Helein D. Bennett National Aeronautics and Space Administration Microchemical Analysis Section John F. Kennedy Space Center Kennedy Space Center, Fla. 32899
analytical Are your analytical samples small like the point of a pin or large like the side of the barn? Do you use statistical sampling, or might your method be described as "catch as catch can"? Are your analytical procedures well described in standard references, or must you adapt or devise methods to fit the problem? All these questions can be answered " y e s " by the chemists at a unique, "on the spot", and sometimes "last m i n u t e " analytical facility at the nation's spaceport where the side of the barn is more likely to be the side of a rocket and statistical sampling and standard methods are the exception rather than the rule. T h e Microchemical Analysis Section at Kennedy Space Center provides nonroutine chemical analysis to all the Center activities and, on request, to other NASA Centers, other federal government agencies, and state and local government agencies. Since the types of problems encountered and the material to be analyzed can be literally anything and the time available for analysis is sometimes extremely short, the laboratory is highly instrumented. Optical microscopy is used frequently during analysis of solids and liquids and sometimes is the sole or major technique used. T h e general analytical approach is illustrated in Figure 1. In determining the course of analysis, there are several additional considerations t h a t are not easily illustrated but may indicate a path different from t h a t in Figure 1. These considerations, a series of questions, include: Where did the sample come from? What is it likely to be? W h a t is nearby or in the same system? W h a t was happening when someone decided an analysis was needed (funny odor, peculiar appearance, etc.)? Why is this analysis needed (safety, materials compatibility, hardware malfunction, etc.)? Is it like some sample analyzed 322 A · ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
previously? T h e answers to these questions may make it possible to use one or two analytical techniques and a minimum length of time to confirm a good deduction. Limited availability of the sample is one other consideration t h a t will dictate a p a t h involving nondestructive methods initially, followed by whichever destructive method will give as much of the information requested as possible. Many of the analytical problems presented to the laboratory are associated with the identification, and sometimes the quantitative analysis, of materials involved in failures of spacecrafts, launch vehicles, or ground support systems at the Center. This often requires a multidisciplinary approach involving not only many of the techniques used in this laboratory b u t also analytical work by two other groups: the Malfunction Investigation Staff in the areas of metallurgical, mechanical, and electronic or electrical failures and the Materials Testing Branch in the areas of properties of materials, oxygen compatibility, and environmental testing. Although the laboratory personnel are occasionally asked to perform analyses at the launch pad or to take samples directly from the pads and other areas, most materials are carried into the Microchemical Analysis Laboratory by the requester (usually an engineer) who may not know which measurements are needed and what they may mean. Consequently, one of the most important services of the laboratory is interpreting analytical chemistry for the customer.
Sample Size and Type Samples arrive in all kinds of shapes, sizes, and containers. Large samples have included an Apollo 12 liquid hydrogen tank nearly 3 ft in di-
The Analytical Approach Edited by Claude A. Lucchesi
Chemists at the launch Pad ameter which was examined by trans mission electron microscopy, electron diffraction, and electron microprobe x-ray analysis to determine the cause of a leak in the solid-state weld be tween the titanium alloy tank and the stainless steel inlet/outlet port ( / ) . Also, a spacecraft lunar adapter (the cone around the lunar module during launch), measuring some 6.4 m high and 7.9 m in diameter at its base, was tested with pH paper to determine t h a t all traces of a hypergolic oxidant (nitrogen tetroxide) propellant spill had been removed. Examples of small samples, the type most often analyzed by the laboratory, are many. Particles on millipore filters have frequently been analyzed to de termine the identity of contaminants in spacecraft fluid systems. Particles in the threads of screw-type fittings and on the pins or sockets of plug-type fittings are also frequent objects for analysis. Most gas and liquid samples arrive in standard containers, b u t in unusual circumstances almost any thing may be used. On one occasion, when a nitrogen system was being dis assembled, an engineer unexpectedly found some liquid in supposedly dry stainless steel tubing and grabbed the nearest container, an ashtray contain ing a few ashes, to catch the liquid for analysis. T h e liquid was identified as water; the ashes were not analyzed. T h e following problems illustrate the analytical approach used at Ken nedy Space Center.
Is There Enough Antioxidant in the Spacecraft Coolant? During the Apollo program, ethyl ene glycol-water solutions were used as heat exchange media in the com mand module and lunar module envi ronmental control systems and in the service module fuel cell system. T h e compositions of two of these solutions are shown in Table I.
Shortly before Apollo 11 was launched, thousands of tiny crystals were found in the ethylene glycolwater coolant of the lunar module, al though few had been found in preced ing Apollo missions. T h e crystals were identified as 2,2'-dithiobisbenzothiazole (Compound I) by the Microchemical Analysis Section using infrared spectroscopy, mass spectrometry, and x-ray diffraction. Compound I is the oxidation product of sodium mercaptobenzothiazole (Compound II) which functions as an antioxidant in the gly col solution. Ν
Ν
V-s—s-< S
δ1
V—S"Na+ H Upon learning t h a t sodium sulfite had been added as an antioxidant dur ing the preparation of the 50% sodium mercaptobenzothiazole solutions used in previous Apollos, Johnson Space Center decided t h a t sufficient sodium sulfite to give a final concentration of 3-6 mg/L should be added to the gly col solution on hand at Kennedy Space Center for use in the first space craft to land on the moon. T h e Microchemical Analysis Section was asked to confirm t h a t "enough" sodium sul fite was present in the final solution to prevent the oxidation of the inhibitor to the resultant precipitate. Several potential colorimetric and polarographic methods of analysis were considered and discarded be cause of erratic results. Initial at t e m p t s to use conventional oxidationreduction titration failed because a voluminous white precipitate preced ed and obscured the normal starch end point of the iodometric titration. When the precipitate was identified as
2,2'-dithiobisbenzothiazole, the titra tion procedure was modified to use a turbidimetric end point detected by a colorimetric accessory to a potentiometric recording titrator (2). A blank was obtained by bubbling nitrogen through the acidified solution to re move the liberated sulfur dioxide. T h e analytical results were of satisfactory precision, having a relative standard deviation of about 5%. Perhaps more important, the concentration deter mined in the on-board fluid was about 4 mg/L, a level judged to be adequate for the lunar landing mission. T h e successful flight of the Eagle in July 1969 ("Tranquility Base here. T h e Eagle has landed.") proved t h a t judg ment, along with thousands of others, to be correct.
What Are These Yellow-Green Crystals? Identifying the precipitate and de termining the sulfite concentration level of the lunar module coolant did not solve all the analytical problems posed by glycol solutions. T h e glycolwater solution used in the fuel cell sys tem of Apollo 16 provided a very puz zling problem. Pale yellow-green nee dlelike crystals were collected on mil lipore filters during flushing of the system. T h e infrared spectrum of the crystals was surprisingly similar to t h a t of 2,2'-dithiobisbenzothiazole, but was missing several sharp bands. This suggested the presence of some other compound similar to mercapto benzothiazole, although this glycolwater solution (Table I) should have contained no compounds of this type. T h e electron microprobe x-ray analyz er showed major quantities of nickel and sulfur associated with the needles, suggesting the presence of nickel mer captobenzothiazole. However, the x-ray diffraction pattern, which was of excellent quality, did not match t h a t
ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977 · 323 A
Figure 1. Identification of unknown material
of the nickel compound prepared in the laboratory as a reference, nor did it match any other pattern, either among the 20 000 in the Powder Diffraction File, searched both manually and by computer, or the reference patterns prepared in this laboratory. T h e few peaks found by mass spectrometry also failed to identify the material. A summary of the initial analytical results is given in Table II. A comparison of the solution composition (Table I) and the analytical results (Table II) revealed no possible source for the yellow-green crystals whose identity was still unknown. T h e systems engineers were asked some questions about the materials used in the fuel cell system. "Is there any nickel in the system?" Well, the tubing in the system is stainless steel which does contain some nickel—and, oh yes, there is a nickel frit in the system, too. But there shouldn't be any nickel in the solution because the pH is too high (7.8) to attack nickel. (Wrong. T h e rate is slow, but traces of nickel could dissolve.) "Is there any. organic material in the system?" Yes. There is a rubber bladder which is necessary to pressurize the system so that the glycol solution can be pumped through the cooling loops of the fuel cell system while the spacecraft is in orbit. "Do you have another bladder we can analyze?" Yes. At this point, the course of the analysis was profoundly affected by the infrared spectroscopist, who had formerly worked for a rubber company. Knowing t h a t various sulfur compounds, such as thiocarbamates and thiazoles are used as accelerators in the curing of rubber, he consulted with a friend in the rubber industry.
With the friend's assistance the infrared spectrum was tentatively identified as t h a t of an oxydiethylene dithiocarbamate salt. However, no reference spectrum was available, and no source of the material was known. Consequently, bis(4-morpholinecarbodithioato)Nickel-II (Compound III), the proper name for the compound, was synthesized in the laboratory. Comparison of the original sample
material with the synthesized material by infrared spectroscopy, mass spectrometry, and x-ray diffraction showed the two materials to be the same. It was theorized t h a t 4,4'-dithiodimorpholine (Compound IV) had been used as an accelerator in the bladder, forming the zinc analog of III during vulcanization of the rubber. (Inorganic zinc compounds are frequently p a r t of
Table I. Formulation (100 Parts by Weight) of Apollo Ethylene Glycol-Water Solutions Lunar module environmental control
Ethylene glycol Water TEAPa NaCap"
35.00 Remainder 1.60 0.18
Service module fuel cell
Ethylene glycol Water Na2HP04 K2B4Or8H20
62.50 Remainder 0.55 0.70
" TEAP = triethanolamine phosphate. * NaCap = 50% solution of sodium mercaptobenzothiazole.
Table II. Analysis of Yellow-Green Crystals Method
Results
Infrared spectroscopy
Similar to but not the same as Compound I
X-ray diffraction
Very sharp lines indicating highly crystalline material, probably very pure. Pattern not in Powder Diffraction File. Not same as lab x-ray pattern of Compound I Major Ni, minor Cu, AI, Mg, Fe
Emission spectrography Electron microprobe Mass spectrometry
324 A · ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
Major Ni and S, highly correlated; low minor to trace Cu
Molecuiar weight peak of 382 m/e. Weak peaks at 86, 130, 1 3 1 , 196, and 260 m/e. (Molecular weight of Compound I is 332)
rubber formulations.) If the zinc compound then migrated to the surface of the bladder or "bloomed", it could react with the nickel ions which had been found to be present in the glycol solution to form Compound III.
A new bladder t h a t had a gray-white bloom was found. T h e infrared spect r u m of the bloom matched t h a t of the zinc analog of Compound III, completing the solution of the analytical problem.
The "Great Green Plague" Unfortunately, not all analytical problems undertaken in the laboratory have neat answers. Corrosion products of stainless steel are frequently found on various samples, but the exact composition of the corrosion product depends on the type of alloy, the corrosive compound(s), and the time the alloy has been exposed to the
corrosive compound(s). T h e product most frequently identified is a hydrated iron oxide, a composition which is consistent with environmental corrosion caused by the Florida coastal climate. However, not all corrosion is due to the environment. One example of this was a stainless steel tubing contaminant found when a mobile launcher t h a t had been downmoded after use in the Apollo program was being refurbished for use in the Skylab program. A brownishto-dark olive drab material t h a t occurred on the interior surface of some of the tubing was found by emission spectroscopy to contain major iron, manganese, and chromium; minor nickel and silicon; and traces of tin and five other metals. T h e numerous individual corrosion products, however, could not all be identified. T h e major ones identified by x-ray diffraction were iron oxide (Fe^C^), chromic oxide (Cr20,i), and manganese oxide (Mn,j04). These highly oxidized compounds were unusual compared to the hydrated iron oxides commonly found. Eventually, hundreds of feet of tubing were found to be contaminated with the "great green plague", and one office in the lab began to resemble a tubing farm as more and more sam-
ples were submitted for analysis. T h e cause of the contamination could not be definitely identified, but it was concluded t h a t the olive drab contaminant most probably was formed during the final annealing stage of the fabrication process. T h e problem was solved by replacing most of the tubing. After cleaning which involved pickling, some of the contaminated tubing was later used in less critical systems.
Acknowledgment T h e analytical contributions by coworkers L. G. Bostwick, R. Burton, W. R. Carman, W. A. Holden, J. F. Jones, R. M. Nichols, T. A. Schehl, L. D. Underbill, former coworkers K. Stevens, and A. C. Danielson of the Uniroyal Corp. are gratefully acknowledged.
References (1) L. G. Bostwick and R. Burton, "Combined Electron Microscope, Electron Diffraction, and Electron Microprobe Analysis of Identical Microstructures in the Debond Area of a Dissimilar Metal Joint", NASA TN D-6327, August 1971. (2) H. D. Bullard, L. D. Underhill, and G. L. Baughman, "Turbidimetric Determination of Sulfite Ion in Inhibited Ethylene Glycol-Water Solutions", KSC-TR1073, September 1970.
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