Method for preparing chromic oxide solid solution coating by adopting physical vapor deposition process

Abstract

The invention discloses a method for preparing a chromium oxide solid solution coating by adopting a physical vapor deposition process, which comprises the following steps of: firstly, mixing chromium nitrate nonahydrate serving as a chromium source and a polyether compound serving as a dispersing solvent by utilizing a coprecipitation method, and adding a stabilizer to prepare a chromium ion solution with a preset concentration; then dropwise adding a precipitator into a chromium ion solution with a preset concentration, uniformly stirring to obtain a Cr (OH) 3 suspension, naturally precipitating at room temperature, then centrifuging, washing, drying, sieving and carrying out heat treatment to obtain nano chromium oxide powder, and finally building a physical vapor deposition device to obtain the chromium oxide nano material. And depositing on the surface of the alumina ceramic under a high-temperature pressureless sintering condition to obtain the chromium oxide solid solution coating. The preparation process is simple and easy to operate, the repeatability is high, the chromic oxide solid solution coating is uniform, the solid solution degree is controllable, and the prepared coating is uniform in morphology, low in secondary electron emission coefficient and capable of being used in the fields of electric vacuum devices, high-voltage-resistant insulating materials and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-vacuum device materials, and particularly to a method for preparing a chromium oxide solid solution coating by a physical vapor deposition process. Background Art

[0002] In high-power microwave tubes, traveling wave tubes and other electro-vacuum devices operating in a vacuum environment, solid insulating materials are widely used. However, in a vacuum environment, solid insulating materials are prone to surface flashover breakdown under the action of a vacuum high-voltage electric field, that is, surface flashover breakdown, which seriously affects the safety, reliability and service life of the operation of electro-vacuum devices, and restricts the improvement of the performance of electro-vacuum devices. With the rapid development of electro-vacuum devices, the surface withstand voltage strength (vacuum withstand performance) of insulating materials has increasingly become a key factor affecting their stability and safety.

[0003] In the past few decades, researchers have proposed various models to explain the surface flashover breakdown phenomenon of solid insulating materials, among which the secondary electron emission avalanche (SEEA) model has been widely recognized in the academic community. The SEEA theory believes that the flashover process can be summarized into three stages: the emission of initial electrons, the secondary electron multiplication of electrons, and the electron-induced desorption gas discharge. Among them, the secondary electron multiplication of electrons is the key stage for the development of surface flashover. Therefore, a low secondary electron emission coefficient (SEEY) is the key factor for suppressing surface flashover of solid insulating materials in a vacuum. Among all types of solid insulating materials, Al 2 O 3 ceramics have been widely used in electro-vacuum devices due to their excellent insulation, mechanical properties and thermal stability. However, the surface secondary electron emission coefficient of alumina ceramics is relatively high (about 6.5), resulting in limited vacuum withstand performance and difficult to meet the increasing performance requirements of modern electro-vacuum devices. While Cr 2 O 3 has a low secondary electron emission coefficient, and the secondary electron emission coefficient is only 0.95. Moreover, alumina and chromium oxide have the same lattice type and can form a continuous solid solution, which is an ideal coating material for improving the surface withstand voltage strength of Al 2 O 3 ceramics. However, current research is less and the preparation process is complex, and the coating thickness, structure and performance are not easy to control. Therefore, those skilled in the art urgently need a method for preparing a chromium oxide solid solution coating by a physical vapor deposition process to realize the preparation of a chromium oxide solid solution coating with a low secondary electron emission coefficient on the surface of alumina ceramics to meet the requirement of improving the vacuum withstand performance of alumina ceramics, which provides great reference significance for improving alumina ceramics in the field of electro-vacuum devices. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a chromium oxide solid solution coating by physical vapor deposition process, which has a simple process and high repeatability, and realizes the preparation of a chromium oxide solid solution coating with a low secondary electron emission coefficient on the surface of alumina ceramics to meet the requirement of improving the vacuum withstand voltage performance of alumina ceramics, providing great reference significance for improving alumina ceramics in the field of electro-vacuum devices.

[0005] The present invention provides a method for preparing a chromium oxide solid solution coating by physical vapor deposition process, comprising the following steps: S1. By using the co-precipitation method, with chromium nitrate nonahydrate as the chromium source and polyether compounds as the dispersion solvent, after mixing, a stabilizer is added to prepare a chromium ion solution with a preset concentration, and then a precipitating agent is dropped into the chromium ion solution and stirred evenly to obtain a Cr(OH) 3 suspension; S2. The Cr(OH) 3 suspension obtained in step S1 is allowed to settle naturally at room temperature to separate the precipitate from the supernatant. The precipitate is centrifugally washed with anhydrous ethanol for multiple times to obtain a pure chromium oxide precursor, then dried, ground and sieved to obtain a nano-sized chromium oxide precursor powder with uniform particle size, and finally calcined in a muffle furnace to obtain a uniform nano-sized chromium oxide powder; S3. The nano-sized chromium oxide powder obtained in step S2 and the alumina ceramic substrate are used to build a physical vapor deposition device, and a chromium oxide solid solution coating is deposited on the surface of the alumina ceramic substrate by physical vapor deposition process.

[0006] Preferably, in step S1, the dispersion solvent is polyethylene glycol solution, polypropylene glycol or polybutylene glycol; the stabilizer is a dilute ammonia water solution with a pH value of 8, and the concentration of the dilute ammonia water solution is 0.5%; the concentration of the chromium ion solution is 0.15 mol / L; the precipitating agent is a 20% ammonia water diluent.

[0007] Preferably, the dosage of the precipitating agent is 80 - 100 ml, and the dropping rate of the precipitating agent is < 10 ml / min.

[0008] Preferably, in step S1, the stirring speed is 300 - 500 r / min.

[0009] Preferably, in step S2, the natural precipitation time is more than 3 h, and the precipitate is centrifugally washed with anhydrous ethanol three times to obtain a pure chromium oxide precursor.

[0010] Preferably, in step S2, the centrifugal washing rotation speed is 4000 r / min and the centrifugal time is 5 min.

[0011] Preferably, in step S2, the drying temperature of the chromium oxide precursor is 100 °C, the drying time is 12 h, and the mesh number of the sieve is 200 mesh.

[0012] Preferably, in the step S2, the maximum calcination temperature of the nano-chromium oxide precursor powder is 800 °C, and the heat preservation time is 1 h.

[0013] Preferably, in the step S3, the physical vapor deposition device built is made of a high-temperature resistant material that is high-temperature resistant, stable and does not react with chromium oxide, and the high-temperature resistant material is a silicate refractory material.

[0014] Preferably, in the step S3, after the physical vapor deposition device is built, it is placed in a muffle furnace and deposited with a coating in an air atmosphere at a temperature of 1300 °C - 1500 °C for a heat preservation time of 1 - 3 h, so that a chromium oxide solid solution coating is deposited on the surface of the alumina ceramic matrix.

[0015] The method for preparing a chromium oxide solid solution coating by a physical vapor deposition process provided by the present invention has the following advantages: 1. The present invention first prepares a nano-chromium oxide precursor by a coprecipitation method, then calcines it in an air atmosphere to obtain nano-chromium oxide powder with uniform particles and good dispersibility. Then, a simple physical vapor deposition device is built using the prepared nano-powder. Finally, while being calcined at a high temperature in a muffle furnace, the nano-powder obtains a large amount of heat energy, overcomes the intermolecular force, forms gaseous molecules that diffuse in the device and finally deposit on the surface of the alumina ceramic to form a chromium oxide solid solution coating; not only is the operation step simple and easy to implement, with high repeatability, but also the raw materials for the whole preparation process are easily available and the cost is relatively low, with strong universality; 2. Compared with the traditional method for preparing nano-chromium oxide powder, the nano-scale chromium oxide powder prepared by the coprecipitation method selected in the present invention, through raw material formulation and process improvement, ensures good dispersibility of the nano-chromium oxide powder and reduces the possibility of sintering of the chromium oxide powder at high temperature during the deposition coating process; 3. In the present invention, a simple physical vapor deposition device system is constructed. Compared with the traditional physical vapor deposition, on the basis of maintaining the advantages of uniform deposited coating and strong bonding force, it has an innovative design with low cost, easy operation and good process compatibility; 4. The present invention provides a chromium oxide solid solution coating suitable for deposition on ceramic matrices such as alumina that can be solid-solved with chromium oxide at high temperature, and can be applied to the preparation of chromium oxide vacuum pressure-resistant coatings with different thicknesses and different chromium oxide solid solution degrees and low secondary electron emission coefficients; 5. The chromium oxide solid solution coating obtained by the simple physical vapor deposition method in the present invention, compared with the traditional physical vapor deposition, has a stronger bonding between the coating and the matrix, and while greatly reducing the secondary electron emission coefficient, does not change the excellent mechanical properties of the alumina ceramic; 6. The preparation process of the present invention is simple and easy to operate, has high repeatability, the chromium oxide solid solution coating is uniform, and the solid solution degree of chromium oxide is controllable. The prepared coating has a uniform morphology and a low secondary electron emission coefficient, and can be used in fields such as vacuum high-voltage insulation materials to meet the growing performance requirements of modern vacuum electronic devices. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the physical vapor deposition device in the present invention; Figure 2 It is an optical photograph of the prepared nano-chromium oxide powder in the present invention; Figure 3 It is a morphology analysis diagram of the prepared nano-chromium oxide powder in the present invention; Figure 4 It is a physical diagram of the samples prepared in Examples 1, 2, 3, and 4; Figure 5 It is a physical diagram of the samples prepared in Examples 4, 5, and 6; Figure 6 It is a morphology analysis diagram of the chromium oxide solid solution coating prepared in Example 1; Figure 7 It is a morphology analysis diagram of the chromium oxide solid solution coating prepared in Example 2; Figure 8 It is a morphology analysis diagram of the chromium oxide solid solution coating prepared in Example 3; Figure 9 It is a morphology analysis diagram of the chromium oxide solid solution coating prepared in Example 4; Figure 10 It is a morphology analysis diagram of the chromium oxide solid solution coating prepared in Example 5; Figure 11 It is a morphology analysis diagram of the chromium oxide solid solution coating prepared in Example 6; Figure 12 It is an element content analysis diagram of the chromium oxide solid solution coating prepared in Example 1; Figure 13 It is an element content analysis diagram of the chromium oxide solid solution coating prepared in Example 2; Figure 14 It is an element content analysis diagram of the chromium oxide solid solution coating prepared in Example 3; Figure 15 It is an element content analysis diagram of the chromium oxide solid solution coating prepared in Example 4; Figure 16 It is an element content analysis diagram of the chromium oxide solid solution coating prepared in Example 5; Figure 17 It is an element content analysis diagram of the chromium oxide solid solution coating prepared in Example 6; Figure 18It is the phase analysis diagram of the chromium oxide solid solution coatings prepared in Examples 1, 2, 3, 4, 5, and 6; Figure 19 It is the phase diffraction peak shift diagram of the chromium oxide solid solution coatings prepared in Examples 4, 5, and 6; Figure 20 It is the secondary electron emission coefficient analysis diagram of the chromium oxide solid solution coatings prepared in Examples 1, 2, 3, 4, 5, and 6. Detailed implementation manners

[0017] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further introduced in detail below in conjunction with the accompanying drawings.

[0018] The present invention provides a method and application for preparing a chromium oxide solid solution coating by a physical vapor deposition process, including the following steps: S1. Using the coprecipitation method, chromium nitrate nonahydrate as the chromium source, polyether compounds as the dispersion solvent, adding a stabilizer after mixing to prepare a chromium ion solution with a preset concentration, and then dropping the precipitant into the chromium ion solution and stirring evenly, with the stirring speed being 300 - 500 r / min, to obtain a Cr(OH) 3 suspension.

[0019] Among them, the dispersion solvent is polyethylene glycol solution, polypropylene glycol or polybutylene glycol; the stabilizer is a dilute ammonia water solution with a pH value of 8, and the concentration of the dilute ammonia water solution is 0.5%; the concentration of the chromium ion solution is 0.15 mol / L; the precipitant is a 20% ammonia water diluent, the dosage of the precipitant is 80 - 100 ml, and the dropping speed of the precipitant < 10 ml / min.

[0020] Among them, the polyether compound is polyethylene glycol, and it can also be polypropylene glycol or polybutylene glycol. The ethylene glycol molecule binds to the surface of the suspension particles through its hydrophilic ether bond and hydroxyl group to form a stable protective film. This protective layer can prevent direct contact and aggregation between particles, thus stabilizing the suspension.

[0021] S2. Naturally settling the Cr(OH) 3 suspension obtained in step S1 at room temperature to separate the precipitate from the supernatant, centrifugally washing the precipitate with absolute ethanol for multiple times to obtain a pure chromium oxide precursor, then drying, grinding and sieving to obtain a nano chromium oxide precursor powder with uniform particle size, and finally calcining in a muffle furnace to obtain a uniform nano chromium oxide powder.

[0022] Among them, in this step, the natural sedimentation time is more than 3 h, the centrifugal washing speed is 4000 r / min, and the centrifugal time is 5 min. The drying temperature of the precursor is 100 °C, the drying time is 12 h, and the mesh number of the sieve is 200 mesh. The highest calcination temperature of the nano-chromium oxide precursor powder is 600 °C, and the heat preservation time is 1 h.

[0023] S3. Build a physical vapor deposition device with the nano-chromium oxide powder and the alumina ceramic substrate described in step S2, and use the physical vapor deposition process to deposit a chromium oxide solid solution coating on the surface of the alumina ceramic substrate.

[0024] Among them, the base of the built physical vapor deposition device is a high-temperature resistant material that is high-temperature stable and does not react with chromium oxide, and the high-temperature resistant material is a silicate refractory material. After building the physical vapor deposition device, place it in a muffle furnace and deposit the coating at a temperature of 1300 °C - 1500 °C in an air atmosphere, and the heat preservation time is 1 - 3 h, so that a chromium oxide solid solution coating is deposited on the surface of the alumina ceramic substrate.

[0025] The present invention prepares nano-chromium oxide by the co-precipitation method. Compared with the traditional preparation method of nano-chromium oxide powder, the present invention uses polyethylene glycol as a dispersant and dilute ammonia water as a precipitant, and controls the nano-chromium oxide powder through the process of grinding and sieving, so that the nano-powder has better dispersibility and more uniform particle size.

[0026] The present invention prepares a chromium oxide solid solution coating on the surface of alumina ceramics by a simple physical vapor deposition method. A large amount of heat energy is obtained by heating the nano-powder at high temperature, overcoming the intermolecular force, forming gaseous molecules that diffuse in the device and finally deposit on the alumina ceramics to form a chromium oxide solid solution coating. It not only has simple and easy operation steps, high repeatability, easily available raw materials and relatively low cost throughout the preparation process, but also has strong universality.

[0027] Compared with the traditional physical vapor deposition, the chromium oxide solid solution coating obtained by the simple physical vapor deposition method of the present invention has a stronger bonding force between the coating and the substrate, greatly reduces the secondary electron emission coefficient, and does not change the excellent mechanical properties of chromium oxide.

[0028] Example 1 This example provides a method for preparing a chromium oxide solid solution coating by a physical vapor deposition process, including the following steps: Step S1: Add 0.05 mol of chromium nitrate nonahydrate to a transparent sealed container, and configure it into a chromium nitrate solution with 125 ml of deionized water. Then add 100 ml of 7.5% polyethylene glycol solution to it. After stirring and mixing, add 100 ml of dilute ammonia water solution with a pH of 8 to configure a chromium ion solution with a concentration of 0.15 mol / L. Then, add 80 ml of 20% ammonia water diluent dropwise to the chromium ion solution and stir magnetically at a speed of 300 r / min until it is uniform to obtain Cr(OH) 3 suspension; Step S2: Let the uniform Cr(OH) 3 suspension in Step S1 be naturally settled at room temperature for 3 h to separate the precipitate from the supernatant. Wash the precipitate three times by centrifugation with absolute ethanol to obtain a pure chromium oxide precursor, and place it in an environment of 100 °C for drying for 12 h. Then, grind the dried chromium oxide precursor and pass it through a 200-mesh sieve to obtain a nano-sized chromium oxide precursor powder with uniform particle size. Finally, calcine it in a muffle furnace at 600 °C for 1 h to obtain a nano-sized chromium oxide powder with uniform particles; Step S3: Build the nano-sized chromium oxide powder and the alumina ceramic substrate described in Step S2 into a preset physical vapor deposition device, and perform physical vapor deposition at a preset calcination temperature of 1300 °C for 1 h to deposit a chromium oxide solid solution coating on the surface of the alumina substrate.

[0029] As Figure 1 、 2 、shown in Figure 3, Figure 1 is the physical vapor deposition device used in each example, Figure 2 is the nano-sized chromium oxide powder raw material prepared by the coprecipitation method, Figure 3 is the morphology analysis diagram of the nano-sized chromium oxide powder. The particle size of the nano-sized chromium oxide powder is uniformly distributed between 60 - 80 nm.

[0030] Figure 4 The leftmost one is the optical photo of the chromium oxide solid solution coating prepared at 1350 °C in Example 1. It can be seen from the figure that due to the lower temperature, the deposition of the chromium oxide solid solution coating is incomplete and the coating color is lighter; Figure 6 is the scanning electron microscope picture of the chromium oxide solid solution coating in Example 1. It can be seen from the figure that there is no obvious coating structure on the sample surface and the surface of the alumina grains is relatively smooth. The reason is that only a small amount of chromium oxide is dissolved into the alumina substrate; Figure 12 is the EDS element content distribution diagram of the chromium oxide solid solution coating in Example 1. It can be seen from the figure that the solid solution content of chromium oxide on the sample surface is about 3.2 wt%.

[0031] Figure 18 The X-ray diffraction pattern of the chromium oxide solid solution coating prepared at 1350 °C in Example 1 in2 O 3 is consistent with the (JCPDS PDF#89-7710) phase; Figure 19 In Example 1, the secondary electron emission coefficient curve of the chromium oxide solid solution coating prepared at 1350 °C is shown. Its δmax is 2.74, which is 22% lower than that of the alumina substrate.

[0032] Example 2 This example provides a method for preparing a chromium oxide solid solution coating by physical vapor deposition, which includes the following steps: Step S1: Add 0.05 mol of chromium nitrate nonahydrate and 125 ml of deionized water into a transparent sealed container to prepare a chromium nitrate solution. Then add 100 ml of 7.5% polyethylene glycol solution, stir and mix, and then add 100 ml of dilute ammonia water solution with a pH of 8 to obtain a chromium ion solution with a concentration of 0.15 mol / L. After that, add 80 ml of 20% ammonia water diluent dropwise to the chromium ion solution and stir magnetically at a speed of 300 r / min until it is uniform to obtain Cr(OH) 3 suspension; Step S2: Let the uniform Cr(OH) 3 suspension obtained in Step S1 be naturally settled at room temperature for 3 h to separate the precipitate from the supernatant. Wash the precipitate three times by centrifugation with absolute ethanol to obtain a pure chromium oxide precursor, and place it in an environment of 100 °C for 12 h of drying. Then grind the dried chromium oxide precursor and pass it through a 200-mesh sieve to obtain a nano-sized chromium oxide precursor powder with uniform particle size. Finally, calcine it in a muffle furnace at 600 °C for 1 h to obtain a nano-sized chromium oxide powder with uniform particles; Step S3: Build the nano-sized chromium oxide powder and the alumina ceramic substrate into a preset physical vapor deposition device, and use a preset calcination temperature of 1400 °C and keep it warm for 1 h for physical vapor deposition, so that a chromium oxide solid solution coating is deposited on the surface of the alumina substrate.

[0033] Figure 4 The second from the left is the optical photograph of the chromium oxide solid solution coating prepared at 1400 °C in Example 2. It can be seen from the figure that due to the lower temperature, the chromium oxide solid solution coating is darker in color than the coating in Example 1; Figure 7 This is the scanning electron microscope picture of the chromium oxide solid solution coating in Example 2. It can be seen from the figure that there is no obvious coating structure on the surface of the sample, and there are some protrusions on the surface. The reason may be due to the insufficient solid solution of chromium oxide in the alumina substrate; Figure 13 This is the EDS element content distribution map of the chromium oxide solid solution coating in Example 2. It can be seen from the figure that the solid solution content of chromium oxide on the surface of the sample is about 7.8 wt%.

[0034] Figure 18Example 2 shows the X-ray diffraction pattern of the chromium oxide solid solution coating prepared at 1400 °C. Since chromium oxide forms a solid solution with alumina at high temperatures, its phase is consistent with the Al 2 O 3 phase (JCPDS PDF#89-7710); Figure 19 Example 2 shows the secondary electron emission coefficient curve of the chromium oxide solid solution coating prepared at 1350 °C. Its δmax is 2.65, which is 24% lower than that of the alumina substrate.

[0035] Example 3 This example provides a method and application for preparing a chromium oxide solid solution coating using a physical vapor deposition process, including the following steps: Step S1: Add 0.05 mol of chromium nitrate nonahydrate and 125 ml of deionized water to a transparent sealed container to prepare a chromium nitrate solution. Then add 100 ml of 7.5% polyethylene glycol solution to it, stir and mix, and then add 100 ml of a dilute ammonia water solution with a pH of 8 to obtain a chromium ion solution with a concentration of 0.15 mol / L. After that, add 80 ml of 20% ammonia water diluent dropwise to the chromium ion solution and stir magnetically at a speed of 300 r / min until it is uniform to obtain a Cr(OH) 3 suspension; Step S2: Let the uniform Cr(OH) 3 suspension in Step S1 settle naturally at room temperature for 3 h to separate the precipitate from the supernatant. Wash the precipitate three times with anhydrous ethanol by centrifugation to obtain a pure chromium oxide precursor, and place it in an environment of 100 °C and dry for 12 h. Then grind the dried chromium oxide precursor and pass it through a 200-mesh sieve to obtain a nano-sized chromium oxide precursor powder with uniform particle size. Finally, calcine it in a muffle furnace at 600 °C for 1 h to obtain a nano-sized chromium oxide powder with uniform particles; Step S3: Build the nano-sized chromium oxide powder and the alumina ceramic substrate in a preset physical vapor deposition device, and use a preset calcination temperature of 1450 °C and hold for 1 h for physical vapor deposition, so that a chromium oxide solid solution coating is deposited on the surface of the alumina substrate.

[0036] Figure 4 The second one on the right is the optical photo of the chromium oxide solid solution coating prepared at 1450 °C in Example 3. It can be seen from the figure that due to the higher temperature, the chromium oxide solid solution coating is darker in color than the coating in Example 2; Figure 8 This is the scanning electron microscope picture of the chromium oxide solid solution coating in Example 3. It can be seen from the figure that there is no obvious coating structure on the sample surface, and a layered structure appears on the surface of the alumina grains. The reason may be that chromium oxide is completely dissolved in the alumina substrate, causing distortion of the alumina grains; Figure 14EDS elemental content distribution map of the chromium oxide solid solution coating in Example 3. It can be seen from the figure that the chromium oxide solid solution content on the sample surface is about 9.5 wt%.

[0037] Figure 18 In Example 3, it is the X-ray diffraction pattern of the chromium oxide solid solution coating prepared at 1450 °C. Since chromium oxide forms a solid solution with alumina at high temperature, its phase is consistent with the Al 2 O 3 (JCPDS PDF#89-7710); Figure 19 In Example 3, it is the secondary electron emission coefficient curve of the chromium oxide solid solution coating prepared at 1450 °C. Its δmax is 2.58, which is 26% lower than that of the alumina matrix.

[0038] Example 4 This example provides a method and application for preparing a chromium oxide solid solution coating by physical vapor deposition process, including the following steps: Step S1: Add 0.05 mol of chromium nitrate nonahydrate and 125 ml of deionized water to a transparent closed container to prepare a chromium nitrate solution. Then add 100 ml of 7.5% polyethylene glycol solution to it, stir and mix, and then add 100 ml of dilute ammonia water solution with PH = 8 to prepare a chromium ion solution with a concentration of 0.15 mol / L. After that, add 80 ml of 20% ammonia water diluent dropwise to the chromium ion solution and stir magnetically at a speed of 300 r / min until it is uniform to obtain Cr(OH) 3 suspension; Step S2: Let the uniform Cr(OH) 3 suspension in Step S1 settle naturally at room temperature for 3 h to separate the precipitate from the supernatant. Wash the precipitate three times by centrifugation with absolute ethanol to obtain a pure chromium oxide precursor, and put it in an oven at 100 °C for 12 h. Then grind the dried chromium oxide precursor and pass it through a 200-mesh sieve to obtain a uniformly sized nano chromium oxide precursor powder. Finally, calcine it in a muffle furnace at 600 °C for 1 h to obtain a uniformly sized nano chromium oxide powder; Step S3: Build the nano chromium oxide powder and the alumina ceramic matrix in a preset physical vapor deposition device, and use a preset calcination temperature of 1500 °C and hold for 1 h for physical vapor deposition, so that a chromium oxide solid solution coating is deposited on the surface of the alumina matrix.

[0039] Figure 4 The rightmost one is the optical photo of the chromium oxide solid solution coating prepared at 1500 °C in Example 4. It can be seen from the figure that due to the high temperature, the chromium oxide solid solution coating is darker in color than the coating in Example 3; Figure 9Figure for the scanning electron microscope image of the chromium oxide solid solution coating in Example 4. It can be seen from the figure that there is no obvious coating structure on the sample surface, and the layered structure on the surface of the alumina grains is more obvious than that in Example 3. The reason may be that the complete solid solution of chromium oxide in the alumina matrix causes distortion of the alumina grains. Figure 15 Figure for the EDS element content distribution of the chromium oxide solid solution coating in Example 4. It can be seen from the figure that the solid solution content of chromium oxide on the sample surface is about 10.0 wt%.

[0040] Figure 18 In Example 4, the X-ray diffraction pattern of the chromium oxide solid solution coating prepared at 1500 °C. Since chromium oxide forms a solid solution with alumina at high temperature, its phase is consistent with the Al 2 O 3 (JCPDS PDF#89-7710) phase. Figure 19 In Example 4, the secondary electron emission coefficient curve of the chromium oxide solid solution coating prepared at 1500 °C. Its δmax is 2.55, which is 27% lower than that of the alumina matrix. Figure 19 In Example 4, the main X-ray diffraction pattern of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 1 h. Among them, the degree of deviation of the main diffraction peak of Example 4 to a smaller angle is smaller than that of Examples 5 and 6, which proves that the degree of solid solution of chromium oxide into alumina is shallower with the reduction of the calcination time.

[0041] Example 5 This example provides a method and application for preparing a chromium oxide solid solution coating by physical vapor deposition process, including the following steps: Step S1: Add 0.05 mol of chromium nitrate nonahydrate and 125 ml of deionized water to a transparent closed container to prepare a chromium nitrate solution. Then add 100 ml of 7.5% polyethylene glycol solution to it, stir and mix, and then add 100 ml of dilute ammonia water solution with a pH of 8 to prepare a chromium ion solution with a concentration of 0.15 mol / L. After that, add 80 ml of 20% ammonia water diluent dropwise to the chromium ion solution and stir magnetically at a speed of 300 r / min until it is uniform to obtain a Cr(OH) 3 suspension; Step S2: Let the uniform Cr(OH) 3 suspension in Step S1 be naturally settled at room temperature for 3 h to separate the precipitate from the supernatant. Wash the precipitate three times by centrifugation with absolute ethanol to obtain a pure chromium oxide precursor, and place it in an oven at 100 °C for 12 h. Then grind the dried chromium oxide precursor and pass it through a 200-mesh sieve to obtain a uniformly sized nano chromium oxide precursor powder. Finally, calcine it in a muffle furnace at 600 °C for 1 h to obtain a uniformly sized nano chromium oxide powder. Step S3: Build the nano-chromium oxide powder and alumina ceramic substrate described in Step S2 into a preset physical vapor deposition device, and use a preset calcination temperature of 1500 °C and hold for 2 h for physical vapor deposition, so that a chromium oxide solid solution coating is deposited on the surface of the alumina substrate.

[0042] Figure 5 The second from the left is the optical photo of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 2 h in the example. It can be seen from the figure that due to the longer deposition time than that in Example 4, the color of the chromium oxide solid solution coating is darker than that in Example 4; Figure 11 This is the scanning electron microscope picture of the chromium oxide solid solution coating in Example 5. It can be seen from the figure that there is no obvious coating structure on the sample surface, and the layered structure on the surface of alumina grains is more obvious than that in Example 4; Figure 16 This is the EDS element content distribution map of the chromium oxide solid solution coating in Example 5. It can be seen from the figure that the chromium oxide solid solution content on the sample surface is about 13.9 wt%.

[0043] Figure 18 In the middle is the X-ray diffraction pattern of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 2 h in Example 5. Since chromium oxide forms a solid solution with alumina at high temperature, its phase is consistent with that of Al 2 O 3 (JCPDS PDF#89-7710); Figure 19 In the middle is the secondary electron emission coefficient curve graph of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 2 h in Example 5, and its δmax is 2.46, which is 30% lower than that of the alumina substrate. Figure 19 In the middle is the main X-ray diffraction pattern of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 2 h in Example 5. Among them, the main diffraction peak of Example 5 shifts to a smaller angle more significantly than that of Example 4, corroborating that the degree of chromium oxide solid solution in alumina is deeper with the increase of calcination time.

[0044] Example 6 This example provides a method and application for preparing a chromium oxide solid solution coating by physical vapor deposition process, including the following steps: Step S1: Add 0.05 mol of chromium nitrate nonahydrate and 125 ml of deionized water to a transparent closed container to prepare a chromium nitrate solution, then add 80 ml of 7.5% polyethylene glycol solution to it, stir and mix, and then add 100 ml of dilute ammonia water solution with PH = 8 to prepare a chromium ion solution with a concentration of 0.15 mol / L. Then, 80 ml of 20% ammonia water diluent is added dropwise to the chromium ion solution and magnetically stirred at a rotation speed of 500 r / min until it is uniform to obtain a Cr(OH)3 suspension; Step S2: The uniform Cr(OH) described in Step S1 3The suspension was allowed to settle naturally at room temperature for 3 h to separate the precipitate from the supernatant. The precipitate was washed three times by centrifugation with absolute ethanol to obtain a pure chromium oxide precursor, which was then dried at 100 °C for 12 h. Subsequently, the dried chromium oxide precursor was ground and passed through a 200-mesh sieve to obtain a nano-sized chromium oxide precursor powder with uniform particle size. Finally, the powder was calcined in a muffle furnace at 600 °C for 1 h to obtain a nano-sized chromium oxide powder with uniform particles. Step S3: The nano-sized chromium oxide powder and the alumina ceramic substrate described in Step S2 were assembled into a preset physical vapor deposition device, and physical vapor deposition was carried out at a preset calcination temperature of 1500 °C for 3 h to deposit a chromium oxide solid solution coating on the surface of the alumina substrate.

[0045] Figure 5 The rightmost one is the optical photograph of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 3 h in Example 6. It can be seen from the figure that due to the longer deposition time than that in Example 5, the color of the chromium oxide solid solution coating is darker than that in Example 5. Figure 11 This is the scanning electron microscope image of the chromium oxide solid solution coating in Example 6. It can be seen from the figure that there is no obvious coating structure on the surface of the sample, and the layered structure on the surface of the alumina grains is more obvious than that in Example 5. Figure 17 This is the EDS element content distribution map of the chromium oxide solid solution coating in Example 6. It can be seen from the figure that the chromium oxide solid solution content on the surface of the sample is about 17.3 wt%.

[0046] Figure 18 This is the X-ray diffraction pattern of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 3 h in Example 6. Since chromium oxide forms a solid solution with alumina at high temperature, its phase is consistent with that of Al2O3 (JCPDS PDF#89-7710). Figure 19 This is the secondary electron emission coefficient curve of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 3 h in Example 6, and its δmax is 2.36, which is 32% lower than that of the alumina substrate. Figure 19 This is the main X-ray diffraction pattern of the chromium oxide solid solution coating prepared by calcination at 1500 °C for 2 h in Example 5. The main diffraction peak of Example 5 is shifted to a smaller angle more significantly than that of Example 4, which proves that the degree of solid solution of chromium oxide in alumina is deeper with the increase of calcination time.

[0047] In summary, the alumina surface chromium oxide vacuum pressure-resistant coating prepared by the PVD method in the present invention uses alumina ceramics as the substrate and nano-chromium oxide powder with a low secondary electron emission coefficient as the coating deposition raw material, enabling the alumina ceramics to obtain a low secondary electron emission coefficient. At the same time, chromium oxide and alumina form a solid solution during the deposition process, enhancing the bonding force between the chromium oxide solid solution coating and the alumina substrate. Ultimately, the ability of the chromium oxide ceramics to inhibit secondary electron emission is enhanced. The secondary electron emission coefficient is less than 2.80, with a minimum of 2.36, a 32% reduction compared to the secondary electron emission coefficient of the alumina substrate, and engineering applications can be achieved. In the present invention, not only the chromium oxide content on the alumina surface can be adjusted to realize the regulation and optimization of the secondary electron emission coefficient of the chromium oxide ceramics, thereby effectively improving the vacuum pressure-resistant performance of the alumina ceramics, but also the excellent mechanical properties of the alumina ceramics are not affected.

[0048] Those of ordinary skill in the art can make various modifications and applications without departing from the essential characteristics of the embodiments. For example, each component detailed in the embodiments can be modified and operated, and the differences related to the modifications and applications can be considered to be included within the scope of protection of the present invention defined by the appended claims.

[0049] The embodiments referred to in this specification mean that the specific features, structures or characteristics described in connection with the embodiments are included in at least one embodiment of the present invention. These terms that appear throughout the specification do not necessarily refer to the same embodiment. In addition, when a specific feature, structure or characteristic is described in connection with any embodiment, it is considered to fall within the scope of these specific features, structures or characteristics that those of ordinary skill in the art can achieve in combination with other embodiments.

Claims

1. A method for preparing a chromium oxide solid solution coating by physical vapor deposition process, characterized in that: The following steps are involved: S1. A coprecipitation method is adopted, wherein chromium nitrate nonahydrate is used as a chromium source and a polyether compound is used as a dispersing solvent. After mixing, a stabilizer is added to prepare a chromium ion solution of a preset concentration, and then the precipitant is added dropwise to the chromium ion solution and stirred evenly to obtain a Cr(OH)3 suspension; S2, allowing the Cr(OH)3 suspension described in step S1 to settle naturally at room temperature to separate the precipitate from the supernatant, washing the precipitate with anhydrous ethanol by centrifugation for multiple times to obtain a pure chromium oxide precursor, then drying, grinding and sieving to obtain a nano-chromium oxide precursor powder with uniform particle size, and finally calcining in a muffle furnace to obtain a uniform nano-chromium oxide powder; S3, constructing a physical vapor deposition device with the nano-chromium oxide powder and the alumina ceramic substrate described in step S2, and using a physical vapor deposition process to deposit a chromium oxide solid solution coating on the surface of the alumina ceramic substrate.

2. The method for preparing a chromium oxide solid solution coating by physical vapor deposition process according to claim 1, characterized in that: In step S1, the dispersing solvent is polyethylene glycol solution, polypropylene glycol or polybutylene glycol; the stabilizer is a dilute ammonia solution with a pH value of 8 and a concentration of 0.5%; the concentration of the chromium ion solution is 0.15 mol / L; and the precipitant is an ammonia diluent with a concentration of 20%.

3. The method for preparing a chromium oxide solid solution coating by physical vapor deposition process according to claim 1, characterized in that: The dosage of the precipitant is 80-100 ml, and the dropping speed of the precipitant is less than 10 ml / min.

4. The method for preparing a chromium oxide solid solution coating by physical vapor deposition process according to claim 1, characterized in that: In step S1, the stirring speed is 300-500 r / min.

5. The method for preparing a chromium oxide solid solution coating by physical vapor deposition process according to claim 1, characterized in that: In the step S2, the natural precipitation time is more than 3 hours, and the precipitate is washed three times by centrifugation with anhydrous ethanol to obtain a pure chromium oxide precursor.

6. The method for preparing a chromium oxide solid solution coating by physical vapor deposition process according to claim 1, characterized in that: In step S2, the centrifugal washing speed is 4000 r / min and the centrifugal time is 5 min.

7. The method for preparing a chromium oxide solid solution coating by physical vapor deposition process according to claim 1, characterized in that: In the step S2, the drying temperature of the chromium oxide precursor is 100° C., the drying time is 12 hours, and the mesh size is 200 meshes.

8. The method for preparing a chromium oxide solid solution coating by physical vapor deposition process according to claim 1, characterized in that: In the step S2, the maximum calcination temperature of the nano-chromium oxide precursor powder is 600° C., and the heat preservation time is 1 hour.

9. The method for preparing a chromium oxide solid solution coating by using a physical vapor deposition process according to claim 1, characterized in that: In the step S3, the physical vapor deposition device constructed is a high-temperature resistant material that is resistant to high temperatures, stable, and does not react with chromium oxide, and the high-temperature resistant material is a silicate refractory material.

10. The method for preparing a chromium oxide solid solution coating by using a physical vapor deposition process according to claim 1, characterized in that: In the step S3, after the physical vapor deposition device is built, it is placed in a muffle furnace in an air atmosphere at a temperature of 1300° C.-1500° C. to deposit the coating for 1-3 hours, so that a chromium oxide solid solution coating is deposited on the surface of the alumina ceramic substrate.

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