ITMI970036A1 - EVAPORABLE GETTER DEVICE WITH REDUCED ACTIVATION TIME - Google Patents

Description

DESCRIPTION of the industrial invention entitled: "EVAPORABLE GETTER DEVICE WITH REDUCED ACTIVATION TIME"

The present invention refers to an evaporable getter device with reduced activation time.

As known, evaporable getter materials are used above all for maintaining the vacuum inside the kinescopes of televisions and computer screens. The use of evaporable getter materials in flat screens, currently under development, is also being studied.

The getter material commonly used in kinescopes is metallic barium, which is deposited as a thin film on an inner wall of the kinescope. For the production of the film, devices are used, known in the sector as evaporable getter devices, which are inserted into the kinescope during its production. These devices consist of an open metal container, in which there are powders of a compound of barium and aluminum, BaAl4, generally with a particle size of less than about 250 μm, and nickel powders, generally with a particle size of less than 60 μm, in a ratio by weight of about 1: 1. Such devices are well known in the art, see for example US patent 5,118,988 in the name of the Applicant. The barium is evaporated by heating the device by induction by means of a coil placed outside the kinescope itself, in an activation process also defined by the English term "flash"; when the temperature in the powders reaches a value between about 800 and 850 ° C, the reaction takes place:

This reaction is strongly exothermic, and brings the temperature of the powders to about 1200 ° C, at which the evaporation of the barium which is deposited on the kinescope walls forming the metal film takes place.

The time required to evaporate all the barium contained in the device, measured from the moment in which energy is started to the device through the coil, is defined in the sector with the English term "Total Time", which will be used in the rest of the text and in the claims also in its abbreviated form TT. For example, to obtain barium films of about 300 mg required by large color picture tubes, the TT required with current getter devices is 40-45 seconds. However, this time represents the slow passage of modern kinescope production lines, so it is a request from manufacturers to have devices that can release barium with lower TT values.

To obtain this result, in principle it is possible to increase the power supplied by the coil, or to increase the reactivity of the powders by decreasing the particle size.

With current getter devices, however, it is not possible to increase the power of the coil. In doing so, in fact, the container of powders heats up too quickly and the heat transferred by this to the powder packet does not have time to spread homogeneously in the packet itself, causing the container to melt.

Also the reduction of the particle size of the powders is not possible, as this leads to an excessive and localized increase in the speed of the reaction between BaAl4 and Ni, with consequent lifting of the powder packet and possible expulsion of fragments from it.

The object of the present invention is to provide an evaporable getter device with a reduced activation time which does not have the drawbacks of the known art.

This object is achieved according to the present invention with an evaporable getter device with reduced activation time comprising a metal container in which there is a mixture comprising:

- BaAl4 compound powder;

- nickel powder; And

powder of a third component selected from aluminum, iron, titanium and their alloys in a quantity comprised between about 0.3% and about 5% of the total weight of the mixture.

The amount of powder of the third component in the powder mixture depends on the component actually used, and is generally 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% and 1.2% in the case of iron and between about 0.5% and 5%. % in the case of titanium. With amounts of the third component lower than those indicated, the desired effect of reducing the evaporation time of barium is not obtained. Conversely, by operating with quantities of the third component higher than those indicated above, the barium flash becomes violent and difficult to control. The weight ratio between nickel and BaAl4 is that of the devices of the known art, it is generally about 1: 1; in particular, getter devices are widely used in the field in which the ratio between nickel and BaAl4 is 5.3: 4.7.

For the purposes of the invention it is not necessary that the third component be of very high purity, and powders of commercial metals or alloys, generally having a purity of about 98-99%, can be used. The particle size of the powder of the third component useful for the purposes of the invention is less than about 80 μπι, and preferably less than about 55 μm.

The nickel and BaAl4 compound powders used in the getter devices of the invention are the same as those used in the devices of the prior art; for nickel, powders with a particle size lower than about 60 μm are generally used, while for the BaAl4 compound, powders with a particle size lower than about 250 μm are generally used.

The metal container can be made of various materials, such as nickel-plated iron or constantan; preferred is the use of AISI 304 or AISI 305 steels, which combine good resistance to oxidation, heat treatments and cold mechanical workability. The shape of the metal container can be any, and in particular any of the shapes known and used in the field, such as for example the shapes of the devices of US patents 4,127,361, 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 realizing evaporable getter devices with reduced activation time that are also frittable; the term frittable means getter devices that can withstand an oxidizing atmosphere at temperatures of about 450 ° C for times up to 2 hours, conditions to which such devices are subjected in some production processes of kinescopes. During the evaporation of barium from frittable getter devices, a greater amount of heat is generated than in normal getter devices, with consequent greater problems in maintaining the packet of powders in the container. Frittable getter devices with a quantity of evaporable barium up to about 200 mg have been produced and sold by the Applicant for some years already. Frittable getter devices which can evaporate higher quantities of barium, and in particular of about 300 mg, instead require the use of particular precautions to take into account their greater reactivity; the patent application entitled "HIGH-PERFORMANCE FRITTABLE EVAPORABLE GETTER DEVICE" in the name of the Applicant, having the same filing date as this application, describes the obtainment of frittable getter devices obtained by adding elements that retard circumferential diffusion heat in the packet and the addition of a discontinuous and essentially flat metal element to the powder packet. By adding a third component to frittable getter devices both of the traditional type and of the high yield type, it is possible to obtain frittable getter devices with equivalent barium emission characteristics but with reduced evaporation times. The invention will be further illustrated by the following examples. These non-limiting examples illustrate some embodiments intended to teach those skilled in the art how to put the invention into practice and to represent the best way considered for carrying out the invention.

EXAMPLE 1

A series of identical getter devices is prepared, using for each a container in AISI 304 steel with a diameter of 20 mm and a height of 4 mm and having a shaped bottom with 1 mm high reliefs as described in US patent 5.118.988 cited in the text. . For each sample, a homogeneous mixture is poured into the container consisting of 767 mg of BaAl4 powder with a particle size of less than 250 μm, 866 mg of nickel powder with a particle size of less than 60 μm and 18 mg of iron powder with a purity of 99% particle size. less than 80 μm. The powder mixture is then compressed inside the container with a special punch. The samples are tested by inserting them one at a time in a glass measuring chamber connected to a pump system, evacuating the chamber and carrying out a barium evaporation test following the methodology described in the ASTM F 111-72 standard; each device is heated by radio frequencies with such power that evaporation begins 12 seconds after the start of heating; the tests differ from each other for the Total Time of the heating, which is made to vary in the different tests between 35 and 45 seconds. At the end of each test the quantity of evaporated barium is detected. Table 1 shows the TT necessary to evaporate a quantity of barium of 300 mg from the devices.

EXAMPLE 2.

A series of identical getter devices is prepared, using a steel container for each one as described in example 1. Inside each container an AISI 304 steel mesh with 1.5 mm light mesh is positioned, resting on the reliefs of the fund. For each sample, a homogeneous mixture is poured into the container consisting of 767 mg of BaAl4 powder with a particle size of less than 250 μm, 866 mg of nickel powder with a particle size of less than 60 μm and 18 mg of aluminum powder with a purity of 99% particle size. less than 50 μm. The powder mixture is then compressed inside the container with a shaped punch so as to form 4 radial depressions on the surface of the package. The samples thus obtained are treated at 450 ° C for 1 hour in air to simulate the frying conditions. A barium evaporation test is then carried out on each sample as in example 1. Also in this case each device is heated by radiofrequencies with such power that evaporation begins 12 seconds after the start of heating, maintaining the heating for a TT different from sample to sample and variable between 35 and 45 seconds, and detecting the TT necessary to evaporate from the devices a quantity of barium of 300 mg.

The test results are reported in Table 1.

EXAMPLE 3 (COMPARATIVE)

The test of example 1 is repeated with a series of samples equal to that of example 1 but which do not contain iron powder, heating the devices by means of radio frequencies with such power that evaporation begins 12 seconds after the start of heating and with different and variable TTs between 35 and 45 seconds. The TT needed to evaporate 300 mg of barium from these samples is reported in Table 1.

EXAMPLE 4 (COMPARATIVE)

The series of tests of Example 2 is repeated using getter devices identical to those of Example 1 but which do not contain aluminum powder. The TT needed to evaporate 300 mg of barium from these samples is reported in Table 1.

Table 1

As can be seen from the results in the Table, with the devices of the invention it is possible to obtain a yield of 300 mg of barium with a TT of 35 seconds, while to obtain the same yield with samples of the prior art, longer times than 5 o are required. 10 seconds.

Claims (10)

CLAIMS 1. Evaporable getter device with reduced activation time comprising a metal container in which there is a mixture comprising: - BaAl4 compound powder; - nickel powder; And - powder of a third component selected from aluminum, iron, titanium and their alloys in a quantity comprised between about 0.3% and about 5% of the total weight of the mixture. 2. Evaporable getter device according to claim 1 wherein when the third component is aluminum its weight percentage in the mixture is between about 0.8% and about 2%. 3. Evaporable getter device according to claim 1 wherein when the third component is iron its weight percentage in the mixture is between about 0.3% and about 1.2%. 4. Evaporable getter device according to claim 1 wherein when the third component is titanium its weight percentage in the mixture is comprised between about 0.5% and about 5%. 5. A device according to claim 1 wherein the weight ratio of nickel to BaAl4 is about 1: 1. 6. Device according to claim 1 wherein the weight ratio of nickel to BaAl4 is 5.3: 4.7. 7. A device according to claim 1 wherein the powder of the third component has a particle size lower than about 80 μm. 8. A device according to claim 7 wherein the third component powder has a particle size of less than about 55 μm. 9. A device according to claim 1 wherein the nickel powder has a particle size of less than about 60 μm. 10. Device according to claim 1 wherein the BaAl4 powder has a particle size lower than 250 μm. R. 1. Evaporable getter device with reduced activation time and frittable comprising: a metal container open at the top; - a mixture of powders in the container, in the form of a package on whose upper surface there are radial depressions, in which the mixture comprises powders of BaAl4, nickel and a third component selected from aluminum, iron, titanium and their alloys, and in which the third component is present in a quantity comprised between about 0.3% and about 5% of the total weight of the mixture; - a discontinuous metal element of essentially flat shape and essentially parallel to the bottom of the container immersed in the packet of powders in a position spaced from the bottom of the container and such as not to emerge from the free surface of the packet itself.