DK143820B - PROCEDURE FOR MAKING AN ELECTRIC RESISTANCE - Google Patents

Description

in 143820

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of producing an electrical resistor, wherein first a glassy enamel resistance mass of a borosilicate glass frit is prepared and about. 75% by weight to approx. 10 wt% finely divided conductive particles of a metal silicide 5 selected from a group consisting of tungsten disilicide, molybdenum disilicide, vanadium disilicide, titanium disilicide, zirconium disilicide, chromium disilicide, and tantalum disilicate, to which a uniform mass is applied, the substrate provided with substrate is burned, and the resulting glassy coating layer is provided with electrical terminals or similar connection means.

A recently marketed type of electrical resistance material is a glassy enamel resistance material comprising a mixture of a glass-free and finely divided particles of an electrically conductive material. The glassy enamel resistance material is laid on the surface of a substrate of an electrical insulating material, usually a ceramic material, and burnt to melt the glass frit. Once cooled, a glass film is provided in which the 20 conductive particles are dispersed. Electrical terminals or terminals are connected to the film to allow the resulting resistance to be connected in the desired circuit.

The materials commonly used for the conductive particles are the precious metals. Although the precious metals carry glassy enamel resistance materials which have satisfactory electrical characteristics, they have the disadvantage of being expensive. The resistors made from the glassy enamel resistance materials containing the precious 30 metals are therefore expensive to manufacture. It is therefore desirable to have a glassy enamel resistance material which utilizes a relatively inexpensive conductive material to provide an electrical resistance which is relatively inexpensive to manufacture. In addition, the conductive material used must be arranged so as to provide a resistance material having a wide range of resistance values and which is relatively stable over this entire range of resistance values. By stable, it is meant that the resistance value of the resistance material 5 does not change or simply changes slightly under certain conditions of use, especially if the material is subject to temperature changes. The change of the resistance value of an electric resistor degree of temperature change is referred to as the "temperature resistance coefficient" of the resistor. The closer the 10 coefficient of temperature resistance is at the value zero, the more stable the resistance to temperature changes.

German Patent Specification No. 21 28 568 discloses a glaze to produce a relatively inexpensive electrical resistance coating which does not contain precious metals. This glaze is made of a finely divided silicide, such as wool fram disilicide, and a glass frit.

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The process according to the invention is characterized in that the firing takes place in a non-oxidizing atmosphere at a temperature which is higher than the melting temperature of the glass-free and 20 lower than the melting temperature of the conductive particles, and which is in the range of from ca. 970 ° C to approx. 1150 ° C.

Hereby a resistance is obtained which is both inexpensive to produce and has been found to have a relatively wide range of resistance values which are relatively stable over the entire range of resistance values.

Particularly conveniently, in certain cases, the coated substrate can be burned in a nitrogen atmosphere.

The invention is explained below with reference to the drawing, which shows a section through a resistor made in accordance with the present invention, seen in exaggerated large scale conditions.

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The vitreous enamel resistance material of the present invention generally comprises a mixture of a vitreous glass frit and fine particles of a metal silicide of the transition elements of groups IV, V and VI of the periodic table.

This metal silicide can be molybdenum disilicide (MoSi2), tungsten disilicide (WSi2), vanadium disilicide (VSi2), titanium disilicide (TiSi2), zirconium disilicide (ZrSi2), ehrome disilicide (CrSi2) or In more detail, the vitreous enamel resistance material of the invention comprises a mixture of a vitreous vitreous and a metal silicide of the above group in a weight ratio of approx. 25% by weight to approx. 90% by weight of glass frit and approx. 75% by weight to approx. 10% by weight of metal silicide.

The borosilicate frites used in the resist material of the invention may be of any known composition having a melting temperature lower than the melting point of the refractory or highly fusible metal silicide. The most commonly used glass frit is borosilicate frit, such as lead borosilicate frit, bismuth, cadmium, barium, calcium or other alkaline earth alkali borosilicate frit. The preparation of such 20 glass fryers is well known and consists e.g. in fusing the constituents of the glass in the form of the oxides of the constituents and pouring this molten composition into water to form the frit. The portion ingredients can, of course, be any compound which will give the desired oxides under the usual deep frying conditions. Eg. For example, boron oxide is obtained from boric acid, silica is made from flint test, barium oxide is made from barium carbonate, etc. The coarse frit is preferably ground in a ball mill with water to reduce the particle size of the frit and to obtain a frit of substantially uniform size.

To prepare the resistance material of the present invention, the glass frit and refractory metal silicide are degraded, such as by milling by a ball mill to a substantially uniform particle size. A mean particle size of between 1 and 2 microns has been found to be appropriate. The glass frit and the refractory metal silicide powder are completely mixed together, such as by grinding by means of a ball mill in water or an organic medium such as butyl carbitol acetate or a mixture of butyl carbitol acetate and toluene. The mixture is then adjusted to an appropriate viscosity for the desired way of applying the resistance material to a substrate by either adding or removing the liquid medium of the material.

10 To produce a resistor with the resistor material of the invention, the resistor material is applied at a uniform thickness to the surface of a substrate. This substrate can be a body of any material that can withstand the firing temperature of the resist material composition. The substrate is generally a body of a ceramic material such as glass, porcelain, refractory, barium titinate or similar materials. The resistance material can be applied to the substrate by coating, dipping, spraying or by application by means of a shielding template. The substrate with the resistance material coating is then burned in a suitable oven at a temperature at which the glass frit is melted, but the conductive particles are not melted. In resistance materials of the present invention, which contain any of the above-mentioned metal silicides other than molybdenum disilicide, it has been found convenient to burn the coated substrate in an inert atmosphere such as argon, helium, nitrogen or a mixture. of nitrogen and hydrogen to obtain a resistance of better stability. As the coated resist is cooled, the vitreous enamel cures so that the resist material binds to the substrate.

The resistance thus obtained according to the invention is provided in the drawing with the general reference numeral 10. This resistance 10 comprises a ceramic substrate 12 which has a layer 14 of the resistant material according to the invention which is coated and fixed thereon. The resistance material layer 14 comprises glass 16 and finely divided particles 18 of a metal silicide embedded in and completely dispersed through the glass 16.

Example 1.

Several resistance materials according to the invention were prepared in which the conductive material was molybdenum silicidal in the various amounts shown in Table 1 and the glass frit was a barium, titanium, aluminum borosilicate glass. Each of the resistance materials was prepared by mixing the glass frit and the molybdenum disilicide particles in a ball mill in butyl carbitol acetate. Resistors of each of the resistors were made by coating cylindrical ceramic bodies with the resistor material and burning the thus-coated ceramic bodies in a conveyor oven for a cycle of about 30 minutes at the temperature shown in Table I and in the atmosphere shown in Table I. A certain number of resistors of each composition were prepared, and the average resistance values and temperature resistance coefficients of the resistors produced from each group are shown in Table I.

Table I

EditPoga ~ Res- Temperature resistance coefficient of silicide firing rate (% per ° C)

(wt%) atmosphere (ohm / α) + 25 ° C to 150 ° C + 25 ° C to -55 ° G

10 1050 ° C-N2 8,900 - 0.0214 - 0.0346 1100 ° C-N2x 1.300 + 0.0066 - 0.0119 25 1020 ° C-N2 500 + 0.0120 + 0.0066 50 970 ° C N2 5 + 0.1117 + 0.1166 60 970 ° C-N2 4.3 + 0.1196 + 0.1222 X Burned during a 20 minute cycle.

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Example 2.

Several resistive materials of the invention were prepared 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 materials was prepared in the same manner as the resistance materials of Example 1, and in the same manner as described in Example 1, resistors were made with each of the resistance materials. These resistors were fired at 1050 ° C in the atmosphere type listed in Table 10 II, and the average resistance values and temperature resistance coefficients for each group of resistors produced are shown in Table II.

Table II

Tungsten- Burn Against- Temperature resistance coefficient disilicide resistance (% per C)

(wt%) atmosphere (ohm / π) + 25 ° C to 150 ° C + 25 ° C to -55 ° C

15 11 air 5,000 + 0.1346 + 0.0984 15 air 2,300 + 0.0547 + 0.0810 20 air 600 + 0.0670 + 0.0957 25 air 219 + 0.1073 + 0.1074 30 air 75 + 0 , 1307 + 0.1286 20 11 N2 875,000 - 0.1010 - 0.1458 15 N2 2.500 - 0.0063 - 0.0077 20 N2 5.000 - 0.0025 - 0.0069 25 N2 2.000 ± 0.0055 - 0, 0039 30 N2 1,500 + 0.0162 + 0.0123 25 50 N2 36 + 0.0638 + 0.0670 60 N2 21 + 0.0635 + 0.0688

Example 3

Several resistive materials of the invention were prepared in which the conductive material was zirconium disilicide 7 in the various amounts listed in Table III and the glass frit was a barium, titanium, aluminum borosilicate glass. Each of the resistors was prepared in the same manner as the resistors of Example 1, and resistors 5 of each of the resistors were prepared in the same manner as described in Example 1. These resistors were fired at 970 ° C in the atmosphere type listed in Table III, and the average resistance values and temperature resistance coefficients for each group of resistors produced are given in Table III.

Table III

". . „„, Temperature resistance coefficient

Zirconium- Burn- Mod- r o

dicilicide dingsstand ^ r * eP

(wt%) atmosphere (ohm / p) + 25 ° C to 150 ° C + 25 C to -55 ° C

15 N2 6.300 ± 0.0021 ± 0.0035 N2 475 + 0.0225 + 0.0232 25 N2 104 + 0.0262 + 0.0278 15 N2 44 + 0.0265 + 0.0277

Example 4

Table IV shows the resistance values and temperature resistance coefficients of a certain number of resistors according to the invention utilizing resistance materials made from the 20 different metal silicides listed in Table IV in the amounts indicated together with a barium and titanium borosilicate glass frit. The resistors were prepared in the same manner as the resistors in Example 1, and the resistors were made with the resistor in the same manner as described in Example 1. The resistors were burned at ca. 1000 ° C in a nitrogen atmosphere.

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Table IV

Against _ Temperature resistance coefficient

Conductive state (% per ° C)

material weight% (ohm / π) + 25 ° C to 150 ° C + 25 ° C to -55 ° C

TiSi 2 124 + 0, ol63 + 0.0161

TiSi2 25 63 + 0.0166 + 0.0181 5 Tisi2 30 41 + 0.01343 + 0.0154 VSi2 20 1.300 + 0.0222 ± 0.0108 VS ± 2 25 275 + 0.0298 + 0.0355 VSi2 30 42 ± 0.0411 + 0.0495

CrSi2 20 275 + 0.0184 + 0.0235 CrSl2 30 99 + ° / ° 568 + 0.0780

TaSi2 50 81 + 0.0319 + 0.0303

Example 5

Several resistance materials according to the invention were prepared in which the conductive material was one of the metal silicides shown in Table V 15 and the glass frit was a barium and titanium borosilicate glass. Each of the resistance materials was prepared in the same manner as the resistance material of Example 1, and the resistors were made with each of the resistance materials in the same manner as described in Example 1. These resistors 20 were burned in a nitrogen atmosphere during a 30 minute cycle at that of Table V. temperature, and the average resistance values and temperature coefficients of the resistors produced are shown in Table V.

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Table V

Conductive Burn- Resistant Temperature Resistance Coefficient Material Resistant (% per C)

(volume%) temperature (ohm / π) + 25 ° C to 150 ° C + 25 ° C to -55 ° C

WSi2 5% 1150 ° C 9K - 0.0148 - 0.0220

MoSi2 6% 1100 ° C 925 + 0.0257 t 0.0215 5 MoSi2 8% 1100 ° C 560 + 0.0327 + 0.0304

MoSi2 10% 1100 ° C 413 + 0.0372 + 0.0360 WSi2 12% 1100 ° C 269 + 0.0268 + 0.0297 WSi2 15% 1100 ° C 179 + 0.0294 + 0.0294

Example 6

Several resistance materials according to the invention were prepared in which 30% by weight of one of the silicides listed in Table VI and 70% by weight of a barium, titanium, aluminum borosilicate frit were used. Each resistor material was prepared in the same manner as the resistor materials of Example 1, and 15 resistors were prepared with each of the resistor materials in the same manner as described in Example 1. These resistors were burned in a nitrogen atmosphere during a 30 minute cycle at that of Table VI. specified temperature. The average equal resistance values, temperature resistance coefficients for the 20 resistors as well as the reaction products for the manufactured against the stop glass are shown in Table VI. The reaction products for the resistance glasses were determined by analyzes of detected X-ray diffraction patterns. The detected products are listed in order of decreasing strength of their diffraction pattern lines.

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Table VI

Burning Temperature Resistance Coefficient (% per ° C)

Metal temp stand n n procilicid rature (ohm / a) +25 C to 150 C +25 C to -55 C ducts WSi2 1100 ° C IK + 0.0206 + 0.0209 6WB, WSi2

MoSi2 1100 ° C 13 + 0.1092 + 0.1010 MoSi2, mo2b5 VSi2 1100 ° C 33 + 0.0931 + 0.1042 VSi2,

BaSi205

CrSi2 1100 ° C 21 + 0.0960 + 0.1266 CrSi2,

CrB2,

BaSi205

TaSi2 1100 ° C non- - - TaSi2,

conductive TaB2, yTaB

TaSi2 1150 ° CX 80 + 0.0340 + 0.0187 TaSi2,

TaB2, yTaB

TiSi2 1100 ° C 9 + 0.0464 t 0.0303 TiSi2, TiB2 "

BaS ^ O ^,

Ti ° 2 ZnSi2 1100 ° C 9 + 0.0526 + 0.0485 ZrSi2,

ZrB2 x 50 wt% TaSi2 burned in nitrogen during a 20 minute cycle.

Analyzes of diffraction pattern data from the resistance glasses listed in Table VI show that the silicon of the metal silicides has a strong tendency to react with the glass during the firing of the resistance material. The remaining metal from the silicon then joins with boron from the glass to form a boride or with barium to form a mixed oxide. Thus, the conductors formed by burning the remaining materials 20 comprise both the metal silicides and their borides.