently, these authors presented evidence indicating that a higher chloride, probably RuCh, may have been i n ~ o l v e d . ~ The present work was undertaken for the purpose of identifying the important gaseous species and determining their thermodynamic properties over the range 600 to 1500" and at chlorine pressures from 0.1 to 1.0 atm. Experimental
atm. Temperatures were measured with standardized Pt, Pt-lO% Rh thermocouples and are believed to be accurate to within f2' below 1000 and to within f4' above that temperature. Pulverized ruthenium sponge (99.995% purity, Johnson Matthey) was employed. The purity of the other materials was the same as in the earlier experiments.5 Analyses.-When quartz reaction tubes were used, the condensing region was cut out and the ruthenium chloride that had condensed was analyzed gravimetrically by hydrogen reduction. When mullite tubes were used, a more complicated analytical procedure was necessary because of appreciable contamination of the condensate resulting from chlorine corrosion of the mullite. Therefore, the technique was to break up the condensing region and to dissolve the material condensed with a KOHKNOs fusion. The ruthenium was then separated as the volatile oxide, precipitated as the hydrated oxide, reduced with hydrogen and weighed as the metal.
Procedure.-The transpiration method was used as described in a previous paper.6 Quartz reaction tubes were used up to 1000°, and mullite reaction tubeE were used above that temperature. Flow rates ranged from 0.01 to 0.1 mmoie/min., depending on temperature and pressure conditions. In this range, studies showed vapor pressures to be independent of flow rate. Chlorine was normally used as the carrier gas; in a few experiments, however, chlorineargon mixtures, made in stainless steel cylinders, were used. In the latter experiments, the total syetem pressure was 1
Results The important vapor species were identified by determining the dependence of vapor pressure on chlorine pressure. Thermodynamic quantities for the species were determined by studying the vapor pressures as a function of temperature. Pressure Dependence.-In the temperature range where RuCl&) is stable over a portion of our chlorine-pressure range, the solid-vapor equilibria to be considered are
(1) This work was supported in part b y the U. S. Atomic Energy Commission under Contract AT(04-3)-164. (2) H. Remy and M. Kohn, 2.anorg. allgem. Cham., 137, 365 (1924); L. Wdhler and P. Bale, ibid., 137, 411 (1924); M. A. Hill and F. E. Beamish. J . A m . Cham. Soe., 72, 4856 (1950). (3) S. A. Shchukarev, N. I. Kolbin and A . N. Ryabov, Zhur Neorg. Khim., 3, 1721 (1958). (4) S. A. Shchukarev. N. I. Kolbin and A. N. Ryabov, ibid., 4, 1692 ( 1959). ( 5 ) W.E. Bell, U. Merten and M. Tagami, J . Phys. Chem., 66, 510 (1961).
sRu(s) zRuCUS)
+
Clz = Ru,Cl,(g)
t7 - 32 (21::
= Ru,Cl,(g)
(1) (2)
We assume the vapor species to be the same over the metal and the chloride. It should be noted
W. E. BELL,M. C. GARRISON AND ULRICHMERTEN
518
Vol. 65
200
100
G 0
t
3
ir
50 J
3 W 0
J
0
E
v)
3
8 Z n"o
20 SLOPE -1.85
x
:s
- i
5
10
3 v) m
a W
a
3
ln v)
W
5.0
a a a 0 a
0 FLOWING Clp
d IC'
L 0.10
I
I
I 0.20
I.o
0.50
FLOWING C l 2 + A
2.0 20
CHLORINE PRESSURE (ATM.),
of chlorine pressure on vapor pressure at 700 and 800".
Fig. 1.-Effect
I.o 0.10
100
0.20
0.50
I.o
2.0
CH LOR INE PR ESSUR E ( ATM. 1.
Fig.3.-Effect, of chlorine pressure on vapor pressure a t 900'. E.
50
2
0
K
Y
5
-. w
J
=
0'
V W -I
20
I
100
0
ln
E
g 5;.-
ln 3
Q
0 -
-
o x
IO
irng
g f
50
o x
5 5
;s 5 % 3-
Y
Lo
5.0
v)
v)
Lo
a
W
g
K K
20
2
x
'
1515 O C SLOPE'= 1.49
W
-I
0
a
150
cn
cn W a
2.0
n
a
t0 I .o
0
I
I
0.20
0.50
CHLORINE PRESSURE (ATM.).
Fig. 2.-Effect
of chlorine pressure on vapor pressure at 850'.
that previous studies6 have shown RuC13 to be the (6) W. E. Bell, M. C. Garrison and Ulrioh Merten, J . Plus. Chem., 64, 145 (1960).
IO CHLORINE PRESSURE ( A T M ),
Fig. 4.-Effect
of chlorine pressure on vapor pressure at three different temperatures.
only stable solid chloride under our conditions. From the equilibrium constant for reaction 1, we obtain
THERMODYNAMIC PROPERTIES OF GASEOUS RUTHENIUM CHLORIDES
March, 1961
519
I00
log PRU.CI~ = log Pch f log K 2
0 EXPERIMENTAL
A similar expression is obtained for reaction 2, and
X
50
SUM OF INDIVIDUAL
PRESSURES we evaluate y/2 and (y - 3x)/2 by studying the effect of chlorine pressure on vapor pressure. Isotherms obtained at 700 and 800,850 and 900" 20 are shown in Figs. 1, 2 and 3, respectively. The break in the 800" isotherm at 0.43 atm. fixes the 5' equilibrium dissociation pressure of RuCls(s), t IO and the result agrees with dissociation-pressure adata reported earlier.6 From the observed slopes, we see that y/2 E 2 aG N mE-' 5.0 and (y - 3z)/2 g 0.5. Thus, y = 4 and 2 = 1, and it is apparent that the principal vapor species ! z x in the temperature range (700 to 900") and chlo- w" s 5' 2 2.0 rine-pressure range investigated is RuC14. In calculating the data in Figs. 1, 2 and 3, ac- mWa: count was taken of the chlorine produced when a I .o the RuCl&) condensed to form R ~ C l s ( s ) . ~ The U0 data were plotted assuming one gaseous molecule n. per ruthenium atom. In three of the experiments 0.50 conducted at 900°, a mixture of argon and chlorine was used as the carrier gas (undiluted chlorine was normally used) with no apparent effect on the results. The consistently low values of y/2 are the ~ " c 1 3 ~ s ' result of a contribution from RuC13(g). DECOMPOSES Pressure-dependence data obtained in the range 1100 to 1500" are shown in Fig. 4. Ruthenium 0.90 1.00 1.10 1.20 metal is the condensed phase under the chlorine pressures used, and reaction 1 is the vaporization IPK x 10: reaction. The observed slopes are 1.45, 1.41 and Fig. 5.-Observed vapor pressures over RuCI3(E) resolved 1.49; thus, y S 3, and the principal vapor species into individual partial pressures of RuCh(g) and RuCl,(g). is Ru,C13. The data do not permit an evaluation of z. However, since the stable solid chloride is RuC13, it seems probable that z = 1, and we shall assume the vapor species to be RuC18. It should be noted that the data in Fig. 4 show no trend which is suggestive of a still lower chloride. The data in Fig. 4 were not corrected for the contribution of RuC14(g), nor were the data in Figs. 1, 2 and 3 corrected for the contribution of RuCldg). Therefore, the isotherms shown represent total vapor pressures. Temperature Dependence.-Since RuCL and X SUM OF INDIVIDUAL PRESSURES RuCl, are the important vapor species under our experimental conditions, the solid-vapor equilibria which must be considered are II
-
\
RuCla(8) = RuClt(g)
+ a Clg = RuC14(gj 3 Ru(s) + 3 Clp = RuCls(g) Ru(s) + 2C12 = RuCli(g)
RuClt(s)
(3) (4)
(5)
(6)
When RuCL(s) is the stable condensed phase at a chlorine pressure of 1 atm., the observed vapor pressure must be the sum of contributions from (3) and (4); and when Ru(s) is the stable condensed phase, the observed pressure must be the sum of contributions from ( 5 ) and (6). Reaction 3 is related to (5) and reaction 4 is related t o (6) by the reaction (7) During a transpiration experiment RuC14(g) decomposes to RuClr(8) on condensstion, and the additional chlorine produced must be subtracted from the total quantity of chlorine collected t o obtain the quantity which passed aver the sample a8 chlorine.
/ /
05 0
i
DECOMPOSES
I 0 70.
I 060 IPK
I
0 80
0 90
x lo3
Fig. 6.-Observed vapor pressures over ruthenium metal resolved into individual partial pressures of RuCla(g) and R ~ I C ~",. API.
-----.\
1-01. G3
520 TABLE I THERMODYNAMIC D A T FOR ~ VAPORIZATION REACTIONS RuCI~(S) RuCl,(g) RuCla(s) 4- '/ZClz = RuCla(g) AHolooo= $67.4 & 3 . 0 kcal./mole AHolooo = f 3 3 . 4 f 2.0 kcal./mole AL%OOO = f53.6 f 3 .O e.u. ASOIOW= f 2 4 . 2 & 2 . 0 e.u. AC, = - 9 . 2 cal./mole/"K. (estimated) ACp = - 6 . 6 cal./mole/"K. (estimated) AH%s = +73.9 f 4 . 0 kcnl./mole = +38.0 f 3 . 0 kcal./mole A 8 h = 4-64.7 f 4 . 0 e.u, AS0z98 = +32.2 f 3 . 0 e.u. Ru(s) f 3/2C12 = ItuCla(g) Ru(B) 2C12 = RuCli(g) A H o l r ~ =f 8 . 3 f 2.0 kcal./mole AH01400 = - 2 4 . 6 It 3 . 0 kcal./mole ASOMOQ = 1 . 0 f 2.0 e.u. A S o ~ t ~= 0 -27.3 f 3.0 e.u. ACp = -4.7 cal./mole/'K. (estimated) AC, = - 2 . 1 cal./molr/OK. (estimated) AHozg8=+13.4 & 3 . 0 kcal./mole AHorps = -22.3 f 4.0 kcaI./mole ASOZ= ~ ~ + 8 . 3 f 3 . 0 e.u. ASo29s = -24.0 i 4 . 0 e.u.
+
+
Ru(s)
+ 35 Clz = RuCL(E)
(7)
In the dissociation-pressure work reported earlier,s we found that for reaction 7 AHolozo= -57.2 rt 1.0 kcaI./mole = -50.9 f 1.0 e.u.
LQP~oZO
and, using an estimated value of 4.5 cal./mole/oR. for ACP, we calculated that AHoZg8= -60.5 & 2.0 kcal./mole A:%?ss = -56.4 f 2.0 e.u.
We found also in the earlier work that RuCls(s) decomposes at 853" under a chlorine pressure of 1 atm. Figure 5 slnows the observed vapor pressures and individual partial pressures of RuC& and RuC14 in equilibrium with RuCle(s) and 1-atm. chlorine pressure, and Fig. 6 shows the pressure data for Ru(s) and I-atm. chlorine pressure. Where possible, the observed pressure points were taken from the pressure-dependence curves ; the remaining points came from additional experiments. The chlorine released on condensation of RuC14 vapor was taken into account in calculating the observed pressures.y The individual partial-pressure curves were arrived at by successive approximations and are drawn so that the sum of the partial pressures best fits the observed pressures. At 853" (see above), the curves change slope by -56.7 kcal.,/molethe heat of reaction 7 at 853". The curves are in accord with the equation In p =
-
AHOo
RT
ACp +-In R
T
+I
Theiniodynamic values for reactions 3 through 6 are summarized in Table I. The AHOT values represent the slopes of the individual partial pressure curves in Figs. 5 and 6 at the mid-point of the temperature range studied. The AS'T values were calculated b:y using the relationship The ACP values were estimated by means of rough rules given by Kubaschewski and Evans.8 C, for RuClr(g') was taken to be 22 cal./mole/"I
