Getter Holder and Electric Discharge Tube Comprising Such a Holder

The invention relates to a getter holder having at least one open cavity with a mainly U-shaped cross-section. Disposed in the cavity is a body consisting of compressed powder of a gettering material which can be released from the body at least partly by heating. The getter holder further comprises means for locking the body in the cavity.

The invention further relates to an electric discharge tube comprising such a holder. Such a getter holder is known from the U.S. Pat. No. 3,457,448. This patent describes an endless gutter-shaped holder in which the means to lock the gettering material compressed in the getter consist of a wire secured to the bottom of the gutter-shaped holder and preferably of a projection or constriction in the outer wall of the holder in which case comparatively large deformations are concerned. Since a getter holder is generally stamped from sheet material, such deformations at right angles to the direction of stamping present problems in detaching of the shaped article from the stamping tools.

It is the object of the invention to provide a getter holder with simple means for preventing particles of solid material from being released therefrom during, as well as after, the evaporation of the gettering material.

According to the invention, in a getter holder comprising at least one open cavity having a mainly U-shaped cross-section, the means to lock the filling in the holder includes of a surface unevenness extending at least over a portion of the inner wall of the cavity.

The invention is based on the recognition of the fact that for good locking of a compressed gettering powder can be obtained without the need for relatively large deformations in the walls of the holder. A slight surface unevenness is sufficient to realize the end envisaged with the invention. As compared with known means for locking the gettering material the invention has the advantage that a slight surface unevenness can be obtained in a simple manner.

According to the invention, the surface unevenness preferably includes at least one groove in at least one of the side walls of the cavity which extends substantially parallel to the bottom plane of the cavity. Such a groove is provided in the sheet material before shaping the holder and the depth thereof is only one to a few tenths of the wall thickness of the holder.

According to a favourable embodiment of the invention, the inner wall of the getter holder has an average surface roughness of at least 0.5 .mu.m. (The roughness is sometimes expressed in the unit "ru" where 1 ru = 1 micro inch .apprxeq. 1/40 .mu.m). According to the invention such roughnesses can be obtained in a simple manner by sand-blasting or chemically. These operations can be carried out prior to or after the formation of the holder. There is however, a slight advantage in roughening the side walls after the formation of the holder because shaping of the holder it is preferable to use sheet material with a surface which is as smooth as possible to minimize detrition of the tools.

The invention will be described in greater detail with reference to the drawing, in which

FIG. 1 is a partial cross-sectional view of a gettering device according to the invention, and

FIG. 2 shows a television display tube with a gettering device shown in FIG. 1.

The gettering device shown in FIG. 1 comprises an angular chromium-nickel-steel gutter 1 made from 0.25 mm thick sheet material. The gutter is 2 mm deep, 5 mm wide and has an outside diameter of 25 mm. A powdered mixture 2 of one part by weight of BaAl.sub.4 and one part by weight of Ni is compressed in the gutter to which mixture is added 0.5% by weight of TiH.sub.2 with respect to the overall weight. The upright walls 6 and 7 of the gutter each have two grooves 3, 4 and 3', 4' which have a depth of approximately 40 .mu.m and extend in a plane parallel to the bottom plane 5 of the holder. The grooves ensure a good locking of the filling in the holder and they are pressed in the sheet material prior to shaping the holder by means of a die.

Good locking of the filling in the holder can also be obtained with a holder whose inner surface has been roughened. Good results have been obtained with a holder having a surface roughness of approximately 1 .mu.m obtained by sand-blasting or by chemical treatment, for example, by pickling the holder with a solution of ferrichloride in hydrochloric acid.

The invention is not restricted to cases in which the powdered mixture is compressed into a body in the getter holder itself. It is also possible to use a precompressed filling which is postcompressed after introduction into the holder.

The television display tube shown in FIG. 2, comprises a glass envelope 10 in which is mounted an electron gun 11 shown diagrammatically in the drawing. A metal strip 12 is welded to the electron gun and at the end thereof is secured a gettering device 13 such as that described with reference to FIG. 1. After evacuation of the tube the barium is evaporated by high frequency heating from the mixture compressed in the holder. The evaporation process is accelerated by an exothermal reaction between the barium-aluminium and the nickel, the aluminium binding to the nickel and the metal of the holder. A short time before and during the evaporation of the barium, the quantity of TiH.sub.2 added to the gettering mixture decomposes. The released hydrogen gas operates as a scattering medium on the evaporating barium. The hydrogen gas itself with the residual gases remaining in the tube is taken up again by the layer of barium thus formed.