CZ7198A3 - Unit with evaporable getter with reduced activation time - Google Patents

Abstract

An evaporable getter device is described adapted for the use in traditional television tubes or flat displays with reduced barium evaporation time. The device comprises, in addition to powders of BaAl4 alloy and nickel used in the known getter devices, powder of a third component selected from iron, aluminum, titanium or their alloys.

Description

Unit with evaporable getter with reduced activation time

Technical field

The invention relates to an evaporable getter unit with a reduced activation time.

BACKGROUND OF THE INVENTION

As is known, evaporable getter materials are mainly used to maintain vacuum within television sets and computer screens. The use of a vaporizable getter is being investigated inside flat displays that are in development.

The getter material commonly used in screens is a metal barium which is deposited in the form of a thin film on the inner wall of the screen. To form such a film, devices are known which are known in the art as evaporable getter units that are inserted into screens during their manufacture. These units consist of an open metal container containing barium-aluminum compound powder inside,

BaAlo having generally a particle size of less than about 250 µm, and a nickel powder, generally having a particle size of less than 60 µm, in a weight ratio of about 1: 1. These units are well known in the art; in this respect, reference can be made, for example, to U.S. Patent 5,118,988, which was filed by the applicant. The barium is vaporized by the induction heating of the unit by means of a coil outside its own screen, in the activation process also referred to as "flash"; when the temperature of the powders reaches a value in the range between about 800 and 850 ° C, the following reaction occurs:

BaAl ₄ + 4 Ni-> Ba + 4 NiAl (I)

This reaction is highly exothermic and achieves a powder temperature of up to about 1200 ° C, at which the barium evaporates and deposits on the walls of the screen to form a metal film.

The time required to vaporize all of the barium contained in the unit, which is measured from the time at which the unit begins to receive energy through the coil, is defined in the art by the term "total time" to be used in the following section and claims. in its abbreviated form TT. For example, about 300 mg is required to obtain barium films for large screen color screens, the required TT for existing getter devices is 40 to 45 seconds. However, this time is a bottleneck in existing vacuum tube production lines. Manufacturers require units that release barium at lower TT values.

To achieve such results, the coil energy can in principle be increased or the reactivity of the powders can be increased by reducing the particle size of the coil.

However, for existing getter units, it is not possible to increase the coil energy. If so, the temperature of the powder reservoir would rise too quickly and there would not be enough time to homogeneously distribute the heat in the powder packet, which would mean melting the reservoir.

Reducing the particle size of the powders is also not possible as this would result in an excessive and local increase in the reaction

velocity between BaAl ₄ and Ni with subsequent acquisition of packet volume of powders and possible dropping of its parts.

It is therefore an object of the present invention to provide a getter getter unit with an evaporable getter having a reduced activation time which does not have the drawbacks of the prior art.

SUMMARY OF THE INVENTION

The present invention provides an evaporable getter unit having a reduced activation time comprising a metal container in which a mixture is present comprising:

powder of BaAl ₄ ;

nickel powder; and

a powder of a third component selected from the group consisting of aluminum, iron, titanium and their alloys in an amount ranging between about 0.3% and about 5% of the total weight of the composition.

The amount of powder of the third component in the powder mixture depends on the component used and generally ranges between about 0.3% and 5%. In particular, the percentage of the third component is preferably between about 0.8% and 2% in the case of aluminum, between about 0.3% in the case of iron and 2% in the case of iron and between 0.5% and 5% in the case of titanium. With a lower amount of the third component than mentioned, the desired reduction in the barium evaporation time does not occur. Conversely, when working with higher amounts of the third component than indicated, the barium flash is violent and difficult to control. The weight ratio between nickel and BaAl ₄ is the same as that of the prior art units, generally about 1: 1; the use of a ratio between nickel and BaAl _{4 of} 5.3: 4.7 is widespread in the art.

For the purposes of the invention, the third component is not required to be of particularly high purity, and so powders of commercially available metals or alloys which generally have a purity of about 98 to 99% can be used. The particle size of the powder of the third component suitable for the purposes of the invention is less than about 80 µm and preferably less than about 55 µη.

The nickel powders and the BaAl ₄ compound used in the getter units of the invention are the same as those used in the getter units of the prior art; for nickel, powders with a particle size of less than 60 μπι are generally used, while for powders of the BaAl ₄ compound, a particle size of less than about 250 μπι is generally used.

The metal container may be made of a variety of materials such as nickel-plated iron or constantane; AISI 304 or AISI 305 steels which exhibit good oxidation and heat load resistance as well as good cold workability are preferred. The metal container may have any shape, and in particular any shape used in the art, such as the shape known from the units of U.S. Pat. Nos. 4,127,361, 4,323,818, 4,486,686, 4,504,765, 4,642,516, 4,961,040, and 118 988.

Of particular interest is the possibility of obtaining evaporable getter units with reduced activation times, which are also fritable. This term refers to those units that can withstand exposure to an oxidizing atmosphere at a temperature of about 450 ° C for up to 2 hours; which are the conditions that these units are subjected to in some screen manufacturing processes. During barium evaporation from the fritter getter unit, more heat is generated than conventional getter units, resulting in greater difficulty in retaining the powder packet.

stack. Frittable getter units with an amount of vaporized barium up to about 200 mg have been manufactured and sold by the applicant for many years. In contrast, cultivable getter units which can evaporate higher amounts of barium and in particular amounts of about 300 mg require a special solution which takes into account their higher reactivity. The Applicant's patented Frittable Getter Getter Unit having a filing date identical to the present application describes the manufacture of fritterable getter units obtained by adding a heat dispersion retarding element along the periphery of the powder packet and adding a discontinuous metal element, substantially flat, to the same packet. By adding the third component to a fritterable getter unit of the traditional type or the high-yield type, it is possible to obtain a fritterable getter unit with comparable barium release properties, but within a shorter evaporation time.

The invention will be further illustrated by the following examples. These non-limiting examples show those skilled in the art how to put this invention into practice and present the best way to practice it.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

A series of mutually identical getter units were made using a container made of AISI 304 steel 20 mm in diameter and 4 mm high with a bottom with 1 mm high projections as described in U.S. Pat. No. 5,118,988. For each sample, a homogeneous mixture was included in the container, which included 767 mg of BaAl ₄ powder with a particle size of less than 250 µm, 866 mg of nickel powder.

having a particle size of less than 60 gm and 18 mg of iron powder having a purity of 99% and a particle size of less than 80 gm. The powder mixture was then compressed inside the container with a suitable punch. The samples were tested individually by placing them in a glass measuring chamber connected to a pumping system that evacuated the chamber and performing a barium evaporation test according to the method described in ASTM F 111-72; each unit is heated under high frequency to such an extent that evaporation begins 12 seconds after the start of heating; the individual tests differed from each other by the total heating time, which ranged between 35 and 45 seconds in the various tests. The amount of evaporated barium was measured at the end of each test. The TT value required to vaporize 300 mg of barium from each unit is given in Table 1.

Example 2

A series of identical getter units were made using a steel container as described in Example 1. Inside the container was a mesh made of AISI 304 steel with a mesh width of 1.5 mm resting on the bottom protrusions. For each sample, a homogeneous mixture was loaded into the container, which included 767 mg of BaAl ₄ powder with a particle size of less than 250 gm, 866 mg of nickel powder of a particle size of less than 60 gm, and 18 mg of 99% pure aluminum powder with a particle size of less 50 gm. The powder mixture was then compressed inside the container by a punch which was shaped to form four radial depressions on the surface of the packet. The samples thus obtained were processed for 1 hour at 450 ° C in air to simulate frying conditions.

Ί

As in Example 1, barium evaporation tests were performed on each sample. Also in this case, each unit was subjected to high-frequency heating at a rate such that the evaporation started 12 seconds after the start of the heating, the heating lasting for TT, which varied between samples and ranged between 35 and 45 seconds, then determined TT needed to evaporate 300 mg barium from the unit.

The test results are shown in Table 1.

Example 3 (comparative)

The test of Example 1 was repeated for a series of samples as in Example 1, but without iron powder, by heating the unit at high frequency so that evaporation started 12 seconds after the start of heating, and using different TTs ranging between 35 and 45 seconds. The TT required to vaporize 300 mg barium from these samples is shown in Table 1.

Example 4 (comparative)

The test series of Example 2 was repeated using the same getter units as in Example 1, but without powdered aluminum. The TT required to evaporate 300 mg of barium from these samples is shown in Table 1.

Example % of the third component total time (s) 1 1.09 (Fe) 35 2 1.09 (AI) 35 3 0 45 4 0 40

As can be seen from the results in the table, a yield of 300 mg barium with a TT of 35 seconds can be obtained for the units according to the invention, while times of 5 or 10 seconds are required to obtain the same result for prior art samples.

Claims (11)

PATENT CLAIMS In CV An evaporable getter unit d a shortened activation time consisting of a metal container that contains a mixture therein, characterized in that the mixture comprises: - powder of compound BaAl ₄ ; nickel powder; and a third component powder selected from the group consisting of aluminum, iron, titanium and alloys thereof in an amount of between about 0.3% and about 5% of the total weight of the composition. Evaporative getter unit according to claim 1, characterized in that when the third component is aluminum, its percentage by weight in the mixture is between about 0.8% and about 2%. Evaporable getter unit according to claim 1, characterized in that when the third component is iron, its percentage by weight in the mixture is between about 0.3% and about 1.2%. Evaporative getter unit according to claim 1, characterized in that when the third component is titanium, its percentage by weight in the mixture is between about 0.5% and about 5%. Evaporative getter unit according to claim 1, characterized in that the weight ratio between nickel and BaAl ₄ is about 1: 1. · « I I • · Unit according to claim 1, characterized in that the weight ratio between nickel and BaAl ₄ is 5.3: 4.7. The unit of claim 1 wherein the powder of the third component has a particle size of less than about 80 µm. in Unit according to claim 7, characterized in that the fl powder of the third component has a particle size of less than about 55 µm. The unit of claim 1, wherein the nickel powder has a particle size of less than about 60 µeα. A unit according to claim 1, wherein the BaAl ₄ powder has a particle size of less than 250 µm. 11. An evaporable getter unit with a reduced activation time that is fritable, comprising: - metal tray open at the top; - a mixture of powders in the container in the form of a packet, on whose upper surface radial depressions are formed; wherein the mixture comprises BaAl ₄ powders, nickel powders and third components selected from aluminum, iron, titanium, and alloys thereof, and wherein the third component is present in an amount of between about 0.3% and about 5% of the total weight of the composition; a discontinuous metallic element of substantially planar shape and substantially parallel to the bottom of the cartridge, which is contained in a packet of powders in a position where it is separated from the bottom of the cartridge and so as not to protrude to the free surface of the packet itself.