MXPA98000380A - Evaporable absorbing device with reduced activation time - Google Patents

Abstract

An evaporable absorber device adapted for use in traditional flat television or visual indicator lamps with reduced evaporation time of the barium is described, the device contains, in addition to the BaAl4 and nickel alloy powders used in the known absorber devices, powder of a third component selected from iron, aluminum, titanium or its alloys

Description

EVAPORABLE ABSORBING DEVICE WITH REDUCED ACTIVATION TIME DESCRIPTIVE MEMORY 5 The present invention relates to an evaporable absorbing device with reduced activation time. fct As is known, the evaporable absorbent materials are mainly used for maintenance of the vacuum inside the image tubes for television sets and computer screens. The use of evaporable absorbent materials in the interior of visual indicators, which are currently in a stage of development, is also under study. 15 The absorber material that is commonly being used in imaging tubes is the metallic barium that is deposited in Thick film forrna on an interior wall of the picture tube. To obtain such a film use is made of devices, known in the field as evaporable devices absorbers, which are introduced into the image tube during its manufacture. These devices are constituted by an open metallic container which contains therein the powder composed of barium and aluminum, BaAl *, which has a particle size at least of About 250 μm, and nickel powders, generally with a particle size of less than 60 jjrn, with a weight ratio of about 1: 1. These devices are well known in the art; reference is made to this for example in the U.S. Patent. 5,118,088 in the name of the applicant. The barium is evaporated by heating the induction device by means of a winding inside the imaging tube or, in an activation procedure also defined as "flash vaporization"; when the temperature of the powders reaches a value in the range of between about 800 and about 850 ° C, the following reaction takes place: 10 BaA + 4 Ni - > Ba + 4 Ni fll (I) This reaction is strongly exothermic and raises the temperature of the powders to approximately 1200 ° C, to which The barium evaporates and is deposited on the walls of the image tube, thus forming the metallic film. The time required to evaporate all the barium contained in the device, which runs from the moment in which the device starts to be supplied with energy by means of the winding, is defined in the branch with the term "total time", which will be used in the following portion of the description and the claims also in its abbreviated form TT. For example, to obtain barium films of approximately 300 and as required by the image tubes of color of large size, the TT required with The present absorbing devices is 40-45 seconds. However, this time corresponds to a slow step in the present method for manufacturing electronic tubes, so it is a requirement of manufacturers to have devices that can release barium with lower TT values. In order to obtain such a result, the energy supplied by the winding can be increased in principle or an increase in the reactivity of the powders can be obtained by reducing its particle size. ^ However, with the available devices absorbers an increase in winding energy is possible. Indeed, by doing so, the powder container raises its temperature too rapidly and there is not enough time for a homogeneous diffusion of the heat in the powder pack, thus giving rise to the melting of the container.

It is also impossible to reduce the particle size of the powders, since this would lead to an excessive and local increase in the reaction rate between T3 Rl4 and Ni with the consequent swelling of the powder packet and the possible release of pieces of this powder. . An object of the present invention is to provide an evaporable-absorbing device which has reduced activation time comprising a metal container in which a mixture is present which includes: - Bafll compound powders?; 25 - nickel powder; and powder of a component component selected from aluminum, iron, titanium and its alloys in a range of between about 0.3% and about 5% of the total weight of the mixture. The amount of the powder of the third component in the powder mixture depends on the component actually employed and is generally in the range of between about 0.3% and 5%. In particular, the percentage of the third component is preferably comprised between about 0.8% and 2% in the case of aluminum, between about 0.3% and 1.2% in the case of iron and between about 0.5% and 5% in the case of titanium. With quantities of the third component that are lower than those indicated, the desired effect is not obtained by reducing the evaporation time of the barium. On the other hand, when operating with quantities of the third components which are higher than those previously indicated, the instantaneous vaporization of the barium is of a violent nature and is difficult to control. The weight ratio between nickel and BaRl is the same as that of the prior art devices, generally about 1: 1; in particular, absorbers are used extensively in this field, which have a relation of 5.3: 4.7 between nickel and Bafl. For the purposes of the invention, the third component is not required to be of particularly high purity and use may be made of powder of commercial metals or alloys, which generally have a purity of about 98-99%. The particle size of the third pulverized component that is useful for the purposes of the invention is less than about 80 μrn and preferably less than about 55 μrn. 5 The nickel powders in the compound BaRl? Which are employed in the absorber devices of the invention are the same as those used in prior art devices; generally, powders with particle size of about 60 μm are used for nickel, while for the compound BaRl, powders having a particle size of less than about 250 μm are generally employed. The metal container can be made of various materials, such as nickel-plated iron or steel; The use of RISI 304 or RISI 305 steels which exhibit an adequate resistance to oxidation and thermal treatment as well as adequate cold workability is preferred. The metal container can have any configuration and in particular any of the known and used configurations in the field, such as that of the devices according to the U.S. Patents. 4,127.3611 - 4,323,818 - 4,486,686 - 4,504,765 - 4,642,516 - 4,961,040 and 5,118,988. Particularly interesting is the possibility of obtaining evaporative absorber devices with a reduced activation time which are also meltable; with this term it is understood that absorbent devices that can Wtf resist an oxidizing atmosphere at a temperature of about 50 ° C for a duration of up to 2 hours; This being the conditions to which such devices have to be subjected in some procedures for manufacturing image tubes. During the evaporation of the barium of the absorbing meltable devices a larger amount of heat is generated than the common devices ? absorbers, with the consequent difficulties more pronounced to maintain the package of powders in the container. The meltable absorbent devices with an amount of evaporable barium is approximately 200 RNG have been manufactured and sold by the applicant for several years. Conversely, melt-sealable absorbent devices that can evaporate larger quantities of barium and in particular about 300 rng requires that particular solutions be adopted to account for its greater reactivity; Patent Application with the title "DEVICE OVERFLOW ABSORBING OUTER HAS HIGH PERFORMANCE OF BARIO "on behalf of the applicant and has the same date of The present invention discloses the manufacture of meltable absorbent devices obtained by the addition of elements that retard the thermal dispersion in the circumferential direction in the powder pack and the addition of a discontinuous metallic element, essentially flat, on the same package. By adding a third component to the melt absorbent devices of either the traditional type or the high performance type, it is possible to obtain meltable absorber devices with characteristics comparable to the barium mission, but for a short time of evaporation. The invention will be further illustrated by means of the following examples. These non-limiting examples show some modalities intended to teach those skilled in the art how to practice the invention and to represent the best considered way to put the invention into practice. 0 EXAMPLE 1 A quantity of absorbent devices all equal to each other is prepared using for each of them a container made of AISI 304 steel having a diameter of 20 nm and a height of 4 millimeters with the lower door configured with elevations of 1 nm in height as described in the Patent of E.U.A. 5,118,988 cited herein. For each sample, a homogeneous sample is poured into the container, which is composed of 767 rnG of pulverized Bafll * having a particle size of 250 μrn, 866 rng of powdered nickel having a particle size of less than 60 μrn and 18 rng pulverized iron with a purity of 99% having a particle size of less than 00 μm. The mixture of the powders is then compressed into the interior of the container with an appropriate stamper. The samples are tested by placing them one at a time in a measuring chamber made of glass, connected to a pumping system, evacuating the chamber and carrying out a barium evaporation test following the method described in the ASTM standard. F 111-72; it heats up every device by means of radio frequencies with such energy that the evaporation begins 12 s after heating has begun; the tests are different from each other in terms of F total heating time, which is varied in the different tests in a range of between 35 and 45 s. At the end 10 of each test the amount of evaporated barium is detected. Table 1 shows the TT required to evaporate the device a barium amount of 300 rng.

EXAMPLE 2 A quantity of absorber devices all identical to one another is used for them using a steel container as described in Example 1. Inside this container is placed an AISI 304 steel net with meshes. of 1.5 rnl wide, resting on the elevations of the lower part. For each sample a homogeneous mixture is poured into the container, consisting of 767 rnG of powdered Bafil * having a rnenoe particle size of 250 μr, 866 rng of powdered nickel having a particle size of less than 60 μm and 1.8 rng of pulverized aluminum with 99% purity and which has a particle size of 50 μrn. It is compressed after mixing the powders inside the container with a stamper configured in such a way that four radial cavities form on the surface of the package. The samples thus obtained are treated at 450 ° C for 1 hour in air to simulate the conditions of the melt seal. A barium evaporation test is then carried out on each sample according to Example 1. Also in this case each device is heated by means of radio frequencies with such energy that evaporation begins 12 s after heating has begun., while maintaining heating during a TT that is different from sample to sample and that varies in a range of between 35 and 45 s, then detecting a value of TT required to evaporate from the devices a barium amount of 300 rng. 5 The results of the test are presented in the Table 1.

EXAMPLE (COMPARATIVE) 3 0 The test is repeated in Example 1 with a series of samples identical to those in Example 1, but without pulverized iron, heating the devices with radio frequencies at a level of energy such that evaporation begins 12 s after heating has begun and only in 5 different TT, variable between 35 and 45 s. The TT required to vaporize 300 barium of these samples is presented in Table 1.

EXAMPLE (COMPARATIVE) 4 The test series of Example 2 is repeated using absorber devices identical to those of Example 1 but without powdered aluminum. The TT required to evaporate 300 barium of these samples is presented in Table 1. * fifteen twenty As shown by the results in the Table, with two devices according to the invention it is possible to obtain a yield of 300 barium Rn with a TT of 35 s, while that obtaining the same performance with the bags of the prior art requires longer time 5 or 10 s longer.

Claims (5)

NOVELTY OF THE INVENTION * CLAIMS

1. Evaporable absorber device with reduced activation time, comprising a metal container with a mixture therein comprising: Compound powder of Bafil? , - nickel powder; and powder of a third component selected from aluminum, iron, titanium or its alloys in an amount between about 0.3% and about 5% of the total weight of the mixture.

2. An evaporative-evaporating device according to claim 1, further characterized in that when the third component is aluminum its percentage in weight in the mixture is between approximately 0.8% and approximately 2%.

3. An evaporable absorber device according to claim 1, further characterized in that when the third component is iron its percentage in 0 weight in the mixture is between approximately 0.3% and approximately 1.2%.

4. An evaporable absorbing device according to claim 1, further characterized in that when the third component is titanium its percentage in weight in the mixture is between approximately 0.5% and approximately 5%. tfc

5. A device according to claim 1, further characterized in that the weight ratio between nickel and BaRl ^ is approximately 1: 1. 6.- A device in accordance with the 5 claim 1, further characterized in that the weight ratio between nickel and BaAl4 is about 5.3: 4.7. 7. A device according to claim 1, further characterized in that the powder and the third component have a particle size of less than 10 approximately 80 μrn. 8. A device according to claim 7, further characterized in that the powder and the third component have a particle size of about 55 μm. 9. A device according to claim 1, further characterized in that the powder and the nickel have a particle size of less than about 60 μrn. 10. A device according to claim 1, further characterized by the powder and the Bafll? it has a particle size of about 250 μrn. 11. An evaporable absorber device with reduced activation and melting times, comprising: a metal container open at the top; a mixture of powders in the container, in the form of packages on the upper surface J of which radial cavities are formed, wherein the mixture contains BR powders, nickel and a third component selected from aluminum, iron, titanium and its alloys, and wherein the third component is present in an amount of between about 0.3% and about 5% of the total weight of the mixture; a discontinuous metallic element of essentially flat configuration and parallel to ^ the bottom of the container, which is immersed in the powder pack in a separate position from the bottom of the 10 container, in such a way that it does not emerge to the free surface of the package itself.