Note: Descriptions are shown in the official language in which they were submitted.
;- -
~6~0~
This invention relates to glass seals, more particul-
arly ~o electrical connectors containing hermetic glass seals.
.
Glass seals are provided between electricallyconductive elements in various electrical connectors. The
~ seal usually is required to be hermetic and the glass often is
; ~ required to have a high electrical resistance.
~ Electrical connectors using glass seals of this
type may be employed where exposure to the effects of the
operation of a nuclear reactor is anticipated. This particular
use requires particularly stringent physical and chemical require-
ment of the glass and seal. Typical glass compositions for
such use are described in UOS. Patents Nos. 3,307,958 and
3,519,446.
The present invention provides a hermetic glass seal
between electrically conductive components and particular seal
~` ; st~uctures.
20~
Conventional electrical connector construction
involves an inner metal conductor member, an outer metal
conductor me~er and glass sealingly ~oining the members. The
:. ~
coefficient of thermal expansion of the components of this seal
are such that the outer conductive member exceeds that of the
glass and that of the glass exceeds that of the inner member.
While this çonstruction is satisfactory in some
environments, in others, where the temperature cycles periodically
between l~w and high values, considerable thermal stresses
occur, leading to cracking of the glass seal, to the detriment
of the electrical resistivity and the hermeticity of the seal.
'~
647~4
In accordance with one preferred embodiment of the
invention, it has been found that these difficulties
are ove~come, if inner and outer metal members have coefficients
of thermal expansion exceeding that of the glass. In a
particularly preferred construction, the conductive metal is the
same for the inner member and the outer member, typically
stainless steel having a coefficient of thermal expansion of
about 180 to about 220 x 10 7 in/in/C.
Glasses suitable for use in constructions provided
in accordance with this embodiment of the invention usually have
a thermal expansion of about 40 to about 120 x 10 7 in/in/C.
A hermetic seal between the metal members requires
the use of a glass composition which has solubility for the
oxides of the metals of ~he members. An oxide film is
formed on the metal surface during heating to the temperature
required for sealing.
The seal may be provided in a number of environments
other than electrical connectors. The seal may be provided between
inner and outer metal elements in various electrical packages,
including ~hermocouples.
~arious geometric arrangements may be used in this
inventionf including a single pin passing through a single
circular seal connected to a circulAr outer metal member~ a
.
plurality of pins passing through individual circular seals
connected to a single circular outer metal member, a plurality
of pins or wires passing through a single seal connected to a
single circular outer member and a plurality of pins or wires
passing through individual circular seals connected to a single
rectangular outer metal member.
Glasses for use in seals provided in nuclear environ-
ments should not contain boron oxide due to the changes which
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:1~647S~4
boron undergoes on neutron capture or cobalt oxide due to the
induced radiation brought about by neutron capture. In accordance
with a second embodiment of $he invention, there are provided
hermetîc glass seals formed from boron- and cobalt-free lead-
silica glasses.
Glasses having varying compositions based on lead- -
silica glasses in accordance with thls second embodiment of the
invention give satisfactory hermetic seals in pxior art
seal constructions and in seal constructions in
~10 accordance with the first embodiment of the invention. One
such class of glasses contains alumina and varying quantities of
~ .
~ ~group II metal oxides. Such group II me~al oxides include zinc -
r
oxide, calcium oxide and barium oxide. Other non-alkali fluxing
oxides, such as bismuth oxide, also may be present. Typical
glass compositions according to this class contain lead oxide and
silica in the relative quantities:
~;~PbO about 45 to about 65%
SiO2 about 55 to about 35%
along with the following quantities of other components, the
quantities being based on the total quantity of lead oxide and
silica:
A12O3 about 3 to about 4 wt.%
; ~ ZnO about 7 to about 8 wt.
-~ .
CaO 0 to about 6 wt~%
BaO 0 to about 7 wt.%
Bi2O3 0 to about 7 wt.%
These glass compositions provide satisfactory seals
for use in many enviro~nents. However, it has been found that
while these glass compositions exhibit high resistance at room
and high temperatures and hence could be considered suitable fox
nuclear reactor environments, they are less preferred due to
their high viscosity under no~nal sealing conditions.
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~647~4
Another class of glass compositio~s which is
provided in accord nce with this second embodiment of the
invention consists of a basic lead silica glass containing
varying quantities of lead oxide and silica. The range of
quantitLes is as ~ollows:
PbO about 55% to about ~5 wt~ ~
SiO2 about 45~ to about 15 wt. %
Such glasses exhibit satisfactory low and high temperature
resistivities for many uses and seals produced therefrom are
hermetic. Seals produced from these glasses, however, exhibited
a deteriorated hermeticity upon thermal cycling between high
and low temperatures and hence may be unsuitable for use in
such environments.
The following Table I reproduces data developed
on seals formed using certain members of the lead oxide-silica
glasses prior to thermal cycling. Each of seals exhibited a
resistance at room temperatures exceeding lQ9 ohms and a
resistance at 600F o~ about 108 ohms.
TABLE I
2DGlass Composition ~C/o~ He Leak
wt. ~ x 10 cc/sec.
PbO sio
2 -- ~
100.9 C 10
g3.7 ~10 8
Ç7.5 ~10 8
Differing quantities of various metal oxides may thus be
added to such lead-silica glasses to improve their properties.
Amon~ the additive oxides which may be included, in various
combinations and quantities, are Group II metal oxides including
calcium oxide, magnesium oxide, barium oxide and zinc oxide,
alumina, bismuth oxide, zirconium oxide, cerium oxide, germanium
647~4
oxide and mixtures of soda and potassia.
One such composition contains varying quantities
of germanium oxide, Group II metal oxides and fluxing oxides
and contains lead oxide and silica in the relative quantities:
PbO about 65 to about 85%
S~2 about 35 to about 15~
~: along with the following quantities. of other components, the
quantities being based on the total quantity of lead oxide and
silica:
: GeO2 about 6 to about 18%
: BaO . about 1 to about 9%
CeO2 abou$ 2 to about 3
CaO 0 to about 2%
: ~ MgO 0 to about 2%
; ZnO 0 to about 13%
Bi2O3 0 to about 8%
Al O 0 to about 5
:~ 2 3
Z:r2 to about 2 %
~: 20 While these latter glasses have improved high ~erature
electrical resistivity and higher thermal expansion coefficients,
~ .
the seals exhibit a decreased mechanical strength.
: ~ Standards have b en established in certain jurisdic-
~ tions for seals for use in nuclear environments. There are also
: ~ other practical standards which the glass composition must meet
.~
to provide an effective seal for prolonged use. These standards
include o
.
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1~64~4
i) Glass must not contain boron or cobalt;
ii) C.lass must be sealable at under 1100 C,
iii) Glass must have a coefficient of expansion of
a~out 40 to about 120x 10 7/C;
iv) Seal must have an electrical resist.~nc,e..greater
than 109 ohms a 700F and greater than 108 ohms at 600F;
; v) Glass must have an electrical resistivity to
,~ provide the desired resistance of the seal, typically at least
one order of magnitude greater than the resistance of the seal;
. vi) Glass mus~ have a gradually decreasing viscosity .
: with increasLng temperature to about 104 poise at the sealing
: temperature;
vii) Seal,must be hermetic, typically better than 10 8
~ . .
; ccs of Helium per second,
: ~ viii) Seal must retain it~; integrity after 20 thermal
cycles of 70 - 600 - 700F with stabilization at each tempera-
, ture,
ix) Seal must withstand vibration;
x) Seal must maintain hermeticity in a slightly
. . . .
20~ .acidic atmosphere arising from the presence of ozone; and
xi) Seal must maintain hermeticity in up to 95
:: relative humidity and possible contact with liquid water;
xii) Seal must withstand a.radiation dose of up to
lOOR/hr.
. Glasses conforming to those stringent requirements
have been formulated in accordance with a particularly preferred
aspect of this second embodiment of the invention. One such
class of lead-silica glass composition contains up to 5 mole %
..
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1~647~4
of mixed alkali, i.e. a mixture of sodium oxide and potassium
oxide in similar quantities.
It is known that glasses containing alkali metal oxides
such as sodium and potassium oxide, have low electrical resist-
ivity and hence normally would be expected to be avoided in seals
requiring a very high resistance~ It has been found, however, that
the addition of limited quantities of a mixture of sodium oxide
and potassium oxide in an approximate 1:1 weight ratio to a lead-
silica glass nst only do not decrease the resistance of the glass
~ but also increase its coefficient of thermal expansion.
The addition of the mixed alkali may be made to
~he germanium-containing glass compositions described above to
provide about 2 wt.% of both Na2O and K2O based on the total quan-
tity of lead oxide and silica, in the glass composition.
~ O~her lead-silica-based glasses containing the mixed
; ~ alkali may be provided in accordance with this embodiment of the
invention and also may contain additional components, such as
minor quantities of Group II metal oxides, including calcium oxide,
barium oxide, magnesium oxide and zinc oxide.
,
20 ~ Typical glass ~ompositions of this cla~s contain lead
oxide and silica in the relative quantities:
PbO about 63 to about 66 wt.%
SiO2 about 37 to about 34 wt.%
and the following components, based on the total weight of lead
oxide and silica:~
Na2O about 1 to about 2 wt.
K2O about 2 to about 3 wt.
BaO 0 to about 2 wt. %
MgO 0 to about 1 wt. %
ZnO 0 to about 3 wt. %
CaO 0 to about 3 wt. %
Members of the mixed alkali-added class of glasses along
with their properties in a seal formed from stainless steel
members are set forth in the following TableII:
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6~7~L
, ~a~ u~
~1~ O In n O d' I` ~ t` N
n~O ,1 . . O O I O
~ o
U~ O
O .
._
~ ,01
O
U~~1 U~
.,1 ~3 ~ OU~CO
U~ ~ . . . . . . .
1~ . r-l N In ~ ~ ~) ~U~ O
: ~ E-
.
~ .
~` .
~ O U~ ~ . ~ ~ ~
O ~ . . . , I I . . .
` ~ I`
~ X' I` oo a~
_ _ _
N u~
:- ~ I I I I I ~ i
O N
: ~ ~ ~ I I I I I I I I ~D
_ m_ ~
~ O
o I I ~ I I
H _ _ _ _ ~1
::
IY . . o O N NC`l a;l ~
~a ~ 9 Il')I I
~ ~ ~ i
E~
N
O .
~1 ~ r~ ~
: ~ , ~4 0 I I ~ o 1~ 1
+ ~ o ,I r~a N
~- _ __
. O , ~`1~ 1` ~~ ~
I I O O O O 'O O I
~'.: : S
a~ I
~r ~n
: m ~ 9
: o
ri _ _ _
.
,~ ~ ~ ~ ~~. ~ ~ ~ 9
~ O ~I~ r~
O N . . . . . . .
. ~ ~ K ~ N N N N~1 N N ~1
O .
O Wc~
~1 ~ . . . . . . . .
Z ~ i
, ,
N ~ r ~ ~
O . . . . . . .,. .
,1 ~ r- ~ ~
~ r~
_ , . .
~ .
3 In ~ ~t~ ~ ~ ~ ~ a~
~0 ~ ~.
U~ W U~ .
~6~704
It will be seen from this TableII that each of the
glass compositions has a thermal expansion and the seals have
electrical resistance values well within ~he required ranges. In
all cases, the seals were hermetic and in most cases the seals
withstood thermal cycling.
~ nother class of glass composition uses varying
quantities of Group II metal oxides, in particular barium oxide,
in a lead-silica glass composition to provide superior electrical
resistivity, compression strength and thermal expansion coefficient
properties. Compositions in accordance with this class include
lead ox;de and silica in the following relative quantities:
PbO about 60 to about 80 wt. %
SiO2 about 40 to about 20 wt. %
and the following additional components, in quantities based on
the total weight of lead oxide and silica:
BaO about 2 to about 14 wt.
, ,1
MgO 0 to about 2 wt. %
ZnO 0 to about 3 wt.
CaO 0 to about 3 wt. %
~20 ~ ~ Glasses formulated in this way exhibit excellent sealing
characteristics with the electrical resistance of the seals
:
exceeding subst~ntially the requirements set forth above. Members
of this class of glasses along wi~h their properties in a seal
formed from stainless steel members are set forth in the following
Table III:
.: .
-- 10
~6fl~7
.
t~ .
" o ~ ,` C~ ~ ~ o
C~ o
O ,~ u~ ~ O O
X , a~ o oo 1~ D ~
.
- _...... . .
. o ~ ~o
~ , , , , , , , -, , , . .
~ : ~ . .
.
. ,~ o .
.: - P~ ~ I ~ D .'
~ . ,, ~
~'
Q~ ~: O N N~ ~ D
C) ~
. . O ~1 ~ . . .
.: ~ td . ~ ~~ ~ ~ ~ ~ ~ ~ ~ ~
rJ N ~1 . _I ~1 ~ ~1 ~I r-l r-l ~1
.
. ~ .
N O O In ~ ~ ~ ~ N N ~ N N
0~ ,/ ,.i oo oo ~ CO 00 'CO CO
~n ~ ~ ~ ~ ~ ~, ,~ ~ '
' ~
_ _ .
o o
O a~ ~ ~ ~ ~ ~ `
1~647q~
Each of the seals exhibited a resistance greater than
109 ohms at room temperature and greater than 10 ohms at 600F
and was hermetic after thermal cycling 20 times from 70F to
: 600~
The seals and electrical connectors of the present inven~
tion may be formed by conventional sealing techniques or modi-
fications thPreof, typically at sealing temperatures of about
700 to about 1100C.
: Typically, the seals may be made by forming the glass,
powdering the glass, mixing the powder with a suitable binder,
pressing the mixture to the shape required, sintering seal
- ~ performs to a desired strength, assembling the connector
from i s component parts and sealing the connector by heating
: for about 5 to about 15 minutes at about 700 to about 1100 C.
~ .
The present invention provides glass seals suitable for
various uses including electrical connectors for use in various
environments. Modifications are possible within the scope of
~:~ the invention. ~ :
`:- 20~ :
, ~ .
~ ~ .
., .
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