NASA Reference Publication 1013

Triple Point Determinations

of Monomethylhydrazine and

Nitrogen Tetroxide (2.2 Percent

by Weight Nitric Oxide)

Irwin D. Smith and Patrick M. Dhooge

NOVEMBER 1977

NASA
NASA Reference Publication, 1013

Triple Point Determinations

of Monomethylhydrazine and

Nitrogen Tetroxide (2.2 Percent

by Weight Nitric Oxide)

Irwin D. Smith

Lyndon B. Johnson Space Center

Houston, Texas

and

Patrick M. Dhooge

Lockheed Electronics Gompatiy,:, Inc.

Las Cruces, New Mexico ' ' ':

\'i ..V/:'.; i • ,--•-•,

•

 ; : "

NASA

National Aeronautics

and Space Administration

Scientific and Technical

Information Office

1977

CONTENTS

Section Page

SUMMARY 1

INTRODUCTION ....... . 2

TEST OBJECTIVES 2

TEST FLUIDS , 2

TEST DESCRIPTION 2

Laboratory System 2

Test Stand System ..... , 4

MMH TRIPLE POINT TEST RESULTS 5

Laboratory Results . . . . . . . ............. . 5

Test Stand Results 6

MMH VAPOR PRESSURE TEST RESULTS 7

N204 TRIPLE POINT TEST RESULTS . Q

CONCLUDING REMARKS . n

REFERENCES . . n

111
TABLES

Table Page

I TRIPLE POINT OF MMH USING LABORATORY METHOD ..... i 6

II VAPOR PRESSURE OF MMH .............. . . 9

' I

FIGURES

Figure Page

1 Laboratory apparatus for measurement of triple '

point of fluids ......... ..... . .... : 4

2 Test stand apparatus for measurement of triple .. . ,

point of fluids under spacelike conditions . . .

 :. 4

3 Test stand apparatus equipped with remotely !

operated agitation arm ..... ........ . . ' 5

4 Frozen MMH at conditions approaching the <

triple point ......... ..'•. ........ 7

i 5 Calculated vapor pressure of MMH ........ :.'.'. .

: 8

6 Photograph showing some dark liquid-state

present in bottom of bag 15 seconds after

introduction of the ^04 ............. 1Q

7 Photograph taken a few seconds after that shown in

figure 6, showing frozen N204 on sides of bag ... 10

iv
TRIPLE POINT DETERMINATIONS OF MONOMETHYLHYDRAZINE

AND NITROGEN TETROXIDE (2.2 PERCENT BY WEIGHT NITRIC OXIDE)

By Irwin D. Smith3 and Patrick M. Dhoogeb

Lyndon B. Johnson Space Center

SUMMARY

During the winter of 1975-76, a

series of tests was performed at the

NASA Lyndon B. Johnson Space Center

Uhite Sands Test Facility to ascertain

the triple point of monomethylhydrazine

and nitrogen tetroxide. The triple

point of a material is the set of temperature and pressure conditions at

which that material will exist simultaneously under equilibrium conditions

in the liquid, vapor, and solid phases.

Two methods were used to establish the

triple point. The laboratory method

using a closed system indicated the

triple point of monomethylhydrazine is

219.5 K (-64.7° F) at 11.7 pascals

(0.0017 psia). The laboratory method

is the technique normally used to measure the triple point of fluids. In the

second method, the fluid was exposed to

a specific pressure in a very large

chamber and allowed to cool by evaporation to the equilibrium temperature

for the fluid at the pressure exerted.

This method simulated a spacelike

environment to more properly evaluate

the behavior of monomethylhydrazine

when exposed to the near vacuum of

space. The results obtained using the

second method indicate that a true

triple point situation was not achieved

because of an observed pronounced

tendency of the monomethylhydrazine to

supercool. Once solid-phase material

is obtained in combination with liquid

material, the liquid material over a

period of time converts to the solid

phase. In recognition of these phenomena, the data obtained under spacelike

conditions should more appropriately be

called the effective freezing point

rather than the triple point of the

material. Using this technique, the

effective freezing point under spacelike conditions of monomethylhydrazine

(with agitation) was found to be 211.5 K

(-79.0° F) at 3.72 pascals (0.00054 psia).

without agitation, supercooling was observed to temperatures as low as 207.6 K

(-86.00'F).

As a result of the attempt to

determine the triple point of monomethylhydrazine under spacelike conditions, new

experimental values for the vapor pressure

of the liquid phase were determined at

temperatures between 275.2 K (35.60° F)

and 207.6 K (-86.0° F). The new vapor

pressure data were combined with existing

literature data to permit the generation

of equations for the vapor pressure of

liquid monomethylhydrazine from the normal boiling point to below the normal

freezing point and into the supercooled

temperature range for the fluid.

A laboratory determination of the

triple point of nitrogen tetroxide was

not performed. Tentative values for the

effective freezing point under spacelike

conditions of nitrogen tetroxide containing 2.2 percent by weight nitric oxide

were determined to be 259.4 K (7.2° F)

at 15 444 pascals (2.24 psia).

aNASA Lyndon B. Johnson Space

Center White Sands Test Facility.

bLockheed Electronics Company, Inc.
INTRODUCTION

Personnel at the NASA Lyndon B.

Johnson Space Center (JSC) White Sands

Test Facility (WSTF) performed a series

of Shuttle orbital maneuvering engine

cold-flow tests during the winter of

1975-76 to determine the amount of

residual monomethylhydrazine (MMH) fuel

remaining in the regeneratively cooled

thrust chamber after various purge and

vent sequences. These tests were performed at test chamber pressures of less

than 6.89 pascals (0.001 psia) that were

believed to be below the triple point

pressure of MMH. Freezing of the MMH was

not observed in any of the tests as would

have been expected if the MMH had been

subjected to pressures below the MMH

triple point. An Atlantic Research Corporation report (ref. 1) indicated that

the triple point of MMH was 13.79 pascals

(0.002 psia) at 220.8 K (-62.3° F);

however, the derived value was not

based on experimental data. A thorough

review of the chemical literature also

indicated that the triple point of MMH

had not been experimentally determined.

Hence, WSTF personnel were requested to

determine the triple point of MMH to

assist the Propulsion and Power

Division at JSC in the interpretation

of the data observed in the orbital

maneuvering engine purge and vent, tests.

As an aid. to the reader, where necessary the original units of measure have

been converted to the exact equivalent

value (without regard for the number of

significant digits) in the Systeme International d1Unites (SI). The SI units

are written first, and the original units

are written parenthetically thereafter.

TEST OBJECTIVES

(0.25 psia). A third objective of the

tests was the tentative determination

of the triple point of nitrogen tetroxide ^04) containing 2.2 percent by

weight nitric oxide (NO) under a

space!ike environment.

The

TEST FLUIDS

and N~Q, used in the tests

met the applicable Space Shuttle

requirements. The compositions of the

propellents are provided in the table

on the opposite page.

TEST DESCRIPTION

Laboratory System

The laboratory method used for the

determination of the triple point of MMH

was a modification of the system described

by Colarusso and Semon (ref. 2). The

principal modification consisted of the

addition to the test cell of a means for

measuring the pressure exerted by the

fluid being tested. Figure 1 is a photograph of the test cell. The tube extending into the center of the cell contained

the thermocouple (Chromel-Alumel). The

fluid being tested was placed in the

large-diameter tube surrounding the tube

in the center of the cell. The side tube

with the metal fitting was connected to

the transducer used to measure the pressure exerted by the fluid vapors. The

pressure was measured by a 0- to

6895 pascals (0- to 1-psia full scale)

Datametrics multiple-range Barocell

transducer. Adjustment of the transducer range permitted accurate measurement of pressures as low as 0.69 pascal

(1 x 10-* psia).

The primary objective of the tests

described in this report was the determination of the observed triple point

of MMH under laboratory conditions and

under a spacelike environment. The

secondary objective of the tests was

the acquisition of MMH vapor pressure

data at pressures below 1724 pascals

Specifications, Space Shuttle Fluid

Procurement and Use Control. SE-S0073, rev. B, Feb. 9, 1975. (These

specifications have since been

superceded by SE-S-0073, rev. C, Feb.

14, 1977.)
Composition parameter Requirement Actual

Monomethylhydrazine

Monomethylhydrazine assay,

percent by weight

Water plus soluble impurities,

percent by weight

98.0 (min.)

2.0 (max.)

98.9

1.1

Nitrogen tetroxide

Nitrogen tetroxide assay,

percent by weight . . .

Nitric oxide assay,

percent by weight . . .

N204 plus NO,

percent by weight

Water equivalent,

percent by weight

Chloride content,

percent by weight

97.0 (min.)

1.5 (min.)

to 3.0 (max.)

99.5 (min.)

.20 (max.)

.040 (max.)

97.6

2.2

99.8

.06

<.04

A line at the top of the test cell

connected a liquid nitrogen trap and

vacuum pump to the system; the line

could be isolated from the test cell at

appropriate times in the test^procedure

by a glass vacuum stopcock.

The method used in the laboratory

closely followed that described by

Colarusso and Semon. The procedure

consisted of the following sequence of

actions after the MMH had been placed

in the test cell.

1. Through use of a monochlorotrifluoromethane/dry ice bath surrounding the test cell, the MMH was frozen,

and the space above the MMH was evacuated to remove dissolved gases.

2. The MMH was then allowed to

melt.

3. The process of freezing and

evacuation was repeated several times

(as many as six times) to thoroughly

remove the gases dissolved in the

fluid.

4. After the dissolved gases had

been removed, the temperature and pressure in the cell were monitored as the

temperature of the frozen material was

slowly increased.

5. The triple point was noted by

the presence of liquid around the

center core of frozen fluid and by the

change in the slope of the pressure

curve as a portion of the frozen fluid

transformed to the liquid state.

This method is very similar to

that used by the National Bureau of

Standards to determine the triple point

of fluids, characteristically in a

closed system that limits the amount

of material that may become vapor.

Reproducible results are obtained only,

when the dissolved gas content of the
Figure 1.- Laboratory apparatus for

measurement of triple point of

fluids.

Figure 2.- Test stand apparatus for

measurement of triple point fluids

under spacelike conditions.

fluid has been removed or reduced to

a minimum.

Test Stand System

A very large test stand (401) at

the WSTF was used to acquire triple

point data under spacelike conditions.

This test stand has an internal volume

of approximately 935 cubic meters

(33 000 cubic feet), which may be maintained at a desired vacuum through the

use of mechanical vacuum pumps. Figure 2 shows two identical test setups

used to ascertain the triple point of

MMH under spacelike conditions. Approximately 40 cubic centimeters of MMH were

loaded into the 1.27-centimeter-diameter

(0.5 inch) tubing assembly mounted above

the 6.35-millimeter (0.25 inch) solenoid

valves before closing of the test chamber.

As shown in the photograph, a

5.08-centimeter-long (2 inch) section

of 6.35-minimeter (0.25 inch) tubing

extended below the valve into the

10.16-centimeter-square (4 inch),

10.16-centimeter-high (4 inch), 0.13-

millimeter-thick (5 mil ) polytetrafluoroethylene bag. The bag was

supported by a wire frame to minimize

the conduction of heat into the MMH

contained in the bag. A bare-tip

Chromel-Alumel thermocouple was mounted

with the tip on the bottom of the bag.

The pressure in the test stand was

measured by a Barocell transducer

identical to that used in the

laboratory tests described in the

preceding section.

For each test, the pressure in the

test chamber was reduced to the desired

value by the mechanical vacuum pumps,

and then the MMH was introduced into

the bag by opening the solenoid valve.

The MMH in the bag was monitored (by

television) for the presence of a solid

phase while the temperature and pressure

were continuously recorded. The triple

point in these tests was defined as the

set of temperature and pressure conditions
at which the MMH was present in the bag

in both the liquid and solid phases.

A similar test setup was placed

adjacent to a window in the test stand

as shown in figure 3. This view of the

setup taken from inside the test stand

shows the placement of a solenoidactuated "arm" covered with foam

insulation; the arm was used to softly

strike the bottom of the bag to provide

some agitation to the MMH in the bag.

This setup permitted visual observation

of the MMH in the bag during several

tests.

The test results obtained by this

method provide data that more realistically relate to the behavior of the

fluid in a vacuum of unlimited volume,

because of the large ratio of teststand volume to test-liquid volume.

This spacelike condition requires that

the fluid being tested cool itself

(while in the open) by evaporation of

0.13-mm (5 mil]

,; polytetrafluoroi ethylene bag

a portion of the fluid. These triple

point test conditions more closely

resemble those that might occur in

space and differ significantly from the

laboratory test conditions for the

closely controlled measurement of the

triple point.

MMH TRIPLE POINT TEST RESULTS

Laboratory Results

Before the MMH triple point test,

the test system and procedure were

performance-checked using reagent-grade

carbon tetrachloride (CC1.) as the test

fluid. The literature values for the

triple point of CC14 calculated from

data cited by Moelwyn-Hughes (ref. 3)

are 250.2 K (-9.4° F) at 1082 pascals

(0.157 psia). Two laboratory tests

yielded identical values of 250.2 K

(-9.4° F) at 1069 pascals (0.155 psia).

The nearly perfect agreement with the

literature data confirmed that the test

system and procedure were satisfactory

for measuring the triple point of MMH.

The triple point pressure and

temperature data obtained using the

laboratory test system and procedure

are provided in table I. The data,

obtained on two samples of MMH, indicate that the average values for the

laboratory (closed system) triple point

are 219.4 K (-64.7° F) at 11.72 pascals

(0.0017 psia). Some variation in the

observed pressure may be due to leakage

of air into the test system. In any

event, the variation is not considered

significant because of the limited accuracy in measuring the relatively low

pressures involved.

The observed laboratory values for

the triple point of MMH are reasonably

close to the values of 13.79 pascals

(0.002 psia) at 220.8 K (-62.3° F)

indicated in the literature (but not

experimentally determined) by Atlantic

Research Corporation personnel.

Figure 3.- Test stand apparatus

equipped with remotely operated

agitation arm.
TABLE I.- TRIPLE POINT OF MMH USING LABORATORY METHOD

Sample

no.

1

1

1

1

1

1

1

1

2

2

2

Temperature,

K (OF)

219

219

219

219

219

219

218

219

220

220

220

.7

.2

.2

.2

.2

.2

.2

.7

.2

.2

.2

(-64

(-65

(-65

(-65

(-65

(-65

(-67

(-64

(-63

(-63

(-63

.3)

.2)

.2)

.2)

• 2)

.2)

.0)

.3)

.4)

.4)

• 4)

12

10

9

13

15

13

8

10

10

11

9

Pressure,

Pa (psia)

.41

.34

.65

.79

.17

.79

.96

.34

.34

.72

.65

(0.0018)

(.0015)

(.0014)

(.0020)

(.0022)

(.0020)

(.0013)

(.0015)

(..0015)

(.0017)

(.0014)

Average 219.4 (-64.7)

0.6 1.1

11.47 (0.0017

1.73 + 0.0003)

1.96 0.0003

Test Stand Results

The test system and procedure used

in the test stand triple point tests

conducted under spacelike conditions

were also evaluated using CC14 as a

reference material. Two tests yielded

the following results.

Observed temperature, Observed pressure,

K (0 F) Pa (psia)

248.8 (-11.9)

248.4 (-12.6)

1048 (0.152)

1000 (.145)

In both tests, the CC14 began to freeze

less than 2 minutes after being released

into the polytetrafluoroethylene bag.

It should be noted that, in this

method, cooling of the fluid to the

triple point is accomplished by removal

of heat from the fluid by evaporation into the very large volume of the test stand,

The amount of fluid evaporated does not

significantly affect the pressure in the

test stand. The amount evaporated was

sufficient to approach true vapor pressure

equilibrium conditions as indicated by the

constant temperature of the fluid after

the initial vaporization and subsequent

fluid cooling. The fluid temperature

was observed to remain constant as long

as the test stand pressure remained

constant. Because of the nature of the

cooling process, it is possible for the

fluid to become supercooled below the

triple point. The temperature and pressure values in the preceding paragraph

are lower than the literature and laboratory test values of 250.2 K (-9.4° F) at

1082 pascals (0.157 psia). However, the

differences were considered minor, leading

the experimenters to believe that the

procedure would effectively ascertain the

triple point of MMH under spacelike

conditions.

Before the MMH triple point tests

were conducted using the test stand,
the literature value for the melting

point of MMH was checked in the laboratory and found to be approximately

220.6 K (-62.60 F). Because the melting point of a material is near the

triple point, this temperature datum

was used to guide the triple point

tests conducted under space!ike conditions through comparison of observed

temperatures with the melting point.

Numerous attempts to observe the

triple point of MMH were made. Most

trials failed to produce solid MMH in

combination with liquid MMH but did

yield values of temperature and pressure, which are used in a later section

of this report to construct a new curve

for the vapor pressure of liquid-phase

MMH. On the basis of these tests, it

was concluded that liquid MMH will

supercool rather than freeze when

exposed to a pressure below the vapor

pressure (12.4 pascals (0.0018 psia))

at the normal freezing point (220.7 K

(-62.5° F)). In an attempt to counter

this tendency to supercool, some tests

were performed using the test setup

(fig. 3) in which the liquid MMH in the

bag could be agitated during the

cooling process.

Using that test setup, frozen MMH

was observed in combination with liquid

material approximately 3 minutes after

the MMH was released into the bag.

During this period, the liquid MMH was

agitated several times. When the

frozen MMH appeared, the fluid temperature was 211.5 K (-79.0° F) and the

pressure in the test stand was

3.72 pascals (0.00054 psia). The

quantity of frozen MMH increased with

test time, indicating a nonequilibrium

condition; the frozen MMH was present

in conjunction with liquid MMH for

several minutes. After 10 minutes,

all the MMH remaining in the bag had

frozen, as shown in figure 4.

As previously noted, once solidphase material had been obtained in

combination with liquid-phase material,

the liquid-phase material over a period

of time converted to the solid phase.

In recognition of this phenomenon, the

data obtained under spacelike conditions

Figure 4.- Frozen MMH at conditions

approaching the triple point.

should more appropriately be called the

effective freezing point rather than the

triple point of the material. Therefore,

the test stand tests indicated that the

effective freezing point of MMH under

spacelike conditions was 211.5 K (-79.0° F)

at 3.72 pascals (0.00054 psia).

MMH VAPOR PRESSURE TEST RESULTS

The numerous tests conducted in

the attempt to find the triple point of

MMH under spacelike conditions resulted

in the derivation of data on the temperature of liquid-phase MMH at the test

stand pressure under near-equilibrium

conditions. These results, therefore,

represent the vapor pressure data of the

MMH under stable temperature conditions.

The 15 vapor pressure data points given

in the literature and the 31 points

observed during the test stand triple

point tests are listed in table II. It

should be noted that the vapor pressure
values at several of the 31 temperature

points represent the average of two or

more actual observations.

The data in table II were smoothed

by the least-squares technique to an

equation of the form normally used to

relate vapor pressure as a function of

temperature.

log

vapor \

pressure^

= a + (absolute temp.)

c

(absolute temp.)

where a, b, and c are derived coefficients.

During the least-squares process,

the data were slightly weighted as

indicated in table II at the hightemperature end to compensate for the

large number of low-temperature points.

All the data points were found to fit

the following equations within less

than 3c variation.

689

(0.1)

68.9

. (.01)

6.89

(.001)

.689

•(.00011

Log (Pa) • 9.181 62

1 065. 025 088

K

158 905. 544 5 -

Log Haiti • 5.476 093 - 2E8.727760 .477730.2677

°R °R2

where °R -°F + 459.59

689 400

(100.0)

68940

(10.0)

6894

(1.0)

199.8 222.0 244.3 266.5 288.7 310.9 333.2

(-100) (-60) (-201 (20) (60) (100) (1401

Temperature, K (°F)

(.1)

355.4

(180)

Figure 5.- Calculated vapor pressure

of MMH. (The Systeme International

units correspond closely but not

exactly to this line because of

variation in significant figures.

The original measurements were

taken in customary units.)

log (Pa) =9.181 621 -

 1065f5

 °88

r\

158 905.5445

K

2

log (psia) = 5.476 093 -

; a = 170

2058.727 760

o

477 730.2677

R

; a = 0.0779

The derived equations were used

to provide the smooth calculated values

of vapor pressure at each temperature

listed in table II.

The existing literature values

ranged from 360.1 K (188.52° F) - the

normal MMH boiling point - to 275.2 K

(35.600 F). The new data extend the

vapor pressure data to 207.6 K

(-86.0° F), which is below the normal

freezing point of 220.7 K (-62.5° F);

therefore, these data include some

vapor pressure data for supercooled

MMH. The smoothed data listed in the

tables are graphed in figure 5.

N204 TRIPLE POINT TEST RESULTS

The test setup described earlier

was used to evaluate the behavior of

N204 containing 2.2 percent by weight

NO under spacelike conditions. For

these tests, the small reservoir previously used for MMH was replaced with

a 1-liter bottle containing N204. The

test procedure was similar to that used

for the MMH test, except the solenoid

valve was opened for 2 seconds to

deliver approximately 40 cubic centimeters of oxidizer from the N204 reservoir bottle under its own vapor

8
TABLE II.- VAPOR PRESSURE OF »IH

Observed

K

temperature,3 Observed vapor pressure. Calculated vapor

(OF) Pa (psla) pressure, "

Pa (psla)

Deviation, observed vs.

calculated,

Pa (psia)

Literature data0

360.11

354.67

351.07

343.34

337.81

331.68

325.77

319.72

313.07

309.47

298.36

293.73

290.33

284.93

284.26

(188.52) 99 154 (14.

(178.74) 81 551 (11.

(172.25) 71 423 (10.

(158.35) 53 331 (7.

(148.38) 42 582 (6.

381) 100 181 (14.530)

828) 82 599 (11.980)

359) 72 388 (10.499)

735) 53 938 (7.823)

176) 43 244 (6.272)

(137.36) 33 157 (4.809) 33 515 (4.861)

(126.71) 25 959 (3.

(115.82) 19 650 (2.

(103.86) 14 052 (2.

(97.38) 11 942 (1.

(77.38) 6 666 (.

(69.04) 5 162

(62.92) 4 234 (.

(53.21) 3 046 (.

(52.00) 3 551

765) 25 910 (3.758)

850) 19 671 (2.853)

038) 14 320 (2.077)

732) 11 976 (1.737)

-1027 (-0.149)

-1048 (-.152)

-965 (-.140)

-607 (-.088)

-662 (-.096)

-359 (-.052)

48 (.007)

-21 (-.003)

-269 (-.039)

-34 (-.005)

9668) 6 665 (.9667) .7 (.0001)

7487) 5 136 (.7449) 26 (.0038)

6141) 4 214 (.6112) 20 (.0029)

4418) 3 043 (.4413) 3.4 (.0005)

515) 2 916 (.423) 634 (.092)

Test stand data1*

282.04

275.15

274.26

269.26

267.59

267.04

263.71

263.15

255.37

254.82

247.59

246.48

245.93

244.82

243.15

238.71

238.15

234.82

234.26

230.37

229.26

226.48

225.37

223.15

221.48

218.71

217.59

214.82

210.93

208.71

207.59

(48.00) 3 489 (0.

(35.60) 1 615

(34.00) 1 717 (.

(25.00) 1 027

(22.0) 1 014

(21.00) 1 014

506) 2 537 (0.368) 951 (0.138)

2342) 1 618 (.2346) -2.8 (-.0004)

249) 1 524 (.221)

149) 1 076 (.156)

147) 951 (.138)

147) 917 (.133)

193 (.028)

-48 (-.007)

62 (.009)

96 (.014)

(15.00) 682 (.0989) 717 (.1040) -35 (-.0051)

(14.0) 696 (.

(.0) 352

(-1.0) 347

(-14.0) 177 (.

(-16.0) 177

(-17.0) 152

(-19.0) V34

(-22.0) 125

(-30.0) 84.8 (.

-31.0) 81.4 .

(-37.0 60.0 .

(-38.0) 55.2 .

(-45.0) 36.5 .

(-47.0) 34.5 .

(-52.0) 27.6 .

(-54.0) 17.9 (.

(-58.0) 13.8 (.

101) 688 (.0998) 8.3 (.0012)

0511) 374 (.0543) -22 (-.0032)

0504) 358 (.0519) -10.3 (-.0015)

0256) 194 (.0282) -17.9 (-.0026)

0256) 176 (.0255) .7 (.0001)

0221) 168 (.0243) -15 (-.0022)

0194) 152 (.0220) -18 (-.0026)

0182) 130 (.0189) -4.8 (-.0007)

0123) 85.5 (.0124) -.69 (-.0001)

0118 81.4 (.0118) .0 (.0000)

0087 58.6 .0085 1.38 .0002

0080 55.2 (.0080) .0 (.0000)

0053 37.2 (.0054) -.69 (-.0001)

0050) 33.1 (.0048) 1.38 (.0002)

0040) 24.1 (.0035) 3.4 (.0005)

0026) 21.4 (.0031) -3.4 (-.0005)

0020) 16.5 (.0024) -2.8 (-.0004)

(-61.0) 11.0 (.0016) 13.8 (.0020) -2.8 (-.0004)

(-66.0) 11.0 (.

(-68.0) 7.58 (.

(-73.0) 6.21 (.

(-80.0) 4.14 (.

(-84.0) 3.45 (.

(-86.0) 2.76 (.

0016) 10.3 (.0015) .69 (.0001)

0011) 8.96 (.0013

0009) 6.21 (.0009

0006) 3.45 (.0005

-1.38 (-.0002)

.0 (.0000)

.69 (.0001)

0005) 2.76 (.0004) .69 (.0001)

0004) 2.07 (.0003) .69 (.0001)

"To compensate for the large number of low-temperature data points, the three hightemperature points were weighted in the least-squares process by the following factors.

360.11 K (188.520 F) - 5

354.67 K 178.74° F) - 4

351.07 K (172.250 F) - 3

Additional weighting of the data was restricted by the least-squares program.

bLog (Pa) - 9.181 621 -

 1 065f5 08* - 158 9^544 5; 1700

(Log (psia) = 5.476 093 -

cRef. 4.

dRef. 5.

2 058.727 760 477 730.267 7.

OR (°R)Z

0

 = 0.0779.)
pressure (approximately 137 895 pascals

(20 psia)). As discussed earlier, in

this technique, the effective freezing

point of the fluid under spacelike conditions is actually determined rather

than the triple point. Accordingly,

the effective freezing point of ^04

containing 2 percent by weight NO was

determined to be approximately 259.4 K

(7.2° F) at 15 444 pascals (2.24 psia).

Figures 6 and 7 show the ^64 in the

bag when the temperature was near the

triple point. Figure 6 was taken

approximately 15 seconds after the

oxidizer was introduced into the bag.

The dark (green) liquid-phase oxidizer

can be seen on the bottom of the bag,

and some light-colored (light bluegreen) frozen oxidizer can be seen on

the sides of the bag. Figure 7, taken

Figure 6.- Photograph showing some

dark liquid-state ^0* present in

bottom of bag 15 seconds after introduction of the NoO*.

Figure 7.- Photograph taken a few

seconds after that shown in figure

6, showing frozen N~0, on sides of

bag. Some dark liquid-state N^O,

is still present on bottom of bag.

shortly after figure 6, shows that the

freezing process had progressed further,

but some dark (green) liquid-phase oxidizer was still present on the bottom

of the bag.

Because of limited test time, this

experiment was not repeated at a

slightly higher test stand pressure to

verify the values reported in the preceding paragraph. In several tests

conducted at lower pressures, the oxidizer froze immediately when released

into the bag. The literature value for

the triple point of pure N?04 containing little or no NO was determined in

1938 by Giauque and Kemp (ref. 6) to be

261.9 K (11.730 F) at 18 637 pascals

(2.703 psia).

10
CONCLUDING REMARKS

The tests conducted at the White

Sands Test Facility indicate that the

laboratory (closed system) value for

the triple point of monomethylhydrazine

(MMH) is 219.4 K (-64.7° F) at

11.74 pascals (0.0017 psia). These

values were found to be reasonably

close to the derived values reported

in the literature. It was concluded

that a true triple point determination

could not be made under space!ike

conditions, in which the fluid is

permitted to self-cool by evaporation.

It was observed in tests conducted

under spacelike conditions that, once

solid-phase material was obtained in

combination with liquid-phase material,

the liquid-phase material over a period

of time converted to the solid phase.

In recognition of this phenomenon, the

data obtained under spacelike conditions should more appropriately be

called the effective freezing point

rather than the triple point.

Accordingly, the effective freezing point of MMH with agitation under

spacelike conditions was experimentally

determined to be approximately 211.5 K

(-79° F) at 3.72 pascals (0.00054 psia).

It should be noted (1) that the effective freezing point of MMH under

spacelike conditions was very difficult

to observe because of the tendency of

MMH to supercool below the normal freezing point as a result of the evaporation

of the liquid phase, and (2) that the

effective freezing point may indeed be

even lower than 207.6 K (-86.00 p) in

the absense of agitation.

A side benefit of the various MMH

triple point tests was the acquisition

of new vapor pressure data at

temperatures below 275.2 K (35.60° F).

Literature data for vapor pressure of

MMH did not exist below this

temperature.

The new data were combined with

the previously published data for the

generation of equations yielding the

vapor pressure of MMH in both International System and conventional units.

The temperature range of the data is

from the normal boiling point to 207.6 K

(-86.0° F). This temperature is below

the normal freezing point of 220.7 K

(-62.5° F); therefore, some of the data

represent information obtained on supercooled MMH. All the data were found

to fit the equation satisfactorily.

An approximate value for the

effective freezing point of nitrogen

tetroxide containing 2.2 percent by

weight nitric oxide was also determined

under spacelike conditions. The value

was found to be approximately 259.4 K

(7.2° F) at 15 444 pascals (2.24 psia).

This value differs considerably from

the triple point values of 261.9 K

(11.73° F) at 18 637 pascals (2.703 psia)

determined using the 1938 laboratory

triple point technique on nitrogen

tetroxide containing little or no nitric

oxide.

Lyndon B. Johnson Space Center

National Aeronautics and Space

Administration

Houston, Texas, August 5, 1977

986-15-00-00-72

REFERENCES

1. Gift, Ralph D.; Simmons, John A.;

et al.: Study of Propel 1 ant

Valve Leakage in a Vacuum:

Final Report, June 7, 1965, to

Aug. 15, 1966. NAS9-4494,

Atlantic Research Corporation,

Alexandria, Virginia, Oct. 28,

1966.

2. Colarusso, Vincent G.; and Semon,

Michael A.: Measurement of

Calibration Standards for Thermometry. Analytical Chemistry,

vol. 40, no. 10, Aug. 1968,

pp. 1521-1524.

3. Moelwyn-Hughes, E. A.: Physical

Chemistry. Pergammon Press,

2nd ed. 1961, reprinted with

corrections 1964.

•11
4. Handbook of the Properties of

Unsymmetrical Dimethylhydrazine

and Monomethylhydrazine.

Aerojet General Corp., Rep. 1292,

May 1958.

5. Aston, J. 6.; Fink H. L.; Janz,

G. J.; and Russel, K. E.: The

Heat Capacity, Heats of Fusion

and Vaporization, Vapor Pressures, Entropy and Thermodynamic

Functions of Methylhydrazine.

J. American Chem. Soc., vol. 73,

no. 5, May 1951, pp. 1939-1943.

Giauque, W. F.; and Kemp, J. D.:

The Entropies of Nitrogen Tetroxide and Nitrogen Dioxide. The

Heat Capacity from 15°K to the

Boiling Point. The Heat of

Vaporization.and Vapor Pressure.

The Equilibria N204 = 2N02

= 2ND +62- J. Chem. Phys.,

vol. 6, Jan. 1938, pp. 40-52.

12
. 1. Report No. 2. Government' Accession No.

NASA RP- 1013

4. Title and Subtitle

TRIPLE POINT DETERMINATIONS OF MONOMETHYLHYDRAZINE AND NITROGEN TETROXIDE (2. 2 PERCENT BY

WEIGHT NITRIC OXIDE)

7. Author(s)

Irwin D. Smith, Johnson Space Center, and Patr

Lockheed Electronics Company, Inc.

ick M. Dhooge,

9. Performing Organization Name and Address

Lyndon B. Johnson Space Center

Houston, Texas 77058

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration

Washington, D.C. 20546

3. Recipient's Catalog No.

5. Report Date

November 1977

6. Performing Organization Code

JSC- 12876

8. Performing Organization Report No.

S-475

10. Work Unit No.

986-15-00-00-72

11. Contract or Grant No.

13. Type of Report and Period Covered

Reference Publication

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

A series of tests was performed to ascertain the triple points of monomethylhydrazine and

nitrogen tetroxide. A laboratory method indicated a triple point for monomethylhydrazine,

but tests in a large vacuum chamber indicated that a triple point does not occur in spacelike

conditions because the monomethylhydrazine tends to supercool. Instead, an effective freezing

point (with agitation) was obtained. New experimental values for liquid monomethylhydrazine

vapor pressure were determined for temperatures from 275.2 to 207.6 K. The values were

used to derive vapor pressure equations. Tentative values were obtained for the effective

freezing point of nitrogen tetroxide under spacelike conditions. :

17. Key Words (Suggested by Author(s))

Chemical fuels Vacuum tests

Monomethylhydrazine

Melting points

Vapor pressure

Nitrogen tetroxide

18. Distribution Statement

STAR Subject Category:

28 (Propellants and Fuels)

19. Security Qassif. (of this report) 20. Security Classif. (of this page)

Unclassified Unclassified

21 . No. of Pages 22. Price*

15 $3.50

'For sale by the National Technical Information Service, Springfield, Virginia 22161

NASA-Langley, 1977
National Aeronautics and

Space Administration

Washington, D.C.

20546

Official Business

Penalty for Private Use, $300

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