US2605297A - Electrode for electrical systems - Google Patents

Description

July 29, 1952 R. s. DEAN ELECTRODE FOR ELECTRICAL SYSTEMS Filed Nov. 17, 1950 (MEI/e3 i Mk2.

W E 5 W 4 m m m E V m Patented July 29, 1952 ELECTRODE FOR ELECTRICAL SYSTEMS Reginald S.Dean, Washington, D. C., assignor to Chicago Development Corporation, Riverdale,

Md.,"a corporation of Delaware Application November 17, 1950, Serial No. 196,177

This invention relates to electrodes for electrical systems. It relates particularly to such systems where it is desirable to have a highly electropositive material as an electrode. By an electropositive material is meant one which has an electrode potential in solutions of its ions near that of the alkali metals. Such electropositive materials are also characterized by a low work. function for the thermionic emission of electrons. In the known art these electropositive properties have been found only in alkali metals and in alloys of alkali metals which are rapidly attacked by water. The rapidity of such attack by water and the mechanical and physical properties such as strength and melting point has prevented the practical use of these materials for many purposes for which they are, otherwise, well suited; for example, electrodes in water activated primary cells, electrodes in electronic discharge devices, and the like. I have found that certain alloys of lithium and magnesium possess electropositive properties very close to those of lithium but at the same time are far less reactive with water.

In the figure, curve I, I have illustrated the electrode potential of a series of lithium-magnesium alloys measured against metallic lithium, It will be seen that up to 60% magnesium there is a small increase in the potential against lithium amounting at 60% magnesium to less than 0.3 volt. In curve 2, of the figure, I have illustrated the rate of attack of the alloy by water in arbitrary units. It will be seen that at 60% magnesium the rate of attack is very much less than that of lithium or of lithiummagnesium alloys with less than 50% magnesium. Consequently, in the range of 52-70% magnesium these alloys are within 0.8 volt as electropositive as lithium and yet react much less rapidly with water.

As specific examples of the rate of reaction with water I give the following:

Hydrogen evolution in water per unit surface Alloy 55% Magnesium 60% Magnesium 65% Magnesium 3 ;Claims. (Cl. 136-100) of this invention may bemade by methods known in the art. It is'convenient to make the-alloys by melting together the pure metals in an iron crucible fitted with a thin steel diaphragm at the bottom below which is a suitable mold. The

crucible and the mold are contained in a casing which is maintained full of argon. The whole is heated in a furnace until the metal is at a temperature of 800 C. It is then thoroughly stirred and the diaphragm pierced With a steel rod and the alloy allowed to flow into the mold.-

After cooling in the argon atmosphere the ingots are coated with oil and rolled to the desired form.

I have found that the lithium-magnesium alloys are resistant to attack by air, being protected by a superficial coating. These alloys have been kept for periods up to 6 months in air of 50% relative humidity and have been kept for an indefinite period of time in a dessicator without damage.

Since the lithium-magnesium alloys may be readily rolled primary cells may be formed from them in any of the known ways for making such cells from magnesium. For example, cells made using lithium-magnesium alloys as anode material and silver chloride on silver, as cathode and using sea water as electrolyte showed the following discharge voltages at 0.8 ampere per square inch. A magnesium-silver chloride cell according to the known art is included for comtrolyte.

Similar advantages in discharge voltage are shown against other depolarizers including copper sulphate, manganese dioxide, and silver peroxide.

Cells using the lithium-magnesium alloys of my invention may be activated with pure water since the lithium hydroxide formed is soluble and, therefore, provides a good conducting elec- In the appended claims the term water unless specified to be pure refers to natural waters such as sea water containing enough dissolved salts to make them electrolytes.

I have found the alloys of my invention particularly useful where very high drains and short come-up time are desirable. The alloys of my invention like magnesium acquire a coating on exposure to air, and this coating must be removed before the full voltage of the cell is obtained.

Therefore, when high drain and short come-up time is desired I use an electrolyte other than ordinary water. Dilute acid is highly effective. I have found, for example, that in a cell composed of a 60% magnesium-lithium alloy and silver chloride that the adding of a reserve electrolyte of 5% H2SO4 provides a voltage of 1.60 at 0.8 amperes per square inch and a come-up time of only a few hundredths of asecond.

,The examples of the applications of the electrode of this invention to primary cells are illustrative only. Other uses of the electrodes of this invention will be evident to those familiar with the art. The invention is accordingly not limited to the examples given but only by the appended claims.

What I claim is:

1. An electrode for electrical systems having an electrochemical potential within 0.8 v. as elec tropositive as lithium and a rate of attack by Water less than one-tenth that of lithium, said 4 electrode being formed of an alloy of magnesium and lithium containing 7 52-70% magnesium.

2. A primary cell consisting of an electrode of amagnesium-lithium alloy containing 5270% magnesium and a depolarizing electrode activated by pure Water. 7

3. A primary cell consisting of an electrode of a magnesium-lithium alloy containing 52-70%.

magnesium and a depolarizing electrode, activated by a dilute acid solution.

REGINALD S. DEAN.

REFERENCES CITED 'The following references are of record in the file of this patent:

UNITED STATES PATENTS

Claims (1)

1. AN ELECTRODE FOR ELECTRICAL SYSTEMS HAVING AN ELECTROCHEMICAL POTENTIAL WITHIN 0.8 V. AS ELECTROPOSITIVE AS LITHIUM AND A RATE OF ATTACK BY WATER LESS THAN ONE-TENTH THAT OF LITHIUM, SAID

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