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Патент USA US3069304

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Dec. 18, 1962
J. K. DAVIS
ELECTRICAL METAL OXIDE RESISTOR HAVING
A GLASS ENAMEL COATING
3,069,294
Filed June 3, 1954
INVENTOR.
JIQMES A.’ ?ay/s
Bye/Wu g
United States Patent 0
C6
3,069,294
Patented Dec. 18, 1962
1
2
3,069,294
in its resistance, I have surprisingly found that such dis
solution, if it occurs, is too slight to a?ect seriously the
resistance of the ?lm. Even very thin, high-resistance,
James K. Davis, Corning, N.Y., assignor to Corning
?rst-order ?lms, which are ordinarily unsuitable for re
Glass Works, Corning, N.Y., a corporation of New
York
Filed June 3, 1954, Ser. No. 434,150
7 Claims. (Cl. 117—212)
glazed in accordance with my invention without disrupt
ing or otherwise destroying them and stable high-resist
ELECTRICAL METAL OXIDE RESISTOR HAVING A
GLASS ENAMEL COATING
a)"
"
sistors on account of their extreme instability, can be
ance ?lms can thus be produced.
The improved electrical resistor resulting from such
This invention relates to electrical resistors of the type
method and forming a part of this invention comprises a
ceramic body having on its surface an adherent electro
conductive metal oxide ?lm, spaced metallic terminals on
the body in electrical contact with the ?lm, and a fused
comprising a ceramic body, such as a tube, rod or sheet
of glass, porcelain, sillimanite, or the like, having on its
surface an adherent electroconductive ?lm of metal oxide
and spaced metallic terminals in electrical contact with
the ?lm.
.
Such resistors have heretofore been made by heating
15
the ceramic body to an elevated temperature in the neigh
borhood of 500°~700° C. or higher and contacting it
while so heated with the vapor, or an atomized solution,
of a hydrolyzable inorganic or organic salt or other com
pound of a metal or a mixture of such metal salts or
ceramic enamel covering said ?lm and extending between
the terminals, the thermal expansion coefficients of the
body and the enamel being compatible.
The single FIGURE in the accompany-ing drawing is
illustrative of one embodiment of an electrical resistor
made in accordance with this invention and shows partly
in section a ceramic body provided with an electrocon
compounds, such as the chloride, bromide, iodide, sul
ductive metal oxide ?lm in electrical contact with spaced
metallic terminals ‘and a ceramic enamel covering said
fate, nitrate, oxalate, or acetate of tin, indium, or cadmi
?lm between said terminals._ _ .
.
um, or of tin and antimony, tin and indium, or tin and
In carrying out the process particularly having refer
cadmium either with or without a similar hydrolyzable
25 ence to the drawing, a ceramic body 1 isv ?rst coated
salt or other compound of a modifying metal such as
with an electroconductive metal oxide ?lm 2 by heat
zinc, iron, copper, or chromium. Such procedure re
ing the body, preferably at 500°—700° C. and contacting
sults in the formation of a thin, strongly adherent, elec
it withthe vapors of the desired salt or salts. While an
troconductive surface ?lm of the metal oxide or oxides.
hydrous solutions of the salts may be utilized, 1 have
The thickness of such a ?lm increases with the length
found it preferable to use ‘aqueous solutions thereof con
of time during which the heated body is contacted with
the vaporized metal salt, and its electrical resistance gen
erally decreases as its thickness is increased. Films hav
ing thicknesses from less than the 1st order of inter—
ference colors up to about the 10th order with electrical .55
resistance-s of 1,000,000‘ or more down to 5 or less ohms
per unit square can thus be produced. Higher resistances
can also be obtained by cutting through a ?lm of a given
resistance on a cylindrical ceramic body to shape the ?lm
into a spiral strip of predetermined width and length.
While resistors comprising such electroconductive
?lms are useful for many purposes involving little or no
change in their temperatures, their electrical, thermal,
taining su?icientacidto ‘prevent separation ofv hydrolysis
products. Spaced metallic terminals 3‘ on the resistor
in electrical contact with the electroconductive ?lm and
preferably superimposed on it are formed by conven
tional metallizing, as for example, by ‘applying a silver
containing glaze and ?ring the resistor to fuse the glaze
and unite the silver with the ?lm and/or the ceramic
body. Such methods of preparing electroconductive
metal oxide ?l-ms and electrical resistors comprising them
are described in detail in Patent No. 2,564,706 issued
August 21, 1951, to John M. Mochel.
The coated resistor thereafter has a ceramic enamel 4
applied thereto, according to the invention, by coating
chemical, and mechanical stabilities are inadequate for
the electroconductive ?lm 2 ‘between the terminals 3 with
satisfactory use under all conditions because of undesira 45 a layer of ?nely pulverized ceramic enamel frit, prefera
ble variations and/or permanent changes in their resist
bly by spraying it with a suspension of the frit in water
ances resulting from such instabilities. Such a variation
or other suitable medium. After ‘being dried, the coated
or change may result from failure of the resistance of
resistor is ?red at a temperature high enough to fuse the
the ?lm to return to its initial value after operation un
der an electrical load, or after a thermal change. The
exposure of the ?lm to atmospheric moisture or other
frit without deform-ing the body. Desirably, ?ring takes
gases or vapors or to chemical reagents or to mechanical
found that, when ?red in an atmosphere containing oxy
gen the resistor tends to become polarized and electrical
ly unstable in use, particularly if the electroconductive
abrasion also ‘affects its electrical resistance undesirably.
1 have now discovered that such difficulties can large
place in a neutral or non-oxidizing atmosphere, such as
an atmosphere of nitrogen or argon, since it has been
ly be overcome and the electrical, thermal, chemical and
metal oxide ?lm is of the ?rst order or thinner. Films
mechanical stabilities of such a resistor can be greatly
of the third order or thicker are not as readily affected
improved by covering the exposed portion of the metal
oxide ?lm between the spaced metallic terminals with a
layer of a ceramic glaze or enamel frit having a thermal
and may be ?red in air without seriously objectionable
results.
If either the supporting ceramic ‘body or the ceramic
expansion coe?icient compatible with that of the body 60 enamel composition, and particularly the latter, contains
and fusing the enamel to the ?lm.
By compatible expansion coefficients I mean expansion
coefficients which are similar enough in magnitude so
that stresses, particularly surface tension-a1 stresses, suf
?cient to cause breakage of the resistor or mechanical
a substantial amount of alkali metal oxide, say more than
about 1%, the electroconductive metal oxide ?lm tends to
become electrically unstable under electrical load. Such
instability is believed to be due to migration of alkali
metal ions into the electroconductive ?lm when the ?lm
is heated 'by the passage of an electric current there
damage to the electroconductive metal oxide ?lm, when
through. I have found, however, that this dif?culty can
the resistor is heated or cooled, will not be developed
be overcome and a high electrical stability of the ?lm can
either in the ceramic body or the enamel coating.
be
maintained by utilizing a supporting body and an
While it might be expected that the ?uxes of the enamel
during its fusion would dissolve at least the major por 70 enamel composition, particularly the latter, which con
tain less than 1%, and preferably are substantially free,
tion of the metal oxide ?lm with a corresponding increase
of alkali metal oxide.
3,069,294
4
3
group consisting of an oxide of tin, an oxide of indium,
an oxide of cadmium, oxides of tin and antimony, oxides
of tin and indium, and oxides of tin and cadmium, said
?lm being not thicker than the tenth order of interfer
ence colors, spaced metallic terminals in electrical con
tact with the ?lm, and a ?red-on, ceramic enamel con
To produce an electroconductive metal oxide ?lm of
maximum electrical stability, the surface of the support
ing ceramic body should be relatively smooth and low
in porosity.
The thermal expansion coefficients of the body and the
superposed ceramic enamel should be compatible with
each other. The thermal expansion coe?‘icient of the
enamel, however, is advantageously somewhat lower
than that of the ceramic body because this results in a
desirable slight compressional stress in the surface of the 10
resistor which tends to increase its mechanical and
taining less than 1% of alkali metal oxides covering said
?lm and extending between said terminals, the thermal
expansion coefficients of the body and the enamel being
compatible.
2.‘ The electrical resistor claimed in claim 1 in which
the thermal expansion coef?cient of the enamel is less
than that of the ceramic body.
3. The electrical resistor claimed in claim 1 in which
because it is non-porous and its thermal expansion co
efficient is easily controllable. Other ceramic bodies of 15 the ceramic body is a glass consisting essentially of
low porosity and su?iciently refractory to withstand
59.5% SiO2, 5% B203, 19% A1203, 9% MgO, 7% CaO,
heating at 500°~700° 'C. or ‘higher, such as porcelain and
and 0.5% NazO.
4. The electrical resistor claimed in claim 1 in which
sillimanite, are also suitable.
By way of example only, the following compositions,
the ceramic body is a glass consisting essentially of 62%
calculated from their batches in weight percent on the 20 SiOZ, 15% A1203, 8.3% MgO, and 14.7% OaO.
5. The electrical resistor claimed in claim 1 in which
oxide basis illustrate suitable compositions for carrying
the ceramic enamel consists essentially of 43.9% SiOZ,
out the invention:
thermal strength.
A supporting ‘body of glass is particularly satisfactory
17% B203, 7% A1203, 5% ZnO, 26.9% PbO, and 0.3%
LiZO.
25
6. An electrical resistor comprising a ceramic body
containing less than 1% of alkali metal oxides and hav
ing on its surface ‘an inherent electroconductive ?lm not
thicker than the tenth order of interference colors con
sisting of at least one conducting metal oxide, spaced
metallic terminals in electrical contact with the ?lm, and
a ?red-on ceramic enamel consisting essentially of 44%
SiO2, 17% B203, 7% A1203, 5% ZnO, and 27% PhD
covering said ?lm, and extending between said terminals,
Exp. Coetl‘. X 107."
Softening Point, "O _____ __ _
the thermal expansion coefficients of the body and the
Examples 1 and 2 are glasses which are particularly
adapted for the support of electroconductive metal oxide
35
?lms in the production of the present electrical resistors;
and Examples 3 and 4 are enamels suitable for covering
such ?lms for the improvement of their e-lectri- 40
cal, thermal, chemical, and mechanical stabilities.
I claim:
1. An electrical resistor comprising a ceramic body
containing less than 1% of alkali metal oxides having on
its surface an adherent electroconductive ?lm consisting 45
of at least one conducting metal oxide selected from the
enamel being compatible.
7. The electric resistor claimed in claim 6 in which
the ceramic body is a glass consisting essentially of 62%
SiO2, 15% A1203, 8.3% MgO, and 14.7% CaO.
References Cited in the ?le of this patent
UNITED STATES PATENTS
1,938,674
2,027,413
2,357,473
2,582,081
Terwilliger __________ __ Dec. 12,
Andres ______________ __ Jan. 14,
Jira _________________ -_ Sept. 5,
Sun et al. _____________ __ Jan. 8,
1933
1936
1944
1952
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