US3324049A

US3324049A - Precision resistance element and method of making the same

Info

Publication number: US3324049A
Application number: US528379A
Authority: US
Inventors: Curtis L Holmes
Original assignee: CTS Corp
Current assignee: CTS Corp
Priority date: 1966-02-18
Filing date: 1966-02-18
Publication date: 1967-06-06
Anticipated expiration: 1984-06-06

Description

United States Patent 3,324,049 PRECISION RESISTANCE ELEMENT AND METHOD OF MAKING THE SAME Curtis L. Holmes, Elkhart, Ind., assignor to CTS Corporation, Elkhart, Ind., a corporation of Indiana No Drawing. Continuation of abandoned application Ser. No. 276,064, Apr. 26, 1963. This application Feb. 18, 1966, Ser. No. 528,379

15 Claims. (Cl. 252-514) The present application is a continuation of our copending application entitled Precision Resistance Element, Ser. No. 276,064, filed Apr. 26, 1963, now abandoned, which application is in turn a continuation-in-part of our application entitled, Electrical Resistor and Method of Making the Same, Ser. No. 169,355, filed Jan. 29, 1962, now abandoned.

The present invention relates to resistance elements and, more particularly, to an improvement in the stability of a precision resistance element of the cermet type such as a fixed volumetric resistance element or a thin film resistance element fired onto a surface of a substrate. Recently, with the increasing trend toward miniaturization, the demand for resistance elements having improved characteristics has multiplied mauyfold. The introduction of the cermet resistance element, i.e., a resistance element formed of at least one metal such as one of the noble metals, or an oxide thereof, in a fine particle size, i.e., a size of 325 mesh or smaller, preferably of a molecular size, dispersed ina glass or suitable ceramic material, has enabled manufacturers of resistance elements to produce 'a precision resistance element having a stable shelf life, low no-load humidity characteristics and the like.

Two of the problem areas in the manufacture of a cermet resistance element which have continued to plague the manufacturers are (a) the ditficulty in controlling the temperature coefiicient of resistance, that is, the percentage change in resistance with respect to a change in temperature and b) the stability of a cermet resistance element at various operating loads with respect to time. The temperature coeflicient of resistance of a cermet resistance element has been kept to a minimum, e.g., by combining a conductive material having a positive temperature coefiicient with a conductive material having a negative temperature coefficient. Theoretically, the temperature coefiicient of resistanceof a resistance element could be maintained at substantially zero if the percentages of the conductive materials or particles could be precisely controlled in the end product. Other means well known in the art are also employed. The stability of a cermet resistance element has heretofore remained a problem regardless of what ingredients, elements or compounds were added to the electrically'conductive particles or conductive fraction of the mixture employed in producing the resistance element. Based on the prior art, it has been accepted practice to add one or more metals or the oxide thereof to the electrically conductive portion of a resistance element without changing the form of the metal or oxide thereof, e.g., metal oxides have been combined together in various proportions to produce a resistance element having a desired negative temperature coefiicient. The metal oxides, however, always remained in their original form whether it be crystalline or amorphous. The addition of a metal or an oxide thereof to the conductive fraction of a cermet resistance element has been ineffective since such addition substantially reduces the ohmic resistance of the resistance element without changing the stability thereof. It would, therefore, be desirable to produce a ceramic resistance element having an extremely high stability at various loads and overloads with respect to time without substantially altering the ohmic resistance, i.e., by dissolving the additive in the glass thereby structurally combining the additive with the glass.

Accordingly, it is an object of the present invention to provide a cermet resistance element having higher stability than heretofore available. Another object of the present invention is to improve the stability of a cermet resistance element by adding small percentages of manganese oxide and/or cupric oxide to the admixture of metal particles and powdered glass employed in making cermet resistance elements. A further object of the present invention is to control the temperature coeflicient of resistance of a cermet resistance element by adding a specific ratio of manganese oxide and cupric oxide to the glass employed in the resistance element. Still another obect of the present invention is to improve the stability of a cermet resistance element by adding small amounts of cupric oxide and/or manganese oxide into the raw materials employed in preparing the glass thereby dissolving the oxide in the glass. Further objects and advantages of the present invention will become apparent as the followmg description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

The novel compositions of the present inventions are formulated by adding small percentages of cupric oxide and/or manganese oxide to the glass employed in the preparation of cermet resistance elements. Preferably the oxide of copper and/or manganeseinitially in crystalline form is thoroughly admixed with the raw materials employed in preparing the glass. Whether the oxide of copper and/ or manganese is added to the raw materials forming the glass or after the molten glass is frittered and ground to a powder is not important so long as the admixture is eventually fired at a temperature sufiicient to fuse the powdered glass causing the oxide of copper and/ or manganese to dissolve in the glass and structurally become a part of the glass. An organometallic compound in solution, e.g., a ruthenium resinate, is preferably combined with the powdered glass containing small amounts of the oxide of copper and/ or manganese to produce a precision resistance element having improved stability, i.e., a re sistance element having a very small change in ohmic resistance when subjected to various loads and overloads for a considerable period of time. I

It is to be understood-that the conductive fraction of the resistance material initially need not be an organometallic and can be an organosol, e.g., ground particles colloidally dispersed in an organic liquid. It has been found, however, that organo-metallic compounds in solution such as metal resinates, glycinates, etherates, esterates, and napthanates are preferable since the metal particles are in molecular form and may be readily admixed with the powdered glass. As to the conductive fraction, noble metals and/or the oxides thereof such as gold, silver, platinum, palladium, rhodium, iridium, osmium, and ruthenium are preferable although other metals can be used. Procedurally, and as indicated in the examples, various glass compositions may be utilized, the type of glass not being critical to the practice of the invention. Further, various changes in the glass composition can be made to alter the fusion temperature, coefiicient of thermal expansion, fluidity, solubility and the like by a person skilled in the ceramic art to produce a particular desired characteristic. Generally, if the particular glass utilized in the preparation of the cermet resistance element yields a cermet resistance element having a negative temperature coefficient and, it is desirable to make more positive the temperature coeflicient, 'the'n cupric oxide is admixed with the glass since cupric oxide tends to yield a positive temperature coefficient. On the other hand, if it is desirable to increase further the negative temperature coefiicient of the element, then manganese dioxide is admixed with the glass. If the cermet resistance element has a low temperature coeflicient, then the ratio of manganese oxide and cupric oxide added to the glass is controlled to prevent a change in the temperature coefficient.

The formula for the glass used in the practice of the present invention may be any one of several ordinarily used in the art. An example of the raw materials employed in a particular glass formula is as follows:

Raw materials: Percent B 12 Bi203 PbO 66 SiO 11 In order to assure that the oxide of copper and/ or manganese becomes thoroughly dissolved throughout the glass structure and forms a part thereof, it is preferable that the oxide of copper and/ or manganese be thoroughly admixed with the above raw materials. After a batch of the raw materials and the oxide of copper and/ or manganese have been thoroughly admixed while in a dry state, the batch of the raw materials is placed into a ceramic crucible and heated until a molten glass is formed. When the batch of the raw materials employed in making the glass is heated to a molten mass, the 0xide of copper and/ or manganese loses its original crystalline or amorphous form by dissolving and becoming a part of the glass structure. The molten glass is then poured into water at which time it solidifies and fritters, the solid particles being commonly referred to as glass frit. The glass frit is then ball milled to about 325 mesh in size. Each of the noble metals or the oxides thereof is also milled to a fineness less than 325 mesh in size. The oxide of copper and/ or manganese eventually dissolves and becomes a part of the glass structure even if the oxide of copper and/or manganese is admixed with the glass after it is ground to a powder. Although it is believed that there is less homegeneity of the oxide of copper and/or manganese in the glass by adding the oxides thereof to the powdered glass instead of to the batch of the raw materials forming the glass, the end I result is substantially the same. This is further substantiated by tests indicating that there is substantially no change in the ohmic resistance when an oxide of copper and/or manganese is added to the raw materials or to the powdered glass. There is, however, a definite improvement in the stability regardless of when the oxide of copper and/or manganese is dissolved in the glass. Moreover, the oxide of copper and/or manganese can be admixed with one of the noble metals, e.g., ruthenium, and then admixed with the powdered glass to produce a cermet resistance element having improved stability. When the oxide of copper and/or manganese becomes a part of the glass structure, it is no longer conductive and, therefore, does not substantially affect the ohmic resistance. It does, however, decrease the ohmic resistance somewhat since the additives permit a finer dispersion of the conductive fraction in the glass.

The present invention will be more completely understood by reference to the following examples. In each instance, all parts and percentages are by weight, unless otherwise specified. It is to be noted that the stability of a cermet resistance element comprising a glass not containing an additive of an oxide of copper and/ or manganese was such that the percent change in ohmic resistance after a 72 hour extended oven test at 200 C. was 2.2 percent.

EXAMPLE I Percent Ir 1 Flint 49 Glass 49 M1102 1 The MnO was added to the batch of raw materials employed in making the glass and, after the glass was frittered and ground to the proper particle size, the Ir being present in a 4 percent concentration in an iridium resinate, the flint was added to the glass to produce a precision volumetric resistance element having a percentage change in ohmic resistance of only 0.30 percent after a 72 hour extended oven test at 200 C. Exhaustive tests have indicated that the 72 hour oven. test at 200 C. is comparable to a 1000 hour load life test at C.

EXAMPLE II Composition II was the same as the composition in Example I except that the percent of MnO was increased from 1 percent to 2.5 percent. Aft-er a 72 hour extended oven test at 200 C., the percent change in ohmic resistance was calculated to be 0.15 percent.

EXAMPLE III Percent Ir .7 Ru .3 Flint 49.0 Glass 49.0 MnO 1.0

EXAMPLE IV Composition IV was the same as the composition of Example III except that the amount of MnO was increased to 2.5 percent. The percent change in ohmic resistance after a 72 hour extended oven test at 200 C. was 0.15 percent.

EXAMPLE V Percent Ir .7 Ru .3 Flint 49.0 Glass 49.0 M1102 .5 CuO .5

Composition V was the same as the composition in Example III except that the amount of MnO Was changed to .5 percent and .5 percent of CuO was added. The percent change in ohmic resistance after a 72 hour extended oven test at 200 C. was 0.11 percent.

Composition VI was the same as the composition of Example V except that the amount of MnO was increased to 1.5 percent and the amount of CuO was increased to 1 percent. The percent change in ohmic resistance after a 72 hour extended oven test at 200 C. was .20 percent.

EXAMPLE VII Percent Ir .7 Ru .3 Flint 47.0 Glass 47.0 Mnoz 5-0 Composition VII was the same as the composition of Example III except that the MnO was increased to 5 p rcent. The percent change in ohmic resistance after a 72 hour extended oven test at 200 C. was .13 percent.

EXAMPLE VIII Composition VIII was the same as the composition of Example VI except that Ru and Pt were employed instead of Ir and Ru. After a 72 hour extended oven test at 200 C., the percent change in ohmic resistance was .16 percent.

In the above compositions, the fllint was used solely to give the fixed volumetric resistance element sufiicient body. It is to be understood that other refractory materials besides flint may be employed in preparing and producing fixed volumetric resistance elements as recited in application Ser. No. 169,355, e.g., alumina, beryllia, chromic oxide, feldspar, kaolin, silica, titania, zinc oxide and zirconia. If the filler material, e.g., flint, is deleted from the resistance element, the ingredients may be cast or molded by means well known to a person skilled in the art, for example, by heating the ingredients to a temperature above the softening point of the glass while in a mold. It is to be understood that the above compositions for the improved stability resistance elements can be of the thin film type, the thin film resistance element being of the same composition except that a suitable screening agent is employed instead of the filler in order to screen the mixture onto the surface of a substrate. Preferably, the conductive fraction of the resistance element, that is, the metal particles such as one of the noble metals should be in the range of .5 to 20 percent by weight of the total ingredients used.

Regardless of whether the cermet resistance element is of the fixed volumetric type or of the thin film type, the element is fired at temperatures sufficient to fuse the glass containing the additives for stabilizing the ohmic resistance and the noble metal particles dispersed therein to form a precision cermet resistance element. It has been ascertained by exhaustive tests that even 40 percent of Mn0 and/or CuO can be added to the glass to improve the stability of the resistance element without adversely affecting the characteristics thereof; however, smaller amounts of MnO and/or CuO, such as 1 to 2 percent are most effective in producing the greatest improvement in stability. As shown by the examples, further additions of MnO and/or CuO show only slight improvement in the stability. It is to be understood that the above examples are merely illustrative and not restrictive. Moreover, the present invention may be susceptible of embodiment in other modified forms and that all such modifications which are similar or equivalent hereto come equally within the scope of the claims appended hereto.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A cermet resistance material comprising about 40 to 99 percent by weight of a ceramic glass, .5 to 20 percent by weight of at least one of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru in a finely divided state, and .5 to 40 percent by weight Of M1102.

2. A cermet resistance element comprising fine particles of at least one of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru dispersed in a fused glass, at least .5 percent by weight of M110 dissolved in the glass, and at least one of the refractory materials selected from the group consisting of alumina, beryllia, chromic oxide, feldspar, kaolin, silica, titania,

zinc oxide and zirconia for giving a body to the resistance element.

3. A cermet resistance element comprising a high temperature resistant, electrically nonconductive base, a film of fused glass fired onto a surface of the base, particles of at least one of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru dispersed in the fused glass, and .5 to 40 percent by weight of Mn0 dissolved in the fused glass and forming a part of the glass structure.

4. A cermet resistance element comprising particles of at least one of the noble metals in the amount of .5 to 20 percent by weight selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru dispersed in a fused glass, .5 to 40 percent by weight of MnO dissolved in the glass and structurally forming a part of the glass, and at least one of the refractory materials selected from the group consisting of alumina, beryllia, chromic oxide, feldspar, kaolin, silica, titania, zinc oxide and zirconia for giving a body to the resistance element.

5. A resistance element comprising a high temperature resistant, electrically nonconductive substrate, a film of glass bonded to a surface of the substrate, at least .5 percent by weight of MnO dissolved in the glass and forming a structural part of the glass, and fine particles of at least one of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru dispersed in the glass in an amount of .5 to 20 percent by weight.

6. A resistance element comprising a high temperature resistant, electrically nonconductive base having fired thereonto a film of resistance material comprising 40 to 99 percent by weight of a solidified glass, .5 to 40 percent by weight of MnO dissolved in the glass, and at least .5 to 20 percent by weight of one of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, OS, and Ru in finely divided form dispersed through the solidified glass in electrically conductive relationship.

7. A resistance element comprising a body of solidified glass, at least .5 percent by weight of MnO structurally forming a part of the glass, an inert material for preventing the glass from flowing when fired to fuse the glass, and at least one of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru in a finely divided form dispersed throughout the solidified glass.

8. A cermet resistance material consisting essentially of about 40 to 99 percent by weight of a ceramic glass, at least .5 percent by weight of one of the oxides of the noble metals selected from the group consisting of Ir, Os, and Ru in a finely divided state and dispersed in the glass as a conductive fraction, and .5 to 40 percent by weight of CuO dissolved in the glass and forming a structural part of the glass.

9. A cermet resistance material consisting essentially of about 40 to 99 percent by weight of a ceramic glass, at least .5 percent by weight of at least one of the oxides of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru in a finely divided state and dispersed in the glass as a conductive fraction, and .5 to 40 percent by weight of a compound selected from the group consisting of MnO and CuO dissolved in the glass and forming a structural part of the glass.

10. A resistance element consisting essentially of a high temperature resistant, electrically nonconductive substrate, a film of glass bonded to a surface of the substrate, at least .5 percent by weight of CuO dissolved in the glass and forming a structural part of the glass, and fine particles of at least one of the oxides of the noble metals selected from the group consisting of Ir, Os, and Ru dispersed in the glass as a conductive fraction in an amount of at least .5 percent by weight dissolved in the glass and forming a structural part of the glass.

11. A resistance element consisting essentially of a high temperature resistant, electrically nonconductive substrate, a film of glass bonded to a surface of the substrate, at least .5 percent by weight of a compound selected from the group consisting of MnO and CuO dissolved in the glass and forming a structural part of the glass, and fine particles of at least one of the oxides of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru dispersed in the glass as a conductive fraction in an amount of at least .5 percent by weight.

12. A resistance element consisting essentially of a body of solidified glass, at least .5 percent by Weight of CuO dissolved in the glass and structurally forming a part of the glass, an inert refractory material for preventing the glass from flowing when fired to fuse the glass, and at least one of the oxides of the noble metals selected from the group consisting of Ir, Os, and Ru in a finely divided form dispersed throughout the solidified glass as a conductive fraction.

13. A resistance element consisting essentially of a body of solidified glass, at least .5 percent by Weight of a compound selected from the group consisting of MnO and CuO dissolved in the glass and structurally forming a part of the glass, an inert refractory material for preventing the glass from flowing when fired to fuse the glass, and at least one of the oxides of the noble metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os, and Ru in a finely divided form dispersed throughout the solidified glass as a conductive fraction.

14. A method for improving the stability of a cermet resistance element comprising the steps of: adding .5 to 40 percent by weight of a compound selected from the group consisting of MnO and CuO to a batch of raw materials employed in the preparation of a glass, heating the batch of raw materials containing the compound to form a molten glass, dissolving the compound in the molten glass, fritting the molten glass by pouring the molten glass into Water, removing the fritted glass from the water, grinding the fritted glass to a size of less than 325 mesh, and adding in a fine particle size .5 to 20 percent by weight of at least one of the oxides of the metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os and Ru to the ground glass.

15. A method for improving the stability of a cermet resistance element comprising the steps of: admixing glassforming raw materials for preparing a glass, heating the raw materials to form a molten glass, fritting the molten glass by pouring the glass into water, removing the fritted glass from the water, grinding the fritted glass to a size of less than 325 mesh, adding .5 to 40 percent by weight of a compound selected from the group consisting of Mn0 and CuO and .5 to 20 percent by weight of at least one of the oxides of the metals selected from the group consisting of Ag, Au, Pd, Pt, Rh, Ir, Os and Ru to the ground glass to form a composition, firing the composition to produce a ceramic resistance element having a stability of less than 1.0 percent.

References Cited UNITED STATES PATENTS 3,154,503 10/1964 Janakirama-Rao 2525l4 LEON D. ROSDOL, Primary Examiner.

J. D. WELSH, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE" OF CORRECTION Patent N00 3,324,049 June 6, 1967 Curtis Lo Holmes error appears in the above numbered pat- It is hereby certified that t the said Letters Patent should read as ent requiring correction and the corrected below.

line 40, for "homegeneity" read homogeneity column 5, line 19, for "fllint" read flint column 6, lines 70 and 71, strike out "dissolved in the glass and forming a structural part of the glass'h Column 3,

Signed and sealed this 28th day of November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims

1. A CERMET RESISTANCE MATERIAL COMPRISING ABOUT 40 TO 99 PERCENT BY WEIGHT OF A CERAMIC GLASS, .5 TO 20 PERCENT BY WEIGHT OF AT LEAST ONE OF THE NOBLE METALS SELECTED FROM THE GROUP CONSISTING OF AG, AU, PD, PT, RH, IR, OS; AND RU IN A FINELY DIVIDED STATE, AND .5 TO 40 PERCENT BY WEIGHT OF MNO2.

15. A METHOD FOR IMPROVING THE STABILITY OF A CERMET RESISTANCE ELEMENT COMPRISING THE STEPS OF: ADMIXING GLASSFORMING RAW MATERIALS FOR PREPARING A GLASS, HEATING THE RAW MATERIALS TO FORM A MOLTEN GLASS, FRITTING THE MOLTEN GLASS BY POURING THE GLASS INTO WATER, REMOVING THE FRITTED GLASS FROM THE WATER, GRINDING THE FRITTED GLASS TO A SIZE OF LESS THAN 325 MESH, ADDING .5 TO 40 PERCENT BY WEIGHT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF MNO2 AND CUO AND .5 TO 20 PERCENT BY WEIGHT OF AT LEAST ONE OF THE OXIDES OF THE METALS SELECTED FROM THE GROUP CONSISTING OF AG, AU, PD, PT, RH, IR, OS AND RU TO THE GROUND GLASS TO FORM A COMPOSITION, FIRING THE COMPOSITION TO PRODUCE A CERAMIC RESISTANCE ELEMENT HAVING A STABILITY OF LESS THAN 1.0 PERCENT.