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AD NUMBER

AD807349

NEW LIMITATION CHANGE

TOApproved for public release, distributionunlimited

FROMDistribution authorized to U.S. Gov't.agencies and their contractors;Administrative/Operational Use; FEB 1967.Other requests shall be referred to US AirForce Rocket Propulsion Laboratory, Attn:RPPR/STINFO, Edwards AFB, CA 93523.

AUTHORITY

AFRPL ltr 27 Oct 1971

THIS PAGE IS UNCLASSIFIED

b 4 , AFRPL-TR-67-50

HALOGEN PASSIVATION STUDIES

Contract No. F04611-67-C-0033

W. A. Cannon, W. D. English, and N. A. Tiner

Astropower Laboratory, Missile & Space Sys*ems DivisionA Division of Douglas Aircraft Company, Inc.

TECHNICAL REPORT AFRPL-TR-67-50

Fehruary 1967

"This document is zu7.jcct tc &pecial export controls and Br-Amittal to foreign governments or foreign nationals maybe made only"with prior approval of AFRPL (RPPR/STINFO), Edwards, California93523.11

Air Force Rocket P-'opalhon '•aboiatc'-yResearch and Technrlogy Divisio.)

Air Force Sysiamu CommandEdwards Air Force Base, California

NOTICES

When Government drawings, specifications, or other data are used for anypurpose other than in connection with a definitely related Governmerit pro-curement operation, the United States Government thereby incurs no rea-ponsibility nor any obligation whatsoever; and the fact that the Governmentmay have formulated, furnished, or in any way supplied the said drawings,specifications, or other data, is not to be regarded by implication or bther-wise as in any manner licensing the holder or any other person or corporation,or conveying any rights or permission to manufacture, use, or sell anypatented invention that may in any way be related thereto.

mA

AFRPL-TR-67 -50

HALOGEN PASSIVATION STUDIES

Contract No. F04611-67-C-0033

W. A. Cannon, W. D. English, and N. A. Tiner

Astropower Laboratory, Missile & Space Systems DivisionA Division of Douglas Aircraft Company, Inc.

TECHNICAL REPORT AFRPL-TR-67-50

February 1967

"This document is subject to special export controls and each trans-mittal to foreign governments or foreign nationals may be made onlywith prior approval of AFRPL (RPPR/STINFO). Edwards, California93523.1"

Air Force Rocket Propulsion LaboratoryResearch and Technology Division

Air Force Systems CommandEdwards Air Force Base, California

!i

FOREWORD

This report was prepared by Astropower Laboratory, Advance Systemsand Technology, Missile and Space Systems Division, Douglas AircraftCompany under Air Force Ccntract F04611-67-C-0033. The contract wasadministered by the Air Force Rocket Propulsion Laboratory, Research andTechnology Division, Air Force Systems Command, Edwards Air ForceBase, California, with Lt. Ralph Fargnoli as Project Engineer.

This report covers word done on the halogen passivation studies duringthe period from I November 1966 to 31 3anuary 1967. The report was pre-pared by W. A. Cannon and W. D. English, under the supervision of N. A.Tiner.

Publication of this report does not constitute Air Force approval of thereport's findings or conclusions. It is published only for the exchange andstimulation of ideas.

W. H. Ebelke, Colonel, USAFChief, Propellant Division

ABSTRACT

This progress report covers experimental work accomplished duringthe period from 1 November 1966 to 31 January 1967. During this timeexperiments were carried out to define requirements which must be met toresnove organic contaminants f."c-n metal surfaces during pzssivation influorine. Metal coupons, porous stainless steel discs and glass capillarieswere contaminated with various organic materials and exposed to gaseousfluorine and chlorine trifluoride vapor under a variety of conditions simu-lating typical passivation procedures. The conventional passivation proce-dures at room temperature and at moderate pressure are ineffective forremoval of thin smears of organic contaminants from metal substrates.

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TABLE OF CONTENTS

Section I INTRODUCTION AND SUMMARY I

Section II EXPERIMENTAL 3

1. Reaction of Gaseous Fluorine withPotential System Contaminants 3

a. Apparatus and Procedures 3b. Contaminants 4c. Observations 5

2. Reaction of Chlorine Trifluoridewith System Contaminants 10

a. Apparatus and Procedure 10b. Observations 10

3. Reaction of Gaseous Fluorine withContaminated Porous Stainles Steel 10

a. Apparatus and Procedures 10b. Contaminant Fluids 10c. Observations 12

4. Reaction of Gaseous Fluorine with DyePenetrant Fluid in Glass Capillaries 12

a. Apparatus and Procedure 12b. Contaminant 12c. Observations Iz

5. Presence of Residual Oils in RolledAluminum Sheet Stock 12

Section IW FUTURE WORK 15

Iw

SECTION I

INTRODUCTION AND SUMMARY

This is the first of a series of quarterly reports covering work donefrom I Novembt~r 1966 through 31 January 1967 on Contract No. F04611-67-C-0033. The major objectives of the subject contract are: (1) investi-gation of methods for producing the most suitable passive films on variousmetals; (2) tc.tlig effectiveness of the passivation procedure on systemhardware components; and (3) preparing detailed procedures for obtainingthe most durable passive surfaces.

The work has been divided into four phases for the purpose of pursuingthe technical objectives of the contract. These phases are to be approachedconsecutively and are outlined in order as follows:

Phase I - Passive Surface Investigationa. Role of Contaminantsb. Residual Fluorinec. Mechanical Stability

Phase 11 - Analysis of Passivation Methods

Phase III - Testing of Passivation Methods (developed in Phase II todemonstrate effectiveness, practicability and reliability)

Phase IV - Recapitulation of Passivation Methods (to prepare a designguide for simple systems)

The major technical effort described in the first quarterly report dealswith Phase I investigations, primarily the role of contaminants.

Reactions of fluorine and chlorine trifluoride with gross potential sys-tem contaminants are described. The results to date have not been en-couraging from the standpoint of relying on passivation for removal of finaltraces of contaminants. Fluorine and chlorine trifluorid. in the concentra.tions proposed for passivation of metal surfaces react only slightly with

* typical organic contaminants when the latter are present an thin smears ona metal substrate.

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SECTION 1

EXPERIMENTAL

1. REACTION OF GASEOUS FLUORINE WITH POTENTIAL SYSTEM

CONTAMINANTS

a. Apparatiis and Procedures

The reactions of fluorine gas with typical system contaminants hasbeen investigated as part of the Phase I studies dealing with the role of con-taminants in the passivation process. It was desired, inscfar as possible,to expose typical contaminants to fluorine in a manner simulating a passiva-tion process. Two test methods were employed. The first method was astatic fluorine exposure test in which the contaminant, smeared on a metal(nickel ZOO) coupon, was evacuated then exposed to fluorine in a closed sys-tem. A glass vessel was used so that reaction could be observed directly.The second test system had a double-ended glass tube through which eithernitrogen or fluorine, or any desired mixture of the two gases, could beflowed continuously over the specimen. Schematics of the two systems areshown in Figure 1.

Two different modes of fluorine injection were used with each of thetest systems. One mode used a slow. incremental buildup of fluorine pres-sure or concentration while the other provided a sudden application of themaximum fluorine pressure or concentration to the test specimen. The de-tailed procedures are described below.

(1) Static System - Incremental Pressure Buildup

With the specimen in place in the Pyrex tube, the system isfirst evacuated. Gaseous fluorine is admitted to a pressure of one psia fora period of five minutes, then the tube is again evacuated. The alternatefive-minute pressurisations with gaseous fluorine :ind evacuations are con-tinued at pressure levels of 2, 4, 8, and 15 pSia. The specimen is keptunder continuous observation from behind a safety shield during the ex-posure. Neglecting the time required to bring the pressures to the desiredlevels and for pumping out the fluorine between exposures, the specimensare exposed for a total of 25 minutes at gradually increasing fluorine pres.sure.

(2) Static System - Sudden Pressure Buildup

The contaminated specimen is first evacuated, then the sys-tem is abruptly pressurised to 15 pela with fluorine gas. After five minutes,the tube is pumped out. The specimen is kept under continuous observation.

3

(3) Flow System - Incremental Concentration Buildup

With the specimen in place in the Pyrex tube, aflow of gaseousnitrogen at a rate of 100 ml per minute is established through the tube.Gaseous fluorine is then added to the stream in flow increme"-10 of 10 ml/minute with five-minute intervals between increases until the flow rate ofgaseous fluorine is 50 ml/minute. The flow rate of gaseous nitrogen is thendecreased in decrements of 10 ml/minute until only pure fluorine is flowi•rgin the system. After five minutes in pure fluorine the flow is shut off andthe tube is purged with pure nitrogen. The specimen is observed frequentlyduring the test. The total exposure time following this procedure is approxi-mately 75 minutes with a gradually increasing partial pressure of fluorine.

(4) Flow System - Sudden Concentration Buildup

With the specimen in place in the tube, a nitrogen flow rateof 100 ml/minute is established. The flow of gaseous fluorine is abruptlyincreased to 50 ml/minute while the nitrogen flow rate is simultaneouslydecreased to zero. After five minutes the fluorine flow is stopped and thetube purged with pure nitrogen.

(5) Static System - High Pressure

For static test exposures of contaminated specimuns it higherpressures, an all metal system was used. This was similar to the staticsystem shown in Figure I except that the Pyrex tube was replaced with anequivalent section of one inch O.D. stainless steel tubing closed at one endand having an AN closure at the other end for connection to the gas manifold.

b. Contaminants

The following representative contaminants have been used in thisphase of the investigation.

Vaseline - Petroleum Jelly U.S. P

KEL-F 90 - Halocarbon Stopcock Grease

Pydraul AC - Phosphate Type Industrial Hydraulic Fluid

Polyurethane - Polyurethane Foam Insulation

Acrylic Lacquer - Commercial Clear Lacquer in Aereol Dispenser

Coupons 0.5" x Z" were cut from 0. 0Z5" nickel 200 sheet stock. Alimited number of similar coupons of 2014 aluminum, 316 stainless steel,and Monel 400 were also used in this pha&e of the investigation. The edgesof the coupons were filed to remove burrs. All coupons were acid etchedand LOX cleaned to ce-•iove corrosion products and traces of oil and grease.Thin, uniform films of cucvtaminants were applied individually to one side ofseparate coupons. Vasellne and KEL-F 90 were applied by smootf lng onwith glass rods. The Pydraul AC was applied as a small droplet from a

4

glass rod. It did not spread uniformly on the surface of substrute, howevei.The polyurethane foam was mixed and cured in place on the coupon. It doesnot foam uniformly duc apparently to low temperature during cure. Theacrylic lacquer was applied as a single wet coat from the aerosol dispenser.After final weighing the specimens were stored in a dust-free envirowmentuntii ready for e:posure.

Due to difference in film application the loading varied considerablyamong the various contaminants. In later experiments an effort was madeto m•ih.tain the loading at a level near 50 mg per coupon. The calculat'dfilm thickness for vaseline at this loading is 4. 5 mils.

c. Ob6 rvations

Table I gives the data for a series of tests of contaminated nickelcoupons exposed to fluo:ine gas in the static system at a maximum pressureof one atmosphere and at room temperature. Except for the KEL-F 90specimens and oneof the polyurethaneo-coated specimens, small weightgains were observed. None of the films ignited. Minor changee in appear-ance were observed only for vaseline and Pydraul AC while the 1tbers wereunchanged.

Tablo- ili gives data for a similar series of experiments with theflow system. Similar results were obtained. Generally either weight gainsor very small weight losses were observed.

Different alloys were used for coupons in the series of static sys-n m experiments in Table IMI. Only vaseline was used as the contaminant.

All specimens except one lost weight, but the weight changes were smallcompared to the total amount of contaminant present.

In view of the apparent minor amount of reaction taking place in theexperiments described above, contaminants were exposed to fluorine gas at50 psig for one hour in a static system at room temperature. The. data arepresented in Table IV. Even at this pressure there was no ignition, but therelative weight gains of the vaseline film were greater. KEL-F 90-coatedspecimens lost weight.

T!,ege e- -)eriments confirm that fluorine gas under conditions ofpressure, concentration and temperature frequently employed for systempassivation, iu relatively ineffective for reacting with and removing typicalorganic system cortamninants. Although some materials do undergo partialreaction, as evidenced by weight changes and alterations of appearance, thereactioi.s appear to be limited largely to fluorination reactions rather thancomplete reaction to volatile reaction products.

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2. REACTION OF CHLORINE TRIFLUORIDE

WITH SYSTEM CONTAMINANTS

a. Apparatus and Procedure

The static system (Figure 1) was used and chlorine trifluoridevapor was introduced abruptly to the evacuated system containing the con-taminated coupon. A maximum pressure of one atmosphere was used withthe system initially at room temperature.

b. Observations

The results for vaseline and KEL-F 90 contaminated nickel 200coupons are given in Table V. The vaseline film ignited in chlorine tri-fluoride proving that this medium is more reactive than fluorine at equiva-lent pressure. However, the residue left weighed approximately 50 percent more than the original vaseline film. The KEL-F 90 film liquified andbubbled. This behavior is attributed to the reaction of the chlorine tri-fluoride with the finely-divided silica used as a thickener in the grease, toform silicon tetrafluoride.

3. REACTION OF GASEOUS FLUORINE WITH CONTAMINATED

POROUS STAINLESS STEEL

a. Apparatus and Procedures

Filtermet stainless steel (type 316) filter elements in disc form1/ 16" thick and I/2" diameter were impregnated with Halocarbon oil anddye penetrant fluid. Samples covering a range of porosities from about 30to 50 per cent were used. Mean pore sizes were on the orderof'30 microns.

Impregnation was carried out by immersing the discs in the re-spective fluid, heating under vacuum to about 500 - 600C to remove airfrom pores, then releasing the vacuum and cooling the specimens under theimpregnating fluid. Finally the specimens were removed from the fluid andthe surfaces superficially dried by blotting with absorbent paper. The im-pregnated specimens were tested for reaction with fluorine by exposure inthe static test system to fluorine gas at one atmosphere for one hour atroom temperature.

b. Contaminant Fluids

Halocarbon Oil - Series 13-21 Halocarbon Products Corporation.

Dye Penetrant Fluid - Contrast Dye Penetrant-MIL- L-25135,Group 1. This material partially volatilized during the vacuum impregnationof the porous stainless steel discs.

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The results of the exposure of the contaminated specimens tofluorine gas are given in Table VI. The Halocarbon impregnated specimenswere unchanged in weight or appearance. The Dye Penetrant-impregnatedspecimens burst into flame upon itiltial pressurization with fluorine. Theflame subsided after a few seconds after which pressurization with fluorinewas resumed and exposure continued for one hour. The weight losses of thespecimens ranged from 10 to nearly 50 per cent of the original weight ofcontaminant.

4. REACTION OF GASEOUS FLUORINE WITH DYE PENETRANTFLUID IN GLASS CAPILLARIES

a. Apparatus and Procedure

Two Pyrex glass capillaries, one 100 micron and the other 30micron inside diameter were filled with Dye Penetrant fluid. One inchsections of each capillary were broken out and the filled capillaries exposedindividually in flowing fluorine gas in the flow system (see Figure 1). Thetubes were kept under continuous observation with a binocular microscopeduring the exposure.

b. Contaminant

Dye Penetrant Solution - Contrast Dye Penetrant-MIL- L-25135,Group 1.

c. Observations

After about five minutes exposure the dye penetrant fluid in the100 micron capillary turned black or dark blue at the meniscus. Thischange from the initial red color penetrated further into the fluid in thecapillary to a depth of about 400 microns after one hour. The meniscuswas originally 700 microns inside the capillary and did not recede furtherduring the exposure of one hour. In view of these observations it seemsthat only a very slow reaction takes place due to slow diffusion into and outof the capillary.

The observations with the 30 micron capillary were similar except

the depth of discoloration in the fluid was only about 100 microns.

5. PRESENCE OF RESIDUAL OILS IN ROLLED ALUMINUM SHEET STOCK.

It has been observed in previous activities unrelated to this project thatsome commercial aluminum and copper foils have oils or fatty acids rolledinto fissures or surface defects and that these materials are not readilyremoved by any conventional degreasing process. The contaminants fre-quently reveal themselves during vacuum work with the foils at which timeit is found that surfaces are slow to outgas under high vacuum. When heated

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to several hundred degrees in vacuum the foils may release considerableamounts of fatty acids which condense in coolez parts of the vacuum sys-tem. The implication of these observations is that during the rollingprocess, a fatty acid, probably stearic acid, is used to lubricate the rollsand that this material is forced under high pressure into minute fissures inthe surface. The passageways connecting these fissures with the surfaceare either partially closed off or are of such small dimensions that normalcleaning and degreasing operations are inefficient.

A total of 50 specimens 1/2" x 4" were sheared from 2014 aluminumsheet stock. These were LOX cleaned by a conventional technique describedas follows:

Dye wiped off with acetone

Oakite dip for 30 seconds, followed by immediate water flush

Dried in nitrogen

Vapor degreased in trichlorethylene

Dipped in Freon

Dried in nitrogen

Following the cleaning process the strips were enclosed in plastic bagsand were handled only with degreased forceps.

The degreased strips (total area ZOO square inches) were sealed into a30 mm OD Pyrex tube which in turn was connected to a high vacuum systemwith a 5 nun Pyrex tube. The large tube was heated slowly with a tubefurnace t- 00oC while under a vacuum of 10-5 torr or -ower. As the tern-perature . -oached 200O( a slight fogging inside the 5 mm connecting tubewas noted a- a point immediately outside the tube furnace. The fogging in-creased until finally discrete, oily droplets could be obiserved. When nofurther increase in volume of the oil could be detected, the tube was cooledwhile still under vacuum. Finally the section of the connecting tube con.taining the oil was cut out. The total quantity of molecularly distilled oilwas estimated to be about I milligram. It was identified from its infraredspectrum as a fatty acid.

Identical experiments were carried out with aluminum 2024 and nickel200 specimens. The results were completely negative, i. e., no trace ofmaterial was molecularly distilled from the materials.

Within the limited scope of the experiments, it seems that either nocontamination problem exists with commercial sheet stock used in this pro-ject or that the problem is minor. It is probable that one milligram of con-taminant per 200 square inches of sheet stock represents an insignificantlevel of contamination. If any problem arises in this regard, it should be asimple manner to remove most or all of any contamination of this type by amild etching of the sheet stock prior to degreasing.

14

SECTION III

FUTURE WORK

The projected Phase I studies to be completed in the next quarterly

period are outlined as follows.

1. ROLE OF CONTAMINANTS

Additional work will include impact testing of contaminated porousstainless steel and aluminum test coupons. The contaminated porous bodieswill be exposed to various passivation cycles, then will be subjected to im-pact tests in the ABMA drop weight tester in liquid fluorine.

Surface contaminated coupons will be subjected to various passivation

procedures and impact tested as described above.

2. EFFECT OF RESIDUAL FLUORINE

Work will be initiated on the effects of residual fluorine on corrosionof matal surfaces.

3. MECHANICAL STABILITY TESTS

The flexure tests for passivated bellows specimens will be completedduring the next quarterly period.

15

UNCLASSIFIEDsecudy Cisasificatica

HAOGEMNT ASIVTION SATU RDIE

Qurtpoerl Reporat- ovebe 196truh3 a Uary ASSIFIEMAUOissi(leE and Spae ytem Divsio a &ROU

A. A. Canoon, Do !as Engciaht Cmand, Inc.Aie

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Ga. COTAC 0A G~5.IWRHANT NO. s

his document is subject to special export controls and each transmittal to foreignoverninents or foreign nationals may be made only with prior approval of AFRPLRPPR/STINYQ *) Edward, California 935Z3.I. SUPPL9SMEUARY 00n.3 it. SPft$00100 WI.IARY ACTIVITY

Air Force Rocket Propulsion LaboratoryResearch and Technology Division rlAir Force Systems Command

13 ASS?3ACY Edwards Air Force Base. Californiaia 35Z3

This progress report covers experimental work accomplished during the periodfrom I November 1966 to 31 January 1967. Di~ing this time experiments werecarried out to define requirements which must be met to remove organic con-taininanits fromn metal surfaces during passivation in fluorine. 'Metal coupons,porous stainless steel disc* and glass capillaries were contaminated with variousorganic materials and exposed to gaseous fluorine and chlorine trifluoride vaporunder a variety of conditions simulating typiral phissivation procedures. Theconventional passivation procedures at room temperature and at moderate pres-sure are ineffective for removal of thin smears of organic contaminants frommetal substrates.

PoD D I AN 1473 UNCLASSIFIED

Secet~ cas.*cas4

UNCLASSIFIEDseti4 Clagnific,•ift

KEY WORcS LINK A LINK 0 LINK CROLM WT ROLE WT ROLE WT

FluorinePassivationFluorinating AgentsChlorine T rifluorideNickel AlloysStainless SteelAluminum AlloysMonelContaminationHydraulic FluidHalocarbon GreasePolyurethaneAcrylic LacquerDye PentrantPetroleum JellyVacuum Impregnation

INS'TRUCTIMNS

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