Non-evaporable getter module

Abstract

The present invention is related to a getter module (1) of non-evaporable getter (NEG) material, improved for the use in high and ultra-high vacuum equipment by providing a specific ratio between microscale and macroscale porosity.

Description

[0001] NON-E VAPORABLE GETTER MODULE

[0002] The present invention is inherent to a getter module of non-evaporable getter (NEG) material, improved for the use in high and ultra-high vacuum equipment.

[0003] Non-evaporable getter materials have been widely used in the field of high and ultra-high vacuum applications, such as scientific instruments, particle accelerators, synchrotrons and fusion facilities. Indeed, due to the large pumping speed for active gases, especially for H2 at ambient temperature, pumping systems based on NEG materials are widely used. Moreover, NEG pumps are very compact and vibration-free devices able to deliver very high pumping speed with minimal power requirement and no electromagnetic interference.

[0004] In this field, one of the main issues is represented by the optimization of the getter performance, specifically the gas pumping speed and sorption capacity.

[0005] NEG pumps are typically made of a plurality of disks of getter material, stacked on one or more central supports, as described in EP 0742370 and EP 0753663 both in the applicant's name, aiming at maximizing both the pumping speed and sorption capacity in a compact configuration.

[0006] However, such typical geometry of getter cartridges leads to conductance limitations, i.e. a reduction of pumping speed given by narrow spacing between the disks. This is especially relevant for residual active gases with high atomic mass, such as CO, CO2, O2, N2.

[0007] Therefore, the purpose of the present invention is to overcome the above-cited problems and increase the getter efficiency, by optimizing the macrostructure combined with a specific microstructure of the getter module.

[0008] A typical approach to improving the performance of a getter pump is represented by the realization of getter modules with a macroscale porous structure which increases the getter surface and consequently the diffusion capacity from the surface to the bulk getter material, as reported for example in documents KR101742622, GB 1490311 and CN116275106 or in the paper titled “Additively manufactured ultra-high vacuum chamber below 10'10bar” in the name of Cooper et al, 201 Olin Library Cornell University, Ithaca, NY 14856, 15.03.2019, XP081549978. However, the inventors proved that the surface increase via a macroscale porosity is not enough to satisfy the required performances in high and ultra-high vacuum applications. Specifically, it was found that the crucial features, which allow reaching the desired effects in terms of pumping speed and sorption capacity, are represented by a specific interconnected microscale structure and its relative morphology. The SEM images in the attached figures clearly show that the specific morphology given by the microscale cavities of the present invention, and their synergy with the macroscale surface, are not reported in or deducible from the prior art documents cited above.

[0009] The object of the present invention is thus to provide a limited encumbrance NEG module for high and ultra-high vacuum occupying a macroscale volume and having a macroscale surface area, characterized by a porous structure with an interconnected microscale porosity giving a microscale surface area.

[0010] The key feature of the present getter module is thus represented by a specific relation between its microscale and macroscale surface areas, and a specific relation between its macroscale volume and its encumbrance. Specifically, said relation is measured by using the O / T ratio wherein c is defined as the ratio between the microscale surface area and the macroscale surface area; and r is defined as the ratio between the macroscale volume and the getter module encumbrance.

[0011] Herein the “macroscale surface area” is defined as the effective surface area of the getter module structure, assumed as perfectly smooth; the macroscale surface area possibly includes macroscale cavities and other internal surfaces exposed to other elements, such as a heater. Indeed, in a particularly preferred embodiment, the getter module can comprise a plurality of macroscale cavities, formed in the external sides of the getter module, which can be interconnected to each other.

[0012] The “microscale surface area” is the effective surface area of the getter module structure, considering the rough and porous morphology of the module microstructure, including possible macroscale cavities and internal surfaces exposed to other elements, such as a heater. In other words, the “microscale surface area” is greater than the “macroscale surface area” due to the area of the microscale cavities resulting from the porosity of the microstructure.

[0013] Specifically, the macroscale surface area is calculated from the CAD figures of the getter module assumed as perfectly smooth, while the microscale surface area is calculated from a surface measurement per unit of volume (obtained via TAC scan, with a resolution of 5 microns - High resolution 3D tomographic scan), multiplied by the volume of the module, i.e. the macroscale volume.

[0014] The “macroscale volume” is indeed defined as the actual volume occupied by the getter module structure, considered as perfectly smooth, excluding any possible empty space contained within its outer limits.

[0015] The “encumbrance” is the maximum volume occupied by the getter module considered as solid and perfectly smooth, including possible macroscale cavities making up a macroscale porosity of the module but excluding the extra-volume possibly occupied within its outer limits by other elements of a getter pump, such as a heater. In other words, the “encumbrance” is equal to the “macroscale volume” plus the volume of the macroscale porosity, when present.

[0016] Specifically, inventors have surprisingly found that the pumping speed for getterable gases such as H2 and CO is maximized and improved with respect to the prior art when said O / T ratio is comprised between 7 and 80, preferably between 10 and 30.

[0017] Inventors have found that the choice of such parameter is important for obtaining a synergistic effect of the micro structure and macrostructure in the getter module. A value of O / T=1 refers to a perfectly smooth getter module (macroscale surface area equal to microscale surface area), without microscale and macroscale cavities (encumbrance equal to macroscale volume). Note that this is the lowest possible value, since o>l and T<1 due to the definitions above, whereby O / T=1 only when both o=l and T=1.

[0018] When macroscale porosity is present, the macroscale cavities are characterized by a cross-sectional area comprised between 3 mm2and 2000 mm2, preferably between 19 mm2and 710 mm2, wherein the cross-section is defined as the intersection of the macroscale cavity with a plane perpendicular to the axis of the cavity. Said cross-section can have an irregular, polygonal, elliptical or circular shape.

[0019] The interconnected cavities of the microscale porosity characterize the porous microstructure of the getter module, at a microscopic level, with a characteristic dimension, defined as the greatest dimension of a microscale cavity (i.e. the pores size), comprised between 50 and 500 pm. Indeed, the getter module herein disclosed is characterized by a melted and interconnected microstructure of the bulk of the getter module, and additional microparticles with a diameter comprised between 5 and 50 pm which adhere to the melted microstructure in a coral-like framework, increasing the effective getter module microscale surface area.

[0020] The bulk density of the getter module is defined as the ratio between the mass of the getter module and the macroscale volume and, in a preferred embodiment, it is comprised between 0.4 and 3.5 g / cm3.

[0021] In one embodiment, the porous getter module is made of a material selected in the group consisting of Ti, Zr, V, Hf, Nb, and alloys based on them as main chemical element, wherein the main element is defined as the most abundant and thus further elements can be comprised in the alloy composition. Specifically, the additional elements can be selected among Al, Mo, Si, Fe, Ni or Co.

[0022] Said alloys are preferably selected among TiAIV, TiMo, TiSiVFeAl, ZrVTi, ZrTiVAl, ZrVFe, ZrCo, ZrAl, ZrFe, or ZrNi alloys.

[0023] The getter module according to the present invention can be prepared as a cylinder, a disk or a block using a method selected among additive manufacturing, Metal Injection Molding (MIM), Suspension Plasma Spray (SPS) or binder jetting.

[0024] In a preferred embodiment, the getter module is made by an additive manufacturing method selected in the group consisting of Laser Powder Bed Fusion (L-PBF), Electron Powder Bed Fusion (E-PBF), Digital Light Processing (DLP), Stereolitography (SLA), Fused Deposition Modelling (FDM) and Direct Energy Deposition (DED).

[0025] The present invention also relates to a getter pump comprising at least a getter module according to the present invention and one or more internal or external resistance heaters.

[0026] Said heaters, for instance, can be in-vacuum central rods installed on the same flange of the getter pump, external coils or in-vacuum coils.

[0027] The invention will be illustrated also by the following non-limiting figures where:

[0028] Figures 1 to 10 are schematic views showing possible macroscale porosities characterizing the getter modules according to the present invention.

[0029] Figure 1 shows a cylindrical getter module characterized by an external surface, provided with passing hexagonal macroscale cavities of maximum cross section of 22 mm2, connected to an internal solid surface, and a magnified view of the porous microstructure of the module.

[0030] Figure 2 shows a cylindrical getter module with passing hexagonal macroscale cavities of maximum cross-section of 70 mm2.

[0031] Figure 3 shows a cubic getter module with passing circular macroscale cavities with a maximum cross-section of 20 mm2.

[0032] Figure 4 shows a cylindrical getter module similar to Fig.1 but with passing circular macroscale cavities with a maximum cross-section of 20 mm2both in the internal and external surfaces.

[0033] Figure 4A is a longitudinal cutaway view of the getter module of Fig.4.

[0034] Figure 5 shows a cylindrical getter module similar to Fig.2 but with passing square macroscale cavities with a maximum cross-section of 25 mm2.

[0035] Figure 6 shows a getter module in a solid disk configuration.

[0036] Figures 7 to 10 show an assembly of two cylindrical getter modules stacked to form a getter cartridge, each cartridge having a different type of macroscale porosities.

[0037] Figure 11 shows a getter module in a solid cylinder configuration.

[0038] Figures 12 to 14 are SEM images of the microstructure of a getter module made of Ti grade 5 alloy according to the present invention, at three different magnification scales respectively of 300X, 140X and 120X.

[0039] Figures 15 to 17 are SEM images of a comparative example, a commercially available getter alloy (ZrFeV), which does not have the morphologic features of the present invention at the same three different magnification scales of 300X, 140X and 120X.

[0040] Figures 18 to 20 are SEM images of another comparative example, a commercially available getter alloy (ZrVTiAl), which does not have the morphologic features of the present invention at the same three different magnification scales of 300X, 140X and 120X.

[0041] Figures 12 to 14 clearly show the melted and interconnected microstructure which characterizes the bulk of the getter module and the additional micro-particles adhered to the bulk. Figures 15 to 17 refer to the microstructure which characterizes the bulk of a getter module obtained by press sintering with space holder; while figures 18 to 20 refer to the microstructure of a getter module obtained by press sintering process. Said figures clearly show that neither of these two comparative examples has an interconnected pattern of microscale porosity.

[0042] Figure 1 shows an example of a getter module 1 with a macroscale porosity, resulting from an external surface 2 provided with passing hexagonal macroscale radial cavities 3. Said external surface 2 is connected to an internal solid surface 4 through stringers 5 so that the space between surfaces 2 and 4 is divided into a plurality of longitudinal cavities 6 that connect the longitudinally aligned radial cavities 3. Said stringers 5 could also be provided with openings such that all cavities 3, 6 around the module 1 are interconnected.

[0043] Figures 4, 4A show an example of a getter module 1 with a macroscale porosity similar to that of Fig.1, but in this case resulting from a perforated cylindrical shell. More specifically, the macroscale radial cavities 3 are circular and pass through both the external surface 2 and the internal surface 4, and similar circular longitudinal cavities 6 are formed in correspondence with the longitudinally aligned radial cavities 3.

[0044] EXAMPLES

[0045] Hereinafter, the invention will be explained in more detail with reference to the following non-limiting examples. Modifications or variations of the embodiments here exemplified, obvious to an expert in the art, are encompassed by the appended claims.

[0046] The effectiveness of getter modules characterized by an optimized value of O / T is shown in table 1, where experimental results from some tested getter modules are reported. All tested getter modules, except C3, have been obtained by additive manufacturing technique but using different parameters: the getter powder undergoes a localized laser-melting process to obtain different microscale and macroscale configurations. The last reported getter module (i.e. C3) was made by press sintering technique, which is not encompassed by the appended claims.

[0047] In addition to the geometrical characteristics that have been previously described (microscale and macroscale surface area, macroscale volume, encumbrance and O / T), the getter mass and the pumping performances of each getter module are also reported. In particular, pumping speed for CO is reported, as well as pumping speed for CO per unit mass of the getter module, which is a good indication of how much effectively the getter mass is employed in a given getter module.

[0048] Samples are reported, from left to right, from the lowest O / T to the highest O / T. The tested getter modules with the lowest (i.e. Cl) and the highest (i.e.C2 and C3) values of O / T are out of the optimal range defined in the present invention and are reported as comparative examples.

[0049] Pumping speed for CO has been measured according to a standard procedure (ASTM F798-97), well known by an expert in the art. Microscale surface area values have been obtained by tomographic analysis as previously explained.

[0050] List and description of samples (S1-S5) and comparative examples (C1-C3):

[0051] • SI: getter module in a disk configuration (Figure 6) made of Ti grade 5 alloy.

[0052] • S2: getter module in a disk configuration (Figure 6) made of Ti grade 21 alloy.

[0053] • S3 : getter module in a double-stacked configuration with hexagonal macroscale radial cavities (Figure 8) made of Ti grade 5 alloy.

[0054] • S4: getter module in a double-stacked configuration with hexagonal macroscale radial cavities (Figure 9) made of Ti grade 5 alloy.

[0055] • S5: getter module in a double-stacked configuration with a 3D pattern (Figure 10) made of Ti grade 5 alloy.

[0056] • Cl : getter module in a disk configuration (Figure 6) made of Ti grade 5 alloy.

[0057] • C2: getter module in a cylindrical block configuration (Figure 11) made of Ti grade 5 alloy.

[0058] • C3: getter module in a cylindrical block configuration (Figure 11) made of ZrVTiAl alloy.

[0059] Table 1.

[0060] Samples SI, S2 and comparative example Cl, all in a disk configuration having the same macrostructure, highlight the impact of the microstructure on getter module performance. Indeed SI, S2 and Cl have been realized by additive manufacturing techniques modulating the different parameters in order to obtain different morphologies, different microstructures and consequently different O / T ratio values. At equal T, samples SI and S2, having higher c thanks to a much larger microscale porosity and microscale surface area, are within the optimal O / T range encompassed by the appended claims, whereas Cl is below it. In particular it can be observed that SI, S2 pumping performances are greatly superior compared to those of Cl.

[0061] In parallel, samples S3-S5 and comparative example C2 and C3, having a high microstructure surface area, highlight the impact of the macrostructure on getter module performance. Indeed, comparative examples C2 and C3 fall outside the optimal O / T range and their pumping performances are lower compared to samples S3-S5. The pumping performances of samples S3-S5 are clearly better than commercially available getter modules typically used in a getter pump represented by C3, whose manufacturing technique results in a high but not efficiently arranged microscale porosity and microscale surface area, as clearly evidenced by the SEM images (see Figures 12-14 representative of samples according to the invention compared with Figures 18-20 relative to the comparative example C3). Thus, the performances of samples S3-S5 clearly prove that a good synergy between macroscale and microscale structure is the key for an effective getter module.

Claims

1. CLAIMS1. A high and ultra-high vacuum getter module (1) made of non-evaporable getter material having:- a macroscale surface area corresponding to the effective surface area of the module (1) considered as perfectly smooth,- a microscale surface area corresponding to said macroscale surface area and the area of microscale cavities resulting from an interconnected microscale porosity of the microstructure of the module (1),- a macroscale volume corresponding to the volume occupied by the module (1) considered as perfectly smooth, excluding any possible empty space contained within its outer limits,- an encumbrance corresponding to the volume occupied by the module (1) considered as solid and perfectly smooth, including the volume of possible macroscale cavities (3, 6) making up a macroscale porosity of the module (1) but excluding the extravolume possibly occupied within its outer limits by other elements of a getter pump, whereby the encumbrance is equal to said macroscale volume plus the volume of the possible macroscale porosity, wherein- the microstructure of the module (1) is characterized by cavities with a characteristic dimension comprised between 50 and 500 pm,- the macroscale porosity of the module (1) is characterized by macroscale cavities (3, 6) with a cross-section comprised between 3 mm2and 2000 mm2, and- the module (1) has a O / T ratio comprised between 7 and 80, preferably between 10 and 30, where c is defined as the ratio between said microscale surface area and the macroscale surface area, and T is defined as the ratio between the macroscale volume and said encumbrance.

2. A getter module (1) according to claim 1, wherein it further comprises a macroscale porosity formed by a plurality of radial macroscale cavities (3) formed in the external sides of the module (1) and a plurality of longitudinal macroscale cavities (6).

3. A getter module (1) according to claim 2, wherein said plurality of macroscale cavities (3, 6) are interconnected to each other.

4. A getter module (1) according to claim 2 or 3, wherein the macroscale cavities (3, 6) have a cross-section comprised between 19 mm2and 710 mm2.

5. A getter module (1) according to claim 4, wherein the macroscale cavities (3, 6) are characterized by an irregular, polygonal, elliptical or circular cross-section.

6. A getter module (1) according to any of the previous claims, wherein its microstructure is characterized by the presence of getter micro-particles with a diameter comprised between 5 and 50 pm connected to the microstructure in a coral-like framework.

7. A getter module (1) according to any of the previous claims, wherein it is characterized by a bulk density comprised between 0.4 and 3.5 g / cm3.

8. A getter module (1) according to any of the previous claims, wherein it is made of a material selected in the group consisting of Ti, Zr, V, Hf, Nb and their alloys based on them as main element.

9. A getter module (1) according to claim 8, wherein the alloys further comprise at least an element selected among Al, Mo, Si, Fe, Ni or Co.

10. A getter module (1) according to claim 9, wherein the alloys are selected in the group consisting of TiAIV, TiMo, TiSiVFeAl, ZrVTi, ZrTiVAl, ZrVFe, ZrCo, ZrAl, ZrFe and ZrNi.

11. A getter module (1) according to any of the previous claims, wherein it is shaped like a cylinder, a disk or a block.

12. A getter module (1) according to any of the previous claims wherein it is made by additive manufacturing, Metal Injection Molding (MIM), Suspension Plasma Spray (SPS) or binder jetting.

13. A getter module (1) according to claim 12, wherein the additive manufacturing method is selected in the group consisting of Laser Powder Bed Fusion (L-PBF), Electron Powder Bed Fusion (E-PBF), Digital Light Processing (DLP), Stereolitography (SLA), Fused Deposition Modelling (FDM) and Direct Energy Deposition (DED).

14. A getter pump comprising at least a getter module (1) according to any of claims 1 to 13 and at least an internal or external resistance heater.

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