DE2010479C3 - Metal capillary cathode with a porous emission material carrier protected against humidity - Google Patents

Description

The invention relates to a supply cathode, in particular a ready-to-install one, in a normal atmosphere storage-stable MK cathode. in which the stock substance either consists of alkaline earth carbonate, in particular Rarium or barium strontium carbonate, or also from alkaline earth oxide, in particular barium oxide, consists, and in the case of the porous sintered emission material carrier covering the supply a tungsten disk, which in particular also has an osmium and / or Has rhenium coating, consists.

The invention is of particular importance for those MK cathodes whose stock is either storage-stable Alkaline earth carbonates or also of moisture-sensitive alkaline earth oxides and therefore either without further ado or with special care on the basis of appropriate Precautions can be stored approximately indefinitely.

In practice it has been shown that MK cathodes, with z. B. to lower the operating temperature \ Vi,! frame disc covered with osmium. in operation only then the expected exit ar'-jits low " or reduce the operating temperature if sufficient for the osmium. Diffusion annealing has been carried out.

Abc even then there may still be deviations from a lower exit temperature, namely whenever the additional layer until or in the company /. B. a considerable amount

ίο number us. Carbon compounds exposed wire '. Protection against this is provided by an additional rhenium layer. which is also formed accordingly by an annealing.

The application of tungsten covered with rhenium

disk enables, among other things, the introduction of lacer-resistant alkaline earth carbonate supply. because rhenium does not lead to carbide formation. Through this vsiid achieved that the required Monday work and the storage of the MK cathodes themselves can take place in atmospheric air. To However, longer experience in production could be observed that the against the in operation released carbon dioxide protective rhenium layer against water vapor partial pressures during storage

times that they "extend over weeks and months, is sensitive. It was found that, depending on the relative humidity and the warehouse / s: ' the rhenium surface oxidizes at different rates can be. This has an effect

from the fact that increased work functions are observed during the first 300 to 500 hours upon start-up will.

The object on which the invention is based is therefore to create emission disks, if necessary with additional metal coating, made of osmium and / or rhenium to be modified in such a way that a Storage at high relative humidity is also made possible for longer periods of time.

This is achieved with one described in the first paragraph Storage cathode, especially storage-stable and ready-to-install MK cathode, according to the Invention in that the tungsten disc with an additional dense, impermeable to moisture Protective coating made of a hydrophobic substance which is soluble in an organic solvent is provided.

This measure is based on the knowledge that the cathode surface protects against water vapor must be and that the protective coating must be made of a material which during heating, namely when starting up, without a reaction with the emission surface, leaving no residue decomposed. In contrast to the conditions of earlier times, when still so-called bare tungsten disks were used, z. B. with osmium and / or rhenium covered disks with such organic Coatings are provided. Because rhenium does not form carbides with carbon and so does it If it takes some time for this to diffuse into the tungsten base, it can now be a long one Range of organic substances offer appropriate protection. In practice z. B. a thin layer of paraffin dissolved in chloroform, the desired effect; about it In addition, such a sealing of the porous disk was achieved that even MK cathodes with barium oxide as emission stock are storable.

3 ⁴

But this basically results in a second 3 mm ^Du [ ^chm ™, ^ Γίη thin polyacrylic

Possibility of creating storage-stable MK vapors from the solvent

Cathode, namely those with barium oxide as saureester-1-ilm verou _Erfindunu be in stock, which even have the advantage that when starting more kin / unu _schematic tiCch dargestellheizen None Significant gas evolution occurs. ³ Hand one in the ^ "for ^r _u There are parts. Of course, this means that the meaning of th ^A .usfuhrungsbusp.Lh. ^ _{SiUndnis der Erfm} dun, cathodes -nil carbonate supply and with osmium or those not unnecessary u - ^ remains rhenium-covered tungsten disc. geniin- not ^bel ^ ^a ^ "training shown to partially in section

^ J _cB u

practical implementation be, a training guide for ^Io's il fl fldß Gt bjhaltei '^^ "' ^ '

With

D, c practical implementation be, e IJ ^^ aS ^

tiihrunusbeispiel is done as follows: Purified b-jhaltei '^^ "-' ^ '^ ^. ^ _olyenL . _n end of a ii lk t M) bi give iM unü u hib 3

ehrunusbeispiel is done as follows: Gerg ^ ^ ^^ _olyenL . _{In the} end of paraffin with a solidification point of about .M) to give iM unü up _mksionssto iTirUcrscheibe 3 7 (1 C is dissolved in chloroform in such a way that a porous sinteredLii. ^ J ^ _and ^ _{lit (lie!> cr} colorless, at room temperature saturated solution e.g. ^v y ° ^ttram , _rh . _{m (} j _{L. n isl} on the active over hdfit Rhemum covered « Hanse 4 J ^ i -rbu ^ J ^ _hb 3 first

colorless solution, saturated at room temperature, y, _rh . _{m (} j _{L. n isl} On the active over arises, from which on a = r., t Rhemum covered « Hanse 4 J ^ i -rbu ^ J ^ _{riiaerschelbe} 3 initially tungsten disk with eg 3mm diameter is approximately flat du. tr. mis "'. _ - _{d or} rhenium-H 015 ml LÖM.iiü are applied: after vermn a thin Usm.u ^^ _{and / was} /. B. solvent one of the pores is layered ^ ⁱⁿ " ^ _b " _the cathode. She will

ild in front of the ^Ζυ ™ ™

üun.ven Ue ^ solvent becomes one of the pores a ^ _{b of the} cathode. she will

filling paraffin pad made of 0.25 mg. in front of the ^Ζυ ™ ..., _{m wci} teren thin

In another example! ²⁰ λ turn ubcrüLt - ^ ^^ _organischc "

(II ml of a 40 "., itien polyacrylic acid * .ter solution in protective coating 3 a _rophobic substance. AK

z. B. mineral spirits (4.0 ml Plexisol P 550) in LO ml »gsmmd ^^ in 1 _Schulzüb erzug has

Butyl acetate with 0.1 g of phthalic acid to 2-ethyl ester for moisture and uichia. . ^

on a tungsten disc covered with rhenium made of paraffin bcv.

1 sheet of drawings

Claims (4)

Patent claims: 1. Storage cathode, especially lukewarm and ready-to-install MK cathode. where the Storage substance from alkaline earth compounds such as /. B. barium carbonate or barium oxide and in the case of the porous sintered emission material carrier covering the supply from tungsten in particular an additional excess of osmium and / or rhenium having its active surface, thereby g e k e π η ζ e i c h η e t. that the tungsten disk with an additional dense, moisture-impermeable protective cover made of one in one organic solvent soluble hydrophobic substance is provided. 2. Ve- ⁽ ahren for the production of a supply cathode according to claim 1, characterized in that the tungsten disk is immersed in a solution of hydrophobic substance and then dried. 3. Method of manufacturing a supply cathode according to claim 2, characterized in that paraffin is used as the hydrophobic substance Freezing point 50 to 70 C in chloroform to form a solution saturated at room temperature is resolved and that of it on a tungsten disk \. η z. Ii. 3 mm diameter 0.015 ml corresponding to a total amount of approx 0.25 mg can be applied. 4. A method for preparing a supply cathode according to claim 1 or 2, characterized in that that 0.1 ml of a 40 "strength polyacrylic acid ester solution in, for example, mineral spirits (4.0 ml Plexisol P 550), 1.0 ml butyl acetate and 0.1 g phthalic acid - to 2 - ethyl ester on one with rhenium coated tungsten disc of 3 mm diameter is applied so that after evaporation, a thin polyacrylic acid ester film remains.