Electric lamp and discharge devices – Electrode and shield structures – Cathodes containing and/or coated with electron emissive...
Reexamination Certificate
1996-09-19
2001-04-24
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Electrode and shield structures
Cathodes containing and/or coated with electron emissive...
C313S3460DC, C445S051000, C445S050000
Reexamination Certificate
active
06222308
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an emitter material for a cathode ray tube (CRT) used in television, a display or the like.
BACKGROUND OF THE INVENTION
Conventionally, alkaline earth metal carbonate for a cathode ray tube has been synthesized by adding sodium carbonate aqueous solution or ammonium carbonate aqueous solution into a binary mixed aqueous solution comprising barium nitrate and strontium nitrate, or a ternary mixed aqueous solution comprising above-mentioned binary mixed aqueous solution and calcium nitrate, at a predetermined addition rate and reacting therewith to thus precipitate binary (Ba, Sr) carbonate or ternary (Ba, Sr, Ca) carbonate. The method includes, for example, a sodium carbonate precipitating method. This sodium carbonate precipitating method represents synthesizing alkaline earth metal carbonate by adding a sodium carbonate aqueous solution as a precipitant into a binary mixed nitrate aqueous solution comprising barium nitrate and strontium nitrate or a ternary mixed nitrate aqueous solution comprising barium nitrate, strontium nitrate and calcium nitrate. The method using the binary solution is shown in the following Chemical Formula 1 and the method using the ternary solution is shown in the following Chemical Formula 2.
(Ba, Sr) (NO
3
)
2
+Na
2
CO
3
→(Ba, SR)CO
3
+2NaNO
3
Formula 1
(Ba, Sr, Ca) (NO
3
)
2
+Na
2
CO
3
→(Ba, Sr, Ca)CO
3
+2NaNO
3
Formula 1
When the binary carbonate and ternary carbonate synthesized by the sodium carbonate precipitating method are analyzed by X-ray (wave length is 0.154 nm) diffraction analysis, the diffraction patterns are obtained as in FIG.
18
and FIG.
19
. According to FIG.
18
and
FIG. 19
, there is observed to be one peak respectively in a part of the interplanar spacing ranging from 0.33 nm to 0.40 nm or in the part of a diffraction angle ranging from 22 to 27° (the part between the two dotted lines in FIG.
18
and FIG.
19
). The number of the peak does not change regardless of how the synthesizing condition such as reaction temperature or concentration of the aqueous solution or the like is changed during synthesis of carbonate. Moreover, if sodium carbonate is replaced by ammonium carbonate, the same result can be obtained.
Next, yttrium oxide is added into the above mentioned alkaline earth metal carbonate in an amount of 630 wt.ppm to make a mixture. Then, this mixture is dispersed into a solution in which a small amount of nitrocellulose is added into a mixture medium containing diethyl oxalate and diethyl acetate to make a dispersion solution. This dispersion solution is coated onto the cathode base and thermally decomposed under vacuum to make an emitter for a cathode containing alkaline earth metal oxide as a main component. Then, the relationships between the operating time and the emission current remaining ratio at the current densities of 2A/cm
2
and 3A/cm
2
are shown in FIG.
20
. The line “a” represents the relation in the case where the binary carbonate is employed for an emitter and the current density is 2A/cm
2
. The line “b” represents the relationship in the case where the ternary carbonate is employed for an emitter and the current density is 2A/cm
2
. The line “d” represents the relationship in the case where the binary carbonate is employed for an emitter and the current density is 3A/cm
2
. The line “e” represents the relationship in the case where the ternary carbonate is employed for an emitter and the current density is 3A/cm
2
. The emission current remaining ratio is the normalized value of the emission current with respect to the operating time based on the initial value of the emission current as 1 (the ratio of the emission current with respect to the operating time in the case of setting the initial value of the emission current as 1), and it can be said that the larger the emission current remaining ratio, the better the emission characteristic. As is apparent from
FIG. 20
, in the operations at the current density of 3A/cm
2
, the emission current remaining ratio is quite low in both binary and ternary carbonate. It can be said that the allowed value of the current density of these emitters is approximately 2A/cm
2
.
Recently, as a CRT has a larger screen size, higher brightness and higher resolution, the higher density of emission current has been demanded. However, if the conventional emitter materials for CRTs are used at the current density above 2A/cm
2
, a sufficient lifetime cannot be maintained. Thus, the conventional emitter materials cannot be employed for a CRT that is aiming at a larger screen size, higher brightness and higher resolution.
THE SUMMARY OF THE INVENTION
The object of the present invention is to provide an emitter material for a CRT aiming at a larger screen size, higher brightness, and higher resolution.
In order to obtain the above-mentioned object, the emitter materials for a CRT of the present invention comprise mixed crystal or solid solution of at least two kinds of alkaline earth metal carbonate, wherein at least one alkaline earth metal carbonate is dispersed or separated in the mixed crystal or solid solution. The mixed crystal or solid solution herein denotes the crystalline solid containing not less than two kinds of salts. Moreover, the dispersion herein denotes the state where mixed crystal or solid solution particles and general salt crystalline particles are mixed. The separation denotes the state where each of the same kind of components distribute locally in groups in one crystal of carbonate.
It is preferable in the above-mentioned composition in which at least one alkaline carbonate is dispersed in the above mentioned mixed crystal or solid solution that the average particle size of the crystalline particles dispersed in the mixed crystal or solid solution is not less than one-third nor more than three times as large as the average particle size of the above-mentioned mixed crystal or solid solution. The average particle size herein represents the average value of individual diameters in the direction of the long axis (in the case of spherical crystal, the average value of the diameter) of the crystalline particles.
It is preferable in the above-mentioned composition that the average size of the crystalline particles is in the range from 2 to 5 &mgr;m.
It is preferable in the above-mentioned composition that an X-ray diffraction pattern of alkaline earth metal carbonate has two peaks or more in the interplanar spacing ranging from 0.33 nm to 0.40 nm.
The other means for analysis and identification includes the means of analyzing the distributional state of Ba, Sr and Ca in the crystalline particles of carbonate that is an emitter material by the use of an X-ray microanalyzer.
It is preferable in the above-mentioned composition that the at least two kinds of alkaline earth metal carbonate comprise barium carbonate and strontium carbonate.
It is preferable in the above-mentioned composition that the alkaline earth metal carbonate comprising barium carbonate and strontium carbonate is dispersed or separated in an amount of not less than 0.1 to less than 70 wt. %.
It is preferable in the above-mentioned composition that the at least two kinds of alkaline earth metal carbonate comprise three kinds of carbonate; barium carbonate, strontium carbonate and calcium carbonate.
It is preferable in the above-mentioned composition that alkaline earth metal carbonate comprising three kinds of carbonate; barium carbonate, strontium carbonate and calcium carbonate is dispersed and separated in an amount of not less than 0.1 wt. % to less than 60 wt. %.
It is preferable in the above-mentioned composition that the emitter material for a CRT further comprises at least one material selected from the group consisting of rare earth metal, rare earth metal oxide and rare earth metal carbonate.
It is preferable in the above-mentioned composition that yttrium atoms are added into the emitter material for a CRT by the coprecipitation method in an amount of 550-950 ppm with respe
Hayashida Yoshiki
Ozawa Tetsuro
Sakurai Hiroshi
Haynes Mack
Matsushita Electronics Corporation
Merchant, Gould, Smith, Edell, Welter & Schmidt, P.A.
Patel Nimeshkumar D.
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