Abstract An application of metal particles comprised substantially of nickel to a nickel containing cathode substrate is followed by the application of potentially emissive materials comprised of nickel coated carbonates of barium and/or strontium and/or calcium. The particles and nickel coated carbonates are diffusion bonded or welded to the substrate and to each other after the cathode is mounted in a tube, simultaneously with activation of the cathode. The coating thus provided is very adherent and reduces arcing during high voltage applications. An alternate embodiment for further increasing adherence of the emissive material comprises adding a nickel etching agent, such as barium nitrate, to the potentially emissive material suspension. During the temperature increase noted above to activate the cathode, the etching material first melts and densifies the carbonates and then decomposes to etch the nickel particles and the substrate. Further heating changes the etching material and stops the reaction.
The invention of claim 1 wherein said processing temperature is about 1,100*C.
Claim 2
Dependent Claim
22 words
The invention of claim 2 wherein said second volatile suspension contains a nickel etching agent having an activation temperature of about 600*C.
Claim 3
Dependent Claim
12 words
The invention of claim 3 wherein said etching agent is barium nitrate.
Claim 4
Independent Claim
109 words
A method of making thermionic cathodes which comprises the steps of first forming on a nickel containing substrate a first layer of particles comprised substantially of nickel by spraying said particles in a first volatile suspension from a first spraying source; then spraying thereover a potentially emissive material in a second volatile suspension from a second spraying source, said potentially emissive material comprising nickel coated carbonates of barium and/or strontium and/oR calcium, said nickel comprising from 2 to about 7 percent by weight of said carbonates; and subsequently firing said cathode at a temperature above the minimum sintering temperature of said nickel particles but below the melting temperature thereof.
Claim 5
Dependent Claim
12 words
The invention of claim 5 wherein said firing temperature is about 1,100*C.