9960

COMPATIBILITY OF TANK COATINGS AND MATERIALS WITH LIQUID PROPELL/AN t o

SUMMARY REPORT

December 1965 Through September 1968

For

Picatinny Arsenal Project

Order No. A1-8-RFO-01-D1-GG

Commanding Officer

Picatinny Arsenal, Dover, N.J. 0780 1 Attn: Code SMUPA DL-2

Liquid Rocket P ropulsion Laboratory

To

NATIONAL BUREAU OF STANDARDS
I
NATIONAL BUREAU OF <3 « i“t NDARDS REPORT

MBS PROJECT

3120465 December 5, 1968

MBS REPORT

9960

COMPATIBILITY OF TANK COATINGS AND MATERIALS WITH LIQUID PROPELLANTS

By

J. P. Young, G. I. Reid, and V. A. Lamb

SUMMARY REPORT

December 1965 Through September 1968

For

Picatinny Arsenal Project

Order No. A1-8-R F 0 34-0 1 - D 1 - G

G

To

Commanding Officer

Picatinny Arsenal, Dover, N.J. 07801

Attn: Code SMUPA DL-2

Liquid Rocket Propulsion Laboratory

NATIONAL BUREAU OF ST

for use within the Government, and review. For this reason, thr whole or in part, is not author Bureau of Standards, Washingtc

the Report has been specifically

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

ss accounting documents intended

subjected to additional evaluation

listing of this Report, either in

e Office of the Director, National

ry the Government agency for which

opies for its own use.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Compatibility of Tank Coatings and Materials with Liquid Propellants

Summary Report of Work Done from December 19&5 through September 1968

By the National Bureau of Standards., Washington, D 0 C 0 20234

1 o Bac kg round of Prob 1 em

The high tensile strength (up to 300,000 psi), and hardness of l 8$>

Ni Maraging steel permit fabrications for high pressure use that weigh

less and are less bulky than when made from lower density metals. These

characteristics are desirable for material from which to make liquid

propellant tanks for rockets.

During the Fall of 19^5 NBS was asked by Picatinny Arsenal for information on the feasibility of using metallic coatings to protect liquid fuel

rocket tanks from corrosion by the fuel and at the same time protect the

fuel from catalytic decomposition by the relatively active Maraging steel

and minimize formation of metal salts in the fuel that could have an adverse

effect on rocket engine performance. Electroless nickel was considered as

a likely coating for the interior surfaces of assembled Maraging steel fuel

tanks because it could be applied without use of electrodes and without

current and its thickness over complex and recessed surfaces was very

uniform. Other metals suc t

~> as nickel, cadmium and silver were also considered because there were conflicting reports of the reactivity of electroless nickel with liquid rocket fuels,^^

1. Compatibility of Materials with Rocket Propellants and Oxidizers,

DMIC Memo 201, Battel le Memorial Inst,, Jan, 1965°

As a preliminary step in the program, several specimens of heattreated, 18°lo Ni Maraging steel were coated with electroless nickel,

electroplated nickel and tungsten and sent to Picatinny Arsenal for

testing and evaluation., Concurrently, a program was initiated at MBS

to apply numerous metallic coatings to 18^ Maraging steel specimens and

to expose these specimens to liquid rocket fuels to determine their

suitability for application and use in liquid rocket fuel tanks . The

program also included the experimental application of the more promising

coatings to one-half scale and full scale liquid rocket fuel tanks for

development of methods of application and for further testing of the

coatings

.

2. Tests for E xposi n g Coa t ings on Maragin g Stee l

It was requested by Picatinny Arsenal that the tests of the coatings

and fuel be made at the most rigorous condition that might be expected to

occur during storage of missile rocket motors. In storage sheds in the

desert, e.g., temperatures of l6o°F might be expected to be reached, while

in artic regions the temperature could drop to ~65°F. Since chemical reactions are usually most rapid at the higher temperatures, the specimens

were to be exposed to the fuel at l6o°F except for a few tests to be run

at room temperature for comparison.

The planned storage life of the rocket motors was about six years.

Therefore, exposure tests must be at least of one year duration to be

meaningful. Some of the more promising materials were to be exposed to

the fuel for longer periods of time.

2

The liquid rocket fuel to be used in the tests was MHF-3,? a combination of hydrazine compounds containing 8GJo monomethyl hydrazine and 1 4$

( 2 ) anhydrous hydrazine. The fuel would be freshly mixed and sealed with

the specimen in a suitable test unit. The test unit would determine the

rate of catalytic decomposition of the fuel by measuring the volume of

evolved gas or by pressure increase in a closed system. Gas evolution

from the fuel is proportional to fuel decomposition and is a critical

factor in the storage of fuel.

3 . Eq uipment for E xposure

Many metals cause catalytic decomposition of hydrazine and its

derivatives, and many non-metals either react with or are dissolved by

( 2 ) hydrazines. Therefore, the materials of the exposure-test units had to

be selected carefully. It was found that most of the pipe fittings and

gages on the market were made from stainless steels that were reported to

be incompatible with the fuel. Glass was inert to the fuel but making

joints and valves leak-proof was very difficult.

3« 1 Glass Units

Because of the difficulty of procuring metal fittings of the

correct composition, the first units were made of glass. Trial and error

(3) (4) and the experience gained by other workers' } ' J resulted in a completely

fusion-sealed unit without valves, ground glass joints etc.

2. fhe Handling and Storage of Liquid Propellants. Office of the Director

of Defense Research and Engineering, U.S. Government Printing Office,

1963 . 3 . Dr. A. J. Beardell, et al, Thioxotropic Packaged Liquid Propellants,

Report RMD 5020-F, Contract No. n 600( 1 9)59348 (Navy Bur. l/ep„).

1 Oct. 1962 to 30 Sept. I 963 .? Thiokol Corp., Reaction Motors Div.,

Danvil 1 e, N . J

.

4. Advanced Packaged Liquid Propellants Research, RMD-5074-Q.1 , Contract

No. 65 - 6570 , 12 August 1965 . Thiokol Corp., Reaction Motors Div.,

Danville, N.J.

3

These units incorpora ted a chamber for holding the fuel and the specimen

and had an attached manometer to measure any gas released by catalytic

decomposition or by reaction with the specimen,, A diagram of the unit

is shown in Figure 1« Mercury was used for the manometer fluid,, Although

( 2 ) supposedly reactive with the fuel mercury had been used in contact with

MHF-3 by others ^ ^

The units were made from pyrex glass tubing. The ends of the

specimen chamber were left open for loading the unit with the specimen and

fuel. All areas which the fuel vapor contacted were arranged to be below

the surface of the constant temperature bath to reduce the transfer of the

fuel to the manometer side of the unit by condensation. Only the manometer

tube containing mercury protruded from the surface of the bath. A porous

frit with holes too small to permit the passage of mercury was installed

between the test chamber and the manometer to prevent accidental amalgamation of the specimen. The enlargement in one side of the manometer tube

formed a mercury chamber which permitted use of the shallow temperature bath

and resulted in a compact unit.

3.2 Meta 1 Units

A source of supply of compatible 3®b stainless steel fittings was

finally located and several metal test units were assembled with a test

chamber machined from solid stock. The units consisted of a test chamber with

a bolted cover connected to a bleed valve and a pressure gage as shown in

Figure 2. A pyrex glass cup held the fuel and specimen., electrically

insulating the latter from the metal test chamber. No gages could be obtained

made from JOk stainless steel so gages of pi 6 stainless steel were used.

k

The metal units were much more expensive than the all-glass^ fusionsealed units. They were also less reliable mainly because of difficulty in

obtaining sufficiently tight valve and cover seals,. Only four of the

metal units were used for fuel tests at l6o°F.

3 . 3 Cons t ant Tempera ture Bath s

Baths were constructed to maintain the units at l6o°F. They

consisted of insulated metal or glass tanks with internal spacer blocks

to position the units during the testo Several fluids for the baths were

considered but water was decided upon for reasons of safety

.

4 . Tests of Coatings in MHF-3

4.1 P reparation o f t he Specimen s

Small specimens (15 cm

2

) were used for the testing of a number of

coatings and some other materials. Specimens to be plated were cut from

Maraging steel sheet which had been heat-treated. The surface was chemically

or mechanically descaled., e 1 ectropol ished and given a nickel strike before

being plated with the coatings to be tested. The strike was necessary

because the inherent passivity of Maraging steel prevents the adhesion of

( 5 ) deposits unless special procedures are used. ' It consisted of acid nickel

chloride solution which was more reactive with the Maraging steel surface tha

standard plating solutions. The strike bath was used for plating the

specimen for only about one minute after a one minute immersion. The various

deposits were immediately applied over this very thin nickel coating. After

plating^ the specimens were carefully rinsed and dried. They were weighed

before and after plating to check deposit thickness and establish a basis for

determining loss of weight due to corrosion by the fuel.

5. G. DiBari (international Nickel Co.) Plating 52^ 1159 09^5)

4 o 2 L oading o f Test Unit s

The units were loaded through the open bottom of the tube forming

the specimen chamber. After placement of the specimen, the bottom of the

chamber was sealed by fusing and drawing the glass,, then cooled and flushed

with dry nitrogen . The narrow top of the specimen chamber,, through which

the fuel would later be loaded, was then sealed by fusion,. The units were

pumped down to a low pressure and all the seals were checked with a spark

type, high voltage leak tester,, The mercury was then added to the manometer

and the units pressurized to the limit of the manometer tube with

nitrogen as an added leak check of the entire unit,, After ten days to two

weeks,, if no leak was shown by a drop of the mercury column,, the units were

opened by breaking the seal at the top of the specimen chamber and the fuel

added to cover the specimen,, A plastic syringe attached to a long, flexible

Teflon tube was used to introduce the fuel to the lower end of the bulb.

A temporary closure was then made with Teflon tubing. This charge of fuel

was left in place about a week to flush and precondition the specimen and

interior surface of the unit. The fuel was then removed with the syringe

and replaced with fresh fuel. The filling tube was then resealed by fusion,

after which the unit was flushed with nitrogen to remove air introduced

during sealing. This was accomplished by pushing a small Teflon tube through

the mercury into the chamber above the mercury and through this tube successively pressurizing with nitrogen and then bleeding several times. After inspection of the seal under magnification, to check for complete fusion, the unit

was placed in the constant temperature bath to begin the test. The metal,

bomb-type units were leak-checked, loaded and flushed with nitrogen in similar

steps. Loading of fuel was done in a fume hood with the necessary protective

6

gloves, clothing, and transparent shielding.

5 ° Exposure Tests

5 o 1 Measurement of Evolved Gas

The glass manometer type units had a centimeter scale attached to

the manometer tube which allowed reading the change in the height of the

mercury column which indicated changes in the pressure and volume of the

gas evolved from the fuelo Evolved gas in the bomb type units was

indicated by an increase in the gage reading.,

5 ° ^ Calculation of Rate of Fuel Decomposition

The rate of fuel decomposition was expressed in terms of the

volume of gas evolved in a given time, or in terms of the pressure developed

(6) in a given time in a tank of defined size and ullage' '

.

For the glass units, both pressure and volume change as gas is

evolved by decomposition of the fuelo The equation:

AV -

V 2

P2"V

1 P (0

gives the amount of gas evolved, measured at atmospheric pressure (p ), where

a

Vj and are initial and final total volume in the unit and

p^

and p^ are

initial and final pressure, respectively. The volume of the zero point

of the manometer was determined from initial calibration of the unit. From

this value and measured shift of manometer level, and were calculated.

Height of the mercury in the manometer plus atmospheric pressure yielded

values of

p^

and p^. The amount of gas evolved as calculated from equation (l),

is due in part to decomposition at the surface of metallic specimen, due to its

6. V. A. Lamb, et al, Surface Protection of Maraging Steel, NBS Progress

Reports Nos NBS 9377 and NBS 9638- Contract No. A 1 -8~RF03^--01 ~D 1 -GG,

Picatinny Arsenal, Dover, N.J.

7

catalytic effect, and in part from inherent tendency for the fuel to

decompose at other locations., e.g., in the liquid itself, in the vapor

phase, and at the glass fuel interfaces. The latter are referred to as

"background decomposition". The "background" has been determined in

identical units except that no metal specimen was present. V, due to

background decomposition , which was found to be very small in the case of

MHF-3 in glass units., is subtracted from V of equation (

1 ) to obtain the

amount of gas evolved due to the effect of the metallic specimen itself.

For the bomb-type units.,

V, (p2

-p,

AV =

Pa

In this case, the initial gas volume in the unit, Vj is constant.

Since the rate of gas evolved due to contact of a given metal with

the fuel will be proportional to the area of the metal and to time of contact,

reactibility may be expressed in terms of a single coefficient defined as rate

of gas evolved per unit area per unit time, or

AV

rate coefficient = -7——^

— = cnF

J /cm2/day (3)

The rate of decomposition has also been expressed in terms of tank

pressure after one year, assuming a one cubic foot tank with 10$ ullage,

and with the entire inner surface active. Pressure in this assumed tank will

obviously be proportional to the rate coefficient defined previously. It

can be shown that the relationship is:

P = (IO560) (rate coefficient) ( 4 ) y 3 g

8

where P is gage pressure in psi after one year. The numerical factor

Y;3

takes account of tank surface., ullage^ and conversion of the rate coefficient

from metric units to psi. In a tank with 5$ ullage instead of \QPjo ullage

the pressure would be doubled 0

The above relationships are all based on the simple gas laws.

The calculations of AV, rate coeficient, and P are laborious, especially

when as many as 50 units are under test at one time. Manual calculations for

three months of data from 30 units required approximately two man-weeks. The

calculations have therefore been programmed for the computer and require only

about 8 hours to punch on tape and to calculate the data from 50 units,

6 . Results o f Tests of Specimens Ex posed to MHF-5

It was initially considered that a test for the duration of one year

would be sufficient to give reliable data on a given specimen. Later it was

decided to run several of the more promising materials for a longer period

because rate changes after prolonged exposure occurred in a few cases.

However^ enough data has been accumulated to give the initial performance of

the various materials tested.

Most of the tests were run on specimens consisting of a metallic coating

on \&Io Ni Maraging steel. Some uncoated materials such as bare Maraging

steel and several stainless steels were also tested,

6 . 1 Room Temperature Tes ts

Three metallic coatings on Maraging steel plus bare Maraging steel

were exposed at room temperature. The lowest rates were obtained with cadmium

and zinc while cobalt caused nearly as much decomposition of fuel as did the

bare Maraging steel .

9

Rate curves for these specimens are shown in Figure 3° In calculated tank

pressure per year, the spread was from 51 psi for the cadmium coating to

1+32 psi for bare Maraging steel „

6 e 2 Tests a t 1 6o° F

The tests run at l60°F approximately corroborate the findings at

room temperature, except for cobalt, which accelerated to nearly ten times

that for bare Maraging steel » Rate curves for several of the coatings and

materials are shown in Figure 4. The slightly lower rates for cadmium and

zinc at i6o°f was attributed to the formation of a protective oxide film

at the higher temperature. Bar graphs for these and most of the other

specimens tested are shown in Figure 5® Grouped according to rate of fuel

decomposition , the various coatings and materials are as follows:

Low Activity: 0 to 80 psi/year calculated tank pressure - silver,

cadmium, standard electroless nickel, zinc, tin-nickel

alloy, tin, lead, tungsten, 50/50 lead-tin solder,

3^7 stainless steel, aluminum foil, and two titanium

alloys, 6 A 1 - 4 V and 3 A 1 - 11 Cr- 15 V.

Moderate Activity: 80 to 250 psi/yr - gold, nickel, stainless

Maraging steel, electroless nickel from the proprietary

borohydride bath,, chromium, and Teflon coated Maraging

steel

o

High Activity: 250 to 10,000 psi/yr - Cobalt, 19$ Maraging steel,

molybdenum, iron, electroless nickel from the

alkaline bath, AM-355 stainless steel and Inco - 718°

6 c 3 Sup p lementary Experiments with MHF-3 F uel

6„3°1 Porosity Tests

Tests were made to determine the effect of porosity in

coatings of silver and cadmium on Maraging steel exposed to Mh'F-3 at loO°F 0

Simulated pores were made in the coatings by drilling through the coatings

just deep enough to expose the Managing steel . Pore diameters ranged from

0.013 inch to 3/8 inch. The decomposition rates were calculated on the

basis of the area of Maraging steel exposed by the pores. It was found that

the rate of fuel decomposition is roughly proportional to pore area. Fuel

exposed to the Maraging steel -silver couple decomposed at a higher specific

rate, based on the exposed area of Maraging steely than that exposed to

Maraging steel alone. The contrary effect., occurred with the cadmium plated

specimen. The rate of gas evolution., based on the area of Maraging steel

exposed, was smaller than that for Maraging steel alone. It is hypothesized

that there may be a bimetallic, electrolytic effect., the cathodic silver

exerting an accelerating effect and the anodic cadmium a protective effect.

6.3.2 Effect o f t he Ratio of Area of Metal to Volume of Fuel on MHF-3 Fuel Decomposition

Units were set up which contained 100 cm2 of nickel surface

compared to about 15 cm2for the usual specimen tested. The decomposition

rates at l6o°F showed that, for a range of area/volume from 0.5 to 6.8,

there was no significant difference in the rate coefficient of fuel decomposition .

6.3.3 Decomposition Rate of Surface Area and Fuel Volume

Experiments were designed to show the effects of glass or

metal areas and fuel volume on the rate of fuel decomposition designated as

"background rate". It was found that the glass-vapor interface and the

liquid-glass interface area have a negligible effect on decomposition of the

fuel. The dominant factor in "background" decomposition is the volume of

the fuel. That is, sel f-decomposition in the liquid phase. This rate is,

however, very small, of the order of 0.0002 cm

3 of gas/day/cm3 at l6o°F.

6.3.4 Effect of Contact Between Metal and Fuel Vapor

The fuel decomposition rate of a Maraging steel specimen

exposed at l60°F to the fuel vapor phase only, was initially very low. But

the rate gradually increased to more than 60°jo of that for contact with the

liquid. This indicated that condensation of liquid on the metal surface

became an important factor with increase in time.

7 . Results of Examination of Specimens and MHF-3 Fuel After Tests

A number of the tests that had run for a year or more at room temperature and at l6o°F were discontinued. The units were disassembled carefully

and the fuel and any corrosion products were retained for examination.

7 . 1 Corrosion of Metals

Electroless nickel on Maraging steel showed no loss in weight of the

coating while zinc was the most severely corroded of the metals tested. Both

cadmium and nickel underwent appreciable corrosion and some other metals a

lesser amount. In the case of the nickel there was a tendency toward pitting

on some specimens. This attack occurred both at room temperature and at loO°F.

The cross-section of a nicke 1 -pi ated, welded Maraging steel specimen showed

good coverage of the nickel over the weld. The following metals had no

weight loss or, at most, a few milligrams, which corresponded to the loss of

a few microinch in thickness: cobalt, Maraging steel, lead, tungsten, tinnickel alloy, tin, iron, molybdenum and silver. The concentrations of metal

salts that were dissolved in the MHF-3 fuel are shown in Figure 8.

There was no correlation between the activity of a metal in

accelerating decomposition of the fuel and corrosive attack on the metal.

Thus, bare molybdenum, one of the most active decomposers of fuel, was uncorroded, while zinc, one of the least active, was severely corroded.

12

Standard electroless nickei had a low activity and was not corroded.

In the special porosity tests, only the silver plated specimens

have been examined to date, A cross section of one of the drilled "pores"

showed slight corrosion of the exposed Maraging steel at the sides of the

pore beneath the silver, causing slight undercutting and enlargement of the

pore cavity in the Maraging steel.

7 . 2 Effects of MHP-3 Fuel Used in Tests

In cases where corrosion occurred, there was discoloration of the

fuel or a precipitate or both. This was caused by the salts formed due to

dissolution of the metal Involved. The concentrations of the dissolved salts

were evidenced by a coloring and darkening of the fuel and were determined

by evaporating a known volume of fuel and weighing the residue. These values

ranged from 0.02 g/1 for silver through 0.27 for zinc to 16.3 g/1 for the

fuel from a nickel plated specimen in the form of a Maraging steel tube with

aluminum end caps. The original unexposed fuel contained 0.04 g/1 of

dissolved solids which was deducted to give the preceding values.

The salts which were obtained from the fuel and scraped from the

specimens and dried could not be detonated by impact. This indicates that

they were not azides.

8 . General Con c 1 usions from Resu l ts of Tests of Metals In MHF-3

The results thus far obtained from exposure tests and subsequent

examination of coatings on Maraging steel indicate that several show

promise. Coatings in the group having low rates of fuel decomposition

mentioned earlier ( 6 0 2 ), had a satisfactorily low catalytic effect on

decomposition of MHF-3 and could be considered for use in coating fuel

13

tanks with the exception of zinc, which was excessively corroded,, The

most interesting are those coatings which were least active in fuel decomposition , were least corroded, lowest in cost and the most easily applied

,

Of the low activity coatings thus far tested, silver was the least active,

cadmium the lowest in cost and electroless nickel the most easily applied .

Silver might be ruled out because of its initial cost which leaves electroless

nickel and cadmium as the most practicable coatings for fuel tanks, based on

results obtained to this point in the inves tigation

.

9 • Experimental Plating of Fuel Tanks

Fittings designed for plating one-half scale fuel tanks are shown in

Figure 6. These Maraging steel tanks were plated through a small hole in

one end. Plating solution was circulated by pump from a reservoir, through

a filter and then into a hollow internal anode and thus to the bottom of the

tank. Solution from the top of the tank was conducted by a return line back

to the reservoir.

Two tanks were plated by this method, one each with nickel and cadmium.

Several tanks were plated with electroless nickel. Similar equipment was

used, but with no current supplied to the inlet tube. A hot water bath was

used to maintain the near-boiling temperature necessary for plating electroles

nicke 1

.

A carbon steel, Simula ed full size rocket fuel tank was designed with

a bolted-on end in place of the usual welded end to allow disassembly for

inspection after havxng been plated while ful ly assembled. A rocket assembly

was used to agitate the plating solution contained in the tank and to prevent

the collection of gas in upper corners which would prevent plating or reduce

plate thickness in those areas. This tank was plated with electroless nickel

o

The solution was introduced and circulated through a small hole in the top.

A band heater on the outside was used to maintain plating temperature. A

smooth and continuous deposit about 2 mils thick was obtained on the inside of

the tank. Since this tank was plated^ changes made in the design include a

comparatively large opening in the top of the tank so that all types of

plating can be done more easily.

Y - -

. 10. I

ests of Materials Exposed to Aerozine-50

As an extension of the tests of materials exposed to MHF-3 four specimens

have been exposed to Aerozine-50 (anhydrous hydrazine 50$ and unsymmet rica

1

dimethyl hydrazine 50$ by volume). In contact with 18$ Maraging steely its

rate of decomposition was approximately 1+0 times greater than that of MHF-3.

However., the rates with titanium and Teflon were near zero after deducting the

background rate which was about four times that for MHF-3« A sprayed coating

of Teflon on aluminum gave a high rate of fuel decomposition possibly because

of reaction with residual solvents or plasticizers in the coating.

1 1 . Tests _of Various Materials in Oxidizers

At the request of the sponsor^ the program was extended to test the

interactions between tank material and oxidizers.

11.1 Equipment for Exposing Specimens to Oxidizers

The glass units designed for fuel tests could not be used for

tests Involving oxidizers because of the two chosen for testing^ the nitrogen

tetroxide^ or NTO^ had a vapor pressure which was too high for practical

manometer length and the hydrofluoric acid inhibitor in the Inhibited red

( 2 ) fuming nitric acid ; or IRFNA^ attacked the glass. v ' Therefore,, it was

necessary to use all stainless steel units.

15

In view of the high vapor pressure of the NTO at l6o°F, it was

decided that a bomb design like that of Figure 2 would not be sufficiently

leak-proof. To run tests in this oxidizer, high-pressure bombs were

purchased. These stainless steel units had a compression ring seal and

compression fittings. However, it was necessary to use an additional

aluminum foil gasket under the compression ring to obtain a seal that

permitted no detectable leak in two weeks at a pressure of 300 psig.

The unit used with the IRFNA was similar to the unit shown in

Figure 2 except that the glass liner was not used. Metal specimens in both

types of bombs were insulated from metallic contact with the unit by a small

Teflon cap at each end of the specimen.

An oil bath was used for maintaining the temperature of the bombtype units. It consisted of a stainless steel tank deep enough to cover the

large,, high-pressure units and included a shelf for the smaller bombs

containing IRFNA. As in the water baths for units containing fuel, the

temperature was maintained at l6o°F by a resistance heater coupled to an

electronic controller.

11.2 Exposure of V ari ous Materials to Oxidizers

The decomposition rates of NTO and IRFNA caused by contact with

Maraging steel. Teflon (TFE), and 301 stainless steel (cryogenic form - aged)

were relatively low, as shown in Figure 8 . A unit has just been started

containing a specimen of titanium. The background rate for a unit containing

NTO without a specimen was 0.0417 crrr'/day.

A separate test of NTO in the form of a thin-walled tank of 301

stainless steel (cryogenic form - unaged) was run at 90 °F and 10$ ullage.

Thus far there has been no measurable evolution of gas.

16

Specimens exposed to IRFNA at l6o°F were Teflon (TFE)^ Maraging

steel j Teflon-coated 606I-T6 aluminum and 301 stainless steel (cryogenic

form - aged). After the first few weeks of testing^ the oxidizer decomposition rate suddenly increased rapidly. It was assumed that the

inhibitor^ 0.7^ hydrogen fluoride^ had been depleted to a level that was

no longer effective. After refilling the units with fresh oxidizer and

inhibitor no further rapid rise in pressure has occurred.

17


Figure 1 . Most recent design of glass test unit for measuring

gas evolved from decomposition of fuel 0

Features

1. No Part of bulb assembly projects from l6o°F bath^

reducing condensation in upper parto

2, Cross-arm slopes toward bulb,, so any condensation in

this portion of bulb assembly drains back to bulb,

3® Glass frit retards diffusion to and condensation

of vapor into manometer side. It also prevents accidental transfer of mercury to fuel bulb.

4. Completely sealed unit prevents leaks.

5 . Initial flushing with nitrogen and periodic bleeding

are accomplished through a 2 mm diameter Teflon tube

inserted from the atmosphere side through the mercury

column

.



Figure 2„ Metal Test Unit

A. Specimen

Bo Fuel

C. Aluminum gasket

D. Pipe fittings, 1/8-inch stainle

Eo Inlet flushing valve, stainless

F. Outlet flushing valve, stainles

Go Safety relief valve, stainless

Ho Hose connection, stainless stee

lo Pressure gage, stainless steel

J« Glass liner

K» Vessel,

s steel

s tee 1

steel

teel

stainless steel
H XI

/Z/MmMMM Scale. ' I/I

240

220

200

ISO

160

140

120

100

SO

60

40

20

0

Rai

200 300 400

Time (days)

Figure 3

of gas evolution from MPIF-3 in contact v/ith indicated metals at

mperature . Metal ares, of each specimen approximately 15 cm2 c

100

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Figure 6. Arrangement for Plating Maraging Steel Cylinder

Scale: schematic wlevi, 1" = 4"

detail of head^ 1" = 1"

Arrows show flow of plating solution*

A. Cylinder

B. Combination anode and inlet tube for

plating solution

C. Plating solution in reservoir tank

D * Pump

E. Filter

F» Detail of inlet tubej 5/1 6 " o.d OJ 1/4" i„d OJ stainless steel

Go Nickel plate on inlet tube^ l/l6" thick

Ho Fabric bag surrounding anode

I. PVC plug

Jo PVC tubing for plating solution exit

K. Taper pipe thready 3/4" NPT


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Concentration

of

dissolved

salts

in

MHF— 3

fuel

from

test

units

as

determined

by

evaporation.

Deducted

0.04

g/l

solids

in

unexposed

fuel.

Dissolved

metal

salts a

iv

aca

necessarily

proportional

to

amount

of

corrosion

as

usually

some

precipitate

was

formed.

The

generally

lower

concentrations

at

l60°F

are

explainer

by

formation

ofa

greater

amount

of

precipitate

ora

protective

oxide.

301

Stainless

steel

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