Tungsten-scandium-based impregnated cathode, preparation method and application

Abstract

The invention provides a tungsten-scandium-based impregnated cathode and a preparation method and application thereof, and belongs to the technical field of hot cathode materials. The preparation method of the tungsten-scandium-based impregnated cathode provided by the invention comprises the following steps: adding ammonium metatungstate and scandium nitrate into water to obtain a mixed solution; freeze-drying the mixed solution to obtain uniformly mixed precursor powder; performing heat treatment on the precursor powder to obtain a porous tungsten scandium rod; the porous tungsten-scandium rod is subjected to post-treatment, and the tungsten-scandium-based impregnated cathode is obtained; wherein the concentration of ammonium metatungstate in the mixed solution is 0.1-0.4 g / mL; the ratio of ammonium metatungstate to scandium nitrate in the mixed solution is that the content of tungsten in the porous tungsten-scandium rod is 95-99 wt%, and the content of scandium oxide is 1-5 wt%; the freeze-drying temperature is lower than-50 DEG C, the freeze-drying vacuum degree is lower than 20 Pa, and the freeze-drying time is 48-72 hours.

Description

Technical Field

[0001] The invention belongs to the technical field of hot cathode materials, and in particular relates to a tungsten-scandium-based impregnated cathode, a preparation method and an application thereof. Background Art

[0002] Cathode emission performance is one of the key factors that determine the output power and life of vacuum electronic devices. As vacuum electronic devices develop towards high frequency and high power, the requirements for cathode miniaturization and high current density are getting higher and higher. Compared with ordinary barium tungsten cathodes, scandium-containing cathodes have higher emission current density and lower operating temperature, and are considered to be the most promising hot cathodes that meet the requirements of high-power small vacuum electronic devices.

[0003] The preparation of tungsten-scandium-based cathodes includes raw material mixing operations, among which mechanical mixing is the earliest and simplest raw material mixing method, but there are problems such as uneven raw material mixing and non-uniform particle size. The widely used co-precipitation method is a liquid phase raw material mixing method that meets the requirements of uniform mixing, but it needs to consider factors such as solution temperature, stirring rate, titration rate, precipitant selection and solution pH value, and it has to go through processes such as filtration, washing, drying and crushing. The complexity of the process makes it difficult to ensure repeatability and the cost is high. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a tungsten-scandium-based impregnated cathode, a preparation method and an application, in order to at least partially solve the above technical problems. The specific technical solutions provided by the present invention are as follows.

[0005] As a first aspect of the present invention, a method for preparing a tungsten-scandium-based impregnated cathode is provided, comprising: Adding ammonium metatungstate and scandium nitrate into water to obtain a mixed solution; freeze-drying the mixed solution to obtain a uniformly mixed precursor powder; The precursor powder is heat treated to obtain a porous tungsten-scandium rod; Post-processing the porous tungsten-scandium rod to obtain a tungsten-scandium-based impregnated cathode; Wherein, the concentration of ammonium metatungstate in the mixed solution is 0.1~0.4 g / mL; The ratio of ammonium metatungstate and scandium nitrate in the mixed solution is such that the content of tungsten in the porous tungsten-scandium rod is 95-99wt%, and the content of scandium oxide is 1-5wt%; The freeze-drying temperature is less than -50°C, the freeze-drying vacuum is less than 20Pa, and the freeze-drying time is 48~72h.

[0006] As a second aspect of the present invention, a tungsten-scandium-based impregnated cathode is provided, which is prepared by the above method.

[0007] As a third aspect of the present invention, there is provided an application of the above-mentioned tungsten-scandium-based impregnated cathode, including use in preparing any one of vacuum electronic devices, particle accelerators, medical accelerators, high-performance electron microscopes, and vacuum coating equipment.

[0008] In an embodiment of the present invention, a mixed solution of ammonium metatungstate and scandium nitrate is freeze-dried to obtain a precursor powder with uniform distribution of elements and particle size, and then the precursor powder is heat-treated and post-treated to obtain a tungsten-scandium-based impregnated cathode. Ammonium metatungstate and scandium nitrate are evenly mixed in an aqueous solution to ensure uniform distribution of elements at the solution level. The mixed solution is then frozen into a solid, and the water forms ice crystals, which are evenly distributed throughout the solid and wrap the ammonium metatungstate and scandium nitrate therein. In a vacuum or low-pressure environment, the ice crystals directly sublimate into water vapor, while the ammonium metatungstate and scandium nitrate remain in place to form a precursor powder with uniform particle size and element distribution. Therefore, the present invention uses freeze-drying technology to provide a precursor powder with uniform distribution of elements and particle size, so that the further obtained tungsten-scandium-based impregnated cathode has better emission performance, further promoting the practical application of tungsten-scandium-based impregnated cathodes. The preparation method of the tungsten-scandium-based impregnated cathode provided by the present invention only requires mixing the raw materials and then freeze-drying them to obtain a precursor powder with uniform element and particle size distribution. The preparation process is simple and less equipment is used, which can save process equipment and shorten the process flow. In particular, compared with large-scale complete sets of equipment to produce fine powders, the preparation method provided by the present invention has low cost and meets the requirements of high repeatability and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The flowchart of the preparation method of the tungsten-scandium-based impregnated cathode in the present invention;

[0010] Figure 2 Schematic diagram of the structure of the tungsten-scandium-based impregnated cathode in Example 1 of the present invention;

[0011] Figure 3 This is a scanning electron microscope image of scandium oxide doped tungsten powder in Example 1 of the present invention;

[0012] Figure 4 The DC volt-ampere characteristic curve of the tungsten-scandium-based impregnated cathode in Example 1 of the present invention;

[0013] Figure 5 The pulse voltammetric characteristic curve of the tungsten-scandium-based impregnated cathode in Example 1 of the present invention;

[0014] Figure 6 The DC volt-ampere characteristic curve of the tungsten-scandium-based impregnated cathode in Example 2 of the present invention;

[0015] Figure 7 The pulse voltammetric characteristic curve of the tungsten-scandium-based impregnated cathode in Example 2 of the present invention;

[0016] Figure 8 is a DC volt-ampere characteristic curve of the tungsten-scandium-based impregnated cathode in Example 3 of the present invention;

[0017] Fig. 9 This is a pulse voltammetric characteristic curve of the tungsten-scandium-based impregnated cathode in Example 3 of the present invention. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0019] As a typical scandium-containing cathode, the key technology of tungsten-scandium-based impregnated cathode lies in the preparation of precursor powder with suitable particle size and uniform mixing, and the decomposition, reduction, pressing and sintering process to obtain tungsten-scandium rod with controllable porosity, and finally obtain tungsten-scandium-based impregnated cathode with high emission performance through emission material impregnation, cathode precision machining and appropriate welding methods. When the elements and particle size distribution in the precursor powder are uneven, the emission performance, conductivity, thermal stability, mechanical strength and durability of the tungsten-scandium rod impregnated cathode prepared using it will fluctuate, thereby affecting the overall performance and reliability of the tungsten-scandium rod impregnated cathode. In order to prepare a tungsten-scandium-based impregnated cathode with good performance, it is necessary to optimize the preparation process of the precursor powder to obtain a precursor powder with suitable particle size and uniform element distribution.

[0020] Accordingly, the present invention prepares a precursor powder with uniform particle size distribution and uniform element distribution by freeze drying technology. Freeze drying belongs to a liquid phase synthesis method, and can obtain a powder with uniform microscopic particle size and uniform element distribution. The freeze drying process does not cause chemical changes, but only physical changes, so the environmental factors have little impact and the sample preparation has good repeatability. At the same time, the freeze drying process is simple, the cost is low, and it is practical.

[0021] Specifically, as a first aspect of the present invention, a method for preparing a tungsten-scandium-based impregnated cathode is provided, such as Figure 1 As shown, steps S1-S4 are included.

[0022] S1: Add ammonium metatungstate and scandium nitrate into water to obtain a mixed solution.

[0023] S2: freeze-drying the mixed solution to obtain a uniformly mixed precursor powder.

[0024] S3: heat-treating the precursor powder to obtain a porous tungsten-scandium rod.

[0025] S4: Post-processing the porous tungsten-scandium rod to obtain a tungsten-scandium-based impregnated cathode.

[0026] Wherein, the concentration of ammonium metatungstate in the mixed solution is 0.1-0.4 g / mL, preferably 0.2-0.4 g / mL, for example, 0.1 g / mL, 0.2 g / mL, 0.3 g / mL, 0.4 g / mL. The ratio of ammonium metatungstate to scandium nitrate in the mixed solution is such that the content of tungsten in the porous tungsten-scandium rod is 95-99 wt%, and the content of scandium oxide is 1-5 wt%, for example: when the content of tungsten is 95%, the content of scandium oxide is 5%, when the content of tungsten is 97%, the content of scandium oxide is 3%, when the content of tungsten is 99%, the content of scandium oxide is 1%, and the ratio of ammonium metatungstate to scandium nitrate is adjusted by the mass relationship of tungsten and scandium oxide in the porous tungsten-scandium rod. The freeze-drying temperature is less than -50°C, preferably -80 to -50°C, for example -50°C, -60°C, -70°C, -80°C, -90°C. The freeze-drying vacuum is less than 20Pa, preferably 3 to 20Pa, more preferably 3 to 16Pa, for example 3Pa, 5Pa, 10Pa, 15Pa, 20Pa. The freeze-drying time is 48 to 72h, for example 48h, 54h, 60h, 66h, 72h.

[0027] In an embodiment of the present invention, a mixed solution of ammonium metatungstate and scandium nitrate is freeze-dried to obtain a precursor powder with uniform mixing and uniform particle size distribution, and then the precursor powder is heat-treated and post-treated to obtain a tungsten-scandium-based impregnated cathode. The preparation method of the tungsten-scandium-based impregnated cathode provided by the present invention only requires mixing the raw materials and then freeze-drying to obtain a precursor powder with uniform element and particle size distribution. The preparation process is simple and less equipment is used, which can save process equipment and shorten the process flow. In particular, compared with large-scale complete sets of equipment to produce fine powders, the preparation method provided by the present invention has low cost and meets the requirements of high repeatability and strong practicality.

[0028] According to an embodiment of the present invention, freeze drying the mixed solution includes using liquid nitrogen to quickly freeze the mixed solution of ammonium metatungstate and scandium nitrate into a solid, and then using a freeze dryer to maintain a low temperature and low vacuum environment to obtain a dry precursor powder. According to the three-phase diagram of water, when the temperature is lower than 0.01°C and the pressure is lower than 611Pa, water will not appear in a liquid phase, so theoretically the freeze drying process must meet this condition. The freeze drying time is mainly related to the water content in the solution. The mixed solution prepared with 100~200ml water can completely dissolve 39.8~38.19g ammonium metatungstate and 1.08~5.42g scandium nitrate (for example: 39.8g ammonium metatungstate and 1.08g scandium nitrate are dissolved in 150mL water, 39.8g ammonium metatungstate and 5.42g scandium nitrate are dissolved in 200mL water, 38.19g ammonium metatungstate and 1.08g scandium nitrate are dissolved in 100mL water, 38.19g ammonium metatungstate and 5.42g scandium nitrate are dissolved in 180mL water. At this time, the mixed solution is a clear and transparent solution, which is more conducive to the uniform distribution of elements in the precursor powder. The specific addition amount can be adjusted according to the use). At the same time, completely dried precursor powder is obtained after freeze drying for 48~72h. The most important condition affecting the freeze drying effect is the vacuum degree, followed by temperature and time. When the vacuum degree is insufficient, the water-containing solid will melt during the freeze-drying process. During the freeze-drying process, the low temperature is maintained so that the frozen solid does not melt. If the freeze-drying time is insufficient, the obtained precursor powder will contain a small amount of water, which will reduce the dispersion and uniformity of the precursor powder. Therefore, the vacuum degree of freeze-drying is preferably 3~20Pa, and the freeze-drying temperature is preferably -80~-50℃.

[0029] According to an embodiment of the present invention, heat treating the precursor powder includes: decomposing and reducing the precursor powder, grinding and screening to obtain scandium oxide doped tungsten powder; pressing and sintering the scandium oxide doped tungsten powder to obtain a porous tungsten scandium rod.

[0030] The precursor powder is decomposed to obtain a mixed powder of tungsten oxide and scandium oxide. The decomposition is carried out under air conditions, the decomposition temperature is 500-600°C, for example, 500°C, 525°C, 550°C, 575°C, 600°C, and the decomposition time is 2-3h, for example, 2h, 2.2h, 2.5h, 2.8h, 3h. This process decomposes ammonium ions and nitrate ions to generate nitrogen oxides for discharge. The mixed powder of tungsten oxide and scandium oxide is reduced to obtain scandium oxide-doped tungsten powder. The reduction is divided into two stages, both of which are carried out under a hydrogen atmosphere. The reduction temperature of the first stage is 500-600°C, for example, 500°C, 525°C, 550°C, 575°C, and 600°C. The reduction time of the first stage is 0.5-1.5h, for example, 0.5h, 0.7h, 1h, 1.2h, and 1.5h. The reduction temperature of the second stage is 900-1000°C, for example, 900°C, 925°C, 950°C, 975°C, and 1000°C. The reduction time of the second stage is 1-2h, for example, 1h, 1.2h, 1.5h, 1.8h, and 2h. This process reduces tungsten oxide to tungsten powder. After the reduction is completed, it is ground and sieved to avoid agglomeration to obtain scandium oxide-doped tungsten powder with a narrow particle size distribution and uniform element mixing. Among them, the particle size of the scandium oxide doped tungsten powder is 200-325 mesh, for example, it can be 200 mesh, 250 mesh, 300 mesh, 325 mesh. The narrow particle size distribution means that the particles of the scandium oxide doped tungsten powder are similar in size. During the sintering process, the contact area between the scandium oxide doped tungsten powder particles is larger, which is conducive to the diffusion and bonding between the particles, thereby improving the sintering density and uniformity. It is further conducive to the improvement of the mechanical strength and thermal stability of the subsequently prepared tungsten scandium-based impregnated cathode, as well as the emission and transmission of electrons in the tungsten scandium-based impregnated cathode, thereby improving the emission performance of the tungsten scandium-based impregnated cathode.

[0031] Scandium oxide doped tungsten powder is pressed to obtain a tungsten-scandium rod. The pressing is isostatic pressing, the pressing pressure is 100-150MPa, for example, 100MPa, 110MPa, 120MPa, 130MPa, 140MPa, 150MPa, and the pressing time is 5-10min, for example, 5min, 6min, 7min, 8min, 9min, 10min. The tungsten-scandium rod is sintered to obtain a porous tungsten-scandium rod, the sintering temperature is 1600-1800℃, for example, 1600℃, 1650℃, 1700℃, 1750℃, 1800℃, and the sintering time is 20-30min, for example, 20min, 22min, 25min, 28min, 30min. During isostatic pressing, the pressure applied in all directions is equal, so that the pore size of the obtained tungsten-scandium rod is consistent and evenly distributed. Molding pressing or other general techniques only apply pressure in a fixed direction, resulting in inconsistent pore sizes and uneven distribution of the tungsten-scandium rods. This problem will be further magnified after further sintering. The uniformity of the pore size of the tungsten-scandium rod after pressing directly determines the pore uniformity of the porous tungsten-scandium rod after high-temperature sintering. Using isostatic pressing, controlling the pressing time and pressure, and further adjusting the subsequent sintering temperature and time, the pore size of the porous tungsten-scandium rod is controlled at 22~25%. The porous tungsten-scandium rod within this pore size range can optimize the impregnation amount of the cathode substrate when the active salt is subsequently impregnated, thereby improving the emission performance of the final tungsten-scandium-based impregnated cathode.

[0032] According to an embodiment of the present invention, post-processing the porous tungsten-scandium rod includes: impregnating the porous tungsten-scandium rod with active salt to obtain a cathode substrate, wherein the active salt includes barium oxide, calcium oxide and aluminum oxide, and the molar ratio of barium oxide, calcium oxide and aluminum oxide is 4:1:1; the impregnation temperature is 1700-1750°C, for example, it can be 1700°C, 1710°C, 1720°C, 1730°C, 1740°C, 1750°C, and the impregnation time is 2-3min, for example, it can be 2min, 2.5min, 3min; welding the cathode substrate to the cathode support tube to obtain a tungsten-scandium-based impregnated cathode, wherein the welding is low-temperature brazing, the welding solder is tungsten-cobalt powder, and the welding temperature is 1400-1500°C, for example, it can be 1400°C, 1425°C, 1450°C, 1475°C, 1500°C. Before welding, the shape of the cathode substrate can be processed as needed to meet the actual application. For example, the cathode substrate can be processed into a cathode cake by a precision lathe, and the surface finish of the cathode cake is relatively high. The working temperature of the tungsten-scandium-based impregnated cathode is 900~1150℃, so the melting point of the solder and the welding temperature need to be higher than this value. Therefore, the welding temperature is 1400~1500℃, and the solder is tungsten-cobalt (W-Co) powder. The cathode support tube is generally made of molybdenum metal, which has a melting point of about 2600℃. The main component of the cathode substrate is tungsten, which has a melting point of about 3400℃. The melting point of the tungsten-cobalt solder used is much lower than the melting point of the parent material, and higher than the maximum working temperature of the cathode (1150℃). At this time, the welding of the cathode substrate and the cathode support tube will neither affect the precipitation of the impregnated active salt in the cathode substrate, nor affect the emission performance of the tungsten-scandium-based impregnated cathode due to the immersion of the solder into the cathode support tube.

[0033] In an embodiment of the present invention, ammonium metatungstate and scandium nitrate are dissolved in water to obtain a mixed solution. The mixed solution is rapidly frozen using liquid nitrogen to obtain a frozen solid, and then a low-temperature low-vacuum environment is maintained for a period of time to obtain a dry precursor powder. The precursor powder is then thermally decomposed and thermally reduced, and then ground and sieved to obtain a scandium oxide-doped tungsten powder with a uniform mixture and a narrow particle size distribution. A tungsten-scandium rod is obtained by isostatic pressing, and a porous tungsten-scandium rod with controllable porosity is obtained by sintering. Finally, a tungsten-scandium-based impregnated cathode is obtained by impregnating active salts, machining cathode cakes using a precision lathe, and brazing the cathode cakes with a cathode support tube. The present invention optimizes the preparation process of scandium oxide doped tungsten powder by freeze drying, thermal decomposition, thermal reduction, grinding and screening, obtains precursor powder with uniform element and particle size distribution, and obtains porous tungsten scandium rod with controllable pore size through isostatic pressing and sintering, thereby further improving the emission performance of the tungsten scandium-based impregnated cathode obtained after salt impregnation, precision machining and brazing, which is beneficial to the practical application of the tungsten scandium-based impregnated cathode.

[0034] As a second aspect of the present invention, a tungsten-scandium-based impregnated cathode is provided, which is prepared by the above method.

[0035] According to an embodiment of the present invention, the present invention uses freeze-drying technology to provide a precursor powder with uniform element and particle size distribution, so that the further obtained tungsten-scandium-based impregnation cathode has better emission performance, further promoting the practical application of tungsten-scandium-based impregnation cathode.

[0036] As a third aspect of the present invention, there is provided an application of the above-mentioned tungsten-scandium-based impregnated cathode, including use in preparing any one of vacuum electronic devices, particle accelerators, medical accelerators, high-performance electron microscopes, and vacuum coating equipment.

[0037] The present invention is further described below by examples and related test experiments. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is obvious that one or more embodiments may also be implemented without these specific details. And, in the absence of conflict, the details in the following embodiments may be combined into other feasible embodiments at will. All instruments, consumables and reagents in the following examples, if not otherwise specified, may be obtained from commercial sources.

[0038] Example 1

[0039] In this Example 1, a tungsten-scandium-based impregnated cathode is prepared, wherein the content of tungsten is 99wt% and the content of scandium oxide is 1wt%. The preparation method is as follows.

[0040] 1. Start the freeze dryer and pre-cool for 2 hours to make the cold trap temperature reach -80℃.

[0041] 2. Take a 500ml beaker, clean it with anhydrous ethanol and deionized water in turn, and dry it. Take 39.8g of ammonium metatungstate and 1.08g of scandium nitrate (analytical grade), completely dissolve them in 150mL of deionized water, and use a magnetic stirrer to stir thoroughly until the solution is transparent and free of precipitation to obtain a mixed solution.

[0042] 3. Take a 2000ml stainless steel cup, clean it with alcohol and deionized water, dry it, and add about 1000ml of liquid nitrogen. Drop the mixed solution into liquid nitrogen to quickly freeze it into a solid, then put it into the cold trap in the freeze dryer, turn on the machine pump, and the vacuum degree quickly drops to less than 3Pa. The freeze drying process is maintained for 72h, keeping the cold trap temperature <-50℃ and the vacuum degree <20Pa. In this process, the solvent (deionized water) fully sublimates to obtain a dry precursor powder.

[0043] 4. Place the precursor powder in a muffle furnace and keep it at 550°C for 2 hours to make NO 3- Ion, NH 4+ The ions decompose to generate nitrogen oxides which are discharged, and a mixed powder of tungsten oxide and scandium oxide is obtained.

[0044] 5. Place the mixed powder of tungsten oxide and scandium oxide in a hydrogen furnace, keep it at 550°C for 1 hour, then increase the temperature to 950°C and keep it for 1.5 hours to obtain scandium oxide-doped tungsten powder, in which the tungsten content is 99wt% and the scandium oxide content is 1wt%.

[0045] 6. Grind the scandium oxide doped tungsten powder in an agate mortar and sieve it to obtain the scandium oxide doped tungsten powder with a particle size between 200 mesh and 325 mesh.

[0046] 7. The scandium oxide doped tungsten powder is isostatically pressed at a pressure of 100 MPa for 5 minutes to obtain a tungsten scandium rod. The tungsten scandium rod is sintered in a hydrogen furnace and kept at 1650°C for 30 minutes to obtain a porous tungsten scandium rod with a porosity of 22-25%.

[0047] 8. Place the porous tungsten-scandium rod in a molybdenum boat and immerse it in 411 salt (i.e., active salt with a molar ratio of barium oxide, calcium oxide, and aluminum oxide of 4:1:1) at 1700°C for 3 minutes. After cooling to room temperature, obtain a cathode substrate.

[0048] 9. The cathode substrate is precisely machined by a CNC lathe to obtain a cathode cake with a diameter of 2.5 mm and a smooth surface.

[0049] 10. The cathode cake and the cathode molybdenum support tube are welded by low temperature brazing at a temperature of 1450°C and the solder is tungsten-cobalt powder to obtain Figure 2 Tungsten-scandium based impregnated cathode shown.

[0050] 11. Load the tungsten-scandium-based impregnated cathode into the test bench, degas, activate and age it, and then test the DC and pulse voltammetric characteristics of the tungsten-scandium-based impregnated cathode.

[0051] Example 2

[0052] In this Example 2, a tungsten-scandium-based impregnated cathode is prepared, in which the tungsten content is 97wt% and the scandium oxide content is 3wt%. The preparation method is the same as that of Example 1. The difference from Example 1 is that the mass of ammonium metatungstate is 39g, and the mass of scandium nitrate is 3.25g.

[0053] Example 3

[0054] In this Example 3, a tungsten-scandium-based impregnated cathode is prepared, in which the tungsten content is 95wt% and the scandium oxide content is 5wt%. The preparation method is the same as that of Example 1. The difference from Example 1 is that the mass of ammonium metatungstate is 38.19g, and the mass of scandium nitrate is 5.42g.

[0055] Furthermore, the tungsten-scandium-based impregnated cathodes prepared in Examples 1-3 were tested and characterized.

[0056] Figure 3 This is a scanning electron microscope image of scandium oxide doped tungsten powder in Example 1 of the present invention.

[0057] like Figure 3 As shown, it can be seen that submicron scandium oxide-doped tungsten powder with uniform distribution and uniform particle size was prepared.

[0058] Figure 4 The DC volt-ampere characteristic curve of the tungsten-scandium-based impregnated cathode in Example 1 of the present invention; Figure 5 The pulse voltammetric characteristic curve of the tungsten-scandium-based impregnated cathode in Example 1 of the present invention; Figure 6 The DC volt-ampere characteristic curve of the tungsten-scandium-based impregnated cathode in Example 2 of the present invention; Figure 7 The pulse voltammetric characteristic curve of the tungsten-scandium-based impregnated cathode in Example 2 of the present invention; Figure 8 is a DC volt-ampere characteristic curve of the tungsten-scandium-based impregnated cathode in Example 3 of the present invention; Fig. 9 This is a pulse voltammetric characteristic curve of the tungsten-scandium-based impregnated cathode in Example 3 of the present invention, wherein the pulse width is 100 μs and the frequency is 100 Hz.

[0059] like Figure 4 As shown in Figure 2, when the cathode operating temperature is 950℃, 1000℃, 1050℃, and 1100℃, the inflection point current density is 2.51A / cm 2 、3.45A / cm 2 , 4.53A / cm 2 、6.74A / cm 2 .like Figure 5 As shown, when the cathode operating temperature is 950℃, 1000℃, 1050℃, and 1100℃, the inflection point current density is 8.01A / cm 2 、15.06A / cm 2 , 25.27A / cm 2 、34.57A / cm 2 .like Figure 6 As shown, when the cathode operating temperature is 950℃, 1000℃, 1050℃, and 1100℃, the inflection point current density is 1.49A / cm 2 , 2.10A / cm 2 , 2.96A / cm 2 、3.96A / cm 2 .like Figure 7 As shown in Figure 2, when the cathode operating temperature is 950℃, 1000℃, 1050℃, and 1100℃, the inflection point current density is 8.80A / cm 2 , 15.27A / cm 2 , 23.37A / cm 2 、33.49A / cm2 .like Figure 8 As shown in Figure 2, when the cathode operating temperature is 950℃, 1000℃, 1050℃, and 1100℃, the inflection point current density is 0.73A / cm 2 , 1.14A / cm 2 , 2.04A / cm 2 、3.18A / cm 2 .like Fig. 9 As shown in Figure 2, when the cathode operating temperature is 950℃, 1000℃, 1050℃, and 1100℃, the inflection point current density is 5.73A / cm 2 , 9.45A / cm 2 、14.25A / cm 2 、19.80A / cm 2 . The inflection point, also known as the saturation point, means that as the voltage increases, the rate of increase of the current gradually slows down or stops increasing. The magnitude of the current density directly reflects the electron emission ability of the tungsten-scandium-based impregnated cathode at a specific voltage. As the operating temperature increases, the electron emission ability of the tungsten-scandium-based impregnated cathode will increase, resulting in an increase in current density. In the space charge limited region, the cathode emission current density satisfies the cube-two law. Therefore, the inflection point current density of the transition from the space charge limited region to the temperature limited region in the double logarithmic volt-ampere characteristic curve is usually used as the evaluation standard for the cathode performance. From Figure 4-Figure 9 By comparison, it can be seen that according to the test results of tungsten-scandium-based impregnated cathodes with scandium oxide contents of 1wt%, 3wt% and 5wt% respectively, the emission current density is the largest when the scandium oxide content is 1wt%, indicating that when the doped scandium content is too high, substances that are not conducive to cathode emission will be generated.

[0060] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a tungsten-scandium-based impregnated cathode, comprising: Adding ammonium metatungstate and scandium nitrate into water to obtain a mixed solution; freeze-drying the mixed solution to obtain a uniformly mixed precursor powder; Heat treating the precursor powder to obtain a porous tungsten-scandium rod; Post-processing the porous tungsten-scandium rod to obtain a tungsten-scandium-based impregnated cathode; Wherein, the concentration of ammonium metatungstate in the mixed solution is 0.1-0.4 g / mL; The ratio of ammonium metatungstate and scandium nitrate in the mixed solution is such that the content of tungsten in the porous tungsten-scandium rod is 95-99wt%, and the content of scandium oxide is 1-5wt%; The freeze-drying temperature is less than -50°C, the freeze-drying vacuum is less than 20Pa, and the freeze-drying time is 48 to 72 hours.

2. The method according to claim 1, wherein: The freeze drying temperature is -80~-50°C, and the freeze drying vacuum degree is 3~20Pa.

3. The method according to claim 1 or 2, wherein: The step of heat treating the precursor powder comprises: Decomposing and reducing the precursor powder, grinding and screening to obtain scandium oxide-doped tungsten powder; The scandium oxide doped tungsten powder is pressed and sintered to obtain a porous tungsten-scandium rod.

4. The method according to claim 3, wherein: The particle size of the scandium oxide doped tungsten powder is 200-325 mesh.

5. The method according to claim 3, wherein: Decomposing and reducing the precursor powder includes: Decomposing the precursor powder under air conditions at a decomposition temperature of 500-600° C. for 2-3 hours to obtain a mixed powder of tungsten oxide and scandium oxide; The mixed powder is reduced in a hydrogen atmosphere, and the reduction is divided into two stages. The first stage reduction temperature is 500-600° C., the first stage reduction time is 0.5-1.5 h, and the second stage reduction temperature is 900-1000° C., the second stage reduction time is 1-2 h, to obtain scandium oxide doped tungsten powder.

6. The method according to claim 3, wherein: The pressing is isostatic pressing, the pressing pressure is 100-150 MPa, and the pressing time is 5-10 min; The sintering temperature is 1600-1800°C, and the sintering time is 20-30 minutes; The porous tungsten-scandium rod has a porosity of 22-25%.

7. The method according to claim 1, wherein: Post-processing the porous tungsten-scandium rod includes: Impregnating the porous tungsten-scandium rod with active salt to obtain a cathode substrate; The cathode substrate is welded to the cathode support tube to obtain a tungsten-scandium-based impregnated cathode.

8. The method according to claim 7, wherein: The active salt comprises barium oxide, calcium oxide and aluminum oxide, and the molar ratio of the barium oxide, calcium oxide and aluminum oxide is 4:1:1; The immersion temperature is 1700-1750°C, and the immersion time is 2-3 minutes; The welding is low temperature brazing, the welding solder is tungsten cobalt powder, and the welding temperature is 1400-1500°C.

9. A tungsten-scandium-based impregnated cathode prepared by the method according to any one of claims 1 to 8.

10. A use of the tungsten-scandium-based impregnated cathode as claimed in claim 9, wherein: The applications include use in preparing any one of vacuum electronic devices, particle accelerators, medical accelerators, high-performance electron microscopes, and vacuum coating equipment.

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