The presence of oxygen in a gas is detected by contacting an article, such as a film, comprising poly(ethylenenaphthalene-dicarboxylate) with a gas and simultaneously exposing the article to ultraviolet light. The article is subsequently heated and the presence of oxygen in the gas is indicated by thermoluminescence

Hendricks, H. D.

English

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|\ NATIONAL AERONAUTICS AND SPACE ADMINISTRATION <J /
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f(NASA-Case-LAR-10668-1) METHOD OF N73-16106
DETECTING O X Y G E N IN A GAS Patent (NASA) ;
5 p CSCL 07D
Dnclas
00/06 52667
TO: RSI/Scientific & Technical Information Division
Attention: Miss Winnie M. Morgan
FROM: GP/Office of Assistant General Counsel for
Patent Matters
SUBJECT* Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
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The following information is provided:
U.S. patent No. ; 2^,
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NASA patent Case No.
NOTE - If this patent covers an invention made by a corporate
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Pursuant to Section 305(a) of the National Aeronautics and
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the Specification, following the words "... with respect to
an invention of ...M
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Enclosure
Copy of patent cited above
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https://ntrs.nasa.gov/search.jsp?R=19730007379 2020-03-17T07:46:20+00:00Z
PATENTEDJAH 91973 3.709,663
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INVENTOR.
HERBERT D. HENDRICKS
ATTORNEYS
PATENTED JAH 91973
SHEET 2 OF 2
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3,709,663
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INVENTOR.
HEBERT D. HENDRICKS
ATTORNEYS
United States Patent
Hendricks [45]
3,709,663
Jan. 9, 1973
[54] METHOD OF DETECTING OXYGEN IN
A GAS
[75] Inventor:
t "
Herbert
Va.
D. Hendricks, Hampton,
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration
[22] Filed: Aug. 17,1971
[21] Appl. No.: 172,459
[52] U.S. Cl 23/232 R, 23/232 E, 23/254 R,
23/254 E, 250/71 R, 250/83.3 UV
[51] Int.Cl GOln 21/22, GOln 21/34
[58] Field of Search 23/232 E, 254 E; 73/23;
250/43.5, 71, 83.3 UV
[56] References Cited
UNITED STATES PATENTS
3,612,866 10/1971 Stevens 23/254 X
Primary Examiner—Morris O. Wolk
Assistant Examiner—R. E. Serwin
Attorney—Howard J. Osborn et al.
[57] ABSTRACT
The presence of oxygen in a gas is detected by con-
tacting an article, such as a film, comprising
poly(ethylenenaphthalenedicarboxylate) with a gas
and simultaneously exposing the article to ultraviolet
light. The article is subsequently heated and the
presence of oxygen in the gas is indicated by ther-
moluminescence.
7 Claims, 2 Drawing Figures
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3,709,663
1 2
METHOD OF DETECTING OXYGEN IN A GAS The film samples are cleaned with absolute ethanol and
then stored in a desiccator until used. When a measure-
The invention described herein was made by an em- ment is to be made, a-sample is placed in a quartz tube
ployee of the United States Government and may be and degassed by heating at 130° C and vacuum pump-
manufactured and used by or for the Government for 5 ing to 5X1 Or2 torr for a period of 2 hours. This is done
governmental purposes without the payment of any in order to start each sample with the same prior histo-
royalties or therefor. ry. After this sequence, a gas to be tested is admitted
nt
° <h* "" * * Atmospheric pressure and al-BACKGROUNDOFTHEINVENTION lowed to contact with the film. (This sequence of
The present invention relates to a method for detect- degassing the sample and reaction of the gas is not es-
ing the presence of oxygen in a gas. In one aspect, the sential to produce luminescence and is included to
invention relates to a method for detecting the have a standard point of reference for each sample.
presence of oxygen in a gas and, in another aspect, to a Preliminary test samples showed thermoluminescence
method of determining the amount of oxygen in a gas. after exposure to ambient room conditions including
There many known methods of determining the fluorescent lights). The sealed quartz tube and the gas
presence of oxygen in a gas. However, several of these and sample disc therein are then exposed to ultraviolet
methods require the use of devices that are cumber- light from a 1 50-watt dispersed-beam xenon lamp. The
some, expensive, or both and there is a need for a sim- light intensity in the area of the samples is approximate-
pie and inexpensive reliable technique. This need is
 2o 'y 0.23 mW/cm2 as determined by a TRW Model 43A
particularly acute in spacecraft and other installations radiometer. The samples are exposed for various
where weight and bulkiness are of primary importance. lengths of time to the ultraviolet radiation. The control
It is an object of the present invention to provide a time of exposure for most tests is 1 6 hours unless other-
simple and reliable technique for detecting the wise indicated. The samples are next removed from the
presence of oxygen in a gas. It is still a further object to 25 quartz tube and immediately evaluated as described
provide such a technique which can be utilized to below.
determine the amount of oxygen present in a gas. A Madison Research Company Model S-2L TLD
BRIEF SUMMARY OF THE INVENTION Systel? and **°ciated test accessories is used to mea-
sure the total thermally stimulated luminescence from
The foregoing and other objects which will be ap- 30 the sample disc. A sample to be evaluated is placed in
parent to those having ordinary skill in the art are the silver heater pan and then heated to 1 30° C in 1 5
achieved according to the present invention by provid- seconds. The total thermally stimulated luminescence
ing a method including the steps of exposing a is detected by an Electra Megadyne, Inc. (EMI)
poly(ethylenenaphthalenedicarboxyplate) article to ul- photomultiplier (9536S) which is an integral part of the
traviolet light and simultaneously contacting the article TLD system. A test sequence is conducted to deter-
with a gas, subsequently heating the exposed article to mine the luminescence as a function of the heater-
a temperature of at least about 70° C, preferably about timer temperature cycle. The results of this study show
1 30° C, and detecting thermoluminescence induced by that the relative integrated light output (RILO) slowly
said heating. The amount of oxygen in the gas can be .„ increases from approximately 71° until a maximum
determined by employing conventional testing ap- value is reached around 1 30°. At temperatures higher
paratus to measure the amount of thermolu- than 130°, there is a leveling off or a decrease of the lu-
minescence. minescence output. At temperatures higher than 180°,
DETAILED DESCRIPTION ""f 'CS beg'n l° fon? in the SampleS' j? Ume mterva'45 of 15 seconds was chosen to give a high temperature
There follows a detailed description of a preferred rise per unit of time in order to observe any individual
embodiment of the invention, together with accom- emission peaks in the luminescence output. FIG. 1
' panying drawings. However, it is to be understood that shows a typical readout from the TLD system used dur-
the detailed description and accompanying drawings ing the experiment. The common parameter for all of
are provided solely for the purpose of illustrating a 50 the data on the figure is time on the abscissa. The
preferred embodiment and that the invention is capa- dashed curve indicates the temperature cycle and the
ble of numerous modifications and variations that will two solid curves the photomultiplier current output due
be readily apparent to those skilled in the art without to luminescence of a sample disc contacted with gas
departing from the spirit and scope of the invention. samples containing different amounts of oxygen.
FIG. 1 is a schematic representation of thermolu- 55 The spectral distribution of the luminescence is mea-
minescence as a function of time for gas samples with sured with the aid of Optics Technology, Inc., Spec-
different amounts of oxygen, and of heating tempera- trocoat monopass filters (bandpass at full width half
ture used to induce thermoluminescence as a function maximum was less than 20 nm) placed in the TLD
of time; and system between the sample and the photomultiplier.
FIG. 2 is a curve showing the relationship between The same filters were used to identify the wavelengths
thermoluminescence and the wavelength of incident of light most effective in exciting the photochemical
light. reactions in the polymer film.
Discs of poly(ethylenenapthalenedicarboxylate) are Several initial tests were made that indicated that
provided in 0.254 mm thickness and 7.35 mm diame- thermally stimulated luminescence from the polymer
ter. The film is commercially available poly(ethylene- film could be obtained simply by exposing the samples
2,6-napthalenedicarboxylate) having a glass transition to room conditions, which included fluorescent lamp il-
temperature of 1 30° C and a melting point of 255° C. lumination, and then heating in the silver pan of the
3,709,663
TLD system. To reproduce and evaluate various
parameters, a controlled test sequence was utilized. It
was found that samples would not luminesce if kept in
darkness. Also, a sample that would repeatedly lu-
minesce would not do so if kept in a vacuum. However, 5
a sample exposed to air or oxygen and ultraviolet would
luminesce even after repeated cycling. Therefore, it is
necessary to have both ultraviolet radiation and oxygen
or air present for a reaction with the polymer before lu-
minescence could occur. Another means of measuring 10
the effect of the gaseous environment on the process is
by monitoring the relative integrated light output due
to the luminescence process. A typical example for
gases containing different amounts of oxygen is shown
in FIG. 1. Curve A shows luminescence (as indicated IS
by photomultiplier output) as a function of time for a
first gas sample having a relatively large amount of ox-
ygen, and Curve B represents luminescence as a func-
tion of time for a second gas sample having a less
amount of oxygen. As will be seen, both the peak of 20
Curve B and the area under Curve B (relative in-
tegrated light output) provide an indication of the
quantity of oxygen in the gas being analyzed. Ac-
cordingly, the present system can be utilized to make
quantitative determinations, simply by providing a se- 25
ries of curves as shown in FIG. 1 for known gases and
known exposure conditions and comparing these with
curves produced from samples contacted with gases
having unknown quantities of oxygen.
While in the foregoing examples, samples were ex- 30
posed to a light intensity of about 0.23 mW/cm2 for
about 16 hours, much less exposure can be used. For
example, using identical equipment, excellent results
are obtained after 2 hours exposure. The minimum
amount of exposure required is largely a function of the 35
sensitivity of the detection equipment used. However,
in general, a practical minimum exposure time is about
5-or 10 minutes and a practical minimum intensity is
about that of room light or 20 to 30 foot-candles.
A determination was made of the effect of other 40
gases such as He, N2, COj, Ar, and nitrous oxide on the
luminescence process, but contributions to light output
were insignificant when compared to oxygen. During
the investigation of the effect of temperature and time
cycle on the luminescence of the polymer film it was 45
found that the luminescence emission occurred at tem-
peratures above about 70° C. The effect of the
beginning of the luminescence and the upswing of the
glass transition temperature was briefly investigated.
There is an inflection point at about 130° C in the curve 50
showing relative integrated light.output as a function of
temperature. The glass transition temperature as deter-
mined by torsional braid analysis is near 130° C and it is
reasonable to conclude that there is a connection
between the observed luminescence and freedom of "
movement of the polymer chain segments.
A series of tests was conducted to determine the
lifetime of the luminescence reaction. This series of
tests was conducted over a period of over 400 hours. It
was found that the luminescence process was still ac-
tive after this period of time even though the samples
were stored in vacuum and darkness. The lu-
minescence output after this series of tests was still ap-
proximately 30 percent of that at the start of the test.
Therefore, the process is a long-lived one. Another
brief investigation was made of some 22 other
monomers, polymers, and inorganic compounds in-
cluding Mylar, polyethylene, and the monomer of
poly (ethylene-2,6-naptha!enedicarboxy late) under
similar test conditions. No significant luminescence
was observed in any of the other materials.
As ultraviolet light was exciting the oxygen-polymer
system, the wavelengths of excitation were determined.
By using the monopass filters previously described, a
number of samples were exposed to different
wavelengths of light. The resultant thermally stimu-
lated luminescence for all wavelengths of emission is
shown in FIG. 2 as a function of the excitation
wavelength. The .dashed line portion of the curve in-
dicates extrapolation. The excitation wavelength re-
gion investigated was from 230 to 800 nm. From the
figure, it can be seen that the prime wavelengths excit-
ing the reactions are approximately 330 and 390 nm,
and that a suitable range is from about 300 to about
430 nm. Wavelengths of emission from the PEN 2,6
centered around 400 and 465 nm and ranged from 370
to 500 nm. It has been determined that the lu-
minescence is deactivated by degassing after a thermal
cycle. Thus, polymer films can be re-used after the
stimulation of the luminescence process.
While the invention has been disclosed in connection
with precise measuring equipment, it will be apparent
that the presence of oxygen can be very simply deter-
mined by contacting film with the gas in question in the
presence of ultraviolet light and subsequently heating
to about 100° C to observe the existence of lu-
minescence. The ultraviolet light does not need to be
intense, ordinary sunlight or the room-light from
fluorescent lamps being sufficient. In space applica-
tions, of course, no external light source is necessary
and in dark places such as mines, undersea, etc., a small
and conventional source of ultraviolet light is suitable.
What is claimed is:
1. A method of detecting the presence of oxygen in a
gas comprising the steps of: exposing an article com-
prising pory(ethylenenaphthalenedicarboxylate) to ul-
traviolet light and simultaneously contacting the article
with a gas; heating the exposed article to a temperature
of at least about 70° C; and detecting thermolu-
minescence induced by said heating.
2. A method according to claim 1 wherein said arti-
cle comprises a film of poly(ethylene-2,6-
naphthalenedicarboxylate).
3. A method according to claim 1 wherein the ex-
posed article is heated at a temperature of up to about
180° C.
4. A method according to claim 1 wherein the ex-
posed article is heated at about the glass transition tem-
perature of poly (e thy lenenapthalenedicarboxy late).
5. A method according to claim 1 including the step
of measuring the amount of thermoluminescence in-
duced by said heating.
6. A method according to claim 5 including the
further step of determining the amount of oxygen
present in said gas from the measured amount of ther-
moluminescence.
7. A method according to claim 1 wherein the ul-
traviolet light has a wavelength of from 300 to about
430 nm.


Method of detecting oxygen in a gas

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