DE1213059B - Supply cathode or ion source and process for their manufacture - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

HOIj

German KL: 21g-13/04

Number: 1213 059

File number: N 25602 VIII c / 21 g

Filing date: September 30, 1964

Opening day: March 24, 1966

The invention relates to a supply cathode or ion source, the emitting part of which consists of a porous Metal body is made.

In an ion source, which is used, among other things, in an ion propulsion motor, cesium vapor or another material of low ionization voltage flows through porous metal with a high melting point, e.g. B. tungsten, which has a relatively high exit potential and is kept at a high temperature in order to bring about a contact ionization of the vapor flowing through in this way. The ions evaporating on the ionization surface are accelerated outwards by an electrostatic field. As is known, the resulting reaction force can be used to propel the ionizer in the opposite direction. Both an increase in the percentage of steam that leaves the surface in the ionized state and a uniform distribution of the steam flowing out over the ionizing surface provide a better degree of efficiency. Both requirements are best met by very my pores, which are regularly distributed over the surface. Calculations show that an ideal ionizing surface would have pores with a diameter of about Ιμΐη (0.5 to 2μΐη), which should be spaced from one another at a distance of 1 to a few μm (1.0 to 4.0 μm). This means a pore density on the surface of 10 ⁷ pores cm ² . The requirement for constant dimensions contradicts the requirement for fine porosity. Ion sources must be used for a long time, e.g. B. a few hundred hours or more, at high temperature, e.g. B. 1100 to 1200 ° C, during which time the dimensions of the pores and their mutual distance must not change. In addition, the macroscopic dimensions of the porous body must also remain unchanged, since these also determine the geometry of the ion acceleration system. In addition, the porous body forms the closure of the space in which the steam is generated and in which no leaks are allowed to occur, which could arise, among other things, from shrinking or abandonment of the porous body.

Porous bodies with very fine pores generally tend, if they are kept at a high temperature for a long time, to strongly re-sinter, whereby not only a strong grain growth occurs and the number of pores becomes smaller and their dimensions larger, but also macroscopic deformations at the same time the shape occur supply cathode or ion source and process
for their manufacture

Applicant:

N. V. Philips' Gloeilampenfabrieken,

Eindhoven (Netherlands)

Representative:

Dipl.-Ing. E. E. Walther, patent attorney,

Hamburg 1, Mönckebergstr. 7th

Named as inventor:

Roberto Levi, New York, N. Y .;

Gary C. Irons, Stamford, Conn. (V. St. A.)

Claimed priority:

V. St. ν. America October 4, 1963 (313 859)

can. Dopings, with which the grain growth could be prevented, can be made with regard to ion emission poisoning cannot be used. It is also necessary that the starting material not too strong for the porous body made of very fine powder with spherical grains consists of different dimensions; however, this material is relatively expensive. Editing is too of bodies with very fine pores after impregnation with copper or the like. Considerably more difficult than machining coarsely porous bodies; Furthermore, bodies with very fine pores can also contribute deform the required treatment temperatures.

The aforementioned disadvantages of porous bodies of fine porosity for ion sources apply in general also for porous bodies that form part of the cathode of a discharge tube.

The invention aims to provide a porous body that has more favorable properties than the known body.

This is done by the fact that in the case of a supply cathode or ion source, its emitting part consists of a porous metal body, according to the invention the porous metal body has larger pores, so that no structural changes occur at the operating temperature, and with a thin,

609 539/329

is covered on its surface emitting layer, the porosity of which is so fine that a uniform Emission results.

According to a development of the invention, the layer of fine porosity can thereby be applied to the surface be applied that a fine metal powder is sprayed onto the coarsely porous body and the layer obtained in this way is firmly sintered for a short time at a relatively low temperature. Whereas for the sintering of a whole body temperatures of more than 2100 ° C for a few hours are required for a long time, sintering at about 1800 ° C for about a quarter of an hour is sufficient for the thin layer long. Grain growth can hardly occur. In order to achieve good adhesion, can the coarsely porous body is slightly oxidized on the surface; it is also possible to use an oxide of To apply metal and sinter it in a reducing atmosphere, with the oxide in the Metal is converted. The material can not only be sprayed, but also painted or brushed on will; the covering can also be applied cataphoretically, in this case one obtains extremely smooth layers.

It is not necessary that the coarsely porous body and its finely porous emitting surface layer consist of the same metal. For the porous surface, for. B. a metal with the the most favorable exit potential can be selected; the. Choice of the coarsely porous metal can be determined by this be that it should be possible to solder or weld this part.

When the porous body forms part of a cathode of a discharge tube, the finely porous Layer are applied after the coarsely porous part is impregnated with alkaline earth metal compounds has been.

The invention is explained in more detail with reference to the drawing, in which

F i g. 1 schematically shows a simple ion motor and

F i g. 2 an enlargement of part of the emitting Surface represents.

In Fig. 1, 1 denotes the chamber with a supply of the substance to be ionized, e.g. B, liquid cesium, which is kept at the required temperature by the heating element 2. 3 denotes a control element for the steam flow to the steam space 4, the envelope 5 of which is steam-tight and which is closed by a porous lomsation body 6 with an emitting surface 8; the ionization body and the damping space 4 are kept at the required high temperature with the heating coil 7. The electrodes 9 form the acceleration arrangement for the ions. 2 shows that the ionization body 6 consists of a coarsely porous part of it and a finely porous surface layer 11 with a surface 8. The coarsely porous part 10 consists of tungsten with a density of 60 to 88%, the density of compact tungsten. This coarsely porous body is made of tungsten particles with dimensions of 1 to 6 mm which, after being compressed ^{, were sintered at a pressure of about 2.5 t / cm 2} for about 4 hours in a neutral or a reducing atmosphere. The body obtained in this way has grains with dimensions between 3 and 20 μm, between which there are pores of 1 to 12 μm, on average pores of 5 μm with an average spacing of 15 μm. The body has 2 · 10 ⁵ pores / cm ² on the surface. If desired, this - coarsely porous body in a certain. Shape, e.g.

'with a hollow surface, can be used by the body with z. B. Impregnated copper and mechä = nisch is processed, after which the copper is evaporated. This procedure is well known. It will in this way z. B. a porous metal body with

ίο a hollow surface of about 5 · 10 cm and a thickness of a good 1 mm.

A layer of fine tungsten particles with a mean diameter is placed on this coarsely porous body of 0j8 μηι (from 0.5 to 1.0 μπι) applied.

A suspension is made from this powder which contains 70 g of powder in 100 cm ^{3 of} amyl acetate and to which a small amount of collodion is added. The suspension is applied using a conventional syringe in a layer that is at least *

ao stem equal to the thickness of a part and the upper limit of which is determined by the adhesion and the strength. After evaporation of the amyl acetate in the whole hydrogen during a quarter is * would be reduced at 1800 ° C, wherein the fine powder sinters together ¹ and adheres to the carrier while simultaneously burns the binder. In a certain case, the finely porous layer produced in this way is 20 μm thick; it has ent © density ^{of 8Ö 6} h, with the grains having a dimension of "0.5 to 6 μm, on average 3 μm. The diameter of the pores fluctuates between. 1 and 3 μm and averages 2 μm; the The mean distance is 3.5 μm. There are 4 · 10 ⁶ pores on one square centimeter of the surface

shows that the structure of the finely porous surface comes pretty close to the ideal case, what the Sintering of the distant surface layer during vet * relatively short time at not too high a temperature. As a result of the gföb porous

Underlay, the entire body retains its dimensions during operation.

To improve the adhesion of the finely porous layer, the coarsely porous body can be slightly oxidized beforehand, e.g. by heating in air 500 ° C for half an hour.- The surface then takes on a dark color aö. The oxidizing and heating should not be continued for so long that the color becomes yellowish, since the incorrectly porous layer then does not adhere. The oxide becomes during solid sintering the finely porous layer is reduced. Instead of one Oxidation can also be done by sandblasting the surface be roughened.

Another method is tungsten oxide applied and reduced,

In all cases it can reduce the thermal Radiation the surface can be polished or sanded.

Claims (4)

Patent claims: 1. Storage cathode or ion source, whose emitting part made of a porous metal body consists, characterized in that the porous metal body (10) has larger pores has, so that no structural changes occur more at the operating temperature, and with eittef thin, emitting on its surface layer (11) is covered, the porosity of which is so fine that an even emission results. 2. A method for producing a porous metal body for a supply cathode or Ion source according to claim 1, characterized in that on the surface of a coarsely porous Body is a fine powder of a metal or a reducible compound thereof is attached, which is sintered in a short time at a relatively low temperature. 3. The method according to claim 2, characterized in that the coarsely porous body the surface is oxidized or roughened beforehand. 4. The method according to claim 2, characterized in that the finely porous layer is applied after the roughly porous body has been impregnated. 1 sheet of drawings