NOTES
Sept., 1958 The results of the surface tension measurements on t,he two binary nitrate melts are given in Tables I and 11. Surface tension isotherms were plotted and compared with isotherms calculated from Guggenheim's equation for the dependence of the surface tension of an ideal binary mixture on its ~omposit~ion. The surface tension isotherms for these systems show small, negative deviations from ideality. These deviations are greater for AgN03-KN03 than for Ag?J03-NaN03, in agreement with previous findings that the surface tensions of binary mixtures of salts with a common anion show increasing deviations from ideality with increasing difference in the size of the replacing cat,ions.485 TABLEI1 SURFACE TENSION IN THE SYSTEM AgNOr-KNO," Mole % KNO3
8.12
29.58
52.83
Temp. OC.
Surface tension (dynes/ om.)
252 252 256 304 306 324 325 326 356
139.7 138.9 138.5 135.3 135.5 134.8 133.8 134.3 132.8
254 254 300 302 328
132.0 132.3 125.4 125.0 124.0
'I remp., OC.
Surface tension (dynes/ cm.)
87.05
324 324 325 326 351 352 352 353
115.1 115.8 114.8 114.6 112.6 113.5 112.3 112.3
100,oo
358 358 398 398 419 420 454 454 473 473 494 496 546 546 594 595
111.9 111.8 109.6 108.7 106.9 107.0 104,2 104.3 102.9 102.9 101.5 101.3 97.0 97.6 93.8 93.8
Mole % KNOa
254 123.9 256 123.9 276 122.7 276 122.5 296 120.7 298 120.7 324 118.7 324 118.7 354 116.9 71.60 276 119.3 119.4 276 298 117.4 117.4 302 302 117.8 322 115.9 323 115.6 325 116.3 355 114.0 a Density data given by Bloom and Rhodes.6
1143
and the proportionality of transference numbers to mole fraction' all substantiate the idea that little or no ionic association takes place in these melts. It is interesting to compare the surface tensions of the three pure nitrate melts a t corresponding temperatures above their melting points. The surface tensions of the pure alkali metal nitrates and chlorides decrease regularly with increase in size of the alkali metal i0n.9 Silver nitrate does not fit into this pattern since its surface tension is higher than that of NaN03 despite the fact that the ionic sizes are comparable. This is 'indicative of stronger ionic interactions in a AgN03 melt compared to a NaN03 melt. This can be attributed to (a) smaller interionic separation in a AgN03 melt compared to a NaN03 melt despite the fact that the radii of the ions are approximately the same in the solid state, and (b) increased covalent character in the interactions in a AgN03 melt compared to a NaN03 melt attributed in part to the 18-electron shell of a transition type ion like Ag+ being more easily deformed (polarized) than is the inert gastype shell. The maximum probable error in y is f 0.2 dyne/ em., except a t high mole % AgN03 where peculiar bubble formation always became a problem, probably as a result of a high viscosity; the error here may be as much as f 1 dyne/cm. (8) F. R. Duke and R . Fleming, J. Electrochem. Sac., in press. (9) F . M . Jaeger, 2. anoro. Chem., 101, 1 (1917).
VAPOR PRESSURE OF THORIUM TETRAFLUORIDE BY A. J. DARNELL A N D F. J. KENESHEA, JR. Contribution f r o m the Research Department o f Atomics International Canoga Park, Cal. Received April 86,1968
No experimental determination of the vapor pressure of thorium tetrafluoride is reported in the literature although an estimate has been made by Brewer.2 I n the present work, the Knudsen3 effusion method was used to determine the vapor pressure of the solid and the quasi-static method of Rodebush and Dixon4 was used to determine the vapor pressure of the liquid. These two methods were used to extend the measurements over as wide a range as practicable in the solid and liquid states in order to obtain values for the heats of sublimation and vaporization of T h R . A mass spectrographic analysis was made to determine the gaseous species vaporizing from ThF4.
The surface tension data, the additivity of molar volume^,^^^ the small, negative deviations from additivity of c o n d u ~ t i v i t yand ~ , ~molar refractivity6
Experimental The ThF4 used in these experiments was obtained from the A. D . Mackay Company. An X-ray diffraction pattern of the sample showed only ThF4 lines. Chemical analysis thorium, of the salt gave a value of 75.3 f 0.2 weight
(3) E . A. Guggenheim, Trans. Faraday Sac., 41, 150 (1945). (4) N. K . Boardman, A. R. Palmer and E. Heymann, Trans. Faraday SOC.,61, 277 (1955). (5) V. K. Semenchenko and L. P. Shikhobalova, Zhur. Fiz. Khim., 21, G12 (1947). (6) H. Bloom and D. C. Rhodes, THISJOURNAL, 80, 791 (1956). (7) J. Byrne, H. Fleming and F.E. W. Wetmore, Can. J. Chem., 30, 922 (1952).
(1) This investigation was supported b y the U. S. Atomic Energy Commission, under Contract A T ( l l-l)-GEN-S. (2) L. Brewer, "The Fusion and Vaporization Data of the Halides," Paper 7 in "Chemistry and Metallurgy of Miscellaneous Materials: Thermodynamics," Ed. by L. Quill, McGraw-Hill Book Go., New York, N . Y . , 1950. (3) M. Knudsen, Ann. Physik, 29, 179 (1909). (4) W. H. Rodebush and A. L. Dixon, Phye. Rev., 28, 851 (1926).
1144
Vol. G‘2
NOTES
(theoretical 75.33). Weight loss experimmts also showed less than 0.2% volatile impurities. The melting point was determined by thermal analysis to be 1110 & 2’ which is to be compared with a literature value5 of 11 11 ’. Temperature measurements were made with Pt-Pt, 10% Rh thermocouples calibrated at the melting point of recrystallized sodium chloride. The ternpcrature of the ThF4 was held constant during vapor pressure determinations by means of a Leeds and Northrup potentiometric type controller-recorder. Nickel cells were used to contain the ThF4 in the effusion and quasistatic experiments. A corrosion test with molten ThF4 showed less than 0.005% Ni contamination from the crucible. Effusion Method.-The effusion cell was fitted with a screw cap and interchangeable thin lids with various orifice diameters. The inside dimensions of the cell were ‘/p inch by 1 inch. The cell was heated by a Marshall tube furnace adjusted to obtain a uniform temperature (&2’) region extending 1 inch beyond the ends of the cell. The error in the effusion time was kept below 1% by maintaining the heat-up and cool-off intervals of the cell short in comparison to the total time of the run. The quantity of material effused was determined from the weight loss of the cell during an experiment. In one run, the effusate was collected on a cylindrical tantalum collector; within experimental accuracy, the amount collected was equal to the weight loss of the cell. The effusate was analyzed by X-ray diffraction and chemical analysis and was found to be ThF4. Quasi-static Method.-The quasi-static method in essence yields the pressure at which the salt boils for a given temperature. This method is descrihed by Rodebush and Dixon4 and was used by Fiock and Rodebush6 to measure the vapor pressure of some of the alkali halides. The nickel cell used here is similar to the quartz cell used by Fiock and Rodebush.6 T h e nickel tubes were welded into the top of the cell to hold the reflux capillaries. The upper end of one of these tubes was connected to a vacuum system through a stopcock. The upper end of the other tube was connected to an absolute manometer filled with H$04. A differential manometer containing Amoil-5 was connected between the two tubes. Two thermocouple wells were placed in the cell: one immersed in the liquid salt and the other in the vapor immediately above the liquid. The temperature of the liquid and vapor always agreed within 3” and values obtained for the liquid were used in the calculations. The nickel cell was enclosed in an evacuated porcelain tube to prevent collapse of the cell. This was necessary because a t the temperatures used, nickel does not have sufficient mechanical strength to withstand an external pressure of one atmosphere. The cell and protection tube were mounted vertically in a Hoskins Model FHS-304 tube furnace. Vapor pressure measurements were made by starting with an inert gas pressure greater than the vapor pressure of the salt, then reducing the pressure in the system by small increments until the first “permanent difference” was obtained in the differential manometer. At this condition, the vapor pressure of the salt was equal to the pressure of the inert gas a t the absolute manometer. Mass Spectrometric Investigation of Vapor.-The vapor effusing from an inductively heated Knudsen cell containing ThF4 was examined with a Bendix time-of-flight mass spectrometer using 75-volt electrons. The nickel cell containing the salt was mounted in a manifold so that the vapor would pass into the ionizing region of the mass spectrometer. This system was connected to a conventional vacuum pump which provided a background pressure of less than 5 X mm. The temperature of the salt was determined by “sighting” into the cell orifice with an optical pyrometer. Inspection of the positive ion fragments formed from ThF4 vapor was made over the temperature range 900 to 1200”.
siire was cnlciiltited from the Knudsen effusion equation
where q = grams of material effused K = Clausing7 factor a = area of orifice in cm.2 t = time interval in sec. T = temperature, OK. ill = molecular weight of vapor
Three orifices were used with area ratios of approximately 1 to 4 to 8. The pressures obtained were independent of hole size within the experimental accuracy of the determination, indicating that the vapor wzts a t equilibrium with the solid. Effusion experiments were performed up to pres sures of 0.1 mm.; above this pressure, the viscous flow contribution complicates the treatment of the effusion data. TABLE 1 VAPORPIZESSURB OF SOLIDTHORIUM TETRAFLUORIDE BY KNUDSEN EFFUSION METHOD
Temp., OK.
Wt. loss, e.
Time, sec.
Orifice”
Pressure, atm.
c 1.21 X 3 . 3 2 X los 0.0150 1055 2 . 0 6 X IOW7 3 . 3 8 X 106 c ,0259 1066 c 3.31 X .0295 2.42 X lo4 1077 8.55 X 2 . 3 5 X 105 a ,0066 1113 c 8.36 X 2 . 3 8 X 106 .0724 1113 a 4.33 X 1 . 5 2 X 106 ,0212 1166 c 6.08 X 1 . 2 0 X lo4 ,0256 1184 7.41 X 6 . 3 5 X lo4 c ,1651 1186 1.39 X 1 . 3 0 X 106 a ,0386 1212 a 1.87 X ,0354 6 . 0 2 X lo4 1214 a 2.47 X .0480 6 . 2 2 X lo4 1218 b 2.38 X 1.35 X lo4 1225 ,0515 a 7.54 X ,0393 1.70 X lo4 1277 a 1.23 X 1.47 X lo4 ,0552 1297 Orifice areas (cm.2) and Clausing correction factors ( K ) were, respectively, a , 0.00196, 0.65; b, 0.00815, 0.82; C , 0.0164, 0.86.
The data from the quasi-static experiments are given in Table 11. This method has been used by Fiock and Rodebushe in the pressure range 6 to 55 mm. To check the applicability of the method below 6 mm., measurements were made on sodium chloride; the results down to 1.5 mm. agreed with those in the literature.63* Below this pressure, the quasi-static method gave low and erratic results. This probably was due to effusion of the inert gas through the vapor tubes at these low pressures making it difficult to detect the “permanent difference” in pressure between the two legs of the cell. The upper limit of the quasi-static pressure measurements was set by the loss of mechanical strength of the nickel cell a t high temperatures. The results from the two methods are plotted in Results and Discussion Fig. 1. Equations for the vapor pressure of the The experimental data obtained from the effusion so!id and of the liquid were obtained by least experiments are presented in Table I. The pres(5) W. J. Asker, E. R. Segait and A. W. Wylie, J . Chem. Soc., 4470 (1952). (6) E. F . Fiock and W. H. Rodebush, J . A m . Chem. Soc., 48, 2523 (1926).
(7) (a) P . Clausing. Ann. Physik, 12,961 (1932); (b) 6 . Dushman, “Scientific Foundations of Vacuum Technique,” John Wiley and Sons Inc., New York, N. Y.,1949, p. 96. (8) K. K. Kelley, U. S. Bureau of Mines Bulletin 383, Washington, D. C., 1935.
Sept., 1958
1145
XOTES
TABLE I1 VAPORPRESSURE OF LIQUIDTHORIUM TETRAFLUORIDE BY THE QUASI-STATIC METHOD Temp., OK.
Pressure, atm.
Temp.,
1437 1450 1466
x 10-3 x 10-3 3 . 0 7 x 10-3 2.64: x 10-3 3.91 x 10-3 3.96 x 10-3 4.09 x 10-3 5.03 x 10-3 5.88 x 10-3
1.501 1529 1532 1535 1555 1575 1575 1595
2.03
:$. 15
1466
1460 1470 1477 1484 1499
OK.
Pressure, atm.
6.07 x 9.34 x 8.77 x 9.71 X 1.33 x 1.72 X 1.71 X 2.44 X
10-3
10-3 10-3 10-3
10-2
squares treatments of the log P us. 1/T data. The equations are sublimation log
Phtrn) =
-
+
(16,860 f 190) T (9.105 i 0.160), (1055-1297°1C.)
(2)
(15,270 zk 310) T (7.940 f 0.206), (1427-1595'K.)
(3)
vaporization log P ( s t m ) =
-
+
Vapor pressure measurements were not carried out a t the melting point because neither method is applicable in this pressure range. Comparison of the results was made by extrapolating equations 2 and 3 to the melting point (1383°K.); vapor presatmosphere, sures of 8.2 X lop4 and 7.9 X respectively, were obtained. The heats of sublimation and vaporization a t the mid-temperatures in each set of experimental data are AH11,6(subl)= 77.1 f 0.9 koal./mole AHlr18(vap) = 69.9 f: 1.5 kcal./mole
(4) (5)
The AC, of vaporization (- 19 cal./deg./niole) estimated for the other tetrahalides of thorium by L. Brewer, and reported in N.B.S. Circular 5OOj9 was used in the free energy of vaporization equation
-.
I xi04 T OK
Fig. 1.-Plot
of log P us. 1/T for thorium tetrafluoride.
and 232 also were observed. These masses are attributed t o ionization of ThF4(,, to ThF3+, ThF2+, T h F + and Th+. Corresponding peaks for the dimer of ThF, mere not observed over the temperature range of these measurements. Acknowledgments.-The authors wish to thank Dr. T. A. Milne and Dr. S. J. Yosim for the helpful discussions concerning these results, Mr. W. A. McCollum for assistance in performing the experiments and Mr. L. Silvernian for carrying out the cheinical analyses.
- ACpT In T + I T (6) The constants AHo and I are evaluated from (3) T H E ABSORPTION SPECTRUM OF THE A P T = AH0
as 98,660 and - 194.50, respectively. Equation G gives a normal boiling point of 1953°K. for ThF4. Application of this AC, correction to (5) yields AH1963(vap) = 61.6 kcal./mole, AS1953(vap) = 3 1.5 cal./deg./mole. Some conclusions may be drawn regarding the vapor species of ThF4 by comparing the vapor pressure data from the two methods. The quasi-static method gives the total pressure above the salt. The results from the effusion method were calculated by assuming the salt vaporized as the monomer. The agreement of the two sets of data on extrapolation t o the melting point represents good evidence that ThF4 vaporizes as the monomer. This conclusion is substantiated by mass spectrographic studies made on ThF4effusing from a Knudsen cell. The predominant peak mas due t o mas8 289; smaller peaks representing masses of 270, 251 (9) F. D. Rossini. D. D. Wagman, W. H. Evans, S. Levine and I. Jaffe, Selected Values of Chemical Thermodynamic Properties, National Bureau of Standards, Circular 500 (1952).
TITANIUM(1V)-HYDROGEN PEROXIDE COMPLEX BY DAVIDLEWIS Department o f Chemistry, The City College, New York SI, N . Y Receaved March 26, 1958
The colored complex formed by the reaction 01 Ti(1V) and hydrogen peroxide in strong acid solution, usually AI sulfuric acid, is characterized by an absorption band with a maximum a t 405-10 mp and a molar absorptivity of ca. 730. Most measurements of this spectrum have been made on solutions or less in Ti(IV), since this is the analytically useful range of the colored complex. Reeves and Jonassen' have examined the spectral behavior of more concentrated solutions; they report that above a concentration of 1.2 X 10-8M Ti(IV) the maximum shifts progressively toward (1) R. E. Reeves and H. B. Jonassen, J . Am. Cham. SOC.,76, 5354 (1 954).
