Non-evaporative getter coating method and vacuum components

Abstract

This invention provides a non-evaporative getter coating method that can coat a vacuum vessel with an NEG film that does not easily degrade in exhaust capacity when the vacuum vessel is repeatedly opened to the atmosphere, and a vacuum component that does not easily degrade in exhaust capacity when the vacuum vessel is repeatedly opened to the atmosphere. [Solution] The non-evaporative getter coating method includes forming a film of a low-temperature activatable non-evaporative getter alloy on the inner wall surface of a vacuum component by a cold spray method.

Description

Technical Field

[0001] The present disclosure relates to a method for coating a non-evaporable getter and a vacuum component coated with a non-evaporable getter.

Background Art

[0002] In the field of vacuum science and technology, a NEG pump equipped with a non-evaporable getter (NEG) is known as a vacuum pump that consumes less energy and enables evacuation over a wide pressure range. As described in Patent Document 1, it is known to use a sputtering method to coat the inside of a vacuum vessel with a NEG material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The evacuation ability of the NEG film on the inner wall surface of a vacuum vessel obtained by forming a NEG material film on the inner wall surface of the vacuum vessel using a sputtering method deteriorates by repeating the atmospheric opening of the vacuum vessel. It is required to coat the NEG film so that the evacuation ability is less likely to deteriorate when the atmospheric opening of the vacuum vessel is repeated.

[0005] An object of the present disclosure is to provide a non-evaporable getter coating method capable of coating a NEG film with less likelihood of a decrease in evacuation ability when the atmospheric opening of a vacuum vessel is repeated, and a vacuum component with less likelihood of a decrease in evacuation ability when the atmospheric opening of the vacuum vessel is repeated.

Means for Solving the Problems

[0006] (1) A non-evaporative getter coating method according to one embodiment of the present disclosure includes forming a low-temperature activatable non-evaporative getter alloy on the inner wall surface of a vacuum component by a cold spray method.

[0007] (2) The non-evaporative getter coating method described in (1) above may include forming a film of the non-evaporative getter alloy on the inner wall surface of the vacuum component with a thickness of 100 μm or more.

[0008] (3) In the non-evaporative getter coating method described in (1) or (2) above, the non-evaporative getter alloy may be activated at a temperature of 250°C or lower while it is formed on the inner wall surface of the vacuum component.

[0009] (4) A vacuum component according to one embodiment of the present disclosure is a vacuum component having an inner wall surface. A non-evaporable getter alloy that can be activated at 250°C or below is deposited on the inner wall surface to a thickness of 100 μm or more and remains in a state that can be activated at 250°C or below. [Effects of the Invention]

[0010] According to the non-evaporative getter coating method of this disclosure, a NEG film is coated that does not easily degrade in exhaust capacity when the vacuum vessel is repeatedly opened to the atmosphere. Furthermore, according to the vacuum component of this disclosure, the exhaust capacity does not easily degrade when the vacuum vessel using the vacuum component is repeatedly opened to the atmosphere. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1(a) illustrates the adsorption of gas by an NEG film deposited by the method according to this disclosure. Figure 1(b) illustrates the adsorption of gas by an NEG film deposited by the method according to the comparative example. [Figure 2] This figure illustrates an example of the configuration of a spray device used in the method described herein. [Figure 3]Figure 3(a) is an electron microscope image of NEG alloy particles produced by a planetary ball mill. Figure 3(b) is an electron microscope image of NEG alloy powder collected from the surface of Figure 3(a). [Figure 4] This figure illustrates an example of the configuration of an apparatus for evaluating the exhaust capacity of an NEG film deposited by the method described herein. [Figure 5] This figure shows the difference in pressure over time with and without the NEG film. [Figure 6] This is a graph of the X-ray diffraction spectrum of an NEG film. [Figure 7] This graph shows an example of the relationship between the NEG membrane pumping speed and the pressure in the first chamber. [Figure 8] These graphs show examples of the relationship between the pressure in the first chamber and the exhaust velocity of the NEG membrane, as well as the relationship between the pressure in the first chamber and the pressure ratio between the first and second chambers. [Modes for carrying out the invention]

[0012] In the field of vacuum science and technology, it is possible to exhaust gases with low energy consumption and over a wide pressure range. As a vacuum pump capable of achieving high vacuum levels, NEG pumps equipped with a non-evaporable getter (NEG) are attracting attention. NEG pump technology is widely used in technologies requiring the maintenance of ultra-high vacuum, such as accelerators, synchrotron radiation sources, beamlines, and photoelectron spectroscopy equipment. The technology of coating the inner wall surface of a vacuum vessel or vacuum piping, i.e., the surface in contact with the space that maintains the vacuum, with an NEG film and then baking it to turn the inner wall surface of the vacuum vessel or vacuum piping into a vacuum pump is also called NEG coating. Hereinafter, vacuum vessels or vacuum piping will also be collectively referred to as vacuum components.

[0013] As a method for NEG coating related to the first comparative example, a method of depositing an NEG film on the inner wall surface of a vacuum component using the magnetron sputtering method can be considered. However, when depositing an NEG film using the sputtering method, it is difficult to make the thickness of the NEG film thicker than 3 μm.

[0014] The evacuation ability of the NEG film on the inner wall surface of a vacuum vessel or a vacuum pipe obtained by forming the NEG material on the inner wall surface of the vacuum vessel or the vacuum pipe deteriorates by repeating the atmospheric opening of the vacuum vessel. It is required to coat the NEG film so that the evacuation ability is less likely to deteriorate when the atmospheric opening of the vacuum vessel is repeated.

[0015] Hereinafter, embodiments of a non-evaporable getter coating method according to the present disclosure and a vacuum component coated with a non-evaporable getter will be described in detail with reference to the drawings.

[0016] (Comparison between the NEG film according to the present disclosure and the NEG film according to the first comparative example) The non-evaporable getter (NEG) coating method according to the present disclosure is a method of forming a NEG film by a cold spray method. The NEG film formed by the method according to the present disclosure has a thickness of 100 μm or more as shown in Fig. 1(a). On the other hand, as a method according to the first comparative example, it is conceivable to form a NEG film by a sputtering method. The NEG film formed by the method according to the first comparative example, that is, the sputtering method has a thickness of about 1 μm as shown in Fig. 1(b). The upper limit of the thickness of the NEG film formed by the sputtering method is about 3 μm.

[0017] In Figs. 1(a) and (b), the leftmost figure marked RT represents the state of gas molecules adsorbed by the NEG film when the temperature of the NEG film is at room temperature, for example, about 20°C to 25°C, at an initial stage after activating the NEG film. The white circles represent hydrogen atoms. The black circles represent carbon atoms. The gray circles represent oxygen atoms. At the initial stage, approximately the same number of gas molecules are adsorbed by the NEG film in both the thick NEG film formed by the method according to the present disclosure and the thin NEG film formed by the method according to the first comparative example.

[0018] Next, the figure described as 180°C in the center represents the state of the molecules of the gas desorbed from the NEG film when the temperature of the NEG film rises to 180°C. In the thin NEG film according to the first comparative example of FIG. 1(b), there are more gas molecules remaining in the NEG film without being completely desorbed from the NEG film than in the thick NEG film according to the present disclosure of FIG. 1(a).

[0019] Next, the figure described as RT on the far right represents the state of the gas molecules adsorbed by the NEG film when the temperature of the NEG film returns to room temperature after repeatedly raising and lowering the temperature of the NEG film. In the thin NEG film according to the first comparative example of FIG. 1(b), due to the large number of gas molecules remaining in the NEG film, the amount of gas that can be adsorbed when reaching room temperature is less than the amount of gas that can be adsorbed by the thick NEG film according to the present disclosure of FIG. 1(a). That is, the ability of the thick NEG film according to the present disclosure to adsorb gas, i.e., the evacuation ability, is less likely to deteriorate than the evacuation ability of the thin NEG film according to the first comparative example by repeatedly raising and cooling the temperature.

[0020] Also, the thick NEG film according to the present disclosure is larger in volume than the thin NEG film according to the first comparative example. Due to the large volume, when repeatedly opening the atmosphere of the vacuum component on which the NEG film is formed, the evacuation ability of the NEG film is less likely to deteriorate.

[0021] Also, the larger the volume of the NEG film, the larger the amount of gas that can be adsorbed. Due to the large amount of gas that can be adsorbed, the evacuation speed of the thick NEG film according to the present disclosure is greater than the evacuation speed of the thin NEG film according to the first comparative example.

[0022] (NEG Coating Method According to the Present Disclosure) The NEG coating method according to the present disclosure forms a coating 3, i.e., a NEG film, by spraying NEG alloy particles 2 onto a substrate 1 using a cold spray device 10 illustrated in FIG. 2. The cold spray device 10 includes a thermal spray gun 11, a supersonic nozzle 12, a powder transport gas valve 13, a powder supply device 14, a powder introduction path 15, a high-pressure operating gas valve 16, a gas heater 17, and a gas introduction path 18.

[0023] The cold spray apparatus 10 according to this disclosure flows powder conveying gas from a powder conveying gas valve 13 to a powder supply device 14, and the flow of powder conveying gas supplies NEG alloy particles 2 from the powder supply device 14 to the thermal spray gun 11 through a powder introduction passage 15. The cold spray apparatus 10 also flows high-pressure operating gas from a high-pressure operating gas valve 16 to a gas heater 17, heats the high-pressure operating gas in the gas heater 17, and flows the heated high-pressure operating gas from the gas heater 17 to the thermal spray gun 11 through a gas introduction passage 18 to generate a supersonic flow of high-pressure operating gas in the supersonic nozzle 12. The supersonic nozzle 12 may be a tapered cylindrical nozzle, but may also be a nozzle of various other shapes.

[0024] The NEG alloy particles 2 introduced into the thermal spray gun 11 are accelerated by the supersonic flow of high-pressure working gas generated in the supersonic nozzle 12, and collide with the substrate 1 at high speed while remaining in a solid state, undergoing plastic deformation on the surface of the substrate 1 to form a coating 3.

[0025] The powder transport gas and the high-pressure working gas may be inert gases such as nitrogen gas. The high-pressure working gas is heated in the gas heater 17 to a temperature lower than the melting point or softening temperature of the NEG alloy. The cold spray device 10 generates a supersonic flow of the high-pressure working gas such that the velocity at which the NEG alloy particles 2 collide with the substrate 1 is equal to or greater than the critical velocity. The critical velocity is the velocity at which the NEG alloy particles 2 begin to plastically deform due to kinetic energy upon collision with the substrate 1, thereby forming the coating 3.

[0026] As described above, the cold spray device 10 can deposit NEG alloy particles 2 onto the surface of the substrate 1 at a temperature lower than the melting point or softening temperature. Because the film can be deposited at a low temperature, crystallization does not progress when the NEG alloy particles 2 become an NEG film on the substrate 1. As a result, changes in the activation temperature of the NEG film during deposition are suppressed. In addition, when the NEG alloy particles 2 collide with the substrate 1, they undergo plastic deformation to form a coating 3, which increases the adhesion and bonding rate of the coating 3 to the substrate 1. Furthermore, the coating 3 can be made thicker than 100 μm.

[0027] The cold spray apparatus 10 may be an apparatus having a general configuration for performing film deposition using a general cold spray method.

[0028] (Creation of NEG alloy particles that can be activated at low temperatures) As described above, when a film 3 of NEG alloy particles 2 is formed in the cold spray device 10, changes in the activation temperature of the NEG alloy particles 2 are suppressed. The NEG coating method according to this disclosure forms a low-temperature activated NEG film by introducing low-temperature activated NEG alloy particles as NEG alloy particles 2 into the powder supply device 14 of the cold spray device 10.

[0029] In this disclosure, low-temperature activatable NEG alloy particles were created using a mechanical alloying method. In the mechanical alloying method, alloying is promoted by pressurizing multiple types of metal powders that will form the NEG alloy, thereby creating the NEG alloy. The NEG alloy is created by alloying under pressure without heating. As a result, the NEG alloy is created in an amorphous state where crystallization is less likely to occur. The activation temperature of the amorphous NEG alloy is lower than that of the crystallized NEG alloy. Therefore, the NEG alloy created by the mechanical alloying method is expected to be activated at low temperatures.

[0030] In this disclosure, mechanical alloying was performed using a planetary ball mill. The NEG alloy produced in this disclosure is a Ti-V-Zr alloy. Figure 3(a) shows an example of an electron microscope image of NEG alloy particles 2 produced by a planetary ball mill. The NEG alloy particles 2 are formed in a form in which NEG alloy powder adheres to the surface of balls used in the planetary ball mill. Figure 3(b) shows an example of an electron microscope image of NEG alloy powder extracted from the surface of the balls and observed. The metal combination of the NEG alloy is not limited to Ti-V-Zr as described above, but may be other combinations.

[0031] (Evaluation of the exhaust capacity of the NEG membrane) As described above, the NEG coating method in this disclosure allows for the formation of a film 3 of an NEG alloy with a low activation temperature as an NEG film using a cold spray apparatus 10.

[0032] Here, the exhaust capacity of the NEG membrane was evaluated using the evaluation apparatus 20 illustrated in Figure 4. The evaluation apparatus 20 comprises an evaluation chamber 21, an orifice 22, a first vacuum gauge 23, a second vacuum gauge 24, a scroll pump 25, a turbomolecular pump 26, and valves 27-29. The scroll pump 25 is a pump that achieves a low vacuum, i.e., a vacuum in which the pressure inside the container is relatively high, and may be replaced with other types of pumps such as a rotary pump. The turbomolecular pump 26 is a pump that achieves a higher vacuum than the scroll pump 25, i.e., a vacuum in which the pressure inside the container is relatively low, and may be replaced with other types of pumps such as an oil diffusion pump. With valves 27 and 28 open, the evaluation apparatus 20 preemptively exhausts from inside the evaluation chamber 21 using the scroll pump 25, and then exhausts inside the evaluation chamber 21 to a high vacuum using the turbomolecular pump 26. The evaluation chamber 21 is purged with nitrogen gas by opening valve 29.

[0033] The evaluation chamber 21 is divided by an orifice 22 into a first chamber 21A located closer to the turbomolecular pump 26 and a second chamber 21B located further away from the turbomolecular pump 26. The pressure in the first chamber 21A is measured by a first vacuum gauge 23. The pressure in the second chamber 21B is measured by a second vacuum gauge 24.

[0034] Here, the NEG alloy film 3, i.e., the NEG film, deposited on the surface of the substrate 1, is housed in the second chamber 21B of the evaluation chamber 21. The evaluation apparatus 20 heats and activates the NEG film in the evaluation chamber 21, then cools it to room temperature and measures the pressure in the first chamber 21A and the pressure in the second chamber 21B, respectively. The pressure in the second chamber 21B is lower than the pressure in the first chamber 21A if the NEG film housed in the second chamber 21B has sufficient exhaust capacity. Based on the difference between the pressure in the first chamber 21A and the pressure in the second chamber 21B, the exhaust velocity of the NEG film housed in the second chamber 21B is calculated.

[0035] <Confirmation of the exhaust capacity of the NEG membrane using the cold spray method> First, as a preliminary experiment, it was confirmed whether the NEG film, formed by spraying NEG alloy particles 2 onto the surface of a substrate 1 using a cold spray device 10, had exhaust capacity. Samples were prepared with the NEG film formed on the surface of a Cu plate as the substrate 1, and samples without the NEG film formed. Each of these samples was then placed in the second chamber 21B of the evaluation chamber 21, heated to activate the NEG film, and then cooled, and the change in pressure in the second chamber 21B was measured.

[0036] The measurement results of the pressure change in the second chamber 21B are illustrated in the graph in Figure 5. The horizontal axis of the graph in Figure 5 represents time, and the vertical axis represents the pressure in the second chamber 21B. "NEG present" corresponds to the sample on which the NEG film was deposited. "NEG absent" corresponds to the sample on which the NEG film was not deposited. During the initial activation period, the pressure in the vacuum chamber increased for all samples, but after cooling to room temperature following activation, it was found that the pressure in the vacuum chamber for "NEG present" was lower than the pressure in the vacuum chamber for "NEG absent". In other words, preliminary experiments confirmed that the NEG film deposited using the cold spray device 10 has an exhaust capacity.

[0037] <Confirmation of exhaust capacity of NEG film that can be activated at low temperatures> Next, the exhaust capacity of a low-temperature activatable NEG film, fabricated by mechanical alloying, was confirmed. The NEG film according to this disclosure was found to be activatable at 250°C.

[0038] On the other hand, for comparison, an NEG film activated at high temperatures was prepared. The activation temperature of an NEG film tends to increase as the crystallization of the NEG alloy progresses. Therefore, as a second comparative example, an NEG film deposited by the atomization method was prepared. The atomization method is a method of depositing a film by promoting alloying by heating the NEG alloy material. The NEG film related to the second comparative example was said to be activatable at 450°C.

[0039] Figure 6 shows the X-ray diffraction spectrum of the NEG alloy according to this disclosure and the X-ray diffraction spectrum of the NEG alloy according to the second comparative example. The horizontal axis of the graph in Figure 6 represents the X-ray diffraction angle, and the vertical axis represents the X-ray diffraction intensity. The X-ray diffraction spectrum of the NEG alloy according to this disclosure does not have a significant peak. Therefore, it can be seen that crystallization has not progressed in the NEG alloy according to this disclosure, that is, the amorphous state is maintained. On the other hand, the X-ray diffraction spectrum of the NEG alloy according to the second comparative example has a peak. Therefore, it can be seen that crystallization is progressing in the NEG alloy according to the second comparative example. As described above, the activation temperature of an amorphous NEG alloy is lower than that of a crystallized NEG alloy. Therefore, in this disclosure, by adopting particles containing an amorphous NEG alloy prepared using the mechanical alloying method as NEG alloy particle 2, an NEG film with a low activation temperature is formed.

[0040] Here, after the NEG films according to the present disclosure and the second comparative example were housed in the second chamber 21B of the evaluation chamber 21 and activated, the pumping velocity of the NEG films according to the present disclosure and the second comparative example was measured. The measurement results are shown in the graph in Figure 7. The horizontal axis of Figure 7 represents the pressure in the first chamber 21A of the evaluation chamber 21. The vertical axis represents the pumping velocity of the NEG film. The pumping velocity is calculated based on the difference between the pressure in the first chamber 21A and the pressure in the second chamber 21B.

[0041] As shown in Figure 7, the NEG film according to the second comparative example achieved a higher pumping speed when activated at 450°C than when activated at 250°C. On the other hand, the pumping speed of the NEG film according to the present disclosure when activated at 250°C was about the same as that of the NEG film according to the second comparative example when activated at 450°C. In other words, it was found that the NEG film according to the present disclosure can be activated at low temperatures.

[0042] Furthermore, the pumping speed and the pressure ratio between the first chamber 21A and the second chamber 21B were measured as the pumping capacity of the NEG film according to this disclosure, and the results are shown in the graph of Figure 8. The horizontal axis of Figure 8 represents the EXG1 pressure. The EXG1 pressure is the pressure inside the first chamber 21A. The vertical axis of Figure 8 represents the pumping speed and the pressure ratio, respectively. The pressure ratio is calculated as EXG1 pressure / EXG2 pressure. The EXG2 pressure is the pressure inside the second chamber 21B. From the graph of Figure 8, it can be seen that the NEG film according to this disclosure can achieve a higher pumping speed as the EXG1 pressure decreases, that is, as the vacuum increases.

[0043] (summary) As described above, the non-evaporative getter coating method according to this disclosure involves depositing a low-temperature-activatable non-evaporative getter (NEG) alloy onto the inner wall surface of a vacuum component using a cold spray method. By depositing the NEG film using the cold spray method, crystallization of the NEG film is less likely to occur. As a result, the NEG film becomes low-temperature-activatable, just as it was before deposition. Because the NEG film is low-temperature-activatable, the equipment required to raise the temperature of the vacuum component coated with the NEG film is simplified.

[0044] Furthermore, by depositing the NEG film using the cold spray method, the thickness of the NEG film can be increased to approximately 100 μm or more. A thicker NEG film results in a larger volume. This larger volume means that when vacuum components with the NEG film deposited are repeatedly exposed to the atmosphere, the exhaust capacity of the NEG film is less likely to deteriorate.

[0045] Furthermore, the larger the volume of the NEG film, the greater the amount of gas it can adsorb. A larger amount of adsorbed gas leads to a higher exhaust velocity.

[0046] The thin NEG film produced by the sputtering method, cited as the first comparative example, is prone to degradation due to its small volume and is vulnerable to vacuum leaks. Furthermore, the NEG film produced by the atomization method, cited as the second comparative example, requires activation at high temperatures. In contrast to these comparative examples, the NEG film formed by the non-evaporative getter coating method according to this disclosure has the advantages of being less prone to degradation even with repeated exposure to the atmosphere, being highly resistant to vacuum leaks, and being activateable at low temperatures.

[0047] Another comparative example is a component formed from a low-temperature activatable NEG alloy in the shape of a pill; however, pill-shaped components are difficult to place inside vacuum components. On the other hand, with the non-evaporative getter coating method according to this disclosure, the NEG film is directly deposited on the inner wall surface of the vacuum component, making it easy to place inside the vacuum component.

[0048] For example, the method according to this disclosure may be applied to the deposition of an NEG film on the inner wall surface of a beamline of a high-current accelerator. Beamlines of high-current accelerators are susceptible to temperature changes. Repeated expansion and contraction of the beamline due to temperature changes makes it prone to leakage. By deposition of a thick NEG film on the inner wall surface of a beamline of a high-current accelerator using the method according to this disclosure, when leakage occurs in the beamline of the high-current accelerator, the leaked air is exhausted by the NEG film, and the pressure inside the beamline of the high-current accelerator is maintained at a low level.

[0049] Furthermore, experiments have confirmed that the secondary electron emission coefficient (SEY) of the NEG film deposited by the method of this disclosure is almost the same as that of the NEG films of the first and second comparative examples. Therefore, when an NEG film is deposited on the inner wall surface of a beamline of a high-current accelerator using the method of this disclosure, it is expected that the beam instability in the beamline will be suppressed to the same or less extent compared to when an NEG film is deposited using the method of the comparative examples.

[0050] The non-evaporative getter coating method described herein is applicable to the deposition of NEG films in synchrotron radiation accelerators, colliders, or heavy ion accelerators requiring differential pumping systems. Furthermore, the non-evaporative getter coating method described herein is also applicable to electron microscopy.

[0051] While embodiments relating to this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are included within the scope of this disclosure. For example, the functions included in each component or step can be rearranged in a logically consistent manner, and multiple components or steps can be combined into one or divided. While embodiments relating to this disclosure have been described primarily in terms of apparatus, embodiments relating to this disclosure can also be realized as methods including steps performed by each component of the apparatus. Embodiments relating to this disclosure can also be realized as methods, programs, or storage media recording programs executed by a processor in the apparatus. These should also be understood to be included within the scope of this disclosure. [Explanation of Symbols]

[0052] 1 circuit board 2 NEG alloy particles 3 Coating 10. Cold spray system (11: thermal spray gun, 12: supersonic nozzle, 13: powder conveying gas valve, 14: powder supply device, 15: powder inlet, 16: high-pressure operated gas valve, 17: gas heater, 18: gas inlet) 20. Evaluation equipment (21: evaluation chamber, 21A: first chamber, 21B: second chamber, 22: orifice, 23: first vacuum gauge, 24: second vacuum gauge, 25: scroll pump, 26: turbomolecular pump, 27-29: valves)

Claims

1. A non-evaporative getter coating method comprising depositing a low-temperature activatable non-evaporative getter alloy onto the inner wall surface of a vacuum component by a cold spray method.

2. The non-evaporative getter coating method according to claim 1, further comprising forming a film of the non-evaporative getter alloy on the inner wall surface of the vacuum component to a thickness of 100 μm or more.

3. The non-evaporative getter coating method according to claim 1 or 2, wherein the non-evaporative getter alloy is activated at 250°C or below while in a film-formed state on the inner wall surface of the vacuum component.

4. A vacuum component having an inner wall surface, A vacuum component in which a non-evaporable getter alloy, which can be activated at temperatures below 250°C, is deposited on the inner wall surface to a thickness of 100 μm or more, while remaining in a state that can be activated at temperatures below 250°C.

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