CN109899261B - Nozzle machining process suitable for micro-Newton field emission electric propulsion system - Google Patents
Nozzle machining process suitable for micro-Newton field emission electric propulsion system Download PDFInfo
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Abstract
The invention discloses a nozzle processing technology suitable for a micro-Newton field emission electric propulsion system, wherein the nozzle structure suitable for the micro-Newton field emission electric propulsion system is characterized in that a main body is an emitter array consisting of nozzle micro-pipelines, and one-dimensional nano materials are uniformly deposited on the inner wall and the outer surface of each micro-pipeline. The invention mainly adopts a semiconductor micro-nano processing technology, obtains an ideal emitter nozzle structure by etching an SOI silicon chip, takes the emitter nozzle structure as a substrate, introduces one-dimensional nano materials with proper appearance and performance into the outer surface and the inner pipe wall of the substrate for uniform coating, realizes the purposes of surface modification and functionalization, increases the hydraulic resistance of the inner pipe wall while increasing the array of emitting points on the surface of the nozzle pipe orifice to reduce the flow rate and ensure that the emitter works in an ionic system, so that the current generated by a propellant is utilized to the maximum extent under the condition of not generating liquid drops, thereby improving the performance of the propeller.
Description
Technical Field
The invention belongs to the research field of spacecraft propulsion technology and micro-nano processing preparation, and particularly relates to a nozzle processing technology suitable for a micro-Newton level field emission electric propulsion system.
Background
The development of the aerospace field greatly promotes the application of the electric propulsion technology in the aspects of spacecraft attitude adjustment, orbit control, accurate positioning, resetting and the like. For micro satellites and spacecraft, miniaturization and high integration of propeller size, weight, and capability of providing stable low thrust are required, whereas propellant efficiency of electric propulsion technology is several times to several tens times that of chemical propulsion technology. Therefore, an electric propeller based on the micro-newton level becomes a potential solution.
Among them, the electric nozzle propeller is well suited for precision drag compensation and attitude control and primary propulsion of small satellites, and the electric nozzle propeller developed by Busek corporation to counteract the solar pressure has been successfully flown in the space technology (ST7) mission of NASA as the first application case. The minimum thrust, power, area and high efficiency of each emission point and the scalability of the thrust required by small satellites make micromachining technology an ideal method for manufacturing electric nozzle propellers by emission point arrays.
Such micro-arrays can be classified into two types, depending on the way the propellant is delivered to the emission points, one is that each emission point is fabricated on a flat surface with protruding tips, and the propellant reaches its tip through capillary wetting or porous media on its surface, called an external feed array. Another array of emission points is a tube made by etching silicon, connected to a sealed manifold filled with propellant, to drive the flow of propellant by applying a pressure drop, called an in-feed array. Both of these thrusters are based on the field emission effect, forming an ion beam by applying a high potential of several kilovolts between an extraction electrode and the tip or nozzle orifice wetted by the liquid propellant, forming a taylor cone on the tip or nozzle orifice due to the interaction of the surface tension of the propellant and electrostatic forces.
For the externally fed array, f.a.hill et al achieve the purpose of lowering the starting voltage and enhancing the transmission efficiency by introducing highly wettable carbon nanotubes on the emission surface to increase the number of emission points and regulate the hydraulic resistance of the emission surface. For in-feed arrays, typically the orifice diameter needs to be as low as a few microns to provide a pressure drop between the manifold and the emission point tip, but this is limited by the manufacturing process limits and manufacturing tolerances of the etch back, allowing for differences in flow rates between emission points, which directly affect the co-directional variation in surface current. To solve this problem, Krpoun et al put microbeads in the micro-pipe to adjust the hydraulic resistance inside the emission point because the flow rate inside the emission point is inversely proportional to the hydraulic resistance according to theoretical analysis. However, this technique cannot ensure uniform control of the filling inside the emission point, cannot ensure that the microbeads remain in place during the service life, is also prone to clogging, and is not easy to clean. If can combine these two kinds of feedback modes through introducing one-dimensional nano-material, the appropriate application is in field emission electric propulsor system, when promoting surface emission dot matrix column number purpose, can also realize advantages such as more convenient regulation and control transmission pipeline hydraulic resistance. To date, no such binding has been reported in the literature.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention aims to provide a nozzle processing technology suitable for a micro-Newton level field emission electric propulsion system, and correspondingly obtains a nozzle structure and a processing method suitable for the micro-Newton level field emission electric propulsion system, mainly adopts a semiconductor micro-nano processing technology, an ideal emitter nozzle structure is obtained by etching an SOI silicon wafer, and is taken as a substrate, one-dimensional nano materials with proper appearance and performance are introduced into the outer surface of the substrate and the inner pipe wall to be uniformly coated, so that the purposes of surface modification and functionalization are realized, the emission point arrays on the surface of the nozzle orifice are increased, the hydraulic resistance of the inner pipe wall is increased, to reduce the flow rate and to operate the projectile in an ionic system to maximize the use of the current generated by the propellant without producing droplets, thereby enhancing the performance of the propeller.
In order to achieve the above objects, according to one aspect of the present invention, there is provided a nozzle structure suitable for a micro-newton-grade field emission electric propulsion system, the body is an emitter array composed of nozzle micro-pipes, characterized in that one-dimensional nanomaterials are uniformly deposited on the inner walls of the micro-pipes, and one-dimensional nanomaterials are also deposited on the outer surfaces of the emitter array.
As a further preference of the present invention, the nozzle micro-channel comprises a nozzle emitter tip, i.e. a propellant outlet, and a propellant transporting micro-channel; the one-dimensional nanomaterial deposited on the outer surface area of the exit port forms a plurality of micro-emitters.
As a further preferred aspect of the present invention, the one-dimensional nanomaterial is at least one of a nanotube, a nanowire, and a nanorod;
preferably, the nanotube is a carbon nanotube or a metal carbide nanotube, and the nanowire is a metal nanowire, a metal oxide nanowire or a metal nitride nanowire; the nano-rods are metal nano-rods, metal oxide nano-rods or metal nitride nano-rods.
In a further preferred embodiment of the present invention, the nozzle microchannel is fabricated from an SOI silicon wafer.
According to another aspect of the invention, a nozzle structure processing method suitable for a micro-Newton field emission electric propulsion system is provided, which is characterized in that the method comprises the steps of respectively carrying out array pattern manufacturing and etching processing on the top layer and the back surface of an SOI silicon wafer for many times through a photoetching process to obtain an emitter array structure of a nozzle micro-pipeline; the inner pipe walls of the nozzle micro-pipeline are in sectional type two-by-two communication due to multiple etching;
then, coating a growth buffer layer, a catalytic layer or a seed crystal layer on the outer surface of the emitter array structure and the inner pipe wall of the micro pipe; and then growing on the buffer layer, the catalytic layer or the seed crystal layer to obtain a one-dimensional nano material, thereby obtaining the nozzle structure suitable for the micro-Newton field emission electric propulsion system.
As a further preferred aspect of the present invention, the buffer layer, the catalytic layer, or the seed layer is grown, specifically, by using atomic layer deposition or an aqueous solution method;
when the one-dimensional nano material is a carbon nano tube, specifically, growing the catalyst layer by utilizing an atomic layer deposition or aqueous solution method; before growing the catalyst layer by utilizing atomic layer deposition, a buffer layer is grown by utilizing atomic layer deposition;
when the one-dimensional nano material is a nano wire of zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride or titanium carbide, or a nano rod of zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride or titanium carbide, the growth of ZnO or TiO is specifically carried out by utilizing an atomic layer deposition or aqueous solution method2The seed layer of (1).
As a further preferred aspect of the present invention, the growth of the one-dimensional nanomaterial is specifically a vapor deposition method or an aqueous solution method;
when the one-dimensional nano material is a carbon nano tube, growing by using a vapor deposition method; preferably, the vapor deposition method is PECVD or TCVD;
when the one-dimensional nano material is a nanowire of zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride or titanium carbide, or a nanorod of zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride or titanium carbide, an aqueous solution method, an electrochemical deposition method or a chemical vapor deposition method is specifically utilized.
As a further preferred aspect of the present invention, the SOI wafer is further subjected to ultrasonic cleaning and oxygen cleaning in an organic solution before the photolithography process is performed.
Through the technical scheme, compared with the prior art, the internal feed type and the external feed type are integrated, the whole is mainly based on the internal feed type, a small part of the surface of the top end of the nozzle belongs to the external feed type, and the external feed type emission is realized by utilizing the part of the nano material; specifically, the liquid flows through the micro-channel modified by the nano-material, and through the capillary wetting action of the nano-material on the outer surface of the exit port, the micro-liquid is distributed on the surface of the nano-material emitter in the area to form the external feeding type emission under high pressure. The nozzle structure in the invention has the following advantages in particular:
(1) introducing one-dimensional nano material on the outer surface of the structure, increasing the utilization degree of the structure surface, increasing the number of emission point Arrays at the nozzle orifice, and simultaneously, the top of the one-dimensional nano material has a thinner tip, reducing the starting voltage and enhancing the current transmission efficiency (according to the formula in "High-through High electronic Liquid sources Using Arrays of micro electrically porous Emitters With Integrated emitter Grid and Carbon Nano Flow Control Structures" published by France Ann Hill et al
And experimental conclusions. Wherein, VstartIs the initial voltage of the liquid in the external feeding type emission, gamma is the surface tension of the liquid, and R is the emitter tipRadius, epsilon0Is the dielectric constant of free space, G is the distance of the emitter tip from the edge of the extraction electrode).
(2) The introduction of one-dimensional nanomaterials into the tube wall of the structure can more reliably and stably regulate and control the Hydraulic Resistance and flow rate in the tube by controlling the morphology and performance of the nanomaterials, reduce ion emission current, and enable the propeller to work in an ideal state, thereby increasing the propulsion efficiency (according to the analysis in "Microtextile electrode spinning apparatus with High Hydrogen Resistance Channels" published by Enric Grustan-Gutierrez et al). In the bead filling in the prior art, the controllability of the filling of the internal micro beads is not high, but the method for growing the nano material adopted by the invention has better controllability and is more suitable for manufacturing a structure with good uniformity; the one-dimensional nano material (such as carbon nano tube, zinc oxide nano rod and the like) has adjustable physical appearance, large specific surface area, suitability for surface functionalization and stable structure. In addition, the specific surface area of the one-dimensional nano material is larger, and the one-dimensional nano material is subjected to functional treatment, so that the hydraulic flow resistance of the inner wall of the pipeline can be further effectively adjusted.
(3) The difficulty of a semiconductor processing technology can be reduced by the aid of the one-dimensional nano material, the diameter of a pipe orifice is further reduced by overcoming the processing limit, and the equivalent diameter can reach the submicron level (for example, a pipeline with the diameter as low as several microns can be etched by the aid of a semiconductor etching technology, and the equivalent diameter can reach the submicron level by the aid of the one-dimensional nano material); and the growth of the nano material can be compatible with the batch manufacturing of wafer level processing, and the complexity and difficulty of flow resistance regulation in the tube can be reduced.
Drawings
FIG. 1 is a schematic cross-sectional view of the nozzle after growing one-dimensional nanomaterials on the outer surface and inner tube wall.
FIG. 2 is a schematic cross-sectional view of a nozzle substrate obtained by subjecting an SOI silicon wafer substrate to a complete photolithography process.
Fig. 3 is a detailed schematic view of the top of the nozzle array.
Fig. 4 is a detailed schematic view of the top of the nozzle array after growth of one-dimensional nanomaterials.
The meanings of the attached symbols in the figures are as follows: 100 is a nozzle array, 101 is the inner tube wall of the nozzle, 102 is the surface of the nozzle outlet; 200 is an integral one-dimensional nano material, 201 is a nano material of the inner pipe wall of the nozzle, and 202 is a nano material of the outlet of the nozzle (both 201 and 202 belong to 200).
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1
The micro-Newton electric propulsion system based on the field emission effect adopts a semiconductor micro-nano processing technology to manufacture a nozzle structure. Firstly, array pattern manufacturing and etching are respectively carried out on the top layer and the back surface of the SOI silicon chip substrate through a photoetching process, and an array type ideal nozzle structure is obtained. Then the outer surface of the nozzle and the inner pipe wall are coated with auxiliary layers such as a catalyst layer or a seed crystal layer and the like required by the growth of the one-dimensional nano material, and then the one-dimensional nano material is grown on the auxiliary layers.
The specific processing process is as follows:
(1) cleaning an SOI silicon wafer substrate and carrying out pretreatment such as cleaning, firstly carrying out photoetching process on top silicon of the SOI silicon wafer to manufacture an array graph, obtaining emitter tips of a nozzle upper thin pipe and a micro pipe (the upper thin pipe and the emitter tips both belong to one part of the micro pipe) through etching steps such as DRIE, RIE and the like, then carrying out photoetching processing on the back of the SOI substrate to obtain a complete nozzle micro pipe array 100 after etching, wherein the shapes of the tips can be different according to the etching effect to reduce the surface area of the top end; the inner pipe walls of the nozzle micro-pipelines are in sectional type two-by-two communication due to multiple times of etching, the diameter of each section is increased section by section from top to bottom, and the arrangement of the specific inner wall diameter can be adjusted as required and can be several to hundreds of micrometers;
(2) the outer surface and the inner pipe wall of the substrate are coated with auxiliary layers such as a buffer layer, a catalytic layer or a seed crystal layer by adopting an atomic layer deposition method, an aqueous solution method and the like, a clamp or a gasket and the like are needed in the growth process, the nozzle substrate is properly fixed, and the front side and the back side of the nozzle substrate can be ensured to be fully contacted with sediments or reactants. For example, for growing carbon nanotubes, it is necessary to fix a nozzle substrate by a jig or a gasket, place the nozzle substrate in a cavity for atomic layer deposition, and perform the growth of a buffer layer and a catalyst layer step by step, or coat the catalyst layer by an aqueous solution method or the like; for nano materials such as zinc oxide and the like, a film for coating a ZnO seed crystal layer by adopting an atomic layer deposition method, an aqueous solution method and the like in the same placing mode is needed;
(3) the growth of the one-dimensional nanomaterial 200 is performed by a suitable method on the nozzle substrate coated with the auxiliary layer, and the nozzle substrate is also fixed by a clamp or a gasket or the like to ensure sufficient contact between the reactant and the substrate. For example, the growth of the carbon nanotubes may be performed by PECVD, TCVD, etc. of the nanomaterial 200; the growth of the zinc oxide nanomaterial may be carried out by growing the nanomaterial 200 by an aqueous solution method or the like. Finally, the required inner tube wall nano material 201 and outlet port nano material 202 are obtained on the inner tube wall 101 and the outlet port surface 102 of the nozzle.
The exit port nanomaterials 202 (i.e., the one-dimensional nanomaterials deposited on the outer surface area of the exit port) form a plurality of micro-emitters.
The substrate adopted by the invention is an SOI silicon wafer. In addition, fig. 1, 2 and the like show only one specific example of the shape structure of the cavity, and the cavity may take other shapes and structures as required; for example, the cavity portion shown in the lower portion of fig. 2 may have other shapes besides the cavity of the stepped cylinder. The specific material type of the one-dimensional nano material can be flexibly adjusted, taking the nano wire as an example, the nano wire can be a metal nano wire, a metal oxide nano wire or a metal nitride nano wire, such as zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride material and the like, and the nano rod is also similar. In addition, the seed crystal layer can be selected according to the difference of the one-dimensional nanometer materials to be grownOther materials as seed layers (e.g. TiO)2Etc.), and the thickness of the seed crystal layer, etc. can be adjusted correspondingly according to the structure of the nano material to be grown or the requirement of the length-diameter ratio; the buffer layer and the catalyst layer are the same.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A nozzle structure suitable for a micro-Newton field emission electric propulsion system is characterized in that a main body is an emitter array consisting of nozzle micro-pipes, one-dimensional nano materials are uniformly deposited on the inner walls of the micro-pipes, and one-dimensional nano materials are also deposited on the outer surfaces of the emitter array;
the nozzle micro-pipeline comprises a nozzle emitter tip and a micro-pipeline for conveying the propellant, wherein the nozzle emitter tip is a propellant outlet; the one-dimensional nano material deposited on the outer surface area of the exit forms a plurality of micro emitters; the inner pipe walls of the nozzle micro-pipelines are communicated in a segmented mode in pairs, and the equivalent diameter of the pipe orifice reaches the submicron level.
2. The nozzle structure of claim 1, wherein the one-dimensional nanomaterial is at least one of a nanotube, a nanowire, and a nanorod.
3. The nozzle structure suitable for use in a micro-Newton field-emission electric propulsion system of claim 2, wherein said nanotubes are carbon nanotubes or metal carbide nanotubes and said nanowires are metal nanowires, metal oxide nanowires or metal nitride nanowires; the nano-rods are metal nano-rods, metal oxide nano-rods or metal nitride nano-rods.
4. The nozzle structure suitable for use in a micro-Newtonian field emission electric propulsion system of claim 1, wherein said nozzle micro-tunnel is fabricated from SOI silicon wafer.
5. The method for processing a nozzle structure suitable for a micro-Newton field emission electric propulsion system, as claimed in any one of claims 1-4, wherein the method comprises performing array patterning and etching processes on the top and back of the SOI silicon wafer respectively for a plurality of times by photolithography to obtain an emitter array structure of the nozzle micro-channel; the inner pipe walls of the nozzle micro-pipeline are in sectional type two-by-two communication due to multiple etching;
then, coating a growth buffer layer, a catalytic layer or a seed crystal layer on the outer surface of the emitter array structure and the inner pipe wall of the micro pipe; and then growing on the buffer layer, the catalytic layer or the seed crystal layer to obtain a one-dimensional nano material, thereby obtaining the nozzle structure suitable for the micro-Newton field emission electric propulsion system.
6. The method for processing the nozzle structure suitable for the micro-Newton field emission electric propulsion system, according to claim 5, wherein the buffer layer, the catalytic layer or the seed layer is grown, in particular, by using an atomic layer deposition or aqueous solution method;
when the one-dimensional nano material is a carbon nano tube, specifically, growing the catalyst layer by utilizing an atomic layer deposition or aqueous solution method; before growing the catalyst layer by utilizing atomic layer deposition, a buffer layer is grown by utilizing atomic layer deposition;
when the one-dimensional nano material is a nano wire of zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride or titanium carbide, or a nano rod of zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride or titanium carbide, the growth of ZnO or TiO is specifically carried out by utilizing an atomic layer deposition or aqueous solution method2The seed layer of (1).
7. The method for processing the nozzle structure suitable for the micro-Newton field emission electric propulsion system in accordance with claim 5, wherein the growth of the one-dimensional nano material is specifically a vapor deposition method or an aqueous solution method;
when the one-dimensional nano material is a carbon nano tube, growing by using a vapor deposition method; the vapor deposition method is PECVD or TCVD;
when the one-dimensional nano material is a nanowire of zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride or titanium carbide, or a nanorod of zinc oxide, manganese oxide, vanadium oxide, tungsten oxide, titanium nitride or titanium carbide, an aqueous solution method, an electrochemical deposition method or a chemical vapor deposition method is specifically utilized.
8. The method of claim 5, wherein said SOI wafer is further subjected to ultrasonic cleaning and oxygen cleaning in an organic solution before said photolithography process.
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