US1966220A

US1966220A - Method of producing a photo-electric tube

Info

Publication number: US1966220A
Application number: US531048A
Authority: US
Inventors: Harvey C Rentschler
Original assignee: Westinghouse Lamp Co
Current assignee: Westinghouse Lamp Co
Priority date: 1929-02-28
Filing date: 1931-04-18
Publication date: 1934-07-10
Anticipated expiration: 1951-07-10
Also published as: FR690673A

Description

July 10, 1934. H. c. RENTSCHLER El" AL 1,966,220

METHOD PRODUCING A PHOTO ELECTRIC TUBE Original Fi led Feb. 28, 19 9 INVENTORS H. c. REA/7.50945? 11.5 HE/V ATTORN EY Fatented July 1Q, 1934;

NET? gTTE FTE FQE

METHOD OF PRODUCING A PHOTO-ELEC- ERIC TUBE Harvey C. Rentschler, East Orange, and Donald E. Henry, Bloomfield, N. 5., assignors to Westinghouse Lamp Gompany, a corporation of Pennsylvania Olaims.

This application is a division of application Serial Number 343,532 filed February 28, 1929 by the present applicants and assigned to thesame assignee as the present application.

5 The invention relates to a photo-electric tube of the type employing as the photo-sensitive material, an oxide or sub-oxide of an alkali metal, such as caesium.

One form of photo-electric tube to which my invention particularly relates comprises an envelope of glass containing a cathode or photosensitive electrode having a surface of silver, with a film of an oxide or sub-oxide of an alkali metal, such as caesium thereon. It has been found that when the surface of the cathode is provided with such a film of caesium-oxide or sub-oxide, the sensitivity of the tube to light in the red and yellow region of the spectrum is increased several fold. It is essential, however, in order to maintain the sensitivity of the tube in this region, that there be no free caesium or other alkali metal in the envelope.

The method which has been employed, heretofore, in producing photo-electric tubes of this material is briefly as follows:

The cathode, which may consist of a plate of silver or silver plated copper, is mounted in the envelope with an anode and after exhaustion of the envelope oxygen is admitted and a discharge created between the anode and cathode to oxidize the silver. The oxygen is then exhausted and the alkali metal introduced. The bulb and contents are then heated up to effect a reaction between a portion of the caesium and the silver oxide to form a film of caesium oxide or sub-oxide, on the cathode. The heating is continued for a sufficiently long period and temperature to vaporize the excess free caesium out of the bulb through the exhaust system. A Difiiculty has been experienced with this procedure due to the high temperature required to vaporize all the caesium out of the envelope. This must be done with great care and in view of this high temperature baking it is necessary to employ an all glass manifold on the pumping system.

The process is slow and tedious and not well suited for factory production, wherein it is desirable to employ the regular rubber exhaust connections. This heating may also break down some of the active caesium-sub-oxide and result in a tube of low sensitivity.

One of the objects of the present invention is to produce a simplified process of manufacturing a photo-electric tube of this nature.

Another object of the invention is to provide a novel means of removing free caesium from a photo-electric tube employing, as the light sensitive material, a compoundof caesium.

Other objects and advantages will hereinafter appear.

In accordance with the invention we provide within the envelope a getter substance which is inert or at least less active with respect to the alkali metal than is the oxidized silver surface of the cathode, at the reaction temperature of the silver oxide and alkali metal, but which reacts with the alkali metal at a slightly higher temperature to form solid, stable compounds thereof. The reaction temperature of the getter with the alkali metal should not be so high as to cause the m cathode to be heated to the dissociation temperature of the oxide or sub-oxide of the alkali metal when the getter is heated to such reaction temperature.

By the use of such a getter material the tube, after oxidation of the silver surface of the cathode, may be exhausted, the alkali metal generated, the gas filling, if any, introduced and the tube permanently sealed prior to the production of the film of the sub-oxide of the alkali metal. The film of alkali metal oxide or sub-oxide may be produced on the cathode by heating the Whole tube to a temperature at which the alkali metal reacts with the silver oxide. The excess free alkali metal may then be cleaned-up by heating the getter to 35 the reaction temperature thereof with such metal while the bulb and other contained parts are heated to a sufiicient temperature to prevent the alkali metal from depositing thereon.

The getter preferably consists of a quantity 90 of lead glass constituting a portion of the envelope although a compound may be employed either as a coating on some portion of the bulb or its contents, or in a suitable container or capsule. Other methods of introducing the getter will be apparent, a number of which are disclosed in the accompanying drawing.

Reference is had to the drawing for a more complete understanding of the invention.

Fig. 1 is an elevation of a tube embodying my invention, showing the envelope in section, in which a portion of the glass envelope constitutes the getter material.

Figs. 2, 3, 4 and 5 are fragmentary views of a 1% photoelectric tube showing modified methods of utilizing the getter material.

Referring to Fig. l, a photo-electric tube is shown comprising an envelope 6 having the upper or body portion 7 formed of lime glass or other glass not attacked by caesium vapor and a lower or neck portion 8 formed of lead glass.

The envelope contains a plate cathode 9 which in cross section may be of V-shape or semi-circular and which conveniently may consist of silver or silver plated copper. The cathode 9.is supported from the press 10 by

support wires

11 and 12, the latter of which is joined to a leadingin conductor 13. An anode, in the form of a wire 14, which may be of nickel, is positioned within the concavity of the cathode, and is supported above the press by

supports

15 and 16, the former of which is connected to a leading-in wire 17.

A capsule 18 is supported above the electrode assembly by a wire 19 welded to the upper end of the anode. The capsule contains a chemical mixture capable, when heated, of generating caesium vapor in the device.

A mixture which we prefer to employ in the capsule 18 consists of caesium-dichromate and silicon, the silicon serving as a reducing agent for the caesium-dichromate. A small proportion of a metal such as misch metal or aluminum may be added to the mixture to expedite the reaction and to decrease the reaction temperature.

The method of producing the tube is as follows: After the electrodes are sealed into the envelope, the tube is baked out and exhausted through the exhaust connection 20 in the usual manner. After the bulb has cooled it is filled with oxygen at a pressure of about 1.6 mm. and a direct current discharge is passed between the silver plated copper, as cathode and the wire anode, using about 800 to 1000 volts and a low current of about to 100 milliamperes. This discharge is continued until the proper degree of oxidation has been obtained, which may require only a very short time.

The preferred degree of oxidation is obtained when the plate color shows a green color, at least in spots. The oxygen is then pumped out and the capsule 18 heated by high frequency. induction current to generate the caesium metal in the tube, and if it is desired to employ a gaseous atmosphere in the tube,- argon or other gas is introduced at the proper pressure. The tube is then sealed off.

All of the above operations may be conducted on the usual tube exhaust system using rubber connections to the exhaust manifold. The bulb is next placed in an oven and heated to about 125 C. for about 5 minutes to cause a reaction between the caesium vapor and the oxidized silver, producing probably a sub-oxide of caesium. At this temperature there is no appreciable reaction between the caesium and the lead glass portion of the envelope so that all the caesium is available for forming the sub-oxide film on the cathode.

The excess caesium is then cleaned up by heating the lead glass portion in a second adjacent oven at about 350 to 400 C. at which temperature the caesium reacts with the lead oxide content of the lead glass, forming stable solid caesium compounds. During this treatment the lime glass portion of the tube is maintained at a temperature of about 125 C. to prevent condensation of the caesium in the lime glass portion of the tube and to drive it over to the lead glass portion. Higher heating of the lime glass portion should be avoided in order not to destroy or impair the caseium oxide or sub-oxide film on the cathode. This heating operation should be continued until the free caesium is entirely cleaned up but ordinarily 5 to 20 minutes will be sufficient.

The bulb is then thoroughly cooled and a reading taken to determine the photo sensitivity in the red and yellow portions of the spectrum. If the emission is below normal, the entire bulb may be again heated for about 3 minutes at 200 to 250 C. generally, the occasional tubes which do not have the normal photo-electric sensitivity after the first treatment will be greatly improved by this latter treatment.

It is absolutely essential to remove all the free caesium from the tube by this clean-up action, since small quantities of free caesium if left in the tube deposit on the cathode and destroy the sensitivity of the tube in the red and yellow region, and tends to cause electrical leakage between the leading-in wires.

After the tubes have been heat treated they may be seasoned under normal operating conditions for several hours in order to remove all traces of residual gases in the envelope other than the monatomic gases.

In Fig. 2 we have indicated the getter as consisting of a coating 21 applied to the interior of the neck portion of the bulb. In this case the entire bulb may be constructed of lime glass. A compound which may be used is lead oxide applied to the bulb before sealing in the mount.

In Fig. 3 the getter is shown as consisting of a ring of oxidized copper 22 supported on the stem tube 23 and capable of being heated by high frequency induction currents. With this construction the getter may be heated independently of the cathode so that the danger of reducing the caesium sub-oxide film during clean up of the excess caesium, is eliminated.

During heating of the getter ring 22 the bulb should be baked to a sufiicient temperature to vaporize the free caesium from all parts of the device. -In place of using an oxidized copper surface for the getter material suitable compounds capable of reacting with the caesium may be applied to the ring 22 and heated by induction.

We have shown, in Fig. 4, a getter capsule 24 suspended from one of the electrode supports in a position to be conveniently heated by high frequency induction currents. This capsule may contain a material such as copper oxide, or spongy lead oxide which when heated above the temperature required to form the caesium sub-oxide film on the cathode, cleans up the excess caesium.

Fig. 5 shows the getter material in the form of a coil 25 of oxidized copper, having its opposite ends connected to the cathode supports by

conductors

26 and 27. A separate leading-in

conductor

28 and 29 is provided for each of the cathode supports so that the coil 25 may be heated to the reaction temperature by passing electric current directly therethrough to prevent short circuiting of the coil through the cathode, one of the cathode supports is provided with an insulating head 26' intermediate the press and the cathode. Any suitable getter material may also be supported within the coil 25 as to be heated thereby.

In employing the various forms of getters illustrated the caesium sub-oxide film is first produced on the cathode and the getter then activated to clean up the excess caesium under such conditions that the caesium sub-oxide film is not decomposed.

It is obvious that changes may be made in the embodiments described without departing from the invention and we desire to include all such changes within the scope of the invention.

What is claimed is:

1. The steps in the method of producing a light sensitive device having a film 01' an oxide of an alkali metal on a metallic cathode, comprising oxidizing the surface of the cathode, introducing an alkali metal into the envelope, heating the oathode to effect a reaction between said alkali metal and the oxidized cathode and cleaning up all of the excess free alkali metal by chemical action at a temperature above that necessary to cause said reaction between the alkali metal and the oxidized cathode.

2. The steps in the method of producing alight sensitive device having an oxide of an alkali metal on a metallic cathode, comprising oxidizing the surface of the cathode, introducing caesium metal into the envelope, heating the cathode to the reaction temperature of the alkali metal with the metallic oxide and cleaning up all of the excess free caesium with lead oxide.

3. The steps in the method of producing a light sensitive device having a film of caesium suboxide on a metallic cathode, comprising forming the envelope in part only of lead glass, oxidizing the surface of the cathode, introducing caesium into the envelope, heating the envelope to a temperature sufliciently high to cause a reaction between the caesium and the oxidized cathode, and then increasing the temperature of the lead glass portion of the envelope to the reaction temperature of the caesium with the lead glass while maintaining the remainder of the envelope at a lower temperature.

4. The steps in the method of producing a photo-electric tube having a film of caesium suboxide on a metallic cathode, comprising forming the envelope in part only of lead, glass, oxidizing the surface of the cathode, producing caesium in the envelope, heating the envelope to about 125 C. to cause a reaction between the caesium and the oxidized cathode and then heating lead glass portion only of the envelope to about 350 to 400 C. to cause a reaction between the excess caesium and the lead glass, while maintaining the remainder of the envelope at about 125 C.

5. The steps in the method of producing a photo-electric tube having a film of an alkali metal compound on a metallic cathode comprising oxidizing the surface of said cathode, generating an alkali metal in the envelope, heating the cathode to effect a reaction between the alkali metal and the oxidized cathode and subsequently activating a getter while maintaining the envelope at an elevated temperature and by chemical action cleaning up all of the excess alkali metal.

6. The steps in the method of producing a photo-electric tube having a film of caesium suboxide on a metallic cathode, comprising forming the envelope in part only of lead glass, oxidizing the surface of the cathode, introducing a quantity of caesium therein, heating-the envelope to about 125 C. for about five minutes to cause a reaction between the caesium and the oxidized cathode to iform a film of caesium sub-oxide on the cathode, and subsequently heating the lead glass portion of the envelope at about 350 to 400 C. for 5 to 20 minutes to clean-up the excess free caesium, while maintaining the remainder of the envelope at a temperature of about 125 C.

and rendering excess alkali metal therein ineffec- 7. The steps in the method of producing a lightsensitive device including an enclosing envelope,

which comprise forming a deposit of a lightsensitive material in said envelope and by chemical action rendering ineffective the excess photosensitive material contained therein.

8. The steps in the method of producing a lightsensitive device including a container, which comprise depositing a layer of an alkali metal therein tive by chemical action.

9. The steps in the method of producing a lightsensitive device including a container, which comprise depositing a layer of an alkali metal therein and rendering ineifective excess alkali metal therein by a chemical action between said excess alkali metal and another substance having a component thereof whose temperature of vaporization is greater than that of said alkali metal.

10. The steps in the method of producing a light-sensitive device including a container, which comprise depositing a layer of alkali metal on an oxidized surface located in said container, oxidizingsaid alkali metal and reacting excess free metal with a metal oxide to render said free excess alkali metal ineffective.

11. The steps in the method of producing a light-sensitive device including a container which comprise depositing a layer of caesium therein by reducing a non-hygroscopic compound of caesium therein and rendering excess caesium ineffective by chemical action.

12. The steps in the method of producing a light-sensitive device including a container which comprise depositing a layer of caesium therein by flashing an admixture of caesium dichromate and silicon to liberate caesium and by chemical action rendering ineffective excess free caesium contained therein.

13. The steps in the method of producing a light-sensitive device, including a container which comprise depositing a layer of caesium onto an oxidized surface, converting the caesium to a sub-oxide and rendering ineffective the excess free caesium by chemical action between the same and a compound that is stable at the temperature of said sub-oxide formation.

14. The steps in the method of producing a light-sensitive device including a metallic base layer, comprising oxidizing the surface of the base, introducing an alkali metal into the envelope, heating the base to effect a reaction between said alkali metal and the oxidized base, and cleaning up the excess free caesium by chemical action.

1 5. The steps in the method of producing a light-sensitive device, including an oxide of an alkali metal on a metallic cathode, comprising oxidizing the surface of the cathode, introducing 185 an alkali metal into the envelope, heating the cathode to the reaction temperature of the alkali metal with the metallic oxide and cleaning up the excess free caesium with lead oxide.

HARVEY C. RENTSCHLER. DONALD E. HENRY.