MXPA98000378A - Evaporable absorbing mitting device that has a high perance of ba - Google Patents

Abstract

An evaporable absorber device that can be sealed by melting is described, being capable of releasing quantities of barium of at least 300 mg for use in traditional type of tubes or flat exposures, the device comprises a container in which there is an alloy mixture of BaAl4 and nickel powder, in the form of a packing on the upper surface of which there is a variable number of radial voids, a discontinuous metal member is provided inside the packing

Description

EVAPORABLE ABSORBING DEVICE OUE HAS A HIGH PERFORMANCE OF BARIUM DESCRIPTIVE MEMORY The present invention relates to an evaporable "meltable" absorber with a high barium yield. As is known, the evaporable absorbent materials are mainly used for maintaining vacuum inside image tubes for television and computer screens. The use of evaporable absorbent materials within flat exhibits, now in a state of development, is also under study. The absorbing material that is commonly used in imaging tubes is metallic barium that is deposited in the form of a thin film on an inner wall of the tube. To obtain this film, devices known in the field as evaporating absorber devices are used, which are introduced into the tube during its manufacture. These devices comprise an open metal container comprising in the interior powders of a barium-aluminum compound, BaAl ", and nickel powders, Ni, in a weight ratio of approximately 1: 1. The barium is evaporated by inductively heating the device by means of a coil on the outside of the image tube itself, in a defined activation procedure -i amble as "instant vaporization"; When the temperature in the powders reaches a value of about 800 ° C, the following reaction occurs. BaA + 4 Ni Ba + 4 Nifil (I) Fs + reaction is quite exothermic and raises the temperature of the < -, dust'-, at approximately 1200 ° C, where the evaporation of barium occurs; the barium vapors are then sublimated on the walls of the + ubo to form the metallic film. Absolute evaporable devices are well known in the art; for example the Pa + of E.U.ñ. No. 5,118,988 in the name of the application + e, describes absorbent devices in which some voids are formed in the free surface of the powder package to retard the propagation of heat within the package in a circumferential direction, thereby allowing a vaporization instant line of controlled barium. The Patent of E.U.A. No. 3,558,962 discloses an absorber device wherein a metallic element, preferably a wire mesh, is immersed in the powder packing in a generic position for the purpose of making the temperature inside the powder packing more uniform. The procedures for the manufacture of image tubes, both of the traditional type and of the plane, involve a step of welding together two portions of glass, which is carried out in a so-called "melt welding" operation, causing a paste Glass with a melting temperature of about 450 ° C melts or softens between the two portions in the presence of air. In traditional image tubes, an absorber device may be inserted after sealing by melting through the neck provided to house the electronic gun; however, in this case the size of the absorber is conditioned by the diameter of the cue and the precise placement of the device within the image tube is difficult. On the other hand, in the case of wool displays, it is virtually impossible to place the absorber device after the step of sealing by melting. Accordingly, image tube manufacturers have an increasing tendency to insert the absorber device before sealing by melting. During the melt sealing step, the absorbing device is exposed, at a temperature of about 450 ° C, to atmospheric gases and steam-released by the low melting glass paste. The main result is the oxidation of the nickel surface. During the instantaneous vaporization of barium, the nickel oxide gives origin with aluminum to a quite exothermic reaction, difficult to control; this can lead to the emergence of powder packing, the ejection of chips therefrom or the partial melting of the container, thus being harmful to the correct operation of the absorber device and the tube as an integer. These problems can be overcome in theory by supplying the device with less dust during the instant vaporization operation; this would lead to a more controlled evaporation of barium, but with a longer evaporation time, which can not be accepted in the image tubes industry. The evaporable absorber devices that can withstand the melt seal without alterations, or without causing the aforementioned disadvantages, are defined as "meltable". The absorbing meltable devices are already manufactured and sold by the applicant. These di positive can be manufactured with traditional technologies as long as some critical values are not exceeded: in particular, it is impossible to go beyond certain given thicknesses of the powder packaging, since with too much thickness the amount of heat generated in the body of the The packing of powders dissipates only slowly, thus giving rise to problems as described above. It has been discovered empirically that the ratio between the amount of barium comprised in the device, given in mg, and the diameter of the device, given in m, should not be greater than about 10. Due to reasons for the manufacture of image tubes, the maximum possible diameter of the absorber devices is approximately 20 mm, so that the maximum amount of barium that can be evaporated from the meltable absorber devices manufactured with traditional technologies is approximately 200 mg. However, large size image tubes require evaporated barium amounts of at least 300 mg and such demand can not be met by the meltable diameters in accordance with the prior art. The absorbent meltable devices capable of evaporating quantities of barium of RNs of 200 RN will be defined in the following part of the description and in the claims, as well as the "high yield type". Even resorting to solutions according to the prior art, which allows excellent results in the case of absorbent devices which are not meltable, it is impossible to obtain meltable absorbent devices with a high yield: in fact, making radial voids in the surface of the packaging of powders as described in the US Patent No. 5,118,988 mentioned, the barium evaporation operation after sealing by melting causes, however, the swelling of the package itself or the ejection of chips therefrom. In the devices according to the Patent of E.U.A. 3,558,962 a metal member, preferably a wire mesh, is dipped into the powder pack in a generic position. Describe the case where the mesh is in contact with the bottom of the container or even welded to the bottom of the container, or compressed on the free surface of the powder container. Also in the case both of these positions of the mesh do not allow to obtain absorbing diabetic melts, giving rise to the problems as described above.

The production of absorbing meltable devices without dimension limits, and therefore of high performance devices, is the object of several patents. The Patent "Je E.U.A. No. 4,127,361 of the Applicant describes absorbent devices that can be made meltable by means of a protective layer of organosilanes; Despite its efficiency, this cover procedure is very slow and therefore not acceptable for industrial production. The Patent of E.U.A. i.342.662 and JP Hei 2-6185, both assigned to Toßhiba, describe evaporable absorbent devices that are meltable (in the following defined simply as absorbing meltable devices) obtained by covering, all the powder packing with a glass type film. boron oxide containing up to 7% silicon oxide, or only nickel with a glass film of boron oxide only. However, the manufacture of such devices is difficult, since the film must have a controlled and reproducible thickness. The object of the present invention is to provide an evaporable absorber device that is free from the disadvantages of the prior art. In accordance with the present invention this object achieves with a device "evaporable evaporable absorber with a high barium yield comprising: a metal container open in the iupepoi part; a mixture of "le B Al *" po rts, and nickel in the container, formed as a packing on the upper surface where radial holes are provided; a discontinuous metal member of essentially planar shape and substantially parallel to the bottom of the container; further characterized in that the metallic member is immersed in the powder pack in a position separated from the bottom of the container and so as not to immerse in the free surface of the package itself. The invention will be described in the following with reference to the drawings in which: - Figure 1 shows some possible embodiments of discontinuous metallic members that can be used in the devices of the invention; Figures 2 to 6 show views in cut section of some possible embodiments of absorber devices according to the invention. For the purposes of the invention, it is necessary for a metal member to submerge in the powder pack in such a position to be separated from the bottom and not to come to the surface. In fact, the induction heating of the absorbing device occurs mainly by virtue of the container and the metal member immersed in the powder, which then transfers heat to the powders of the absorbing material. It has been observed that in the contact areas between the metal member and the bottom of the container the heat transfer of the powders is almost efficient and local overheating occurs; If these areas of contact are many or they extend excessively, the undissolved heat causes the dust to rise and in some cases parts of the device melt. Conversely, if the metallic member exits the free surface of the package, the surface itself is sub-surface in areas that are poorly bonded together and during flash vaporization are subjected to being expelled into the image tube. The metallic member can make various metals, such as iron alloys, nickel alloys or aluminum alloys; it is preferred to use AISI 304 steel for its easy cold working capacity. The metal member may have different shapes, provided it is discontinuous and essentially flat. The condition of discontinuity is necessary since the member will not obstruct the release of the barium vapors produced in the powder portion between the member itself and the bottom of the container. This condition can be obtained through the majority of the different geometrical forms. In Figure 1, show some possible modalities are shown: for example, the metal member can be formed by a metal cutting template having a hatched shape, like the element 10 in the drawing, which shows a central hole for help the release of barium from underlying powders; it may be a cut template showing a multiplicity of holes distributed on the surface in a random or orderly manner, as exemplified by member 12; or it can be a wire mesh as described in the U.S. Patent. 3,558,962 mentioned. The member must be essentially flat in order to be submerged in the powder pack, "it usually has a thickness of a few millimeters, without making contact with the bottom of the container and without leaving the surface of the powders. The condition that the metal member should not be in contact with the bottom of the container can be obtained in several ways. Some modalities are shown in figure 2 to 6, where several metallic members are represented according to various methods used to keep them at a distance from the bottom, but each of the different types of member (template cut in striped form, template Hole, wire mesh or others) can be used in each of the configurations described in the following. A possible absorber device of the invention is shown in cross-section in FIG. 2; said device 20 is obtained by pouring a first powder portion 22 onto the bottom of the container 21, placing a flat metallic member 23 on the upper surface thereof and covering the latter with the remaining portion 24 of powders. Finally, the powders are compressed in the container with a die configured in such a way that radial holes 26, 26 'are formed in the upper surface 25 of the package .... The weight ratio between the amount of powder placed in the container before and after placing the metal member 23 it determines the level of the member member within said package and is therefore chosen in such a way that the member will not come to the surface 25n not even where the recesses 26, 26 'are located ...; In general, good results are obtained when said ratio is between approximately 1: 2 and 1: 3. In another possible embodiment, as exemplified in Figure 3a, the metal member 23 can be deformed locally in this manner by obtaining therein some "feet" 34; As shown in Figure 3b depicting in cross section an absorber 30 according to the invention, when the member 33 is placed in the container 31 where the powders 32 are present, the feet 34 maintain it at a predetermined distance. adjusted from bottom 35 of the container. Also in the case of the upper surface 36 of the powder container are the radial recesses 37, 37 '.... Again, as shown in FIG. 4, which shows in cross-section another possible absorber 40 of the invention. , it is possible to obtain deformations 44 in the side walls 45 of the container 41, where the powders 42 are present, and to place the metal member 43 in the deformations 44; in the upper surface 46 of the powder packing form the holes 47, 47 '....

Finally, as exemplified in Figure 5 < While still showing another cross-sectionalization device 50 possible in accordance with the invention, it is possible to obtain elevations 54 on the bottom 55 of the container 51 comprising the powders 52, whereby supports are formed on which the member can rest. metallic; also in this cavity on the upper surface 56 of the powder packing, gaps 57, 57 'are formed. This last possibility is preferred in case a container is used that contains mechanical support elements of the powder packet as described in the US Patent. 4,462,516 and shown in Figure 6; In this case, the metal member 63 may simply be a flat one and it rests on these mechanical support elements 64. In those cases as exemplifies in FIGS. 2 to 6, the position and size of the deformations. , both of the container and the metal member, determine the position of the latter and are defined in such a way that they do not rise to the upper surface of the powder package, not even where the radial holes are located. The container of the device according to the invention can be any among the containers of the prior art. This is usually made of steel, preferably of the flTSI 304 or 305 type, because of its easy ability to work in cold pre-pressing and because of its good resistance to oxidation conditions during the sealing operation by melting the image tube. The shape of said container is essentially that of a small cylinder, closed at the bottom and open at the upper part, although several modifications of this basic form are possible, such as deformations of the bottom or walls, for example. laterals as previously described. The packaging of powders is composed of a mixture of BaA powder and nickel powder. The particle size of BaAl? Powders is generally less than about 250 μm; the particle size of nickel powder Loeß is generally less than about 60 μrn. The weight ratio between the two materials is usually between about 1.2: 1 and 1: 1.2, preferably the ratio in weight is about 1: 1. The powder packing is formed locally by pouring a loose powder mixture into the container and pressing them with suitable dies. In the upper surface of the package, some holes are formed in the radial direction, in a number that varies from 2 to 8, as described in the Patent of E.U.A. 5,118,988 mentioned. The devices The invention can also be produced in a version containing nitrogen; It is known in the field to use "absorbent devices containing small amounts of nitrogen compounds, such as iron nitride, Fe" N, nitride "Je germanio, GeaN *, or intermediate nitrides of iron and germnanium. The purpose of these components is to generate small pressures of nitrogen in the tube during the step of instantaneous vaporization of barium, thus allowing to obtain barium deposits that are more extended and uniform. The invention will be further illustrated by the following examples. These non-limiting examples show some modalities designed to teach those skilled in the art the mode of carrying out the invention and to represent the method best considered to implement the invention.

EXAMPLE 1 An absorber device is prepared using an AISI 304 steel container having a diameter of 200 mm and height of 4 nm with the bottom configured with elevations of 1 nm as high as those shown in Figure 5. Inside the container is placed a AISI 304 steel mesh with 1.5 in. width mdentations, resting on the bottom elevations. A homogenous mixture is poured into the container, consisting of 775 rnG of BaAl "powder, for a total content of 403 barium rn, and 875 rng of nickel powder. The powder mixture then compresses the inside of the container with a die to form "Jo to form on the surface" the package 4 radial holes. The rnueßtra thus obtained is treated at 450 ° C for 1 hour in air to stimulate the conditions of sealing by melting. The sample is then placed in a glass jar while being connected to a pump system, the flask is evacuated and a barium evaporation test is carried out following the method described in ASTH F 111-72 normal at the same time by heating the device by means of radio frequencies during 35 ße gun gun gun con con con con con con con con Evaporation 15 seconds after heating starts. The result "The test is recorded in Table 1, where there are indicated notes on the details of the evaporation, the appearance of the filter and the amount of evaporated barium.

EXAMPLE 2 The test of example 1 is repeated with a mixture that includes a nitrogen dispenser, formed of 785 mg of nickel powder, 825 rnG of BaAU powder, and 40 mg of FeN. The results of the test are recorded in table 1.

EXAMPLE 3 (COMPARATIVE) The test of example 1 ß repeats, but ßin adding the wire mesh in the powder pack. The results of the test are recorded in table 1.

EXAMPLE 4 (COMPARATIVE) The test of example 1 is repeated, but using to compress the powders in the container a pLano die, of odo < When the surface the packaging does not show radial voids. The results of the test are recorded in table 1.

EXAMPLE 5 (COMPARATIVE) The test of Example L is repeated, but using a container with a flat bottom and causing the wire mesh to rest on the bottom thereof. The results of the test are recorded in table l.

EXAMPLE 6 (COMPARATIVE) The test of Example 1 is repeated, but using a sample in which the ßube mesh is placed on the packing surface. This powder has been obtained by pouring the powder mixture into the container, placing the mesh over the powder and compressing all by means of a flat die. The results of the test are recorded in table 1.

TABLE 1 As can be seen from the results in the table, only the devices according to the invention (examples 1 1 and 2) appear to be meltable, since they show no problems with respect to swelling or ejection of the powder pack or the merger of the container; in addition, these devices allow obtaining a barium yield of 300 mg or more. On the contrary, with all other devices, there are problems with the swelling or expulsion of the powders, totally or partially, or the fusion of the entire device still occurs.

Claims (15)

NOVELTY OF THE INVENTION CLAIMS

1. - Absorbent evaporative melting device - with high barium performance, comprising: a metal container open at the top; a mixture of Ba l and nickel powder in the container in the form of packing on the upper surface where holes and holes are formed; a discontinuous metal member of substantially flat shape and essentially parallel to the bottom of the container; further characterized in that the metal member is immersed in the powder pack in a separate position at the bottom of the container, so that it does not leave the free surface of the package itself.

2. A device according to claim 1, further characterized in that the metal member submerged in the powder package is formed as a metal cut-out template (10) having a striped shape.

3. A device according to claim 1, further characterized in that the submerged metal member in the powder container forms as a cut template (12) which shows a multiplicity of holes distributed on its surface.

4. A device according to claim 1, further characterized in that the metallic member immersed in the powder packing is formed as a powder or a powder. bad the cable.

5. A device (20) in accordance with claim 1, further characterized in that it comprises a container- open in the upper part- (21); a first position (22) of the BaAU package and nickel powder in the bottom of the container; a flat metal member (23) placed in the first powder position and covered with the remaining portion (24) of the BaAU V nickel powder pack; radial holes (26,? _ J.) in the upper surface (25) of the powder packing.

6. A device (30) according to claim 1, further characterized in that it comprises a container open at the top (31); a package (32) of BaAU and nickel powder inserted in the container; a metal member (32) with local deformations «as feet (34) submerged in the powder packet so that the feet are in contact with the bottom (35) of the container; hollow rad aleß (36, 36 '...) on the upper surface (37) of the powder container.

7. A device (40) according to claim 1, further characterized in that it comprises an open container in the upper part (41) with deformations (44) in the side walls (45); a package (42) of BaAU and nickel powder in the container; a flat metallic member (43) supported by the «Jeformaciones; Radial hollows (47, 47 '...) on the upper surface (46) of the packing powder.

8. - A device (50) according to claim 1, further characterized in that it comprises an open container in the upper part (51) in the bottom (55) of which there are elevations (54); a package (52) of BaAU and nickel powder in the container; a flat metal member (53) resting on the elevations; radial holes (57, 57 '...) on the upper surface (56) of the powder packing.

9. A bias in accordance with claim 8, further characterized by "] or the elevations at the bottom of the container have a circular shape- (64).

10. A device according to claim 1, further characterized in that the BaAU powderß have a particle size of less than 250 μr.

11. A device according to claim 1, further characterized in that the nickel powders have a particle size of less than 60 μr.

12. A device according to claim 1, characterized in that the BaAU and nickel powders are present in a weight ratio comprised between approximately 1.2: 1 and 1: 1.2.

13. A device according to claim 12, characterized in that the BaAU and nickel powders are present in a weight ratio of approximately 1: 1.

14. A device according to claim 1, character "Jo" in addition because the gaps in the surface of the powder package are in a number between 2 and 8.

15. A device according to claim 1, characterized in addition, because the powder mixture also comprises a nitrogen-dispensing compound chosen from iron nitride, germnanium nitride or intermediate iron-germanium nitrides.