The present disclosure relates to cathodes for vacuum electronic devices.
Thermionic vacuum electronic devices include vacuum tubes, electric thrusters, gyrotrons, klystrons, travelling wave tubes, thermionic converters, and the like. These devices all rely upon an electron source, which is typically a heated thermionic cathode that thermally emits electrons.
An example of a thermionic cathode is a dispenser cathode. Dispenser cathodes may include a porous construct of tungsten or molybdenum or other metal. These cathodes generally are fabricated before electron-emissive materials are introduced into the construct's pores. Typical formulations of emissive material include various ratios of barium oxide, calcium oxide, and aluminum or strontium oxide. Additional materials such as scandium oxide may also be introduced into the cathode at various stages of the cathode's construction to improve the emission characteristics of the cathode.
Manufacture of cathode surfaces that are properly matched to the geometries of these devices may be difficult and may frequently entail a compromising of the cathode form in a manner that may not be desirable or ideal to the efficient functioning of the device. For example, the spraying method for depositing carbonate on certain classes of thermionic cathodes may result in particle agglomeration, density variation, and high surface roughness of the electron emissive layer. The resulting emission characteristics of the cathode can be detrimentally impacted (such as by non-uniform emission, pitting, and the like), and detrimental agglomeration of particles can result during a defective spray operation. This generally results in variable and undesirable surface roughness and density of the spray coat. Taken together with voids, these factors may create a “patchy” emission effect where areas of the cathode are dissimilar enough that the entire cathode presents as an amalgam of smaller cathodes with different emission characteristics that will broaden and blur the anticipated performance characteristics of the cathode.
Moreover, large-area thermionic cathodes are very expensive. For instance, a 1-inch diameter barium dispenser cathode may cost tens of thousands of dollars.
Disclosed embodiments include cathodes with conformal cathode surfaces, vacuum electronic devices with cathodes with conformal cathode surfaces, and methods of manufacturing the same.
In a non-limiting embodiment, a cathode for a vacuum electronic device includes: a substrate having a predetermined shape; and electron emissive material disposed on at least one portion of at least one surface of the substrate, a shape of the electron emissive material conforming to the predetermined shape of the substrate.
In another non-limiting embodiment, a thermionic vacuum electronic device includes: a cathode including: a substrate having a predetermined shape; and electron emissive material disposed on at least one portion of at least one surface of the substrate, a shape of the electron emissive material conforming to the predetermined shape of the substrate; an anode spaced apart from the cathode; and a heat source thermally couplable to the substrate.
In another non-limiting embodiment, a method of fabricating a cathode for a vacuum electronic device includes: providing a substrate having a predetermined shape; and conformally disposing electron emissive material on at least one portion of at least one surface of the substrate such that a shape of the electron emissive material conforms to the predetermined shape of the substrate.
In another non-limiting embodiment, a method of fabricating a thermionic vacuum electronic device includes: defining a cathode, wherein defining the cathode includes: providing a substrate having a predetermined shape; and conformally disposing electron emissive material on at least one portion of at least one surface of the substrate, a shape of the electron emissive material conforming to the predetermined shape of the substrate; defining an anode that is spaced apart from the cathode; and disposing a heat source proximate the substrate such that the heat source is thermally couplable to the substrate.
The foregoing is a summary and thus may contain simplifications, generalizations, inclusions, and/or omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is NOT intended to be in any way limiting. Other aspects, features, and advantages of the devices and/or processes and/or other subject matter described herein will become apparent in the text (e.g., claims and/or detailed description) and/or drawings of the present disclosure.
Illustrative embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, the use of the same symbols in different drawings typically indicates similar or identical items unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.
Given by way of non-limiting overview, Disclosed embodiments include cathodes with conformal cathode surfaces, vacuum electronic devices with cathodes with conformal cathode surfaces, and methods of manufacturing the same. As will be explained below, in various embodiments illustrative cathodes may conform to a surface of a substrate. As will also be explained below, various illustrative disclosed fabrication techniques may help permit use of various methods of application on substrate surfaces, and/or may help permit large surfaces to be used as cathodes, and/or may help contribute to improving manufacturability of cathodes for complex geometries.
Referring to
It will be appreciated that, in various embodiments, any portion of an electrically insulated surface of the substrate 12 without the electron emissive material 14 disposed thereon electrically isolates the electron emissive material 14. As will be shown below, such electrical isolation isolates the cathode 10 from other electrodes (not shown) of the vacuum electronic device (not shown).
Referring additionally to
While the substrate 12 is shown in
As a result of the variety of possible shapes for the substrate 12, the cathode 10 and vacuum electronics devices that include the cathode 10 may have arbitrary forms as desired for a particular application. For example, it will be appreciated that a polygonal-cylinder geometry helps enable flat cathode surfaces to be placed opposite flat collector surfaces in thermionic vacuum electronic devices.
As another example, curved cathodes 10 can be useful to help contribute to optimizing electron optics in some vacuum electronic devices (such as without limitation ion thrusters, tube amplifiers, klystrons, travelling wave tubes, inductive output tubes, and the like). Such optimization can help provide an opportunity to form curved or alternatively-shaped cathodes that: (a) may be outside the capability of traditional cathode machining; (b) may be better suited to help contribute to optimizing electron emission geometries for more optimized electron optics; (c) rely on shaping ceramic instead of metal composite; and/or (d) can be formed into arbitrary shapes.
In various embodiments, the substrate 12 suitably is made of a material that is a good conductor of heat, that is sufficiently resistant to heat damage, and can provide mechanical support. Thus, in such embodiments the substrate 12 can help protect the electron emissive layer 14 from oxidizing environments and can help provide mechanical support to the electron emissive layer 14. In such cases, the heat source in a thermionic vacuum electronics device that includes embodiments of the cathode 10 is physically separated from the cathode 10.
However, some applications that do not involve such high temperatures. In such embodiments, it will be appreciated that the substrate 12 need not include high thermal conductivity characteristics.
In some embodiments, if desired, the cathode 10 optionally may be separated from the heat source hermetically. That is, in such instances the cathode 10 is not exposed to the same atmosphere as the heat source. For example, in the case of combustion for a thermionic converter, the cathode 10 may be less likely to corrode because the material of the substrate 12 is corrosion-resistant and is compatible with the combustion environment.
In various embodiments, the substrate 12 (or, in some instances, the sides of the substrate 12 or a portion of the substrate 12) may be made of and/or coated with an electrically insulating material. It will be appreciated that, in such embodiments, the electrically insulating material may be any electrically insulating material as desired for a particular application.
In some such embodiments and given by way of non-limiting example, the substrate 12 may be made of one or more ceramic materials such as, without limitation, aluminum oxide, silicon carbide, zirconium oxide, silicon oxide, silicon nitride, and/or a combination thereof. It will be appreciated that ceramic material suitably is used for the substrate 12 in some embodiments because ceramic material is corrosion and oxidation resistant and is compatible with a combustion environment (such as that which may be entailed in thermionic vacuum electronic devices). Resistance to oxidation may also be advantageous in non-combustion heating scenarios. For instance, use of molybdenum disilicide heating elements in air could provide sufficient heat for a thermionic emitter without relying on combustion.
In some other embodiments and given by way of other non-limiting examples, the substrate 12 may be made of one or more metals, a multi-layer ceramic/refractory structure allowing electron transport within the multilayer substrate structure, and/or a ceramic-to-metal graded structure. For example, in some embodiments, if desired the substrate 12 may be made from a metal coated on at least one surface with an electrically insulating material. In such embodiments, illustrative metals may include without limitation stainless steel, copper, molybdenum, titanium, and high temperature alloys. In such embodiments, illustrative insulating materials may include without limitation high temperature ceramics, silicon carbide, silicon nitride, alumina, and other non electically conductive high temperature ceramics. It will be appreciated that such embodiments may provide advantages in terms of stresses.
In various embodiments the electron emissive material 14 may include one or more metals such as, without limitation, tungsten, molybdenum, manganese, titanium, osmium, platinum, nickel, tantalum, rhenium, niobium, and/or a combination thereof. The metal may have any grain size as desired. It will be appreciated that inclusion of such metals in the electron emissive material 14 provides the electrons that are emitted from the electron emissive material 14 when heated.
In various embodiments the electron emissive material 14 may also include one or more electron emission enhancing materials such as, without limitation, barium, calcium, thorium, strontium, barium oxide, calcium oxide, thorium oxide, strontium oxide, scandium oxide, vanadium oxide, lanthanum, lanthanum oxide, molybdenum oxide, cesium, cesium oxide, tungsten oxide, a boride of lanthanum, cerium, cerium oxide, a boride of cerium, scandium, vanadium, carbon, and/or a combination thereof. In some such embodiments, it may be possible to include certain electron emission enhancing components, such as for example thorium oxide, prior to sintering of the cathode structure (discussed below). It will be appreciated that some electron emission enhancing materials, such as for example thorium oxide, may be able to withstand conditions entailed in sintering the cathode without being converted into less desirable compounds and may be able to tolerate longer term exposure to air that would accompany the total manufacturing process time without deteriorating due to exposure to less-controlled conditions or uncontrolled conditions, such as forming hydroxides from humidity in the air, and becoming inert. It will also be appreciated that some other electron emission enhancing materials may be added post-sintering.
In various embodiments, the electron emissive material 14 may be created from a metal slurry that is deposited on the substrate 12. In various embodiments the metal slurry may be embodied as a semiliquid mixture of particles suspended in a fluid. In various embodiments the applied slurry may have a thickness in a range from around one micrometer to around one (or more) millimeter(s).
In some such embodiments, the metal slurry can include metal particles, oxide/ceramic particles, a binder, and a solvent/dispersant. The solvent/dispersant helps keep metal and oxide particles dispersed. The binder helps the freshly-deposited metal slurry to adhere to the substrate 12 as a continuous film. The solvent/dispersant and the binder are boiled/burned off before the firing/sintering process. During the firing/sintering process, oxidized metal particles (such as manganese oxide, titanium oxide, tungsten oxide, molybdenum oxide, cesium oxide, and the like) diffuse into the substrate 12 to form a strong bond between the metallization (that is, the electron emissive material 14) and the substrate 12. In various embodiments the binder may include nitrocellulose, ethyl cellulose, and damar. In some embodiments, the slurry may include other inclusions. For example, barium or scandium compounds may be included to beneficially modify the electron emission properties of the cathode material.
In some such embodiments, the metal slurry may contain particles of arbitrary size (such as, for example, less than 1 micron, less than 5 microns, less than 10 microns, less than 100 microns, and the like). It will be appreciated that sintered properties of the processed electron emissive material 14 can be altered by, among other things, varying the particle size of the slurry. It will be appreciated that a smaller particle size can help favor higher post-sintering density. If the cathode material is intended as a matrix for an impregnated dispenser style cathode, then the porosity of the matrix will be of importance and can be controlled in part by the pre-sintered particle size of the metal slurry. Given by way of non-limiting example, tungsten or molybdenum particles form the matrix that provides the porosity into which smaller, high-electron-emitting particles (such as barium) fit in making a dispenser cathode. The inclusions can also be varied to desired particle size as, for example, the benefit of scandium oxide on cathode emission performance is tied to particle size, in that case being tens of nanometers in diameter.
As shown in
As shown in
In various embodiments, the electron emissive material 14 may have a coefficient of thermal expansion that is equalized toward a coefficient of thermal expansion of the substrate 12. In such embodiments, expansion and contraction of the electron emissive material 14 and the substrate 12 can be equalized during thermal cycles of heating and cooling, respectively. It will be appreciated that equalization of expansion and contraction of the electron emissive material 14 and the substrate 12 during thermal cycles can help contribute to reduction of stresses induced in the electron emissive material 14 and the substrate 12, thereby helping reduce the risk of cracking of the electron emissive material 14 and/or the loss of adhesion between the substrate 12 and the electron emissive material 14. It will be appreciated that, in such cases, selection of materials for the substrate 12 and the electron emissive material 14 can result in reduction of stresses , thereby helping contribute to reducing likelihood of failure of the coating of the electron emissive material 14 or the substrate 12, and thereby helping to affect emissive performance and high temperature operation.
In some embodiments and referring additionally to
Referring additionally to
Referring additionally to
It will be appreciated that, in various embodiments, any portion of at least one electrically insulated surface of the substrate 12 without the electron emissive material 14 disposed thereon electrically isolates the cathode 10 from the anode 24.
In various embodiments, the heat source 26 may include without limitation a combustor, a flame, a heat pipe, an electric heater, an electron bombardment heater, a radiative heater, a solid material, a nuclear heat source, and/or an absorber for a concentrated light source.
In some embodiments and as shown in
In some other embodiments and as shown in
In some other embodiments and as shown in
Other details of the cathode 10 have been described above and need not be repeated for an understanding of disclosed embodiments of the thermionic vacuum electronic device 100.
It will be appreciated the thermionic vacuum electronic device 100 may be used in various applications. For example and without limitation, the thermionic vacuum electronic device 100 of
Illustrative, non-limiting examples of methods of fabricating various embodiments of the cathode 10 and the thermionic vacuum electronic device 100 are set forth below.
Referring additionally to
It will be appreciated that, in various embodiments, any portion of an electrically insulated surface of the substrate 12 without the electron emissive material 14 disposed thereon electrically isolates the electron emissive material 14. As will be shown below, such electrical isolation isolates the cathode 10 from other electrodes of the vacuum electronic device.
In some embodiments and as shown in
In various embodiments and as shown in
In various embodiments and as also shown in
In various embodiments and as also shown in
In some embodiments other than those entailing patterned metal slurry and as shown in
In some such embodiments and as also shown in
In some such embodiments and as also shown in
It will be appreciated that, if desired, density-increasing steps may be performed for the resulting metal matrix. In some instances, it may be desirable to reduce porosity of the metal by employing additional furnace runs in controlled atmospheres or by utilizing follow-up isostatic pressing techniques or other means of densifying the matrix if it is to be used in a dispenser-style capacity.
In some embodiments and as shown in
In some embodiments and as shown in
In various embodiments the electron emissive material is activated. It will be appreciated that the electron emissive material may be activated via heating at a desired temperature for a desired amount of time.
Referring additionally to
In various embodiments illustrative methods of fabricating the thermionic vacuum electronic devices 100 are provided. Referring back to
As shown in
It will be appreciated that, in various embodiments, any portion of an electrically insulated surface of the substrate 12 without the electron emissive material 14 disposed thereon electrically isolates the cathode 10 from the anode 24.
As shown in
One skilled in the art will recognize that the herein described components (e.g., operations), devices, objects, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken limiting.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations are not expressly set forth herein for sake of clarity.
The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components, and/or wirelessly interactable, and/or wirelessly interacting components, and/or logically interacting, and/or logically interactable components.
While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “ a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “ a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that typically a disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase “A or B” will be typically understood to include the possibilities of “A” or “B” or “A and B.”
With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those which are illustrated, or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise.
While a number of illustrative embodiments and aspects have been illustrated and discussed above, those of skill in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, and sub-combinations as are within their true spirit and scope.
The present application claims the benefit of priority of filing from U.S. Provisional Patent Application Ser. No. 62/721,343, filed Aug. 22, 2018, and entitled “Cathodes for Thermionic Electrodes in Vacuum Electronics Having Conformal Cathode Surfaces And Methods Of Manufacturing The Same,” the entire contents of which are incorporated by reference.
Number | Date | Country | |
---|---|---|---|
62721343 | Aug 2018 | US |