US2169643A

US2169643A - Incandescible cathode

Info

Publication number: US2169643A
Application number: US195890A
Authority: US
Inventors: Holst Gilles; Horst Hajo Lorens Van Der
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1933-09-07
Filing date: 1938-03-14
Publication date: 1939-08-15
Anticipated expiration: 1956-08-15
Also published as: GB438227A; NL42650C; BE404739A

Description

Aug. l5, 1939. G. HOLST E1' AL 2,159,643

y mcANnEscILE cATHoDE Original Filed Sept. 6, 1934 f/vvf/vrams .5y ,awa/410%..

Patented Aug. 15, 1939 TENT GFFCE INCANDE SCIBLE CATHODE Gilles Holst and Hajo Lorens van der Horst, Eindhoven, Netherlands, assignors to N. V.

Philips Netherlands Glceilampenfabrieken,

Eindhoven,

Original application September 6, 1934, Serial No. 743,006. Divided and this application March 14, 1938, Serial No. 195,890. lin Germany September 7, 1933 6 Claims.

The present invention, which is a division of our copending U. S. patent application Serial No. 743,006, now Patent No. 2,119,913 relates to incandescible cathodes, and more particularly to cathodes having the large electron-emitting surfaces required for gas-filled discharge tubes, such as rectifying tubes ci large current capacities.

1f such cathodes are to handle large currents they should have a large electron-emitting surlo face, and the specific emissivity, i. e. the electron emission per unit of cathode surface, should be as high as possible for a given temperature. To obtain a large specific emissivity at a given temperature, the cathode surface is usually activated with a surface layer or coating of a material having a high electron emissivity, for instance a highly-emissive oxide, such as barium oxide.

Various constructions have already been proposed to obtain cathodes having a large emitting surface; for instance, according to U. S. Patent No` 2,052,103 to Mulder et al., a large cathode surface is obtained by winding into a roll a metallic gauze provided with a highly-emissive coating. Such construction, however, has certain drawthe wire forming the gauze. More particularly, the gauze is very readily damaged, and this is vaggravated by the fact that the wire forming the gauze, instead of being made of tungsten or other highly refractory metal, is usually made of a lower melting-point metal, such as nickel, in order that the oxide layer will more readily adhere thereto. metals the individual wires of the gauze are liable .'-15 to melt, which may impair the operation of the entire cathode structure. Although the latter drawback can be partly removed by providing a plurality of supply wires connected to various points of the metal-gauze or by Weaving the gauze of alternately arranged tungsten. and nickel wires, such structures are expensive and not entirely satisfactory for handling very large currents.

According to our present invention, these drawbacks are overcome by providing a large-surface cathode body, which may be either directly and/or indirectly heated, in the form oi a composite band which is folded or wound into a coinpact form. This composite band has essentially two components, namely, a single continuous elongated support in the form of a metal wire or metal strip which extends the entire length of the band, and a large surface-area member consisting of a large number of projections which may be individual or be formed as a continuous membacks which are due especially to the thinness of'k When made of such low melting (Cl. Z50-27.5)

ber; the projections being mechanically and electrically connected with the support or may be even integral therewith.

Furthermore, in accordance with the invention the projections of the large surface-area member extend in a direction substantially perpendicular to thesupport, whereby the composite band forms asubstantially flat structure which can ce made in any length in a continuous operation, and then cut into the desired length and assembled into a compact assembly, for instance wound into a roll.

The support is given a suicient cross section to act as a supply conductor for the discharge current, and if desired also for the heating current without danger of melting, and even if some ci the projections should melt away or break oli, the support remains intact and the operativeness of the cathode is substantially unaffected.

referably, the support itself is made oi a high melting-point metal, for instance tungsten, whereas the projecting parts may be formed of a lower melting-point metal, for instance nickel, to which the oxide rmly adheres.

More particularly in accordance with the invention, the composite band is shaped as a comb, in which the support forms the rib or base and the projecting parts form the teeth. 1f the support is to be made of the same material as are the projecting teeth, the composite band can be formed by a single stamping. However, we prefer to make the support of a greater thickness and of' a higher melting point metal than that of the teeth.

The composite band may be heated by passing current through the support and for this purpose the support may be provided with leads which are sealingly carried through the tube envelopes, or, ii also a separate heating element, for instance a lament, is provided, the support ends are electrically connected to the ends of the heating element.

In a preferred embodiment of our invention a composite band according to the invention is wound into a roll, and this roll is surrounded by a helically-wound, directly-heated cathode.

With the above-described constructions it is possible to obtain a five to tenfold increase of the emitter-carrying surface, which results in an equal increase of the discharge current capacity of the cathode.

In order that the invention may be more clearly understood and readily carried into eiect, we shall describe the same in more detail with reference to the accompanying drawing, in which:

Figure l is a side view of a comb-shaped coinposite band shown in evolution; and shows the cross-section of the support,

Figure 2 is a comb-shaped band similar to that shown in Fig. 1 but having a support and teeth made of a single piece of metal,

Fig. 3 is a top View of a cathode structure employing a cathode band shown in Fig. l,

Fig. 4 is a partly sectionalized side elevation of a cathode structure comprising a comb-shaped band as shown in Fig. l, which is surrounded by a directly heated coiled cathode, and

Fig. 5 is a top View, partly in section, of Fig. 4.

The composite band shown in Fig. 1 has the shape of a comb and consists of a supporting wire or band I carrying laterally extending projecting .teeth 2. The composite band may be formed of a supporting part I thicker than the teeth 2, and may be made of a refractory metal, as tungsten; the projecting teeth 2 being preferably made of nickel to which an oxide coating, for instance barium oxide, readily adheres. However, support I rnay also be coated with an electron emissive layer. Such a composite band may be formed in any length and then cut to the desired length.

An alternative construction is shown in Fig. 2 in which the supporting band 3 and the teeth 4 are formed out of one metal strip. This has the advantage that an excellent mechanical and electrical connection of the support and the teeth is obtained.

As shown in Fig. 3, the composite band of Fig. i is rolled into a spiral whose inner end is secured to a central supporting rod 5 and whose indiviclual turns are spaced from each other. The spirally wound composite band is surrounded by a helically wound heating Wire B, which is provided with leads 'l and 8 for the supply of the heating current. The outer end of the support I is electrically connected, preferably by welding, to the supply lead l.

The composite band, preferably including the support I, is coated with an oxide layer and the heating wire 6 is similarly coated. When a heating current is passed through the heating wire 6, one part of the cathode assembly is heated directly and the other part is heated indirectly., If desired, supporting rod 5 may be electrically connected to the supply wire 8, in which case the heating current passes through both the heating wire 6 and the support I, thus giving a cathode assembly in which both parts are heated directly as well as indirectly.

For spacing the turns of the composite band, interposed rods, (not shown) may be used, although good results can be obtained when the successive turns of the band are in contact With each other; provided the apertures and teeth be properly staggered to expose substantially the entire cathode to the discharge. Figs. 4 and 5 show the combination of a cathode structure in accordance with Fig. 1, with a directly heated cathode 9, the latter forming a coiled lament which surrounds and indirectly heats the composite band cathode body I-2.

The helically wound cathode may also be of a composite structure, and as shown, comprises two tungsten wires IO-IO which are coiled and surrounded throughout their whole length with a thin helically wound nickel wire I I, the turns of which lie in direct contact with each other. The unwound end portions of the tungsten wires Iii-I may be nickel plated, so that the entire outer surface of the cathode structure 9 is provided with a nickel surface. The undulated surface of the nickel wire II is especially favourable for the rm adherence of an oxide coating. The ends of the tungsten wires IU--IO are welded or otherwise connected to lead-in rods I2-I 3, which also serve as supports for the cathode. The supporting strip I of the composite cathode band is welded at its inner end to the rod which serves as a supply conductor for the discharge current to the band, which rod is connected at its end to the rod I3. The support I may be directly heated in which case the outer end of the support I may be electrically connected to the lead-in rod I2.

Between the large surface body and the cathode 9 tubes I4 of insulating material (see Fig. 4) for instance of porcelain are provided for spacing, inside of which are disposed metal wires I5 having bent upper end-portions I6 which engage the composite band I-2 and iix the same securely within the cathode 9.

The cathode structure shown in Figs. 3 and 4 provides for an emission which, assuming that the same heating energy is used, may be several times the emission which can be obtained by merely using the helically wound cathode 9.

While we have described our invention in connection with a specic embodiment and in a specific application, we do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What we claim is:

1. A compact incandescible cathode body comprising a composite comb-shaped band having an elongated support for carrying the emission current, and a large number of straight elongated projecting portions spaced from each other and extending substantially perpendicularly to the longitudinal axis of the support, and highly electron-emissive material on the surface of said projecting portions, said band being bent along lines perpendicular to the longitudinal axis of the support into a series of convoluted portions forming a compact body provided over its entire cross section with a large number of ducts extending substantially from end to end of the body and allowing access of the discharge to the interior thereof.

2. A compact incandescible cathode body comprising a metal band having an elongated supporting portion for carrying the emission current and a large number of straight elongated portions extending substantially perpendicularly to the longitudinal axis of the supporting portion and being spaced from each other, and highly electromemissive material on the surface of -`said extending portions, said band being bent along lines parallel to the longitudinal axes of said extending portions into a series of convolutions forming a compact body provided over its entire cross-section with a large number of ducts extending substantially from end to end of the body and allowing access of the discharge to the interior thereof.

3. A compact incandescible body comprising a composite band having an elongated support for carrying the emission current and consisting of a high-melting-point metal, and a large number of straight elongated projecting portions extending substantially perpendicularly to the longitudinal axis of the support and consisting of a low-melting point metal to which electron-emissive materials rmly adhere, and highly electronemissive material on the surface of said projecting portions, said band being bentv along lines perpendicular to the longitudinal axis .of the support into a series of convoluted portions forming a compact body provided over its entire cross section With a large number of ducts extending substantially from end to end .of the Abody and allowing access to the interior thereof.

V4. An incandescible cathode body comprising a composite comb-shaped band having an elongated support for carrying the emission current and a large number of straight elongated projecting portions spaced from each other and extending substantially perpendicularly to the longitudinal axis of the support, highly electron-emissive material on the surface of said projecting portions,

said band being bent along lines perpendicular to the longitudinal axis of the support into a series of convoluted portions constituting a compact body provided over its entire cross section with a large number of ducts extending substantially from end to end of the body and allowing access of the discharge to the interior thereof, and a rod .of conductive material centrally disposed within the body and electrically connected to said support.

5. An incandescible cathode body comprising a composite comb-shaped handhaving an elongated support for carrying the emission current and a large number of straight elongated projecting portions spaced from each other and extending substantially perpendicularly to the longitudinal axis of the support, said band being bent along lines perpendicular to the longitudinal axis of the support into a series of convoluted portions constituting a compact body provided over its entire cross section With a large number of ducts extending substantially from end to end of the body and allowing access of the discharge to the interior thereof, a -directly-heated helically-Wound cathode surrounding said body to heat same tol its proper electron-emitting temperature and having a large surface area, and highly electron-emissive material on the surfaces of said helically-wound cathode and of said projecting portions.

6. An incandescible cathode body comprising a composite comb-shaped band having an elongated support for carrying the emission current and a large number of straight elongated projecting portions spaced from each other and extending substantially perpendicularly to the longitudinal axis of the support, said band being bent along lines perpendicular to the longitudinal axis of the support into a series .of convoluted portions constituting a compact body provided over its entire cross section with a large number of ducts extending substantially from end to end of the body and allowing access of the discharge to the interior thereof, a rod of conductive material centrally disposed Within said body and electrically connected to said support, a directly-heated helically-Wound cathode surrounding said body to heat same to its proper electron-emissive temperature and having a large surface area, highly electron-emissive material on the surfaces of said helically-wound cathode and of said projecting portions, and means supporting said body from said rod and insulatingly spacing said body from said cathode, said means comprising a plurality of insulating members disposed between said band and said cathode, and supporting members secured to said insulating members and to said rod.

GILLES HOLST. HAJO LORENS VAN DER HORST.