KOTES
4035
1
I
I
The Thermodynamic and Physical Properties of
1
by lllichael A. Greenbaum, Justine Weiher, and Milton Farber Research Division, Maremont Corporation, Pasadena, California (Received March 11, 1965)
I
C
I
c 23
I 0.40
I
I
0.60
--+
I 0.00
,
1 GO
fraction of energy
Figure 1. G( -C2Hr) values referred to the energy absorbed by ethylene us. the fraction of energy absorbed by the inert gas: 0, helium; A, neon; M, argon; V, krypton; 0, xenon; 0, nitrogen.
A plot of the G( - CzH4)values referred to the energy absorbed by ethylene molecules against the fraction of energy absorbed by the “inert” gas is shown in Figure 1. The experimental data seem to lie on the same curve and extrapolation a t zero concentration of “inert” gas is the G(-CzH4) for pure ethylene a t 123 mni. of pressure. This trend would indicate that G(-C2H4) does not depend on the nature of the “inert” gas, but on the fraction of energy absorbed by the “inert” gas itself and transferred to the ethylene molecules. It is well known that energy transfer from a noble gas to ethylene is a highly efficient p r o ~ e s s . ~ -Of ~ course, the primary species generated in ethylene are different, depending on the nature of the “inert” gas. The experimental results do not allow one to draw any conclusions on the mechanism of polymerization induced by energy transfer from the “inert” gas to ethylene molecules. The over-all effect on the G (- C2H4) values for ethylene consumption results is about the same whichever the sensitizer. (4) J. L. Franklin and F. H. Field, J . Am. Chem. Soc., 83, 3555 (1961). (5) R. P. Jesse and J. Sadauskis, Phys. Rev., 100, 1755 (1955). (6) R. L.Platsman, J . Phys. Radium, 21, 853 (1960).
The lack of reliable values of the sensible enthalpy of BeO(c) in the vicinity of its melting point, 2825OK., and for the heat of fusion can, in large part, be attributed to the great reactivity of Be0 with almost all container materials at elevated temperatures. The only previous experimental determination of the sensible enthalpy of BeO(c) above 2000°K. was reported by Kandyba, et al., in 1960.’ Based on an analysis of their data combined with several other experimental reports, a value of 15.1 f 0.4 kcal./mole has been derived for the heat of fusion of BeO(c) at the melting point.2 No direct measurement of this quantity has been reported previously, however. As a continuation of an extensive program in these laboratories aimed at the generation of reliable thermodynamic and physical data for compounds of beryll i ~ m , ~a -study ~ of the high-temperature thermodynamic properties of BeO(c) was initiated. After extensive investigation it was determined that rhenium was completely unattacked by solid, liquid, or gaseous beryllium oxide a t temperatures as high as 30OO0K. and under vacuum (10-4 to mm.). The experimental method employed to obtain the requisite thermodynamic data for BeO(c) involved the use of an electron bombardment furnace-drop calorimeter (1) V. V. Kandyba, et al., Dokl. Akad. S a u k S S S R , 131, 566 (1960). (2) “JANAF Thermochemical Tables.” U.S.A.F. Contract No. AF 33(616)-6149,Advanced Research Projects Agency, Washington 25, D. C., March 1964. (3) M. A. Greenbaum, J. N. Foster, RI. L. Arin, and hl. Farber, J . Phys. Chem., 67, 36 (1963). (4) hl. A. Greenbaum, R. E. Yates, XI. L. Arin, M. R. Arshadi, J. Weiher, and hf. Farber, ibid., 67, 703 (1963). (5) hl. A. Greenbaum, M.L. Arin, and AI. Farber, ibid., 67, 1191 (1963). (6) M.A. Greenbaum, R. E. Tates, and M. Farber, ibid., 67, 1802 (1963). (7) M .A. Greenbaum, M.L. Arin, M. Wong, and M. Farber, ibid., 68,791 (1964). (8) R. E.Yates, 11. A. Greenbaum, and M.Farber, ibid., 68, 2682 (1964).
Volume 69, Number 11 November 1965
NOTES
4036
Table I : Experimental Results of B e 0 Enthalpy Measurements Temp.,
O K .
2273 2283 2293 2313 2323 2323 2348 2348 2373 2378 2383 2383 2393 2433 2433 2433 2443 2473 2473 2513 2523 3523
Wt. of BeO,
g.
1.1373 1.0149 1.2237 1.2248 1,1147 0,9228 0,9827 1.2203 1,2208 1,2187 0,9228 0.9228 0.9228 1,1589 1.1475 1.2201 1.2295 1.2274 1,0010 1.2118 1.2309 1.225j
K t . of Re, g.
Mercury intake, g.
1.5636 1.5586 1.5671 1.5661 1,5592 3. 1534 1.6855 0,8170 1.5675 0.8198 3,4999 3.4859 3.4973 1.6855 1.6855 1.5840 2,1544 1.2835 1.6855 1.5817 1.5823 1.5836
91.700 119.001 110.400 99.361 143.088 73.557 73.470 104.970 91.750 96.766 109.409 59.238 59.870 69.977 79.188 69.502 69.039 58.471 64.084 77.313 57.305 64.781
combination which was designed in these laboratories. The calorimeter section of the apparatus is basedupon designs originally developed by the National Bureau of Standardsg--12and subsequently modified by otherinvestigators.I3?l4 A detailed description of the apparatus together with its operation has been presented previously. Heating of the beryllium oxide sample was accomplished by the use of the electron bombardment furnace nientioned above. The sample encased in rhenium was suspended within the furnace by means of a rhenium wire which was attached to a 0.002-in. molybdenum wire. The molybdenum wire was connected to a 110v. variable rheostat. When the sample temperature reached the desired point and equilibrium had been established, the molybdenum wire was broken by means of an electric current, thus allowing the sample to drop into the calorimeter. The beryllium oxide employed was 99.5+2l, pure in the form of 0.375 X 0.25-in. rods encapsulated in rhenium containers 0.012 in. thick. Temperature measurement was accomplished by a Leeds and Sorthrup optical pyrometer previously calibrated according to NBS standards. Temperature was controlled manually to within approximately =!=so. The absolute value of the temperature is considered to be accurate to *20° a t the present time. Calibrations of the calorimeter were carried out using tantalum following the procedure of Hoch and JohnThe Journal of Physical Chemistry
Mercury corrections,
75.347 103.627 92,869 81.889 126.466 57.579 58.672 89,048 73.109 79.716 92.999 42.753 43.215 50,978 60.629 51.142 50.535 38.833 48.070 57.446 36.627 44.455
g.
Heat released, cal.
Re correction, cal.
H - Hm,
1057.1 993.7 1133.1 1129.3 1074.4 1032.8 956.5 1029.2 1204.9 1102.1 1060.7 1065.6 1076.5 1228.1 1199.6 1186.7 1196.1 1269.4 1035.1 1284.2 1336.6 1313.9
121.07 121.73 123.23 123.99 124.70 247.23 136.61 66.00 128.73 67.43 287.44 287.22 290,03 142.49 142.49 133.91 183.29 110.58 145.66 139.66 140.14 140.25
20,569 21,488 20,640 20,528 21,307 21,291 20,866 19,741 22,047 21,234 20,957 21,096 21,314 23,428 23,040 21,581 20,602 23,612 23,111 23,621 24,309 23,951
cal./mole
ston.I3 Agreement between our calibration data and that of Hoch and Johnston is quite good. Corrections for the enthalpy of the rhenium container for the Be0 sample were carried out using the data of Hultgren, Orr, Anderson, and Kelley.16 The melting points of A1203 and Be0 were taken as the calibration points in the temperature range for the experiments. The melting points reported in the literature2 for A1203and Be0 are believed to have an uncertainty within *20°K. The reproducibility of the temperature measurements of the experiments presented herein was within =k5%. Since it was not feasible to take into account heat loss during the actual drop, this has been neglected. It should be pointed out that because of the special design (9) D. C. Ginnings and R. J. Corruccini, J . Res. Natl. BUT.Std., 38, 583 (1947). (10) D. C. Ginnings and R. J. Corruccini, ibid., 38, 593 (1947). (11) D. C. Ginnings, T. B. Douglas, and A. F. Ball, J. A m . Chem. SOC., 73, 1236 (1951). (12) J. C. Southard, ibid., 63, 3142 (1941).
(13) M.Hoch and H. L. Johnston, J. Phus. Chem., 6 5 , 855 (1961). (14) R. A. Oriani and W. K. Murphy, J . A m . Chem. Soc., 76, 343 (1954). (15) .M.A. Greenbaum, J. Weiher, and M.Farber, presented before
the Symposium on Thermodynamics and Thermochemistry, Lund, Sweden, July 18-23, 1963. (16) R. Hultgren, R. L. Orr, P. D. Anderson, and K. K. Kelley, “Selected Values of Thermodynamic Properties of Metals and Alloys,” John Wiley and Sons, Inc., New York, N. Y., 1963.
SOTES
4037
Table 11: Experimental Results of B e 0 Heat of Fusion Measurements
Temp., OK.
2843 2853 2863
Wt. of
W t . of
BeO, g.
Re,
0.9232 0.9232 0.9232
g.
6.0090 5.3674 6.0066
Mercury intake,
Mercury corrections,
g.
g.
114.39 115.68 118.40
78.410 79.462 80.818
Heat released, cel.
Re correction, cal.
Total heat released from BeO, kcal.
Correction for BeO(c) enthalpy, kcal.
Heat of fusion, kcal./mole
2325.4 2313.0 2429.3
620.90 554.60 625.49
46.2 47.6 48.8
28.1 28.2 28.3
18.1 19.4 20.5
2853 f 10“
4 7 . 5 f 0.9‘
28.2 i 0.2”
19.3 A 0.8“
Average.
of the experimental apparatus, it is considered that the heat loss would be very small. This is confirmed in large measure by the agreement of our calibration data for tantalum with the previously reported experimental data. The AlO% for the precision reported for the temperature at which the heat of fusion measurements were made is simply the average of the several actual runs. The sensible enthalpy of BeO(c) was measured calorimetrically between 2270 and 2525OK. using the procedures and apparatus mentioned above. The results of this study are presented in Table I and graphically in Figure 1. A least-squares analysis of the data fitted to an equation of the form y = m x b yields the equation
+
28
16
t i
2200
2300
2400
2500
2600
2700
Temperature, OK.
Figure 1. The sensible enthalpy of BeO(c) as a function of temperature between 2270 and 2525’K. with extrapolation.
H - H298= 13.85T - 11,322 f 875 cal./mole Within the temperature range studied and within the admittedly large limits of error, the heat capacity of BeO(c) appears to be constant. Not included in the line analysis, and so indicated on the graph, are three measured points in the extrapolated region of the curve. These points were not included in the line equation because the rhenium-encased samples began to leak before confirming rune at these higher temperatures could be made. Previous data2 assume there is a phase change at 2323OK., in accordance with the results of other experim e n t ~ , although ~ ’ ~ ~ ~ no phase change in this region was noted by Kandyba.’ This phase transition observed by -4usterman took place over a 30-60’ temperature interval. The present experimental studies of the sensible enthalpy have been made beginning in the range in which phase change was reported. The accuracy of the present study would not permit a phase change observation here and it is presumed the experimental values include any enthalpy increases due to phase change. Determinations of the heat of fusion of Be0 were also carried out in the present study. These are summarized in Table 11. It should be pointed out that the
three different temperatures reported in this table are essentially the same within the limits of temperature capability at present. Thus, based on an average temperature of 2853 f 1O0K.,the net heat of fusion of Be0 is found to be 19.3 f 0.8 kcal./mole where the correction is an extrapolation of the determined enthalpy values reported in this study. The reported error of f0.8 kcal./mole represents the statistical error of the several runs performed. The value 19.3 f 0.8 kcal./mole may be compared with a value of 17 f 1.4 kcal./mole reported by Long and Schofieldl9 and with the value of 15.1 f 0.4 kcal./mole previously reported.2 However, if the gross value for the heat released is corrected using the previous data for the enthalpy of BeO(c) at those temperatures2 instead of using these extrapolated data, the average heat of fusion is found to be 15.6 f 0.8 kcal./mole. This is a difference of only 0.5 kcal./mole from the 15.1 kcal. showing that variation in net heat of fusion may be attributable primarily to variation in enthalpy values of the crystal. (17) S. B. Austerrnan, Bull. Am. Phys. SOC.,7 ( l ) , 28 (1962). (18) T. W. Baker and P. J. Baidock, Nature, 193, 1172 (1962). (19) R. E. Long and H. Z. Schofield, “Beryllia,” AEC-TIS Reactor Handbook, Val. 3, Section 1, 1955, Chapter 1.3.
Volume 69,Number 1 1
A’ovember 1865
