Thermionic tungsten/scandate cathodes and method of making the same

Patent metadata

Field	Value
Publication number	US-11075049-B2
Application number	US-201916601620-A
Country	US
Kind code	B2
Filing date	Oct 15, 2019
Priority date	Apr 10, 2015
Publication date	Jul 27, 2021
Grant date	Jul 27, 2021

Abstract

A thermionic dispenser cathode having a refractory metal matrix with scandium and barium compounds in contact with the metal matrix and methods for forming the same. The invention utilizes atomic layer deposition (ALD) to form a nanoscale, uniform, conformal distribution of a scandium compound on tungsten surfaces and further utilizes in situ high pressure consolidation/impregnation to enhance impregnation of a BaO—CaO—Al2O3 based emissive mixture into the scandate-coated tungsten matrix or to sinter a tungsten/scandate/barium composite structure. The result is a tungsten-scandate thermionic cathode having improved emission.

First claim

What is claimed is:

1. A process for making a thermionic dispenser cathode, the process including the steps of:
providing a starting powder comprising particles of a refractory metal and/or metal alloy;
placing the starting powder inside a furnace having a controlled atmosphere and heating the starting powder in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides to produce a cleaned starting powder;
making a porous preformed compact from the cleaned starting powder;
without exposing the cleaned starting powder to an external atmosphere, placing the porous preformed compact inside a particle atomic layer deposition (ALD) reactor and controllably depositing a conformal nanometer-scale film of a scandium compound on all available surfaces inside and outside of the porous preformed compact to produce a scandium compound-coated compact with a conformal nanometer-scale scandium film having a predetermined thickness uniformly deposited on all of the surfaces thereof;
without exposing the scandium compound-coated compact to air, placing the scandium compound-coated compact in contact with an emissive mixture comprising a barium compound; and
without exposing the scandium compound-coated compact in contact with the emissive mixture to air, subjecting the compact with the contacted emissive mixture to a predetermined pressure P and temperature T greater than a melting point of the emissive mixture so that the emissive mixture becomes a molten emissive mixture that infiltrates the scandium compound-coated compact to form a barium-impregnated scandium-coated compact;
wherein the impregnated compact forms the cathode.

2. The process according to claim 1 , wherein the refractory metal and/or metal alloy is tungsten.

3. The process according to claim 1 , wherein the scandium compound is scandium oxide.

4. The process according to claim 1 , wherein the barium compound is barium-calcium-aluminate.

5. The process according to claim 1 , wherein the pressure P is between about 0.1 and 5 GPa.

6. The process according to claim 1 , wherein the temperature T is between 1,500° C. and 2,100° C.

7. A process for making a thermionic dispenser cathode, the process including the steps of:
providing a sample of a porous refractory metal and/or metal alloy;
placing the sample inside a furnace having a controlled atmosphere and heating the starting powder in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides to produce a cleaned sample;
without exposing the cleaned sample to an external atmosphere, placing the cleaned sample inside an atomic layer deposition (ALD) reactor and controllably depositing a conformal nanometer-scale film of a scandium compound on all available surfaces inside and of the cleaned sample to produce a scandium compound-coated sample with a conformal nanometer-scale scandium film having a predetermined thickness uniformly deposited on all of the surfaces thereof;
without exposing the scandium compound-coated sample to air, placing the scandium compound-coated sample in contact with an emissive mixture comprising a barium compound; and
without exposing the scandium compound-coated sample with contacted emissive mixture to air, subjecting the scandium compound-coated sample with contacted emissive mixture to a predetermined pressure P and temperature T greater than a melting point of the emissive mixture so that the emissive mixture becomes a molten emissive mixture that infiltrates the scandium compound-coated sample to form a barium-impregnated scandium-coated sample;
wherein the impregnated sample forms the cathode.

8. The process according to claim 7 , wherein the refractory metal and/or metal alloy is tungsten.

9. The process according to claim 7 , wherein the scandium compound is scandium oxide.

10. The process according to claim 7 , wherein the barium compound is barium-calcium-aluminate.

11. The process according to claim 7 , wherein the pressure P is between about 0.1 and 5 GPa.

12. The process according to claim 7 , wherein the temperature T is between 1,500° C. and 2,100° C.

13. A process for making a thermionic dispenser cathode, the process including the steps of:
providing a starting powder comprising particles of a refractory metal and/or metal alloy;
placing the starting powder inside a furnace having a controlled atmosphere and heating the starting powder in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides to produce a cleaned starting powder;
making a porous preformed compact from the cleaned starting powder;
without exposing the cleaned starting powder to an external atmosphere, placing the porous preformed compact inside a particle atomic layer deposition (ALD) reactor and controllably depositing a conformal nanometer-scale film of a scandium compound on all available surfaces inside and outside of the porous preformed compact to produce a scandium compound-coated compact with a conformal nanometer-scale scandium film having a predetermined thickness uniformly deposited on all of the surfaces inside and outside thereof;
with the scandium compound-coated compact still in the ALD reactor and without exposing the compact to air, depositing a conformal layer of a barium compound on all available surfaces inside and outside of scandium compound-coated compact; and
without exposing the scandium compound-coated compact with deposited barium layer to air, subjecting the scandium compound-coated compact with deposited barium layer to a predetermined pressure P and temperature T to sinter the compact to full density;
wherein the sintered compact forms the cathode.

14. The process according to claim 13 , wherein the refractory metal and/or metal alloy is tungsten.

15. The process according to claim 13 , wherein the scandium compound is scandium oxide.

16. The process according to claim 13 , wherein the deposited barium layer is barium oxide.

17. The process according to claim 13 , wherein the pressure P is between about 0.1 and 5 GPa.

18. The process according to claim 13 , wherein the temperature T is between 800° C. and 2,100° C.

19. A process for making a thermionic dispenser cathode, the process including the steps of:
providing a sample of a porous refractory metal and/or metal alloy;
placing the sample inside a furnace having a controlled atmosphere and heating the starting powder in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides to produce a cleaned sample;
without exposing the cleaned sample to an external atmosphere, placing the cleaned sample inside an atomic layer deposition (ALD) reactor and controllably depositing a conformal nanometer-scale film of a scandium compound on all available surfaces inside and outside of the cleaned sample to produce a scandium compound-coated sample with a conformal nanometer-scale scandium film having a predetermined thickness uniformly deposited on all of the surfaces thereof;
with the scandium compound-coated sample still in the ALD reactor and without exposing the compact to air, depositing a conformal layer of the barium compound on all available surfaces inside and outside of scandium compound-coated sample; and
with the scandium compound-coated sample with deposited barium layer still in the ALD reactor and without exposing the scandium compound-coated sample with deposited barium layer to air, subjecting the scandium compound-coated sample with deposited barium layer to a predetermined pressure P and temperature T to sinter the sample to full density;
wherein the

Assignees

• Us Gov Sec Navy

Inventors

• Feigelson Boris N
• Wollmershauser James A
• Manandhar Kedar

Classifications

• B22F1/16

  Metallic particles coated with a non-metal (coated with lubricating or binding agents or with organic material B22F1/10) · CPC title

• B22F3/26

  Impregnating {(making ferrous alloys by impregnation C22C33/0242)} · CPC title

• H01J1/144

  with other metal oxides as an emissive material · CPC title

• H01J9/042 Primary

  Manufacture, activation of the emissive part · CPC title

• B22F2999/00

  Aspects linked to processes or compositions used in powder metallurgy · CPC title