CA1064704A

CA1064704A - Glass seal

Info

Publication number: CA1064704A
Application number: CA229,988A
Authority: CA
Inventors: John A. Topping; Peter Mayer; M. Krishna Murthy; Albert H. Brooks
Original assignee: Quality Hermetics Ltd
Current assignee: Quality Hermetics Ltd
Priority date: 1975-06-24
Filing date: 1975-06-24
Publication date: 1979-10-23
Also published as: DE2628282A1

Abstract

GLASS SEAL
ABSTRACT OF THE DISCLOSURE
Hermetic glass seals of high electrical resistivity are provided. Glass compositions suitable for use in such seals and based on lead-silica glasses are described. Glass compositions having particular efficacy in a nuclear reactor environment also are described.

Description

;- -~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 :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.

~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 .
: - 6 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 %

..

-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:

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:

.: .

~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~ :
, ~ .
~ ~ .

., .

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A seal construction comprising an inner electric-ally-conductive member, an outer electrically-conductive member and a glass sealingly joining said electrically-conductive members, said glass being formed from a boron- and cobalt-free lead oxide-silica glass containing the following relative proportions of lead oxide and silica:

.

2. The seal construction of claim 1, wherein said glass is formed from a boron- and cobalt-free lead-silica glass having the following relative proportions of lead oxide and silica:

and the following additional components in quantities based on the total weight of lead oxide and silica:

3. The seal construction of claim 1, wherein said glass is formed from a boron- and cobalt-free lead-silica glass having he following weight proportions of lead oxide and silica:
PbO about 63 to about 66 wt. %
SiO2 about 37 to about 34 wt. %
and the following components in quantities based on the total quantity of lead oxide and silica:

4. The seal construction of claim 1, wherein said glass is formed from a boron- and cobalt-free lead-silica glass having the following relative proportions of lead oxide and silica:

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:

.