US2533387A - Method and apparatus for making dynodes - Google Patents

Description

' Dec. 12, 1950 w. S. MLEAN METHOD AND APPARATUS FOR MAKING DYNODES Filed Nov. 16, 1948 W/ZL/AM f. MC LEA-N INVENTOR.

/4 T TOP/V5 Y Patented Dec. 12, 1950 METHOD AND APPARA'EUS FOR MAKING DYNODES William S. McLean, Woodbury, N. J., assignor to National Union Radio Corporation, Orange, N. 3., a corporation of Delaware Application November 16, 1948, Serial No. 60,333

5 Claims.

This invention relates to electron emitters, and more particularly it relates to methods of preparing emitters of the secondary electronemissive. type such as dynodes and the like.

A principal object of the invention is to provide a simplified method. of producing secondary electron emitters or dynodes.

Another object is to provide a method of producing dynodes whereby they can be manufactured in large quantities with a high degree of uniformity in their secondary electron-emissive powers during their useful life. I A feature of the invention relates to a secondary electron emitter or dynode, comprising a base of oxygen free' copper having a thin layer comprised of barium and magnesium oxides.

Another feature relates to a method of preparing dynodes so as to produce a secondary emission ratio ranging uniformly between certain values, for example 4 to 6, and wherein the completed dynode is capable, of withstanding high heat dissipations without affecting the secondary emission uniformity during its useful life.

A still further feature relates to the novel organization, and succession of apparatus and method steps which cooperate to provide an improved secondary electron emitter or dynode.

Other features and advantages not particularly enumerated, will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawing,

Fig. 1 is an elevational view, partly in section, of a preferred organization of apparatus used in practicing the invention.

Fig. 2 is a sectional View of Fig. 1, taken along the line 22 thereof and viewed in the direction of the arrows.

The dynode prepared according to this invention may be of any desired shape and size, and consists of a base or backing of oxygen-free copper having a coating of barium and magnesium oxides deposited thereon, also in accordance with the invention. Thus, a copper member in the form of a strip or sheet of the desired shape and size, is first polished on the side or sides intended to receive the secondary-emissive ma terials. Any well-known mechanical polishing process may be used if the surface is initially rough, and any well-known polishing material such as that sold under the trade-name Tripoli may be used, in conjunction with a hard bufiing wheel. When the initial roughness has thus been removed, the surface is finished 2 with jewelers rouge in conjunction with a soft cotton polishing wheel. If the initial surface not too rough, it may be necessary only to polish it with the jewelers rouge and the soft bufiing wheel.

The polished copper base or backing is then degreased by means of trichlorethylene or similar degreasing agent, care being taken that during this stage of the process, contamination of the polished surface is avoided. The polished and degreased member is then fired in a reducing atmosphere, for example, in a hydrogen furnace of any well-known construction, at a temperature of approximately 600 C. for approximately one-half hour.

' The next step is to mount the member within a bulb which can be subjected to evacuation. For example, as shown in Figs. 1 and 2, the memeber which has been polished and degreased and subjected to the hydrogen firing, is attached by any well-known means to a Wire or other support 2 which is anchored or sealed in the press 3 of any well-known form of a glass bulb 4 of any suitable shape. The press 3 in the conventional way, is sealed to the glass bulb 4 and is provided with the usual exhaust tubulation 5 by means of which the interior of the bulb can be evacuated. Also mounted on the press 3 is a bafile plate 6 which may be manufactured of carbonized nickel, and having slightly-bent edge portions 1, 8, which act as directors of the flashed material so as to confine it substantially to the surface of dynode I facing the baffie. Attached centrally to the bafile 6 is a wire loop 9 which is formed of a barium-bearing material which when vaporized or flashed, releases barium vapor in the well-known manner. Preferably, the loop 9 is formed of Type 66I3 barium getter, manufactured by Kemet Laboratories, Ltd, Cleveland, Ohio, and identified under the trade-name Kemet Kic Getter. If desired, the U-shaped portion of the loop may be made out of carbonized nickel wire, and the barium wire may be in the form of a straight length i0 which is suitably welded to the lateral arms of the U-shaped frame. In any event, the barium-bearing getter is formed as part of a complete inductive loop which can be raised to a flashing temperature by a suitable high frequency induction coil, the amount of heat generated in the getter loop being determined by the orientation of the high frequency magnetic field with respect to the loop. Also attached to the bafile 6 is a metal flag H inclined towards the dynode, asshown in Fig. 1. Suitably attached .mately one-half hour.

3 to the forward end of the flag H is a quantity of another material l2 which is of a type which releases magnesium vapor when flashed. The material i2 can be flashed independently of the material it by proper orientation and location.

of suitable high frequency induction heating field produced for example by the bombarding coil 63 which can be brought into relatively close proximity with the member H to heat the material I2 to flashing temperature without affecting the loop 9. When it is desired to flash the material in loop 9, another coil M can be positioned so as to control the amount of heat generated in the said loop to control the degree of flashing of the getter material therefrom. It will be understood, of course, that the man ner of selectively and independently flashing the two materials is merely illustrative, and any other well-known manner of timing and independently flashing the materials may be employed. After the various parts have been mounted within the bulb 4 as abovedescribed, the bulb is evacuated and baked-out at a tem perature of approximately 300 C. for approxi- The coil It, such as is conventionally used in radio tube manufacture, issupplied with high frequency heating current, so as to' heat the member I by high frequency inductive heating to a relatively high temperature, for example 850 C. to 875 C. at which it is-"outgassed. As a result of this heating, the member I is thoroughly degassed, and this bombarding process may be repeated several times until the degassing is found to be complete. The

heat developed during this .outgassing is con trolled so that it does not flash either of the materials to be subsequently flashed. Thereafter, the members 9 and i i are also subjected to high frequency heating but to a temperature merely sufficient to degas them without actually raising-th'em to a temperature suflicient to flash either of them.

When all the parts within the bulb 4 have been thus degassed or bombarded, the bulb and its contents are allowed to'cool for approximately ten minutes. Thereafter, the loop 9 is lightly flashed, that is to say, it is subjected to heating for a relatively short period of time just sulficient to vaporize a relatively small portion of the barium therefrom. After the light or partial flashing of the material from loop 9, the getter material i2 is heavily flashed, that is to say, it is heated. rapidly to a very high temperature at which substantially all of the magnesium therein is vaporized and flashed. During the above-described flashing operations, the member t is unheated and therefore the flashed barium and magnesium metals condense or deposit on the member i. By reason of the relatively concave arrangement of the member I and the concave arrangement of the baffle 5, the flashed material is substantially confined to the surface of member I facing the ba-file, and very little getter material is deposited on the opposite surface of the said member After the heavy flashing of the material It, the material in loop is again flashed, this time heavily, or to a high" temperature, so that substantially all the barium is vaporized and deposited on to the member I. After the flashing and deposition of the magnesium and barium on the member I, the parts are allowed to cool. In effect, therefore, the dynode is coated with a thin secondary electronemissive layer comprising a thin under-stratum bombarding operations.

of barium, an intermediate-stratum containing magnesium, and an over-stratum of barium.

The member i which is not yet oxidized is kept within an evacuated bulb 1 until ready to be used in its final device. If desired, the tubulation 5 can be sealed-off after the flashing is complete. When the dynode member thus prepared is ready for assembly into its final device or tube structure, the bulb 4 is broken, and the dynode l is removed therefrom taking care that its surface be not contaminated by handling. It is then assembled in its proper position in the final device or tube. In any event, it is found that the best results are obtained when the above-mentioned step of firing the backing member I, and the flashing operations above described, are not too far apart in time, preferably within twenty-four hours of each other, and the dynode which is not yet oxidized should be kept in the sealed evacuated bulb until ready for use. After the prepared dynode has been removed from bulb 4, it should not be exposed to air longer than six hours. However during this exposure, the outer barium and some o'f'the magnesium are oxidized to produce the desired barium and magnesium oxides. While the manner in which the magnesium is oxidized, at least in part, is not fully understood, it is believed that during the deposition of the flashed barium thereon, some of the magnesium diffuses into the surface portion of the barium.

When the dynode has been assembled in a finished secondary emission tube,,care should be taken'not to overheat the surface of thedyn'odo when the secondary emission tube is being subiected to the conventional heat treatment or Preferably, the finished electron tube with its dynode is subjected tothc usual aging operation, and it has been found that during this operation the surface of dynode must not be overloaded to an extent exceeding .1 watt per square centimeter during the first ten hours of operation.

It has been found that dynodes prepared according to the foregoing process are capable of producing values of secondary emission ratio ranging uniformly from 4 to 6, and the finished dynode surface has been found to withstand heat dissipations of .5 watt per square centimeter for periods of 500 hours or better without sub stantial change of the uniformity of its secondary emission powers.

While certain specific embodiments have been described herein, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A secondary emission dynode-forming member consisting of a backing member of oxygenfree copper having a thin coating of secondary electron-emission material said coating comprising an underlayer of barium, an intermediate layer containing magnesium, and an overlayer of barium.

2..A. dynode-forming member according to claim 1, in which the said underlayer of barium is substantially thinner than the said outer layer of barium.

.3. The method of coating a dynode with sec ondary electron-emissive material which come prises mounting the dynode in an evacuated receptacle in spaced relation to a barium-bearing material and a separate magnesium-bearing material, first flashing the barium-bearing mavaporizable materials whose oxides are efilcient secondary emitters, partially flashing one of the materials, fully flashing the other material, and

then fully flashing the first material.

5. The method of manufacturing a secondary emission dynode, which comprises mounting a metal support backing in an evacuated receptacle in spaced relation to a barium-bearing material and to a separate magnesium-bearing material, first flashing the barium-bearing material lightly to deposit a relatively thin coat on" the surface of said backing, then flashing the magnesium-bearing material heavily to deposit a relatively thick coat of magnesium over the said thin barium coat, then flashing the bariumbearing material heavily to deposit over the magnesium coat a coat of barium which is much thicker than the first-mentioned barium coat, and then subjecting the coated dynode to an oxidizing atmosphere to convert the exposed barium coat and at least part of the magnesium coat to their respective oxides.

' WILLIAM S. McLEAN.

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

UNITED STATES PATENTS Number Name Date 2,178,232 Hickok Oct. 31, 1939 2,178,233 Klatzow Oct. 31, 1939 2,293,177 Skellett Aug. 18, 1942 2,297,467 Gorlich Sept. 29, 1942 2,422,427 Louden June 17, 194'!

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