Patent Application
20050037134
The present invention relates to processes of manufacturing oxide cathode and more particularly to such a process of manufacturing micronized oxide cathode with improved characteristics.
Since Wehnelt found that alkaline earth oxides can be used as material in manufacturing cathodes for emitting effective hot electron in 1904, the characteristics of an oxide cathode are intensively studied. Moreover, oxide cathodes are widely used in many applications such as hot electron cathodes. For hot electron cathodes used in cathode ray tube (CRT) manufacturing processes, the hot electron cathode comprises an oxide cathode, a submerged cathode, and a scandia cathode in which the oxide cathode is the most widely used material as hot electron emission source in the electronics industry due to its advantages such as low material cost, easy manufacturing, and stable properties. As shown in
With respect to conventional oxide cathode, Beynar and Nikonor then proposed a barium atom layer mode for estimating the efficiency of hot electron emission by means of Richardson formula (1) as below:
J=AT2exp(−eφ/KT), φ=φ0+αT (1)
where A=120.4 A/cm2K2; φ is power function; φ is power function at 00K ; and α, is temperature coefficient. The power function of φcan be decreased and the efficiency of hot electron emission can be increased by doping alkaline earth metals.
With respect to the efficiency of hot electron emission in conventional oxide cathode, Loosjer and Vink found a pore conduction mechanism in oxide of the oxide cathode after considerable research and experimentation, and concluded the pore conduction mechanism is an important factor in affecting the efficiency of hot electron emission. In addition, Rutter found a technique of coating nickel on the substrate of oxide cathode in 1979. Saito found a technique of doping scandium oxide in oxide cathode and sputtering tungsten film on nickel alloy substrate for improving the properties of the hot electron cathode in 1986 and 1996. All of these researches had a significant meaning in improving characteristics of hot electron cathode.
In recent years, there is an increasing demand for high picture quality and high brightness of projection TV among vast consumers. As such, how to produce projection TVs having benefits of inexpensive, clear picture, and high brightness is the most important goal among major projection TV manufacturers. Typically, there are many factors in affecting projection TV's picture quality and brightness in which for a projection TV incorporating CRT, picture and brightness generated by red (R), green(G), and blue (B) monochromic CRTs are the most important ones in either directly or indirectly affecting TV's picture quality and brightness.
For solving problems of poor picture quality and insufficient brightness in the conventional projection TVs, a solution proposed by designers and manufacturers of the conventional projection TVs is characterized in increasing the current of electron emission source (e.g., cathode) of each monochromic CRT. This has benefits of generating beams of high energy, significantly increasing screen brightness produced by electrons emitted from the monochromic CRTs, and improving picture quality, brightness, and hue of projection TVs. However, the number of electrons in a single beam will increase significantly duo to increasing current of the single electron emission source of each monochromic CRT. This can gradually increase the section of the beam toward screen of each monochromic CRT due to the increasing repelling force of charges. To the worse, halo may occur. Though such effect can be slightly improved by modifying focusing lens or common lens of electron gun of each monochromic CRT or increasing or enlarging diameter of tube neck of each monochromic CRT, it unfortunately will greatly increase manufacturing cost and complicacy of manufacturing processes.
Thus, it is desirable to provide a novel oxide cathode which can be used to manufacture CRTs of high picture quality and high brightness without greatly increasing manufacturing cost and modifying the existing equipment and manufacturing process.
A primary object of the present invention is to provide a process of manufacturing a micronized oxide cathode comprising the steps of performing a micronized attrition on a cathode material for oxide cathode manufacture in order to decrease an average diameter of particles of the cathode material from the order of micron (e.g., about 2.0 μm) as experienced in the prior art to the order of sub-micron (e.g., about 0.09 μm to 1 μm) as carried out by the present invention, and producing the oxide cathode of the present invention from the micronized cathode material. The micronized oxide cathode of the present invention can effectively improve an efficiency of hot electron emission of the oxide cathode.
One object of the present invention is to perform an attrition on at least one micronized cathode material such as carbonate containing barium by means of nano attrition technology, coat the micronized cathode material on a cathode substrate, and heat the cathode substrate in a vacuum environment to produce the finished oxide cathode. The micronized oxide cathode of the present invention can significantly increase area of hot electron emission of the oxide cathode and improve pore conduction mechanism in the oxide of the oxide cathode.
Another object of the present invention is to sequentially, evenly coat each micronized cathode material on the substrate for forming an oxide cathode having a hierarchical structure. The micronized oxide cathode of the present invention can effectively improve efficiency of hot electron emission of the oxide cathode by incorporating different properties of cathode materials.
Still another object of the present invention is to perform an attrition on a cathode material to form required micronized particles by means of nano attrition technology. High current emission density and efficiency of hot electron emission of the micronized oxide cathode of the present invention are substantially the same as that of strontium oxide cathode. Moreover, quality control of the manufacturing processes is better than that of the well known oxide cathode or strontium oxide cathode.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.
FIGS. 3(a) and 3(b) schematically depict air exhaust effects of cathode material having particles of small diameter and large diameter respectively;
FIGS. 5(a) and 5(b) are photographs illustrating surface flatness of the cathode coated on a cathode substrate before and after performing attrition respectively;
FIGS. 7(a), 7(b), 7(c), and 7(d) are sectional views of an oxide cathode manufactured according to processes of other preferred embodiments of the invention;
FIGS. 8(a), 8(b), 8(c), 8(d), and 8(e) are sectional views of an oxide cathode manufactured according to processes of still other preferred embodiments of the invention;
FIGS. 9(a), 9(b), and 9(c) are photographs illustrating R, G, and B electronic guns which have been tested by CC (cathode condition) in a 15″ color CRT of second test cathode (i.e., hn=35 μm) incorporated according to the invention;
FIGS. 9(a), 9(b), and 10(c) are photographs illustrating R, G, and B electronic guns which have been tested by CC (cathode condition) in a 15″ color CRT of second test cathode (i.e., hr=70 μm) incorporated according to the invention; and
The invention is directed to a process of manufacturing micronized oxide cathode comprising the steps of performing a micronized attrition on a cathode material for oxide cathode manufacture in order to decrease an average diameter of particles of the cathode material from the order of micron (e.g., about 2.0 μm) as experienced in the prior art to the order of sub-micron (e.g., about 0.09 μm to 1 μm) as carried out by the invention, coating the cathode material on a cathode substrate, and heating the cathode substrate in a vacuum environment. As an end, the oxide cathode of the invention is produced. The oxide cathode of the invention has advantages of increasing the area of hot electron emission on the surface of the oxide cathode, increasing the pore conduction mechanism on the oxide, and effectively improving the hot electron emission properties of the oxide cathode.
The well known oxide cathode, as a part of the CRT, is formed of cathode material containing carbonate (e.g., BaCO3, SrCO3, and CaCO3). An average diameter of the cathode material particles is about several microns. As shown in
Heretofore, there is no disclosure of theory substantially close to the real pore model of oxide. But the inventor contemplates that theory of particle arrangement can be adopted to understand the increase of pore density. Based on the theory of particle arrangement, it is assumed that a plurality of cathode material particles having a particle diameter of d are stacked to form a body having diameter D and height h in which a group of pores comprise 8 particles. Further, the following formula (2) can be used to calculate the number of pores Nporosity:
It is seen that the number of pores Nporosity and thus the efficiency of the second electron emission will increase as the particle diameter d of the cathode material decreases.
Moreover, the carbonate component in the cathode material will be dissolved or acted with the reducing agent in the substrate due to heat in the cathode activation process, and will generate CO2 based on the following formula (3):
at 1100°K, BaCO3→BaO+CO2← (3)
At this time, a pumping station must be activated to draw out CO2. Otherwise, an excessive high pressure of CO2 will create a eutectic compound 2BaCO3:BaO, resulting in a cathode coating fuse and an increase of crystalline. To the worse, the eutectic compound not only sinters and fuses the coating of oxide cathode, but also degrades porosity and increases resistance (i.e., significant voltage drop as current flows). Still to the worse, the efficiency of hot electron emission will be decreased due to the weakened electric field. For solving this problem, it is proposed to increase the porosity of oxide cathode and thus increase the escape efficiency of CO2. As shown in FIGS. 3(a) and 3(b), the escape efficiency of CO2 of the particles having a small diameter (see
In view of the above, the inventor proposes to perform an attrition on the well known cathode material powder (or particles) having a diameter of 2.6 μm to form one having a diameter of 0.09 μm to 1 μm (D50) and a diameter difference of the cathode material particles is from 0.25 μm to 0.55 μm (D95-D5=0.25 μm to 0.55 μm) by performing a nano powder attrition in which solid content is still maintained at 25% to 55%. Then, through the experimentation, the Optoelectronic properties thereof can be observed and the particle diameter can also be selected. In a preferred embodiment of the invention, the inventor selects a particle having an average diameter about 0.455 μm as an example as detailed below.
The inventor finds the following differences by comparing the diameters of the well known cathode material particles before and after performing an attrition:
(1) Comparison of average diameter: The average diameter of the well known cathode material particles before attrition is about 5.7 times of that after attrition. Through the application of formula (2), it is found that the number of pores in oxide cathode formed of the cathode material after being worn down by attrition is 185 times (5.73≈185) as that of the well known oxide cathode formed of the cathode material before being worn down by attrition.
(2) Comparison of distributed diameter: The distributed diameter of the well known cathode material particles before the attrition is 4.85 μm which is about 10.5 times of 0.462 μm as the distributed diameter of the well known cathode material particles after the attrition. The particle diameter is reduced significantly with a relatively high concentration of diameter distribution. As such, a more smooth surface is formed on the oxide cathode after coating the oxide cathode (which has been worn down by attrition) on the cathode substrate surface (see
In the preferred embodiment, the process of manufacturing micronized oxide cathode at least comprising the following steps:
(1) Performing a micronized attrition on a cathode material for oxide cathode manufacture by performing a nano powder attrition, and micronized the average diameter of particles to about 0.455 μm (D50). Note that the above is only an embodiment of the invention. It is appreciated by those skilled in the art that the invention is not limited by the embodiment. To the contrary, the micronized cathode material as defined by the invention is that one has an average diameter of particles from 0.09 μm to 1 μm (i.e., in the order of sub-micron) after performing a nano powder attrition on any well known cathode material.
(2) Evenly coating the micronized cathode material 11 on a substrate 12 (see
(3) Heating the substrate 12 in a vacuum environment by means of a heating element 13 for forming an oxide cathode 10 of the invention.
Referring to FIGS. 7(a) to 7(d), other preferred embodiments of the invention are shown. It is possible of sequentially, evenly coating at least one cathode material 21 which has been micronized previously, and a cathode material 22 having at least one well known diameter (having a diameter of at least 1.7 μm, i.e., D50=1.7 μm) on a substrate 23 depending on applications. As a result, an oxide cathode having a hierarchical structure is formed. This can effectively improve efficiency of hot electron emission of the oxide cathode by incorporating different properties of cathode materials. The oxide cathode manufactured by any of the above embodiments comprises four structural characteristics as follows:
(1) As shown in
(2) As shown in
(3) As shown in
(4) As shown in
Note that in practice the invention is limited to a cathode material having one, two, or three layers as described in the above embodiments. While it is appreciated by those skilled in the art that the micronized oxide cathode as defined by the invention is that an oxide cathode formed of multiple layers of cathode material by equivalently arranging the above structure of the invention.
Moreover, in still other preferred embodiments of the invention it is possible of doping at least one micronized cathode material into a cathode material having the well known diameter to form a cathode material 53 having a doped diameter depending on applications. As shown in
In the above preferred embodiments, the invention comprises performing a micronized attrition on a cathode material containing carbonate (e.g., BaCO3, SrCO3, and CaCO3) by performing a nano attrition technology, and decreasing an average diameter of particles thereof to the order of 0.455 μm (D50) with a diameter distribution deviation of 0.462 μm (D95−D5=0.462 μm). We can observe the efficiency of hot electron emission of the formed oxide cathode by means of experimentation. It is found that the efficiency of hot electron emission of the micronized oxide cathode is substantially the same as that of strontium oxide cathode. Moreover, quality control of some manufacturing processes is better than that of the well known oxide cathode or strontium oxide cathode.
The invention produces three test cathodes by the above cathode material powder or particles before and after attrition in which first test cathode is characterized in that a cathode material having a well known diameter (before attrition) with a thickness hr is evenly coated on the substrate. Next, a micronized cathode material (after attrition) with a thickness hn is evenly coated on the cathode material having the well known diameter for forming a structure having at least two layers of cathode material. A second test cathode is characterized in that a micronized cathode material (after attrition) with a thickness hn is evenly coated on the substrate for forming a structure having a single layer of cathode material. A third test cathode is characterized in that a cathode material having a well known diameter (before attrition) with a thickness hr is evenly coated on the substrate for forming a structure having a single layer of cathode material (i.e., the well known cathode). Specifications of the above test cathodes are summarized below.
Thereafter, the inventor mounts each of the above test cathodes in an electronic gun which is then enclosed in a color CRT. The optoelectronic property tests are performed sequentially on each CRT as follows.
(1) Cathode condition (CC) test: It adjusts cathode current to observe processing of cathode surface by taking advantage of electron amplification principle. Phenomena such as black spots, partial dark, etc. are observed if the air escape from cathode is poor. The inventor encloses the electronic guns for the cathode test in a 15″ color CRT prior to performing the CC test. FIGS. 9(a), 9(b), and 9(c) are photographs showing the CC test results of a color CRT having a second test cathode (i.e., hn=35 μm). As compared with FIGS. 10(a), 10(b), and 10(c) which are photographs showing the CC test results of a color CRT having a third test cathode (i.e., hr=70 μm), it is obvious that the color CRT having a second test cathode is preferred in which the CC test shows a stable electric field emission. Next, compare the color CRT having the second test cathode with the color CRT having the third test cathode. It is found that both the CC test results are the same. It is obvious that a CRT having an acceptable CC test can be produced by performing an aging process on the second test cathode.
(2) Maximum cathode current test (or called MIK test): It aims at determining the performance of the aging process, air escape condition, and cathode current emission capability. The inventor encloses a FS (flat square) type electronic gun for each of the above test cathodes in a 17″ color CRT prior to performing the MIK test. Results of the MIK test are summarized in the following table.
The maximum cathode current in each of R, G, and B electronic guns of the second test cathode (i.e., hn=35 μm) is increased about 0.7% to 7.1% as compared with that of the third test cathode (i.e., hr=70 μm). Also, from the above table it is found that the maximum difference between any two of the R, G, and B electrons of the second test cathode is 20 μA which is much smaller than 170 μA obtained from the maximum difference between any two of the R, G, and B electrons of the well known third test cathode. The test result shows that micronized cathode has a more consistent aging process under the same manufacturing conditions. As to three electron guns of the second test cathode and that of the third test cathode, there is no significant difference.
Next, the invention again encloses a F type electronic gun for each of the above test cathodes in a 17″ color CRT prior to performing the MIK test. Results of the MIK test are summarized in the following table.
The maximum cathode current in each of R, G, and B electronic guns of the second test cathode (i.e., hn=35 μm) is increased about 6.0% to 26.0% as compared with that of the third test cathode (i.e., hr=70 μm). Also, from the above table it is found that the maximum difference between any two of the R, G, and B electron guns of the second test cathode is 63 μA which is much smaller than 130 μA obtained from the maximum difference between any two of the R, G, and B electron guns of the well known third test cathode. The test result shows that micronized cathode has a more consistent aging process under the same manufacturing conditions.
(3) The maximum cathode current ratio φ MIK: The maximum cathode current ratio φis defined by formula (4) below:
where the obtained value is required to be more than 83%. The inventor encloses a SRF (superior real flat) type electronic gun for each of the above test cathodes in a 17″ color CRT prior to performing the φ MIK test. Results of the φ MIK test are summarized in the following table.
It is seen that the maximum cathode current in each of R, G, and B electronic guns of the second test cathode (i.e., hn=10 μm and hr=60 μm) is about the same as compared with that of the third test cathode (i.e., hr=70 μm). In other words, there is no significant performance improvement. As to the increased percentage of the second test cathode (i.e., hn=35 μm) in the R, G, and B electrons thereof, 2.0% to 4.2% increase is obtained.
Similarly, the inventor encloses a SRF type electronic gun for each of the above test cathodes in a 17″ color CRT prior to performing the φ MIK test. Results of the φ MIK test are summarized in the following table.
It is seen that an increased percentage of the second test cathode (i.e., hn=35 μm) in the R, G, and B electron guns thereof from 4.3% to 13.7% increase is obtained. As to the increased percentage of the first test cathode in the R, G, and B electron guns thereof, an acceptable increased percentage is also obtained.
(4) Thermal strain (Ik) test: It aims at determining the stability of cathode current versus time for preventing change of color.
(5) Other cathode tests: These tests comprise COEK (cut-off potential voltage) test, RCOEK (ratio of COEK) test, and EWT (emission warm up time) test. Result shows that the distribution of the second test cathodes complies with the specifications.
In view of the above, the process of the invention comprises performing an attrition on oxide cathode particles having the well known average diameter to an average diameter of 0.09 μm to 1 μm by performing a nano attrition technology, and then coating it on a cathode substrate or doping into cathode material having the well known diameter prior to coating on the cathode substrate. As an end, current emission capability is improved effectively. Also, halo phenomenon is not susceptible of occurrence in the beams. Also, micronized cathode not only improves air escape capability and increases resistance to toxic gas but also improves the pre-focus of beam form region in the electronic gun due to more flat surface of the micronized cathode. In addition, not only focus and Moire effects of picture are significantly improved, but also yield of electronic gun or CRT is improved. Additionally, it is noted that when the micronized cathode of the invention is mounted in the electronic gun or CRT high current emission density and electron emission capability as substantially the same as that of the well known expensive strontium oxide cathode can be obtained without involvement of special modification or alteration of the existing equipment or manufacturing process. Further, characteristics about manufacturing process and quality control better than that of the well known oxide cathode or strontium oxide cathode can be obtained.
While the invention has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.
