Analysis of Hydrazine-liquid Ammonia Mixtures by low-Temperature Thermogravimetry Stanley W. Comer, Air Force Rocket Propulsion Laboratory, Edwards, Calif.
of solutions of hydrazine in liquid ammonia required a plot of specific gravity vs. composition. The widely separated boiling temperatures of the two compounds permitted the use of low-temperature thermogravimetry to determine the composition of the mixtures. Thermogravimetry was used because the method is rapid, direct, and accurate. Other methods that were tried involved considerable fabrication and assembly of equipment because of the cryogenic properties of the sample.
-1
EXPERIMENTAL
g
N INVESTIGATION
0 -
40 20
*
r
Table 1.
Specific Gravity of Solutions of NzH4 in NH,
%
Sp. Gr.
Temp., "C.
0.0 7.4 10.9 13.0 15.9 22.2 26.5
0.6986 0.7200 0,7280 0.7346 0,7442 0.7596 0.7749
-45.0 -45.5 -46.5 -46.0 -44.0 -43.5 -43.0
N2H4,
Sample 1 2 3
4 5 6
7
Table II. Replicate Analysis N2H4, % Analysis 1
Analysis 2
3.0
3.1 7.5 17.9 20.5 40.4
7. . 6_
17.9 19.5 41.0
958
ANALYTICAL CHEMISTRY
80
-
Y,
2
c3
Apparatus. T h e r m o g r a v i m e t r i c analysis was performed with a Thermograv (American Instrument Co., Silver Spring, Md.). A Mettler Model H4/14 specific gravity balance was used to obtain the specific gravity of the solutions. A hydrocarbonfilled, low-temperature thermometer (Sargent #S-80135) was used to measure the temperature. Procedure. Liquid ammonia was poured into a 1000-cc. Dewar flask and the specific gravity and temperature were measured. Approximately 40 cc. of hydrazine were added to the ammonia by using a syringe with a 24-gauge hypodermic needle. After temperature and specific gravity were measured, a small amount of solution (0.2 to 0.3 cc.) was poured
60-
100-
IZ0-
160 -
; ; I40
3
180
-
200
I
5
IO
15
IO
20
30
T I M E (MIN.) Figure 1. 150' C.
Thermogram of 40.4 mg. of N2H4in 141.2 mg. of NH3 from -45.0'
from a 1-ml. beaker into a liquid nitrogen-chilled crucible (Coors 000) while both containers were held in the vapor above liquid nitrogen in a large Dewar flask. The crucible was then fil1ed:with liquid nitrogen to keep the sample frozen and to prevent condensation of water by providing a blanket of nitrogen while the crucible was being put into the Thermograv. Weight loss due to evaporation of ammonia was obtained by letting the sample warm up in a nitrogen atmosphere at room temperature. After the ammonia had evaporated, the temperature was raised at a rate of 9 ' C. per minute. RESULTS A N D DISCUSSION
Typical curves are shown in Figure 1. Table I gives the data that were obtained. An empirical equation for the data in Table I, plotting specific gravity us. per cent NzH4,was calculated to be y
=
0.0028372
+ 0.6983
A plot of this equation is subject to two uncertainties : replication error and scatter about the curve.
to
Replication was tested by analyzing a mixture twice. The second analysis was performed approximately 30 minutes after the first, so the test also served to indicate the short-term stability of the mixture. Results are given in Table
11. Scatter was determined by using the equation, given above, to calculate per cent Nd& corresponding to experimental values of specih gravity. The specific gravity values were assumed to be correct. Standard error of estimation (scatter) expressed in units of the abscissa was calculated to be k0.37. The y intercept for the equation was taken as an indication of the accuracy of the procedure. The value obtained was within 0.3% of the literature value for the specific gravity of liquid ammonia a t -45.6'C. Error caused by condensation of water would have been evinced as scatter or m an erroneous y intercept. Carbon dioxide did not interfere because of its low sublimation temperature, Also, there was no residue to indicate the presence of carbazic acid or the ammonium salt of carbamic acid.
