NASA Technical Reports Server (NTRS) 19650009674: Effect of Liquid Nitrogen Dilution on LOX Iimpact Sensitivity

NASA TM X-53208

NASA TECHNICAL
MEMORANDUM

NASA TM X-53208

FEBRUARY 15, 1965

N65-1927S

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EFFECT OF LIQUID NITROGEN DILUTION ON
LOX IMPACT SENSITIVITY

by C. F. KEY AND J, B. GAYLE

Propulsion and Vehicle Engineering Laboratory

NASA

George C Marshall
Space Flight Center ,

Huntsville , Alabama

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TECHNICAL MEMORANDUM X -5 320 8

EFFECT OF LIQUID NITROGEN DILUTION ON
LOX IMPACT SENSITIVITY

By

C. F. Key and J. B. Gayle
George C. Marshall Space Flight Center
Huntsville, Alabama

ABSTRACT

An experimental investigation was carried out to study the decrease
in reactivity of materials with liquid oxygen (LOX) that is caused by
dilution of the LOX with liquid nitrogen (LN 2 ). A wide range of materials
was selected for testing, each of which previously had been shown to
be sensitive to impact in LOX. Tests were made with the ABMA LOX
Impact Tester using LOX/LN 2 mixtures ranging in concentration from
20 percent LOX in LN 2 to pure LOX. The results showed that relatively
large proportions of LN 2 were required to effect an appreciable decrease
in reactivity; however, all materials tested were insensitive to impact
at 10 kg-m in liquid air.

NASA- GEORGE C. MARSHALL SPACE FLIGHT CENTER

TECHNICAL MEMORANDUM X-53208

EFFECT OF LIQUID NITROGEN DILUTION

ON LOX IMPACT SENSITIVITY

By C. F. Key and J. B. Gayle

George C. Marshall Space Flight Center
Huntsville, Alabama

NASA-GEORGE C. MARSHALL SPACE FLIGHT CENTER

TABLE OF CONTENTS

Page

SUMMARY 1

INTRODUCTION 1

EXPERIMENTAL 2

Test Method 2

Sample Preparation 2

Preparation of LOX/LN 2 Mixtures 3

Materials Tested 3

Results 4

CONCLUSIONS 5

REFERENCES 6

iii

4

LIST OF ILLUSTRATIONS

Figure Title Page

1 Test Setup for Determining Change in
Composition of LOX/LN 2 Mixtures in

Dewar ^

2 Orsat Analyses of LOX/LN 2 Mixtures

in Dewar 8

3 Test Setup for Determining Change in

LOX/LN 2 Mixtures With Samples 9

4 Orsat Analysis of LOX/LN 2 Mixtures With
Samples (Nominal Composition, 50% LOX,

50% LN 2 ) 10

5 Effect of LN 2 Dilution on LOX Impact

Sensitivity of Micarta 11

6 Effect of LN 2 Dilution on LOX Impact

Sensitivity of Hexcell 91 LD Honeycomb 12

7 Effect of LN 2 Dilution on LOX Impact

Sensitivity of HT-424 Adhesive 12

8 Effect of LN 2 Dilution on LOX Impact
Sensitivity of Nylon Epoxy Adhesive

FM-1000 i4

9 Effect of LN 2 Dilution on LOX Impact Sensitivity

of E-Bond Rubber Sealant 1018 12

10 Effect of LN 2 Dilution on LOX Impact Sensitivity

of Hexcell Polyurethane Insulation 1414-2. .... 1^

11 Effect of LN 2 Dilution on LOX Impact Sensitivity

of Red Wing Silicone Rubber 17

12 Effect of LN 2 Dilution on LOX Impact Sensitivity
of 5A1-2. 5 Sn Titanium Alloy, 0. 063 -Inch

Thick 18

IV

LIST OF ILLUSTRATIONS (CONCLUDED)

Figure Title Page

13 Effect of LN 2 Dilution on LOX Impact

Sensitivity of Mylar, 1-Mil Thick 19

14 Effect of LN 2 Dilution on LOX Impact

Sensitivity of Magnolia Foam 7015-1 ^9

15 Effect of LN 2 Dilution on LOX Impact
Sensitivity of CPR-20 Insulation Density-

4# /Ft 3 21

16 Effect of LN 2 Dilution on LOX Impact

Sensitivity of CPR 1021-2 Foam 22

17 Effect of LN 2 Dilution on LOX Impact
Sensitivity of HRP Honeycomb Filled With

CPR 1021-1 Foam Bonded to 2016-T6 Aluminum.. 23

18 Effect of LN 2 Dilution on Threshold Valves for

Various Materials 24

v

EFFECT OF LIQUID NITROGEN
DILUTION ON LOX IMPACT SENSITIVITY

By

C. F. Key and J. B. Gayle
George C. Marshall Space Flight Center

SUMMARY

An experimental investigation was carried out to study the decrease
in reactivity of materials with liquid oxygen (LOX) that is caused by
dilution of the LOX with liquid nitrogen (LN a ). A wide range of
materials was selected for testing, each of which previously had been
shown to be sensitive to impact in LOX. Tests were made with the
ABMA LOX Impact Tester using LOX/LN 2 mixtures ranging in
concentration from 20 percent LOX in LN 2 to pure LOX. The results
showed that relatively large proportions of LN 2 were required to effect
an appreciable decrease in reactivity; however, all materials tested
were insensitive to impact at 10 kg- m in liquid air.

INTRODUCTION

Many materials in contact with LOX constitute fire and/or explosion
hazards when subjected to impact, shock, heat, or other forms of
energy; organic materials are especially hazardous under these
conditions. Although the degree of hazard is decreased when LOX/LN 2
mixtures are substituted for LOX, evidence of sensitivity has been
noted for some materials which were tested with mixtures containing
30 percent LOX by weight. However, conclusive evidence to prove that
no hazard exists even with mixtures containing only 20 percent LOX
(liquid air) has not been obtained.

A previous investigation ( tef. 1) indicated that there is a small
but finite probability of occurrence of a catastrophic reaction if damaged
LH 2 insulation is subjected to a suitable stimulus during or subsequent
to LH 2 hold. This occurs because air is condensed within the damaged
insulation and, subsequently, may be enriched in oxygen by reevaporation
and condensation processes.

The possibility of condensation of liquid air on engineering
materials is not limited to LH 2 insulation. Moreover, the probable
extent of enrichment of condensed air by reevaporation and condensation
processes is difficult to assess, either experimentally or analytically.
Therefore, an experimental investigation of the effects of LN 2 dilution
on the LOX impact sensitivity of selected engineering materials was
made to obtain additional information on this problem.

Most of the samples used for this study were prepared by the
Non-Metallic Materials Branch of this division.

EXPERIMENTAL
Test Method

The apparatus used for all of the tests reported herein was the
ABMA LOX Impact Tester. The mechanical features and operational
details of this tester have been described comprehensively in other
reports ( ref. 2) and will not be repeated herein. In principle, this
test involves dropping a standard plummet of known weight (9.04 kg)
from known heights (up to 1. 1 meters) under near-frictionless conditions.
This plummet strikes a pin which is resting on a layer of the material
being tested in the bottom of an expendable aluminum alloy cup. The
remainder of the sample cup is filled with the test mixture. During a
test, a material capable of reacting with the test mixtures will explode
and/or flash brilliantly. The highest energy level that is withstood by
a given material without any indication of sensitivity in 20 trials denotes
the hazard associated with the material under test when it is used in
LOX systems.

Sample Preparation

All metals and elastomers were tested in the form of 11/16-inch
diameter discs. Composite insulations and foams were tested as 1/2-
inch squares. Type 347 stainless steel inserts were used as false
bottoms for the sample cups. This technique was necessitated by the
early discovery that some hard materials could give a false indication
of impact sensitivity under the conditions that are imposed by the test
procedure.

2

Preparation of LOX/LN 2 Mixtures

The LOX/LN 2 mixtures used for the tests reported herein were
prepared by weighing the required amount of LOX and adding the
necessary quantity of LN 2 to give the desired total weight of mixture.

The liquid nitrogen was added to the LOX, and the mixture was stirred
with a precooled spatula.

To check the accuracy of the composition of the mixtures, analyses
were made of control mixtures using an Orsat gas analyzer and a phase
diagram to determine the composition of the liquid. In each instance,
the mixture was analyzed after being made up for varying periods of
time to determine the effect of boil- off on concentration. The details
of the test setup are shown in FIG 1; typical results are given in FIG 2.

Inspection of these data indicates, as expected, that the increase
in LOX concentration on standing was greatest for those mixtures
containing the smallest percentage of LOX. During the 20-minute period
normally required for the testing of 20 samples at any given energy
level, the average deviation from the nominal LOX concentration was
positive and ranged from less than 2 percentage points for the 50/50
mixture to approximately 3 percentage points for the 20/80 mixture.
These deviations would not be expected to influence appreciably the
results which were obtained during this investigation.

In addition, analyses were made of the actual mixture used for
several test samples. This was done by placing samples in the aluminum
test cups which then were placed in a steel tray surrounded by an LN 2
moat. The test mixture was poured into the precooled pan and then ana-
lyzed. The test setup is shown in FIG 3, and typical results (FIG 4)
agree closely with those obtained from the Dewar analyses.

Materials Tested

The materials which were selected for testing represent a wide
range of physical and chemical properties; however, each previously
had been found to be impact sensitive in 100 percent LOX at 10 kg-m.

The materials and the thicknesses in which they were tested were as
follows:

3

Thickness

Material (Inches)

Micarta

0. 063

Hexcell 91 LD Honeycomb

0.25

HT-424 Adhesive

0. 013

FM-1000 Adhesive

0.010

E-Bond Rubber Sealant H1018

0.050

Hexcell Polyurethane Insulation 1414-2

0.250

Redwing Silicone Rubber

0.063

5A1-2. 5Sn Titanium Alloy

0.063

Mylar

0.001

Magnolia 7015-1

0.25

CPR 20 Insulation

0.25

CPR 1021-2 Foam

0.25

HRP Honeycomb filled with CPR 1021-2
Foam, Glued to 2016-T6 Aluminum

0.44

Results

— C

The results are presented graphically in FIG 5 through 17. Each
plotted point represents the percentage of reactions in at least 20 tests.

Results for most of the materials indicate that relatively large
proportions of LN 2 were required to reduce the reaction frequencies
of to increase the threshold energy levels appreciably. This is further
demonstrated in FIG 18 in which the observed threshold levels (the
energy levels corresponding to a zero reaction frequency) are plotted
as a function of the mixture ratio. Inspection of the results indicates
that the rate and extent of decrease vary widely and probably are
characteristic of the individual materials. However, addition of 8
percent of LN 2 to the LOX generally resulted in a decrease in the
threshold energy level, of roughly 1 kg-m.

Even highly sensitive materials apparently did not react in 20/80
mixtures (liquid air). However, reactions were noted with several
materials at only slightly greater LOX concentrations (30/70), and it
is possible that other materials would react with liquid air under suitable
stimuli.

4

Mylar, which gave a reaction frequency of only 20 percent in LOX
at 10 kg-m remained slightly sensitive at a LOX concentration of only
30 percent at an energy level of 8 kg-m.

The relatively large quantities of LN 2 required to desensitize most
materials indicate that desensitization is due to a dilution or inerting
effect rather than to any tendency of the LN 2 to chemically or otherwise
inhibit the reaction.

HRP Honeycomb filled with CPR- 1021-1 foam was impact sensitive
down to 3 kg-m when tested in a 30/70 mixture. It is interesting to
note that the CPR-1021-2 foam tested alone was not sensitive at 10 kg-m
in a 80/20 mixture. The results of these tests indicate the difficulty
in predicting the sensitivity of a composite material from the sensitivity
of its components.

CONCLUSIONS

The results of this investigation indicate the following:

1. The sensitivity of most materials to impact with LOX is
decreased by dilution of the LOX with LN 2 .

2. The extent of dilution necessary to effect an appreciable
decrease in reactivity is large; thus, although all materials tested were
insensitive in liquid air (20 percent LOX), several were sensitive at

30 percent LOX, and the sensitivity of some materials at 50 percent
LOX approached that in pure LOX.

3. The mechanism of the process probab^r involves a simple
inerting action.

4. The sensitivity of a composite material is not a simple
function of the sensitivities of its individual components.

5

REFERENCES

Key, C. F. and Gayle, J. B.: Preliminary Investigation of Fire

and Explosion Hazards Associated with S-H Insulation. NASA
TM X-53144, October 2, 1964.

Lucas, William R. and Riehl, Wilbur A. : An Instrument for

Determination of Impact Sensitivity of Materials in Contact with
Liquid Oxygen, ASTM Bulletin, February I960, pp. 29-34.

NOMINAL COMPOSITION
50 PERCENT LOX

T

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8

amon ni nsoaxo iN3Da3d ihoism

ELAPSED TIME, MINUTES

FIGURE 2. ORSAT ANALYSES OF LOX/LN 2 MIXTURES IN DEWAR

FIGURE 3. TEST SETUP FOR DETERMINING CHANGE IN LOX/LN 2
MIXTURES WITH SAMPLES

9

lN30d3d 'ADN3n03dd N0llDV3d

11

IMPACT ENERGY, kg-m

FIGURE 5. EFFECT OF LN 2 DILUTION ON LOX IMPACT SENSITIVITY OF MICARTA

100 PERCENT LOX

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IMPACT ENERGY, kg-m

FIGURE 7. EFFECT OF LN 2 DILUTION ON LOX IMPACT SENSITIVITY
OF HT-424 ADHESIVE

14

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IMPACT ENERGY, kg-m

FIGURE 10. EFFECT OF LISL DILUTION ON LOX IMPACT SENSITIVITY
OF HEXCELL POLYURETHANE INSULATION 1414-2

UQDH36 'ADH3n03Ud NOIlDYaa

17

IMPACT ENERGY, kg-m

FIGURE 11. EFFECT OF LN 2 DILUTION ON LOX IMPACT SENSITIVITY
ON RED WING SILICONE RUBBER

18

lN33N3d 'ADN3n03dd N0llDV3a

IMPACT ENERGY, k g-m

FIGURE 12. EFFECT OF LN 2 DILUTION ON LOX IMPACT SENSITIVITY
OF 5A1-2. 5Sn TITANIUM ALLOY, 0. 063-INCH THICK

T

T

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T

T

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8 S S S 8

IN 3DM3d ADH3n03dd NOI13V3d

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IMPACT ENERGY, kg -m

FIGURE 13. EFFECT OF LN 2 DILUTION ON LOX IMPACT SENSITIVITY OF MYLAR, 1-MIL THICK

100 PERCENT LOX

t 1 — 1 T

20

lN3Dd3d 'ADN3n03Hd N0I1DV3H

IMPACT ENERGY, kg-m

FIGURE 14. EFFECT OF LN ? DILUTION ON LOX IMPACT SENSITIVITY OF MAGNOLIA FOAM 7015-1

22

iN3Dd3d 'ADNanoaad noiidy3H

IMPACT ENERGY, kg-m

FIGURE 16. EFFECT OF LN 2 DILUTION ON LOX IMPACT SENSITIVITY OF CPR 1021-2 FOAM

lN30H3d 'ADN3nD3dd N0I13V3U

23

IMPACT ENERGY, kg-m

FIGURE 17. EFFECT OF LN 2 DILUTION ON LOX IMPACT SENSITIVITY OF HRP HONEYCOMB
FILLED WITH CPR 1021-1 FOAM BONDED TO 2016-T6 ALUMINUM

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DILUTION ON THRESHOLD VALUES FOR VARIOUS MATERIALS

February 15, 1965

APPROVAL

NASA TM X- 53208

EFFECT OF LIQUID NITROGEN DILUTION
ON LOX IMPACT SENSITIVITY

By C. F. Key and J. B. Gayle

The information in this report has been reviewed for security
classification. Review of any information concerning Department of
Defense or Atomic Energy Commission programs has been made by
the MSFC Security Classification Officer. This report, in its
entirety, has been determined to be unclassified.

This document has also been reviewed and approved for technical
accuracy.

Chief, Chemistry Branch

W. R. LUCAS

Chief, Materials Division

TR r.T .TNTF. /

M- B - ™

Acting Director, Propulsion

and Vehicle Engineering Laboratory

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