Double-insulating-material self-powered detector and production method

Abstract

The invention relates to a double-insulating-material self-powered detector and a production method, the detector comprises a shell, an insulator, an emitter and a signal line, the insulator is of a three-layer composite structure which is sequentially distributed in the axial direction and is integrally sintered and formed, and the insulator comprises a first insulating layer located at the probe end of the detector and made of magnesium oxide ceramics, and a second insulating layer located at the probe end of the detector and made of magnesium oxide ceramics; the first insulating layer is located at the cable end of the detector, the second insulating layer is located at the cable end of the detector and is made of aluminum oxide ceramics, the component gradient transition layer is located between the first insulating layer and the second insulating layer, and the chemical composition of the component gradient transition layer continuously changes in the axial direction. And the 100% magnesium oxide close to the first insulating layer is gradually transited to the 100% aluminum oxide in contact with the second insulating layer. The material distribution of the double-insulating-material self-powered detector insulator along the axial direction is matched with the axial working conditions (high temperature and high radiation at the lower end and low temperature ion pollution at the upper end) of the detector, the characteristics of the insulator material are fully exerted, the service life of the detector is prolonged, and the detection stability of the detector is improved.

Description

Technical Field

[0001] This invention relates to the field of nuclear testing instrument technology, and in particular to a self-powered detector made of double insulating materials and its manufacturing method. Background Technology

[0002] The self-powered detector is used to detect neutron flux in the core of a nuclear reactor. Its main structure consists of a shell, an emitter, an insulator, and a signal line. The two ends of the detector are a probe end and a cable end, respectively. The emitter, located in the probe end, undergoes beta decay after absorbing neutrons, releasing electrons. The current signal is generated through charge accumulation and transmitted to a potentiometer or galvanometer via the signal line that passes through the cable end for measurement. The insulator is used to achieve electrical isolation between the emitter and the shell.

[0003] In existing self-supplied detectors, the insulator is generally a magnesium oxide ceramic tube. This is because magnesium oxide has extremely high resistivity, good irradiation performance, and excellent thermal stability. When the detector is placed in the high-temperature, high-radiation reactor core environment, it can ensure the stability and accuracy of the detector. However, in practical applications, the probe end of the detector is placed in the reactor core environment, while the cable end of the detector is placed in the containment environment. The temperature in the containment environment is lower than that in the reactor core environment (generally not exceeding 100°C and relatively stable), and the neutron flux and radiation level are also lower than those in the reactor core environment. The magnesium oxide ceramic tube generates performance redundancy in the containment environment. Furthermore, there are a large number of alkali metal ions such as sodium ions and potassium ions in the containment environment. The migration of metal ions through the insulator into the sensitive active region can cause the detector performance to drift and fail. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a self-powered detector made of double insulating materials and a method for its production, so as to solve the above problems.

[0005] For the purposes described above, the present invention provides:

[0006] A self-powered detector made of double insulating materials includes a shell, an insulator, an emitter, and a signal line. The insulator is a three-layer composite structure that is sequentially distributed along the axial direction and integrally sintered, comprising:

[0007] The first insulating layer located at the probe end of the detector is made of magnesium oxide ceramic;

[0008] The second insulation layer located at the end of the detector cable is made of alumina ceramic;

[0009] and a composition gradient transition layer located between the first insulating layer and the second insulating layer;

[0010] The chemical composition of the composition gradient transition layer changes continuously along the axial direction, gradually transitioning from 100% magnesium oxide at the junction with the first insulating layer to 100% aluminum oxide at the junction with the second insulating layer.

[0011] Preferably, the composition gradient transition layer consists of at least five axially stacked mixed material sublayers, each of which has a constant and different magnesium oxide mass fraction, which decreases layer by layer in the direction from the first insulating layer to the second insulating layer.

[0012] Preferably, the purity of magnesium oxide or aluminum oxide in the first insulating layer and the second insulating layer is not less than 99.9%.

[0013] Preferably, the first insulating layer, the second insulating layer, and the composition gradient transition layer all contain rare earth oxides as sintering aids and grain boundary modifiers, and the amount of rare earth oxides added accounts for 0.1% to 2% of the total mass of the ceramic material.

[0014] A method for producing the insulator of a self-powered detector made of double insulating materials includes the following steps:

[0015] S1. Slurry preparation and molding:

[0016] Various ceramic slurries are prepared, with the raw material mass ratio of magnesium oxide to aluminum oxide varying along a preset gradient to form at least 7 different ratios ranging from 100% magnesium oxide to 100% aluminum oxide.

[0017] According to the order of magnesium oxide content from high to low, the green body is formed by sequential injection molding in the mold to form a composite green body consisting of a first insulating layer green body, a composition gradient transition layer green body, and a second insulating layer green body, and the adjacent green body layers are bonded in a wet state.

[0018] S2, Green body densification:

[0019] The composite green body is dried and then subjected to cold isostatic pressing at a pressure range of 150 MPa to 250 MPa to eliminate interlayer gaps and obtain a high-density integral green body.

[0020] S3, Integrated sintering:

[0021] The entire green blank is placed in a sintering furnace for co-sintering;

[0022] The sintering process includes: during the heating process, setting up a heat preservation platform in the range of 1200℃ to 1400℃, completing the final densification in a hydrogen or vacuum atmosphere at 1650℃ to 1800℃, and performing controlled cooling after sintering, wherein the cooling rate is no more than 1℃ / minute in the temperature range of 1300℃ to 800℃.

[0023] In step S1, the mass ratios of magnesium oxide to aluminum oxide in the seven ceramic slurries prepared are 100:0, 90:10, 70:30, 50:50, 30:70, 10:90 and 0:100, respectively.

[0024] Preferably, in step S1, when preparing each ceramic slurry, rare earth oxide powder accounting for 0.1% to 2% of the total mass of ceramic powder in the slurry is also added.

[0025] Preferably, in step S3, when the temperature drops below 800°C, the cooling rate is increased to 2°C / minute to 5°C / minute.

[0026] A method for manufacturing a double-insulated self-powered detector includes the following steps:

[0027] S1. An insulator is prepared by the production method of the self-powered detector with double insulating material as described in any one of claims 5-8;

[0028] S2. After soldering the transmitter to the signal line, insert it into the center hole of the insulator from one end of the second insulating layer until the preset position is reached.

[0029] S3. Transfer the insulator, which is assembled with the transmitter and signal line, from one end of the first insulating layer into the outer casing;

[0030] S4. The outer shell is drawn and reduced in diameter to form an interference fit between the outer shell and the outer wall of the insulator. Finally, the entire component is stress-relieved annealed at a temperature of 600℃ to 750℃.

[0031] The beneficial effects of this invention are:

[0032] 1. When the detector is working, the probe end of the detector is in the reactor core environment, and the cable end of the detector is in the containment environment. This allows the first insulating layer to fully utilize its characteristics of stable crystal structure and extremely low secondary electron emission rate at extreme high temperatures in the reactor core environment, ensuring the stability of the signal generation area and the intrinsic purity of the signal. The second insulating layer in the containment environment fully utilizes its excellent alkali metal ion blocking ability and high dielectric constant, providing long-term stable insulation and appropriate hardware filtering for the signal output end. The composition gradient transition layer, through a smooth material transition, avoids local electric field concentration or signal distortion that may be caused by abrupt performance changes, ensuring the stability of the output signal. This ensures that the axial material distribution of the insulator matches the axial operating conditions of the detector (high temperature and strong radiation at the lower end, low temperature and ion contamination at the upper end), fully utilizing the material characteristics to improve the lifespan and detection stability of the detector.

[0033] 2. By interdiffusion bonding at the atomic scale between the composition gradient transition layer and the first and second insulating layers during the integrated sintering process, the clear physical interface between the first insulating layer, the composition gradient transition layer and the second insulating layer is eliminated, making the insulator form a macroscopic whole. This eliminates the risk of interface cracking and delamination caused by the mismatch of the expansion coefficients of the first and second insulating layers, thereby improving the lifespan of the detector.

[0034] 3. The composition gradient transition layer uses multiple layers of mixed materials with varying proportions of magnesium oxide and aluminum oxide to smoothly transition the material distribution of the insulator from pure magnesium oxide in the first insulating layer to pure aluminum oxide in the second insulating layer. This allows thermal stress to be gradually absorbed and released between multiple layers, avoiding concentration at a single interface and improving the thermal shock resistance of the insulator. Furthermore, the smooth transition of material distribution allows parameters such as insulation resistance and dielectric constant to change smoothly along the axial direction, avoiding local electric field concentration or signal distortion that may be caused by abrupt changes in performance between the first and second insulating layers. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the structure of the self-powered detector made of double insulating materials in this invention.

[0037] The diagram is marked as follows:

[0038] 1. Outer shell; 2. Insulator; 21. First insulator; 22. Second insulator; 23. Composition gradient transition layer; 3. Emitter; 4. Signal line. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0040] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0041] Example 1: Production method of insulator for a self-powered detector made of double-insulating materials:

[0042] Includes the following steps:

[0043] S1. Raw material pretreatment and slurry preparation:

[0044] Magnesium oxide nanopowder and aluminum oxide nanopowder with a purity of ≥99.95% were used as matrix raw materials, with the average particle size of magnesium oxide nanopowder being 200 nanometers and the average particle size of aluminum oxide nanopowder being 150 nanometers.

[0045] Yttrium oxide nanopowder with a purity of ≥99.99% was used as a rare earth oxide additive.

[0046] According to the gradient ratio, seven groups of magnesium oxide and aluminum oxide mixed powders with different proportions were accurately weighed. Each group of mixed powders contained 1% rare earth oxide (yttrium oxide nanopowder was used in this example) by mass. The specific ratio is as follows (magnesium oxide: aluminum oxide):

[0047] Slurry A: 100:0 (corresponding to the first insulation layer);

[0048] Slurry B: 90:10;

[0049] Slurry C: 70:30

[0050] Slurry D: 50:50;

[0051] Slurry E: 30:70;

[0052] Slurry F: 10:90;

[0053] Slurry G: 0:100 (corresponding to the second insulation layer);

[0054] Each group of mixed powders was placed in a planetary ball mill with appropriate amounts of solvent (azeotropic mixture of ethanol and xylene), dispersant (phosphate ester) and binder (polyvinyl butyral) and ball milled at 300 rpm for 24 hours to obtain 7 groups of uniform, stable ceramic slurries suitable for casting.

[0055] S2. Sequential grouting forming of composite green body:

[0056] First, slurry A is injected into a tubular mold to form the first layer of pure magnesium oxide green body;

[0057] While the surface of the green body of slurry A is still wet, slurry B to slurry F are injected sequentially and continuously. Before each layer of slurry is injected, it must be ensured that the surface of the previous layer has not dried and formed a skin, so as to ensure that slight interpenetration and interweaving occur between the layers at the interface, laying the initial foundation for atomic interdiffusion in subsequent sintering.

[0058] Finally, slurry G is injected onto the wetted surface of slurry F to form the uppermost pure alumina green blank;

[0059] The obtained seven-layer composite green body was transferred into a drying oven and air-dried at room temperature for 12 hours. Then, the temperature was gradually increased to 50°C and dried for 24 hours to completely remove the solvent. After demolding, the dried composite green body was obtained.

[0060] S3. Cold isostatic pressing densification of composite green bodies:

[0061] The composite green body is encapsulated in a highly elastic rubber mold, placed in a cold isostatic press, and subjected to a pressure of 200 MPa for 10 minutes to eliminate micropores and weak bonding interfaces between layers that may be generated during the slurry molding process. This increases the density of the green body to more than 58% of the theoretical density and obtains preliminary mechanical strength, resulting in an overall green body.

[0062] S4, Integrated sintering:

[0063] The entire green blank is placed in a high-purity alumina sintering box and then placed in a high-temperature sintering furnace to perform an integrated sintering process:

[0064] The temperature was increased from room temperature to 500℃ at a rate of 1℃ / min and held for 2 hours, then increased to 1250℃ at a rate of 3℃ / min and held for 2 hours to complete the initial growth and structural adjustment of the grains.

[0065] Under a hydrogen protective atmosphere, the temperature is raised to 1720℃ at a rate of 5℃ / min and held at this temperature for 4 hours. At this high temperature, magnesium oxide and aluminum oxide form a continuous solid solution through solid-phase diffusion, and the material becomes almost completely dense. Metallurgical bonding is achieved between the layers through atomic diffusion, and the macroscopic interface disappears.

[0066] After sintering, the temperature is reduced at a rate of 2℃ / min. When the temperature drops to the critical range of 1300℃ to 800℃, the cooling rate is controlled at 0.8℃ / min. The slow cooling rate allows sufficient time for the internal stress generated by the difference in thermal expansion coefficients of magnesium oxide and aluminum oxide during the cooling process to fully relax through lattice creep, dislocation movement, etc., preventing cracking or delamination after integrated sintering. After the temperature drops to 800℃, the cooling rate is increased to 3℃ / min until the furnace temperature drops below 200℃ and then cooled with the furnace. This improves production efficiency without affecting the sintering quality.

[0067] The insulator 2 of the self-powered detector made of double insulating materials prepared by the above method is a three-layer composite structure that is sequentially distributed along the axial direction and integrally sintered, including:

[0068] The first insulating layer 21 located at the probe end of the detector is made of magnesium oxide ceramic.

[0069] The second insulation layer 22 located at the end of the detector cable is made of alumina ceramic.

[0070] And a composition gradient transition layer 23 located between the first insulating layer 21 and the second insulating layer 22;

[0071] The chemical composition of the composition gradient transition layer 23 changes continuously along the axial direction, gradually transitioning from 100% magnesium oxide at the junction with the first insulating layer 21 to 100% aluminum oxide at the junction with the second insulating layer 22.

[0072] Specifically, the composition gradient transition layer consists of at least five axially stacked sublayers of mixed materials, each sublayer having a constant and different magnesium oxide mass fraction, which decreases layer by layer along the direction from the first insulating layer 21 to the second insulating layer 22.

[0073] Specifically, the purity of magnesium oxide or aluminum oxide in the first insulating layer 21 and the second insulating layer 22 is not less than 99.9%.

[0074] Specifically, the first insulating layer 21, the second insulating layer 22, and the composition gradient transition layer 23 all contain rare earth oxides as sintering aids and grain boundary modifiers, and the amount of rare earth oxides added accounts for 0.1% to 2% of the total mass of the ceramic material.

[0075] This self-powered detector insulator, made of dual insulating materials, achieves atomic-scale interdiffusion bonding between the first and second insulating layers during integrated sintering via a composition gradient transition layer. This eliminates the distinct physical interface between the first, second, and third insulating layers, forming a macroscopically unified insulator. This eliminates the risk of interface cracking and delamination caused by the mismatch in expansion coefficients between the first and second insulating layers, thus improving the insulator's lifespan and consequently extending the detector's lifespan. Furthermore, the composition gradient transition layer, composed of multiple layers of mixed materials with varying proportions of magnesium oxide and aluminum oxide, smoothly transitions the material distribution of the insulator from pure magnesium oxide in the first layer to pure aluminum oxide in the second layer, allowing thermal stress to be gradually distributed between multiple layers. The absorption and release of materials in a stepwise manner avoids concentration at a single interface, thus improving the thermal shock resistance of the insulator. Furthermore, the smooth transition of material distribution allows the insulation resistance, dielectric constant, and other parameters of the material to change smoothly along the axial direction, avoiding local electric field concentration or signal distortion that may be caused by abrupt changes in performance between the first and second insulating layers, ensuring the stability of the output signal. In the integrated sintering process, the liquid phase formed by rare earth oxides as sintering aids can effectively coordinate the shrinkage differences between magnesium oxide and aluminum oxide during sintering, preventing interlayer cracking during sintering. Moreover, rare earth oxides act as grain boundary modifiers in the integrated sintering process, with rare earth ions preferentially segregating at grain boundaries and sealing them, thereby improving the insulator's resistance to diffusion of alkali metal ions.

[0076] Example 2: Production method of a self-powered detector made of double insulating materials:

[0077] Includes the following steps:

[0078] S1. An insulator is prepared by the method described in Example 1, and the surface of the prepared insulator is ground and cleaned.

[0079] S2. After welding the formed transmitter to the signal line of the coaxial cable, a detection core is formed. The detection core is inserted from one end of the second insulation layer into the center hole of the insulator until the preset position is reached.

[0080] S3. Transfer the insulator, which is assembled with the transmitter and signal line, from one end of the first insulating layer into the alloy outer shell;

[0081] S4. The outer shell is drawn and reduced in diameter to make it tightly wrap around the outer wall of the insulator, forming an interference fit to ensure mechanical stability and good thermal contact.

[0082] S5. Place the drawn detector assembly in an annealing furnace and hold it at 650°C in an argon atmosphere for 2 hours. Then, slowly cool it to below 300°C at a rate of 1.5°C / minute before removing it from the furnace. This achieves stress-relief annealing of the assembly, eliminates the internal stress of the metal introduced by the drawing and diameter reduction, prevents stress corrosion, and ensures the dimensional stability and structural integrity of the detector during long-term use.

[0083] The self-powered detector with dual insulation materials prepared by the above method includes a shell 1, an emitter 3, a signal line 4, and an insulator 2 prepared by the method described in Example 1. When the detector is working, the probe end of the detector is in the reactor core environment, and the cable end of the detector is in the containment environment. This allows the first insulation layer to fully utilize its characteristics of stable crystal structure and extremely low secondary electron emission rate at extreme high temperatures in the reactor core environment, ensuring the stability of the signal generation area and the intrinsic purity of the signal. The second insulation layer, in the containment environment, fully utilizes its excellent alkali metal ion blocking ability and high dielectric constant, providing long-term stable insulation protection and appropriate hardware filtering for the signal output end. The composition gradient transition layer, through a smooth material transition, avoids local electric field concentration or signal distortion that may be caused by abrupt performance changes, ensuring the stability of the output signal. Thus, by layering the first insulation layer, the composition gradient transition layer, and the second insulation layer along the detector axis, the working conditions of the detector axis (high temperature and strong radiation at the lower end, low temperature and ion contamination at the upper end) are matched, fully utilizing the characteristics of the materials to improve the lifespan and detection stability of the detector.

[0084] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in the details for the sake of brevity.

[0085] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A self-powered detector made of double insulating materials, comprising a shell, an insulator, an emitter, and a signal line, characterized in that: The insulator is a three-layer composite structure that is sequentially distributed along the axial direction and integrally sintered, comprising: The first insulating layer located at the probe end of the detector is made of magnesium oxide ceramic; The second insulation layer located at the end of the detector cable is made of alumina ceramic; and a composition gradient transition layer located between the first insulating layer and the second insulating layer; The chemical composition of the composition gradient transition layer changes continuously along the axial direction, gradually transitioning from 100% magnesium oxide at the junction with the first insulating layer to 100% aluminum oxide at the junction with the second insulating layer.

2. The self-powered detector made of double insulating materials according to claim 1, characterized in that: The composition gradient transition layer consists of at least five axially stacked sublayers of mixed materials, each of which has a constant and different magnesium oxide mass fraction that decreases layer by layer in the direction from the first insulating layer to the second insulating layer.

3. The self-powered detector made of double insulating material according to claim 1 or 2, characterized in that: The purity of magnesium oxide or aluminum oxide in both the first and second insulating layers is not less than 99.9%.

4. The self-powered detector with double insulating materials according to claim 1 or 2, characterized in that: The first insulating layer, the second insulating layer, and the composition gradient transition layer all contain rare earth oxides as sintering aids and grain boundary modifiers, and the amount of rare earth oxides added accounts for 0.1% to 2% of the total mass of the ceramic material.

5. A method for producing the insulator of a self-powered detector made of double insulating materials, characterized in that: Includes the following steps: S1. Slurry preparation and molding: Various ceramic slurries are prepared, with the raw material mass ratio of magnesium oxide to aluminum oxide varying along a preset gradient to form at least 7 different ratios ranging from 100% magnesium oxide to 100% aluminum oxide. According to the order of magnesium oxide content from high to low, the green body is formed by sequential injection molding in the mold to form a composite green body consisting of a first insulating layer green body, a composition gradient transition layer green body, and a second insulating layer green body, and the adjacent green body layers are bonded in a wet state. S2, Green body densification: The composite green body is dried and then subjected to cold isostatic pressing at a pressure range of 150 MPa to 250 MPa to eliminate interlayer gaps and obtain a high-density integral green body. S3, Integrated sintering: The entire green blank is placed in a sintering furnace for co-sintering; The sintering process includes: during the heating process, setting up a heat preservation platform in the range of 1200℃ to 1400℃, completing the final densification in a hydrogen or vacuum atmosphere at 1650℃ to 1800℃, and performing controlled cooling after sintering, wherein the cooling rate is no more than 1℃ / minute in the temperature range of 1300℃ to 800℃.

6. The method for producing the insulator of the self-powered detector made of double insulating materials according to claim 5, characterized in that: In step S1, the mass ratios of magnesium oxide to aluminum oxide in the seven ceramic slurries prepared are 100:0, 90:10, 70:30, 50:50, 30:70, 10:90 and 0:100, respectively.

7. The method for producing the insulator of the self-powered detector made of double insulating materials according to claim 5, characterized in that: In step S1, when preparing each ceramic slurry, rare earth oxide powder is also added, accounting for 0.1% to 2% of the total mass of ceramic powder in the slurry.

8. The method for producing the insulator of the self-powered detector made of double insulating materials according to claim 5, characterized in that: In step S3, when the temperature drops below 800°C, the cooling rate is increased to 2°C / minute to 5°C / minute.

9. A method for producing a double-insulated self-powered detector, characterized in that: Includes the following steps: S1. An insulator is prepared by the production method of the self-powered detector with double insulating material as described in any one of claims 5-8; S2. After soldering the transmitter to the signal line, insert it into the center hole of the insulator from one end of the second insulating layer until the preset position is reached. S3. Transfer the insulator, which is assembled with the transmitter and signal line, from one end of the first insulating layer into the outer casing; S4. The outer shell is drawn and reduced in diameter to form an interference fit between the outer shell and the outer wall of the insulator. Finally, the entire component is stress-relieved annealed at a temperature of 600℃ to 750℃.

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