"ϋI§H_ YIELD_-WJJU -_._._._._._. _ANN LAR__RJN_S___._._._._._._§1111fi DEVICE"

Annular ring shaped getter devices are well known in the art and have been described, for example, in US Patents Nos. 3151736, 3381805 and 3385420. In order to have a higher ield of getter metal from such devices it has also been common practice to enlarge or widen the annular channel. Such "wide channel" getter devices have been described in US Patent Nos. 3719433 and 4642516.

However, even these types of device do not allow the evaporation of getter metal vapours in sufficient quantity without incurring the risk of detachment of getter metal vapour releasing material from its holder or even melting of the getter contain¬ er walls.

It is therefore an object of the present invent on to provide an improved wide channel getter device free from one or more of the disadvantages of prior art getter de ices having the same shape.

It is another object of the present invention to provide a wide channel getter device having a high yield of getter metal.

A further object of the present invention is to pro ide a wide channel getter device which does not exhibit melting of the getter container wa I Is .

Yet another object of the present invention- is to provide a wide channel getter device free from

detachment of getter metal vapour releasing material from its holder.

These and other objects and advantages of the present invention will become apparent to those skilled in the art by reference to the following detailed description thereof and drawings wherein:

FIGURE 1 is a top plan view of a first preferr¬ ed embodiment of getter device of the present invention;

FIGURE 2 is a cross-sectional v ew taken along Line 2-2' of Fig. 1;

FIGURE 3 is a top plan view of a second preferred embodiment of a getter device of the present invention;

FIGURE 4 is a cross-sectional view taken along line 4-4' of Fig. 3; and

FIGURE 5 is a graph comparing the flashing (barium evaporation) character stics of getter de ices of the present invention with those of prior art getter devi ces.

Referring now to the drawings and in particu¬ lar to Figs. 1 and 2, in which identical details are identified by identical number, there is shown a first preferred embodiment of an evaporable getter device 100 of the wide channel annular ring shaped type suitable for mounting in an electron tube. Getter device 100 comprises a holder 102, preferably of stainless steel, adapted to support an evaporable getter metal vapour releasing material 104. Holder 102 comprises a vertical outer side wall 106,. a verti¬ cal inner side wall 108 and a bottom 110 which joins said outer side wall 106 to said inner side wall

108. Bottom wall 110 is provided with means 112 for preventing detachment of the getter metal vapour releasing material from the holder. In this first preferred embodiment means 112 is in the form of an annular groove 114 integrally formed in the bottom wall and penetrating into the space formed by outer side wall 106 and inner side wall 108. Annular groove 114 has a generally bulb-shaped cross-section which narrows down adjacent bottom wall 110.

Getter metal vapour releasing material 104 is supported by holder 102 by pressing it into the space defined by said inner, outer and bottom walls. Getter material 104 comprises an upper surface 116 and a plurality of heat transfer retarding means 118, 118', 118", 118'" in said upper surface, adapted to delay the transfer of heat in circumferential direction through the getter metal vapour releasing material when the getter device is heated by currents induced from a RF field created by a coi l positioned outside the electron tube. Preferably the heat transfer retarding means comprises four equally spaced radial grooves compressed into the upper surface of said getter metal vapour releasing material at Least partial¬ ly penetrating into the space formed by said side walls and said bottom wall. In general the radial grooves have a length longer than their width.

Referring now to Figs. 3 and 4 there is shown a second preferred embodiment of an evaporable getter device 200 in the form of a holder 202 having an outer side wall 204 and an inner side wall 206, joined together by a bottom wall 208. Holder 202

supports an evaporable getter metal vapour releasing material 210. Material 210 has an upper surface 212 containing a plurality of heat transfer retarding means 214, 214', 214", 214'". Preferably the heat transfer retarding means comprises four equally spaced radial grooves compressed into the upper surface of said getter metal vapour releasing material at least partially penetrating into the space formed by said side walls and said bottom wall. In general the radiaL grooves have a length longer than their width.

Bottom wall 208 is provided with means 216 for preventing detachment of the getter metal vapour releasing material 210 in the form of a plurality of holes 218 extending through bottom wall 208 and expos¬ ing Lower surface 218 of getter material 210. This prevents excessive pressure build up between the getter material and bottom wall 208.

EXAHPLE_1

This example is illustrative of the beha iour of prior art getter devices. Thirty (30) getter holders were manufactured having an outer side wall diameter of 15 mm and having an inner side wall diameter of 4 mm. The bottom wall has no annular groove. The holder was filled with 1000 mg of 50% BaAl - 50% Ni (by

4 weight ⁾ powder mixture. The upper surface was not provided with heat transfer retarding means. The getters were flashed according to American National Standard ASTH F 111-72 in order to determine the barium yield curves. A total time of 35 seconds was adopted. The yield curves obtained are plotted in Fig. 5 as curve 1. The start time at which the getter

containers commenced to melt is indicated by line A. EXAMPLE_2

This example is i llustrati e of the behaviour of further prior art getter devices. Thirthy (30) getter devices were produced and flashed exactly as for example 1 except that the bottom wall of the holder was provided with a groove as described n US Patent No. 4642516. The yield curve obtained is shown in Fig. 5 as curve 2. The start time at which the getter containers commenced to melt is indicated by line B .

EXAMPLE_3

This example is i llustrative of the present invention. Thirty getter devices were manufactured according to example 2 except that the upper surface of the getter powder mixture was provided with heat transfer retarding means as shown in Figs. 1 and 2. The yield curves obtained are shown in Fig. 5 as curve 3. The start time at which the getter containers commenced to melt is indicated by line C. EXAMPLE_4

This example is i llustrative of the present invention. Thirty getter devices are manufactured according to example 3 except that the groove in the bottom wall was replaced by holes as shown in Figs. 3 and 4. The results are found to be identical with curve 3 and point C on Fig. 5. DISCUSSION

As can be seen from Fig. 5 the prior art getter devices of Example 1 and 2 start to melt when- the getter metal (barium) yield is only slightly

greater than 180 mg which is only about 72% of the barium content of the getter device (250 mg) .

Getter devices of the present invention can yield approximately 230-240 mg of barium before start ^¬ ing to melt which is from 92-96% of the barium content.

The term "getter metal vapour releasing material" as used in the specification and claims herein is meant to include both the material prior to and after getter metal vapour release. This term embraces both the material in the form sold with the getter device and in the form in which it is found in an operating tube wherein the bulk of the getter metal has been evaporated from the material and is in the form of a film on the inside surfaces of the tube .

Although the invention has been described n considerable detail with reference to certain preferred embodiments designed to teach those skilled in the art how best to practice the invention, it will be realized that other modifications may be employed without departing from the spirit and scope of the invent on itself.