Frittable-evaporable getters having discontinuous metallic members, radial recesses and indentations

A frittable evaporable getter device includes a metallic container having a disk-shaped bottom wall and a side wall extending upwardly from the bottom wall. A powder compact having an upper surface in which at least two radial recesses are formed is disposed in the container. The powder compact is formed of a mixture of BaAl.sub.4 powder and nickel powder. A discontinuous metallic member is embedded in the powder compact such that the member does not protrude from the upper surface of the powder compact and the member is spaced apart from the bottom wall of the container. An evaporable getter device having reduced activation time includes a powder compact formed of a mixture of BaAl.sub.4 powder, nickel powder, and between about 0.3% and about 5% by weight based on the total weight of the mixture of a third component selected from aluminum, iron, titanium, and alloys thereof.

CLAIM FOR PRIORITY 
This patent application claims priority under 35 U.S.C. .sctn. 119 from 
Italian Patent Application Serial No. MI97A 000036, filed Jan. 10, 1997, 
and Italian Patent Application Serial No. MI97A 000037, filed Jan. 10, 
1997, both of which are incorporated herein by reference for all purposes. 
BACKGROUND OF THE INVENTION 
The present invention relates generally to getter devices and, more 
particularly, to frittable evaporable getter devices with a high yield of 
barium, frittable evaporable getter devices with a high yield of barium 
and reduced activation time, evaporable getter devices with reduced 
activation time, and an evaporable getter material. Evaporable getter 
materials are used to maintain a vacuum within the interior of picture 
tubes for television sets and computer screens. The use of evaporable 
getter materials within the interior of flat panel displays is also being 
studied in connection with the development of such displays. 
The getter material commonly used in picture tubes is metallic barium. This 
material is deposited in the form of a thin film on an inner wall of the 
tube. To form the thin film, an evaporable getter device is introduced in 
the tube during the manufacturing process. The evaporable getter device 
typically includes an open metallic container in which a powder compact 
containing powder of a compound of barium and aluminum, BaAl.sub.4, and 
powder of nickel, Ni, in a weight ratio of about 1:1 is disposed. In an 
activation process referred to as "flashing," the device is induction 
heated by means of a coil situated outside the tube. When the temperature 
of the powder compact reaches approximately 800.degree. C., the following 
reaction takes place: 
EQU BaAl.sub.4 +4Ni.fwdarw.Ba+4NiAl (I). 
This reaction is highly exothermic and raises the temperature of the powder 
compact to about 1,200.degree. C., at which temperature barium evaporation 
occurs. Barium vapors then sublimate onto the walls of the tube to form 
the metallic thin film. 
Evaporable getter devices are well known in the art. For example, U.S. Pat. 
No. 5,118,988 to della Porta, which is assigned to SAES Getters, S.p.A., 
discloses an evaporable getter device in which a number of radial recesses 
are formed in the free surface of the powder compact to retard heat 
propagation through the powder compact in a circumferential direction and 
thereby obtain a controlled barium flash. U.S. Pat. No. 3,558,962 to Reash 
discloses an evaporable getter device in which a metallic element, e.g., a 
metallic screen, is at least partially buried in the powder compact to 
conduct heat to the center thereof and thereby obtain uniform flashing of 
barium. 
The manufacturing processes for both traditional picture tubes and flat 
panel displays involve the joining of two glass plates in a so-called 
"frit sealing" operation. In this operation a glass paste having a melting 
temperature of about 450.degree. C. is melted or softened between the two 
glass plates in the presence of air. After the frit sealing operation, a 
getter device may be introduced in traditional picture tubes through the 
neck provided for housing the electronic gun. In this case, however, the 
size of the getter device is limited by the neck diameter and precise 
positioning of the device within the picture tube is difficult. On the 
other hand, in the case of flat panel displays, it is practically 
impossible to position the getter device after the frit sealing operation. 
Consequently, picture tube manufacturers tend to insert the getter device 
before the frit sealing operation. One drawback with this practice is that 
the getter device is exposed, at a temperature of about 450.degree. C., to 
atmospheric gases and the vapors released by the low-melting temperature 
glass paste during the frit sealing operation. The primary result of such 
exposure is the oxidation of nickel on the surface of the powder compact. 
During barium flashing, the thus-formed nickel oxide and aluminum undergo 
a highly exothermic reaction which cannot be controlled. This may lead to 
a portion of the powder compact being raised from the bottom of the 
container, the ejection of fragments of the powder compact from the 
container, or the partial melting of the container. These problems are 
detrimental to the proper operation of both the getter device and also the 
tube as a whole. A more controlled barium evaporation could theoretically 
be obtained by supplying the device with less power during the flashing 
operation. This solution would not be acceptable in the picture tube 
industry, however, because it would increase the evaporation time. 
Evaporable getter devices which can withstand frit sealing conditions, 
i.e., exposure to an oxidizing atmosphere at 450.degree. C. for up to two 
hours, without suffering from the above-described drawbacks are referred 
to as being "frittable." Frittable evaporable getter devices are 
commercially available from SAES Getters S.p.A. of Milan, Italy, the 
assignee of the subject application. Such devices can be manufactured 
using conventional technologies provided certain parameters are not 
exceeded. In particular, the thickness of the powder compact cannot exceed 
a certain maximum thickness because, at greater thicknesses, the heat 
generated in the powder compact dissipates slowly, which gives rise to the 
above-described problems. It has been found empirically that the ratio 
between the quantity of barium in the device, in mg, and the diameter of 
the device, in mm, should not be more than about 10. For reasons dictated 
by the process by which picture tubes are manufactured, the maximum 
diameter of frittable evaporable getter devices is about 20 mm. 
Consequently, the maximum quantity of barium that can be evaporated from 
such devices manufactured in accordance with conventional technologies is 
about 200 mg. Large picture tubes currently being produced require at 
least 300 mg of barium, however. As such, conventional frittable 
evaporable getter devices cannot provide the amount of evaporated barium 
required for such large picture tubes. 
For purposes of the discussion herein, frittable evaporable getter devices 
capable of evaporating in excess of 200 mg of barium will be referred to 
as "high yield" devices. Attempts to obtain such high yield devices by 
resorting to prior solutions which have provided excellent results in the 
case of non-frittable getter devices have been unsuccessful. For example, 
when radial recesses are formed in the surface of the powder compact as 
described in U.S. Pat. No. 5,118,988, the barium evaporation process 
following the frit sealing operation causes swelling of the powder compact 
or the ejection of fragments therefrom. Devices formed in accordance with 
U.S. Pat. No. 3,558,962 are also non-frittable because they suffer from 
the problems described above, regardless of whether the metallic screen is 
welded to, or otherwise in contact with, the bottom of the container or is 
pressed into the free surface of the powder compact. 
The production of frittable getter devices without dimensional limits, 
which are consequently high yield devices, is described in various 
patents. For example, U.S. Pat. No. 4,127,361 to Hellier et al., which is 
assigned to SAES Getters S.p.A., discloses evaporable getter devices which 
can be made frittable by means of a protective organosilane coating. In 
spite of its efficiency, the process by which this coating is formed is 
too slow for industrial production. 
U.S. Pat. No. 4,342,662 to Kimura et al. discloses a frittable evaporable 
getter device in which the powder compact is coated with a glass-like film 
of boron oxide containing up to 7% of silicon oxide. Japanese Patent 
Publication No. 2-6185 discloses a frittable evaporable getter device in 
which nickel powder is coated with a film of boron oxide. Both of these 
devices are difficult to manufacture, however, because such films must 
have a controlled and reproducible thickness. 
In addition to frittability, another important characteristic of evaporable 
getter devices is activation time, which refers to the time required to 
evaporate all the barium contained in the device. The activation time, 
which is also referred to as "total time" or "TT," is measured from the 
instant the induction heating coil is supplied with power. The TT for 
conventional getter devices currently being used to manufacture large 
picture tubes which require at least 300 mg of barium is about 40-45 
seconds. This time period corresponds to the slowest step in current 
production lines for picture tubes. Accordingly, an evaporable getter 
device with a shorter TT would enable manufacturers to increase the rate 
at which picture tubes are produced. 
A shorter TT theoretically could be obtained either by increasing the power 
supplied to the coil or by increasing the reactivity of the powders by 
using powders having smaller particle sizes. However, neither of these 
approaches is effective in conventional getter devices. Specifically, when 
the power supplied to the coil is increased, the temperature of the 
container increases too quickly for homogeneous diffusion of heat into the 
powder compact to occur, which may lead to melting of the container. When 
powders having smaller particle sizes are used, an excessive and local 
increase in the reaction rate between BaAl.sub.4 and Ni occurs which may 
cause bulging of the powder compact and ejection of fragments of the 
powder compact from the container. 
In view of the foregoing, there is a need for evaporable getter devices 
which have characteristics such as frittability, high barium yield, and 
reduced activation time and which do not suffer from the above-described 
drawbacks of conventional devices. 
SUMMARY OF THE INVENTION 
Broadly speaking, the invention fills this need by providing evaporable 
getter devices having a specifically positioned metallic member which 
renders such devices frittable. The invention also provides an evaporable 
getter material having reduced activation time which may be used in 
evaporable getter devices. 
In one aspect of the invention, a frittable evaporable getter device is 
provided. This device includes a metallic container having a disk-shaped 
bottom wall and a side wall extending upwardly from the bottom wall. A 
powder compact having an upper surface in which at least two radial 
recesses are formed is disposed in the container. The powder compact is 
comprised of a mixture of BaAl.sub.4 powder and nickel powder. A 
discontinuous metallic member is embedded in the powder compact such that 
the member does not protrude from the upper surface of the powder compact 
and the member is spaced apart from the bottom wall of the container. In 
this embodiment, the metallic member is preferably substantially planar 
and is preferably embedded in the powder compact so that it is 
substantially parallel to the bottom wall of the container. 
In one preferred embodiment, the metallic member includes a central portion 
having an aperture therein and a plurality of projections extending 
radially from the central portion. In another preferred embodiment, the 
metallic member is disk-shaped and has a plurality of holes formed 
therein. 
In another embodiment, the side wall of the metallic container has an 
indentation which extends inwardly toward an inner region defined by the 
bottom wall and the side wall of the container. The metallic member is 
embedded in the powder compact such that the member is at least partially 
supported by the indentation. 
In a further embodiment, the metallic member has a substantially planar 
portion and at least one flange portion extending downwardly from the 
planar portion. In this embodiment, the metallic member is embedded in the 
powder compact such that the at least one flange portion contacts the 
bottom wall of the container. 
In yet another embodiment, the bottom wall of the metallic container has at 
least one indentation which extends upwardly toward an inner region 
defined by the bottom wall and the side wall of the container. The 
metallic member is embedded in the powder compact such that the member 
rests on the at least one indentation. 
The weight ratio of the BaAl.sub.4 powder to the nickel powder is 
preferably between about 1.2:1 and about 1:1.2, and more preferably about 
1:1. In a preferred embodiment, the powder compact further includes a 
nitrogen dispenser compound selected from the group consisting of iron 
nitride, germanium nitride, and intermediate nitrides of iron and 
germanium. 
In another aspect of the invention, an evaporable getter material having 
reduced activation time is provided. This material is formed of a mixture 
of BaAl.sub.4 powder, nickel powder, and between about 0.3%and about 5% by 
weight based on the total weight of the mixture of a third component 
selected from the group consisting of aluminum, iron, titanium, and alloys 
thereof. In the case of aluminum, the preferred amount is between about 
0.8% and about 2% by weight based on the total weight of the mixture. In 
the case of iron, the preferred amount is between about 0.3% and about 
1.2% by weight based on the total weight of the mixture. In the case of 
titanium, the preferred amount is between about 0.5% and about 5% by 
weight based on the total weight of the mixture. The particle size of the 
powder of the third component is preferably less than about 80 .mu.m, and 
more preferably less than about 55 .mu.m. 
In a further aspect of the invention, evaporable getter devices having 
reduced activation time are provided. These devices include a metallic 
container and a powder compact formed of the evaporable getter material of 
the invention disposed in the container. By combining the evaporable 
getter material and the frittable evaporable getter device of the 
invention, a frittable evaporable getter device having reduced activation 
time may be obtained. 
It is to be understood that the foregoing general description and the 
following detailed description are exemplary and explanatory only and are 
not restrictive of the invention, as claimed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made to the present preferred embodiments of the 
invention, examples of which are illustrated in the accompanying drawings. 
In one aspect, the present invention provides evaporable getter devices 
having a specifically positioned metallic member which renders such 
devices frittable. In accordance with the invention, the metallic member 
is embedded in a powder compact disposed in a metallic container such that 
the member does not protrude from the upper surface of the powder compact 
and the member is spaced apart from the bottom wall of the container. When 
a getter device including a metallic container and a metallic member 
embedded in the powder compact is induction heated, the getter material 
powder is heated primarily by heat transferred to such powder from the 
container and the member. It has been observed that the transfer of heat 
to the getter material powder in areas of contact between the metallic 
member and the bottom wall of the container is highly inefficient to the 
point that local overheating takes place. If there are numerous contact 
areas or the overall contact area is extensive, then the non-dissipated 
heat causes the powder compact to swell or to be raised from the bottom of 
the container and, in some cases, parts of the device to melt. 
Accordingly, in the devices of the present invention, the metallic member 
is spaced apart from the bottom wall of the container. It also has been 
observed that if the metallic member emerges at the upper surface of the 
powder compact, then such surface is divided into areas which are not 
tightly bound to one another and, consequently, are prone to being ejected 
within the picture tube during flashing. Accordingly, in the devices of 
the present invention, the metallic member does not protrude from the 
upper surface of the powder compact. 
The metallic member may be made of metals such as, for example, iron 
alloys, nickel alloys, and aluminum alloys. The metallic member is 
preferably made of AISI 304 steel because of its desirable cold 
workability characteristics. 
The metallic member may have a variety of shapes, provided that the member 
is discontinuous and substantially planar. The metallic member must be 
discontinuous so that the member does not obstruct the release of barium 
vapors produced in the underlying getter material powder. The metallic 
member must be substantially planar so that the member can be embedded in 
the powder compact, which generally has a thickness of just a few 
millimeters, without contacting the bottom of the container or emerging 
from the upper surface of the powder compact. 
FIG. 1 shows two embodiments of discontinuous, substantially planar 
metallic members suitable for use in the frittable evaporable getter 
devices of the invention. Metallic member 23 has a hub-and-spoke 
configuration which includes central portion 10 having aperture 12 formed 
therein and a plurality of projections 14 extending radially from central 
portion 10. Aperture 12 and the open spaces between projections 14 
facilitate the release of barium produced in underlying getter material 
powder. Metallic member 23' includes generally disk-shaped portion 16 
which has a plurality of holes 18 formed therein to facilitate the release 
of barium produced in the underlying getter material powder. Members 23 
and 23' may be formed by any suitable technique, e.g., cutting or punching 
the desired shape from a metallic blank. Those skilled in the art will 
recognize that the metallic member may have shapes other than those shown 
in FIG. 1. For example, the metallic member may be a metallic screen as 
described in the above-mentioned U.S. Pat. No. 3,558,962, the disclosure 
of which is hereby incorporated by reference. 
FIG. 2 shows a cross-sectional view of a frittable evaporable getter device 
in accordance with one embodiment of the invention. Device 20 includes 
container 21 having disk-shaped bottom wall 21a and side wall 21b 
extending upwardly from bottom wall 21a. Metallic member 23 (or 23') is 
embedded in powder compact 22 between lower portion 22a and upper portion 
22b. The upper surface 25 of powder compact 22 has a number of radial 
recesses 26, 26' formed therein, as will be discussed in more detail 
below. 
Device 20 may be formed by pouring a first portion of loose powder into 
container 21 such that bottom wall 21a is covered. Metallic member 23 (or 
23') is then placed on the upper surface of the first portion of powder 
and covered with a second portion of loose powder. Finally, the loose 
powder is compressed to form powder compact 22 in container 21. The loose 
powder may be compressed with a shaped punch so that the upper surface 25 
of powder compact 22 has radial recesses 26, 26' formed therein. The 
weight ratio between the first and second portions of loose powder placed 
in container 21 determines the position of metallic member 23 (or 23') 
within powder compact 22. Therefore, the weight ratio is selected so that 
metallic member 23 (or 23') does not emerge from upper surface 25, even 
where radial recesses 26, 26' are located. In general, satisfactory 
results are obtained when the ratio between the first portion of powder, 
which is placed in the container before the metallic member, and the 
second portion of powder, which covers the metallic member, is between 
about 1:2 and about 1:3. 
FIG. 3a shows another embodiment of a metallic member suitable for use in 
the frittable evaporable getter devices of the invention. Metallic member 
33 includes substantially planar portion 34 which has a plurality of holes 
35 formed therein. Planar portion 34 may have any suitable shape but is 
preferably disk-shaped so that it can nest in a disk-shaped container. A 
plurality of flange portions 36 extend downwardly from planar portion 34 
so as to form "feet" which support portion 34. Those skilled in the art 
will recognize that the metallic member also may be formed with one 
continuous flange portion instead of the plurality of flange portions 36 
illustrated in FIG. 3a. 
FIG. 3b shows a cross-sectional view of a frittable evaporable getter 
device in accordance with another embodiment of the invention. Device 30 
is the same as device 20 shown in FIG. 2 except that device 30 includes 
metallic member 33 instead of metallic member 23 or 23'. Metallic member 
33 is embedded in powder compact 22 such that flange portions 36 keep 
planar portion 34 a predetermined distance from bottom wall 21a of 
container 21. Those skilled in the art will recognize that the distance by 
which flange portions 36 separate planar portion 34 from bottom wall 21a 
is a function of the length of flange portions 36. Barium produced in 
lower portion 22a of powder compact 22 is released through holes 35 (as 
shown in FIG. 3a) in planar portion 34 of metallic member 33. Those 
skilled in the art will recognize that device 30 may be formed in a manner 
similar to that described above for device 20 shown in FIG. 2. 
FIG. 4 shows a cross-sectional view of a frittable evaporable getter device 
in accordance with a further embodiment of the invention. Device 40 is the 
same as device 20 shown in FIG. 2 except that side wall 21b includes 
indentation 41 which extends inwardly toward the inner region defined by 
bottom wall 21a and side wall 21b. Indentation 41 at least partially 
supports metallic member 23 (or 23') and keeps member 23 (or 23') from 
contacting bottom wall 21a. As shown in FIG. 4, indentation 41 extends 
around the entirety of side wall 21b. Alternatively, two or more 
indentations may be formed in side wall 21b. 
FIG. 5 shows a cross-sectional view of a frittable evaporable getter device 
in accordance with a still further embodiment of the invention. Device 50 
is the same as device 20 shown in FIG. 2 except that bottom wall 21a 
includes indentation 51 which extends upwardly toward the inner region 
defined by bottom wall 21a and side wall 21b. Metallic member 23 (or 23') 
is placed on indentation 51 so that the area of contact between member 23 
(or 23') and bottom wall 21a is minimized to avoid local overheating as 
discussed above. As shown in FIG. 5, indentation 51 defines a continuous, 
annular channel in bottom wall 21a. Alternatively, two or more 
indentations may be formed in bottom wall 21a. 
FIG. 6 shows a cross-sectional view of a frittable evaporable getter device 
in accordance with yet another embodiment of the invention. Device 60 
corresponds to device 50 shown in FIG. 5 modified to include the 
mechanical anchoring element described in U.S. Pat. No. 4,642,516 to Ward 
et al., the disclosure of which is hereby incorporated by reference. 
Specifically, device 60 includes annular groove 61 formed in bottom wall 
21a which serves to anchor powder compact 22 in container 21. As can be 
seen in FIG. 6, groove 61 has a generally bulb-shaped cross-section. 
Metallic member 23 (or 23') is placed on groove 61 so that the area of 
contact between member 23 (or 23') and bottom wall 21a is minimized to 
avoid local overheating as discussed above. 
Metallic container 21 shown in FIGS. 2, 3b, and 4-6 may be any suitable 
container, e.g., commercially available containers. Such containers are 
typically made of steel, preferably AISI type 304 or 305, because of the 
ease with which it can be cold-worked by pressing and its excellent 
resistance to oxidation during the frit sealing operation. As can be seen 
in, e.g., FIG. 2, the shape of container 21 corresponds to that of a short 
cylinder having a closed bottom end and an open top end. Those skilled in 
the art will recognize that this basic shape may be varied to include, for 
example, one or more indentations in the bottom wall or the side wall as 
described above. 
The powder compact may be comprised of a mixture of BaAl.sub.4 powder and 
nickel powder. The particle size of the BaAl.sub.4 powder is preferably 
less than about 250 .mu.m and the particle size of the nickel powder is 
preferably less than about 60 .mu.m. The ratio by weight between the 
BaAl.sub.4 powder and the nickel powder is preferably between about 1.2:1 
and about 1:1.2, and more preferably about 1:1. As described above, the 
powder compact may be formed by pouring a mixture of loose powder in the 
container and pressing the loose powder with a suitable punch. The punch 
is preferably configured to form a number of radial recesses in the upper 
surface of the powder compact, as described in the above-mentioned U.S. 
Pat. No. 5,118,988, the disclosure of which is hereby incorporated by 
reference. The number of radial recesses formed in the upper surface of 
the powder compact is preferably from two to eight and these recesses 
retard heat dispersion in the powder compact in a circumferential 
direction. 
To reduce the activation time of the frittable evaporable getter devices 
described herein, the powder compact is preferably comprised of a mixture 
of BaAl.sub.4 powder, nickel powder, and between about 0.3% and about 5% 
by weight based on the total weight of the mixture of a third component 
selected from the group consisting of aluminum, iron, titanium, and alloys 
thereof. The preferred amount of the third component in the mixture 
depends on the material used. In the case of aluminum, the preferred 
amount is between about 0.8% and about 2% by weight based on the total 
weight of the mixture. In the case of iron, the preferred amount is 
between about 0.3% and about 1.2% by weight based on the total weight of 
the mixture. In the case of titanium, the preferred amount is between 
about 0.5% and about 5% by weight based on the total weight of the 
mixture. When the amount of the third component in the mixture is less 
than the indicated amounts, the desired effect of reducing the barium 
evaporation time is not obtained. On the other hand, when the amount of 
the third component in the mixture is greater than the stated amounts, the 
barium flash rages out of control. The weight ratio between the nickel 
powder and the BaAl.sub.4 powder in the three-component mixture is 
preferably about 1:1, and more preferably about 5.3:4.7. 
Commercially available powders having a purity of about 98% to 99% of the 
specified materials are suitable for use as the powder of the third 
component. The particle size of the powder of the third component is 
preferably less than about 80 .mu.m, and more preferably less than about 
55 .mu.m. 
In addition to the frittable evaporable getter devices described herein, 
the evaporable getter material having reduced activation time of the 
invention also may be used in conventional evaporable getter devices such 
as shown in FIG. 7. Device 70 includes metallic container 71 mounted on 
antenna support 72 by, e.g., spot welds, as is known in the art. Container 
71 includes side wall 73 which extends upwardly from a disk-shaped bottom 
wall (not visible in FIG. 7) and elevated central portion 74. Powder 
compact 75 is disposed in the annular region defined by side wall 73 and 
central portion 74 and is comprised of a mixture of BaAl.sub.4 powder, 
nickel powder, and between about 0.3% and about 5% by weight based on the 
total weight of the mixture of a third component selected from the group 
consisting of aluminum, iron, titanium, and alloys thereof as described 
above. 
The frittable evaporable getter devices of the invention also may include a 
nitrogen dispenser compound. As is known to those skilled in the art, the 
presence of nitrogen in the picture tube during barium flashing enables 
more extensive and uniform deposits of barium to be obtained. Accordingly, 
it may be desirable to include small quantities of nitrogen compounds such 
as, for example, iron nitride, Fe.sub.4 N, germanium nitride, Ge.sub.3 
N.sub.4, or intermediate nitrides of iron and germanium in the powder 
compact. 
EXAMPLES 
The evaporable getter devices of the invention will now be described in 
terms of specific examples. It should be borne in mind that the examples 
given below are merely illustrative of particular applications of the 
inventive devices and should in no way be construed to limit the 
usefulness of the invention in other applications. 
Example 1 
A getter device was prepared using a container of AISI 304 steel having a 
diameter of 20 mm and a height of 4 mm with the bottom having an 
indentation 1 mm high (see, e.g., FIG. 5). A metallic screen made of AISI 
304 steel and having mesh of 1.5 mm width was placed on the indentation. A 
homogeneous mixture comprised of 775 mg of BaAl.sub.4 powder (for a total 
content of 403 mg barium) and 875 mg of nickel powder was then poured into 
the container. Next, the powder mixture was compressed within the 
container with a punch shaped to form four radial recesses in the surface 
of the resultant powder compact. The thus-formed device was treated at 
450.degree. C. for 1 hour in air to simulate frit sealing conditions. The 
device was then placed in a glass flask connected to a pump system, the 
flask was evacuated, and a barium evaporation test was conducted following 
the method described in standard ASTM F 111-72 while heating the device by 
means of radio frequencies for 35 seconds with a power selected to 
initiate the onset of evaporation after 15 seconds of heating. The result 
of this test is reported in Table 1, which includes notes describing the 
evaporation details, the condition of the remainder of the device, and the 
quantity of evaporated barium. 
Example 2 
The test of Example 1 was repeated using a powder mixture containing a 
nitrogen dispenser compound. Specifically, the powder mixture included 825 
mg of BaAl.sub.4 powder, 785mg of nickel powder, and 40 mg of Fe.sub.4 N. 
The results of this test are reported in Table 1. 
Comparative Example 3 
The test of Example 1 was repeated, but without including the metallic 
screen embedded in the powder compact. The results of this test are 
reported in Table 1. 
Comparative Example 4 
The test of Example 1 was repeated, but a flat punch was used to compress 
the powder mixture so that the upper surface of the powder compact did not 
include radial recesses. The results of this test are reported in Table 1. 
Comparative Example 5 
The test of Example 1 was repeated, but using a container with a flat 
bottom so that the metallic screen rested on the bottom of the container. 
The results of this test are reported in Table 1. 
Comparative Example 6 
The test of Example 1 was repeated, but using a device in which the 
metallic screen emerges from the upper surface of the powder compact. This 
device was prepared by pouring the powder mixture into the container, 
laying the metallic screen upon the loose powder, and compressing the 
screen and the powder mixture simultaneously by means of a flat punch. The 
results of this test are reported in Table 1. 
TABLE 1 
______________________________________ 
EXAMPLE NOTES 
______________________________________ 
1 Intact powder compact; intact container; evaporated 
barium: 300 mg. 
2 Intact powder compact; intact container; evaporated 
barium: 330 mg. 
3 Ejection of the powder compact; evaporated barium: 
non-detectable. 
4 Remarkable central swelling of the powder compact; 
evaporated barium: 300 mg. 
5 Melting of the container; evaporated barium: 
non-detectable. 
6 Ejection of fragments from the surface of the powder 
compact; evaporated barium: non-detectable. 
______________________________________ 
As can be seen in Table 1, the devices formed in accordance with the 
invention (Examples 1 and 2) appear to be frittable because they do not 
exhibit problems such as swelling of the powder compact, ejection of the 
powder compact, or melting of the container. Furthermore, these devices 
allow barium yields of 300 mg or more to be obtained. On the other hand, 
in each of the devices of the comparative examples there is swelling, full 
or partial ejection of the powder compact, or even melting of the whole 
device. 
Example 7 
A number of identical getter devices were prepared using a container of 
AISI 304 steel having a diameter of 20 mm and a height of 4 mm with the 
bottom having an indentation 1 mm high (see, e.g., FIG. 5). A homogeneous 
mixture comprised of 767 mg of BaAl.sub.4 powder having a particle size of 
less than 250 .mu.m, 866 mg of nickel powder having a particle size less 
than 60 .mu.m, and 18 mg of iron powder having a particle size of less 
than 80 .mu.m and a purity of 99% was then poured into each container. 
Next, the powder mixture was compressed within each container with a 
suitable punch to form a powder compact. Each device was then placed in a 
glass flask connected to a pump system, each flask was evacuated, and a 
barium evaporation test was conducted following the method described in 
standard ASTM F 111-72 while heating each device by means of radio 
frequencies with a power selected to initiate the onset of evaporation 
after 12 seconds of heating. The total time (TT) of heating in the tests 
ranged between 35 seconds and 45 seconds. At the end of each test, the 
amount of evaporated barium was detected. The TT required to evaporate a 
barium quantity of 300 mg from each device is reported in Table 2. 
Example 8 
A number of identical getter devices were prepared using a container as 
described in Example 7. A metallic screen made of AISI 304 steel and 
having mesh of 1.5 mm width was placed on the indentation in each 
container. A homogeneous mixture comprised of 767 mg of BaAl.sub.4 powder 
having a particle size of less than 250 .mu.m, 866 mg of nickel powder 
having a particle size less than 60 .mu.m, and 18 mg of aluminum powder 
having a particle size of less than 50 .mu.m and a purity of 99% was then 
poured into each container. Next, the powder mixture was compressed within 
each container with a punch shaped to form four radial recesses in the 
surface of the resultant powder compact. The thus-formed devices were 
treated at 450.degree. C. for 1 hour in air to simulate frit sealing 
conditions. A barium evaporation test was conducted on each device as 
described in Example 7. In each test the device was heated by means of 
radio frequencies with a power selected to initiate the onset of 
evaporation after 12 seconds of heating. The total time (TT) of heating in 
the tests ranged between 35 seconds and 45 seconds. At the end of each 
test, the amount of evaporated barium was detected. The TT required to 
evaporate a barium quantity of 300 mg from each device is reported in 
Table 2. 
Comparative Example 9 
The tests of Example 7 were repeated, but with devices in which the powder 
mixture did not contain iron powder. The TT required to evaporate 300 mg 
of barium from these devices is reported in Table 2. 
Comparative Example 10 
The tests of Example 8 were repeated, but with devices in which the powder 
mixture did not contain aluminum powder. The TT required to evaporate 300 
mg of barium from these devices is reported in Table 2. 
TABLE 2 
______________________________________ 
THIRD COMPONENT 
TOTAL TIME 
EXAMPLE (% by weight) (seconds) 
______________________________________ 
7 1.09 (Fe) 35 
8 1.09 (Al) 35 
9 0 45 
10 0 40 
______________________________________ 
As can be seen in Table 2, in the devices formed in accordance with the 
invention (Examples 7 and 8) barium yields of 300 mg can be obtained with 
a TT of 35 seconds. In the devices of the comparative examples the TT 
required to obtain the same yield of barium is 5-10 seconds longer. 
While this invention has been described in terms of several preferred 
embodiments, there are alterations, permutations, and equivalents which 
fall within the scope of this invention. If should also be noted that 
there are many ways of implementing the evaporable getter devices of the 
present invention so that they are frittable or have reduced activation 
time or both. It is therefore intended that the following claims be 
interpreted as including all such alterations, permutations, and 
equivalents as fall within the true spirit and scope of the present 
invention.