JPH04268111A - Ceramic igniter having long durability - Google Patents

Abstract

PURPOSE: To provide a long life ceramic igniter in which only a slight variation in contact resistance at a contact point after turning-on or -off operation of many times is produced. CONSTITUTION: This ceramic igniter comprises a main body 10 of the ceramic igniter with at least about 20 vol.% of an amount of inclusion of molybdenum disilicide at locations where an electrical contact point should be formed; pads 18, 18' of active metallic brazing material adhered to the main body 10 at each of these locations; and electrical conductive wires 20, 20' fixed to the pads with solder of which melting temperature is higher than about 500 deg.C.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD This invention relates to ceramic igniters and improved methods of making the necessary electrical connections thereto. More specifically, the present invention relates to a ceramic igniter containing molybdenum disilicide, silicon carbide, or a mixture thereof as a conductive ceramic component.

0002

BACKGROUND OF THE INVENTION Ceramic igniters have been known for many years (U.S. Pat. Nos. 3,875,477 and 3,928).
910 and U.S. Reissue No. 29853), the ceramic body does not cause premature igniter failure or substantially increase contact resistance over the long life of the device. Problems continue to arise in making electrical contacts to.

Preparation of ceramic igniters that require conduction of electricity through ceramic components should only be utilized as a physical support for the electrical components, ie, no conduction of electricity through the ceramic is required. This poses substantially different problems than mere physical attachment to a ceramic body. Forming a conductive interface between metals and ceramics not only provides similar thermal expansion properties, but also creates an electrical pathway that remains strong enough to withstand thousands of extreme temperature changes. I need. Furthermore, the metal and ceramic must not react during operation to form an interface that becomes more resistive than either the metal or the ceramic. Any chemical interactions used to create the combined mechanical and electrical connections must also not cause the material composition to deteriorate or change during continued repeated operations. Mechanical failure or chemical degradation or oxidation must both be avoided as both can cause the resistance of the interface to be greater than that of metals and ceramics. The need to combine adhesion with a stable electrical path poses particular problems for long-term, repeated operations such as are required of the igniter of the present invention.

Previous attempts to make electrical connections for ceramic igniters have been various. U.S. Patent No. 3875
No. 477 teaches (i) lightly sandblasting a portion of the silicon carbide igniter in the area where electrical contacts are to be made, and (ii) dipping or thermal spraying the sandblasted end into molten metal. and (iii) using a high alumina type refractory electrical insulation cement. US Patent No. 392
No. 8910 and Reissued Patent No. 29853 disclose a physical slot in a ceramic (SiC) body.
Discloses a gas igniter having conductors joined by hot flame or plasma spraying which not only seeks to secure the electrical conductors inserted into their respective slots, but also to completely and continuously envelop the distal end portion of the igniter. do. Co-pending U.S. patent application Ser. No. 2,583, discloses a ceramic igniter containing molybdenum disilicide in which a simple screw and nut assembly is placed through a machined hole in the ceramic body.

[0005] Each of the above-mentioned connection means suffers from the problem that the resistance increases substantially with long-term use, ie after 100,000 on/off cycles the resistance increases by 5-10% or more. Or they are suffering from the problem of not being able to reproduce them industrially. Such a large increase in resistance is problematic for the igniter industry. This is because, over the long life of the device, the igniter operates at voltages as low as 85% of the standard operating voltage (20V instead of 24.0V), which often occurs during "power savings" or periods of peak power demand. .4V), it must be possible to ignite the fuel gas. Natural gas ignites at about 1050℃, propane gas at about 960℃
ignite it. For example, the available voltage is 85% of the standard voltage.
This could result in an ignition temperature lower than that required for gas ignition, especially in older igniters whose electrical contacts have experienced severe deterioration. Thus, after 100,000 uses, there is no substantial increase in resistance due to the electrical contacts, and preferably no increase in total resistance, i.e. both for the igniter itself and for the electrical contacts. Fewer igniters are required.

US Pat. No. 4,512,871 discloses a heated oxygen sensor in which a conductive circuit is screen printed onto a non-conductive ceramic body, terminating in a pair of pads to which the electrical contacts are made by brazing. This ceramic body is an insulator and serves merely as a physical support. Thus, this US patent does not address the problem of forming improved conductive connections.

[0007] Therefore, it is an object of the present invention to
The change in contact resistance of the contacts is approximately 2% after on/off operation.
An object of the present invention is to produce an improved ceramic igniter that can be manufactured reproducibly in less than 100 liters.

Another object of the invention is to achieve a temperature of 2000
After continuously supplying power for a period of time, the change in contact resistance is approximately 2.5
%.

Yet another object of the invention is to manufacture such an igniter from a ceramic composition comprising molybdenum disilicide, silicon carbide or mixtures thereof as the conductive ceramic.

These and still further objects will become apparent from the detailed description of the invention provided below.

SUMMARY OF THE INVENTION (i) creating a ceramic igniter body having a molybdenum disilicide content of at least about 20% by volume at the locations where electrical contacts are to be made; Make two pads of metal brazing material, and (
iii) Prepare a ceramic igniter by soldering electrical leads to these pads using a solder that melts at temperatures above about 500°C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The ceramic igniter of the present invention includes a non-conductive ceramic in combination with a conductive ceramic. An improved electrical connection to a ceramic igniter is made by creating a pad of brazing material on the igniter and then soldering electrical leads to the pad of brazing material. An igniter prepared using two such electrical connections can be reproducibly manufactured industrially, and furthermore, after undergoing 100,000 on/off operations, approximately Shows a change in contact resistance of less than 2%. Similarly, these igniters can be used at high temperatures (1275-1500°C)
It shows a change in contact resistance of less than about 2.5% after being continuously powered at 26.4V for an hour. The electrically conductive component of the ceramic preferably consists of molybdenum disilicide, silicon carbide or mixtures thereof. More preferably, molybdenum disilicide (MoSi2) and silicon carbide (
SiC) is used. The disclosure and subject matter of this US patent application is incorporated herein by reference.

The igniter preferably contains about 40-70% by volume of the nitride ceramic and a volume ratio of about 1:3 to 3.
; MoSi2 up to 1 and SiC about 30-60% by volume
include. A more preferred igniter composition is Washburn
and as illustrated in FIG. 1 of that US patent application. in this case,
The chemical composition of igniter 10 (FIG. 1) varies from a high resistance portion 12 through an intermediate portion 14 to a highly conductive portion 16. Alternatively, and even more preferably, the intermediate portion 14 is omitted (since it is the container that is being manufactured). The electrically conductive parts are provided with pads 18 and 18' of active metal brazing material according to the invention, to which electrical conductors 20 and 20' are soldered, respectively.

High resistance section 1 of igniter 10 shown in FIG.
2 is preferably comprised of about 50-70% by volume of a nitride ceramic and about 30-50% by volume of MoSi2 and SiC in a volume ratio of about 1:2. Intermediate portion 14, if present, preferably comprises about 50-70% by volume of nitride ceramic and about 1:1 volume ratio of MoS.
i2 and about 30 to 50% by volume of SiC. Highly conductive portion 16 preferably comprises about 45-55 volume percent nitride ceramic and a volume ratio of about 1:1 to about 3:2.
up to 45-55% by volume of MoSi2 and SiC. "High resistance" means 1000 to 16 of that part.
Resistivity at least about 0.04Ω in the temperature range of 00°C
·cm, preferably at least about 0.07 Ω·cm. "Very conductive" or "highly conductive"
means that the resistivity of that part in the temperature range of 100 to 800°C is less than about 0.005 Ω·cm, preferably about 0.00
less than 3 Ω·cm, most preferably about 0.001 Ω·cm
means less than

Nitrides suitable for use as the resistive component of ceramic igniters include silicon nitride, aluminum nitride, boron nitride, and mixtures thereof. Preferably the nitride is aluminum nitride.

The first step in forming the electrical connection of the present invention is to create pads or areas of braze material on opposite ends of the highly conductive portion of the ceramic igniter. To achieve the required high degree of adhesion to ceramics, braze materials containing active metals are utilized. A metal is herein "active" if it has the ability to wet and react with the ceramic material sufficiently to provide adhesion to the ceramic material by the filler metal contained in the brazing material. be considered. Examples of specific active metals include titanium, zirconium, niobium, nickel, palladium, and gold. Preferably the active metal is titanium or zirconium. Besides active metals, brazing materials include silver, copper, indium,
Contains one or more filler metals such as tin, zinc, lead, cadmium and phosphorous. Preferably a mixture of filler metals is used. Most preferably, the braze material comprises titanium as the active metal and a mixture of copper and silver as the filler metal.

Generally, the braze material contains from about 0.1 to about 5% active metal and from about 99.9 to about 95% filler metal by weight percentage. Such brazing materials that are suitable are available from Lucas Milhaupt, Inc. More L
Under the product name of ucanex, also known as GTE Produc.
It is commercially available from TS Corporation under the trade name Cusil. Specific braze materials that have been found useful here include Lucanex
721 and Cusil brazing materials, each nominally 70.5% silver, 27.5% copper and 2%
Contains titanium.

Electrical leads are then connected to the pads of the brazing material by solder. The solder must be able to withstand temperatures of approximately 450° C. during use of the igniter without degrading, and must also have low resistivity. Generally, the melting point of the solder is greater than about 500°C, preferably greater than about 600°C. Suitable such solders include from about 1% to about 90% silver by weight.
, contains about 5 to about 80% copper, about 5 to about 40% zinc, and up to about 40% of one or more metals selected from aluminum, tin, indium, phosphorus, cadmium, and nickel. This is what we are doing. Preferably,
The solder contains about 10-70% silver, about 10-70% copper, about 10-35% zinc, and up to 30% other metals. Most preferably, the solder contains about 15 to 6 silver.
0%, about 10-60% copper, about 12-30% zinc, and up to about 30% other metals.

Such solders that are suitable include Hand
y & HarmonCo. Under the trade name Easy-Flo, also by J. W. Harris Co. , Inc.
It is commercially available under the trade name Safety-Silv. A specific solder found to be useful in the present invention is nominally 45% silver, 15% copper, 16%
Easy- containing % zinc and 24% cadmium
It is Flo 45. Other specific solders that may be used include nominally 56% silver, 22% copper,
Safety- containing 17% zinc and 5% tin
Silv 1200 and nominally 25% silver, 52.5
Safety- containing % copper and 22.5% zinc
Silv 1577 is included.

[0020] In order to solder the conductor to the brazing material pad, it has been found advantageous to first apply solder to the metal conductor. Once the conductor is placed over the braze material pad of the igniter and heated to attach it, solder can flow from the conductor to the braze area to make the connection. This method minimizes the time to heat the brazing material to temperatures above 500°C, and this minimizes oxidation of the pad of brazing material in the air before being coated with solder; To prevent. Oxidation is harmful because it can prevent the formation of a solid chemical bond and can result in mechanical failure and/or electrical interfaces whose resistance is higher than that of metal conductors or ceramic igniters. It is.

The practice of the invention can be further appreciated from the following non-limiting examples and comparative examples. In the following examples, all parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 A bipedal, three-composition hairpin or U-shaped ceramic igniter as shown in FIG. Prepared from molybdenum chloride. In volume percent, the conductive portion contains 50% aluminum nitride, 30% molybdenum disilicide, and 20% silicon carbide, and the middle portion contains 60% aluminum nitride, 20% molybdenum disilicide, and 20% silicon carbide. It contains 20% silicon carbide and the resistive portion contains 60% aluminum nitride, 13% molybdenum disilicide and 27% silicon carbide.

L of active metal brazing paste to form a pad of braze material on each of the legs of the igniter.
ucanex 721 with each leg 0.06″
Brush onto an area of 1.5 mm x 6.4 mm. The paste is heated in a refractory metal furnace to a temperature of 875°C under high vacuum for 10 minutes to form a pad. do.

To attach conventional copper electrical conductors to each pad of brazing material, Easy-Flo 4
5 Use solder (45% silver, 15% copper, 16% zinc and 24% cadmium). Soldering is performed using an oxyacetylene torch as a heating source. Apply standard silver solder flux to the brazing material pad with a brush to clean the surface. The conductor is then heated and solder is brought onto the heated conductor. Molten solder flows onto the conductor in less than about 5 seconds. Place the end of this solder-bearing wire onto the pre-fluxed braze material pad of the igniter and heat with an oxy-acetylene torch to melt the silver solder and apply it onto the braze material in less than about 5 seconds. Allow the water to flow for a while, then move the torch away. The wire is held in place for an additional 5 seconds until the solder solidifies upon cooling.

To evaluate the performance of the resulting electrical connection, the igniter was tested according to the standard American Gas Institute test for evaluating thermoelectric devices, ANSI Test Procedure Z2.
1.20 (1989) pp. 12-13. This test subjects the igniter to 100,000 consecutive on/off cycles and measures the percentage change in resistance of the entire device and igniter body. The resistance change for the electrical connection is then calculated from the difference.

The results obtained from two samples prepared as described above and having average initial igniter temperatures of 1295°C and 1293°C, respectively, are shown in Table 1.

[0027]

[Table 1]

Example 2 The procedure of Example 1 is repeated except that the Lucanex 721 braze material is replaced with Cusil braze material having the same nominal composition. Average initial ignition temperature is 12
The results obtained from two samples at 83°C and 1282°C are shown in Table 2.

[0029]

[Table 2]

Comparative Example A The procedure of Example 1 is repeated using a different solder, Realistic Electrical solder, containing 60% tin and 40% lead. Attempts to solder conductors to brazing material pads using an oxy-acetylene torch, propane torch and electrically heated soldering iron
It did not work. This solder did not bond the conductors to the braze material.

Example 3 The middle part of the ceramic igniter was omitted and the igniter was replaced with 2
The procedure of Example 1 is repeated except that it is evaluated with a 2350 hour continuous current test at 4.0V. Four such samples were evaluated and the rate of change in contact resistance at the end of the test was 0.82.
%, 0.83%, 0.95% and 0%.

Example 4 The procedure of Example 3 is repeated except that the solder is Safety-Silv 1577. The rate of change in contact resistance after a specified period of time during continuous energization tests for a number of samples is shown in Table 3.

[0033]

[Table 3]

Example 5 Repeat the procedure of Example 4 except that the solder is Safety-Silv 1200. Table 4 shows the rate of change in contact resistance after a specified period of time during continuous current testing for a number of samples.

[0035]

[Table 4]

[Brief explanation of the drawing]

1 is a top view of a preferred igniter with a connecting conductor soldered to a brazing material pad according to the invention; FIG.

[Explanation of symbols]

10...Igniter 12...High resistance part 14...middle part 16... Highly conductive part 18, 18'...Brazing material pad 20, 20'...Electric conductor

Claims (1)

[Scope of Claims] [Claim 1] A ceramic igniter comprising the following (i) to (iii). (i) a ceramic igniter body having a molybdenum disilicide content of at least about 20% by volume at the two locations where the electrical contacts are to be made; (ii) an active substance attached to the body at each of the two electrical connection locations; Pad of metal brazing material (ii
i) an electrical conductor attached to the pad of brazing material using a solder that melts at a temperature greater than about 500° C.; 2. wherein the igniter body comprises about 40-70% by volume of a nitride ceramic; The ceramic igniter of claim 1 comprising about 30-60% by volume of a combination of MoSi2 and SiC in a volume ratio of 1:3 to 3:1. 3. The igniter body includes: (1) a high resistance portion containing about 50 to 70 volume % of nitride ceramics and about 30 to 50 volume % of MoSi2 and SiC in a volume ratio of about 1:2; and (ii) about 50-70% by volume of nitride ceramics and about a 1:1 volume ratio of MoSi2.
and a highly conductive portion containing about 30 to 50 volume % of SiC. 4. The ceramic igniter of claim 2, wherein the nitride ceramic is selected from the group consisting of silicon nitride, aluminum nitride, boron nitride, and mixtures thereof. 5. The pad of active metal brazing material comprises an active metal selected from the group consisting of titanium, zirconium, niobium, nickel, palladium, and gold.
The ceramic igniter according to claim 1. 6. The pad of active metal brazing material further comprises at least one filler metal selected from the group consisting of silver, copper, indium, tin, zinc, lead, cadmium and phosphorus. The ceramic igniter according to item 5. 7. The ceramic igniter of claim 1, wherein the pad of active metal brazing material comprises titanium, copper, and silver. 8. The solder contains about 1 to 90% silver, about 5 to 80% copper, about 5 to 40% zinc, and is selected from the group consisting of aluminum, tin, indium, phosphorus, cadmium, and nickel. The ceramic igniter of claim 1, comprising up to about 40% of at least one metal. 9. A method of making electrical contacts to conductive ceramic materials for use at design operating temperatures, comprising:
(i) bonding to a conductive ceramic material to create a pad of active metal braze material; and (ii) melting the pad of braze material at a temperature of at least about 50 degrees Celsius above the maximum design operating temperature of the contact. soldering the electrical conductor using solder. 10. The method of claim 9, wherein the pad of active metal braze material comprises an active metal selected from the group consisting of titanium, zirconium, niobium, nickel, palladium, and gold. 11. The pad of active metal brazing material further comprises at least one filler metal selected from the group consisting of silver, copper, indium, tin, zinc, lead, cadmium, and phosphorus. The method according to item 10. 12. The method of claim 9, wherein the pad of active metal brazing material comprises titanium, copper, and silver. 13. The design operating temperature is at least about 4
10. The method according to claim 9, wherein the temperature is 50<0>C. 14. The solder contains about 1 to 90% silver, about 5 to 80% copper, about 5 to 40% zinc, and is selected from the group consisting of aluminum, tin, indium, phosphorus, cadmium, and nickel. 10. The method of claim 9, comprising up to about 40% of at least one metal. 15. The method of claim 9, wherein the solder is placed on an electrical lead, and the lead is then placed on a pad of brazing material and heated.