US1970768A - Alloy - Google Patents

Description

Patented Aug. 21, 1934 PATENT OFFICE ALLOY Hector Rabezzana, Flint Ann Arbor, Mich,

No Drawing.

, and Ora S. Duflendaclr,

assignors, by mesne assignments, to General Motors Corporati Mich., a. corporation of Delaware Application November 9, 1931,

on, Detroit,

ierialNo. 574,050. In Canada September 17,

4 Claims.

. This invention relates to a new alloy and is a continuation in part of our prior application, Serial Number 519,674, filed March 2, 1931, which in turn was a continuation in part of our prior ,5 application Serial No. 302,904, filed August 30,

1928. In that application there is described and claimed an electrode for spark plugs and similar devices characterized by the presence of amaterial of low work function. Work function may be defined as the amount of work necessary to remove an electron from the element. In the case of spark plugs the incorporation in the electrodes of material of low work function produces a great reduction in the sparking voltage; 1. e., the volt- 5, age required to cause a spark to jump the gap between the electrodes of the plug. As described in our prior application reduction in sparking voltage greatly prolongs the useful life of the plug by increasing the amount of carbon deposit that the plug will stand before becoming short circuited.

It is also very desirable to incorporate in the electrodes of vacuum tubes, such as are used for radio work and current rectification, material of 5j 'low work function so as to secure maximum electronic emission. Electrodes containing such material may be similarly employed in luminous gas and vapor lamps such as the well known neon tube and mercury arclamp.

-1 In our prior application we have disclosed a number of alloys which may be used for electrodes of the class referred to and contain material of'low work function, and the present case is one of a series in which the alloys themselves ;are covered since they are novel and the above mentioned property as well as others fit them especially well for other uses.

To be useful for the purposes above mentioned, the alloys should possess desirable electrical -properties, aside from electronic emission; they should be homogeneous so that the rate of electronic emission will be fairly constant; they should preferably be workable by ordinary drawing methods; and, especially for spark plug work, they should be resistant to heat and corrosion.

Among the alloys with which we have experimented those containing barium have possessed the enumerated properties to an exceptional degree. As a base metal we have found nickel to -be the best as it is resistant to corrosion, alloys well with barium, forming a true solid solution, with the barium uniformly distributed throughout, and the alloy may readily be drawn into wire or ribbon. For many purposes an alloy of nickel 555 and barium will be found to be useful, as such an alloy will possess all the advantages of nickel in resisting corrosion and of barium in reducing the sparking voltage. Nickel is also a fairly good conductor, at least at the lower temperatures and is of relatively low cost. 00 Under the severe conditions of operation to which spark plugs are subjected, such an alloy will not prove to be entirely satisfactory because ofv intercrystalline corrosion. To overcome this difficulty we-propose to add to the nickel-barium alloy a small percentage of manganese, or any other well known deoxidizing agent such as are used'in nickel alloys. A small amount" of magnesium is likewise preferably added to the alloy to deoxidize the alloy melt and to increase its ductility and permit easy drawing. In its preferred form the ingredients of the alloy as used for spark plug electrodes may be in substantially the following proportions:

- Percent Manganese 1.8 Barium- Magnesium a trace Balance nickel The amount of magnesium present in the alloy is so small, so difficult to measure by ordinary methods of chemical. analysis, and so non-uniformly distributed that it has been designated as a trace. It is the residue of about .1% magnesium added to deoxidize the alloy and increase its ductility so as to permit easy drawing.

A barium content of .03% has been chosen for spark plug usebecause the addition of more barium, while reducing the sparking voltage, does 0 not reduce it by an additional amount suillcient to warrant the expense. A barium content as low as .01% will, however, efiect an appreciable lowering of the sparking voltage. A manganese content around 1.8% will be found adequate for spark plug uses but there may be considerable variation in the percentages of both this ingredient and of nickel.

Spark plugs having electrodes of the above alloy have, upon test, shown sparking voltages 25% lower than the average voltages obtainable 1 with electrodes of the usual nickel-manganese alloy, and whereas with the latter material the sparking voltage varied as between successive sparks, when operated under the same conditions, by 1,000 to as much as 4,000 volts, with 1 our improved electrodes the variation in voltage as between successive sparks does not exceed 400 or 500 volts. With the barium alloy, the plug retains these characteristics throughout substantially its entire life for the barium eva'p- 110 crates from the electrode at a rate but little greater than that of the nickel.

We have also found that the barium increases the resistance of the electrodes to corrosion, actual tests show an increase in electrode life of 25%.

In preparing the alloy the barium, which is readily oxidized, is sealed within a can made of ordinary tin plate, or is wrapped in nickel foil and the package is immersed in the molten nickel-manganese alloy. The foil or the can melt and mix with the other ingredients but the amount of foreign material thus introduced is so slight as to have practically no measurable effect on the alloy. The advantage of this method of preparing the alloy is that the barium is kept out of contact with the air and becomes alloyed with the nickel and manganese before it has opportunity to oxidize. Owing to the volatility of the barium, it is desirable that the temperature of the melt should be but little above the melting point of nickel at the time it is introduced and after introduction the melt should be allowed to stand before casting only long enough to insure complete alloying. However to secure a greater barium content such as is needed in vacuum tubes, and the like, and to insure the least waste of barium, it is desirable to em-- ploy the method of procedure described and claimed in the copending application of D. W. Randolph Serial No. 520,704, filed March 6, 1931.

For other uses, as in vacuum tubes, manganese may be omitted for corrosion is not a problem. The larger percentages of barium will also be found preferable for vacuum tube electrodes. We have so far succeeded at times in producing by the processes herein referred to alloys containing as much as .15% barium, although most of the time not more than .04%

} barium was achieved. By the improved method claimed in the Randolph application alloys have consistently been made containing .17% barium, and at times as much as .52% barium has been included. -Microscopic examination of a nickelbarium alloy containing .52% barium showed that. a considerable proportion of the barium was present in the form of inclusions rather than 1n solid solution. Such material has proven difficult, if not impossible, to work.

We have also obtained, by the method set forth in the application of Prof. Maurice deKay Thompson, Serial No. 569,265, flied October 16, 1931, barium nickel alloys containing as high as .8% barium. This method consists briefly insealing a charge of nickel and barium within a suitable container and heating it to temperatures of from 1375 to 1400 C. to insure melting of the nickel. At this temperature the vapor pressure of barium is quite high, and probably assists in the formation of the resulting alloy. An examination of a nickel-barium alloy cotaining .8%

barium made by this method likewise revealed a considerable proportion of the barium in the form of inclusions. It is expected that by improvements in furnace technique now being experimented with, larger percentages of barium may be obtained.

- It must now be apparent that the proportions given in the table above are not critical. The percentages of the ingredients may, for example, be varied within the following range:

Per cent Manganese .5 to 10.0 Barium .01 to- .80 Magnesium a trace Balance nickel 3 This range includes alloys suitable for use for vacuum tube electrodes as well as electrodes for spark plugs. Where the barium content is in excess of about .20%, the alloy will be found more difl'icult to work, and this difliculty will increase with the barium content.

Instead of using nickel as the base metal we may use cobalt, an element of well recognized similar characteristics. Cobalt will not be as satisfactory, however, for spark plug work, where corrosion is a factor, for it has relatively poor corrosion resisting properties. Elsewhere its use may be desirable. In the broader claims we have grouped nickel and cobalt together under the term nickel-cobalt metal.

We have also made and tested alloys of barium with copper, with silicon and with chromium as base metals. The copper-barium alloy is not as resistant to corrosion as is desirable for spark plug work. The same is true of the siliconbarium alloy. Where, as in vacuum tube electrodes, corrosion is not a factor, and the base metal merely furnishes mechanical support for .the electron emitting material, these base metals .5% to 10% manganese. and the balance con-- sisting essentially of nickel, the barium imparting ready electron emissivity to the alloy, materially increasing its resistance to corrosion, and evaporating from the alloy at a rate but little greater than that of nickel thereby assuming a substantially permanently high rate of emission.

2. A ductile, homogeneous, corrosion resisting alloy characterized by ready electron emissivity, a high degree of permanence. and fair heat and electrical conductivity consisting of nickel, barium and manganese in substantially the following proportions: barium .01% to .80%, manganese .50% to 10%, nickel 89.2% to 99.94%.

3. A ductile, homogeneous alloy characterized by ready-electron emissivity, and fair heat and electrical conductivity, containing from approximately .01% to approximately .80% metal, and a deoxidizing agent approximately equal to from .5%'to 10% manganese, the balance consisting essentially of a metal of the group consisting of nickel and cobalt, the barium imparting ready electron emissivity to the alloy.

4. A ductile, homogeneous alloy characterized by ready electron emissivity, and fair heat and electrical conductivity, containing from .01% to .20% metallic barium, .5% to 10% manganese, and the balance consisting essentially of nickel, the barium imparting ready electron emissivity to the alloy, materially increasing its resistance to corrosion and evaporating from the alloy at barium a rate but little greater than that of nickel there-