Note: Descriptions are shown in the official language in which they were submitted.
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The lnvention relates to vitreous enamel resistance
materials, resistors made -therefrom and the method of making
the same.
BACKGROUND
A type of electrical resistance material which has
recently come into commercial use is a vitreous enamel
resistance material which comprises a mixture of a glass frit
and finely divided particles of an electrical conductive
material. The vitreous enamel resistance material is coated
on the surface of a substrate of an electrical insulating
material, usually a ceramic, and fired to melt the glass frit.
When cooled, there is provided a film of glass having the
conductive particles dispersed therein. Terminations are
connected tothe film to permit the resultant resistor to be
connected in the desired circuit. -
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The materials which have been generally used for the
conductive particles are the noble metals. Although the noble
metals provide vitreous enamel resistance materials which have ~ -
; satisfactory electrical characteristics, they have the dis~
advantage that they are expensive. Thus, the resistors made
from the vitreous enamel resistance materials containing the
noble metals are expensive to manufacture. Therefore, it
would be desirable to have a vitreous enamal electrical
resistance material which utilizes a relatively inexpensive
conductive material so as to provide an electrical resistor
which is relatively inexpensive to manufacture. In addition,
the conductive material used must be capable of providing a -~resistance material having a wide range of resistance values
and which is relatively stable over the entire range of the
resistance values. By being stable it is meant that the
resistance value of the resistance material does not change
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or changes only a small amoun-t under operating conditions,
particularly when subjected to changes in -temperature. The
change in resistance value of an elec-trical resis-tor per
degree change in temperature is referred to as -the "temperature
coefficient of resistance" of the resistor. The closer the
temperature coefficient of resistance is to zero, the more
stable is the resistor with xespect to changes in temperature.
SUMMARY
It is an object of the present invention to provide
a novel vitreous enamel resistance material utilizing a
relatively inexpensive conductive material.
It is another object of the present invention to
provide an electrical resistor utilizing a novel vitreous
enamel resistance material.
It is a further object of the present invention to
provide a vitreous enamel resistor having a relatively wide
range of resistance values, which is relatively stable over
the entire range of resistance values and which is relatively
inexpensive to manufacture.
It is astill further object of the present invention
to provide a vitreous enamel resistance material comprising a
mixture of a glass frit and finely divided particles of a metal
silicide selected from the group consisting of molybdemun ;
disilicide, tungsten disilicide, vanadium disilicide, titanium
disilicide, zirconium disilicide, chromium disilicide and
tantalum disilicide.
Other objects will appear hereinafter.
The invention accordingly comprises a composition of
matter and product formed therewith possessing the characteristics,
properties and relation of constituents which will be exemplified
in the composition hereinafter described, and the scope of the
invention will be indicated in the claims.
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More particularly, -there is provided an electrical
resistor comprising a ceramic body containing on the surface
thereof a coating of vitreous enamel resistor composition con-
sisting essentially, of a borosilicate glass and, about 75% to
10% by weight of finely divided particles of a metal silicide
selected from the group consisting of tungsten disilicide, moly-
: bdemun disilicide, vanadium disilicide, titanium disilicide,
zirconium disilicide, chromium disilicide and tantalum disilicide,
mixed with its fired reaction products with said borosilicate
glass, said composition being heated a-t a temperature sufficient
to provide said reaction products.
: There is also provided an electrical resistor of the
vitreous enamel type produced by preparing a vitreous enamel
composition consisting essentially of a borosilicate glass frit
and about 75 to 10% by weight of finely divided conductive
particles of a metal silicide selected from the group consisting
of tungsten disilicide, molybdenum disilicide, vanadium di-
: silicide, titanium disilicide, zirconium disilicide, chromium
disilicide and tantalum disilicide; applying a uniform thick-
ness of the composition to an insulating refractory substrate;
firing the coated substrate at a temperature of about 970C to
1150C at which the glass frit becomes molten and below the
melting temperature of the conductive particles in a non-
oxidizing atmosphere; cooling the resistor to form a glass
matrix having the conductive particles dispersed therein; and
connecting terminations to the vitreous enamel resistor com-
position. ,
There is further provided the method of making an
electrical resistor of the type wherein a vitreous enamel
resistor composition is applied to a substrate comprising:
preparing a vitreous enamel resistor composition consisting
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essentially of a borosilicate glass frit and about 75 to 10%
by weigh-t of finely divided conductive particles of a metal
silicide selected from the group consisting of tungs-ten di-
silicide, molybdenum disilicide, vanadium disilicide, titanium
disilicide, zirconium disilicide, chromium disilicide and
tantalum disilicide; applying a uniform thickness of the com-
position to an insulating refractory substrate; firing the
coated substrate at a temperature of about 970 to 1150C a-t
which the glass frit becomes molten and below the melting
temperature of the conductive particles in a non-oxidizing
atmosphere; cooling the resistor to form a glass matrix having
the conductive particles dispersed therein; and connecting
terminations to the vitreous enamel resistor composition.
BRIEF DESCRIPTION OF DRAWING
The drawing is a cross-sectional view, on a highly
exaggerated scale, of a resistor pxoduced in accordance with
the present invention.
DESCRIPTION OF IN~ENTION
In general, the vitreous enamel resistance material
of the present invention comprises a mixture of a vitreous
glass frit and fine particles of a metal silicide of the transi-
tion elements of Groups IV, V and VI of the periodic chart.
The metal silicide can be molybdenum disilicide (MoSi2),
tungsten disilicide (WSi2), vanadium disilicide (VSi2), titanium
disilicide (TiSi2), zirconium disilicide (ZrSi2), chromium di-
silicide (CrSi2) or tantalum disilicide (TaSi2). More part-
icularly, the vitreous enamel resistance material of the present
invention comprises a mixture of a vitreous glass frit and a
metal silicide of the above-stated group in the proportion of,
by weight, 25% to 90% glass frit and 75% to 10% metal silicide.
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The glass frit used in the resistance material of
the present invention may be oE any well~known composition
which has a melting temperature below that of the refractory
metal silicide. The glass Erits most preferably used are -the
borosilicate frits, such as lead borosilicate frit, bismith,
cadmium, barium, calcium or other alkaline earth borosilicate
frits. The preparation of such glass frits is well known and
consists, for example, in melting together the constituents of
the glass in the form of the oxides of the constituents, and
pouring such molten composition into water to form the frit.
The batch ingredients may, of course, be any compound that will
yield the desired oxides under the usual conditions of frit
production. For example, boric oxide will be obtained from
boric acid, silicon dioxide will be produced from flint,
barlum oxide will be produced from barium carbonate, etc.
The coarse frit is preferably milled in a ball-mill with water
to reduce the particle size of the frit and to obtain a frit
of substantially uniform size.
To make the resistance material of the present in-
vention, the glass frit, and refràctory metal silicide are
broken down, such as by ball-milling, to a substantially uni-
form particle size. An average particle size of between 1 to
2 microns has been found to be preferable. The glass frit, and
refractory metal silicide powder are thoroughly mixed together,
such as by ball-milling in water or an organic medium, such
as butyl carbitol acetate or a mixture of butyl carbitol acetate
and toluol. The mixture is then ad~ustedto the proper viscosity
for the desired manner of applying the resistance material to
a substrate by either adding or removing the liquid medium of
the material.
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To make a resistor with the resistance material of
the present invention the resistance ma-terial is applied to
a uniform thickness on the surface of a substrate. The sub-
strate may be a body of any material which can withstand the
firing temperature of the resistance material composition. The
substrate is generally a body of a ceramic, such as glass,
porcelain, refractory, barium titinate, or the like. The
resistance material may be applied on the substrate by brushing,
dipping, spraying or screen stencil application. The substrate
with the resistance material coating is -then fired in a con-
ventional furnace at a temperature at which the glass frit
becomes molten. For resistance materials of the present in-
vention containing any of the above-stated metal silicides
except molybdenu~ disilicide, it has been found preferable to
fire the coated substrate in an inert atmosphere, such as argon,
helium, nitrogen or a mixture of nitrogen and hydrogen, to
achieve a resistor of better stability. However, for a
resistance material of the present invention in which the metal
silicide is molybdenum disilicide, it has been found that
firing the resistor in air provides a more stable resistor.
When the coated substrate is cooled, the vitreous enamel hardens
to bond the resistance material to the substrate.
As shown in the drawing, the resultant resistor of
the present invention is generally designated as 10. Resistor
10 comprises the ceramic substrate 12 having a layer 14 of the
resistance material of the present invention coated and fixed
thereon. The resistance material layer 14 comprises the glass
16 and the finely divided particles 18 of the metal silicide
embedded within and dispersed throughout the glass 16.
EXAMPLE 1
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A plurality of resistance materials of the present
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invention were made in which the conductive material was moly-
bdenum disilicide in the various amounts shown in Table I and
the glass Erit was a barium, titanium, aluminum borosilicate
glass. Each of the resistance ma-terials was made by mixing
together the glass frit and molybdenum disilicide particles in
a ball-mill in butyl carbitol acetate. Resistors were made
with each of the resistance materials by coating cylindrical
ceramic bodies with the resistance material and firing the
coated ceramic bodies in a conveyor furnace for approximately
a thirty minute cycle, at a temperature and in an atmosphere
as indicated in Table I. A number of resistors of each of the
compositions were made, and the average resistance values and
temperature coefficients of resistance of the resulting resistors
of each group are shown in Table I.
TABLE I
Mblyb, Temper-
denum ature
Disil- And Resis- Temperatuxe Coef. of Resistance
icide Fixing tance (% per C)
20(~ by wt.lAt~.osphexe(ohms~)+25C to 150C+25c to -55C
1020C-Air 1,900 +.0080 +.0053
1020C-Air 490 -+.0109 +.0094
1020C-Air 70 +.0217 +.0222
50- 970C-Air 6 +.1420 +.1465
970C-Air 25 +.1038 +.1038
1050C-N2 8,900 -.0214 -.0346
1100C-N2* 1,300 _.0066 -.0119
1020C-N2 500 +.0120 +.0066
970C-N2 5 +.1117 +.1166
970C-N2 4.3 +.1196 +.1222
...... _ _ .. _ _ _ ~ .. _ _ .. . .
* Fixed on a 20 minute cycle.
EXAMPLE II
A plurality of resistance materials of the pxesent
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invention were made in which the conductive material was tungsten
disilicide in the various amounts shown in Table II, and the
glass frit was a barium, titanium, aluminum borosilicate glass.
Each of the resistance ma-terials was made in the same manner as
the resistance materials of Example I, and resistors were made
with each of the resistance materia]s in the same manner as
described in Example I. The resistors were fired at 1050C
in the type of atmosphere indicated in Table II and the average
resistance values and temperature coefficients of resistance
for each group of the resultant resistors are indicated in Table
II.
TABLE II
Tung-
sten
Disil- FiringResis- Temperature Coef. of Resistance
icide Atmos-tance (% per C~
(% by wt.) phere(ohms/~) +25C to 150C +25DC-to -55C
11 Air5,000 +.1346+.0984
Air2,300 +.0547+.0810
Air600 +.0670+.0957
Air219 ~.1073+.1074
Air 75 +.1307+.1286
11 N2875,000 -.1010 -.1458
N22,500 -.0063 -.0077
N25~000 -.0025 -.0069
N22,000 +.0055-.0039
N21,500 +.0162+.0123
N2 36 +.0638+.0670
N2 21 +.0685+0.588
. . . _ _ _
30 EXAMPLE III
A plurality of resistance ma-terials of the present
invention were made in which the conductive material was
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zirconium disilicide in the various amounts shown in Table III
and the glass frit was a barium, titanium, aluminum borosilicate
glass. Each of the resistance materials were made in the same
manner as the resistance materials oE Example I, and resistors
were made with each of ~he resistance materials in the same
manner as described in Example I. The resistors were fired at
970C in the type of atmosphere indicated in Table III, and the
average resistance values and temperature coefficients of
resistance for each group of the resultant resistors are in-
dicated in Table III.
TABLE III
ZirconiumFiringResis- Temperature Coef. of Resistance
Disilicide Atmos- tance (% per C)
(% by wt.) phere ohms/~)+25C to 150C +25C to -55C
lS N2 6,300 +.0021 +.0035
N2 475 +.0225 +.0232
N2 104 +.0262 +.0278
N2 44 +.0265 +.0277
Air 3,000 +.0130 +.0127
Air 610 +.0184 +.0178
Air 238 +.0285 +.0257
Air 112 +.0334 +.0344
E MPLE IV
Table IV shows the resistance values and temperature
coefficients of resistance of a number of resistors of the
present invention using resistance materials made from the
various metal silicides indicated in Table IV in the indicated
amounts with a barium, titanium borosilicate glass frit. The
resistance materials were made in the same manner as the
resistance materials of Example I and resistors were made with
the resistance material in the same manner as described in
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Example I. The resistors were fired at approximately 1000C in
a Nitrogen atmosphere.
T~BLE IV
Conduct- Tem~erature Coef. of Resistance
ing % byResistance (~ per C)
Material Weight(o ~,/O) +25C to 150C +25C to -55C
TiSi2 15 124 +.0163 -~.0161
TiSi2 25 63 +.0166 ~.0181
TiSi2 30 41 +.0143 +.0154
VSi2 20 1,300 +.0222 +.0108
VSi2 25 275 +.0298 ~.0355
VSi2 30 42 +.0411 _.0495
CrSi2 20 275 +.0184 +.0235
CrSi2 30 99 +.0568 +.0780
TaSi2 50 81 +.0319 +.0303
EXAMPLE V
A plurality of resistance materials of the present
invention were made in which the conductive material was a
metal silicide shown in Table V, and the glass frit was a
barium, titanium borosilicate glass. Each of the resistance
materials was made ln the same manner as the resistance
material of Example I, and the resistors were made with each
of the resistance materials in the same manner as described
in Example I. The resistors were fired in a nitrogen atmosphere
on a 30 minute cycle at a temperature as indicated in Table V
and the average resistance values and temperature coefficients
of resistance for the resultant resistors are shown in Table V.
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TABLE V
ConductingFiring Resis- Temperature Coe:E. of Resistance
~aterialTemper- tance (% per C)
(% by vol.)ature(oh~s/~) +25C to 150C +25C to ~55C
WSi2 5% 1150C 9K -.0148 -.0220
l~bSi2 6% 1100C 925 +.0257 _.0215
MoSi2 8% 1100C 560 +.0327 +.0304
MbSi2 10% 1100C 413 +.0372 +.0360
W~i2 12% 1100C 269 +.0268 -~.02g7
WSi2 15% 1100C 179 +.0294 -~.0294
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EXAMPLE VI
A plurality of resistance materials of the present
invention were made in which 30% by weight of a silicide
shown in Table VI, and 70% by weight of a barium, titanium,
aluminum borosilicate frit were used. Each of the resistance
materials was made in the same manner as the resistance mate-
rials of Example I, and resistors were made with each of the
resistance materials in the same manner as described in
Example I. The resistors were fired in a nitrogen atmosphere
on a 30 minute cycle at a temperature indicated in Table VI.
The average resistance values, temperature coefficients of
resistance of the resistors, and the reaction products for the
resultant resistor glazes are shown in Table VI. The reaction
products for the resistor glazes were determined by analysis
of detected X-ray diffraction patterns. The detected products
` are given in the order of decreasing strength of their dif-
fraction pattern lines.
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TA~E VI
Metal Firing Resis- Temperature Cbef. of
Sili- Temper- tance ~esistance (~ per C) Reaction
cide ature(ohms/d) +25C to 150C +25C to -55C Prcducts
WSi2 1100ClK +.0206 +.0209 ~WB, WSi2
M~Si2 1100C13 +.1092 +.1010 M~Si2~
M2B5
VSi2 1100C33 +.0931 +.1042 VSi2,
BaSi205
CrSi2 1100C21 +.0960 +.1266 CrSi2,
CrB2, BaSi205
TaSi 1100C Non- - -- TaSi2,
Cond. TaB2, ~TaB
TaSi2 1150C* 80 +.0340 +.0187 TaSi2,
TaB2, ~TaB
TiSi2 1100C 9 +.0464 +.0303 TiSi2, TiB2,
BaSi203, TlC2
ZnSi2 1100C 9 +.0526 +.0485 ZrSi2, ZrB2
* 50% by weight of TaSi2 fired in nitrogen on a 20 minute cycle.
Analysis of the diffraction pattern data of the resistor
glazes in Table VI, indicates that during the firing of the
resistance material, the silicon of the metal silicide has a
strong tendency to react with the glass. The remaining metal
of the silicide then combines with boron from the glass to form
a boride or with barium to form a mixed oxide. The conductors
which are formed by firing the resistance materials, thus, in-
clude both the metal silicides and their borides.
It shoulcl be understood that the examples of the resis-
tors and resistance materials of the present invention shown in
Tables I through VI are given merely to illustrate certain de-
tails of the invention and are not to be ta~en as in any way
limiting the invention thereto. The present invention may be
embodied in other specific forms without departing from the
spirit or essential attributes thereof and, accordingly, refer-
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ence should be made to the appending claims~ rather than to the
foregoing specification as indicating the scope of the invention.
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