Thermionic Tungsten/Scandate Cathodes and Methods of Making the Same

Patent metadata

Field	Value
Publication number	US-2016300684-A1
Application number	US-201615093853-A
Country	US
Kind code	A1
Filing date	Apr 8, 2016
Priority date	Apr 10, 2015
Publication date	Oct 13, 2016
Grant date	—

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-Al 2 O 3 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:
providing a powder of refractory metal and/or metal alloy; placing the powder inside a furnace having a controlled atmosphere and heating the powder in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides to produce a cleaned powder; placing the cleaned powder inside a particle atomic layer deposition (ALD) reactor and depositing a conformal nanometer-scale film of a scandium compound on all particles of the powder to produce a scandium compound-coated powder; making a porous preformed compact of the scandium compound-coated powder ; and without exposing the porous preformed compact to air, placing the porous preformed compact in contact with an emissive mixture comprising a barium compound; and without exposing the porous preformed compact with contacted emissive mixture to air, subjecting the porous preformed compact with contacted emissive mixture to a predetermined pressure P and temperature T to form the cathode; wherein T is greater than a melting point of the emissive mixture; and wherein an application of the pressure P and temperature T causes the emissive mixture to infiltrate into the porous preformed compact.

2 . The process according to claim 1 , wherein 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 . A process for making a thermionic dispenser cathode, the process including:
providing a powder of a refractory metal and/or metal alloy; placing the powder inside a furnace having a controlled atmosphere and heating the powder in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides to produce a cleaned powder; making a porous preformed compact of refractory metal and/or metal alloy; and placing the porous preformed compact inside a particle atomic layer deposition (ALD) reactor and depositing a conformal nanometer-scale film of a scandium compound on all available surfaces of the porous preformed compact to produce a scandium compound-coated compact ; 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 with contacted emissive mixture to air, subjecting the porous preformed compact with contacted emissive mixture to a predetermined pressure P and temperature T to form the cathode; wherein T is greater than a melting point of the emissive mixture; and wherein an application of the pressure P and the temperature T causes the emissive mixture to infiltrate into the scandium compound-coated compact.

6 . The process according to claim 5 , wherein the refractory metal and/or metal alloy is tungsten.

7 . The process according to claim 5 , wherein the scandium compound is scandium oxide.

8 . The process according to claim 5 , wherein the barium compound is barium-calcium-aluminate.

9 . A process for making a thermionic dispenser cathode, the process including:
providing a sample of a porous refractory metal and/or metal alloy; placing the sample inside a furnace with controlled atmosphere and heating in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides and produce a cleaned sample; placing the cleaned sample inside an atomic layer deposition (ALD) reactor and depositing a conformal nanometer-scale film of a scandium compound on all available surfaces of the cleaned sample to produce a scandium compound-coated sample; 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 to form the cathode; wherein T is greater than a melting point of the emissive mixture; and wherein an application of the pressure P and the temperature T causes the emissive mixture to infiltrate into the scandium compound-coated sample.

10 . The process according to claim 9 , wherein the refractory metal and/or metal alloy is tungsten.

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

12 . The process according to claim 9 , wherein the barium compound is barium-calcium-aluminate.

13 . A process for making a thermionic dispenser cathode, the process including:
providing a powder of refractory metal and/or metal alloy; placing the powder inside a furnace having a controlled atmosphere and heating the powder in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides to produce a cleaned powder; placing the cleaned powder inside a particle atomic layer deposition (ALD) reactor and depositing a conformal nanometer-scale film of a scandium compound on all particles of the powder to produce a scandium compound-coated powder; 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 to form a scandium- and barium compound-coated powder; and making a porous preformed compact of the scandium- and barium compound-coated powder; and without exposing the porous preformed compact to air, subjecting the porous preformed compact to a predetermined pressure P and temperature T to sinter the compact to full density and form 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 barium compound is barium-calcium-aluminate.

17 . A process for making a thermionic dispenser cathode, the process including:
providing a powder of refractory metal and/or metal alloy; placing the powder inside a furnace having a controlled atmosphere and heating the powder in the flow of hydrogen or hydrogen/inert gas mixture to reduce surface oxides to produce a cleaned powder; making a porous preformed compact of the cleaned powder; placing the porous preformed compact inside a particle atomic layer deposition (ALD) reactor and depositing a conformal nanometer-scale film of a scandium compound on all available surfaces inside and outside of the preformed compact to produce a scandium compound-coated compact; 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 and form the cathode.

18 . The process according to claim 17 , wherein the refractory metal and/or metal alloy is tungsten.

19 . The process according to claim 17 , wherein the scandium compound is scandium oxide.

20 .

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

• B22F2999/00

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

• H01J1/28

  Dispenser-type cathodes, e.g. L-cathode · CPC title

• B22F3/26

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

• H01J1/142

  with alkaline-earth metal oxides, or such oxides used in conjunction with reducing agents, as an emissive material · CPC title