US3479551A - Electron emitting cathodes having a flexible graphite filament with an emissive coating thereon - Google Patents
Electron emitting cathodes having a flexible graphite filament with an emissive coating thereon Download PDFInfo
- Publication number
- US3479551A US3479551A US670263A US3479551DA US3479551A US 3479551 A US3479551 A US 3479551A US 670263 A US670263 A US 670263A US 3479551D A US3479551D A US 3479551DA US 3479551 A US3479551 A US 3479551A
- Authority
- US
- United States
- Prior art keywords
- cord
- electron emitting
- filament
- flexible graphite
- coating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title description 15
- 238000000576 coating method Methods 0.000 title description 11
- 239000011248 coating agent Substances 0.000 title description 10
- 229910002804 graphite Inorganic materials 0.000 title description 8
- 239000010439 graphite Substances 0.000 title description 8
- 229910052746 lanthanum Inorganic materials 0.000 description 8
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 8
- 229910052799 carbon Inorganic materials 0.000 description 7
- 239000000463 material Substances 0.000 description 6
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 description 4
- 239000002002 slurry Substances 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 3
- 229910052721 tungsten Inorganic materials 0.000 description 3
- 239000010937 tungsten Substances 0.000 description 3
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 238000010422 painting Methods 0.000 description 2
- 239000003870 refractory metal Substances 0.000 description 2
- 229910052715 tantalum Inorganic materials 0.000 description 2
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229920000049 Carbon (fiber) Polymers 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- 229940072049 amyl acetate Drugs 0.000 description 1
- PGMYKACGEOXYJE-UHFFFAOYSA-N anhydrous amyl acetate Natural products CCCCCOC(C)=O PGMYKACGEOXYJE-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000010410 dusting Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- MNWFXJYAOYHMED-UHFFFAOYSA-M heptanoate Chemical compound CCCCCCC([O-])=O MNWFXJYAOYHMED-UHFFFAOYSA-M 0.000 description 1
- 238000012994 industrial processing Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 235000012054 meals Nutrition 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
- 239000001117 sulphuric acid Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- HHIQWSQEUZDONT-UHFFFAOYSA-N tungsten Chemical compound [W].[W].[W] HHIQWSQEUZDONT-UHFFFAOYSA-N 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/13—Solid thermionic cathodes
- H01J1/15—Cathodes heated directly by an electric current
Definitions
- An electron emitting cathode comprises a flexible graphite filament having a coating of a material which emits electrons when heated.
- the filament may be tubular and loosely supported on a metal core wire.
- This invention relates to electron emitting cathodes for electron guns and is particularly concerned with elongated emitting cathodes suitable for use in electron irradiation machines.
- an electron gun In an electron irradiation machine intended for industrial processing, it is most desirable to use an electron gun with an elongated emitting cathode since it is then possible to dispense with magnetic scanning as a means of spreading the electron beam over the material being processed.
- emitters have in the past been constructed from refractory metals such as tungsten or tantalum. These metals can be used pure or in a treated state such as thoriated tungsten or tantalum coated with lanthanum boride to provide a low work function emitting film, but many practical difliculties have arisen in attempting to provide a stable lanthanum boride coating on such materials.
- An object of the present invention is to provide a new and improved form of electron emitting cathode particularly suitable for use with electron irradiation machines.
- an electron emitting cathode comprises a flexible graphite or carbon filament having a coating of a material which emits electrons when heated.
- the filament comprises a plaitcd or woven graphite cord of low mass/unit length.
- the plaited or woven cord is tubular and mountable on a wire such that an electron emitting cathode may comprise a central core of refractory metal and a loose fitting graphite or carbon sleeve surrounding said core.
- the croe is formed of tungsten or tantalum wire, and the sleeve is provided with a coating of a material which emits electrons when heated.
- the sleeve may be provided with a coating of lanthanum boride.
- the graphite or carbon sleeve materials are available commercially in the form of tubular plaitcd cords of 1 mm. and 2 mm outside diameters.
- the electrical resistance of the carbon cord is 1.5-2.5 ohms/cm. and for the graphite 0.5-2 ohms/cm. Weights for 2 mm. diameter cords are approximately 1.4 grams/ metre.
- tubular sleeve 1 is loosely mounted on a core wire 2 and the ends 3 of the sleeve are copper plated to provide suitable end connections to the filament electrical supply leads 4.
- the ends of the core wire are held in conventional clamps and connected via leads 6 to an electrical supply to provide a core heating current.
- the core wire may be tensioned by using a simple spring mounting 7 or the core wire and sleeve may be supported magnetically in a manner substantially as described in our co -pending British patent application 35,474/ 66 which describes means of providing a magnetic field transverse to the axis of an emitter cathode such that the interaction between the field and the emitter cathode, when carrying its operating current, supports the weight of the emitter cathode along its length.
- One method of coating the graphite or carbon sleeve comprises applying a slurry, formed from lanthanum oxide, boron and carbon in water, to the cord, drying the cord in air, placing the cord in a vacuum vessel and outgrassing using external heaters and subsequently raising the temperautre of the sleeve to 1700 C. for a few seconds by passing an electrical current through the wire core.
- the slurry may be prepared by grinding together lanthanum oxide, boron and carbon in the proportions 923:1 by weight and adding distilled water.
- the core wire and sleeve is supported in a filament holder and brush coated with a prepared slurry.
- the sleeve is allowed to dry in air and the assembly subsequenlty placed within a vacuum enclosure.
- the enclosure is pumped down to a hard vacuum, i.e. 10 torr approximately, and the cord outgassed for several hours using an external heating source.
- Formation of an emitter coating is achieved by passing an electrical current through the core wire to raise the temperature to approximaetly 1700 C. for a few seconds, whereby a small amount of lanthanum boride is formed on the surface layer of the sleeve.
- the sleeve is allowed to cool before application of a high tension voltage to the filament assembly and the filament is preferably operated at -a temperature 1000-1100 C.
- Other coating methods may include (a) Painting the cord with a slurry of lanthanum boride in amylacetate.
- the cord may be used without a central core wire, for example the coated cord may be formed as an elongated electron emitting cathode by taking a suitable length of cord and copper plating each end to provide electrical connection points or alternatively the cord may be left unplated and the ends clamped between suitable soft meal members.
- the cathode may be tensioned by using a simple spring mounting since the weight of a coated graphite cord 2 mm. dia. approaches 1 /2 ozs. per ft. length and the cathodes vary from a few inches in length to about 10 feet.
- An electron emitting cathode comprising a flexible carbonaceous filament having a coating of a mtaerial which emits electrons when heated.
Landscapes
- Solid Thermionic Cathode (AREA)
Description
ELECTRON EMITTING GATHODES HAVING A FLEXIBLEGRAPHITE FILAMENT WITH AILEMISSIVE COATING THEREON Filed Sept. 25, 1967 United States Patent US. Cl. 313334 4 Claims ABSTRACT OF THE DISCLOSURE An electron emitting cathode comprises a flexible graphite filament having a coating of a material which emits electrons when heated. The filament may be tubular and loosely supported on a metal core wire.
This invention relates to electron emitting cathodes for electron guns and is particularly concerned with elongated emitting cathodes suitable for use in electron irradiation machines.
In an electron irradiation machine intended for industrial processing, it is most desirable to use an electron gun with an elongated emitting cathode since it is then possible to dispense with magnetic scanning as a means of spreading the electron beam over the material being processed.
' Elongated emitting cathodes, generally referred to as emitters, have in the past been constructed from refractory metals such as tungsten or tantalum. These metals can be used pure or in a treated state such as thoriated tungsten or tantalum coated with lanthanum boride to provide a low work function emitting film, but many practical difliculties have arisen in attempting to provide a stable lanthanum boride coating on such materials.
Additionally, such metals are heavy and tend to be brittle after heating in vacuum. In consequence, if emitting filaments more than a few inches long are to be constructed, supporting and tensioning devices for the filament are included every few inches. Various suspension systems have been suggested to overcome the problems but the brittle nature of a thin filament, particularly when cold, remains as a limiting factor in filament life.
An object of the present invention is to provide a new and improved form of electron emitting cathode particularly suitable for use with electron irradiation machines.
According to the invention an electron emitting cathode comprises a flexible graphite or carbon filament having a coating of a material which emits electrons when heated.
Preferably the filament comprises a plaitcd or woven graphite cord of low mass/unit length.
According to one feature of the invention the plaited or woven cord is tubular and mountable on a wire such that an electron emitting cathode may comprise a central core of refractory metal and a loose fitting graphite or carbon sleeve surrounding said core.
Preferably the croe is formed of tungsten or tantalum wire, and the sleeve is provided with a coating of a material which emits electrons when heated.
The sleeve may be provided with a coating of lanthanum boride.
To enable the nature of the invention to be more readily understood one embodiment of the invention will now be described, solely by way of example, with reference to the accompanying drawing which illustrates a preferred form of cathode construction.
,The graphite or carbon sleeve materials are available commercially in the form of tubular plaitcd cords of 1 mm. and 2 mm outside diameters. The electrical resistance of the carbon cord is 1.5-2.5 ohms/cm. and for the graphite 0.5-2 ohms/cm. Weights for 2 mm. diameter cords are approximately 1.4 grams/ metre.
-In the preferred form of the invention as shown in the drawingthe tubular sleeve 1 is loosely mounted on a core wire 2 and the ends 3 of the sleeve are copper plated to provide suitable end connections to the filament electrical supply leads 4. The ends of the core wire are held in conventional clamps and connected via leads 6 to an electrical supply to provide a core heating current. The core wire may be tensioned by using a simple spring mounting 7 or the core wire and sleeve may be supported magnetically in a manner substantially as described in our co -pending British patent application 35,474/ 66 which describes means of providing a magnetic field transverse to the axis of an emitter cathode such that the interaction between the field and the emitter cathode, when carrying its operating current, supports the weight of the emitter cathode along its length.
One method of coating the graphite or carbon sleeve comprises applying a slurry, formed from lanthanum oxide, boron and carbon in water, to the cord, drying the cord in air, placing the cord in a vacuum vessel and outgrassing using external heaters and subsequently raising the temperautre of the sleeve to 1700 C. for a few seconds by passing an electrical current through the wire core.
The slurry may be prepared by grinding together lanthanum oxide, boron and carbon in the proportions 923:1 by weight and adding distilled water.
In one example the core wire and sleeve is supported in a filament holder and brush coated with a prepared slurry. The sleeve is allowed to dry in air and the assembly subsequenlty placed within a vacuum enclosure. The enclosure is pumped down to a hard vacuum, i.e. 10 torr approximately, and the cord outgassed for several hours using an external heating source. Formation of an emitter coating is achieved by passing an electrical current through the core wire to raise the temperature to approximaetly 1700 C. for a few seconds, whereby a small amount of lanthanum boride is formed on the surface layer of the sleeve. The sleeve is allowed to cool before application of a high tension voltage to the filament assembly and the filament is preferably operated at -a temperature 1000-1100 C.
Other coating methods may include (a) Painting the cord with a slurry of lanthanum boride in amylacetate.
(b) Cataphoretic deposition of lanthanum boride using an electrolyte of methyl alcohol with a minor proportion of sulphuric acid or (c) Painting the cord with a dilute organic cement to produce a tacky surface and subsequently dusting with a dry lanthanum boride powder, allowing the cord to dry, and subsequent heat treating the coated cord at about 1500 C. for 20 minutes in a vacuum approaching 10" torr.
It will be appreciated that the cord may be used without a central core wire, for example the coated cord may be formed as an elongated electron emitting cathode by taking a suitable length of cord and copper plating each end to provide electrical connection points or alternatively the cord may be left unplated and the ends clamped between suitable soft meal members.
The cathode may be tensioned by using a simple spring mounting since the weight of a coated graphite cord 2 mm. dia. approaches 1 /2 ozs. per ft. length and the cathodes vary from a few inches in length to about 10 feet.
3 With a 4 ft. length of cathode the tension required to keep the cathode within acceptable limits of straightness does not exceed of the breaking strength of the cord which is 10 lb. at room temperatures and increases up to double this amount at elevated temperatures, say 1600 C. Advantageously, the coefiicient of linear expansion of the coated cord is low being approximately 4x 10* C. 1 and thus tensioning devices do not have to counter instabilities due to excess changes in length. A cord 1 mm. diameter and weighing approximately 1 oz./ 100 ft. has also proved suitable for some application.
We claim:
1. An electron emitting cathode comprising a flexible carbonaceous filament having a coating of a mtaerial which emits electrons when heated.
2. An electron emitting cathode according to claim 1 wherein the filament comprises a plaited or woven cord of low mass/unit length.
3. An electron emitting cathode according to claim 2 wherein the cord is tubular.
4. An electron emitting cathode according to claim 2 wherein the cord is coated with lanthanum boride.
References Cited UNITED STATES PATENTS 638,838 12/1899 Fessenden 3l3334 X 1,701,356 2/1929 Bruckel et al 313341 X 2,083,196 6/ 1937 Liebmann 313-334 2,246,176 6/1941 Hull 31334l X 2,563,573 8/1951 Baker 3l3-341 FOREIGN PATENTS 1,382,015 2/1964 France.
JOHN W. I-I-UCKERT, Primary Examiner A. 1. JAMES, Assistant Examiner US. Cl. X.R. 3 l3-337, 341, 346
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4295666 | 1966-09-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US3479551A true US3479551A (en) | 1969-11-18 |
Family
ID=10426699
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US670263A Expired - Lifetime US3479551A (en) | 1966-09-26 | 1967-09-25 | Electron emitting cathodes having a flexible graphite filament with an emissive coating thereon |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US3479551A (en) |
| GB (1) | GB1204316A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3663857A (en) * | 1969-02-13 | 1972-05-16 | Avco Corp | Electron emitter comprising metal oxide-metal contact interface and method for making the same |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US638838A (en) * | 1899-08-25 | 1899-12-12 | Grant Mccargo | Pencil for incandescent lamps. |
| US1701356A (en) * | 1923-06-09 | 1929-02-05 | Gen Electric | Electrical discharge device |
| US2083196A (en) * | 1935-10-02 | 1937-06-08 | Liebmann Gerhard | Heating element for high-voltage cathodes |
| US2246176A (en) * | 1938-11-30 | 1941-06-17 | Gen Electric | Thermionic discharge device |
| US2563573A (en) * | 1951-08-07 | Hot cathode electron tube which re | ||
| FR1382015A (en) * | 1964-02-11 | 1964-12-14 | Philips Nv | Glow lamp and its manufacturing process |
-
1966
- 1966-09-26 GB GB04684/67A patent/GB1204316A/en not_active Expired
-
1967
- 1967-09-25 US US670263A patent/US3479551A/en not_active Expired - Lifetime
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2563573A (en) * | 1951-08-07 | Hot cathode electron tube which re | ||
| US638838A (en) * | 1899-08-25 | 1899-12-12 | Grant Mccargo | Pencil for incandescent lamps. |
| US1701356A (en) * | 1923-06-09 | 1929-02-05 | Gen Electric | Electrical discharge device |
| US2083196A (en) * | 1935-10-02 | 1937-06-08 | Liebmann Gerhard | Heating element for high-voltage cathodes |
| US2246176A (en) * | 1938-11-30 | 1941-06-17 | Gen Electric | Thermionic discharge device |
| FR1382015A (en) * | 1964-02-11 | 1964-12-14 | Philips Nv | Glow lamp and its manufacturing process |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3663857A (en) * | 1969-02-13 | 1972-05-16 | Avco Corp | Electron emitter comprising metal oxide-metal contact interface and method for making the same |
Also Published As
| Publication number | Publication date |
|---|---|
| GB1204316A (en) | 1970-09-03 |
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