lemental fluorine is the most powerful oxidizing agent E k nown. Its superior performance as an oxidizing agent for various rocket fuels has resulted in the current plans for including propulsion systems utilizing liquid fluorine in some of the NASA satellite and space missions. Fluorine is not included as the oxidizer in any operational propulsion system today for reasons which stem from the problems of corrosion, high reactivity, and toxicity associated with this material. T h e program reported here centers around questions related to corrosion and chemical reactivity. Considerable data have been reported on the corrosion of metals by liquid fluorine (2, 4, 7, 77, 78). Most of the data are for exposure periods of less than one day, although limited data exist for continuous exposure u p to 100 hours (7, 7 7 ) , and for cyclic exposure to gas and liquid for periods u p to three and one-half months (78). The early data show negligible corrosion, while the latest data (7) show significant corrosion rates in many of the tests run. The experiences of organizations such as General Chemical Go., North American Aviation, NASA, and Bell Aerospace Go. with large liquid fluorine storage tanks have indicated that corrosion in this type of service is minor. However, no large set of organized data taken under uniform conditions has been available. In this study, metals were exposed to corrosive action of liquid fluorine for periods up to one year in duration. The metals tested were those most commonly of interest for this service-alloys of aluminum, titanium, copper, magnesium, nickel, and stainless steel. Samples were exposed in both the stressed and the unstressed states, and tensile strength of certain metals was tested after fluorine exposure. I n all cases, it was concluded that the corrosive action of fluorine in a dry system, free from contaminants, is negligible, and that stress corrosion and cracking are not likely to occur in metals exposed to liquid fluorine. All metals tested had the same yield strength after exposure as before. Techniques of passivation (77) of metals prior to use in liquid fluorine systems were also determined in the course of this study. The several passivation techniques now in use ( 3 ) involve two basic steps-thorough cleaning of the metal surface and exposure to fluorine gas at room temperature prior to exposure to liquid (5, 7, 9, 70,
Lorrosion ot metals by
liquid fluorine Corrosion of materials of construction is insignificant, tensile strength is unaffected, stress corrosion does not occur
ALAN H. SINGLETON JAMES F. TOMPKINS, JR. SIDNEY KLEINBERG C. J. STERNER
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47
TABLE I . -__
Metal Nickel Monel 304 Stainless 410 Stainless 420 Stainless A r m c o Steel
-
0 003 0.003 0.003 0.063
steel steel steel
15-7 Ph Mo
Copper M a g n e s i u m HK 31 M a g n e s i u m A Z 31 Aluminum I100 Aluminum 6061 Titanium A1 10 AT T i t a n i u m C120 AV
CORROSION I N L I Q U I D FLUORINE-PASSIVATED
1
0.001 0.003 0.674 0.344 0.209 0.184 0.281 0.227
1
0.ooa
I
0.016 0.008
0.012 0.004
j
0.011 0.002
0.001
0.009 0.003 0.015 0.031 0.039 0,044 0.033 0.042 0.040
0.006
1
0.007
0.002
I 1 ~
SAMPLES
0.002 0.001 0.005 0.001 0,008
0.053 0.004 0.025
a L!r?.’otethat these samples were inadvertently exposed to moisture at the end of the one-year test. can be cunsidered as expressing maximum corrosive penetration due to liquidjluorine exposure.
72-74). These investigations show that it is very necessary to have all hydrocarbons removed from the metal surface. Hydrocarbons invariably form either elemental carbon or combustible liquids in this service, as described in the section entitled “Effect of Surface Contaminants’’ below. The need for the second passivation step, exposure to low pressure or dilute fluorine gas, is not so clear. We recommend that this procedure be followed as a precautionary measure. Coupons exposed to liquid fluorine without prior passivation do not corrode at an accelerated rate (see “Short-Term Tests”), but exposure of metal powders to fluorine gas shows that a protective film does, in fact, form. This film is about 10 A. thick, as determined in the section “Fluoride Film Studies.”
These measurements are probably high, therefore, and
CORROSION OF METALS IN LIQUID FLUOR1NE Alloys of aluminum, titanium, copper, magnesium, nickel, and stainless steel were immersed in liquid fluorine for periods u p to a year in duration, and corrosive penetration was measured by weight loss. Specially designed sample cells contained the samples. Fluorine was kept in the liquid state by immersing the entire cell in a Dewar flask of liquid nitrogen. Two designs of equipment were used-one for the test period of a year, one for shorter term tests. Summary of Short-Term Tests PASSIVATED SAMPLES. Coupons 2 in. x l/z in., 0.050 to 0.125 in. thick, were tested in the cells shown in
TABLE II.
CORROSION I N L I Q U I D FLUORINEU NPASS I VATED SAM PLES
EXPOSURE TIME-6
Metal Nickel Monel 304 Stainless steel
316 Stainless steei 347 Stainless steel 420 Stainless steel Copper Aluminum 1100
Figure 7. Interior of one of the test cabinets used in the short-term exposure of metal coupons to liquidjuorine. Each cabinet is connected to aj7uorine supply cylinder housed i n a separate roam. To the left, two sample cells are shown, and to the right, two Dewar cylinders are in place around the sample cells 48
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
0.001 0.007 0.003 0.001 0,001 0.045
__
Aluminum 2017 Aluminum 5052 Aluminum 6061 Titanium A1 10 A T Titanium C120 AV Cup ro - n i c k e I (30y0 n 1 c k e I) C a r t r i d g e brass Everdur ____
HOURS
1,
1 ~
I 1
1
~
~
I
-
~enetratzon, Inches X
-__
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
_ _
009 011 002 004 004 007 006 053 015 008 004 022
008 007 001 002
-
Figure 2. Samples were passivated by cleaning and by prior exposure to fluorine gas for 30 minutes. The metals listed in Table I were tested. The low corrosion rates shown in the table resulted. UNPASSIVATED SAMPLES. Sample size and equipment were the same as for the passivated tests above. The procedure was changed as noted in the section below. The coupons were cleaned, but were not exposed to fluorine gas. No significant difference resulted over a two-week period, as shown in Table 11. STRESSED SAMPLES. Samples were immersed in liquid fluorine in the short-term testing equipment for a period of two weeks. During this time, the samples were stressed to their yield points in the manner shown in Figure 3. The metals involved were all those listed in Table I. Examination by microscope at 6 0 x before and after a dye check treatment failed to detect any signs of corrosion cracking or accelerated corrosion.
STAINLESS STEEL NUTS AND BOLTS (8)
Summary of long-Term Tests PASSIVATED SAMPLES. Metals listed in Table I were tested. T h e low corrosion rates shown in the table resulted. Samples were passivated by a 90-minute exposure to fluorine gas. T h e equipment was arranged as shown in the flow diagram, Figure 5. Sample cell was as given in Figure 4 ; sample and rack, as in Figure 6. TENSILE TESTS. Equipment, procedure, and samples were the same as in the long-term tests. Five samples of each metal were exposed to liquid fluorine for one year. A like number of samples was stored in the liquid nitrogen Dewar which contained the fluorine test cell. Metals tested included stainless steel (304, 410), aluminum (1100, 6061), titanium (A110 AT, C120 AV), highstrength steel (Armco 15-7 Mo), magnesium (HK-31, AZ-31), copper, nickel, and Monel. At the end of the test period, the samples were processed for corrosion rate data, and then tested to failure in a Tinius-Olson tensile testing machine. No significant differences in strengths were found between the sample sets.
Figure 2. Sample cells used in short-term immersion tests. The cells are of Monel metal tubing, P/d-in. inside diameter, ’/s-in. wall thickness. The top j a n g e , bottom plate, and inlet and outlet lines are all Monel metal welded to the cells. Rupture disks are cut as required from 0.005-in. copper sheet stock, with effective bursting area approximately 7 in. in diameter
Short-Term Testing
Sample
Preparation
and
Corrosion
Measurements.
The materials tested in this phase of the program consisted of various alloys of aluminum, stainless steel, titanium, magnesium, nickel, and copper (listed in Table I). The samples were in the form of coupons with nominal dimensions of 2 inches by l / z inch, which varied in thickness from 0.050 to 0.125 inch. The effective corrosion area was generally about 2 square AUTHOR A l a n H. Singleton as Project Manager, Research and Development Department of A i r Products and Chemicals, Inc., Allentown, P a . H e w a s co-author of the article “Technical Aspects of Ortho-Parahydrogen Conversion,” published i n IQEC, M a y 7 9 6 4 . J a m e s F. T o m p k i n s , Jr., and Sidney Kleinberg are both with A i r Products and Chemicals, Inc., the former a s M a n a g e r , Chemacal Process Development Section, the latter a s Senior Chemical Engineer. Charles J . Sterner i s Senior Process Engineer with Amerzcan Cryogenics, Inc. T h i s work w a s sponsored by the Aeronautical Systems Division of the A i r Force Systems Command, United States Air Force, under Contract No. AF 3 3 ( 6 7 6 ) - 6 5 7 5 .
Figure 3. Stress corrosion samples. Curved bars, held in compression by a holder of the same material, were exposed to liquidjuorine in the short-term testing apparatus. Two samples were tested in each cell for a period of two weeks
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inches. Usually the sample surfaces were polished, but in some cases they were tested as received from the supplier. All sample coupons were deburred, cleaned with trichloroethylene or acetone, and dried in a stream of nitrogen gas. They were then weighed on an analytical balance before being loaded into the cells. All sample handling after the drying step was done with clean stainless steel forceps. Up to four samples were tested in one cell at the same time. After exposure, the samples were removed from the cell with metal tongs and stored in a desiccator before being reweighed and photographed in color. Attempts were made to remove any corrosion products either by scrubbing with a toothbrush and water or by rubbing with a soft pencil eraser. When the samples had been cleaned and dried as well as possible, they were weighed again. Corrosive penetration was based on the lower weight. Equipment, T o handle fairly large quantities of fluorine over an extended time period, a rather elaborate equipment arrangement was required. Fluorine tanks and test cells were placed in sealed cabinets maintained under slight negative pressure by an exhaust system. Details of these auxiliary items of equipment will not be given here. One test cabinet, arranged as shown in Figure 1, accommodated four sample cells. Manifolds within the cabinet were arranged so that all operations could be performed from the outside. Each test cabinet had its own fluorine cylinder and exhaust system. Each of the four fluorine test cells was separately connected to a fluorine disposal system. All lines in contact with fluorine were constructed of Monel; all valves were of Monel with Teflon packing. The sample cell, the heart of the apparatus, was constructed as shown in Figure 2. Two types of sample cells were used for the immersion test program, the only difference between the two being the length of the cell. I t was found that the shorter ones were somewhat easier to handle. Monel metal partitions were used inside the cell to separate samples which were being tested concurrently. Each sample cell had its own pressure gage reading from 30 inches Hg vacuum to 60 p.s.i.g. The gages were built with Monel metal bourdon tubes. The sample cells were placed in stainless steel Dewar cylinders. Manifolds were used to supply fluorine to the cells, remove fluorine from the cells, supply nitrogen gas to purge the cells, and supply either liquid or gaseous nitrogen to the Dewar cylinders. Procedure. After samples were placed in a cell and the rupture disk was tightened in place, the cell was evacuated and then sealed by closing the manifold valves. Vacuum was held for several hours to check for leaks. Fluorine gas was admitted to the cell until the pressure rose to 6.5 p.s.i.a. The cell was sealed again for a thirty-minute period, after which the cell and samples rvere considered to be passivated. The Dewar cylinder was then filled with liquid nitrogen. 50
INDUSTRIAL A N D ENGINEERING CHEMISTRY
About fifteen minutes after adding liquid nitrogen, stabilization of the cell pressure indicated that the cell was cooled to the operating temperature and the liquefaction of the remainder of the fluorine could begin. An external supply reservior contained sufficient fluorine gas to fill a sample cell with liquid fluorine to a level about ‘ / z inch above the top of a sample coupon. Five to ten minutes were required to complete the liquefaction of all of the fluorine. The cell was sealed for the duration of the test period, and liquid nitrogen level was maintained above the top of the test cell. At the end of a test period, the liquid nitrogen was evaporated by flowing room-temperature nitrogen into the Dewar cylinders, and the fluorine (now a gas) was bled to the disposal system. After the cell was thoroughly purged with nitrogen, the samples were removed. In the unpassivated tests, the tests were begun by sealing and purging the cells in the manner described above. At this point, however: the cells w ~ cooled e to -320’ F. Fluorine was then liquefied in the cells without first exposing the samples to room temperature fluorine gas. -411 other steps were then performed in exactly the same manner used for the passivated tests. long-Term Testing
Sample
Preparation
and
Corrosion
Measurement.
Samples were machined from 1,’4-inchrod, as shown in Figure 6. Metals tested included alloys of aluminum, copper, magnesium, nickel, stainless steel, and titanium. The test specimens were degreased, cleaned, dried, weighed, and placed in assigned spaces in the specimen rack. Samples were held in liquid fluorine for one year. An equipment failure, which occurred while the fluorine was being exhausted from the system at the conclusion of the test, resulted in exposure of the samples to water. They were immediately removed, dried, and weighed. After being cleaned in the same manner as used in the short-term tests, the samples were reweighed and corrosion rates were calculated. The presence of moisture, which might cause formation of hydrofluoric acid, would be expected to increase the rates of corrosion. The figures given in Table I would therefore represent maximum corrosive penetration due to liquid fluorine. Equipment. An apparatus was designed to hold 60 samples under liquid fluorine for one year in a leaktight system. The sample container was constructed as shown in Figure 4. A series of manifolds (Figure 5) could be used for introducing fluorine, removing fluorine, introducing nitrogen or helium, or evacuating the container. The system was protected by a 400-p.s.i.g. copper rupture disk in the nozzle of the container in a line which exhausted to a 20-foot deep lime pit used for fluorine disposal. A special rack was made to hold specimens upright in the container (Figure 6). The holes in the rack were drilled so that the liquid fluorine could easily flow between the rack, container, and specimens. Since
galvanic corrosion does not appear likely in the liquid fluorine environment, no attempt was made to electrically insulate the samples from each other. T h e liquid fluorine container was placed upright and centered in a large flanged Dewar vessel. The Dewar was placed in a large box insulated with glass wool and located behind an oak barricade. The liquid level in the Dewar was measured and controlled by a differential pressure controller which opened a solenoid valve to introduce liquid nitrogen when the level dropped below the top of the specimens in the container. Procedure. All components of the system were degreased, cleaned, and dried. The test rack was placed in the fluorine test cell and the upper cap of the vessel was welded in place. T h e entire system was leak-tested with a helium leak detector, and the cover flange was bolted down on the Dewar. The remainder of the operations were performed from the operating side of the barricade.
e
+ LIME DISPOSAL PI1
RUPTURE DISK
dl
% IN. MONEL TUBING
j
DEWAR COVER F L ~ N G E
4 IN. SCHED. WELDED
4 IN. SCHED.
Figure 4. Sample cell used in long-term immersion tests.
The top
p+e cap was welded on after the cell was loaded with the rack and samples. The cover flange shown was bolted onto the Dewar, which contained liquid nitrogen. The entire assembly was then packed in a large box insulated with glass wool and located behind an oak barricade
Figure 5. P+ing diagram for long-term immersion tests. Manifolds can be used f o r introducing fluorine, removing fluorine, purging with nitrogen or helium, or evacuating the container
The system was purged with dry nitrogen and evacuated. Passivation was accomplished by exposure to fluorine gas at 8.5 p.s.i.a. for 90 minutes at room temperature. The Dewar was filled with liquid nitrogen and five pounds of fluorine were condensed over a period of 90 minutes. The one-year test period passed without incident and with a minimum amount of attention. Sufficient fluorine was present in the system at the conclusion of the run to completely cover the samples. At the conclusion of the test period, the fluorine was vaporized and the nitrogen purging step was begun. An unfortunate equipment failure occurred at this point. As part of the purging procedure, vacuum was drawn on the system. The rupture disk on the container failed, and water (which had accumulated from rain) was drawn into the system from the limestone pit used for fluorine disposal. The container was immediately opened.
% THRE@S/IN. IN. X 28
n
0.790 IN. DIAMETER NECKED DOWN TO 0.188 IN. MACHINED LENGTH 2% IN.
Figure 6 . Specimen test rack and typical specimen used in the longterm exposure tests
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FLUORIDE FILM STUDIES Because of the large body of data obtained, only a portion is presented here. 'The reader is referred to Refererence 8 for complete results. Film thicknesses resulting from the reaction of gaseous fluorine with metal surfaces were detected by measuring change in fluorine gas pressure in a constant volume system containing a metal powder. The metal was in the form of a fine powder, the surface area of which was previously determined by nitrogen adsorption utilizing the technique of Arunauer, Emmett, and 'Teller ( 7 ) . I n computing film thickness it was assumed that uniform
consisted of copper tubing to which a pressure gage was connected. The second volume included a copper coil and a Monel sample holder. The first volume was manifolded to a line through which gaseous fluorine could be introduced or removed. Included were provisions for a nitrogen purge and for system evacuation. The first volume could be brought to 50 p.s.i.g. pressure. When the valve separating the volumes was opened and the pressures were equalized, the pressure was slightly below 1 atmosphere absolute. The pressure in the system could be read to within 1 rnm. of Hg. When fluorine reacted with the powder to form a metal fluoride, thus reducing the system pressure, the pressure reduction was converted to a fluoride film thickness by appropriate calculations. Precautions were taken to ensure that the metal equipment parts were passivated, that the system was free from leaks, and that the system and metal powder contained no moisture. Equipment was standardized with nitrogen before and after each run. After reaction was apparently complete, fluorine was introduced a second time to provide a "zero time'' pressure reading and to check completeness of reaction.
*
EFFECT OF SURFACE CONTAMINANTS
Figure 7. Test apparatus for measurement ofJuoridej1m thickness on metal powders. Relation between volume I and volume 2 is such that the apparatus will be slightly below atmospheric pressure when value 2 is opened, volume I is pressured to 50 p.s.i.g. while vdume 2 is evacuated. For runs above ambient temFerature, the sjstem is immersed in a constant temperature bath
reaction took place over the entire surface of the sample, that films formed were metal fluorides in their highest oxidation states, and that the films had densities equivalent to those reported (6). Pressure during runs averaged about 0.65 atmospheres absolute. The sensitivity and accuracy of the pressure-volume-surface area measurements were such that accuracy is within one Angstrom unit. The results of the tests conducted at room temperature are given in Figure 8. Most of the reaction took place in the first 10 to 20 minutes with very little reaction occurring in the last three hours of the tests. Determining Film Thickness. The experimental setup shown in Figure 7 was used for studying the reaction of metal powders with fluorin? gas. Two volumes separated by a valve formed the important part of the equipment. The first volume (small compared to the second) 52
INDUSTRIAL A N D ENGINEERING CHEMISTRY
A number of tests was conducted to determine the effect of traces of hydrocarbons on the metal surfaces. I t had been argued that the fluorine might, in fact, act to clean the metal, producing inert and harmless substances. These tests were conducted with fluorine gas using the short-term testing apparatus. No Dewar flask was necessary as the tests were carried out at room temperature. A series of small metal dishes one inch in diameter were made of brass, copper, aluminum, titanium, nickel, and Monel in thicknesses of 0.001, 0.005, 0.010, 0.062 and 0.125 inchw. Solutions of hexadecane in trichloroethylene were prepared in varying concentrations. Hexadecane was deposited on the metal surface by metering a small quantity of solution onto the dish and evaporating the trichloroethylene in a vacuum oven at 80" F. Oil films weighing from 1 to 60 milligrams and varying in thickness from 0.001 to 0.060 inch were deposited. The dishes were placed in the small Monel cells, Figure 2 , which were sealed and thoroughly evacuated. Fluorine, chlorine trifluoride, or mixtures of the two were then introduced into the cell at pressures ranging from 1 to 5 atmospheres. The extent of reaction of the hexadecane film with the gas was noted by pressure surges as the gas was added to the test cell. After a reasonable time, the gas was evacuated and the dish was weighed and inspected. I n general, removal of hexadecane films from metal surfaces by reaction with gaseous fluorine was unsuccessful. Instead of the film being removed, most samples actually gained weight. Often a deposit of finely divided carbon was left on the surfaces when gaseous fluorine was
TIME OF EXPOSURE, MIN.
Figure 8. Formation ofjuoridefilms on metal powders, all data at 86’ F . Note that the major part of the reaction occurs during the $rst few minutcs of exposure, with little further reaction during the remainder of the test
exposed to the oil. Reaction was closest to completion at the high pressures when the thinnest metal dishes were used. The thin coupon absorbs the least amount of heat from the reaction of the gaseous fluorine with the hexadecane, and the high pressure favors a faster reaction. When C1F3 or mixtures of C1F3 and Fz were used, an oily deposit was observed on the metal dish. Infrared analysis of this oil indicated its structure to be identical to Hooker Fluorolube oil MO-10. I t was believed that the C1F3 reacted with the hydrogen in the hydrocarbon to replace it with fluorine or chlorine, leaving the carbon skeleton intact. With fluorine gas, a waxy solid was sometimes observed. None of the residual films contained compounds with carbon-hydrogen bonds. Detailed results and observations of these tests are reported in Reference 8. Conclusions
It is concluded that the corrosive action of fluorine on metals in a dry system free from contaminants is negligible. Stress corrosion and cracking is not likely to occur with metals exposed to liquid fluorine. Passivation of small metal systems with low pressure or dilute fluorine gas is not a requisite for safe operation; however, this technique does increase the probability of safe operation and is recommended as a final treatment prior to liquid exposure. I t has been shown that hydrocarbons invariably form either elemental carbon or combustible liquids when exposed to gaseous fluorine ; hence, extreme care must be exercised in eliminating
such contaminants prior to gas exposure. I t has been shown that exposure of metals to low pressure fluorine gas results in the formation of a very thin film of metal fluoride, on the order of 10 Angstrom units in thickness. Essentially no deterioration of tensile properties of metals takes place from exposure to liquid fluorine for a one-year period, LITERATURE CITED (1) Brunauer, S., Emmett, P. H., Teller, E., J.A m . Chem. SOC.60, 309 (1938). ”Corrosion of Titanium and Titanium Base Alloys in Liquid k d Ga’seous huorine,” Technical Memorandum, Battelle Memorial Institute.,Ami1 30. 1958. . . (3) Gakle, P. S.! White:, L. E., “Design Handbook for Liquid Fluorine Ground Handling Equipment, WADD T R 60-159, Dec. 1960. (4) Gundzik, R. M. Fuller C. E. “Corrosion of Metals of Construction by Alternate Exposure to Liquid &d Gaieous Fluorine,” NACA T N 3333, Dec. 1954. ( 5 ) Hale, C. F., Barber E J. Bernhardt H A. Rapp K. E., “High Temperature Corrosion Study,” 1n;erirn Report AEdD-4295, Nov.’f 958 to May 1959. (6) Hodgeman, C. D. “Handbook of Chemistry and Physics,” 40th ed., Chemical Rubber Publ. Go., bleveland, 1958. (7) Jackson R. B. “Corrosion of Metals and Alloys by Fluorine General Chemical Div. Publ:, A1Ii;d Chemical Corp., Final Rept., Contract N o , AF 04(611)-3389, March 1960. (8) Kleinberg, S., Tompkins, J . “Compatibility of Various Metals with Liquid Fluorine,” Air Products and CBernicals, Inc., ASD T D R 62-250, May 1 9 6 2 . (9) Landau, R., “Corrosion by Fluorine and Fluorine Compounds,” Corrosion 8, 284 (1952). (10) Landau, R . , Rosen, R., “Industrial Handling of Fluorine,” IKD.ENG.CHEM. 99, 281 (1947). (11) Millaway E. E. Covington, L. C., “Resistance of Titanium to Gaseous and Liquid Fluo;ine,” ?itanium Metals Gorp. of America Publ., 1959. (12) Schmidt, H., “Compatibility of Metals with Li uid Fluorine at High Pressures and Flow Velocities,” NACA R M E58Dl1, July 12, 1958. (1 3) Schmidt, H . , Rothenberg, E., “Some Problems in Using Fluorine in Rocket Systems,” Pror. of Propellant Thermodynamics and Handling Conf., p. 183, Ohio State Univ. Special Rept. No. 12, July 1959. (14) Slesser, C., Schram, S., “Preparation, Properties and Technology of Fluorine and Organic Fluoro Compounds,” p, 139, McGrawlHill, New York, 1951. (15) Sterner, C., Singleton, A., “Compatibility of Various Metals and Carbon with Liquid Fluorine,” Air Products and Chemicals, Inc., \\’ADD T R 60-436, Aug., 1960. (16) Ibid.,WADD T R 60-819, March 1961. (17) Uhlig, H . H., “The Corrosion Handbook,” p. 21, M’iley, 1948. (18) White E. L. Fink F. W., “Materials of Construction for Handling Liquid Fluorine,” Proc: Prop’ellant Thermodynamics a n d Handling Conf., Ohio State Univ. Special Rept., No. 12, July 1959. ( 2 ) Ericson, G . L., Boyd W. K. Miller P. D
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