CA1169468A - Electrode for discharge lamp with yttrium and lanthanum oxide electron emission material - Google Patents
Electrode for discharge lamp with yttrium and lanthanum oxide electron emission materialInfo
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- CA1169468A CA1169468A CA000357799A CA357799A CA1169468A CA 1169468 A CA1169468 A CA 1169468A CA 000357799 A CA000357799 A CA 000357799A CA 357799 A CA357799 A CA 357799A CA 1169468 A CA1169468 A CA 1169468A
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Abstract
W.E. 48,922 An electrode for a discharge lamp, such as a high pressure metal vapor lamp or fluorescent lamp comprises an electrode substrate and an electron emission material on the substrate. The emission material comprises a mixture of yttrium oxide and lanthanum oxide.
me molar ratio of lanthanum oxide, yttrium oxide is in the range of 1 : 9 to 19 : 1 and the emission material contains in addition, barium-strontium-calcium tungstate and an alkaline earth metal oxide. The electrode so produced improves the luminous flux maintenance of a metal vapor discharge lamp and reduce the starting voltage of fluorescent lamps in neither case producing black depositions on the ends of the tube.
me molar ratio of lanthanum oxide, yttrium oxide is in the range of 1 : 9 to 19 : 1 and the emission material contains in addition, barium-strontium-calcium tungstate and an alkaline earth metal oxide. The electrode so produced improves the luminous flux maintenance of a metal vapor discharge lamp and reduce the starting voltage of fluorescent lamps in neither case producing black depositions on the ends of the tube.
Description
iS~6~ W,E. 48,922 -BAC~ R~7~ ~F TH~ INVENTIO~
FIELD OF THE INVENTION
. . _ The present invention relates to an electrode used in high pressure metal vapor discharge lamps such as a high pressure 5 mercury vapor discharge lamp in which mercury and a rare gas are filled; a high pressure sodium vapor discharge lamp in which mercury, a rare gas and sodium are filled; a metal vapor discharge lamp in which mercury, a rare gas and a metal halide are filled or low pres-sure discharge lamps such as a fluorescent lamp. More particularly, 10 it relates to an improvement of an electron emission material on the electrode.
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DESCRIPTION OF THE PRIOR ARTS:
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In a high pressure metal vapor discharge lamp such as a high pressure mercury vapor discharge lamp, a mixture of barium, strontium, calcium tungstate (Ba2 xSrxCaWO6 x is 0 to 0. 5), beryllium oxide (BeO) and yttrium oxide (YzO3) has been used as an electron emission material coated on the electrode. In the electron :
emission material, a solid solution of BeO and Y2O3 is formed whereby a lumen maintenance and a starting characteristic are advantageously 20 excellent and stable during a long time operation~of the lamps.
However, BeO contained in the electron emission material is toxic to human body and the handling of the electron emission material should be carefully considered and the improvement of productivity is disadvantageously prevented.
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W.E. 48,922 Moreover, in a high pres~alre }netal vapor discharge lamp using the electron emission material, a phenomenon of the formation of black deposit is often found in the initial period, The black deposit is gradually changed to be white during the operation and it does not affect to the life characteristic of the lamp. However, it causes slightly low luminous flux value in the initial lightening period, In a metal halide lamp, a rare earth metal oxide has been usually used as the electron emission material. Yttrium oxide is ~, especially effective since it has excellent electron emitting character-. 10 istic, However, yttrium oxide has high melting point whereby the adhesion of the component on the electrode substrate is not satisfactori-ly attained to peel off the electron emission material during the operation of the discharge lamp. This causes deterioration of the ` activity of electron emission and the black coloring of the arc tube of ;~ . 15 the lamp is formed to cause a short life.
In a fluorescent lamp, an electron emission material of a mixture of barium, strontium, calcium carbonate and zirconium oxide is coated on a coil made of tungsten and the carbonate is thermally decomposed into oxides such as barium oxide in the step of preparing electrodes of ~ fluorescent lamp, The conventional electron emission material is reduced by tungsten as the electrode substrate during the operation of the discharge lamp and barium oxide (BaO) is converted into barium metal (Ba) by the following reaction.
6BaO + W ~ Ba3WO6 ~ 3Ba, ' W . E~ 8, 922 The barium metal contributes to the electron emission from the electrode, however, a part of the barium metal is sputtered in the arc space and is ad1lered on the inner wall of the arc tube. A black coloring may be cA~sed at the en~l of the arc tube when the quantity of the barium 5 metal is much. Zirconium oxide is incorporated to decrease the reduction by the electrode subs~raie and to decrease the sputtering of the barium metal. The end blacking of the tube can be decreased by the incorporation of zirconium oxide, however, it may cause deterio-ration of the activity of electron emission of the electrode. When such 10 electrode is used in the fluorescent lamp, the starting voltage is disadvantageously high.
SUMMARY OF THE INVENTION:
:, It is an object of the present invention to overcome the ` ~ disadvantages of the conventional electrode and to provide an electrode 15 in which an adhesion of an electron emission material on an electrode substrate is remarkably improved and which has excellent electron emitting activity to result less luminous flux deterioration in a metal vapor discharge lamp. The foregoing and other objects of the present invention have been attained by using an electron emission material 20 comprising yttrium oxide and lanthanum oxide.
The other object of the present invention is to provide an electrode of a discharge lamp in which a starting voltage of the discharge lamp is lowered and an arc tube end blacking is decreased.
This is attained by using an electron emission material comprising 25 yttrium oxide and lanthanum oxide.
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W.E. 48,922 ~he other object o~ the present invention is to provide an electrode of a dischargSe larnp by which an initial deterioration of luminous flu~ is decreased and which does not contain toxic BeO so as to elimillate a special handlil1g operation and to attain a normal operation and to improve its productivity. This is attained by using an electron emission material comprising yttrium oxide and lanthanum - o~ide.
BRIEF DESCRIPTION OF THE DRAWINGS:
-Figure 1 is a front view for showing a structure of a metal vapor discharge lamp; and Figures 2, 3 and 4 are respectively sectional views of various structures of the electrode of the metal vapor discharge lamp.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The electrode of the metal vapor discharge lamp of the ` 15 present invention will be illustrated.
The rnetal vapor discharge lamp has the structure shown in Figure 1 wherein the reference numeral (1) designates an arc tube made of a transparent quartz glass in which mercury, a rare gas and a metal halide are filled and (2a) and (2b) designate electrodes which are placed at both ends of the arc tube to face each other and are respectively connected through each molybdenum foil (3a), (3b) sealed at each end of the arc tube (1) to each lead wire (4a), (4b);
and (5) and (5) designate heat reserve layers coated at each end of the arc tube (1); (6) and (~) designate supporting plates which are , ' . ~ .
W,E . ~8, 9~2 placed at each end of the arc tube (1) and welded on each frame (9), (10) so as to hold the arc tube (1) in an outer tube (14); and (7) desig-nates a ribbon lead wire which connects the lead wire (4a) to the frame (9); (11) designates a stem lead which is welded to the frame (9); (12) designates the other stem lead; (8) designate an arch shaped wire for connecting the lead wire (4b) to the stem lead (12); and (13) designates a base which is placed at one edge of the outer tube and is connected to the stem leads (11), (12).
As shown in Figure 2, each of the electrodes (2a), (2b) comprises an electrode core (15) made of a heat resistant metal such as tungsten and an inner coil (16) and an outer coil (17) which are wound on the electrode core; and an electron emission material (18) which is formed by coating on the inner coil (16) and the outer coil (17) and sintering it at high temperature.
The present invention will be illustrated by certain examples and references as the comparison.
A conventional embodiment will be illustrated.
A tungsten rod having a diameter of 0. 9 mm is used as , the electrode core (15) and a tungsten wire having a diameter of 0. 5 mm is used as the inner coil (16) and the outer coil (17) so as to form the electrode substrate.
An electron emission material of only yttrium oxide is admixed with nitrocellulose lacquer and butyl acetate and the mixture is milled in a ball mill for 24 hours to prepare a suspension.
The electrode substrate is dipped into the suspension to coat the electron emission material on the inner coil (16) and the outer coil (17) and this is dried and sintered in an argon atmosphere at 1800C
for 2 minutes so as to bond the electron emission material (18) on the electrode substrate.
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The electrodes ~2a~J ~2~ coated with the electron emission material (18) are used for preparing a 400 W metal vapor discharged lamp equipped with the arc tube (1) having an inner diameter of 18 mm and a gap between the electrodes (2a), (2b) of 44 mm in which suitable 5 quantities of mercury, argon gas, scandium iodide and sodium iodide are filled. The life test of the 400 W metal vapor discharge lamp is carried out. The lumen maintenance was 50% after 9000 hours of operation Examples of the present invention will be illustrated.
Lanthanum oxide is mixed with yttrium oxide at various ratios to form the electron emission material (18). The electrodes (2a), (2b) are prepared by coating the electron emission material on the electrode substrate. Various 400 W metal vapor discharge lamps are prepared by using the electrodes and the life tests are carried out 15 as set forth in said reference. The results of the life tests are shown in Table 1.
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~1.E. 48,922 Ta~le I
Lumen mainte-. Composition of electron nance after emission material 9000 hours of (mol %) (3peration Ref, Y2O3 (100 mol ~o) 50 Exp. 1-1 Y203(99. 7 rnol %) - La203(0. 3 mol %) 55 _ Exp. 1-2 Y2O3(99. 5 mol %) - La2O3(0. 5 mol %) 60 , _ Exp, 1-3 Y2O3(90 mol %) - La2O3(10 mol %) 68 Exp- 1-4¦ Y2O3(80 mol ~o) - La2O3(20 mol %) 75 : Exp. 1-5 Y2O3(40 mol %) La2O3(60 mol %) 65 Exp. 1-6 Y2O3(20 mol %) - La2O3(80 mol ~0) 61 Exp. 1-7 Y2O3(17 mol %) - La2O3(83 mol %) 56 .
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~J.E. 48, 922 As it is sho~sln in Table 1, the lumen maintenance of the metal ~apor ~ise~ar~ ~mps using the electron ernission material shown in Examples are remarka~3y superior to that of the metal vapor discharge lamp using only yttrium oxide as the electron emission material (18).
The reason why the lumen maintenance of Examples are superior to that of Reference is considered as follows.
~ttrium oxide has a high melting point. When it is sintered after coating on the electrode substrate, the adhesion of yttrium oxide as the electron emission material (18) on the electrode substrate is not high enough and the electron emission material (18) is peeled off from the electrode substrate during the operation of the discharge lamp. When the electron emission material of only ytttrium oxide is used as the conventional case, the luminous flux is reduced for a long lS time operation. However, when the electron emission material (18) of a mixture of yttrium oxide and lanthanum oxide is used as Examples, the mixture forms a solid solution or a complex compound of yttrium oxide and lanthanum oxide to decrease a melting point. Thus, the ~` electron emission material is highly spread on the electrode substrateto improve the adhesion and accordingly, the peeling-off of the electron emission material in the discharge lamp is decreased whereby the excellent electron emitting activity of yttrium oxide is maintained for a long time to provide a discharge lamp having less luminous flux ~; deterioration.
Moreover, as shown in Table 1, the optimum result is attained by using a mixture incorporating 0. 5 to 80 mol ~0 of lanthanum ~` oxide. When a content of lanthanum oxide is less than 0. 5 mol %, the - effect of lowering of a melting point is too small to adhere it on the electrode substrate and the lumen maintenance is less than 60% to be ., '`
' . ' , W.E. 48,922 small effect f~r imp.7~0ving t~e lumen mairltenance When it is more than 80 mol %, a content of yttrium oxide coated on the electrodes (2a)J (2b) is relatively smaller so as to decrease the electron emitting activity Therefore, the effect for improving the lumen maintenance is disadvantageously small In the examples, yttrium oxide has been used as the electron emission material. Thus, it is possible to incorporate a small amount of tungsten and/or molybdenum powder into the mixture.
In the examples, the structure of the electrode shown in Figure 2 has been used. The structure of the electrode is not limited to said feature and can be the other features, for example, the electrode shown in Figure 3 wherein the inner coil (16) is wound on the electrode core (15) so as to remain rough wound parts and the ~ outer coil (17) is wound on the inner coil to form the electrode sub-; 15 strate and the electron emission material (18) is filled in the space ; ~ in the electrode substrate; or the electrode shown in Figure 4 whereinonly inner coil (16) is wound on the electrode core (15) to form the ~' electrode substrate and the electron emission material (18) is coated on the electrode substrate The present invention can be applied for various kinds of the structures of the electrodes `~ In the examples, scandium iodide and sodium iodide have .
been filled in the arc tube of the metal vapor discharge lamp.
ThusJ it is possible to apply the present invention for the metal vapor discharge lamps in which the other halide such as dysprosium iodideJ
; 25 thallium iodide and indium iodide is filled.
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' W.E. 4~,922 1~ ~c~ 3rda~e with the above-mentioned embodiment, the electrodes prep~re~ by using the electron emission material consist-ing of yttrium oxide and lanthanum oxide are used in the metal vapor discharge lamp containing the metal halide in the arc tube.
Therefore, the adhesion of the electron emission material on the electrode substrate is remarl~ably superior and the electron emitting acti~ity is highly maintained for its long life and the luminous flux deterioration is small and a life of the lamp is long.
The other embodiment of the electrode of a high pressure mercury vapor discharge lamp will be illustrated.
Certain examples and a reference of the embodiment will be illustrated, In Reference, a tungsten rod having a diameter of 1, 2 mm is used as the electrode core (15) and a tungsten wire having a diameter of 0. 6 mm is used as the inner coil (16) and the outer coil (17) so as to form the electrode substrate An electron emission material (18) of a mixture of 15. 2 mol % of barium- strontium calcium tungstate (Ba1 8Sr0 2CaWO6), 76. 3 mo] % of beryllium oxide (BeO) and 8, 5 mol % of yttrium oxide (Y2O3) is admixed with nitrocellulose lacquer and butyl acetate and the mixture is milled in a ball mill for 24 hours to prepare a suspen-sion. The electrode substrate is dipped into the suspension to coat the electron emission material on the electrode substrate and this is dried and sintered in an argon atmosphere at 1700C for 2 minutes so as to bond the electron emission material (18) on the electrode substrate, The electrodes (2a), (2b) coated with the electron emission material (18) are used for preparing a d~00 W high pressure mercury vapor discharge lamp equipped with the arc tube (1) having an inner ',' . , ~
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W.E . 48, 922 diameter of 7 8 mm and an arc length of 71~ mm in which suitable quantities of mercury and argon gas for starting are filled, The lamps are.burned on a cycle of 15 minutes On and 15 minutes Off and lumen maintenace after 50 times and after 600 times are measured.
5 The lumen maintenace is 86% after 50 times. ~ black deposition is found on the inner wall of the arc tube in the lamp. Beryllium and barium components are found by an analysis of the black deposition.
The lumen maintenance is 70% after 6000 times.
Examples of the present invention will be illustrated.
10 Lanthanum oxide (La2O3) and yttrium oxide (Y2O3) are mixed with barium, strontium and calcium tungstate (Bal 8Sr0 zCaWO6) at various ratios to form each electron emission material (18).
The electrodes (2a), (2b) are prepared by coating the electron emission material on the electrode substrate. Various ~00 W high pressure 15 mercury vapor discharge lamps are prepared by using the electrodes and the life tests are carried out as set forth in said reference.
The results of the life tests are shown in Table 2.
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W.E . l~8, 922 Table 2 Composition of electron e~-nission ma terial tmol (to) 2 3 2 3 Bal 8Sr0 2CaW6 La2O3 ¦ Y2O3 ¦ BeO (molar ratio) Ref, 15.2 - I 8.5 176.3 Exp . 2- 1 1 5 . 2 4 ~T 80 . O _ 1 : 1 7 Exp. 2-2 15. 2 8. 5 76. 3 _ 1: 9 Exp 2-3 ¦ 15. 2 21. 2 63. 6 _ 1: 3 Exp 2-4 ¦ 15. 2 70. 7 14. 1 _ 5: 1 33xp. 2 5 1 15. 2 ~ 4. 2 1 _ 19: 1 Exp. 2-6 ¦ 15.2 1 81.4 ¦ 3~4 ¦ ~ 24: 1 ¦ Lumen m~intenar ~ce (%) I after 50 times after 6000 times :~ l Ref. 1 86. 0 70. 0 Exp. 2-1 ¦ 91. 0 65. 0 Exp. 2-2 ¦ 95. 0 76. 0 Exp . 2- 3 9 8 . 0 80 . 0 Exp, 2-4 9 6 . 0 7 8 . 0 Exp, 2-5 93. 0 74. 0 Exp. 2-6 90. 0 64. 0 ''~
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W.E. 48,922 ~s it is shown in Table 2, the lumen maintenace (after 50 times) of the lamps using the electron emission material (18) compris-ing La2O3 and Y2O3 and Bal 8Sr0 2CaWO6 are superior to that of the conventional electron emission material including BeO and YzO3.
When the molar ratio of La2O: Y2O3 is in a range of 19 1 to 1: 9, the lun~en main-tenance after 6000 times is superior to that of the conventional one, ` The reason of these characteristics is considered as follows .
In the conventional electron emission n^~aterial (18), a solid solution is formed by BeO and Y2O3 so as to improve the adhesion in the electrode substrate and a formation of an active barium component in operation is kept in a desired rate, However, the electron emission material (18) is coated on the electrode substrate and dried and bonded ` 15 on it by sintering it at high temperature BeO in the solid solution partially reacts with the tungstate in the electron emission material (18) to form a complex compounds having relatively low melting point such as BeO- 3BaO. When an arc spot is shifted to the position forming the complex compounds on the electrode, the complex compounds are suddenly heated to high temperature so as to selectively vaporize Be and Ba to adhere them on the inner wall of the arc tube.
Therefore, the deterioration of the luminous flux in the initial stage of operation is caused On the other hand, when the electron emission material (18) including La2O3 and YzO3 is used, a solid solution or a stable complex compound is formed by La2O3 and Y2O3. Moreover, La2O3 and Y2O3 are not reactive to the tungstate. Therefore, the formation `~ of the active barium from the electron emission material (18) is kept at a desired rate in a stable condition during the mitial and the long time of operation and the lumen maintenance is stable during the life.
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W.E . 48, 922 lh As described above, when the molar ratio of La2O3 to Y2O3 is in a range of 19: 1 to 1: 9, the above-mentioned effect is remarkable. When the molar ratio of La2O3 to Y2O3 is greater than 19: 1, the melting point of the solid solution is too high and the adhesion of the electron emission material (18) to the electrode substrate is deteriorated and the lumen maintenance after 6000 times is slightly lower than that of the conventional one as shown in Table 2.
When the molar ratio of La2O3 to Y2O3 is less than 1: 9, the melting point of the solid solution is too high and the adhesion of the electron emission material (18) to the electrode substrate is deteriorated and the lumen maintenance after 6000 times is lower.
In said examples, the effects of the present invention have been shown in the cases that the mol % of the barium- strontium-calcium tungstate is the same as that of the conventional one.
Thus, the similar effect can be attained even though the mol % of the tungstate is different.
The effect of the present invention can be attained even though a small amount of ~12O3, SiO2 or tungsten is included into siad electron emission material (18) of the present invention.
In the examples, the structure of the electrode shown in , Figure 2 has been used. The structure of the electrode can be the other features, for example~ the electrode shown in Figure 3 wherein the inner coil (16) is wound on the electrode core (15) so as to remain rough wound parts and the outer coil (17) is wound on the inner coil to form the electrode substrate and the electron emission material (18) is filled in the space in the electrode substrate to be sintered.
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E~ ac~ord~ e ~Ti~ t~e foll~ring er~bodiment, the electron emission m~L~erial of ~ mixture of barium oxide, calcium oxide, lanthanum oxide and yttrium oxide is used to improve the luminous flux deterioration in the initial period of operation and to improve the productivity of the discharge lamp since a toxic beryllium oxide is not used.
The embs~diment of an electrode of a high pressure mercury vapor discharge lamp will be illustrated.
Certain examples and a reference of the embodiment will be illustrated.
In Reference, a tungsten rod having a diameter of 1. 2 mm is used as the electrode core (15) and a tungsten were having a diameter of 0. 6 mm is used as the inner coil (16) and the outer coil ` (17) so as to form the electrode substrate.
An electron emission material (18) of a mixture of 42. 3 mol % of BaO, 16. 5 mol '~/c of CaO, 37. 1 mol % of !3eO and 4 1 mol % of Y2O3 is admixed with nitrocellulose lacquer and butyl acetate and the mixture is milled in a ball mill for 24 hours to prepare a suspen-sion. The electrode substrate is dipped into the suspension to coat the electron emission material on the electrode substrate and this is dried and sintered in an argon atmosphere at 1700C for 2 minutes so as to bond the electron emission material (18) on the electrode substrate .
The electrodes (2a), (2b) coated with the electron emission material (18) are used for preparing a 400 W high pressure mercury vapor discharge lamp equipped with the arc tube (1) having an inner diameter of 18 mm and an arc length of 70 mm in which suitable quantities of the mercury and argon gas for starting are filled.
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, ~!.E. 48,922 The life tests are carried out as set forth in said reference and the lumen maintenance after 50 times ar~d ~0~0 times are measured.
The lumen maintenance is 85% after 50 times. A black deposition is found on the inner wall of the arc tube in the lamp.
5 13eryllium and barium components are found by an analysis of the black ~leposltion The lumen maintenance is 62% after 6000 times.
Examples of the present invention will be illustrated.
Barium oxide (BaO), calcium oxide (CaO) as alkaline earth metal oxides and lanthanum oxide (La2O3) and yttrium oxide (Y2O3) 10 are mixed at various ratios to form each electron emission material (18). The electrodes (2a), (2b) are prepared by coating the electron emission material on the electrode substrate. Various 400 W high pressure mercury vapor discharge lamps are prepared by using the electrodes and life tests are carried out as set forth in said reference.
i~ 15 The results of the life tests are shown in Table 3 - , , , . ~ .... : -.
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, W.E. 48,922 Table 3 Composition of electron emission material (mol %) La2O3 Y2O
BaO ¦ CaOJ La23 Y2O3 BëO (molar ratio) Ref, 42, 3¦ 16, 5 ~ 4, 1 37, 1 _ Exp, 3-1 42, 316, 5 3, 238, 0 _ 1: 12 _ _ _ _ Exp, 3-2 42, 316, 5 4,237, 0 _ 1: 9 Exp, 3 - 3 42,316. 5 10. 330.9 1 : 3 Exp, 3-4 42, 316. 5 ¦36,05. Z _ 7: 1 Exp. 3-5 42. 316, 5 ¦39, 12, 1 ¦ - 19: 1 Exp. 3-6 42, 316, 5 139, 41, 8 1 - 22: 1 .
Lumen maintenance (%) ., after 50 times ¦ after 6000 time~s _ I` Ref, 85, 0 62,0 . ~ _ Exp, 3- 1 90,0 58, 0 Exp, 3-2 93,0 69,0 _ Exp. 3-3 97,0 73.0 Exp, 3-4 95,0 1 70, 0 _ Exp. 3-5 92,0 67.0 Exp, 3- 6 89, 0 56, 0 ~: -;`
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As it is shown in Table 3, the lumen maintenance (after 50 times) of the lamps using the electron emission material (18) including La2O3 and Y203 are superior to that of the conventional electron emission material including BeO and Y2O3. When the molar ratio of La2O3: Y2O3 is in a range of 19: 1 to 1: 9 the lumen maintenance after 6000 tirrles is superior to that of the conventional one.
The reason of these characteristics is considered as follows.
In the conventional electron emission material (18), a solid solution is formed by BeO and Y2O3 so as to improve the adhesion in the electrode substrate and a formation of an active barium component in operation is kept in a desired rate. ~owever, the electron emission material (18) is coated on the electrode substrate and dried and bonded on it by sintering it at high temperature. BeO in the solid solution par-tially reacts with BaO in the electron emission ma-terial (18) to form a complex compounds having relatively low melting point such as BeO- 3BaO. When an arc spot is shifted to the position forming the complex compounds on the electrode, the complex compounds are suddenly heated to high temperature so as to selectively vaporize Be and Ba to adhere them on the inner wall of the arc tube Therefore, the deterioration of the luminous flux in the initial stage of operation is caused.
On the other hand, when the electron emission material (18) including La2O3 and Y2O3 is used, a solid solution or a stable complex compound is formed by La2O3 and Y2O3. Moreover, La2O3 and Y2O3 are not reactive to BaO. Therefore, the formation of the active barium from the electron emission material (18) is kept at a desired rate in a stable condition during the initial and the long time of operation and the lumen maintenance is stable during the life.
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W .E . 48, 922 As descrihed abo~eJ when the molar ratio of La203 to YzO3 is in a range of 19: 1 to 1: 9, the above-mentioned effect is remarkable. When the molar ratio of La2O3 to YzO3 is greater than 19: 1, the melting point of -the solid solution is too high and the 5 adhesion of the electron emission material (18) to the electrode substrate is deteriorated and the lumen maintenance after 6000 times is slightly lol,~rer than that of the conventional one as shown in Table 3.
When the molar ratio of La2O3 to Y2O3 is less than 1: 9, the melting point of the solid solution is too high and the adhesion of the 10 electron emission material (18) to the electrode substrate is deteriorated and the lumen maintenance after 6000 times is lower.
In said examples, the effects of the present invention have been shown in the cases that the mol % of BaO and CaO is the same as that of the conventional one. Thus, the similar effect can be 15 attained even though the mol % of BaO or CaO is different.
The cases incorporating BaO and CaO as the alkaline earth metal oxide have been shown. In this embodiment, it is enough to contain at least BaO as the alkaline earth metal oxide. That is, the alkaline earth metal oxide can be only BaO or a combination of BaO
zo and SrO or a combination of BaO, CaO and SrO.
The effect of the present invention can be attained even though a small amount of Alz03, SiO2 or tungsten is included into said electron emission material (18) of the present invention.
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W.E. 48,92 ln the examples, the structure of the electrode shown in Figure 2 has been used. The structllre of the electrode can be the other feature shown in Figure 3 wherein the inner coil (16) is wound on the electrode core (15) so as to remain rough wound parts and the outer coil (17) is wound on the inner coil to form the electrode substrate and the electron emission material (18) is filled in the - space in the electrode substrate to be sintered.
The oxides have been incorporated in the electron emission material (18) in said embodiment. Thus, it is possible to use carbonates or oxalates and to convert them into oxides by sintering them after coating the electron emission material on the electrode substrate.
In accordance with the above-mentioned embodiment, the electron emission material comprising the alkaline earth metal oxide including at least BaO and La2O3 and Y2O3 is used, to improve the luminous flux deterioration in the initial period and to improve the productivity of the discharge lamp since a toxic beryllium oxide is not used.
The embodiment of an electrode of a fluorescent lamp will be illustrated.
Certain examples and a reference of the embodiment will be illustrated.
In Reference, a 40 W fluorescent lamp equipped with electrodes coated with an electron emission material consisting of "~ 25 40 mol % of BaO, 30 mol % of SrO, 26 mol % of CaO and 4 mol % of Zr2 is prepared, ~- The electrode is prepared by mixing zirconium oxide with barium carbonate, strontium carbonate and calcium carbonate and admixing the mixture with nitrocellulose lacquer and butyl acetate ~ .
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W.E. 48,922 in a ball mill to prepare a suspensio~ and coating the suspension on adouble wound coil o~- a triple wound coil made of tungsten and heating it in an exhausting process.
A life test of the 40 W fluorescent lamp is carried out.
5 The starting voltage at O~C is 160 V and the lumen maintenance after 3000 hours of operation is 85~10.
The examples of the present invention will be illustrated.
Each 40 W fluorescent lamp equipped with electrodes coated with an electron emission material consisting of La2O3 and 10 YzO3 at each ratio shown in Table 4 is prepared and the life test is carried out as set forth in Reference. The results are shown in Table 4 Table 4 Lumen Composition of electron maintenance emission material (mol %) after 3000 hours _ _ Exp. 4-1 ¦ Y2O3(93 mol %) - La2O3(7 mol %) 85 Exp. 4-2 Y2O3(90 mol %) - La2O3(10 mol %) 87 _ _ Exp. 4-3 Y2O3(75 mol %) - La2O3(25 mol ~0) 95 _ _ Exp. 4-4 Y2C)3~10 mol %) - La2O3(90 mol %) 89 _ _ Z0 Exp. 4-5 Y2O3(7 mol %) - La2O3(93 mol %) 85 .
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W.E. 48,9~2 .P~S I~L ~S shGl,~n }n T~ble 4, the lumen maintenance of the fluorescent lamps using the electron emission material comprising 10 to 90 mol % of La203 and 90 to 10 mol % of Y203 are remarkably superior to that of the electron emission material comprising ZrO2 The reason of the different characteristics is considered as f ollow ~ .
In the conventional electron emission material, ZrOz prevents a reaction of BaO with tungsten of the electrode substrate to control the formation of Ba whereby a sputtering of Ba in the arc space can be decreased, however this is not enough and E3a is gradually deposited at the end of the tube during the life of the lamp so as to cause coloring.
On the contrary, in the electron emission material of the present invention, Laz03 and Y203 are used instead of Ba component.
Both Laz03 and YzO3 have heat resistance and good characteristics of emission. When both Laz03 and YzO3 are combined, a mixed crystal or a complex compound is formed to improve the electron emitting characteristic. As a result, the combination of Laz03 and Y203 imparts the electron emitting characateristic substantially the same zo as that o$ the conventional one even though an alkaline earth metal oxide such as BaO is not incorporated. Therefore, the starting voltage of the fluorescent lamp using said combination is not inferior to that of the conventional fluorescent lamp using the known electron emission material.
The combination of La203 and Y203 performs the electron emission as the electron emission of a semiconductor without sputtering the metal element in the arc space in the operation as that ot the conventional one ::
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W.E. 48, 922 ~3 Therefore, the coloring at l~e end OI ~ne tube is not caused.
As described above, it is preferable to combine 10 to 90 mol % of La~03 and 90 to 10 mol % of Y203, since a desired improve-ment of the electron emitting characteristic of the combination of 5 La2O3 and Y2O3 is not found out of the range In the examples, the electron emission material consisting of La2O3 and YzO3 has been used.
The effect of the present invention can be attained even though a small amount of A12O3J SiO2, ZrO2 or tungsten is included 10 in said electron emission material.
In the examples, the oxides have been shown as the electron emission material. Thus, the effect of the present invention can be attained by using a compound which is thermally convertible to the oxide such as a carbonate and heating it to convert it into the oxide.
In accordance with this embodiment, the electron. emission material consisting of lanthanum oxide and yttrium oxide is used to obtain a fIuorescent lamp having less black coloring at the end of the tube, The other embodiment of the present invention will be 20 illustrated The reference is the same as the above-mentioned :R eference . La2 03 and Y2 03 are combined with barium - strontium .
calcium tungstate (Bal 8SrO 2CaWO6) at various ratios as the electron emission material.
Each 40 W fluorescent lamp equipped with electrodes coated 25 with each of the electron emission materials shown in Table 5 is prepared and the life test set forth in the above-mentioned embodiment is carried out. The results are shown in Table 5 .
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W.E . 4~, 922 able 5 ~a23 Total of Composition of electron Y O La203 and emission material (mol %) 2 3 Y O
Bal 8SrO 2CaW6 La23 ¦ Y203 ratio) Exp, 5-1 90 O- 8 ¦ 9~ 2 1: 12 1 10 Exp, 5-2 90 1. 0 ¦ 9. 0 1 : 9 ¦ 10 Exp. 5-3 90 2-5 1 7-b 1 3 1 10 .
Exp. 5-4 90 9. O 1. O 9 : l 10 Exp. 5-5 90 9. 5 O, 519: 1 10 Exp. 5-6 90 9. 6 0.424: 1 10 Exp. 5-799, 4 O, 15 O. 451: 3 O, 6 Exp. 5-899. 0 0. 25 O. 75 1 : 3 Exp. S-9~70. 0 7. 5 22. 5 1 : 3 ¦ 30 _ . I
Exp. 5- lC65. 0 8. 8 26.2 1 : 3 ¦ 35 .
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, ~3~ W.E:. 48,922 T~ble 5 ~continued) ____ _ _ j Starting voltage ¦ Lumen maintenance after ¦
i at 0C (V) _ l 3000 hours of operation(lo) Exp, 5- 1 i 16~l ¦ 85 Exp. 5-2 ¦ 155 ¦ 87 Exp. 5-3 ¦ 150 ¦ 95 Exp. 5-4 ¦ 150 ¦ 90 Exp. 5-5 ¦ 155 85 Exp. 5- 6 160 85 Exp. 5-7 160 72 Exp. 5-8 ¦ 155 87 Exp. 5-9 ¦ 155 ¦ 85 _ i: Exp. 5-10 j 170 70 ~ .
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~i.E. 48,9~2 As ~i ~s sh~rn i~ Table 5, when the electron emission material compri~in~ Bal ~3Sr~ 2CaWO6 and La703 and Y203 at a molar ratio of ~az~3 Y2O3 of 19 1 to 1: 9 and 1 to 30 mol % of a content of La2O3 and Y2O3 are used, the starting voltages are 5 lower and the lumen maintenance are improved in comparison with those of the conventional electron emission material.
The reason of these characteristics is considered as follows .
In the conventional electron emission material, ZrO2 10 prevents a reaction of BaO with tungsten of the electrode substrate to control the formation of Ba whereby a sputtering of Ba in the arc space can be decreased, however, the work function of the electron emission material is increased to cause higher starting voltage of the fluorescent lamp.
con~a~
On the ~, in the electron emission material of the present invention, both La2O3 and Y2O3 are used. Both La2O3 and YzO3 have heat resistance and a good characteristic of electron emission When both La2O3 and Y2O3 are combined a mixed crystal or a complex compound is formed to improve the electron emitting 20 characteristic ~s a result of the combination of La2O3-Y2O3 with Bal gSr0 2CaWO6, the electron emitting characteristic of Bal 8Sr0 2CaWO6 is further improved by the addition of LazO3-Y2O3.
Therefore, the starting voltage of the fluorescent lamp may be lowered and the lumen deterioration may be decreased.
;9~
W .E . 48, 922 As desc~ibed above, it is preferable to combine La2O3 and Y2O3 in a range of a molar ratio of 19: 1 to 1: 9 since a desired iml?rovement of the electron emitting characteristic of the combination of La2O3 and Y2O3 is not found out of the range, It is preferable to use 1 to 30 mol % of the total of La2O3 ancl Y2O3. When the total is less than 1 mol %, the effect of La2O3-Y2O3 for improving the electron emitting characteristic is not high enough and the starting voltage of the fluorescent lamp is high. When it is more than 30 mol '~0, a content of Bal 8SrO 2CaWO6 as the source of Ba is relatively small and the electron emission is not enough and a black coloring at the end of the tube is caused.
In the examples, Ba1 8SrO 2CaWO6 has been used as the barium- strontium- calcium tungstate. The effect of the present invention can be attained by using the other tungstate having the formula Ba2 xSrxcaw6 (x is 0 to 0- 5)-The effect of the present invention can be attained even though a small amount of A12O3, SiO2, ZrO2 or tungsten is included in the said electron emission material.
In the examples, the tungstate and lanthanum oxide and yttrium oxide have been shown as the electron emission material.
Thus, the effect of the present invention can be attained by using a compound which can be converted into said compound such as a I mixture of barium carbonate, strontium carbonate and calcium - 25 carbonate with tungsten oxide and La2O3 and Y2O3 and heating it to convert it into the above-mentioned electron emission material.
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~ :' W.E . 48, 922
FIELD OF THE INVENTION
. . _ The present invention relates to an electrode used in high pressure metal vapor discharge lamps such as a high pressure 5 mercury vapor discharge lamp in which mercury and a rare gas are filled; a high pressure sodium vapor discharge lamp in which mercury, a rare gas and sodium are filled; a metal vapor discharge lamp in which mercury, a rare gas and a metal halide are filled or low pres-sure discharge lamps such as a fluorescent lamp. More particularly, 10 it relates to an improvement of an electron emission material on the electrode.
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DESCRIPTION OF THE PRIOR ARTS:
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In a high pressure metal vapor discharge lamp such as a high pressure mercury vapor discharge lamp, a mixture of barium, strontium, calcium tungstate (Ba2 xSrxCaWO6 x is 0 to 0. 5), beryllium oxide (BeO) and yttrium oxide (YzO3) has been used as an electron emission material coated on the electrode. In the electron :
emission material, a solid solution of BeO and Y2O3 is formed whereby a lumen maintenance and a starting characteristic are advantageously 20 excellent and stable during a long time operation~of the lamps.
However, BeO contained in the electron emission material is toxic to human body and the handling of the electron emission material should be carefully considered and the improvement of productivity is disadvantageously prevented.
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W.E. 48,922 Moreover, in a high pres~alre }netal vapor discharge lamp using the electron emission material, a phenomenon of the formation of black deposit is often found in the initial period, The black deposit is gradually changed to be white during the operation and it does not affect to the life characteristic of the lamp. However, it causes slightly low luminous flux value in the initial lightening period, In a metal halide lamp, a rare earth metal oxide has been usually used as the electron emission material. Yttrium oxide is ~, especially effective since it has excellent electron emitting character-. 10 istic, However, yttrium oxide has high melting point whereby the adhesion of the component on the electrode substrate is not satisfactori-ly attained to peel off the electron emission material during the operation of the discharge lamp. This causes deterioration of the ` activity of electron emission and the black coloring of the arc tube of ;~ . 15 the lamp is formed to cause a short life.
In a fluorescent lamp, an electron emission material of a mixture of barium, strontium, calcium carbonate and zirconium oxide is coated on a coil made of tungsten and the carbonate is thermally decomposed into oxides such as barium oxide in the step of preparing electrodes of ~ fluorescent lamp, The conventional electron emission material is reduced by tungsten as the electrode substrate during the operation of the discharge lamp and barium oxide (BaO) is converted into barium metal (Ba) by the following reaction.
6BaO + W ~ Ba3WO6 ~ 3Ba, ' W . E~ 8, 922 The barium metal contributes to the electron emission from the electrode, however, a part of the barium metal is sputtered in the arc space and is ad1lered on the inner wall of the arc tube. A black coloring may be cA~sed at the en~l of the arc tube when the quantity of the barium 5 metal is much. Zirconium oxide is incorporated to decrease the reduction by the electrode subs~raie and to decrease the sputtering of the barium metal. The end blacking of the tube can be decreased by the incorporation of zirconium oxide, however, it may cause deterio-ration of the activity of electron emission of the electrode. When such 10 electrode is used in the fluorescent lamp, the starting voltage is disadvantageously high.
SUMMARY OF THE INVENTION:
:, It is an object of the present invention to overcome the ` ~ disadvantages of the conventional electrode and to provide an electrode 15 in which an adhesion of an electron emission material on an electrode substrate is remarkably improved and which has excellent electron emitting activity to result less luminous flux deterioration in a metal vapor discharge lamp. The foregoing and other objects of the present invention have been attained by using an electron emission material 20 comprising yttrium oxide and lanthanum oxide.
The other object of the present invention is to provide an electrode of a discharge lamp in which a starting voltage of the discharge lamp is lowered and an arc tube end blacking is decreased.
This is attained by using an electron emission material comprising 25 yttrium oxide and lanthanum oxide.
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W.E. 48,922 ~he other object o~ the present invention is to provide an electrode of a dischargSe larnp by which an initial deterioration of luminous flu~ is decreased and which does not contain toxic BeO so as to elimillate a special handlil1g operation and to attain a normal operation and to improve its productivity. This is attained by using an electron emission material comprising yttrium oxide and lanthanum - o~ide.
BRIEF DESCRIPTION OF THE DRAWINGS:
-Figure 1 is a front view for showing a structure of a metal vapor discharge lamp; and Figures 2, 3 and 4 are respectively sectional views of various structures of the electrode of the metal vapor discharge lamp.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The electrode of the metal vapor discharge lamp of the ` 15 present invention will be illustrated.
The rnetal vapor discharge lamp has the structure shown in Figure 1 wherein the reference numeral (1) designates an arc tube made of a transparent quartz glass in which mercury, a rare gas and a metal halide are filled and (2a) and (2b) designate electrodes which are placed at both ends of the arc tube to face each other and are respectively connected through each molybdenum foil (3a), (3b) sealed at each end of the arc tube (1) to each lead wire (4a), (4b);
and (5) and (5) designate heat reserve layers coated at each end of the arc tube (1); (6) and (~) designate supporting plates which are , ' . ~ .
W,E . ~8, 9~2 placed at each end of the arc tube (1) and welded on each frame (9), (10) so as to hold the arc tube (1) in an outer tube (14); and (7) desig-nates a ribbon lead wire which connects the lead wire (4a) to the frame (9); (11) designates a stem lead which is welded to the frame (9); (12) designates the other stem lead; (8) designate an arch shaped wire for connecting the lead wire (4b) to the stem lead (12); and (13) designates a base which is placed at one edge of the outer tube and is connected to the stem leads (11), (12).
As shown in Figure 2, each of the electrodes (2a), (2b) comprises an electrode core (15) made of a heat resistant metal such as tungsten and an inner coil (16) and an outer coil (17) which are wound on the electrode core; and an electron emission material (18) which is formed by coating on the inner coil (16) and the outer coil (17) and sintering it at high temperature.
The present invention will be illustrated by certain examples and references as the comparison.
A conventional embodiment will be illustrated.
A tungsten rod having a diameter of 0. 9 mm is used as , the electrode core (15) and a tungsten wire having a diameter of 0. 5 mm is used as the inner coil (16) and the outer coil (17) so as to form the electrode substrate.
An electron emission material of only yttrium oxide is admixed with nitrocellulose lacquer and butyl acetate and the mixture is milled in a ball mill for 24 hours to prepare a suspension.
The electrode substrate is dipped into the suspension to coat the electron emission material on the inner coil (16) and the outer coil (17) and this is dried and sintered in an argon atmosphere at 1800C
for 2 minutes so as to bond the electron emission material (18) on the electrode substrate.
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W.E. 4g,92~
The electrodes ~2a~J ~2~ coated with the electron emission material (18) are used for preparing a 400 W metal vapor discharged lamp equipped with the arc tube (1) having an inner diameter of 18 mm and a gap between the electrodes (2a), (2b) of 44 mm in which suitable 5 quantities of mercury, argon gas, scandium iodide and sodium iodide are filled. The life test of the 400 W metal vapor discharge lamp is carried out. The lumen maintenance was 50% after 9000 hours of operation Examples of the present invention will be illustrated.
Lanthanum oxide is mixed with yttrium oxide at various ratios to form the electron emission material (18). The electrodes (2a), (2b) are prepared by coating the electron emission material on the electrode substrate. Various 400 W metal vapor discharge lamps are prepared by using the electrodes and the life tests are carried out 15 as set forth in said reference. The results of the life tests are shown in Table 1.
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~1.E. 48,922 Ta~le I
Lumen mainte-. Composition of electron nance after emission material 9000 hours of (mol %) (3peration Ref, Y2O3 (100 mol ~o) 50 Exp. 1-1 Y203(99. 7 rnol %) - La203(0. 3 mol %) 55 _ Exp. 1-2 Y2O3(99. 5 mol %) - La2O3(0. 5 mol %) 60 , _ Exp, 1-3 Y2O3(90 mol %) - La2O3(10 mol %) 68 Exp- 1-4¦ Y2O3(80 mol ~o) - La2O3(20 mol %) 75 : Exp. 1-5 Y2O3(40 mol %) La2O3(60 mol %) 65 Exp. 1-6 Y2O3(20 mol %) - La2O3(80 mol ~0) 61 Exp. 1-7 Y2O3(17 mol %) - La2O3(83 mol %) 56 .
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~J.E. 48, 922 As it is sho~sln in Table 1, the lumen maintenance of the metal ~apor ~ise~ar~ ~mps using the electron ernission material shown in Examples are remarka~3y superior to that of the metal vapor discharge lamp using only yttrium oxide as the electron emission material (18).
The reason why the lumen maintenance of Examples are superior to that of Reference is considered as follows.
~ttrium oxide has a high melting point. When it is sintered after coating on the electrode substrate, the adhesion of yttrium oxide as the electron emission material (18) on the electrode substrate is not high enough and the electron emission material (18) is peeled off from the electrode substrate during the operation of the discharge lamp. When the electron emission material of only ytttrium oxide is used as the conventional case, the luminous flux is reduced for a long lS time operation. However, when the electron emission material (18) of a mixture of yttrium oxide and lanthanum oxide is used as Examples, the mixture forms a solid solution or a complex compound of yttrium oxide and lanthanum oxide to decrease a melting point. Thus, the ~` electron emission material is highly spread on the electrode substrateto improve the adhesion and accordingly, the peeling-off of the electron emission material in the discharge lamp is decreased whereby the excellent electron emitting activity of yttrium oxide is maintained for a long time to provide a discharge lamp having less luminous flux ~; deterioration.
Moreover, as shown in Table 1, the optimum result is attained by using a mixture incorporating 0. 5 to 80 mol ~0 of lanthanum ~` oxide. When a content of lanthanum oxide is less than 0. 5 mol %, the - effect of lowering of a melting point is too small to adhere it on the electrode substrate and the lumen maintenance is less than 60% to be ., '`
' . ' , W.E. 48,922 small effect f~r imp.7~0ving t~e lumen mairltenance When it is more than 80 mol %, a content of yttrium oxide coated on the electrodes (2a)J (2b) is relatively smaller so as to decrease the electron emitting activity Therefore, the effect for improving the lumen maintenance is disadvantageously small In the examples, yttrium oxide has been used as the electron emission material. Thus, it is possible to incorporate a small amount of tungsten and/or molybdenum powder into the mixture.
In the examples, the structure of the electrode shown in Figure 2 has been used. The structure of the electrode is not limited to said feature and can be the other features, for example, the electrode shown in Figure 3 wherein the inner coil (16) is wound on the electrode core (15) so as to remain rough wound parts and the ~ outer coil (17) is wound on the inner coil to form the electrode sub-; 15 strate and the electron emission material (18) is filled in the space ; ~ in the electrode substrate; or the electrode shown in Figure 4 whereinonly inner coil (16) is wound on the electrode core (15) to form the ~' electrode substrate and the electron emission material (18) is coated on the electrode substrate The present invention can be applied for various kinds of the structures of the electrodes `~ In the examples, scandium iodide and sodium iodide have .
been filled in the arc tube of the metal vapor discharge lamp.
ThusJ it is possible to apply the present invention for the metal vapor discharge lamps in which the other halide such as dysprosium iodideJ
; 25 thallium iodide and indium iodide is filled.
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' W.E. 4~,922 1~ ~c~ 3rda~e with the above-mentioned embodiment, the electrodes prep~re~ by using the electron emission material consist-ing of yttrium oxide and lanthanum oxide are used in the metal vapor discharge lamp containing the metal halide in the arc tube.
Therefore, the adhesion of the electron emission material on the electrode substrate is remarl~ably superior and the electron emitting acti~ity is highly maintained for its long life and the luminous flux deterioration is small and a life of the lamp is long.
The other embodiment of the electrode of a high pressure mercury vapor discharge lamp will be illustrated.
Certain examples and a reference of the embodiment will be illustrated, In Reference, a tungsten rod having a diameter of 1, 2 mm is used as the electrode core (15) and a tungsten wire having a diameter of 0. 6 mm is used as the inner coil (16) and the outer coil (17) so as to form the electrode substrate An electron emission material (18) of a mixture of 15. 2 mol % of barium- strontium calcium tungstate (Ba1 8Sr0 2CaWO6), 76. 3 mo] % of beryllium oxide (BeO) and 8, 5 mol % of yttrium oxide (Y2O3) is admixed with nitrocellulose lacquer and butyl acetate and the mixture is milled in a ball mill for 24 hours to prepare a suspen-sion. The electrode substrate is dipped into the suspension to coat the electron emission material on the electrode substrate and this is dried and sintered in an argon atmosphere at 1700C for 2 minutes so as to bond the electron emission material (18) on the electrode substrate, The electrodes (2a), (2b) coated with the electron emission material (18) are used for preparing a d~00 W high pressure mercury vapor discharge lamp equipped with the arc tube (1) having an inner ',' . , ~
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W.E . 48, 922 diameter of 7 8 mm and an arc length of 71~ mm in which suitable quantities of mercury and argon gas for starting are filled, The lamps are.burned on a cycle of 15 minutes On and 15 minutes Off and lumen maintenace after 50 times and after 600 times are measured.
5 The lumen maintenace is 86% after 50 times. ~ black deposition is found on the inner wall of the arc tube in the lamp. Beryllium and barium components are found by an analysis of the black deposition.
The lumen maintenance is 70% after 6000 times.
Examples of the present invention will be illustrated.
10 Lanthanum oxide (La2O3) and yttrium oxide (Y2O3) are mixed with barium, strontium and calcium tungstate (Bal 8Sr0 zCaWO6) at various ratios to form each electron emission material (18).
The electrodes (2a), (2b) are prepared by coating the electron emission material on the electrode substrate. Various ~00 W high pressure 15 mercury vapor discharge lamps are prepared by using the electrodes and the life tests are carried out as set forth in said reference.
The results of the life tests are shown in Table 2.
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W.E . l~8, 922 Table 2 Composition of electron e~-nission ma terial tmol (to) 2 3 2 3 Bal 8Sr0 2CaW6 La2O3 ¦ Y2O3 ¦ BeO (molar ratio) Ref, 15.2 - I 8.5 176.3 Exp . 2- 1 1 5 . 2 4 ~T 80 . O _ 1 : 1 7 Exp. 2-2 15. 2 8. 5 76. 3 _ 1: 9 Exp 2-3 ¦ 15. 2 21. 2 63. 6 _ 1: 3 Exp 2-4 ¦ 15. 2 70. 7 14. 1 _ 5: 1 33xp. 2 5 1 15. 2 ~ 4. 2 1 _ 19: 1 Exp. 2-6 ¦ 15.2 1 81.4 ¦ 3~4 ¦ ~ 24: 1 ¦ Lumen m~intenar ~ce (%) I after 50 times after 6000 times :~ l Ref. 1 86. 0 70. 0 Exp. 2-1 ¦ 91. 0 65. 0 Exp. 2-2 ¦ 95. 0 76. 0 Exp . 2- 3 9 8 . 0 80 . 0 Exp, 2-4 9 6 . 0 7 8 . 0 Exp, 2-5 93. 0 74. 0 Exp. 2-6 90. 0 64. 0 ''~
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W.E. 48,922 ~s it is shown in Table 2, the lumen maintenace (after 50 times) of the lamps using the electron emission material (18) compris-ing La2O3 and Y2O3 and Bal 8Sr0 2CaWO6 are superior to that of the conventional electron emission material including BeO and YzO3.
When the molar ratio of La2O: Y2O3 is in a range of 19 1 to 1: 9, the lun~en main-tenance after 6000 times is superior to that of the conventional one, ` The reason of these characteristics is considered as follows .
In the conventional electron emission n^~aterial (18), a solid solution is formed by BeO and Y2O3 so as to improve the adhesion in the electrode substrate and a formation of an active barium component in operation is kept in a desired rate, However, the electron emission material (18) is coated on the electrode substrate and dried and bonded ` 15 on it by sintering it at high temperature BeO in the solid solution partially reacts with the tungstate in the electron emission material (18) to form a complex compounds having relatively low melting point such as BeO- 3BaO. When an arc spot is shifted to the position forming the complex compounds on the electrode, the complex compounds are suddenly heated to high temperature so as to selectively vaporize Be and Ba to adhere them on the inner wall of the arc tube.
Therefore, the deterioration of the luminous flux in the initial stage of operation is caused On the other hand, when the electron emission material (18) including La2O3 and YzO3 is used, a solid solution or a stable complex compound is formed by La2O3 and Y2O3. Moreover, La2O3 and Y2O3 are not reactive to the tungstate. Therefore, the formation `~ of the active barium from the electron emission material (18) is kept at a desired rate in a stable condition during the mitial and the long time of operation and the lumen maintenance is stable during the life.
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W.E . 48, 922 lh As described above, when the molar ratio of La2O3 to Y2O3 is in a range of 19: 1 to 1: 9, the above-mentioned effect is remarkable. When the molar ratio of La2O3 to Y2O3 is greater than 19: 1, the melting point of the solid solution is too high and the adhesion of the electron emission material (18) to the electrode substrate is deteriorated and the lumen maintenance after 6000 times is slightly lower than that of the conventional one as shown in Table 2.
When the molar ratio of La2O3 to Y2O3 is less than 1: 9, the melting point of the solid solution is too high and the adhesion of the electron emission material (18) to the electrode substrate is deteriorated and the lumen maintenance after 6000 times is lower.
In said examples, the effects of the present invention have been shown in the cases that the mol % of the barium- strontium-calcium tungstate is the same as that of the conventional one.
Thus, the similar effect can be attained even though the mol % of the tungstate is different.
The effect of the present invention can be attained even though a small amount of ~12O3, SiO2 or tungsten is included into siad electron emission material (18) of the present invention.
In the examples, the structure of the electrode shown in , Figure 2 has been used. The structure of the electrode can be the other features, for example~ the electrode shown in Figure 3 wherein the inner coil (16) is wound on the electrode core (15) so as to remain rough wound parts and the outer coil (17) is wound on the inner coil to form the electrode substrate and the electron emission material (18) is filled in the space in the electrode substrate to be sintered.
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W.E. 48,922 1~
E~ ac~ord~ e ~Ti~ t~e foll~ring er~bodiment, the electron emission m~L~erial of ~ mixture of barium oxide, calcium oxide, lanthanum oxide and yttrium oxide is used to improve the luminous flux deterioration in the initial period of operation and to improve the productivity of the discharge lamp since a toxic beryllium oxide is not used.
The embs~diment of an electrode of a high pressure mercury vapor discharge lamp will be illustrated.
Certain examples and a reference of the embodiment will be illustrated.
In Reference, a tungsten rod having a diameter of 1. 2 mm is used as the electrode core (15) and a tungsten were having a diameter of 0. 6 mm is used as the inner coil (16) and the outer coil ` (17) so as to form the electrode substrate.
An electron emission material (18) of a mixture of 42. 3 mol % of BaO, 16. 5 mol '~/c of CaO, 37. 1 mol % of !3eO and 4 1 mol % of Y2O3 is admixed with nitrocellulose lacquer and butyl acetate and the mixture is milled in a ball mill for 24 hours to prepare a suspen-sion. The electrode substrate is dipped into the suspension to coat the electron emission material on the electrode substrate and this is dried and sintered in an argon atmosphere at 1700C for 2 minutes so as to bond the electron emission material (18) on the electrode substrate .
The electrodes (2a), (2b) coated with the electron emission material (18) are used for preparing a 400 W high pressure mercury vapor discharge lamp equipped with the arc tube (1) having an inner diameter of 18 mm and an arc length of 70 mm in which suitable quantities of the mercury and argon gas for starting are filled.
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, ~!.E. 48,922 The life tests are carried out as set forth in said reference and the lumen maintenance after 50 times ar~d ~0~0 times are measured.
The lumen maintenance is 85% after 50 times. A black deposition is found on the inner wall of the arc tube in the lamp.
5 13eryllium and barium components are found by an analysis of the black ~leposltion The lumen maintenance is 62% after 6000 times.
Examples of the present invention will be illustrated.
Barium oxide (BaO), calcium oxide (CaO) as alkaline earth metal oxides and lanthanum oxide (La2O3) and yttrium oxide (Y2O3) 10 are mixed at various ratios to form each electron emission material (18). The electrodes (2a), (2b) are prepared by coating the electron emission material on the electrode substrate. Various 400 W high pressure mercury vapor discharge lamps are prepared by using the electrodes and life tests are carried out as set forth in said reference.
i~ 15 The results of the life tests are shown in Table 3 - , , , . ~ .... : -.
.
, W.E. 48,922 Table 3 Composition of electron emission material (mol %) La2O3 Y2O
BaO ¦ CaOJ La23 Y2O3 BëO (molar ratio) Ref, 42, 3¦ 16, 5 ~ 4, 1 37, 1 _ Exp, 3-1 42, 316, 5 3, 238, 0 _ 1: 12 _ _ _ _ Exp, 3-2 42, 316, 5 4,237, 0 _ 1: 9 Exp, 3 - 3 42,316. 5 10. 330.9 1 : 3 Exp, 3-4 42, 316. 5 ¦36,05. Z _ 7: 1 Exp. 3-5 42. 316, 5 ¦39, 12, 1 ¦ - 19: 1 Exp. 3-6 42, 316, 5 139, 41, 8 1 - 22: 1 .
Lumen maintenance (%) ., after 50 times ¦ after 6000 time~s _ I` Ref, 85, 0 62,0 . ~ _ Exp, 3- 1 90,0 58, 0 Exp, 3-2 93,0 69,0 _ Exp. 3-3 97,0 73.0 Exp, 3-4 95,0 1 70, 0 _ Exp. 3-5 92,0 67.0 Exp, 3- 6 89, 0 56, 0 ~: -;`
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.
1JJ.E. 48,922 1~
As it is shown in Table 3, the lumen maintenance (after 50 times) of the lamps using the electron emission material (18) including La2O3 and Y203 are superior to that of the conventional electron emission material including BeO and Y2O3. When the molar ratio of La2O3: Y2O3 is in a range of 19: 1 to 1: 9 the lumen maintenance after 6000 tirrles is superior to that of the conventional one.
The reason of these characteristics is considered as follows.
In the conventional electron emission material (18), a solid solution is formed by BeO and Y2O3 so as to improve the adhesion in the electrode substrate and a formation of an active barium component in operation is kept in a desired rate. ~owever, the electron emission material (18) is coated on the electrode substrate and dried and bonded on it by sintering it at high temperature. BeO in the solid solution par-tially reacts with BaO in the electron emission ma-terial (18) to form a complex compounds having relatively low melting point such as BeO- 3BaO. When an arc spot is shifted to the position forming the complex compounds on the electrode, the complex compounds are suddenly heated to high temperature so as to selectively vaporize Be and Ba to adhere them on the inner wall of the arc tube Therefore, the deterioration of the luminous flux in the initial stage of operation is caused.
On the other hand, when the electron emission material (18) including La2O3 and Y2O3 is used, a solid solution or a stable complex compound is formed by La2O3 and Y2O3. Moreover, La2O3 and Y2O3 are not reactive to BaO. Therefore, the formation of the active barium from the electron emission material (18) is kept at a desired rate in a stable condition during the initial and the long time of operation and the lumen maintenance is stable during the life.
~ ' ,~
W .E . 48, 922 As descrihed abo~eJ when the molar ratio of La203 to YzO3 is in a range of 19: 1 to 1: 9, the above-mentioned effect is remarkable. When the molar ratio of La2O3 to YzO3 is greater than 19: 1, the melting point of -the solid solution is too high and the 5 adhesion of the electron emission material (18) to the electrode substrate is deteriorated and the lumen maintenance after 6000 times is slightly lol,~rer than that of the conventional one as shown in Table 3.
When the molar ratio of La2O3 to Y2O3 is less than 1: 9, the melting point of the solid solution is too high and the adhesion of the 10 electron emission material (18) to the electrode substrate is deteriorated and the lumen maintenance after 6000 times is lower.
In said examples, the effects of the present invention have been shown in the cases that the mol % of BaO and CaO is the same as that of the conventional one. Thus, the similar effect can be 15 attained even though the mol % of BaO or CaO is different.
The cases incorporating BaO and CaO as the alkaline earth metal oxide have been shown. In this embodiment, it is enough to contain at least BaO as the alkaline earth metal oxide. That is, the alkaline earth metal oxide can be only BaO or a combination of BaO
zo and SrO or a combination of BaO, CaO and SrO.
The effect of the present invention can be attained even though a small amount of Alz03, SiO2 or tungsten is included into said electron emission material (18) of the present invention.
.
.~
W.E. 48,92 ln the examples, the structure of the electrode shown in Figure 2 has been used. The structllre of the electrode can be the other feature shown in Figure 3 wherein the inner coil (16) is wound on the electrode core (15) so as to remain rough wound parts and the outer coil (17) is wound on the inner coil to form the electrode substrate and the electron emission material (18) is filled in the - space in the electrode substrate to be sintered.
The oxides have been incorporated in the electron emission material (18) in said embodiment. Thus, it is possible to use carbonates or oxalates and to convert them into oxides by sintering them after coating the electron emission material on the electrode substrate.
In accordance with the above-mentioned embodiment, the electron emission material comprising the alkaline earth metal oxide including at least BaO and La2O3 and Y2O3 is used, to improve the luminous flux deterioration in the initial period and to improve the productivity of the discharge lamp since a toxic beryllium oxide is not used.
The embodiment of an electrode of a fluorescent lamp will be illustrated.
Certain examples and a reference of the embodiment will be illustrated.
In Reference, a 40 W fluorescent lamp equipped with electrodes coated with an electron emission material consisting of "~ 25 40 mol % of BaO, 30 mol % of SrO, 26 mol % of CaO and 4 mol % of Zr2 is prepared, ~- The electrode is prepared by mixing zirconium oxide with barium carbonate, strontium carbonate and calcium carbonate and admixing the mixture with nitrocellulose lacquer and butyl acetate ~ .
-~
.~ ~ . :
- ,.
-.
W.E. 48,922 in a ball mill to prepare a suspensio~ and coating the suspension on adouble wound coil o~- a triple wound coil made of tungsten and heating it in an exhausting process.
A life test of the 40 W fluorescent lamp is carried out.
5 The starting voltage at O~C is 160 V and the lumen maintenance after 3000 hours of operation is 85~10.
The examples of the present invention will be illustrated.
Each 40 W fluorescent lamp equipped with electrodes coated with an electron emission material consisting of La2O3 and 10 YzO3 at each ratio shown in Table 4 is prepared and the life test is carried out as set forth in Reference. The results are shown in Table 4 Table 4 Lumen Composition of electron maintenance emission material (mol %) after 3000 hours _ _ Exp. 4-1 ¦ Y2O3(93 mol %) - La2O3(7 mol %) 85 Exp. 4-2 Y2O3(90 mol %) - La2O3(10 mol %) 87 _ _ Exp. 4-3 Y2O3(75 mol %) - La2O3(25 mol ~0) 95 _ _ Exp. 4-4 Y2C)3~10 mol %) - La2O3(90 mol %) 89 _ _ Z0 Exp. 4-5 Y2O3(7 mol %) - La2O3(93 mol %) 85 .
' .
.;
.
:
.
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.
: ' :
W.E. 48,9~2 .P~S I~L ~S shGl,~n }n T~ble 4, the lumen maintenance of the fluorescent lamps using the electron emission material comprising 10 to 90 mol % of La203 and 90 to 10 mol % of Y203 are remarkably superior to that of the electron emission material comprising ZrO2 The reason of the different characteristics is considered as f ollow ~ .
In the conventional electron emission material, ZrOz prevents a reaction of BaO with tungsten of the electrode substrate to control the formation of Ba whereby a sputtering of Ba in the arc space can be decreased, however this is not enough and E3a is gradually deposited at the end of the tube during the life of the lamp so as to cause coloring.
On the contrary, in the electron emission material of the present invention, Laz03 and Y203 are used instead of Ba component.
Both Laz03 and YzO3 have heat resistance and good characteristics of emission. When both Laz03 and YzO3 are combined, a mixed crystal or a complex compound is formed to improve the electron emitting characteristic. As a result, the combination of Laz03 and Y203 imparts the electron emitting characateristic substantially the same zo as that o$ the conventional one even though an alkaline earth metal oxide such as BaO is not incorporated. Therefore, the starting voltage of the fluorescent lamp using said combination is not inferior to that of the conventional fluorescent lamp using the known electron emission material.
The combination of La203 and Y203 performs the electron emission as the electron emission of a semiconductor without sputtering the metal element in the arc space in the operation as that ot the conventional one ::
`
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', ' ~ ~9'~
W.E. 48, 922 ~3 Therefore, the coloring at l~e end OI ~ne tube is not caused.
As described above, it is preferable to combine 10 to 90 mol % of La~03 and 90 to 10 mol % of Y203, since a desired improve-ment of the electron emitting characteristic of the combination of 5 La2O3 and Y2O3 is not found out of the range In the examples, the electron emission material consisting of La2O3 and YzO3 has been used.
The effect of the present invention can be attained even though a small amount of A12O3J SiO2, ZrO2 or tungsten is included 10 in said electron emission material.
In the examples, the oxides have been shown as the electron emission material. Thus, the effect of the present invention can be attained by using a compound which is thermally convertible to the oxide such as a carbonate and heating it to convert it into the oxide.
In accordance with this embodiment, the electron. emission material consisting of lanthanum oxide and yttrium oxide is used to obtain a fIuorescent lamp having less black coloring at the end of the tube, The other embodiment of the present invention will be 20 illustrated The reference is the same as the above-mentioned :R eference . La2 03 and Y2 03 are combined with barium - strontium .
calcium tungstate (Bal 8SrO 2CaWO6) at various ratios as the electron emission material.
Each 40 W fluorescent lamp equipped with electrodes coated 25 with each of the electron emission materials shown in Table 5 is prepared and the life test set forth in the above-mentioned embodiment is carried out. The results are shown in Table 5 .
- :, .~ ~
. ,~ . . . . . . . . . .
W.E . 4~, 922 able 5 ~a23 Total of Composition of electron Y O La203 and emission material (mol %) 2 3 Y O
Bal 8SrO 2CaW6 La23 ¦ Y203 ratio) Exp, 5-1 90 O- 8 ¦ 9~ 2 1: 12 1 10 Exp, 5-2 90 1. 0 ¦ 9. 0 1 : 9 ¦ 10 Exp. 5-3 90 2-5 1 7-b 1 3 1 10 .
Exp. 5-4 90 9. O 1. O 9 : l 10 Exp. 5-5 90 9. 5 O, 519: 1 10 Exp. 5-6 90 9. 6 0.424: 1 10 Exp. 5-799, 4 O, 15 O. 451: 3 O, 6 Exp. 5-899. 0 0. 25 O. 75 1 : 3 Exp. S-9~70. 0 7. 5 22. 5 1 : 3 ¦ 30 _ . I
Exp. 5- lC65. 0 8. 8 26.2 1 : 3 ¦ 35 .
.
,~ ' ;~ :
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, ~3~ W.E:. 48,922 T~ble 5 ~continued) ____ _ _ j Starting voltage ¦ Lumen maintenance after ¦
i at 0C (V) _ l 3000 hours of operation(lo) Exp, 5- 1 i 16~l ¦ 85 Exp. 5-2 ¦ 155 ¦ 87 Exp. 5-3 ¦ 150 ¦ 95 Exp. 5-4 ¦ 150 ¦ 90 Exp. 5-5 ¦ 155 85 Exp. 5- 6 160 85 Exp. 5-7 160 72 Exp. 5-8 ¦ 155 87 Exp. 5-9 ¦ 155 ¦ 85 _ i: Exp. 5-10 j 170 70 ~ .
, .. ~ .
, .
~i.E. 48,9~2 As ~i ~s sh~rn i~ Table 5, when the electron emission material compri~in~ Bal ~3Sr~ 2CaWO6 and La703 and Y203 at a molar ratio of ~az~3 Y2O3 of 19 1 to 1: 9 and 1 to 30 mol % of a content of La2O3 and Y2O3 are used, the starting voltages are 5 lower and the lumen maintenance are improved in comparison with those of the conventional electron emission material.
The reason of these characteristics is considered as follows .
In the conventional electron emission material, ZrO2 10 prevents a reaction of BaO with tungsten of the electrode substrate to control the formation of Ba whereby a sputtering of Ba in the arc space can be decreased, however, the work function of the electron emission material is increased to cause higher starting voltage of the fluorescent lamp.
con~a~
On the ~, in the electron emission material of the present invention, both La2O3 and Y2O3 are used. Both La2O3 and YzO3 have heat resistance and a good characteristic of electron emission When both La2O3 and Y2O3 are combined a mixed crystal or a complex compound is formed to improve the electron emitting 20 characteristic ~s a result of the combination of La2O3-Y2O3 with Bal gSr0 2CaWO6, the electron emitting characteristic of Bal 8Sr0 2CaWO6 is further improved by the addition of LazO3-Y2O3.
Therefore, the starting voltage of the fluorescent lamp may be lowered and the lumen deterioration may be decreased.
;9~
W .E . 48, 922 As desc~ibed above, it is preferable to combine La2O3 and Y2O3 in a range of a molar ratio of 19: 1 to 1: 9 since a desired iml?rovement of the electron emitting characteristic of the combination of La2O3 and Y2O3 is not found out of the range, It is preferable to use 1 to 30 mol % of the total of La2O3 ancl Y2O3. When the total is less than 1 mol %, the effect of La2O3-Y2O3 for improving the electron emitting characteristic is not high enough and the starting voltage of the fluorescent lamp is high. When it is more than 30 mol '~0, a content of Bal 8SrO 2CaWO6 as the source of Ba is relatively small and the electron emission is not enough and a black coloring at the end of the tube is caused.
In the examples, Ba1 8SrO 2CaWO6 has been used as the barium- strontium- calcium tungstate. The effect of the present invention can be attained by using the other tungstate having the formula Ba2 xSrxcaw6 (x is 0 to 0- 5)-The effect of the present invention can be attained even though a small amount of A12O3, SiO2, ZrO2 or tungsten is included in the said electron emission material.
In the examples, the tungstate and lanthanum oxide and yttrium oxide have been shown as the electron emission material.
Thus, the effect of the present invention can be attained by using a compound which can be converted into said compound such as a I mixture of barium carbonate, strontium carbonate and calcium - 25 carbonate with tungsten oxide and La2O3 and Y2O3 and heating it to convert it into the above-mentioned electron emission material.
. ' .~
~ :' W.E . 48, 922
2~
~ n ~cc~ar~e ~ t~ t~s embodiment, the electron emission material consistin~g o~ barium^ s~runtium. calcium tungstate-(Baz xSrxCaWOG: x is 0 to 0, 5) and lanthanum oxide and yttrium oxide is used to obtain a fluorescent lamp having a lower starting 5 voltage and less black coloring at the end of the tube.
- The other embodiment of the present invention will be illustrated, The reference is the same as the above-mentioned Reference. Laz03 and Y203 are combined with a triple oxide of BaO, SrO and CaO at various ratios as the electron emission material.
10 Each 40 W fluorescent lamp equipped with electrodes coated with each of the electron emission material shown in Table 6 is prepared and the life test set forth in the above-mentioned embodiment is carried out.
The results are shown in Table 6.
~., . .
.
: -W .E . 48,922 T~e 6 Composition of electron L 23 Total of emission material (mol ~0) ~23 2 3 I _ (molar and Y2O3BaO I SrO CaO I La2O3 Y2O3 ratio) (mol %) _ Exp. 6-1¦ 37. 5 28, 1"4. 4 0. 8 9. 2 ¦ 1 : 12 10 Exp. 6-237. 5 28.1 24.4 1.0 9.0 1 : 9 10 _ Exp. 6-3¦ 37. 5 28. 124. 4 2. 5 7. 5 1 : 3 10 _ Exp. 6-437.5 28.1 24.4 9.0 1.0 9 : 1 10 . -Exp. 6-537. 5 28. 124.4 9. 5 0. 5 lS: 1 10 Exp. 6-6¦ 37. 5 28. 124. 4 9. 6 0. 4 24 : 1 10 Exp. 6-7¦ 41. 4 31. 126.9 ¦ 0. 15 0. 45 1 : 3 0. 6 ~-- .
Exp.6-8 ¦ 41. 2 ¦ 31. 0 ¦ 26. 8 ¦ 0. 25 0.75 1 : 3 ¦ 1 ¦
. I l I I _ Exp.6-9 ¦ 29. 2 ¦ 21, 9 ¦ 18.9 1 7, 5 22. 5 ¦ 1 : 3 ¦ 30 I I I i l l I
¦ Exp,8-10¦ 27, 1 20. 3 ¦ 17. 6 1 8. 8 1 23,2 1 1 : 3 1 35 :
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W.E. 48,922 Table 6 (continued) ¦ Starting voltage Lumen maintenance after ¦ at 0C (V) 3000 hours of operation(%) Exp,6-l 160! 85 Exp. 6-2 155 ¦ 86 .
Exp. 6-3 140 92 Exp. 6-4 145 88 _ Exp. 6-5 155 85 Exp. 6-6 160 ¦ 85 Exp. 6-7 ¦ 160 ¦ 70 ,.~ _ I
Exp. 6-8 155 ¦ 85 _ Exp. 6-9 ¦ 155 85 _ Exp. 6-10 ¦ 170 1 70 . -:~' .
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W.E . 48, 922 ~ r~ the exa-rnples shown in Table 6, the molar ratios of Ba, Sr and Ca in th~e el~ctron emission material are the same as : b.75: o.v~.
As it is shown in Table 6, when the electron emission S materials comprising La203 and Y203, at a molar ratio of La23: Y203 of 19 . l to l: 9 and 1 to 3~ mol % of a content of La203 and Y203 are used, the starting voltage are lower and the lumen maintenance are improved in comparison with those of the conventional electron emission material containing ZrO2.
The reason of these characteristics is considered as follows .
In the conventional electron emission material, ZrO2 presents a reaction of BaO with tungsten of the electrode substrate to control the formation of Ba whereby a scattering of Ba in the arc 15 space can be decreased, however, the work function of the electron emission material is increased to cause higher starting voltage of the fluorescent lamp.
On the contrary, in the electron emission material of the present invention, both La203 and Y203 are used. Both La203 and Y203 have heat resistance and a good characteristic of electron emission. When both La203 and YzO3 are combined, a mixed crystal or a complex compound is formed to improve the electron emitting characteristic. As a result of the combination of La203-Y203 with the alkaline earth metal oxide such as BaO, the reaction of BaO with 25 the electrode substrate is reduced and the electron emitting character-istic is improved. Therefore, the starting voltage of the fluorescent lamp may be lowered and the lumen deterioration may be decr eased.
'~
.
. . ~. ~ .
,, , ' ' - ` ~
.
W.E. 48,922 ~s descr;l~e~ a~7e, it is preîerable to combine La203 and Y2O3 in a ranE~e of a molar ratio of 19: 1 to 1: 9 since a desired improvement of the electron emitting characteristic of the combina-tion of La2O3 and Y2O3 is no-t found out of the range.
It is preferable to use 1 to 30 mol % of the total of La2O3 and Y2O3. When the total is less -than 1 mol %, the effect of La2O3-Y2O3 for improving the electron emitting characteristic is not high enough and the starting voltage of the fluorescent lamp is high.
When it is more than 30 mol %, the effect for reducing the reaction is too much, and the electron emission is not enough and a black coloring at the end of the tube is caused.
In the examples, the alkaline earth metal oxides of Ba, Sr and Ca at molar ratios of 1: 0, 75: 0. 65 have been combined with La2O3 and Y2O3. The effect of the present invention can be attained by using the other molar ratios of the alkaline earth metal oxides or the combination of BaO and SrO or BaO and CaO or only BaO.
The effect of the present invention can be attained even though a small amount of Al2O3, SiO2, ZrO2 or tungsten is included in the said electron emission material.
In the examples, the electron emission material has been shown as the oxides. Thus, the effect of the present invention can be attained by using a compound which can be converted into the oxides such as carbonates, for example, coating the mixture of the alkaline earth metal carbonates, La2O3 and Y2O3 on the electrode substrate and heating it to convert the carbonates into the oxides.
In accordance with this embodiment, the electron emission material consisting of the alkaline earth metal oxide including barium oxide and lanthanum oxide and yttrium oxide is used to obtain a fluorescent lamp having a lower starting voltage and less black coloring at the end of the tube.
~ .
~' ~, .
,
~ n ~cc~ar~e ~ t~ t~s embodiment, the electron emission material consistin~g o~ barium^ s~runtium. calcium tungstate-(Baz xSrxCaWOG: x is 0 to 0, 5) and lanthanum oxide and yttrium oxide is used to obtain a fluorescent lamp having a lower starting 5 voltage and less black coloring at the end of the tube.
- The other embodiment of the present invention will be illustrated, The reference is the same as the above-mentioned Reference. Laz03 and Y203 are combined with a triple oxide of BaO, SrO and CaO at various ratios as the electron emission material.
10 Each 40 W fluorescent lamp equipped with electrodes coated with each of the electron emission material shown in Table 6 is prepared and the life test set forth in the above-mentioned embodiment is carried out.
The results are shown in Table 6.
~., . .
.
: -W .E . 48,922 T~e 6 Composition of electron L 23 Total of emission material (mol ~0) ~23 2 3 I _ (molar and Y2O3BaO I SrO CaO I La2O3 Y2O3 ratio) (mol %) _ Exp. 6-1¦ 37. 5 28, 1"4. 4 0. 8 9. 2 ¦ 1 : 12 10 Exp. 6-237. 5 28.1 24.4 1.0 9.0 1 : 9 10 _ Exp. 6-3¦ 37. 5 28. 124. 4 2. 5 7. 5 1 : 3 10 _ Exp. 6-437.5 28.1 24.4 9.0 1.0 9 : 1 10 . -Exp. 6-537. 5 28. 124.4 9. 5 0. 5 lS: 1 10 Exp. 6-6¦ 37. 5 28. 124. 4 9. 6 0. 4 24 : 1 10 Exp. 6-7¦ 41. 4 31. 126.9 ¦ 0. 15 0. 45 1 : 3 0. 6 ~-- .
Exp.6-8 ¦ 41. 2 ¦ 31. 0 ¦ 26. 8 ¦ 0. 25 0.75 1 : 3 ¦ 1 ¦
. I l I I _ Exp.6-9 ¦ 29. 2 ¦ 21, 9 ¦ 18.9 1 7, 5 22. 5 ¦ 1 : 3 ¦ 30 I I I i l l I
¦ Exp,8-10¦ 27, 1 20. 3 ¦ 17. 6 1 8. 8 1 23,2 1 1 : 3 1 35 :
~`
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W.E. 48,922 Table 6 (continued) ¦ Starting voltage Lumen maintenance after ¦ at 0C (V) 3000 hours of operation(%) Exp,6-l 160! 85 Exp. 6-2 155 ¦ 86 .
Exp. 6-3 140 92 Exp. 6-4 145 88 _ Exp. 6-5 155 85 Exp. 6-6 160 ¦ 85 Exp. 6-7 ¦ 160 ¦ 70 ,.~ _ I
Exp. 6-8 155 ¦ 85 _ Exp. 6-9 ¦ 155 85 _ Exp. 6-10 ¦ 170 1 70 . -:~' .
:;
:,. :
. . .
''' ` :
:
:' :
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~ ..... , . ~ . -.:, ,.:
, . " " : ~.
- , ., , ~ . . .
W.E . 48, 922 ~ r~ the exa-rnples shown in Table 6, the molar ratios of Ba, Sr and Ca in th~e el~ctron emission material are the same as : b.75: o.v~.
As it is shown in Table 6, when the electron emission S materials comprising La203 and Y203, at a molar ratio of La23: Y203 of 19 . l to l: 9 and 1 to 3~ mol % of a content of La203 and Y203 are used, the starting voltage are lower and the lumen maintenance are improved in comparison with those of the conventional electron emission material containing ZrO2.
The reason of these characteristics is considered as follows .
In the conventional electron emission material, ZrO2 presents a reaction of BaO with tungsten of the electrode substrate to control the formation of Ba whereby a scattering of Ba in the arc 15 space can be decreased, however, the work function of the electron emission material is increased to cause higher starting voltage of the fluorescent lamp.
On the contrary, in the electron emission material of the present invention, both La203 and Y203 are used. Both La203 and Y203 have heat resistance and a good characteristic of electron emission. When both La203 and YzO3 are combined, a mixed crystal or a complex compound is formed to improve the electron emitting characteristic. As a result of the combination of La203-Y203 with the alkaline earth metal oxide such as BaO, the reaction of BaO with 25 the electrode substrate is reduced and the electron emitting character-istic is improved. Therefore, the starting voltage of the fluorescent lamp may be lowered and the lumen deterioration may be decr eased.
'~
.
. . ~. ~ .
,, , ' ' - ` ~
.
W.E. 48,922 ~s descr;l~e~ a~7e, it is preîerable to combine La203 and Y2O3 in a ranE~e of a molar ratio of 19: 1 to 1: 9 since a desired improvement of the electron emitting characteristic of the combina-tion of La2O3 and Y2O3 is no-t found out of the range.
It is preferable to use 1 to 30 mol % of the total of La2O3 and Y2O3. When the total is less -than 1 mol %, the effect of La2O3-Y2O3 for improving the electron emitting characteristic is not high enough and the starting voltage of the fluorescent lamp is high.
When it is more than 30 mol %, the effect for reducing the reaction is too much, and the electron emission is not enough and a black coloring at the end of the tube is caused.
In the examples, the alkaline earth metal oxides of Ba, Sr and Ca at molar ratios of 1: 0, 75: 0. 65 have been combined with La2O3 and Y2O3. The effect of the present invention can be attained by using the other molar ratios of the alkaline earth metal oxides or the combination of BaO and SrO or BaO and CaO or only BaO.
The effect of the present invention can be attained even though a small amount of Al2O3, SiO2, ZrO2 or tungsten is included in the said electron emission material.
In the examples, the electron emission material has been shown as the oxides. Thus, the effect of the present invention can be attained by using a compound which can be converted into the oxides such as carbonates, for example, coating the mixture of the alkaline earth metal carbonates, La2O3 and Y2O3 on the electrode substrate and heating it to convert the carbonates into the oxides.
In accordance with this embodiment, the electron emission material consisting of the alkaline earth metal oxide including barium oxide and lanthanum oxide and yttrium oxide is used to obtain a fluorescent lamp having a lower starting voltage and less black coloring at the end of the tube.
~ .
~' ~, .
,
Claims (11)
1) In an electrode for a discharge lamp comprising an electrode substrate and an electron emission material on said electrode substrate, the improvement comprising said electron emission material consisting of a combination of 0.5 to 80 mole % of lanthanum oxide with 99.5 to 20 mole % of yttrium oxide.
2) In an electrode for a discharge lamp comprising an electrode substrate and an electron emission material on said electrode substrate, the improvement comprising:
said electron emission material consisting of the combination of 10 to 90 mole % lanthanum oxide with 90 to 10 mole % of yttrium oxide.
said electron emission material consisting of the combination of 10 to 90 mole % lanthanum oxide with 90 to 10 mole % of yttrium oxide.
3) In an electrode for a discharge lamp comprising an electrode substrate and an electron emission material on said electrode substrate, the improvement comprising:
said electron emission material comprising a mixture of yttrium oxide and lanthanum oxide.
said electron emission material comprising a mixture of yttrium oxide and lanthanum oxide.
4) The electrode of Claim 3 wherein the molar ratio of lanthanum oxide to yttrium oxide is in the range of 1 : 9 to 19 : 1 in said electron emission material.
5) The electrode of Claim 3 wherein the molar ratio of lanthanum oxide to yttrium oxide is in the range of 1 : 9 to 19 : 1 and the total content of lanthanum oxide and yttrium oxide in said electron emission material is in the range of 1 to 30 mole %.
W.E. 48,922
W.E. 48,922
6) The electrode of Claim 3, 4 or 5 wherein said electron emission material further comprises barium.
strontium?calcium tungstate having the formula Ba2-xSrxCaWO6 wherein x is 0 to 0.5.
strontium?calcium tungstate having the formula Ba2-xSrxCaWO6 wherein x is 0 to 0.5.
7) The electrode of Claim 3, wherein said electron emission material comprises an alkaline earth metal oxide component which at least contains barium oxide.
8) The electrode of Claim 7, wherein said alkaline earth metal oxide component is barium oxide.
9) The electrode of Claim 7, wherein said alkaline earth metal oxide is a combination of barium oxide and calcium oxide.
10) The electrode of Claim 7, wherein said alkaline earth metal oxide is a combination of barium oxide and strontium oxide.
11) The electrode of Claim 7, wherein said alkaline earth metal oxide is a combination of barium oxide, strontium oxide and calcium oxide.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000357799A CA1169468A (en) | 1980-08-07 | 1980-08-07 | Electrode for discharge lamp with yttrium and lanthanum oxide electron emission material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000357799A CA1169468A (en) | 1980-08-07 | 1980-08-07 | Electrode for discharge lamp with yttrium and lanthanum oxide electron emission material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1169468A true CA1169468A (en) | 1984-06-19 |
Family
ID=4117591
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000357799A Expired CA1169468A (en) | 1980-08-07 | 1980-08-07 | Electrode for discharge lamp with yttrium and lanthanum oxide electron emission material |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1169468A (en) |
-
1980
- 1980-08-07 CA CA000357799A patent/CA1169468A/en not_active Expired
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