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US 11,075,049 B2Granted
Thermionic tungsten/scandate cathodes and method of making the same
AssigneeThe Government of the United States of America, as represented by the Secretary of the Navy
InventorsBoris N. Feigelson, James A. Wollmershauser, Kedar Manandhar
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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.
Claims24
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.
5 more elements
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.
4 more elements
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.
5 more elements
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 sintered sample forms the cathode.
4 more elements
Dependencies are inferred from the claim text.