US3366562A - Method of conducting electrolysis in a solid ionic conductor using an electron beam - Google Patents

Description

United States Patent 3,366,562 METHOD OF CONDUCTING ELECTROLYSIS IN A SOLiD IONEC CONDUCTOR USlNG AN ELEC. TRON BEAM Abner Brenner, Chevy Chase, Md, assignor to the United States of America as represented by the Secretary of Commerce Filed Apr. 29, 1965, Ser. No. 452,034- 3 Claims. (Cl. 204-164) This invention relates to electrolysis, and more particularly to the electrolysis of solid electrolytes by means of a beam of electrons.

It is well known that the electrons emitted by the tungsten filament of an ordinary incandescent lamp may be used to deposit metallic sodium in the soda glass envelope of the lamp. In the typical demonstration of this effect, the lamp envelope is partially immersed in a molten sodium nitrate bath, the filament is energized, and an electronaccelerating voltage is applied between the filament and molten bath. With a short time, a deposit of metallic sodium forms on the interior surface of the envelope. The accepted explanation for the deposit is that the sodium ions in the molten bath migrate through the heated glass envelope, receive an accelerated electron, and deposit out as sodium atoms.

The above-described process has found limited application, primarily in the preparation of photoelectric tubes and the like. One of the principal reasons for this limited application is that the process is restricted to the deposition of metals on the interior surfaces of glass envelopes that are capable of being fitted with filaments, evacuated, and immersed in molten salt baths, The restriction on the shape of the glass member is especially severe, and precludes many desirable applications.

Accordingly, an object of this invention is to provide an electron-beam electrolysis which is not restricted to envelope-shaped glass members.

Another object is to provide an electron-beam electrolysis which does not require the use of the molten salt bath of the prior art.

Another object is to provide an electron-beam apparatus and method for electrolyzing any material which at a predetermined elevated temperature is a substantially solid electrolytic conductor.

A further object is to provide an electron-beam apparatus and method for depositing metal coatings on selected surfaces of shaped bodies of glass, ceramic, solid salt or the like.

A still further object is to provide an electron-beam apparatus and method for obtaining metals of high purity.

These and other objects of the present invention are achieved by forming a small body of a material which at a predetermined elevated temperature is a substantially solid electrolytic conductor. The body is electrically connected to a metallic anode, and the body and anode are positioned adjacent to an electron-emissive cathode. The space surrounding the cathode, body, and anode is evacuated to permit the flow of electrons from the cathode to the body, and an electron-accelerating potential is connected between the cathode and anode. The body is heated to the predetermined temperature at which it is a substantially solid electrolyte, whereby the impinging electrons neutralize the mobile ions thereof, converting them into atoms. The vacuum, temperature and accelerating potential are maintained until the body is electrolyzed to the desired degree. In this manner the electrolysis of the body is precisely controlled, enabling one to modify the body as desired.

The invention will be further described with reference to the accompanying drawing, in which the sole figure is 3,366,562 Patented Jan. 30, 1968 Zoe an elevation view, sectioned in part, of an apparatus embodying the principles of the present invention.

In the figure, the reference numeral M denotes an elongated cylindrical vacuum chamber consisting of separable upper and lower portions 11 and 12, respectively. The portions 11 and 12 preferably are constructed of glass or other transparent material, and are provided with circular ground-glass flanges l3 and 14, respectively. The upper portion 11 has a pair of short, integrally-formed tubes 15, 16 extending vertically upwardly therefrom, and an integrally-formed horizontal arm 17 that connects the vacuum chamber 10 to a vacuum diffusion pump 18. Extending vertically downwardly from the lower portion 12 of the vacuum chamber 10 is a single integrally-formed short tube 19.

The tubes 15 and 16 are fitted with conventional feedthrough vacuum seals 20 and 21 which slidably carry a pair of rods 22, 23 of copper or other highly-conductive metal. The rods 22, 23 extend into the lower portion of 12 of the vacuum chamber 10 and electrically connect to an electron-emissive cathode 24. The cathode 24 advantageously consists of a helical coil of wire 25 the ends of which are screwed, clamped, or otherwise fastened to the rods 22, 23. The wire 25 preferably comprises a material suitable for providing incandescent filaments, such as tungsten, thoriated tungsten or the like.

The rods 22, 23 at their upper ends are connected by conductors 26 to an adjustable electrical current source 27 capable of supplying suflicient current to heat the coil 25 to incandescence. The current supplied by source 27 may be either direct or alternating current.

The tube 19 extending downwardly from the vacuum chamber 10 is provided with a conventional feed-through vacuum seal 28 that slidably supports an electricallyinsulative tube 29. A wire 36 extends through the tube 29 and is connected, as by brazing, to the underside of a flat, horizontal, metallic anode 31. Thermally disposed against the anode 3]. is an electrical temperature sensor 32 such as thermocouple, thermistor, or the like. A pair of insulated conductors 33 extend from the temperature sensor 32 through the insulative tube 29 to an associated electrical temperature indicating device 34!. The conductors 33 are retained in the tube 29 by any convenient means, for example, by friction or by a high temperature cement.

The tube 29 preferably is ceramic, and the anode 31 preferably is platinum or other metal capable of fusion to the ceramic tube 2%. The top of tube 29 is fused to the underside of the anode 31 so as to maintain a vacuum in chamber 10.

The anode 31 is electrically connected to the underside of a small body 35 of material to be electrolyzed. The body 35 covers the top surface of the anode 31 and preferably extends down the vertical sides of the anode, so as to prevent the electrons emitted by cathode 24 from directly contacting the anode. The body 35 may be formed in any convenient manner, as by cutting, molding, or the like, from any of the well-known materials such as glasses, ceramics, salts and the like, which at predeterminable elevated temperatures conduct electrolytically (ionically) and yet remain substantially solid. The determination of suitable materials and their solid-conduction temperatures may readily be effected by those skilled in the art.

A particularly convenient method of shaping the body 35 and connecting it to the anode 31 comprises melting the material of the body 35 and casting the material about the anode 31, whereby the material makes good electrical contact with the anode 31 along the top and side surfaces thereof, as illustrated in the figure.

An adjustable high voltage source 37 and milliammeter 38 are connected in series between one of the rods 22, 23, for example, rod 22 and the wire 30 attached to the anode 31. The voltage source 37 may be direct-current, in which case the anode wire 30 should be connected to the positive lead of the source. Alternatively, the voltage source 37 may be alternating-current, since the cathode 24 and anode 31 are inherently rectifying. In either case, the voltage of the source 37 should be adjustable from several hundred to several thousand volts, preferably about 100-3000 volts.

To raise the body 35 to its predetermined solid-conduction temperature, the lower portion 12 of the vacuum chamber 10 is Wound with a suitable heating coil 41 comprising an induction coil, resistance coil, or the like. An adjustable current source 42 is connected to the coil 41 to energize the coil.

. Inthe operation of the apparatus shown in the figure, the vacuum chamber 10 initially is separated into the upper and lower portions 11, 12. The anode 31 is removed from the lower portion 12 by disconnecting the Wires 30 and 33 from their associated elements 38 and 34, respectively, and withdrawing the ceramic tube 29 upwardly from the feed-through vacuum seal 28. The body 35 is then firmly attached to the anode 31, and the ceramic tube 29 is replaced in the seal 28. The upper and lower portions 11 and 12 are mated at the flanges 13, 14, and the spacing between the top of the body 35 and the coil 25 is adjusted to about 1-10 cms. and preferably about 2-5 cms. by manually moving the ceramic tube 29 in its seal 28, and/or the rods 22, 23 in their seals 21, 22. The vacuum pump 13 is turned on and operated until the vacuum in chamber 10 is about 10- -10- torr, as indicated on a suitable vacuum gauge 43 connected to the chamber 10. The adjustable current source 27 is connected to the rods 22, 23 via the leads 26, and the source 27 is turned on and adjusted until the coil 25 is brightly incandescent. In many instances the heat produced by the coil 25 is sufiicient to raise the body 35 to its predetermined solid-conduction temperature, as measured by the sensor 32 and indicating device 34. If the indicated temperature approximately equals the predetermined temperature, the high voltage source 37 and milliammeter 38 are connected between the rod 22 and the anode Wire 30. The source 37 is turned on and adjusted to produce an electrolysis current of about 1-100 milliamperes, preferably about -50 milliamperes, depending on the area of the body 35 being electrolyzed, and the electron-emitting properties of the coil 25. If the indicated temperature of body 35 due to the heat of the cathode coil 25 does not approximate the solid-conduction temperature of the body, the heating coil 41 is connected to its source 42, which is then turned on and adjusted to supply sufficient heat to the body 35 to raise it to the solid-conduction temperature.

The vacuum in the chamber 10 is maintained at about 10- --10 torr during the electrolysis, while the temperature of the body 35 is maintained at the solid-conduction temperature, by adjusting the heating source 42 if necessary. The entire chamber 10 preferably is air-cooled by means of a fan or the like 45 to dissipate any excessive heat and protect the glass of chamber 10. The cathode coil 25 is maintained at a bright incandescence, and the electrolysis current is maintained at about 10-50 milliamperes by adjusting the high voltage source 37 as required. As the electrolysis proceeds, a metal film forms on the top surface of the body 35, if the material of the body is a glass, ceramic, salt or the like. It is believed that the metal forms from the combination of electrons, that are boiled from the cathode coil 25 and accelerated by the high voltage of source 37 to the body 35, and the mobile metal ions in the body 35 that is at its solidconduction temperature. An electrode reaction also occurs at the interface between the body 35 and anode 31, as evidenced by a corrosion of the body 35 in this region. If gases are produced they are withdrawn from the chamber 10 by the vacuum pump 18, and may be recovered thereat by any of the means well known in the art.

The present invention contemplates the formation of thin uniform layers of metals on the top surface of the body 35, to provide metallic coatings on ceramic, glass, or other nonmetallic bodies. It is further contemplated that the shape of the coating may be controlled by sweeping the electron beam projected from the cathode coil 25 to the anode 31. The electrostatic and electromagnetic means for accomplishing such sweeping are well known in the art and may readily be applied to the present invention by those skilled in the art.

Since the present invention enables one to electrolyze solid" materials into metals without contacting the metal with an electrode, the invention may provide a method of obtaining metals, especially the rare earth metals, in a high purity state. It is contemplated, in this connection, that means he provided to continually scrape the deposited metal from the body, so as to enable the electron beam to continually see the body being electrolyzed.

In using the apparatus illustrated in the drawing and following the procedure described above: (1) a small solid body of silver chloride was electrolyzed and a coating of silver on the body was obtained; (2) a small solid body of nickel chloride dissolved in potassium chloride was electrolyzed and a coating of nickel on the body was obtained; and (3) a small solid body of zirconium oxide was electrolyzed and a coating of zirconium on the body was obtained.

While the present invention has been described by way of specific illustrative embodiments, it will readily be apparent to those skilled in the art that many modifications and variations may be effected within the scope and spirit of the invention. Accordingly it is intended that the invention cover all such modifications and variations as fall within the meaning of the appended claims.

What is claimed is:

1. The method of electrolyzing a solid material which at a predetermined elevated temperature is a substantially solid ionically conductive material, comprising the steps of:

(a) electrically connecting a small body of said material to a metallic anode,

(b) positioning said body and anode from about 2-5 centimeters from an electron-eniissive cathode,

(c) evacuating the space surrounding said cathode, body and anode to a pressure of about 10- -10- torr,

(d) heating said body to said predetermined temperature,

(e) applying an electron-accelerating potential between said cathode and anode, and

(f) maintaining said vacuum, predetermined temperature, and potential until said body is electrolyzed to a desired degree.

2. The method set forth in claim 1, wherein said solid material is a member of the class consisting of glass, ceramic, and salt.

3. The method set forth in claim 1, wherein said electron-accelerating potential is about -3000 volts.

References Cited UNITED STATES PATENTS 3,267,015 8/1966 Morley 204l92 3,305,473 2/1967 Moseson 204298 3,329,601 7/1967 Mattox 204-192 3,336,211 8/1967 Mayer 204192 HOWARD S. WILLIAMS, Primary Examiner.

ROBERT K. MIHALEK, Examiner.

Claims (1)

1. THE METHOD OF ELECTROLYZING A SOLID MATERIAL WHICH AT A PREDETERMINED ELEVATED TEMPERATURE IS A SUBSTANTIALLY SOLID IONICALLY CONDUCTIVE MATERIAL, COMPRISING THE STEPS OF: (A) ELECTRICALLY CONNECTING A SMALL BODY OF SAID MATERIAL TO A METALLIC ANODE, (B) POSITIONING SAID BODY AND ANODE FROM ABOUT 2-5 CENTIMETERS FROM AN ELECTRON-EMISSIVE CATHODE, (C) EVACUATING THE SPACE SURROUNDING SAID CATHODE, BODY AND ANODE TO A PRESSURE OF ABOUT 10-4-10-5 TORR, (D) HEATING SAID BODY TO SAID PREDETERMINED TEMPERATURE, (E) APPLYING AN ELECTRON-ACCELERATING POTENTIAL BETWEEN SAID CATHODE AND ANODE, AND (F) MAINTAINING SAID VACUUM, PREDETERMINED TEMPERATURE, AND POTENTIAL UNTIL SAID BODY IS ELECTROLYZED TO A DESIRED DEGREE.