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Патент USA US2406419

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Patented Aug. 27, 1.946
1v Harold
‘ __
- I‘
Washburn‘iand Harold Wiley,‘ Pasa; '
de'nzuzv?ali?; iassi'gnors to Consolidated’ l-Ene
gineeringrGorporation,Pasadena,{Cali'f.,'ia.co1T§-' _ ,A.
I ‘ Y
’ sporation,o?Galifornia;fz
:1 heating of the ?lament“ itself is begunwThe?la
This: invention: is - con'cerne
gaugesjprovided with :a ?lament; employed: as‘ an :' ment isheated slowly. over a two hour .period
electronvsource. -- a The invention‘ ;is';.sparticular-ly
applicableto the mass :spectrometer iz(which .isxao -* ‘
-. .1
til a temperature-of ZZQOjKelyin .is attained. :. .
Under the , foregoing conditions, :the’ heatingiof . :.- 5
type- of»ion_izationv gauge), gandiprovidesmeans for .15, the ?lament takes placein theli-presence. of se‘vé ; ,
eliminating ‘ gas-sensitivity» .in' ?laments employed 1 eral
Thus carbondioxide,
carbon .mone
in spectrometers and other gauges *as electron
In vacuum tube techniques itiiswcustomaryto
hydrocarbonsaretreleaseditrom-fglass and metal I .1',
1 i
surfaceswithimthe envelope.
In the presence of . , . ,
treat metallic- ?lamentsfsay‘rtungsten ?laments, 10 the oxides of carbon and-the hydrocarbonivaporsl
with hydrogen ‘or other-"reducing gases prior to
the ?lament becomes, free fromogass-sensitivity,
using the ?laments as an electron source. Thus
it is customary to heat the ?lament in an atmos
phere of hydrogen to a cherry red prior to evacu
ation of the Vacuum tube containing the ?lament. 15
gaseous oxides of carbon and hydrocarbon vapors ‘
causes a formationof a stable layer of some com
This procedure, although satisfactory from many
standpoints, causes the ?lament to become gas
sensitive in the sense that the introduction of
gas into the region of the ?lament brings about
(1) a variation in the intensity of the electron, .20
‘emission of the ?lament (2) a variation in the
‘density of the electron emission, i. e. in the cross
section of an emitted electron beam. Both of
these phenomena are objectionable in ionization
gauges and particularly in mass spectrometers,
because each introduction of gas changes the cali
bration of the instrument.
As a result of our investigations, we have dis
covered that metallic ?laments and particularly
tungsten ?laments can be rendered free of gas- '
sensitivity by treating them with a liquid hydro
carbon prior to evacuation and heating. Prefer
ably the hydrocarbon is an aromatic compound.
For example, a pure tungsten ?lament can be
treated with a liquid para?in hydrocarbon or with .
benzene (CsHs) or other liquid ring compound
prior to being placed in the envelope of a mass
spectrometer. If the ?lament is then subjected
and accordingly more useful in’ mass spectrom
etry. It may be that the treatment with the
pound of the metal (say tungsten) with carbon"
and oxygen on the surface of the ?lament and
that this layer acts as an armor to‘ prevent car
bonization of the ?lament and development ‘of
tungsten carbide at depth therein, andQthat in
some manner this prevents gas sensitivity by pre
venting absorption'of gases on the ?lament.
Whatever be the explanation, the fact remains
that ?laments treated as described above are free
from gas-sensitivity.
We have found that leakage of air into the
envelope of a mass spectrometer over long pe
riods will cause ?laments to attain gas-sensitivity
even though they are treated as described here
inbefore. Thus the presence of air within a spec
trometer at a pressure of. 10-6 mm. of mercury
for a period of 48 hours may cause the ?lament
to become gas-sensitive. If, however, this ?la
ment has been subjected to pre-treatment with
a hydrocarbon in accordance with the invention,
this gas-sensitivity is merely temporary and may
be cured by eliminating the air within the en
velope and introducing, say a C3, C4 or C5 hydro
carbon 1. e. a hydrocarbon having as its nucleus
to heating to a red heat after evacuation to a‘
low pressure, say 5><10—_7 mm. of mercury, it will 40 either 3, 4 or 5 carbon atoms for a considerable
period, say 24 hours.
be free from gas-sensitivity under most condi
It is desirable, in order to preserve the free
Our invention will be more thoroughly under
dom from gas-sensitivity attained through the
stood in the light of the following detailed de
treatment of the invention, to maintain a con
scription of the presently preferred practice:
centration of a C3, C4 or C5 hydrocarbon in the
In accordance with this practice, the ?lament
spectrometer during idle periods. ‘Thus if the
is thoroughly washed in a liquid hydrocarbon,
spectrometer is not in use over a week end, the
say in benzene. Subsequently it is placed in the
presence of n-butane within the envelope at a
envelope of the spectrometer and the envelope
pressure of say 10*6 mm. of mercury tends to pre
is then heated and simultaneously evacuated, the
serve the calibration of the instrument. This
heating serving to drive occluded substances from
treatment with C3, C4 or C5 hydrocarbons will
the wall of the envelope and from the metal and
cure gas-sensitivity of Va ?lament temporarily,
- other parts of the spectrometer enclosed in the
even though the ?lament has not been subjected
envelope. When the pressure in the envelope has
been reduced to a low value, say 5X 10-6 mm. Hg, 55 to the pre-treatment described hereinbefore,
'Without the pre-treatm ent, however, the cure is
only temporary.’
We claim:
adapted for service as electron emitters in ioniza
‘tion gauges, the improvement which comprises
treating the ?lament with a liquid hydrocarbon
and subsequently heating it to redness in an
1. In the treatment of metallic ?laments adapt
ed for service as electron emitters in’ ionization , ,- evacuated envelope .in the presence of a minute
gauges, the improvement which comprises treat-1. , proportion of. an oxide of’ carbon plus the hydro
ing the ?lament with a liquid hydrocarbon and
subsequently heating it in an evacuated envelope
carbon adhering to the?lament from the prior
.,,tre'atment, thereby reducing gas sensitivity of ‘the
in the presence of a'minute amount of the hydro
carbon adhering to the ?lament’as a result of L10 , 5. Inithe: treatment of ‘metallic- ?laments
the prior treatment, thereby reducing gas sensi-v ‘ adapted for service as electron emitters in ioni
" tivity of the ?lament. ‘
_zation gauges, the improvement ‘which comprises _
treatingthe' ?lament with benzeneland subse
quentlyiheatingliteinan evacuated envelope in
a‘ 2. Inthe treatment of tungsten ?laments'adapt- 1 7 ed for service as electron emitters in'ionization
gauges, the improvement which comprises treat 15 the presence of a minute proportion of the ben
adhering to the ?lament from the prior '
ing the ?lament with a liquid hydrocarbonand , ‘ ?zlene
subsequently heating it in an evacuated envelope
ge@§me§§> thereby reducing’ gas sensitivity of the
in the presence of a minute amount of the hydro
carbon adheringto the ?lament as a result of "the ' "
prior treatment, thereby reducing gas sensitivity
In‘YT-ithe ; treatment a of‘ metallic ?laments - 7
adapted for service as electron emitters in ioni
, >zation ‘gauges, thelimprovement iwhichtcomprise's l;
3.1m the treatment or‘ metallic-~?laments
adapted for service as electron emitters in i'oni’za-V
tion'sgauges, the improvement which comprises
treating the ?lament’ with-a‘ liquid aromatic hy-‘v
treating the ?lament with- a liquid hydrocarbon-1 l h v
and subsequently heating it in an evacuatedi-ent-fh; "
velopein the‘ presencelof-noamore than that ‘mi-
25 nuteproportion of the hydrocarbon which-‘adheres, _
drocarbon and subsequently heating it in an evac
to the ?lamentinthe prior treatment, the -Vpres_v a
uated envelope in the presence of a minute amount 7 ' sure in the envelope being below 5><~10rb mm; Hg
of the hydrocarbon‘adheringl to the?lament as a " during the heating, thereby reducingljgasis'ensiir ‘
result of the prior, treatment,"thereby reducing Y‘ tivity of the ?lament;
gas sensitivity of the?lament.
_, 4. In *the treatment ‘of metallic ?laments
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