US2391458A - Spark gap electrode - Google Patents

Description

Dec. 25, 1945. F. R. HENsl-:L 2,391,458

SPARK GAP ELECTRODE Filed March 14, 1944 fag-f IN V EN TOR.

' aifz E Hifel wcznemrw Patented Dec. 25, 19.45

sPAm GAP, Emcmona Franz R. Hensel, Indianapolis,- Ind., assigner P. R. Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware v v Application March 14, 1944, serial 10,526,350

s claims. (ci. 12a-169) This invention relates to improvements `in spark gap electrodes and more particularly to metallic electrodes suitable for use in spark plugs, ignition systems, high frequency generators, high frequency induction furnaces, etc.

Objects of the invention are: to provide elece trical spark gap electrodes having improved operating characteristics, as well as to provide .a composition from which such electrodes may be formed.

A more specific object of the invention is to provide metallic materials which have, due to the structural composition thereof, more resistance to pitting and metal transfer during operation, which are less susceptible to oxidation, and which operate in an improved manner, as compared with materials heretofore used in the same fields of application.

Other objects will in part be obvious and will in part appear hereinafter from the following description taken in connection with the accompanying drawing in which:

Figure 1 illustrates a side view partly in sectionof the invention as applied to a spark plug electrode;

Figure 2 shows a modified form of electrode, and

Figure 3 shows an end view of Figure 1.'

The invention accordingly comprises improved products possessing the features and properties which will be exemplified in the embodiments hereinafter described and the scope of the application of which will be indicated in the claims.

Many different types of materials have been proposed heretofore for use in spark plug electrodes and similar electrodes subjected to severe oxidizing and/or corrosive atmospheres and/or other deleterious influences. Of the materials used heretofore, either singly or in combination with other metals, tungsten and platinum are among the most conspicuous. However, these materials suffer from a number of disadvantages Which are not encountered in a more recent member of the group of refractory or precious metals, namely rhenium, and this invention, therefore, contemplates 'the use of rhenium in spark gap electrodes such asspark plug electrodes, for example.

Comparative tests which were carried out by heating rhenium and tungsten Wires, in air at 1000 C., indicated that rhenium Wire possesses considerably higher heat and oxidation resistance than tungsten `Wire, the rhenium wire having a useful life about three times as long as that of the tungsten wire. Similar tests were carried out with a mixture` of `air and nitrogen, the oxygen content .being approximately 10%. In this mixture, rhenium could be heated to 1600 C. before oxidation 'started-and the rate of oxldatio was only one-third that of tungsten. f

In hydrogen atmospheres containing a 'small percentage of water vapor, rhenium wires were extremely stable up to the highest temperatures, whereas tungsten was attacked after a relatively short time. When rhenium wire was first heated in moist hydrogen at 2000 C. and then in moist nitrogen, it was possible to heat therhenium wire in the lattercase up to 2300 C., without any evidence of attack. The wire had to be heated tov 2500 C. before any deleterious oxidation occurred. -These results appear to lead to the conclusion that rhenium may be rendered passive by giving it a heat treatment in moist hydrogen.

The present invention proposes to take advantage of the above findings, by formingv electrodes from at least one of the following materials: (l) solid metallic rhenium; (2) a rhenium-plated rod having a core of one of the materials tungsten, molybdenum, or an alloy of tungsten and copper, or tungsten and silver; (3) a rhenium-plated rod having a core of a material consisting of molybdenum about 5%, copper or nickel about 5%, and the remainder tungsten plus rhenium; (4) rhenium-base compositions or alloys containing platinum group metals such as ruthenium, rhodium,

palladium, osmium, iridium and platinum in percentages ranging from 0.5 to 49%; y(5) rheniumbase compositions or alloys containing refractory metals of the group comprising tungsten, molybdenum and tantalum in percentages ranging from .0.5 to 49%; (6) a rhenium composition or alloy of high density produced by creating a liquid phase during sintering. 'I'he elements producing such a liquid phase may be either nickel and copper or low melting point eutectic compositions of molybdenum with an iron-base metal such as nickel, iron or cobalt. Usually the rhenium content of such compositions will vary from 'l0 to the balance being the metals constituting the low melting point phase.

Referring to the drawing, Figure l shows an embodiment of the invention as applied to the construction of a, spark plug, only that portion thereof which is shown in longitudinal section being a part of this invention. As shown, the spark plug comprises an insulator I 0 formed of conventional insulating materials such as a ceramic composition, said insulator surrounding the central electrode which comprises an upper portion Il made 0f any suitable metallic composition used heretofore, and a lower section I! which according to this invention may be made of solid metallic rhenium or any of the materials set forth under 4, 5 and 6 above. The side electrode I5 may be formed of rhenium or rhenium-base or rhenium-plated material as de scribed above, or of any other suitable material.

In the modiiled embodiment of the invention which is shown in Figure 2, the central electrode may comprise a core 20 upon which has been plated a sheath 24 of rhenium. The core 20 may be formed of any of the materials set forth under 2 or 3 above.

Figure 8 shows a bottom end view of the .spark plug construction of Figure 1, i2 being the centrai electrode and I5 being the side electrode.

The method per se of eiecting the electrodeposition of metallic rhenium upon the spark gap core materials is not a Dart of the present invention since a suitable plating method has been described and claimed in U. S. Patent 2,138,573, patented November 29, 1938, to C. G. Fink and Pincus Deren. By using the method disclosed in said patent, bright and hard deposits of rhenium metal may be obtained from various aqueous solutions of rhenium. Rhenium electro-plates readily and rapidly, and its plating solutions have a good throwing power and give good current eillciencies. Plates of any desired thickness may be easily obtained, and the plates are extremely resistant to attack by oxidizing and corrosive gases at high temperatures, i. e., under conditions such as are encountered in the use of spark gap and spark plug electrodes. If desired, rhenium may be co-deposited upon the core of an electrode or similar member with a metal or metals such as nickel and cobalt.

While the present invention, as toits objects and advantages, has been described herein al carried out in a specific embodiment thereof, the invention is not to be limited thereby but is intended to be covered broadly within the spirit and scope of the appended claims.

What is claimed is:

l. A spark gap electrode containing rhenium.

2. A spark plug electrode composed entirely of metallic rhenium.

3. A spark gap electrode, at least the working surface portion of which is composed predominantly of rhenium.

4. A spark gap electrode having a body of refractory metal and a working surface layer inte- Iglliral therewith composed predominantly of rhe- 5. A spark gap electrode having a, body of refractory metal and a working surface layer integral therewith composed of rhenium.

6. A spark gap electrode having a core formed of a refractory metal composition and a working face layer formed of rhenium.

7. A spark gap electrode having a core formed of a. refractory metal composition and a working ,face layer thereon formed of electrodeposited rhenium.

8. A spark gap electrode, at least the working

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