GB2075252A - Surge diverter - Google Patents

Abstract

A low threshold voltage gas discharge surge diverter carries, on the sufaces of its electrodes (2,3), a substance (4,5) with high electron emissibility which has constituent parts comprising an alloy containing barium and nickel and which is produced, for example, by pressing onto the electrodes a mixture of nickel powder and a barium-containing substance e.g. BaH2, BaS, BaS4, BaBr or BaN6 and then heat treating the same during sealing of the surge diverter. The barium-nickel alloy may contain 60-99.8 wt.% nickel and 0.2-40 wt.% barium, and the nickel may be doped with radioactive nickel 63. <IMAGE>

Description

SPECIFICATION A surge diverter and method of production This invention relates to surge diverters having a gastight insulator or housing in which are housed electrodes arranged in spaced relationship opposite each other, at least one of the electrodes including a barium-containing substance of high electron emissibility.

In surge diverters of this type, the substance of high electron emissibility serves to reduce the ignition voltage to a desired stable low value, for example in low voltage systems such as specifically in telephone systems. For example, for this purpose substances are suitable which contain alkaline earth metals or alkaline metals. Barium has proved to be particularly suitable. However, the use of pure elementary barium brings with it considerable problems.

In German patent specification 19 50 090 there is described a surge diverter with an activating layer made of a barium-aluminium alloy arranged on the electrodes. This has the disadvantage that, in use, this layer easily pulverises, especially when subjected to heavy electrical stress, and forms a layer of dust on the inside of the insulator housing which in time leads to a deterioration of the insulating properties.

For improving the properties of such surge diverters, German patent specifications 2537 964 and 26 19866, for example, describe processes whereby potassium bromide or titanium hydride is added to the barium aluminium alloy This has the disadvantage that the mixture of the individual constituent parts has to be applied to the electrode in the form of a paste with a binder and the binder has to be replaced and removed by a special manufacturing process. The manufacture of such surge diverters is therefore complicated and costly and thus hardly suitable for use in mass-production techniques.

It is an object of the present invention to provide a surge diverter with a low threshold voltage having improved long term stability and long operating life without detrimental effect on the electrical properties during operation and heavy electrical stress. A further object is to provide a method for economically mass-producing such surge diverters.

In accordance with one feature of the invention there is provided a surge diverter having a gastight insulator housing, in which are housed electrodes arranged in spaced relationship opposite each other, at least one of the electrodes including a bariumcontaining substance of high electron emissibility; characterised in that the barium-containing substance comprises an alloy containing barium and nickel as constituent parts.

In accordance with another feature of the invention there is provided a method for producing the aforementioned surge diverter in which the electrodes are joined to the housing by heat fusion; characterised by the process stage whereby prior to the joining of the electrodes with the insulator housing a mixture of nickel powder and a bariumcontaining substance is pressed onto the surface of at least one of the electrodes.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is an axial cross-sectional view of one embodiment of a surge diverter in accordance with the invention; and Figure 2 is a view, similar to that of Figure 1, of a second embodiment.

In Figure 1, is shown a surge diverter with a cylindrical insulator housing 1, for example made from an aluminium oxide ceramic pipe. Into the two open ends of this pipe 1 there are fused, in a gastight manner, two electrodes 2 and 3, for example of an Fe-Ni or Fe-Ni-Co molten alloy so that the centre parts of these electrodes 2 and 3 are facing each other in spaced relationship.

The diameter of the insulator housing for surge diverters used in communications systems, specifically in telephone systems, for example is 5 to 8 mm.

It is useful in this case to use a ceramic pipe having a wall thickness of 1 to 1.5 mm and electrodes having a thickness of 0.5 to 1.0 mm.

The two electrodes 2 and 3 are provided each with a layer 4 and 5 of high electron emissibility on their oppositely arranged facing surfaces. These substances are preferably arranged in recesses 6 and 7 of the electrode facing surfaces. For achieving improved adhesiveness the centre surfaces of the electrode facing surfaces can each be provided with grooves 8 and 9 in the form of a grid similarto the pattern of a wafer iron. The substances 4 and 5 atthe same time contain barium and nickel in one alloy.

Preferably the proportion of nickel is 60 to 99.8 wt % and the barium is 0.2 to 40 wt %. A particularly useful combination has proved to be a mixture consisting of 95 wt % nickel and 5 wt % barium.

The-gastight inner chamber 15 of the surge diverter is filled with a suitable inert gas, for example argon, and preferably also containing hydrogen. For preventing undesirable ignition delays it is possible to add a small amount of tritium in a known manner.

Additionally, known ignition aids in the form of ignition strips etc. may also be provided.

Figure 2 shows an example of a surge diverter which differs from that shown in Figure 1 by the application of the layer of high emissibility on the electrodes. In contrast to Figure 1, the electrodes in Figure 2 have surface centre pieces 10 and 11 on which the respective high emissibility layers 12 are applied in such a manner that their edges 13 extend over the edges of the electrode centre pieces.

A surge diverter according to the invention, for example the type described with reference to Figure 1, can be produced as follows: In the central recesses 6 and 7 of the electrodes 2 and 3, prior to their fusion with the insulator housing, is pressed a mixture of a barium-containing substance and nickel powder without binding agents. This barium-containing substance may contain elementary barium or may be composed of a thermally decomposible barium salt, such as for example Ba H2, BaS, BeS4, BaBr and BaN6. The wafer iron-like structure of the grooves 8 and 9 ensures a sufficiently good adhesion.The electrodes thus pretreated are then gastightiy joined by heat fusion with the insulator housing in a known manner, such as for example as described in Swiss Patent Specification 378 765; preferably by means of a suitable intermediate layer. This is effected by arranging the parts together, if necessary provided with suitable intermediate layers, and heating in a vacuum to, for example, 450"C and subsequent heating to approximately 950"C in an inert atmosphere corresponding to the desired gas filling.

During this heat treatment the barium compound decomposes and forms a solid substance containing barium and nickel as constituent parts. It is to be expected that this substance will be present, for example, in the form of a barium-nickel alloy.

Surprisingly, surge diverters with such an activating substance on the electrodes showed substantial advantages over previous surge diverters having different barium alloys as the activating substance; especially with barium aluminium alloys. It was also shown that the pulverisation of the activating su bst- ance in operation, especially when subjected to strong electrical stresses, was less when using an activating substance with barium and nickel than when using other known barium-containing activating layers.Such surge diverters therefore showed a considerably improved retention of the insulation on the inner walk ofthe housing, even with longer operating times and therefore substantially improved long term stability which, according to the chemical properties of barium-nickel alloys, was entirely unexpected for those skilled in the art.

Also the production of the surge diverters in accordance with the invention is considerably simplified since the activating substance can be applied without binding agents and the pumping and gas filling stages are therefore considerably simplified.

Apart from that there is an absence of undesirable residues from the binders. Also, the formation of the activating substance can be effected simultaneously by a single temperature treatment during heat fusion of the electrodes with the ceramic bodies. The method according to the invention is therefore particularly useful for clean and economical massproduction processes.

It should also be noted that the inventive idea can be used with other types of surge diverters, especiallythose having more than one pair of electrodes such as with so-called twin-path surge diverters. In place of a ceramic housing another insulator housing may be used, for example a glass body. Furthermore, another known fusion technique can be used. The nickel powder may also be doped with radioactive nickel 63 so as to disperse, in this case with the addition of tritium to the filling gas, as described in German patent specification 2446063.

Although it is generally useful to provide both electrodes with an activating layer, especially in the case of A.C. surge diverters, when used in D.C.

systems it may be sufficient to provide only the electrode acting as the cathode with a corresponding layer or substance for reducing the electron output operation.

A surge diverter manufactured in accordance with the method described is particularly suitable for protecting against excessive voltages of low voltage apparatus and systems such as telephone installations where a stable low voltage is required and maintained over extended operating periods even when subjected to strong electrical stresses.

Claims (11)

1. A surge diverter having a gastight insulator housing (1), in which are housed electrodes (2,3) arranged in spaced relationship opposite each other, at least one of the electrodes including a bariumcontaining substance (4,5) of high electron emissibility; characterised in that the barium-containing substance (4,5) comprises an alloy containing barium and nickel as constituent parts.

2. A surge diverter according to claim 1; characterised in that the barium-containing substance (4,5) comprises 60 to 99.8 wt % nickel and 0.2 to 40 wt% barium.

3. A surge diverter according to claim 2; characterised in that the barium-containing substance (4,5) comprises a weight component of nickel in the region of 95% and a weight component of barium in the region of 5 wt %.

4. A surge diverter according to any one of claims 1 to 3; characterised in that the nickel contained in the substance (4,5) is doped with radioactive nickel 63.

5. A method for producing a surge diverter according to any one of claims 1 to 4, in which the electrodes (2,3) are joined to the housing (1) by heat fusion; characterised by the process stage whereby prior to the joining of the electrodes (2,3) with the insulator housing (1) a mixture of nickel powder and a barium-containing substance is pressed onto the surface of at least one of the electrodes (2,3).

6. A method according to claim 5; characterised in that the barium-containing substance is composed of elementary barium.

7. A method according to claim 5; characterised in that the barium-containing substance contains a barium salt.

8. A method according to claim 5; characterised in that the barium-containing substance is at least a compound from the group BaH2, BaS, BaS4, BaBr, BaN6.

9. A method according to any one of claims 5 to 8; characterised in that during the heat fusion of the electrodes (2,3) with the housing (1) said mixture is heated to a temperature lying above the decomposition temperature of the barium-containing substance.

10. A method according to claim 5 and substantially as herein described.

11. A surge diverter according to claim 1 and substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawing.