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Aug- 13, 1963
I
'
LIGHT
K. B. MGAFEE, JR
DE
TECTOR USING THIN WALLED
3,100,368
ASS TUBES FOR DIFFUSION
Filed Aug. 20, v1958
- 2 Sheets-Sheet 1
DIFUS/ON
;
lNl/EA/TOR
A’. 8. Mc AFEE, ‘JR.
_
A
ORNE V
Aug. 13, 1963
K. B. M0
LIGHT GAS DETECTORAFEE,
USING JR
THIN WALLED
GLASS TUBES FOR DIFFUSION
Filed Aug. 20, 1958
3,100,868
2 Sheets-Sheet 2
F/G. 2
PL ‘or CF PERMEAB/L IT)’ ors/L/cA GLASS r0 VARIOUS GASES
He //V S/L ICA
I727
'
727
393
227
I27
60
I3
—23
TEMPERATURE °c.
)X/l/EA/fOR
K. 8. Mc AFEE, JR.
Tim/6 2/2,?
A TTORNEV -
United States Patent 0
1C6
_
11
2 .
and la wall'thickjness of three mils. The closed ends of
3,100,868
the tubing are sealed in ‘a gas-‘tight ?oating head 9 of,
for example, epoxy resin ‘arranged to keep the tubes in a
?xed position. The open ends‘ of the tubing pass through
va gas-tight seal It} of, for example, ‘epoxy resin which
"LIGHT GAS DETECTOR U§ING THIN WALLED
GLASS TUBES FOR DIFFUSIGN
Kenneth 18. Median, in, Summit, N.J., assign'or. to Beli
Telephone Laboratories, incorporated,‘ New York, NJEL,
a corporation of New York
provides a gas-tight barrier between-enclosure 11 and en
closure 12 with the latter enclosure common to the open
ends h of tubes '6; Neck 13 is connected to an ionization
Filed Aug. 20, 1958, SeruNo. 756,115
r
3,100,868
Patented Aug. 13, 19:53
6 (Jlaims. (Ci. 324-33)
manometerwhich comprises a housing 14 having outlet
The invention relates to a process ‘and apparatus for 10 15 provided ‘with valve 16 leading to a diiiusion pump,
the detection of gases.
‘
l
.
_
not shown. Housingld encloses ?lament 17 having ten
Large pipelines ‘are today carrying vast quantities of
hydrogen and helium. Laboratories and industries are
volts impressed thereon, anode 18 having’plus 150‘ volts
impressed thereon, and cathode 19 having minus ?fteen
using increasing ‘amounts of the tracer gases such as hy
‘volts impressed thereon.
drogen, helium, deuterium, tritium and neon. Vessels 15
that ‘are to be pressurized ‘are tested with tracer gases
to insure against leaks. As a result, there is an increasing
demand for a simple, inexpensive and portable gas de
tector that is highly sensitive'to the tracer gases enumer
ated above.
‘
.
-
"
through the leak goes into inlet 2 of the detector, dif
fuses through the tubing 6 and hence into the detecting
20
One prior ‘art device used for these purposes is the
.
‘
In operation, the detector which operates at room pres
sure is placed in the vicinity of a leak. The gas escaping
element which is maintained ‘at a partial vacuum of 10"6
millimeters of mercury. The gas atoms ?owing into the
detecting element are ionized by electrons from ?lament J
This device has‘ the disadvantage,
\17. The resulting ions ?ow to cathode 19 .and‘induce a
however, of being expensive and bulky. Where the gas
current thereon.
current, which is Ia measure of the
to be detected is combustible, it may be detected by the
amount of gas diffusing through the tubing can be meas
change of the burning rate of a ?ame, for example, the 25 ured by a galvanometer, for example by a Veeco Vacuum
use of hydrogen detectors inmines. The disadvantages
Gage, which ampli?es the current before measurement.
of such detecting means including insensitivity and danger
Since under normal operating conditions the tubing walls
mass spectrometer.
to the operator are apparent. ‘
v
“
are ‘virtually impermeable to atmospheric gases, the en
in accordance with this invention, there is described‘ a
‘re measured induced current is due to the leak. If there
device particularly adapted to ‘the detection of helium. 30 is a gas in the atmosphere to which the detector is sensi
The device is also sensitive to tracer gases such?as hydro- ‘
» .‘gen, deuterium, tritium ‘and neon. ‘ The ;devic'e~isjrugged,
' inexpensive, portable and can ‘be'kept‘in' storage‘ for long‘ .
periods of time withoutdeterioration,
. .
tive, thegalvanometer can be adjusted to give a com
pens‘ate-d zero reading before being placednext to the‘
‘leak.
‘a
,
j
’
‘
‘
Although speci?cvalues have been used in describing ‘
The detectionv of gases by this device is dependent upon
the‘device ‘of FIG. 1,‘it is ‘to be understood that these
the selectivity of thinwalled glassytubingqto‘the enumer
values‘are-exemplary only.
ated gases. _ The‘ sensitivity of' the device ‘to varying
I
_‘
i
The detector is designed to operate at room pressure
' . amounts of one or all of the'igases is proportional to the
‘with a‘ partial vacuum; for ‘example, 1of'_1(l—3 to 10'10
surface area of'the' tubing which is increased by using a
millimeters of mercury maintained inside the tubing and
multiplicity of tubing The tubing is arranged so as to be 40 detecting unit. The amount of gas per secondildi?uising
' contacted on the outside by a gas mixture containing
one or more of ‘the enumerated gases. One ‘end of the
through the tubing is ‘a function‘of the'diameter of the"
tubing to ‘the ‘wall thickness.‘ - A ratio of from four ‘to
one to six'to one islpreferred. The time'for diffusion
tubing is closed while the other end opens into‘ia common
enclosure.
The ‘actual detection of the gas or gases
' is desirably, small, in the orderof one second or ‘less.
that diffuse through the tubing Walls ‘is achievedby‘a 45
detecting element such ‘as unionization manometer which
is connected to the common receptacle‘.
_
“
‘time is proportional to ithelwall‘ thickness squared
over the diffusion constant.
7
l
.. V
T ubing having ‘an outside diameter ranging from one ‘ '
A more complete understanding of the features of this ‘1 ‘ mil to ?fty mils ‘and ‘a wall thickness varying from 0.2
invention together with additional objects thereof may
mil to ten mils is suitable These limits are based on prac
be gained from the following description in conjunction
tical considerations.‘ Thinner tubing is generally undesir
with the accompanying drawings in which: ' 7
FIG. 1 is ‘a frontrelevational view partially in section
showing at detecting element in conjunction with a sens
ing element; and
' able only from the standpoint of fragility; thicker tubing
although operative‘necessitates ‘additional bulk and affects 7
only portability.
.
In general it is preferable to form the tubes of a glass
FIG. 2 on coordinates of permeability. versus tempera 55 which includes at least a total aggregate of seventy-?ve
ture is a plot of permeability of ‘a preferred glass material
percent of one or more of the “glass-forming” substances
to various gases.
With reference now more speci?cally to the drawings,
the device shown in FIG. 1 is thirty-six inches long and
[silica (SiO2), boron oxide (B203), aluminum‘ oxide
(A1203), and phosphorus trioxide (P203). Glasses oom~
prising ‘at least seventy-?ve percent of silica and glasses
utilizes a sensing element comprising a gas-tight metal 60 comprising at least seventy-?ve percent of silica and a
jacket 1 formed ‘for example of “Kovar” metal having
gas inlet ‘2, gas outlet 3, ‘and ‘an insulated heating Wire 4
maximum of ?fteen percent boron oxide (B203) ‘are
among the better glasses for the purposes of this inven
encircling the surface. One end of the jacket 1 is closed
tion. For example, fused silica glass (100% silica),
by metal cap 5. The jacket 1 encloses approximately two
chemical Pyrex glass [81% silica (SiOZ), 13% boron ox_
65
miles of silica tubing 6 having closed ends 7 and open ends
ide (B203), 2% aluminum oxide (AlzOghand 4% sodium
8. The tubes have outside diameter of seventeen mils
oxide (NaQO) and/or potassium » oxide (KQOH and
‘3,100,863
“Vycor” glass ,[96% silica (SiOZ), 3% boron oxide
(B203), and'1% aluminum oxide (Al2O3)] have been
successfully used in the’device of this invention. Silica
tubes have been found to be particularly advantageous,
Percent helium
Original
'
having at room'tetnperature a permeability to helium‘ as
much as one thousand times greater than that for hy
drogen, the next smallest atom.
End pressure
pressure
Di?erence
(mm. 'Hg)
1.
3. 4=><10—7
5. 2><10,~5
> 1. 22><1()-a
0.
0.
O.
3.8><10-1
5.8><10-7
3.6)(10-7
4. 2X10-7
4. l><10—°
8. 0><10-7
4.1X10-7
8 80x10-5
5 20><10—°
1 18><10—a
4.4x10-1
4 73x10-7
0.0004 _____________________ __
Referring to FIG. 2, the eifect of temperature on the
permeability of silica tubing to various ‘gases is plotted.
What is claimed is:
At room temperature exceptionally pure helium is dif 10
fused through the silica tubing even though the initial gas
' mixture: may contain hydrogen and neon.
This results
since helium with its atoms only 2A. in diameter diffuses
through the walls or" the tubing, whereas hydrogen, the
next smallest atom, While being only twenty-?ve percentv
'
'
V
which a gas to be detected diffuses and a detecting element
sensitive to the gas 'diifusing through the glass tubes.
2. The detecting device in accordance with claim 1
‘wherein the tubes are made of a glass having a silica
content of at least seventy-?ve percent.
3. The detecting device in accordance with claim '1
larger than helium, has a diffusion constant through the
tubing one thousand timessmaller. Larger gas molecules
such as, methane with a diameter of 2.5 A. has such small
diifusion, constants that they will not-pass through the
glass tubing'in any signi?cant quantity.
As‘ theoperating temperature is raised, for example, by
“Nichrome” fWl-f? ti surroundingmellic jacket 1, kinetic
.
1. A gas detecting device comprising a sensing element
having a multiplicity of thin walled glass tubes having 'an
outside diameter varying from. one mil to ?fty mils and
a Wall thickness varying from \0.2 mil to ten mils through
20' wherein the tubes are made of a glass comprising a mini
mum of seventy-?ve percent silica (SiO2) and a maximum
'of ?fteen percent boron oxide (B203).
energy is imparted to gas molecules surrounding the
,
4. The detecting device in accordance with claim'l
wherein the tubes are made of a glass comprising at least
ceramic tubing 6. This energy increases the diffusion con->
At approxi-j 25 a total aggregate of seventy-?ve percent of one or more
rnately 165° "C. hydrogen commences to diffuse through
of the glass forming substances selected from the group
thevtubing in appreciable amounts. 'At an even more
consisting‘ of silica (SiOg‘), boron oxide (B203), alu
elevated temperature, approximately 270° C, neon com
minum oxide (A1203), and phosphorus trioxide (P203).
stantrof each of the gases in the mixture.
' mences to‘ diffuse through the tubing in appreciable
amounts. The temperature range of this, device may vary
5. The detecting device-in accordance with claim 1
so1wherein
means is provided for maintaining 1a‘ partial
from room temperature to 400° for Pyrex tubing, and
I ' vacuum of 10*3 to 10"10 millimeters of mercury; '
' from room temperature'to 800° C. for silica tubing With
6. A gas detecting device comprising a gas-tight jacket
out ‘any deteriorating effects on the tubing. It is evident .I’ having a gas inlet‘ and a gas outlet, a heating wire en
that by using two or more sensing elements operating at ,- circling said jacket, a multiplicity of thin walled glass
selected temperatures vin combination with a detecting
tubes having an outside diameter varying from one mil
element, itis possible to detect any one gas of the group
to fifty mils and a Wall thickness varying from 0.2'mil to
consisting-of helium,rhydrogen, deuterium, tritium, or
ten mils enclosed by said jacket, said .tubes'being sealed
at one end and opening into a common enclosure at the
As an alternative arrangement, the gas mixture may
40 other end, said enclosure being connected with 'an ioniza- ' ,
1 ‘be admitted to the‘in’side of the glass tubing. :The gas ‘ tion manometer,‘ and means for‘ countingthejions pro-: '
to'be detected then diffuses out'ot‘ the tubing and ‘news - 'iduced by said manometer. 1
neon from a gas mixture.
' intoi the detecting element-
7
.
.
'
I VThe detector of the present invention
capable of ' ‘
‘ '
References 'Citediin' thei?leoftthisilpatent
‘ ' i‘ V
detecting leaks of very small'magnitude. For. example,
the following table showsvthe sensitivity of a detector of
45"., i - f
this invention using Pyrex tubing to varying percentages
‘of helium present in a gas mixture. The operating tem
perature-was maintained at 357° C. to 392° C. and a
' ,Yeeco" vacuum gage‘ .was used to measure the induced
" current .on the cathode ‘of the ionization- manometer.
In this example,the induced current was read as a func- ’
5
UNITEDSTATESPAIENIS
_
2,400,940
McCollum
2,526,038
__
,
72,671,337
2,734,592
2,909,919
"____ __I,
'
May 28, 1-946v '
__"_____‘ Oct.‘17, 1950
Hulsberg _____________ __ Mar. 9, .1954
1 Jones __'_ __________ __-,___ Feb. 14, 1956
Myer _______________ __ Oct. 27, 1959
Schaschlet a... __________ __ Ian. 12, 1960
2,921,210
tion-of the difference multiplied ‘by a factor of 23.6 be
tween the end pressure ‘reading and the original pressure .
_ reading on the ‘manometer.
g
'
'
' 7 431,507
.
,
FOREIGN
PATENTS
,
Germany ___.__'_ ________ __' July 8,1926
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