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Mass spectrometer studies of high vacuum materials
VACUUM Classified V a c u u m
II --
Vacuum
Apparatus
and
Auxiliaries
--
II
Contd.
occupying 1.4 ft. 8 of space. The box containing the tube was pressure-tight in order to prevent an evacuation of the rocket i n s t r u m e n t section, pressurised at one atmosphere, in case the glass envelope of the t u b e should break. The t u b e was connected b y a b r a s s bellows to the outside of the rocket. The outlet was protected b y a rubber stopper during the take-off which was forced out by the pressure differential shortly afterwards. The operation of t h e i n s t r u m e n t was started b y a timer at 100 km. altitude: The resolution of the i n s t r u m e n t was about 1 in 25. Sommaire : L ' o n a adapt6 u n spectrom~tre de masse ~ fr6quence radiophonique du t y p e B e n n e t t ~ l'usage darts des fus6es, en liaison avec des recherches ~t h a u t e altitude au del~ de 150 kin.
Abstract No. and References
Article by J. W. TownsendJr.
Rev. 8ci. lnstrum. a3, Oct, 1952 538-541
Mass Spectrometer Studies of H i g h V a c u u m Materials See Abstract No. : 28/II
21/II
Brazing Vacuum-Tight Joints in H i g h Nickel Alloys See Abstract No. : 33/II
22/II
z6
--
MATERIALS
--
26
Glass Surfaces in a High V a c u u m Germany. In the p a s t the behaviour of glass surfaces exposed to a v a c u u m was mainly of interest to t h e valve and bulb m a n u f a c t u r e r the problem being the prevention of gas evolution from the glass surface. Recent developments in v a c u u m coating added to this t h e necessity of eliminating layers of foreign m a t t e r from t h e glass surface prior to deposition. The present article surveys relevant research work bearing on b e t h problems. Substances can be bound to t h e glass surface in three different ways: (1) By chemical binding, (2) b y absorption and (3) by adsorption. As' it is not always possible to make certain which of the three conditions apply it is the c u s t o m to speak generally of absorption. The absorption m e c h a n i s m h a s b e e n investigated theoretically by F a j a n s and W e y l who stipulated t h a t the chemical behaviour of a t o m s and ions present in the b o u n d a r y face is governed b y t h e structure of the electron shell surrounding the nucleus. In certain materials the forces within t h e a t o m remain stabilised although a few surplus electrons are removed from the outer shell during an ionisation proces~ Ions of this kind are O z-', F-, Na +, Mg 2+, A1 s+, Sit+, K +, Ca z+ and B 8+. In others the removal of electrons from the exterior orbits will cause effective polarisation of the charge of t h e ion. Ions of this class are Cd s+, Zn =+, Sn =*, and P b s+. A P h 2+ ion in the b o u n d a r y face for instance can be polarised b y the field of force in t h e glass. I t will t h e n act like a P b 4+ ion with respect to the body of the glass, b u t like a neutral lead a t o m with respect to the area surrounding the glass. A n Si4+ ion in the b o u n d a r y face on the other h a n d has two free valencies which cannot be s a t u r a t e d from within the glass as it does n o t react to t h e internal field force. T h e latter, therefore, will show a t e n d e n c y to absorption from without. This h a s been confirmed by experiment. A freshly broken glass surface will cover itse~lf rapidly with O H ions in places where Si ions are present. These layers are i n s t r u m e n t a l in forming a water skin b u t t h e OH ions can be replaced b y ions of the fluoride groups which promote the formation of hydrophobic films. L a n g m u i r investigated the evolution of gases and vapours from glass of the t y p e used in valves a n d bulbs and found t h a t essentially water vapour was liberated. Harris and Schumacher investigated six glasses giving a proper chemical analysis as shown in the table reproduced below.
23/II
Chemical Analysis of Glasses Examined by Harris and Schumacher 1 Si0, '
January 1953
69.93
2 69.40
•
3
4
64,64
5'
61.50
72.05
6 65.47
AltO,
1.54
0.78
0.20
0.57
2.21
2.99
Fe=O,
0.19
0.]4
0.04
0.11
0.05
0.51
PbO
1.44
Spurious Amounts
21.66
22,55
6.11
20.20
CaO
3.17
5.15
0.02
0.21
0.05
0.22
MgO
0.03
4.09
0.02
0.36
0.09
O.13
NatO
21.02
16.67
9.10
8.14
4.23
6.40
K=O
0.10
0.20
3.20
3.76
1.12
3.59
PrO,
0.08
0.16
0.75
0.34
Spurious Amounts
Spurious Amounts
Sb=O=
0.05
O.lO
--
Spurious Amounts
--
--
MnO=
0,09
0.19
0.19
0.01
0.073
.BtO,
2.36
3.12
2.27
.14.07
--
0.37
Vacuum Vol, I l I No I
84
II --
Vacuum
Apparatus
and
Auxiliaries
--
II
Contd.
occupying 1.4 ft. 8 of space. The box containing the tube was pressure-tight in order to prevent an evacuation of the rocket i n s t r u m e n t section, pressurised at one atmosphere, in case the glass envelope of the t u b e should break. The t u b e was connected b y a b r a s s bellows to the outside of the rocket. The outlet was protected b y a rubber stopper during the take-off which was forced out by the pressure differential shortly afterwards. The operation of t h e i n s t r u m e n t was started b y a timer at 100 km. altitude: The resolution of the i n s t r u m e n t was about 1 in 25. Sommaire : L ' o n a adapt6 u n spectrom~tre de masse ~ fr6quence radiophonique du t y p e B e n n e t t ~ l'usage darts des fus6es, en liaison avec des recherches ~t h a u t e altitude au del~ de 150 kin.
Abstract No. and References
Article by J. W. TownsendJr.
Rev. 8ci. lnstrum. a3, Oct, 1952 538-541
Mass Spectrometer Studies of H i g h V a c u u m Materials See Abstract No. : 28/II
21/II
Brazing Vacuum-Tight Joints in H i g h Nickel Alloys See Abstract No. : 33/II
22/II
z6
--
MATERIALS
--
26
Glass Surfaces in a High V a c u u m Germany. In the p a s t the behaviour of glass surfaces exposed to a v a c u u m was mainly of interest to t h e valve and bulb m a n u f a c t u r e r the problem being the prevention of gas evolution from the glass surface. Recent developments in v a c u u m coating added to this t h e necessity of eliminating layers of foreign m a t t e r from t h e glass surface prior to deposition. The present article surveys relevant research work bearing on b e t h problems. Substances can be bound to t h e glass surface in three different ways: (1) By chemical binding, (2) b y absorption and (3) by adsorption. As' it is not always possible to make certain which of the three conditions apply it is the c u s t o m to speak generally of absorption. The absorption m e c h a n i s m h a s b e e n investigated theoretically by F a j a n s and W e y l who stipulated t h a t the chemical behaviour of a t o m s and ions present in the b o u n d a r y face is governed b y t h e structure of the electron shell surrounding the nucleus. In certain materials the forces within t h e a t o m remain stabilised although a few surplus electrons are removed from the outer shell during an ionisation proces~ Ions of this kind are O z-', F-, Na +, Mg 2+, A1 s+, Sit+, K +, Ca z+ and B 8+. In others the removal of electrons from the exterior orbits will cause effective polarisation of the charge of t h e ion. Ions of this class are Cd s+, Zn =+, Sn =*, and P b s+. A P h 2+ ion in the b o u n d a r y face for instance can be polarised b y the field of force in t h e glass. I t will t h e n act like a P b 4+ ion with respect to the body of the glass, b u t like a neutral lead a t o m with respect to the area surrounding the glass. A n Si4+ ion in the b o u n d a r y face on the other h a n d has two free valencies which cannot be s a t u r a t e d from within the glass as it does n o t react to t h e internal field force. T h e latter, therefore, will show a t e n d e n c y to absorption from without. This h a s been confirmed by experiment. A freshly broken glass surface will cover itse~lf rapidly with O H ions in places where Si ions are present. These layers are i n s t r u m e n t a l in forming a water skin b u t t h e OH ions can be replaced b y ions of the fluoride groups which promote the formation of hydrophobic films. L a n g m u i r investigated the evolution of gases and vapours from glass of the t y p e used in valves a n d bulbs and found t h a t essentially water vapour was liberated. Harris and Schumacher investigated six glasses giving a proper chemical analysis as shown in the table reproduced below.
23/II
Chemical Analysis of Glasses Examined by Harris and Schumacher 1 Si0, '
January 1953
69.93
2 69.40
•
3
4
64,64
5'
61.50
72.05
6 65.47
AltO,
1.54
0.78
0.20
0.57
2.21
2.99
Fe=O,
0.19
0.]4
0.04
0.11
0.05
0.51
PbO
1.44
Spurious Amounts
21.66
22,55
6.11
20.20
CaO
3.17
5.15
0.02
0.21
0.05
0.22
MgO
0.03
4.09
0.02
0.36
0.09
O.13
NatO
21.02
16.67
9.10
8.14
4.23
6.40
K=O
0.10
0.20
3.20
3.76
1.12
3.59
PrO,
0.08
0.16
0.75
0.34
Spurious Amounts
Spurious Amounts
Sb=O=
0.05
O.lO
--
Spurious Amounts
--
--
MnO=
0,09
0.19
0.19
0.01
0.073
.BtO,
2.36
3.12
2.27
.14.07
--
0.37
Vacuum Vol, I l I No I
84