Specific heat, enthalpy, and entropy of uranyl fluoride

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Title:
Specific heat, enthalpy, and entropy of uranyl fluoride
Series Title:
United States. Atomic Energy Commission. MDDC ;
Physical Description:
5 p. : ill. ; 27 cm.
Language:
English
Creator:
Wacker, Paul F
Cheney, Ruth K
National Bureau of Standards
U.S. Atomic Energy Commission
Publisher:
Technical Information Division, Oak Ridge Directed Operations
Place of Publication:
Oak Ridge, Tenn
Publication Date:

Subjects

Subjects / Keywords:
Specific heat   ( lcsh )
Entropy   ( lcsh )
Enthalpy   ( lcsh )
Uranium fluorides   ( lcsh )
Uranium   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Bibliography:
Bibliography: p. 5.
Restriction:
"Date Declassified: July 9, 1947"
Statement of Responsibility:
by Paul F. Wacker and Ruth K. Cheney.
General Note:
Manhattan District Declassified Code

Record Information

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University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 005023761
oclc - 277770454
System ID:
AA00009337:00001


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MDDC 1096




UNITED STATES ATOMIC ENERGY COMMISSION







SPECIFIC HEAT, ENTHALPY, AND

ENTROPY OF URANYL FLUORIDE



by
Paul F. Wacker
Ruth K. Cheney


S
National Bureau of Standards


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UN IV 0nF PL L'B






US DEPOSITOPY


This document consists of 5 pages.
Date of Manuscript: Unknown
Date Declassified: July 9, 1947


This document is issued for official use.
Its issuance does not constitute authority
to declassify copies or versions of the
same or similar content and title
and by the same authorss.





Technical Information Division, Oak Ridge Directed Operations

Oak Ridge. Tennessee




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SPECIFIC HEAT, ENTHALPY, AND
ENTROPY OF URANYL FLUORIDE
By Paul F. Wacker and Ruth K. Cheney

ABSTRACT
The heat capacity of uranyl fluoride was measured from 13* to 418'K using a vacuum-type
calorimeter equipped with thermostated radiation shields. From the data soobtained, the enthalpy
H H' was calculated to be 63.96, 77.62, and 108.15 int. joules per gram at 298.16, 338.16, and
423.16"K respectively, while the entropy was calculated to be 0.4400, 0.4830, and 0.5635 int joules
per degree-gram at the same temperatures. No evidence of a transition was found. The values of
the specific heat, enthalpy, entropy, and free energy are tabulated at live degree intervals of
temperature.

INTRODUCTION
This investigation of the thermodynamic properties of uranyl fluoride was undertaken in connec-
tion with the Manhattan project and is a part of the program carried on during the war by the Heat
and Power Division of the National Bureau of Standards.

MATERIAL

The uranyl fluoride used in this investigation was prepared by H. F. Priest of Columbia University.
The material was placed in the sample container after being dried at 130"C for [our hours. Air was
removed by pumping until a high vacuum was obtained, helium was admitted at a pressure of 20 mm
Hg, and the container was sealed with solder. The helium was added to promote the rapid attainment
of thermal equilibrium. The observed heat capacity was adjusted for the presence of this helium.
Before the material was used in the calorimeter, an analysis made by the SAM Laboratories of
the Carbide and Carbon Chemicals Corporation showed the sample to contain 77.19 weight per cent
of uranium and 12.64 weight per cent of fluorine. Following the calorimetric measurements, the
Uranium Section of the National Bureau of Standards found the sample to contain 77.28 per cent of
uranium and 12.1 per cent of fluorine. The theoretical percentages are 77.28 and 12.33. Spectroscopi
tests for 34 elements showed less than 0.07 weight per cent impurity. The difficulties in fluorine anal-
ysis are such that it is probably improper to base any conclusions regarding purity of the sample on
observed fluorine content.

APPARATUS AND PROCEDURE
The calorimeter used in this investigation was of the ad.abatic, vacuum type described by
Southard and Brickwedde.' The sample container was the one used in the determination of the heat
capacities of GR-S rubber and polyvinyl chloride.'
The system, including the measuring circuits, was very siLlilar to that used by Scott, Meyers,
Rands, Brickwedde, and Bekkedahl4 to determine the heat capacity of butadiene, except for the follow-
ing: The apparatus was designed for measuring the heat capacitie.- of solids and so had no filling tube
or attendant parts. The shield was suspended by means of fine wire. and the sample container was in
turn suspended from the shield by means of linen cord. A copper, rather than an aluminum, shield was
used on the bottom of the sample container to prevent heat losses from the exposed ends of the heater.
The sample-container heater was located in the thermometer well, which was filled with lead-tin
eutectic solder. The side and bottom shield heaters were controlled individually. In order to improve
MDDC 1096 [











MtDDC 1096


the ease of controlling the radiation shields at temperatures above the c e point, an auxiliary heater
was wrapped un the outer wall of the vacuum chamber, and the chamber was surrounded by a stirred
oil bath. The auxiliary heater was used to keep this wall at a temperature only slightly below that of
the shields ard sample container. Its use resulted in a substantial improvement in shield control.
Temperatures were measured with platinum resistance thermometer LI5 (thermometer PI, whose
calibration is described by Hlege and Brickwedde.6
The methods of measurement and of calculation were similar to those described in the paper on
butadiene The tare heat capacity measurements were made on the empty sample container, while
the gross heal capacity measurements were made with 58.015 grams of uranyl fluoride in the con-
tainer. Due to the negligible vapor pressure of the material, it was unnecessary to correct the heat
capacities for vaporization. Specific heat measurements were regularly made with both high and low
heating rates, the rates varying as much as from 0.63 to 2.18 degrees per minute. This procedure
provided a test for a large proportion of the errors which might occur in the measurement of heat
capacity, but would not hal, revealed an error whose magnitude per unit time was proportional to the
heating rate.

CALCULATIONS AND RESULTS
The observed heat capacity data were plotted as deviations from empirical equations. From the
resulting deviationri curves, values were read at uniform temperature intervals, and tables were con-
structed giving both the gross and tare heat capacities at 2.5-degree intervals below 115"K and at
5-degree intervals at higher temperatures.. Subtraction of the tare from the gross heat capacity gave
the net heat capacity, which was extrapolated to 0K by means of the Debye equation, C = 0.8359
D(117.T). This tquation represented the experimental data satisfactorily at 20, 25, and 30"K.
Due to graphical methods involved in getting the table of net heat capacities, small irregularities
could be detected in the higher differences. To reduce these, an analytical smoothing process was
applied The smoothed value corresponding to a given unsmoothed value was found by multiplying the
unsmooLhed value and the four adjacent unsmoothed values on either side of it by a set of coefficients.
A number of such smoothing processes have been devised. The one adopted in the present work was
developed by Harold W. Wooley. In it the coefficients were chosen to minimize the squares of the
random parts of the first differences in such a manner that the process would make no significant
change in functions for which the fourth and higher differences were negligible. The smoothing oper-
ation introduced no changes in the table as large as the probable experimental error.
The enthalpy was calculated Irom the formlua H = JC" dT, while the entropy was obtained from
the equation S = / (C T1 dT The free energy was calculated from the relation F = S" dT and
also from the relation F = H' TS'. This provided a check on the accuracy of the integration.
Simpson's rule was used at the higher temperatures. Between 20* and 115"K, a tabular integration
formula Involvin, four rather than three successive tabular entries was used, while below 200 the inte-
gralb were obt.-ncd directly from the Debye equation. The results are presented in Table 1. The
dashed lines in Figure 1. representing 1/2 per cent of the h=-t capacity, show the temperature trend of
the specific heat.

DISCUSSION
Although tests were made for transitions, none were found.
The probable error in the tabulated values of the specific heat of the sample used in this investi-
gation is estimated to 'e 0.1 per cent from 40 to 250"K. BeloW 40" the error is larger, perhaps reach-
ing 1 per cent at 20"K. Since radiatioc becomes an important source of error above room temperature,
the probable error above 250'K may be as large as 0.5 per cent. These estimates do not include errors
due to impurities in the sample. Although there is probably no reliable evidence for more than 0.07
weight per cent impurity in the sample, thlack of detailed knowledge of the purity does introduce some
uncertainty in the results.









MDDC 1096


Table 1. Heat capacity, enthalpy, entropy, and free energy of uranyl fluoride.


T CU H'- H' S.
'K lnt.jg-"K-' Int.jg-' Int.jg-' "K-'


0 0.
5 .00051
10 .00403
15 .01231
20 .02333
25 .03386
30 .04478
35 .05567
40 .06637
45 .07747
50 .08909
55 .10191
60 .11549
65 .12713
70 .13573
75 .14362
80 .15261
85 .16310
90 .17378
95. .18226
100 ..18847
105 .19439
110 .2007
115 .2070
120- .2132
125 .2193
130 .2252
135 .2308
140 .2362
145 .2413
150. .2463
15,. .2510
100 .2556
185 .2598
190 .2640
175 .2679
110 .2717
185 .2753
190 .2788
195 .2822
200. .2854
205 .2886
210 .2917


0.
.00064
.01014
.0492
.1378
.2803
.4768
.7280
1.0331
1.3925
1.8086
2.2855
2.6292
3.4371
4.0951
4.7933
5.5333
6.3220
7.1647
8.0560
8.9834
9.9404
10.928
11.947
12.998
14.079
15.190
16.331
17.498
18.692
19.911
21.154
22.421
23.710
25.019
26.349
27.698
29.066
30.451
31.854
33.273
34.708
36.159


-IF'-H) T C' H"- H S' -(F- HI
Int.jg- "K Int.jg-1 K"' Int.jg- Int.lg-'"K- Int.jgg


0.
.00017
.00135
.00440
.00943
.01575
.02288
.03060
.03874
.04719
.05595
.06503
.0744b
.08420
.09395
.10358
.11313
.12269
.13232
.14196
.15147
.16081
.16999
.17905
.18800
.19682
.20554
.21415
.22264
.23102
.23928
.24743
:25547
.26340
.27122
.27893
.28653
.29403
.30141
.30870
.31589
.32297
.32997


0.
.00021
.00339
.01690
.050b
.1133
.2096
.3431
.5163
.7310
.9887
1.2910
1.6396
2.0363
2.4817
2.9756
3.5174
4.1070
4.7443
5.4302
6.1638
6.9446
7.7713
8.6440
9.5620
10.524
11.530
12.579
13.671
14.806
15.981
17.198
18.455
19.752
21.089
22.464
23.878
25.330
26.818
28.343
29.906
31.502
33.135


215 .2949
220 .2979
225 .3008
230 .3037
235 .3064
240 .3090
245 .3116
250 .3142
255 .3166
260 .3190
265 .3214
270 .3237
275 .3259
280 .3280
285 .3300
290 .3320
295 .3339
300 3357
305 .3374
310 .3390
315 .3406
320 .3422
325 .3438
330 .3454
335 .3470
340 .3486
345 .3502
350 .3517
355 .3532
360 .3546
365 .3560
370 .3572
375 .3584
380 .3596
385 .3607
390 .3617
395 .3627
400 .3638
405 .3648
410 .3658
415 .3668
420 .3678
425 .3688


37.626 .33687
39.107 .34368
40.604 .35041
42.116 .35705
43.641 .36361
45.179 .37009
46.731 .37649
48.295 .38281
49.872 .38905
51.462 .39523
53.063 .40133
54.676 .40735
56.300 .41331
57.934 .41920
59.579 .42503
61.235 .43079
62.900 .43648
64.574 .44210
66.256 .44767
67.947 .45317
69.647 .45860
71.354 .46398
73.069 .46930
74.792 .47456
76.523 .47976
78.262 .48492
80.009 .49002
81.764 .49507
83.526 .50007
85.296 .50502
87.072 .50992
88.855 .51477
90.645 .51957
92.440 .52433
94.241 .52904
96.046 .53370
97.858 .53831
99.674 .54288
101.495 .54741
103.321 .55169
105.153 .55633
106.989 .56073
108.831 .56508


34.802
36.503
38.238
40.006
41.808
43.643
45.510
47.408
49.337
51.298
53.290
55.310
57.362
59.443
61.555
63.694
65.862
68.058
70.284
72.536
74.814
77.121
79.454
81.814
84.199
86.612
89.049
91.512
94.000
96.512
99.050
101.611
104.196
106.806
109.440
112.098
114.776
117.480
120.206
122.954
125.725
128.518
131.330










MDDC 1096


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REFERENCES

1. Southard, J. C. and F. G. Brickwedde, Low temperature specific heats. I. An improved calorimeter
for use from 12* to 300K. The heat capacity and entropy of napthalene, J. Am. Chem. Soc. 55:
4378 (1933).

2. Rands, Robert D., Jr., W. Julian Ferguson, and John L. Prather, Specific heat and increases of
entropy and enthalpy of the synthetic rubber GR-S from 0 to 330K, J. Research NBS 33: 63 (1944)
RP1595.

3. Rands, Robert D., Jr. and Robert E. McCoskey, unpublished.

4. Scott, Russell B., Cyril H. Meyers, Robert D. Rands, Jr., Ferdinand G. Brickwedde, and Herman
Bekkedahl, Thermodynamic properties of 1,3-butadiene in the solid, liquid, and vapor states, J.
Research NBS 35: 39 (1945) RP1661.
5. Hege, Harold J. and Ferdinand G. Brickwedde, Intercomparison of platinum resistance thermometers
between 190" and 445'C, J. Research NBS 35: 217 (1942) RP1454.


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