A glass suitable for glass-to-metal seals that has a resistance to attack by moisture and a high coefficient of linear thermal expansion is introduced. Linear expansion covers the range from 12 to 14 x 10 to the minus 6 C between room temperature and 500 C. The glass is essentially composed of, by molar percent, about 9% of K2O, about 10% of Na2O, about 70% of SiO2, about 6% Al2O3, and about 5% of MgO

Hirayama, C.

English

NASA Technical Reports Server

REPLY TO
ATTN OF: GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
MAY 1 1974
TO: KSI/Scientific & Technical Information Division
Attn: Miss Winnie M. Morgan
FROM: GP/Office of Assistant General
Counsel for Patent Matters
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No.
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NASA Patent case No.
PA
NOTE! - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
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Pursuant to Section 305 (a) of the National Aeronautics and
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Enclosure
https://ntrs.nasa.gov/search.jsp?R=19740012950 2020-03-17T14:48:06+00:00Z
United States Patent t » 9 ]
Hirayama
[ i i ] 3,804,703
[45] Apr. 16, 1974
[ 54] GLASS-TO-METAL SEALS COMPRISING
RELATIVELY HIGH EXPANSION METALS
[75] Inventor: Chikara Hirayama, Murrysville, Pa.
[73] Assignee: The United States of America as
represented by the Administration of
the National Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: Apr. 21, 1970
[21] Appl. No.: 30,498
[52] U.S. Cl 161/196, 106/52, 117/129,
65/DIG. 11
[51 ] Int. Cl B32b 17/06
[58] Field of Search 106/52; 161/196; 117/129;
68/DIG. 11,59
[56]
3,121,628
2,581,639
References Cited
UNITED STATES PATENTS
2/1964
1/1952
Loehrke 106/52 X
Duncan et at 106/52 X
2,643,020
2,776,900
6/1953
1/1957
Dacton 106/52
Duncan et al 106/52
OTHER PUBLICATIONS
Yolf, M. B; Chemically Resistant Glasses, in Technical
Glasses; London, 1961, p. 93.
Yolf, M. B.; Sealing Glasses, in Technical Glasses,
London, 1961, pp. 22-24, 323, 332-334 & 345.
Primary Examiner—L. Dewayne Rutledge
Assistant Examiner—W. R. Satterfield
Attorney, Agent, or Firm—N. T. Musial; G. E. Shook;
J. R. Manning
[57] ABSTRACT
A moisture resistant solder glass characterized by a
linear coefficient of expansion of from about 12 to 14
x 10-S/°C between room temperature and 500°C and
consisting essentially of, by molar percent, about 9%
of K2O, about 10% of NazO, about 70% of SiO2, about
6% A1ZO3, and about 5% of MgO.
3 Claims, 2 Drawing Figures
Unclas
00/15 36174 J
PATENTED APR 161974 3,804,703
ELECTRICAL STAINLESS
INSULATIONY 14 f STEEL TUBE
HEATER
RESISTANCE
WIRE
69
63
57
51
45
39
33
27
21
15
9
3
0
50 100
WITNESSES
et =13.02-
200 300 400
TEMPERATURE,°C
BY
FIG.2.
500 550
INVENTOR
a Hirayama
ATTORNEY
3,804,703
„ . . , - , . ! 2
GLASS-TO-METAL SEALS COMPRISING alloy having a high thermal expansion coefficient of
RELATIVELY HIGH EXPANSION METALS about 13.5 X ICTTC.
The sheath 14 is preferably composed of an alloy
The invention described herein was made in the per- containing approximately 32% nickel, 21% chromium,
formance of work under a NASA contract and is sub- 5 and 46% iron and is generally sold under the trademark
ject to the provisions of Section 305 of the National Inconel. Other types of stainless steel may be used, all
Aeronautics and Space Act of 1958. Public Law of which have a thermal coefficient of linear expansion
85-568 (72 Stat. 435; 42 U.S.C. 2457). of about 12 X Kr6/°C.
OAr- f r -bn i iMr» nc'-ruc IKIWCVTTI/™ As shown in FIG * the interior of the sheath 14 isBACKGROUND_OF THE INVENTION ,„
 fl]led wjth an electrical insulation material 16 for sup.
1. Field of the Invention porting the heater resistance wire 12 substantially cen-
This invention relates to a solder glass having a rela- trally of the sheath and to prevent any electrical short
lively low melting point and, more particularly, to a between the wire and the sheath. The insulation 16 is
glass suitable for glass-to-metal seals and having resis- preferably composed of highly compacted powdered or
tance to attack by moisture and a high coefficient of 15 pulverized magnesium oxide. The wire 12 may be of
linear thermal expansion. any configuration such as. an elongated rod extending
2. Description of the Prior Art axially of the sheath 14 from one end to the other. The
Glass to metal sealed assemblies are extensively used wire 12 has terminal portions which extend from oppo-
in the electronic and electrical industry. The type of site open ends of the sheath 14. The wire end portions
metal varies from the low expansion alloys, such as Ko- 20 are sealed within the end portions of the sheath 14 by
var, to the high expansion metals such as copper and a solid insulator such as the glass closure 18.
aluminum. Between these extremes are the relatively In accordance with this invention the glass closure 18
low-cost alloys, such as cold rolled and ordinary stain- comprises compositions, in molar percent, of from
less steel, whose linear expansion coefficients are about about 60 to about 75% of SiO2, from about 1 4 to about
1 3 X 10-8/°C. 25 25% of K2O and Na2O, from about 3 to about 10 molar
The fabrication of Kovar-to-glass assemblies are well percent of A12O3, and from about 3 to 8% of MgO.
established. Such glasses have low expansion coeffici- Minor amounts of incidental impurities may be present.
ents matchine substantially the coefficients of the Ko- The better alloys are composed of from about 67 to
var. However, where the metal involved in a glass-to- 72% of SiO2, from a total of about 1 7 to 22% of K2O
metal seal is a metal having a high expansion coeffici- 30 and Na2O in equimolar amounts, from about 4 to 8%
ent such as cold rolled and stainless steel, a glass having of AI2O3, and from about 4 to 7% MgO. The preferred
a comparable coefficient of expansion is not readily alloy composition is about 70% of SiO2, about 9% of
available. That is particularly true where a resistance to K2O, about 1 0% of Na2O, about 6% of AI2O3, and about
moisture by the glass is necessary. Associated with the 5% of MgO for achieving a satisfactory combination of
foregoing is the need for a glass having chemical dura- 35 primary characteristics; namely, ( 1 ) a high thermal ex-
bility and a relatively low working temperature. pansion coefficient of about 13 x 10~8/°C between
_ , __ _ . „ . ,__ room temperature and 500°C, and (2) resistance to at-
SUMMARY OF THE INVENTION tack by moisture and other chemicals.
In accordance with this invention it has been found SiO2 provides the glass network and may be present
that the foregoing problems and disadvantages may be 40 in an amount varying from 60 to 75 molar percent.
overcome by providing a glass having a composition Generally, below 60% of SiO2 the composition loses the
which includes K2O, Na2O, SiO2, A12O3, and MgO. A resistance to moisture at a rapid rate 'and above 75% of
glass having that composition is characterized by an ex- SiO2 the coefficient of thermal expansion decreases. It
pansion coefficient of between 1 2 and 1 4 x 1 0~8/°C has been found that where less than about 65% of SiO2
and an excellent resistance to attack by moisture. is present another metal oxide, except alkali metal ox-
Moreover, the glass has excellent chemical durability ides, may be added such as oxides of boron, calcium,
and a relatively low working temperature such as and barium. Such metal oxides, however, when added
650°C. to the glass result in higher melting temperature and
RRIFF nPdPRlPTlON OF THF DRAWING 50 lower thermal expansion coefficient; and the resistanceBRIEF DESCRIPTION OF THE DRAWING 50
 tQ moisture of this glass is good
FIG. 1 is a sectional view of a plug-in type heating el- K2O and Na2O are used to help maintain the. high
ement for an electric range; and thermal expansion coefficient and to provide a low
FIG. 2 is a graph showing thermal expansion mea- softening temperature. The latter property is desirable
surements for duplicate samples of glass versus temper- in order to enable fusion of the glass-to-metal at lower
ature in degrees centigrade. handling temperature, such as. about 650°C. K2O and
DFSrRIPTIOlM OF THF PRFFFRRFD * °f fr°m ab°Ut 7 tO 12'5DESCRIPTION F THE PREFERRED
 mo,ar percent Below 7% a therma, expansion coeffici-
EMBODIMENT
 ent is sacrjf-lced and abOve 12.5% the moisture resis-
As shown in FIG. 1 an end portion of a heating ele- tance and electrical resistivity decreases. K2O and
ment for a surface heater of an electric range is gener- Na2O may be used preferably together in amounts up
ally indicated at 10. It includes an elongated heater re- to 25 molar percent. Above 25% of K2O and Na2O
sistance wire 12 disposed within a sheath 14 with insu- combined the glass loses moisture resistance although
lation 16 disposed between the wire and the sheath. A it has a high expansion coefficient. The preferred mix-
glass closure 18 is disposed within the open end of the ,. ture of K2O and Na2O is maintained at about 1 to 1 or
sheath 14 between the wire and the sheath. The heater equal molar ratios with the preferred composition in-
resistance wire 12 is disposed substantially at the axis eluding about 9 molar percent of K2O and about 10
of the sheath 14 and is composed of a heat resistance molar percent of Na2O. It has been found that either
3,804,703
one of K2O and Na2O may be used singly, but with
equal molar amounts of these compounds a more desir-
able combination of resistance to moisture and coeffi-
cient of thermal expansion are obtained.
Other alkali metal oxides than K2O and Na2O may be
used such as oxides of cesium, rubidium, and lithium.
Aside from the disadvantage of the higher cost for ce-
sium and rubidium, it is believed that the large ion size
of cesium and rubidium would result in a weaker elec-
trostatic bond to the silicate network. For that reason
it is preferred to use the oxides of potassium and so-
dium in equal molar combinations as indicated above
because their ion sizes are comparable with holes in
the glass network.
A12O3 has the double function of improving the resis-
tance to moisture of the glass and improving the
strength of the glass network; that is, A12O3 makes the
SiO2 network tighter and therefore more stable. The
amount of A12O3 employed in the glass ranges from
about 3 to 10 molar percent. Above 10% the thermal
coefficient of expansion decreases rapidly because alu-
minum is a small trivalent ion. Below 3% of AI2O3 there
is insufficient amount of AI2O3 present to contribute
significantly to tightening of the glass network.
MgO is used to insure moisture resistance for the
glass. For that purpose an element such as magnesium
having a small ion is preferred. Calcium oxide could be
used but the calcium ion is larger than that of magne-
sium. Beryllium oxide would be better, but beryllium
involves a toxicity problem. Barium oxide is less desir-
able than MgO, because the barium ion is much larger
than that of magnesium and therefore would cause an
expanded glass network, whereby the bond between
the metal and the glass is weaker. Although MgO may
be added in the range of from about 3 to 8 molar per-
cent, it is preferably added in proportion to A12O3 so
that the total amount of A12O3 and MgO is not above
about 18 molar percent. Above that amount the soften-
ing temperature of the glass increases. Accordingly, the
preferred amounts of A12O3 and MgO are 6% and 5%,
respectively. In addition, where the total of A12O3 and
MgO is above 18 molar percent the thermal expansion
coefficient decreases rapidly.
The following example is illustrative of the present
invention.
EXAMPLE
Duplicate samples of glass of molar compositions,
having 9% K2O, 10% Na2O, 70% SiO2, 6% AI2O3, and
5% MgO were prepared from common laboratory rea-
gents. The glass samples were fused in a globar furnace
with continuous stirring, then cast onto a slab. The slab
was subsequently annealed and sections of glass sam-
ples were cut for measurements.
The thermal expansion measurements for the dupli-
5 cate samples is shown in FIG. 2. The sag point (viscos-
ity of approximately 10'" poises) of the glass is about
530°C for both samples. From the expansion curves in
FIG. 2 the annealing point of the glass is estimated to
be about 450°C. The thermal coefficient of expansion,
10 calculated from the linear part of the curves, is about
13.1 X Mr6/°C for the samples.
Moreover, the glass samples were not attacked by
boiling water during a two hour immersion test period.
This is attributed to the fact that the silicate glass is sta-
15 bilized by the presence of equimolar amounts of K2O
and Na2O. In addition, the presence of A12O3 and MgO
increased the chemical durability of the glass. Due to
the equimolar content of K2O and Na2O the electrical
properties of the glass were deemed highly satisfactory.
20
The thermal expansion coefficient of the glass of this
invention matches very closely that of cold rolled and
stainless steels and of nickel and nichrome alloys.
These metals also have expansion coefficients of about
25 13 x 10~B/°C between room temperature and 500°C.
The high expansion coefficient as well as satisfactory
electrical and chemical properties are an advantage for
this glass were used in a heating element such as shown
in FIG. 1.
30 Various modifications may be made within the spirit
of this invention.
What is claimed is:
1. A glass-to-metal seal comprising a metal and a
glass, wherein said metal is characterized by a linear
35 coefficient of expansion of about 13 X 10~6/°C and said
glass is characterized by a linear thermal expansion co-
efficient of from about 12 to 14 X 10~6/°C and good re-
sistance to moisture penetration and consisting essen-
tially of, by molar percent, from about 60 to 75% of
40 SiO2, from about 7 to 12.5% each of K2O and Na2O,
from about 3 to 10% of A12O3, and from about 3 to 8%
of MgO.
2. The glass-to-metal seal of claim 1 wherein said
glass consists essentially of about 67 to 72% of SiO2,
45 from about 17 to 22% of K2O and Na2O, from about 4
to 8% of Mf)3, and from about 4 to 7% of MgO.
3. The glass-to-metal seal of claim 2 wherein said
glass consists essentially of about 70% of SiO2, about
9% of K2O, about 10% of Na2O, about 6% A12O3, and
50 about 5% of MgO.
55
60
65


Glass-to-metal seals comprising relatively high expansion metals

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