Method for preparing a multi-layer tube and a thermionic energy converter including the multi-layer tube

Abstract

An embodiment of the present application provides a method for preparing a multi-layer tube, comprising: using machining to obtain an initial metal rod with a depression in the middle position along the axial direction; using a plasma spraying process to spray a ceramic layer at the depressed position of the initial metal rod; sleeveing a first metal tube on the outside of the initial metal rod, and sleeved two end heads on both ends of the initial metal rod; welding the two end heads to the first metal tube respectively; welding the initial metal rod and the first metal tube sleeved on the outside of the initial metal rod so that the initial metal rod, the ceramic layer and the first metal tube are combined with each other; cutting off the two ends of the combined initial metal rod and the two ends of the first metal tube to expose the cross-section with the ceramic layer; and forming a through hole extending in the axial direction in the center of the initial metal rod to obtain a multi-layer tube.

Description

Technical Field

[0001] Embodiments of the present application relate to a method for preparing a tubular structure, and more particularly to a method for preparing a multilayer tube and a thermionic energy converter comprising the multilayer tube. Background Art

[0002] In the modern industrial field, higher requirements are placed on the performance and functions of materials, and it is difficult for a single material to meet multiple different functions at the same time.

[0003] Both metal and ceramics have good high-temperature resistance, among which metal is a conductive material and ceramic is an electrical insulating material. In order to meet the application needs of achieving electrical insulation between two layers of metal tubes, in the prior art, electrical insulation under temperature conditions of 1500°C is generally carried out by gap insulation. In order to ensure the stability of the gap between the inner tube and the outer tube, a ceramic positioning block with an insulating function is usually installed between the inner and outer tubes. There are great difficulties in installing the positioning block between thin-walled tubes (tube wall <1mm). The accuracy of insulation positioning is difficult to guarantee under high temperature conditions. Insufficient positioning accuracy can easily lead to deformation of thin-walled metal tubes. The deformation exceeds the gap, which will cause the insulation between the inner and outer tubes to fail. At the same time, due to the existence of the gap, the thermal conductivity between the inner and outer tubes is reduced, and there will be a large temperature difference between the inner and outer tubes.

[0004] Existing methods for making multilayer tubes have difficulty combining metal and ceramic, and producing thin-walled ceramic structures that meet precision requirements. Consequently, the prior art lacks a method for making multilayer tubes with metal inner and outer layers and ceramic in the middle. Summary of the Invention

[0005] In view of the above problems, the present application is proposed to provide a method for preparing a multilayer tube that overcomes the above problems or at least partially solves the above problems.

[0006] According to the first aspect of an embodiment of the present application, a method for preparing a multilayer tube is provided, comprising: obtaining an initial metal rod having a depression in the middle position along the axial direction by machining; spraying a ceramic layer at the depressed position of the initial metal rod by a plasma spraying process; sleeved a first metal tube on the outside of the initial metal rod, and sleeved two end heads on both ends of the initial metal rod; welding the two end heads to the first metal tube respectively; welding the initial metal rod and the first metal tube sleeved on the outside of the initial metal rod so that the initial metal rod, the ceramic layer and the first metal tube are combined with each other; cutting off the two ends of the combined initial metal rod and the two ends of the first metal tube to expose a cross-section with the ceramic layer; and forming a through hole extending in the axial direction at the center of the initial metal rod to obtain the multilayer tube.

[0007] According to a second aspect of an embodiment of the present application, a thermionic energy converter is provided, comprising: a multilayer tube prepared by the preparation method described in the first aspect of the embodiment of the present application, the multilayer tube being used as an emitter of the thermionic energy converter; a plurality of receiving electrodes axially sleeved on the outside of the multilayer tube, the plurality of receiving electrodes being respectively connected to the multilayer tube via a plurality of connectors; and an end plug connected to one end of the multilayer tube.

[0008] This method is used to prepare a multi-layer tube composed of metal and ceramic, with the inner and outer layers being metal tubes and the middle layer being a ceramic layer. On the one hand, this method meets the application needs of mutual insulation between the inner and outer metal tubes under high temperature conditions. On the other hand, it enables the inner and outer metal tubes and the ceramic layer to form a whole, thus avoiding a large temperature difference between the inner and outer metal tubes.

[0009] The thermionic energy converter provided in an embodiment of the present application includes a multilayer tube prepared by the preparation method of the above embodiment, so that multiple power generation units can be connected in series on one thermionic energy converter, and the output voltage of the thermionic energy converter can be increased from approximately 1V to a maximum of more than 5V, and the thermoelectric conversion efficiency of the thermionic energy converter can be increased by more than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a planar schematic diagram of the initial metal rod;

[0011] Figure 2 is a cross-sectional view of an initial metal rod sprayed with a ceramic layer;

[0012] Figure 3 It is a schematic diagram of the assembly of the initial metal rod, the first metal tube and the two end pieces;

[0013] Figure 4 It is a schematic diagram of the interior of the ceramic layer and a schematic diagram of the compositions of the first transition layer, the pure ceramic layer, and the second transition layer in the ceramic layer;

[0014] Figure 5 is a cross-sectional view of a multilayer tube prepared by the preparation method of the present application;

[0015] Figure 6 is a cross-sectional view of a multilayer tube prepared by the preparation method of the present application; and

[0016] Figure 7 4 is a cross-sectional view of the thermionic energy converter of the present application.

[0017] In the picture:

[0018] 1- initial metal rod; 11- depression;

[0019] 2-ceramic layer; 21-first transition layer; 211-coating; 22-pure ceramic layer; 23-second transition layer;

[0020] 3- first metal tube;

[0021] 4-terminal;

[0022] 5-receiving pole;

[0023] 6-Connector;

[0024] 7-end plug;

[0025] 8- Second metal tube. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of this application. Obviously, the described embodiment is only one embodiment of this application, not all embodiments. Based on the described embodiments of this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in this application should have the usual meanings understood by people with ordinary skills in the field to which this application belongs. If the full text involves descriptions such as "first" and "second", the "first" and "second" descriptions are only used to distinguish similar objects, and cannot be understood as indicating or implying their relative importance, order of precedence, or implicitly indicating the number of technical features indicated. It should be understood that the data described by "first" and "second" can be interchangeable under appropriate circumstances. If "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes Solution A, Solution B, or solutions that meet both A and B.

[0028] According to the inventive concept of one aspect of the present application, a method for preparing a multi-layer tube is provided, comprising: using machining to obtain an initial metal rod having a depression in the middle position along the axial direction; using a plasma spraying process to spray a ceramic layer at the depressed position of the initial metal rod; sleeveing a first metal tube on the outside of the initial metal rod, and sleeved two end heads on both ends of the initial metal rod; welding the two end heads to the first metal tube respectively; welding the initial metal rod and the first metal tube sleeved on the outside of the initial metal rod so that the initial metal rod, the ceramic layer and the first metal tube are combined with each other; cutting off the two ends of the combined initial metal rod and the two ends of the first metal tube to expose a cross-section with a ceramic layer; and forming a through hole extending in the axial direction in the center of the initial metal rod to obtain a multi-layer tube.

[0029] Figure 1 is a planar schematic diagram of the initial metal rod; Figure 2 is a cross-sectional view of an initial metal rod sprayed with a ceramic layer; Figure 3 It is a schematic diagram of the assembly of the initial metal rod, the first metal tube and the two end pieces.

[0030] According to the exemplary embodiment of this application, please refer to Figure 1-Figure 3 , provides a method for preparing a multi-layer tube, comprising: using machining to obtain an initial metal rod 1 having a recess 11 in the middle position along the axial direction. Using a plasma spraying process to spray a ceramic layer 2 at the position of the recess 11 of the initial metal rod 1. Putting a first metal tube 3 on the outside of the initial metal rod 1, and putting two end heads 4 on both ends of the initial metal rod 1. Welding the two end heads 4 to the first metal tube 3 respectively. Welding the initial metal rod 1 and the first metal tube 3 put on the outside of the initial metal rod 1 so that the initial metal rod 1, the ceramic layer 2 and the first metal tube 3 are combined with each other. Cutting off the two ends of the combined initial metal rod 1 and the two ends of the first metal tube 3 to expose the cross-section with the ceramic layer 2. Forming a through hole extending in the axial direction in the center of the initial metal rod 1 to obtain a multi-layer tube.

[0031] In this embodiment, a ceramic layer 2 is sprayed onto the recess 11 of the initial metal rod 1 using a plasma spraying process, so that the ceramic layer 2 is embedded within the recess 11 of the initial metal rod 1. This not only allows the ceramic layer 2 to be bonded to the initial metal rod 1, but also facilitates control of the thickness of the ceramic layer 2. A first metal tube 3 is sleeved onto the exterior of the initial metal rod 1, and two end caps 4 are sleeved onto the ends of the initial metal rod 1. The two end caps 4 are welded to the first metal tube 3, respectively, so that the initial metal rod 1 is sealed within the first metal tube 3 and the two end caps 4. This facilitates welding of the initial metal rod 1 and the first metal tube 3 sleeved onto the exterior of the initial metal rod 1, thereby bonding the initial metal rod 1, the ceramic layer 2, and the first metal tube 3 to each other. Furthermore, the ends of the bonded initial metal rod 1 and the first metal tube 3 are removed to expose a cross-section containing the ceramic layer 2, and a through hole extending axially is formed in the center of the initial metal rod 1 to obtain a multilayer tube.

[0032] This method is used to prepare a multi-layer tube composed of metal and ceramic, with the inner and outer layers being metal tubes and the middle layer being a ceramic layer. On the one hand, this method meets the application needs of mutual insulation between the inner and outer metal tubes under high temperature conditions. On the other hand, it enables the inner and outer metal tubes and the ceramic layer to form a whole, thus avoiding a large temperature difference between the inner and outer metal tubes.

[0033] It should be noted that the diameter of the recess 11 of the initial metal rod 1 having the recess 11 in the middle position along the axial direction is ΦA, and the diameter of the two ends of the initial metal rod 1 is ΦB. After the ceramic layer 2 is sprayed onto the recess 11 of the initial metal rod 1 using a plasma spraying process, the diameter of the initial metal rod 1 needs to be processed to ΦC. ΦB includes the processing allowance and the ceramic layer compression allowance, and ΦC includes the ceramic layer compression allowance. The ceramic layer compression allowance is the amount of compression of the ceramic layer 2 when the initial metal rod 1 and the first metal tube 3 sleeved on the outside of the initial metal rod 1 are welded using a hot isostatic pressing diffusion welding process. The ceramic layer compression allowance is set to 10 to 30% of the thickness of the ceramic layer 2.

[0034] Furthermore, in the process of processing the initial metal rod 1 to a diameter of ΦC, it is not recommended to use coolant when processing the ceramic layer 2. If it must be used, deionized water should be used as the coolant, and the coolant cannot be recycled to ensure the cleanliness of the ceramic layer 2 to the greatest extent.

[0035] Figure 4 It is a schematic diagram of the interior of the ceramic layer and a schematic diagram of the compositions of the first transition layer, the pure ceramic layer, and the second transition layer in the ceramic layer.

[0036] In some exemplary embodiments, referring to Figure 3-Figure 4 Spraying the ceramic layer 2 at the position of the recess 11 of the initial metal rod 1 using a plasma spraying process includes sequentially spraying a first transition layer 21 , a pure ceramic layer 22 and a second transition layer 23 at the position of the recess 11 of the initial metal rod 1 using a plasma spraying process.

[0037] It should be noted that, in this embodiment, the materials of the first transition layer 21 and the second transition layer 23 are both a mixture of metal and ceramic.

[0038] In some exemplary embodiments, referring to Figure 3-Figure 4 A first transition layer 21, a pure ceramic layer 22, and a second transition layer 23 are sprayed in sequence at the position of the recess 11 of the initial metal rod 1 using a plasma spraying process, including spraying in sequence at the position of the recess 11 of the initial metal rod 1 a first transition layer 21, a pure ceramic layer 22, and a second transition layer 23 including five coating layers 211 with increasing ceramic mass fractions, using a plasma spraying process.

[0039] Through the above-mentioned setting, since the materials of the first transition layer 21 and the second transition layer 23 are both a mixture of ceramic and metal, the mass fraction of the ceramic in the coating 211 on the side close to the initial metal rod 1 in the five layers of coating 211 in the first transition layer 21 is less than the mass fraction of the ceramic in the coating 211 on the side close to the pure ceramic layer 22, thereby making the bonding between the ceramic layer 2 and the initial metal rod 1 become a metal-to-metal bonding, thereby improving the bonding strength between the ceramic layer 2 and the initial metal rod 1.

[0040] Similarly, the mass fraction of the ceramic in the coating 211 close to the first metal tube 3 in the five-layer coating 211 in the second transition layer 23 is less than the mass fraction of the ceramic in the coating 211 close to the pure ceramic layer 22, thereby turning the bonding between the ceramic layer 2 and the first metal tube 3 into a metal-to-metal bonding, thereby improving the bonding strength between the ceramic layer 2 and the first metal tube 3.

[0041] It should be noted that in this embodiment, the five coating layers 211 in the first transition layer 21 have approximately equal thicknesses, and the five coating layers 211 in the second transition layer 23 have approximately equal thicknesses. The thickness of the coating layer 211 in the second transition layer 23 on the side close to the first metal tube 3 should have a machining allowance.

[0042] In some exemplary embodiments, referring to Figure 3-Figure 4 , a first transition layer 21, a pure ceramic layer 22 and a second transition layer 23 are sprayed in sequence at the position of the recess 11 of the initial metal rod 1 using a plasma spraying process, including spraying a first transition layer 21, a pure ceramic layer 22 and a second transition layer 23 including five layers of coating 211 with ceramic mass fractions of 0, 20%, 40%, 60% and 80% in sequence at the position of the recess 11 of the initial metal rod 1 using a plasma spraying process.

[0043] In some exemplary embodiments, the spraying thickness of the pure ceramic layer 22 is 70% of the total thickness of the first transition layer 21 , the pure ceramic layer 22 , and the second transition layer 23 .

[0044] In some exemplary embodiments, referring to Figure 3-Figure 4 The total thickness of the first transition layer 21 , the pure ceramic layer 22 and the second transition layer 23 sprayed at the position of the recess 11 of the initial metal rod 1 is equal to the depth of the recess 11 of the initial metal rod 1 .

[0045] In some exemplary embodiments, referring to Figure 3 The two end pieces 4 are respectively welded to the first metal tube 3 using vacuum electron beam welding or vacuum laser welding.

[0046] It should be noted that before welding the two end pieces 4 to the first metal tube 3, the initial metal rod 1, the first metal tube 3 and the two end pieces 4 which are sleeved on the outside of the initial metal rod 1, need to be placed in a vacuum chamber with a degree of vacuum better than 1×10 -2 Pa vacuum chamber for more than 2 hours, and the welding position should be more than 10 mm away from the ceramic layer 2. The overall leakage rate inside the first metal tube 3 and the two end caps 4 after welding is less than or equal to 1.0×10 -9 Pa·m 3 / s.

[0047] In some exemplary embodiments, referring to Figure 3 The initial metal rod 1 and the first metal tube 3 sleeved on the outside of the initial metal rod 1 are welded using a hot isostatic pressing diffusion welding process.

[0048] In some exemplary embodiments, the welding conditions for welding the initial metal rod 1 and the first metal tube 3 sleeved outside the initial metal rod 1 using a hot isostatic pressing diffusion welding process include: Ar gas environment, 200MP pressure, temperature of 1700-1750°C and welding time less than or equal to 2 hours.

[0049] In some exemplary embodiments, the method for preparing the multilayer tube of this embodiment further includes cleaning the surface of the initial metal rod 1 before spraying the ceramic layer 2 onto the recess 11 of the initial metal rod 1 using a plasma spraying process.

[0050] In some exemplary embodiments, the method for preparing the multilayer tube of this embodiment further includes cleaning and vacuum degassing the initial metal rod 1, the first metal tube 3 and the two end heads 4 before inserting the first metal tube 3 onto the outside of the initial metal rod 1 and inserting the two end heads 4 onto both ends of the initial metal rod 1.

[0051] In addition, it should be noted that, in this embodiment, the metal material in the first transition layer 21 and the second transition layer 23 is the same as the material of the initial metal rod 1. The metal material in the first transition layer 21 and the second transition layer 23 can also be set to be the same as the material of the first metal tube 3. The metal material in the first transition layer 21 and the second transition layer 23 can also be set to molybdenum.

[0052] The oxygen content of the metal powder used in the first transition layer 21 and the second transition layer 23 is less than 500 ppm.

[0053] The ceramic material in the first transition layer 21 and the second transition layer 23 is the same as the material of the pure ceramic layer 22 .

[0054] The purity of the ceramic powder used in the first transition layer 21 and the second transition layer 23 is 99.99%.

[0055] The initial metal rod 1 is made of one of tungsten, molybdenum, niobium, and tantalum. The first metal tube 3 is made of one of tungsten, molybdenum, niobium, and tantalum. The initial metal rod 1 is preferably made of molybdenum, and the first metal tube 3 is preferably made of niobium.

[0056] The material of the pure ceramic layer 22 is aluminum oxide or scandium oxide. The material of the pure ceramic layer 22 is preferably aluminum oxide.

[0057] Figure 5 is a cross-sectional view of a multilayer tube prepared by the preparation method of the present application; Figure 6 4 is a cross-sectional view of a multilayer tube prepared by the preparation method of the present application.

[0058] A multilayer tube prepared by any of the above-described methods, such as Figure 5-Figure 6 As shown, the wall thickness of the first metal tube 3 is less than 1 mm. The thickness of the ceramic layer 2 is less than 1 mm. The wall thickness of the second metal tube 8 is less than 1 mm. Furthermore, using any of the preparation methods described above, a metal-ceramic composite multilayer tube with an outer diameter greater than 15 mm, a minimum wall thickness less than 2.5 mm, and a maximum length of not less than 700 mm can be produced.

[0059] Figure 7 4 is a cross-sectional view of the thermionic energy converter of the present application.

[0060] According to the exemplary embodiment of this application, please refer to Figure 7 A thermionic energy converter is provided, comprising a multilayer tube prepared by any of the methods described above, a plurality of receiving electrodes 5, and an end plug 7. The multilayer tube serves as the emitter of the thermionic energy converter. The plurality of receiving electrodes 5 are axially sleeved on the outside of the multilayer tube and are connected to the multilayer tube via a plurality of connectors 6. The end plug 7 is connected to one end of the multilayer tube.

[0061] In this embodiment, by applying the multilayer tube prepared by the preparation method described in the above embodiment to a thermionic energy converter, multiple power generation units are connected in series on one thermionic energy converter. This increases the output voltage of the thermionic energy converter from approximately 1 V to a maximum of over 5 V, and improves the thermoelectric conversion efficiency of the thermionic energy converter by over 20%.

[0062] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of this application. It should be understood that the above is only a specific embodiment of this application and is not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application should be included in the scope of protection of this application.

Claims

1. A method for preparing a multilayer tube, comprising: An initial metal rod (1) having a recess (11) at a middle position along an axial direction is obtained by machining; Spraying a ceramic layer (2) at the position of the depression (11) of the initial metal rod (1) using a plasma spraying process; The first metal tube (3) is sheathed on the outside of the initial metal rod (1), and two end caps (4) are sheathed on both ends of the initial metal rod (1); Welding the two end caps (4) to the first metal tube (3) respectively; Welding the initial metal rod (1) and the first metal tube (3) sleeved on the outside of the initial metal rod (1) so that the initial metal rod (1), the ceramic layer (2) and the first metal tube (3) are combined with each other; Cutting off both ends of the combined initial metal rod (1) and both ends of the first metal tube (3) to expose a cross section having the ceramic layer (2); as well as forming a through hole extending in an axial direction at the center of the initial metal rod (1) to obtain the multilayer tube; The method of spraying a ceramic layer (2) at the position of the depression (11) of the initial metal rod (1) using a plasma spraying process comprises: A first transition layer (21), a pure ceramic layer (22), and a second transition layer (23) are sequentially sprayed at the position of the recess (11) of the initial metal rod (1) using a plasma spraying process; The method comprises spraying a first transition layer (21), a pure ceramic layer (22) and a second transition layer (23) in sequence at the position of the depression (11) of the initial metal rod (1) using a plasma spraying process, comprising: A first transition layer (21) comprising five coating layers (211) with successively increasing ceramic mass fractions, a pure ceramic layer (22), and a second transition layer (23) comprising five coating layers (211) with successively decreasing ceramic mass fractions are sprayed in sequence at the position of the recess (11) of the initial metal rod (1) using a plasma spraying process.

2. The method for preparing a multilayer tube according to claim 1, wherein: The method comprises spraying a first transition layer (21), a pure ceramic layer (22) and a second transition layer (23) in sequence at the position of the depression (11) of the initial metal rod (1) using a plasma spraying process, comprising: A first transition layer (21) comprising five coating layers (211) with ceramic mass fractions of 0, 20%, 40%, 60% and 80%, a pure ceramic layer (22) and a second transition layer (23) comprising five coating layers (211) with ceramic mass fractions of 80%, 60%, 40%, 20% and 0 are sprayed in sequence at the position of the recess (11) of the initial metal rod (1) using a plasma spraying process.

3. The method for preparing a multilayer tube according to claim 1, wherein: The spraying thickness of the pure ceramic layer (22) is 70% of the total thickness of the first transition layer (21), the pure ceramic layer (22) and the second transition layer (23).

4. The method for preparing a multilayer tube according to claim 1, wherein: The total thickness of the first transition layer (21), the pure ceramic layer (22) and the second transition layer (23) sprayed at the position of the recess (11) of the initial metal rod (1) is equal to the depth of the recess (11) of the initial metal rod (1).

5. The method for preparing a multilayer tube according to claim 1, wherein: The two end heads (4) are respectively welded to the first metal tube (3) by using vacuum electron beam or vacuum laser welding.

6. The method for preparing a multilayer tube according to claim 1, wherein: The initial metal rod (1) and the first metal tube (3) sleeved on the outside of the initial metal rod (1) are welded using a hot isostatic pressing diffusion welding process.

7. The method for preparing a multilayer tube according to claim 6, wherein: The welding conditions for welding the initial metal rod (1) and the first metal tube (3) sleeved on the outside of the initial metal rod (1) using a hot isostatic pressing diffusion welding process include: an Ar gas environment, a pressure of 200 MPa, a temperature of 1700-1750° C., and a welding time of less than or equal to 2 hours.

8. The method for preparing a multilayer tube according to claim 1, further comprising: Before spraying the ceramic layer (2) onto the recess (11) of the initial metal rod (1) using a plasma spraying process, the surface of the initial metal rod (1) is cleaned.

9. The method for preparing a multilayer tube according to claim 8, further comprising: Before the first metal tube (3) is sleeved onto the outside of the initial metal rod (1) and the two end heads (4) are sleeved onto both ends of the initial metal rod (1), the initial metal rod (1), the first metal tube (3) and the two end heads (4) are cleaned and vacuum degassed.

10. A thermionic energy converter comprising: A multilayer tube prepared by the preparation method according to any one of claims 1 to 9, wherein the multilayer tube is used as an emitter of the thermionic energy converter; A plurality of receiving electrodes (5) are sleeved on the outside of the multilayer tube in the axial direction, and the plurality of receiving electrodes (5) are respectively connected to the multilayer tube via a plurality of connecting pieces (6); as well as An end plug (7) is connected to one end of the multi-layer tube.

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