CA1046131A - Method of manufacturing a dispenser cathode, and dispenser cathode manufactured according to said method - Google Patents
Method of manufacturing a dispenser cathode, and dispenser cathode manufactured according to said methodInfo
- Publication number
- CA1046131A CA1046131A CA243,153A CA243153A CA1046131A CA 1046131 A CA1046131 A CA 1046131A CA 243153 A CA243153 A CA 243153A CA 1046131 A CA1046131 A CA 1046131A
- Authority
- CA
- Canada
- Prior art keywords
- cathode
- dispenser cathode
- emissive
- barium
- dispenser
- 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
Links
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
- H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
- H01J1/28—Dispenser-type cathodes, e.g. L-cathode
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/02—Manufacture of electrodes or electrode systems
- H01J9/04—Manufacture of electrodes or electrode systems of thermionic cathodes
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Solid Thermionic Cathode (AREA)
Abstract
ABSTRACT
By polishing the emisive surface of a dispenser cathode comprising a porous compressed metal body with aluminum oxide, which dispenser cathode con-tains barium scandate and a dispensing compound, a cathode can be obtained having a very large admissible current density and a long life.
By polishing the emisive surface of a dispenser cathode comprising a porous compressed metal body with aluminum oxide, which dispenser cathode con-tains barium scandate and a dispensing compound, a cathode can be obtained having a very large admissible current density and a long life.
Description
~ PHN 7863 1046~31 The invention relates to a method of manu-facturing a dispenser cathode consisting at least of a heat-ing member and a porous compressed metal body which has an :
emissive surface and which contains in its pores barium scandate (Ba3Sc409) as a compound for dispensing barlum to the emissive surface.
The invention also relates to a dispenser cathode manufactured according to the method. -Such a dispenser cathode is known from United States Patent Specification 3,358,178 by Avraam Iljich Figner and which issued on December 12, 1967, which describes ~-how a mixture of powdered tungsten and barium scandate or a mixture of powdered tungsten-rhenium with barium scandate is compressed to form a body having an emissive surface. Such dispenser cathodes contain 5-30 % by weight of barium scandate (Ba3Sc409), the remainder being tungsten or a tungsten-rhenium mixture or alloy. The work function measured for this type of cathode is between 2.0 and 2.1 volts, and the resulting admissible current density is 1 - 4 A/cm2 at 1050 - 1150C. Compared with previously known cathodes comprising, for example, barium cal-cium aluminate, these values of current density are so low that -the use of such barium scandate cathodes is iustified only for very specific applications, for example, in U.H.F. tubes, gas discharge tube, and the like.
It is an object of the invention to provide a method of manufacturing a dispenser cathode which has a con-siderably higher admissible current density than known compar- -~
able cathodes at a comparable cathode temperature, or the same admissible current ,:
emissive surface and which contains in its pores barium scandate (Ba3Sc409) as a compound for dispensing barlum to the emissive surface.
The invention also relates to a dispenser cathode manufactured according to the method. -Such a dispenser cathode is known from United States Patent Specification 3,358,178 by Avraam Iljich Figner and which issued on December 12, 1967, which describes ~-how a mixture of powdered tungsten and barium scandate or a mixture of powdered tungsten-rhenium with barium scandate is compressed to form a body having an emissive surface. Such dispenser cathodes contain 5-30 % by weight of barium scandate (Ba3Sc409), the remainder being tungsten or a tungsten-rhenium mixture or alloy. The work function measured for this type of cathode is between 2.0 and 2.1 volts, and the resulting admissible current density is 1 - 4 A/cm2 at 1050 - 1150C. Compared with previously known cathodes comprising, for example, barium cal-cium aluminate, these values of current density are so low that -the use of such barium scandate cathodes is iustified only for very specific applications, for example, in U.H.F. tubes, gas discharge tube, and the like.
It is an object of the invention to provide a method of manufacturing a dispenser cathode which has a con-siderably higher admissible current density than known compar- -~
able cathodes at a comparable cathode temperature, or the same admissible current ,:
- 2 - ~
. .
, , P~l~'.78~3 '' 104~131 11~-5-1~75 denslty at a considerably lower cathode temperature.
Another ob~ect of the invention is to provide a dispenser cathode which is partic~llarly SUi t-able for use in television display tubes, camera tubes, and the like.
,According to the ~nvcntion a method of mam~factllring a dispenser cathode of the kind men-tioned in the first paragraph is characterized in that the emissive surface of the barium scandate-containing porous metal body is polished so that a high-gloss surface is obtained.
The invention is based on the recogni-tion of the fact that the ustlal sintering of the cathode - results in the formation of too thick a layer of barium scandate on the emissive surface. The result Or polish-ing the surface Imtll said layer has disappeared is that ~ft~ aotiv~tloll ~ tl.~ ~atll~d~, a l~y~r is fo~med ~t the surface of the emissive body which is one or a few molectlles thick and consists at least of scandium oxide and bari,um oxide. This activation is accelerated,,b,y the firlng of t,he cathode, and also causes any liquid which , ,has been used du,ring the pvlishing ,treatment and whi,ch ' ' is still present in the oathode to evaporate more rapid-ly. Said polishing is preferably carried out with (an) aluminium oxide (plate). Any residue of aluminium oxide on the emissive stlrface has no detrimental influence on the emission after activation of the cathode', in con-trast to the case when, for example, diamond powder is used for the polishing: then a carbon layer is formed from any residue of diamond powder, and this redttces the emission considerably. ~;
~y interac,tlon of the scandium oxide , ,' :
PIIN.7863 104tj131 nnd the bariuln oxid~, the cmlssive surface has a relative-ly low work functioIl of approximately 1.7 volts. The very thin layer of scandium oxide and barium oxide thercfore characterizes a dispenser cathode mamIfactured according to the invention. The presence of the oxides can be demonstrated with Auger electron spectroscopy.
The worlc function of t.7 volts corresponds to an admissible current density of approximately 100 A/cm2 at 1050C. Therefore a cathode according to the invention can be used at a much lower operating temperature than the cathode known from the-above-mentioned United States Patent Specification 3,358,178, which an ample current density can nevertheless be obtained. It has been found that cathodes embodying the invention have the largest admissible density when they are polished so as to have as high a glass as can readily be obtained. Although it i8 known that the roughness of the emissive surface of known oxide cathodes influences the electron emission, this influence is opposite to the influence of the polishing in the present invenbion: in kno~n carbonate ca*hodes, the larger snrface area resulting from a larger degree of roughness results in a larger current density;
A further advantage is that in a polished cathode embodying the invention, the rate of evaporation of the d~spensing compount, barium scandate, can be considerably less than in a corresponding non-polished cathode, since a lower temperature can be used to obtain the same current density. As a result~ a long life of ~ 10,000 hours or more can be obtained. Another advantage is that the use of a tungsten-rhenium alloy or mixture is no Ionger necessary, and t~mgsten alone will suff*ce.
~ 4 .
.. .
~}IN.78G3 -` 10~f~131 Cnthodes accordinG to the invention are particularly suitable for use in electric dischar~e tll~CS
in which cathodes hav'ing an emissive surrace with a diameter smaller than 5 mm are reqlllred with a high ad-mlsslble cllrrent density, for exampl~ television display tubes, camera tubes,and the like. With such a dimension, the shrinkage occurring in the coIlrse of mam~facttlre is not large.
The mam1racttlre and advantages of a dispenser cathode according to the invention will now be described in greater detail with reference to the drawing which is a longitudinal view, partly in cross-section of a dispenser cathode according to the invention.
The cathode shown in the drawing consists - of an emissi~e body 1 which is compressed from tl1ngsten particles which are mainly smaller than 5/tIm~ and barium scandate. The tungsten powder, before being mixed with tha barium ~candate, i5 ~ired for 30 minIltes at 14G0C
in a hydrogen atmosphere. The barium scandate (Ba3Sc~09) is manuractured by mixing and grinding barium'car~onate w~th scandium oxidé in'a molar ratio of'3 : 2 -in a ball ; mill a~d Imder hexane; After the evapora'tion of the ~.exane, the powder is fired for 16 hours at approximately 1000C
.. . . . . . . . . .
in alr-an'd then'ground and mixed again in a ball mill mder hexane. After the evaporation of the hexane and drying, the scandate powder thus formed is fired in air at 1200C for 16 hours and again pulverised until the powder particlea have dimensions Or approximately 5-50~1m-The tungsten powder and the barium scan-` date powder are then mixed in a weight ratio of 9 - 1 and compressed at a pressure of approximately 20 x 103 - kg/cm2 to form the emissive body 1.
The emissive body 1 is surrounded by a . . ~,., .......... .
~ _5_ .. . .
.
PlIN.7863 i04~131 1 4-5-'I975 metal cylinder 2, preferably of molybdenum. Said cylinder contains a hoating member 3 consisting of a tun~sten wlre filament which is covered with alumininm oxide, and al ~o has a partition 4, likewise preferably of molyb-denum, so as to prevent ernission from the emissive body 1-to the heating member 3. Prior to assembly in the cylinder, the emissive body is heated in 5 minutes from room temperature to 1550C in a hydrogen atmosphere and fired at said temperature for 5 mimltes, after which it is gradually cooled.
After assembling the emissive body 1 in -~ .
the cylinder 2, the emissive snrface 5 is Polished with an aluminium oxide plate using a liquid alcohol until it ' has become highly glossy. After polishing, the cathode is vlbrated ultrasonically in freon for approximately one mimlte and is then dried. The dry cathode is now fired in pure hydrogen at 1200C for approximately 5 ~ -, minutes and after cooling is ready for assembly in an electron discharge tube. Because~the cathode is hydros-2~ . ,copic,.it.is.recommendable to stor,e.it in,dry argon or. , , in-a desiocator. ' ' .................. . . . ' ..
, Cathodes mamlfactured as described have , a larger admissible current.denslty than c.omparable known cathodes. The maximum admissible current density in the centre of known barium strontium oside cathodes is appro- - ' ximately 1.5 A/cm2. This is approximately 2.5 times the average current density through the whole of the emissive surface. The better the emission of the cathode, the smaller oan be the radius of the emissive surface required to obtain the same electron-beam cl~rrent. For television display tubes~ a beam current of 1.5 to 2.0 mA is necessary. With a grid e1 (not shown) ad.jacent to t~e ~ ' ` .
. ~ -6-PlIN.7863 , 14-5-1',)75 1~)4tj131 cathode and having a hole of diamcter o.6 mm, the eIfec-tive emissive area Or the cathode is the same as the area of the hole in ~1r i.e. ~ rO2, where r is the radius of said hole, provided that g1 draws no current. With a maximum current density ~max of 1-5 A/cm2 and an average current density ~, thls provides an electron beam current I Or:
I 5 fr r 2 . J = ~ r~2 . 2a5 = 1.7 mA, which is sufficient.
In a dispenser cathode according to the -invention, ~max = 100 AJcm2. With the same geometry as discussed above, said cathode would supply at the same temperature~ an electron beam current which is approxi-mately 67 times as large. This means that to obtain the same current the cathode temperature can be considerably decreased~ or the st~trfaoe area of the cathode can be reduced. ~n additional advantage of small cathodes is that they rapidly reach the desired emission temperature when heated from ambient temperature.
; 20 Since the essence of the invention is the polishing of the emissive cathode stlrface~ methods of maslufacturis~g dispenser cathodes other than that des-cribed above but whlch will ~e readily apparent t~ those skilled in the art will of course be within the scope of the invention, provided that the polishing forms part of the method.
,~ . .
, 7_.
~;
. .
, , P~l~'.78~3 '' 104~131 11~-5-1~75 denslty at a considerably lower cathode temperature.
Another ob~ect of the invention is to provide a dispenser cathode which is partic~llarly SUi t-able for use in television display tubes, camera tubes, and the like.
,According to the ~nvcntion a method of mam~factllring a dispenser cathode of the kind men-tioned in the first paragraph is characterized in that the emissive surface of the barium scandate-containing porous metal body is polished so that a high-gloss surface is obtained.
The invention is based on the recogni-tion of the fact that the ustlal sintering of the cathode - results in the formation of too thick a layer of barium scandate on the emissive surface. The result Or polish-ing the surface Imtll said layer has disappeared is that ~ft~ aotiv~tloll ~ tl.~ ~atll~d~, a l~y~r is fo~med ~t the surface of the emissive body which is one or a few molectlles thick and consists at least of scandium oxide and bari,um oxide. This activation is accelerated,,b,y the firlng of t,he cathode, and also causes any liquid which , ,has been used du,ring the pvlishing ,treatment and whi,ch ' ' is still present in the oathode to evaporate more rapid-ly. Said polishing is preferably carried out with (an) aluminium oxide (plate). Any residue of aluminium oxide on the emissive stlrface has no detrimental influence on the emission after activation of the cathode', in con-trast to the case when, for example, diamond powder is used for the polishing: then a carbon layer is formed from any residue of diamond powder, and this redttces the emission considerably. ~;
~y interac,tlon of the scandium oxide , ,' :
PIIN.7863 104tj131 nnd the bariuln oxid~, the cmlssive surface has a relative-ly low work functioIl of approximately 1.7 volts. The very thin layer of scandium oxide and barium oxide thercfore characterizes a dispenser cathode mamIfactured according to the invention. The presence of the oxides can be demonstrated with Auger electron spectroscopy.
The worlc function of t.7 volts corresponds to an admissible current density of approximately 100 A/cm2 at 1050C. Therefore a cathode according to the invention can be used at a much lower operating temperature than the cathode known from the-above-mentioned United States Patent Specification 3,358,178, which an ample current density can nevertheless be obtained. It has been found that cathodes embodying the invention have the largest admissible density when they are polished so as to have as high a glass as can readily be obtained. Although it i8 known that the roughness of the emissive surface of known oxide cathodes influences the electron emission, this influence is opposite to the influence of the polishing in the present invenbion: in kno~n carbonate ca*hodes, the larger snrface area resulting from a larger degree of roughness results in a larger current density;
A further advantage is that in a polished cathode embodying the invention, the rate of evaporation of the d~spensing compount, barium scandate, can be considerably less than in a corresponding non-polished cathode, since a lower temperature can be used to obtain the same current density. As a result~ a long life of ~ 10,000 hours or more can be obtained. Another advantage is that the use of a tungsten-rhenium alloy or mixture is no Ionger necessary, and t~mgsten alone will suff*ce.
~ 4 .
.. .
~}IN.78G3 -` 10~f~131 Cnthodes accordinG to the invention are particularly suitable for use in electric dischar~e tll~CS
in which cathodes hav'ing an emissive surrace with a diameter smaller than 5 mm are reqlllred with a high ad-mlsslble cllrrent density, for exampl~ television display tubes, camera tubes,and the like. With such a dimension, the shrinkage occurring in the coIlrse of mam~facttlre is not large.
The mam1racttlre and advantages of a dispenser cathode according to the invention will now be described in greater detail with reference to the drawing which is a longitudinal view, partly in cross-section of a dispenser cathode according to the invention.
The cathode shown in the drawing consists - of an emissi~e body 1 which is compressed from tl1ngsten particles which are mainly smaller than 5/tIm~ and barium scandate. The tungsten powder, before being mixed with tha barium ~candate, i5 ~ired for 30 minIltes at 14G0C
in a hydrogen atmosphere. The barium scandate (Ba3Sc~09) is manuractured by mixing and grinding barium'car~onate w~th scandium oxidé in'a molar ratio of'3 : 2 -in a ball ; mill a~d Imder hexane; After the evapora'tion of the ~.exane, the powder is fired for 16 hours at approximately 1000C
.. . . . . . . . . .
in alr-an'd then'ground and mixed again in a ball mill mder hexane. After the evaporation of the hexane and drying, the scandate powder thus formed is fired in air at 1200C for 16 hours and again pulverised until the powder particlea have dimensions Or approximately 5-50~1m-The tungsten powder and the barium scan-` date powder are then mixed in a weight ratio of 9 - 1 and compressed at a pressure of approximately 20 x 103 - kg/cm2 to form the emissive body 1.
The emissive body 1 is surrounded by a . . ~,., .......... .
~ _5_ .. . .
.
PlIN.7863 i04~131 1 4-5-'I975 metal cylinder 2, preferably of molybdenum. Said cylinder contains a hoating member 3 consisting of a tun~sten wlre filament which is covered with alumininm oxide, and al ~o has a partition 4, likewise preferably of molyb-denum, so as to prevent ernission from the emissive body 1-to the heating member 3. Prior to assembly in the cylinder, the emissive body is heated in 5 minutes from room temperature to 1550C in a hydrogen atmosphere and fired at said temperature for 5 mimltes, after which it is gradually cooled.
After assembling the emissive body 1 in -~ .
the cylinder 2, the emissive snrface 5 is Polished with an aluminium oxide plate using a liquid alcohol until it ' has become highly glossy. After polishing, the cathode is vlbrated ultrasonically in freon for approximately one mimlte and is then dried. The dry cathode is now fired in pure hydrogen at 1200C for approximately 5 ~ -, minutes and after cooling is ready for assembly in an electron discharge tube. Because~the cathode is hydros-2~ . ,copic,.it.is.recommendable to stor,e.it in,dry argon or. , , in-a desiocator. ' ' .................. . . . ' ..
, Cathodes mamlfactured as described have , a larger admissible current.denslty than c.omparable known cathodes. The maximum admissible current density in the centre of known barium strontium oside cathodes is appro- - ' ximately 1.5 A/cm2. This is approximately 2.5 times the average current density through the whole of the emissive surface. The better the emission of the cathode, the smaller oan be the radius of the emissive surface required to obtain the same electron-beam cl~rrent. For television display tubes~ a beam current of 1.5 to 2.0 mA is necessary. With a grid e1 (not shown) ad.jacent to t~e ~ ' ` .
. ~ -6-PlIN.7863 , 14-5-1',)75 1~)4tj131 cathode and having a hole of diamcter o.6 mm, the eIfec-tive emissive area Or the cathode is the same as the area of the hole in ~1r i.e. ~ rO2, where r is the radius of said hole, provided that g1 draws no current. With a maximum current density ~max of 1-5 A/cm2 and an average current density ~, thls provides an electron beam current I Or:
I 5 fr r 2 . J = ~ r~2 . 2a5 = 1.7 mA, which is sufficient.
In a dispenser cathode according to the -invention, ~max = 100 AJcm2. With the same geometry as discussed above, said cathode would supply at the same temperature~ an electron beam current which is approxi-mately 67 times as large. This means that to obtain the same current the cathode temperature can be considerably decreased~ or the st~trfaoe area of the cathode can be reduced. ~n additional advantage of small cathodes is that they rapidly reach the desired emission temperature when heated from ambient temperature.
; 20 Since the essence of the invention is the polishing of the emissive cathode stlrface~ methods of maslufacturis~g dispenser cathodes other than that des-cribed above but whlch will ~e readily apparent t~ those skilled in the art will of course be within the scope of the invention, provided that the polishing forms part of the method.
,~ . .
, 7_.
~;
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of manufacturing a dispenser cathode consisting at least of a heating member and a porous compressed metal body which has an emissive sur-face and which contains in its pores barium scandate (Ba2Sc4O9) as a compound for dispensing barium to the emissive surface, characterized in that the emissive surface of the barium scandate-containing porous metal body is polished so that a high-gloss surface is ob-tained.
2. A method as claimed in Claim 1, charac-terized in that the emissive surface is polished with (an) aluminium oxide (plate).
3. A dispenser cathode manufactured accor-ding to a method as claimed in Claim 1, characterized in that the emissive surface has after activation of the cathode a very thin layer which is one or a few molecules thick and which contains scandium oxide and barium oxide.
4. A dispenser cathode as claimed in Claim 3, characterized in that the average diameter of the emissive surface is smaller than 5 mm.
5. An electric discharge tube having a dispenser cathode as claimed in Claim 3 or 4.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7500248A NL7500248A (en) | 1975-01-09 | 1975-01-09 | PROCEDURE FOR MANUFACTURING A PRESSED COMPLIANCE CATHOD AND COMPLIANCE CREDIT MANUFACTURED IN ACCORDANCE WITH THIS PROCESS. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1046131A true CA1046131A (en) | 1979-01-09 |
Family
ID=19822961
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA243,153A Expired CA1046131A (en) | 1975-01-09 | 1976-01-08 | Method of manufacturing a dispenser cathode, and dispenser cathode manufactured according to said method |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5193659A (en) |
| CA (1) | CA1046131A (en) |
| FR (1) | FR2297490A1 (en) |
| GB (1) | GB1522387A (en) |
| NL (1) | NL7500248A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL8201371A (en) * | 1982-04-01 | 1983-11-01 | Philips Nv | METHODS FOR MANUFACTURING A SUPPLY CATHOD AND SUPPLY CATHOD MANUFACTURED BY THESE METHODS |
| GB2173943A (en) * | 1985-04-18 | 1986-10-22 | Noblelight Limited | Improvements in and relating to cathodes |
| JPH0850849A (en) * | 1994-05-31 | 1996-02-20 | Nec Kansai Ltd | Cathode member and electronic tube using it |
| FR2840450A1 (en) | 2002-05-31 | 2003-12-05 | Thomson Licensing Sa | CATHODO-EMISSIVE BODY FOR CATHODE IMPREGNATED WITH ELECTRONIC TUBE |
-
1975
- 1975-01-09 NL NL7500248A patent/NL7500248A/en not_active Application Discontinuation
- 1975-10-24 GB GB4380075A patent/GB1522387A/en not_active Expired
-
1976
- 1976-01-07 JP JP133976A patent/JPS5193659A/en active Granted
- 1976-01-08 CA CA243,153A patent/CA1046131A/en not_active Expired
- 1976-01-09 FR FR7600399A patent/FR2297490A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| NL7500248A (en) | 1976-07-13 |
| DE2558784A1 (en) | 1976-07-15 |
| JPS5616499B2 (en) | 1981-04-16 |
| FR2297490B1 (en) | 1980-03-28 |
| GB1522387A (en) | 1978-08-23 |
| JPS5193659A (en) | 1976-08-17 |
| DE2558784B2 (en) | 1977-05-26 |
| FR2297490A1 (en) | 1976-08-06 |
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