JP2004031081A - Impregnated cathode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally stable impregnated cathode with less evaporation which can be used for a discharge lamp of a high output. <P>SOLUTION: The impregnated cathode is formed by impregnating an impregnation material composed of barium aluminate which is a compound with a stoichiometric composition of an aluminum oxide and an oxide of IIa group element, or a compound composed by substituting a part of barium of an aluminum oxide by calcium, in a porous part of a cathode body made of a metal with a high melting point. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an impregnated cathode, and more particularly to an impregnated cathode suitable for a high-power discharge lamp.
[0002]
[Prior art]
The impregnating material of the typical oxide mixture of the impregnated cathode has a mixing ratio of 4: 1: 1 (hereinafter referred to as 411 impregnating material) or 6: 1: 2 in terms of BaO: CaO: Al ₂ O ₃ . (Hereinafter referred to as a 612 impregnating material), each of which has BaO in excess of the stoichiometric composition. If this barium calcium aluminate is impregnated in the porous voids of the cathode body made of a high melting point metal such as tungsten or molybdenum, the barium-oxygen dipole (Ba- O dipole) is formed. As described above, it is known that the BaO-excessive impregnating material forms a Ba-O dipole at a low temperature, the work function is lowered by this formation, and a high current density (〜１０10 A / cm ² ) is obtained.
[0003]
In particular, by sputtering any one of rhenium, osmium, iridium, and ruthenium by several hundred to several thousand angstroms on the electron emission surface of the impregnated cathode, a lower work function can be obtained, and a higher current density can be obtained. (〜20 A / cm ² ) is also known to be obtained.
[0004]
For this reason, the impregnated cathode is used as a cathode for a high-definition CRT, taking advantage of the feature of high current density. In addition, since the cathode surface is made of a metal having a high melting point, it is also used for a cathode for a high-output electron tube, taking advantage of its relatively high heat resistance and ion bombardment.
[0005]
In order to obtain a high current density at a lower temperature, a 411 impregnating material having a barium-rich composition is often used as an impregnating composition for such an impregnated cathode used in a CRT or an electron tube.
[0006]
The impregnated cathode is also used for a discharge lamp, and the impregnating material used in this application is a 612 impregnating material that has a more stable and lower-evaporation characteristic than the 411 impregnating material. If this 612 impregnating material is used and the lamp output is limited to 150 W or less, the tip of the cathode is less deformed than the tungsten cathode containing thorium oxide conventionally used in this field, and a long life can be obtained.
[0007]
[Problems to be solved by the invention]
However, if an impregnated cathode having a conventional impregnating material is used for the cathode of a discharge lamp having an output exceeding 150 W, the temperature at the tip of the cathode is too high, and the evaporation of BaO from the impregnating material cannot be ignored. For this reason, the glass tube wall is quickly stained, and the light output is reduced. At the same time, the evaporation causes the impregnating material to be lost from the vicinity of the cathode surface, so that the electron emission characteristics are rapidly deteriorated. Then, the decrease in the electron emission characteristics further increases the cathode tip temperature, and accelerates the deterioration of the lamp characteristics. Alternatively, the cathode itself is melted and deformed.
[0008]
As described above, when the conventional impregnated cathode is used for a discharge lamp having an output of more than 150 W, there is a problem that the tube life is reached in a short time.
[0009]
An object of the present invention is to solve the problem that the conventional impregnated cathode is limited in its application range to a discharge lamp having an output of 150 W or less, and has low evaporation and is thermally stable which can be used for a discharge lamp exceeding 150 W. To provide an impregnated cathode suitable for high-power applications.
[0010]
[Means for Solving the Problems]
The invention according to claim 1 comprises a cathode body made of a high melting point metal and having a porous void portion, and a compound having a stoichiometric composition of aluminum oxide and an oxide of Group IIa, and And an impregnating material impregnated in the porous material.
[0011]
The invention according to claim 2 is the impregnated cathode according to claim 1, wherein the impregnating material is barium aluminate having a stoichiometric composition or a part of barium of the barium aluminate is calcium, magnesium, or strontium. Or a compound substituted with any one of the above.
[0012]
Such invention in claim 3, in impregnated cathode according to claim 1, wherein the impregnation _{material, Ba 3 Al 2 O 6,} BaAl 2 O 4, Ba 3-x Ca x Al 2 O 6 ( where 0 <x <3), or _{Ba 1-y Ca y Al 2} O 4 ( where 0 <was impregnated cathode, characterized in that either y <1).
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 are views showing an impregnated cathode according to the embodiment. 1 is an impregnated cathode and 2 is a molybdenum lead. Here, FIG. 1 shows a shape often used for a flash lamp, and FIG. 2 shows a shape often used for a short arc lamp.
[0014]
In the present embodiment, as the impregnating material for the impregnated cathode, Ba ₃ Al ₂ O ₆ , which is a barium aluminate having a stoichiometric composition, or Ba, which is a compound obtained by substituting a part of barium of the barium aluminate with calcium, is used. _2.5 Ca _0.5 Al ₂ O ₆ is used. Hereinafter, characteristics of the impregnated cathode using these compounds will be described.
[0015]
The melting point of the Ba ₃ Al ₂ O ₆ impregnated material and the Ba _2.5 Ca _0.5 Al ₂ O ₆ impregnated material obtained by substituting a part of the barium with calcium exceeds 1600 ° C. On the other hand, the conventional 411 impregnating material and 612 impregnating agent form a eutectic of such a compound and barium oxide, and thus have a melting point of about 1400 ° C. The former has a high melting point because it forms a compound, but the latter has a lower melting point than the complete compound because it is a mixture of oxides. Thus, Ba ₃ Al ₂ O ₆ and Ba _2.5 Ca _0.5 Al ₂ O ₆ used in the present embodiment can be said to be more thermally stable impregnating materials.
[0016]
Next, the thermionic emission characteristics will be described. Conventional impregnating materials 411 and 612 impregnating materials already have excess barium, and are formed on the cathode surface at a relatively low temperature (about 900 ° C.) at a monoatomic layer (electron emission). There is free barium which contributes to the formation of a thin layer (at the atomic level of Ba).
[0017]
On the other hand, the Ba ₃ Al ₂ O ₆ impregnated material and the Ba _2.5 Ca _0.5 Al ₂ O ₆ impregnated material used in the present embodiment have no excess barium, and therefore have sufficient catalytic reduction action with tungsten metal. There is no liberated barium unless the cathode is heated to a temperature that can occur. However, if the cathode temperature is sufficiently raised, the reducing action of tungsten is enhanced, and a sufficient amount of free barium to form a monoatomic layer may be generated.
[0018]
According to experiments performed by the inventor, the impregnated material of the present embodiment has a slightly lower thermoelectron emission characteristic than the conventional impregnated material at a temperature lower than the general operating temperature (1050 ° C.) of the impregnated cathode. In some cases, when the cathode temperature was 1100 ° C. or higher, characteristics equivalent to those of the conventional 612 impregnated material were obtained. In particular, when a cathode for a discharge lamp is used, at least the cathode temperature becomes 1100 ° C. or more during operation, so that the degradation of the thermionic emission characteristics on the low temperature side does not pose a problem.
[0019]
Further, since it is more thermally stable and lower in evaporation than the conventional impregnating material, it is suitable for a higher output lamp. In fact, it can be used for discharge lamps with an output exceeding 200 W.
[0020]
Next, a method for manufacturing the impregnated cathode will be described with reference to FIG.
[0021]
(1). Cathode assembling step: This is a step of joining a tungsten cathode body having a porous void portion with a shaped cathode tip to a molybdenum lead. As will be described later, a caulking method is used for the joining method because the impregnating material of the present embodiment has a high impregnation temperature.
[0022]
(2). Basis weight, mixing step: Here, BaCO ₃ , CaCO ₃ , and Al ₂ O ₃ , which are the raw materials of the impregnating material, are stoichiometrically converted to Ba ₃ Al ₂ O ₆ or Ba _2.5 Ca _0.5 Al ₂ O. _The basis weight is adjusted so as to match the compound composition of Compound No. ₆ . That is, in the case of Ba ₃ Al ₂ O ₆ , BaCO ₃ : CaCO ₃ : Al ₂ O ₃ = 6: 0: 2 (molar ratio) (hereinafter, referred to as 602 impregnated material), Ba _2.5 Ca _{0. 5 In} the case of Al ₂ O ₆ , the raw material of the impregnating material is adjusted to have a mixing ratio of BaCO ₃ : CaCO ₃ : Al ₂ O ₃ = 5: 1: 2 (molar ratio) (hereinafter referred to as 512 impregnating material). To obtain an impregnating material containing no excess BaO as in the prior art. Next, the previously weighed BaCO ₃ , CaCO ₃ , and Al ₂ O ₃ are mixed in an alumina mortar or the same ball mill for about 10 hours to obtain a mixture.
[0023]
(3). Pretreatment step: Here, the mixture obtained in the step (2) is subjected to a heat treatment in an air furnace (condition: 1400 ° C., 5 hours) to further homogenize, and at the same time, barium aluminate or A compound in which a part of the barium of the barium aluminate is replaced by calcium is formed. Since barium aluminate, particularly 602 impregnated material, has a strong water absorption, it is desirable to proceed to the next step immediately after this heat treatment.
[0024]
(4). Impregnation step: Here, the compound is impregnated into the porous void portion (porosity of about 20%) of the tungsten cathode produced in the cathode assembly step (1). The impregnation condition of the hydrogen furnace at this time is desirably about 1750 ° C. for about 3 minutes in the case of 602 impregnated material and 512 impregnated material. If the impregnation temperature at this time is low, the impregnation amount is not always sufficient, and pores exist inside the cathode. If the temperature is higher than this, the porosity of the porous tungsten may decrease or the composition of the impregnating material may change.
[0025]
(5). Post-processing step: Here, the first post-processing (1) and the second post-processing (2) are performed successively. First, the first post-treatment (1) is a step of controlling the amount of impregnation near the cathode surface by physical-chemical treatment (removing the impregnating material on the cathode surface after impregnation). By this step, the initial impregnation of the impregnating material when operated as a discharge lamp cathode can be suppressed, and the stain on the tube wall can be reduced. In addition, since there is a region where no impregnating material is formed on the cathode surface, when an arc discharge operation is performed, the porous tungsten at the cathode tip portion becomes densely self-consistent, and the mechanical strength is improved. The above contributes to extending the life of the lamp. The second post-treatment (2) is a step of stabilizing the impregnated material once melted and solidified by impregnation by aging. Since the composition of the impregnating material used in the present embodiment is a compound, the aging process improves the crystallinity and is thermally stabilized.
[0026]
The embodiment has been described above, but the present invention is not limited to this, and various modifications are possible. For example, in the above embodiment, Ba ₃ Al ₂ O ₆ was used as barium aluminate, but a BaAl ₂ O ₄ compound having a similar stoichiometric composition may be used. In this case, the raw materials of the impregnating material are mixed such that BaCO ₃ : CaCO ₃ : Al ₂ O ₃ = 1: 0: 1 (molar ratio). Another difference is that the impregnation condition is 1950 ° C. This BaAl ₂ O ₄ compound contains a little barium, but is useful similarly to the above-mentioned Ba ₃ Al ₂ O ₆ compound.
[0027]
Further, as compounds obtained by substituting calcium part of barium of the barium _aluminate, it was used _{Ba 2.5 Ca 0.5 Al 2 O 6} , Ba 3-x Ca x Al 2 O 6 ( where 0 < Any composition represented by x <3) may be used. This is composed of a solid solution in which Ba ₃ Al ₂ O ₆ and Ca ₃ Al ₂ O ₆ are fused at a predetermined ratio.
[0028]
Further, BaAl ₂ O compounds by substituting ₄ parts of barium with calcium _{Ba 1-y Ca y Al 2} O 4 ( where, 0 <y <1) may be any compositions shown in. This is composed of a solid solution in which BaAl ₂ O ₄ and CaAl ₂ O ₄ are mixed at a predetermined ratio.
[0029]
Further, in the above, oxides such as Al ₂ O ₃ , BaCO ₃ , and CaCO ₃ are used as raw materials. However, another oxide of Group IIa such as MgCO ₃ and SrCO ₃ can be used as a raw material, and the barium aluminate compound barium is used. It is also possible to use an impregnated material with a compound in which a part of is replaced by magnesium, strontium, or the like. On the electron emission surface of the impregnated cathode, any one of rhenium, osmium, iridium, and ruthenium is sputtered for several hundred to several thousand angstroms to obtain an impregnated cathode having a low work function and a high current density. be able to.
[0030]
【The invention's effect】
As described above, when the impregnated cathode of the present invention is used as a cathode for a discharge lamp, it is low in evaporation and thermally stable as compared with the conventional impregnated cathode for a discharge lamp, and can be used for a discharge lamp with a higher output. It becomes possible. That is, the conventional impregnated cathode can be mounted only on a discharge lamp having an output of 150 W or less, but the impregnated cathode of the present invention can be used for a discharge lamp exceeding 200 W. Further, since the evaporation is low, the service life can be extended.
[Brief description of the drawings]
FIG. 1 is a side view of an impregnated cathode according to an embodiment of the present invention.
FIG. 2 is a side view of an impregnated cathode according to another embodiment of the present invention.
FIG. 3 is an explanatory view of a manufacturing process of the impregnated cathode of the present invention.
[Explanation of symbols]
1: Impregnated cathode, 2: Molybdenum lead

Claims (3)

A cathode body made of a high melting point metal and having a porous void portion, and an impregnation made of a compound having a stoichiometric composition of aluminum oxide and an oxide of Group IIa and impregnated in the porous void portion of the cathode body. And an impregnated cathode. 2. The impregnating material according to claim 1, wherein the impregnating material is barium aluminate having a stoichiometric composition or a compound obtained by substituting a part of barium of the barium aluminate with any one of calcium, magnesium, and strontium. 3. Impregnated cathode. The impregnation _{material, Ba 3 Al 2 O 6,} BaAl 2 O 4, Ba 3-x Ca x Al 2 O 6 ( where, 0 <x <3), or _{Ba 1-y Ca y Al 2} O 4 ( provided that , 0 <y <1), the impregnated cathode according to claim 1, wherein

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