GB2619340A

GB2619340A - Vacuum component and vacuum apparatus

Info

Publication number: GB2619340A
Application number: GB2208125.1A
Authority: GB
Inventors: David Smith Paul; Charles Lamb Peter
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2022-06-01
Filing date: 2022-06-01
Publication date: 2023-12-06
Also published as: FR3136263B3; JP3246256U; GB202208125D0; DE202023102974U1; FR3136263A3; CN220435043U; CZ37705U1

Abstract

A vacuum component for a vacuum apparatus, such as a tube 10, comprises a wall element 12 having an outer surface 14 outside the vacuum and an inner surface 16 inside the vacuum, a layer heating element 20, such as a metallic or ceramic resistive heater, connected to the outer surface, and a non-evaporable getter (NEG) material layer 26 connected to the inner surface at a position corresponding to the position of the heating element. The NEG material layer may comprise a dense NEG material layer 28 and a columnar NEG material layer 30, which layers may cover the complete inner surface of the component. Thermal insulation may be included to provide a thermal barrier to prevent heat from the heating element spreading to other components of the vacuum apparatus.

Description

Intellectual Property Office Application No G132208125.1 RTM Date:23 November 2022 The following term is a registered trade mark and should be read as such wherever it occurs in this document:

KANTHAL

Intellectual Property Office is an operating name of the Patent Office www.gov.uk /ipo

VACUUM COMPONENT AND VACUUM APPARATUS

The present invention relates to a vacuum component for a vacuum apparatus and a vacuum apparatus having such a vacuum component.

When objects are placed under vacuum, gas embedded within the material and on the surface, evolves from their surfaces. The generation of gas by this process is known as outgassing. Outgassing becomes a progressively significant proportion of the total gas load once a vacuum chamber is roughed down to below 0.1 mbar. For ultra-high vacuum systems (10-7 mbar or less), outgassing is the most important factor influencing degassing and the time to ultimate pressure.

Outgassing can be reduced by eliminating elastomer, hydrocarbon oil and greases from the vacuum pumps; avoiding other materials known to have poor outgassing performance, such as mild steel or porous surfaces; and using clean-room techniques to avoid contamination.

Traditional heat sources may comprise wire heating elements built into the 5 vacuum system or a component thereof or tapes, cables and bands that are attached to or wound round the system's external surfaces, which are in turn covered in lagging or other insulation.

Traditional heating methods of this type have been found to present certain disadvantages. For instance, when a heating cable is employed it may be difficult to achieve uniform contact between heat source and the surface: resulting in variable surface temperatures and poor heat transfer.

Depending on the specifics of the system, cold spots may not degas adequately, or conversely may facilitate condensation or sublimation, which in turn may have a deleterious effect on the overall system pressure and/or performance. Quilted jacket heaters ameliorate some of these problems. -2 -

In certain applications it is desirable to provide supplementary pumping and measures how to reduce outgassing from pipework in narrow tubes and inaccessible locations. One example of this being SEM columns where in some circumstance the system is pumped down with a TMP which is then turned off to minimise vibrations and then mechanically passive pumps in the form of NEG (Non Evaporable Getter) or Ion pumps are employed to maintain high vacuum/low pressures during measurement. In many cases access is restricted, and the passive pumps are connected at some distance from the column via long thin tubes reducing the pump performance of those pumps.

Prior to use, any NEG material must be activated by heating it to relatively high temperatures above 200°C in a low pressure (<1E-6mbar) environment. However, conventional heating is sometimes not possible in inaccessible areas of the vacuum apparatus and usually the heat is not localized to the NEG material alone. This non-localisation of the high temperature region causes excessive outgassing from other components which may partially saturate or poison the NEG coating during the cooldown cycle.

The use of a multilayer heater coating deposited on an external surface of vacuum components has been previously described in GB2569996A to initiate out-gassing of the vacuum components prior use. However, even when heating up the vacuum component initially for degassing, the material to be used by the vacuum apparatus is limited such that use of porous material in the vacuum apparatus is usually not possible.

In addition, even for usual vacuum materials such as stainless steel or aluminium, outgassing is a time-consuming process. Furthermore, accumulation of contaminants over time in these materials is possible and thus, the process of outgassing must be repeated. This again causes the problems if a passive pump is used since the material of the passive pump might be saturated or poisoned. -3 -

Thus, it is an object of the present invention to provide a vacuum component for a vacuum apparatus for generating and maintaining an ultra-high vacuum.

The problem is solved by a vacuum component according to claim 1 and a vacuum apparatus according to claim 15.

According to the present invention the vacuum component for a vacuum apparatus comprises a wall element having an outer surface outside the vacuum and an inner surface inside the vacuum. Thus, the outer surface may exhibit ambient pressure wherein the inner surface may exhibit vacuum and is an interior surface of the vacuum component and/or the vacuum apparatus. Further, a layer heating element is connected to the outer surface to heat the vacuum component. According to the present invention an NEG material layer is connected to the inner surface at a position corresponding to the position of the layer heating element. Thus, the area covered by the layer heating element at least partially and preferably fully overlaps with the area covered by the NEG material layer at opposite sides of the wall element. By the layer heating element, the NEG material layer can be activated. Thus, with the direct combination of the layer heating element and the NEG material layer, a passive vacuum pump inside the vacuum component is provided which can be activated. At the same time the NEG material layer may act as barrier layer to the material of the wall element preventing excessive outgassing of the wall element. Thus, by the layer heating element initial degassing of the wall element of the vacuum component can be reduced. In addition, due to overlap of the layer heating element and the NEG material layer the heat is localized to the NEG material layer preventing overheating of other components of the vacuum apparatus. Therein, the layer heating element may provide a homogenous heating allowing a homogenous activation of the NEG material.

Preferably, the heating element is a resistive heater or a conductive heater. -4 -

Preferably, the layer heating element is built according to GB 2569996, wherein the content of this application is fully incorporated herein by reference.

Preferably, the layer heating element covers the complete or almost complete outer surface of the vacuum component. Thereby, homogenous heating of the wall element of the vacuum component is provided and degassing of the vacuum component is possible.

Preferably, the heating element comprises a heating layer coated onto the outer surface and preferably separated from the vacuum component by an electrical insulator layer. Thus, starting from the outer surface first there may be an electrical insulator layer followed by a heating layer built as resistive heating layer or conductive heating layer.

Preferably, the NEG material layer covers the complete or almost complete inner surface of the vacuum component. Thus, the complete or almost complete inner surface of the vacuum component is either used for passive pumping and/or a complete barrier is provided preventing or minimizing outgassing of the vacuum component.

Preferably, the NEG material layer has a thickness between 100nm and 1000nm, more preferably between 300nm and 1000nm and most preferably between 400nm and 600nm.

Preferably, the NEG material layer is a quaternary alloy based for example on Ti-Zr-Hf-V but could also be any tertiary alloy such as Hf-Zr-V, Ti-Zr-Hf, Ti-HfV, Ti-Zr-V, a binary alloy for example Zr-V or single element for example Zirconium. The quaternary alloy Ti-Zr-Hf-V might be preferred as it has improved pumping speed at relatively low activation temperatures (150°C to 200°C). -5 -

Preferably, the NEG material layer comprises a dense NEG material layer acting as a barrier layer. Additionally, or alternatively the NEG material layer comprises a columnar NEG material layer providing an increased surface due to the surface structure of the columnar NEG material layer in order to increase pump performance of the NEG material.

Preferably, the NEG material layer comprises at least two layers starting from the inner surface of the wall element. A first layer is a dense NEG material layer acting as a barrier and a second layer is a columnar NEG material layer. Thus, by the combination of these two layers at the same time outgassing of the wall element of the vacuum component is prevented or minimized and sufficient pump performance of the NEG material is enabled.

Preferably, the NEG material layer and/or the layer heating element are partially and preferably fully surrounded by one or more thermal insulators. By the thermal insulators overheating of other components of the vacuum apparatus connected to the vacuum component are prevented. At the same time unintentional outgassing of those parts are also prevented or minimized. At the same time the heat generated by the layer heating element is localized to NEG material layer enhancing efficiency of the activation of the NEG material layer.

Preferably, the one or more of the thermal insulators are a thermal mass. The thermal mass might be one or more flanges if the vacuum component is a pipe. By the flanges additional material is present having an increased heat capacity compared to the wall element reducing heat transfer. At the same time due to the increased surface of the flanges, cooling of the thermal masses is enabled. Therein, in particular thermal masses may have a roughened outer surface or cooling fins at the outer surface to be able to efficiently dissipate heat to the ambient. -6 -

Preferably, the one or more thermal insulators are a thinned wall section. By the thinned wall section heat conduction is reduced. Therein, the thinned wall section may have a wall thickness compared to the wall element of less than 80%, preferably less than 60% and more preferably less than 40%. The lower limit is only set by the stability of the vacuum component.

Preferably, the one or more thermal insulator is an insulation material with lower heat conductivity compared to the material of the component and/or the wall element.

Preferably, the thermal insulation material is a ceramic material or plastic, wherein the thermal insulation material at the inner surface is preferably covered by the NEG material layer.

Preferably, the vacuum component is built as a tube.

Further, the present invention relates to a vacuum apparatus comprising at least one vessel containing a vacuum and at least one vacuum pump connected to the vessel. Therein, the vacuum pump may be built as turbomolecular vacuum pump. Further, the vacuum apparatus comprises a vacuum component as described above. In particular, the vacuum component is a tube connecting the vessel with the vacuum pump.

In the following the present invention is described in more detail with reference to the accompanying figures.

The figures show: Figure 1 a first embodiment of the present invention, Figure 2 a further embodiment of the present invention, -7 -Figure 3 a further embodiment of the present invention and Figure 4 a detailed view of the present invention.

Referring to figure 1 showing a vacuum component according to the present invention built as tube 10. The tube 10 has a wall element 12 having an outer surface 14 and an inner surface 16. By the wall element an inner volume 18 is defined. In the mounted state a vacuum is presented in the inner volume 18. Although, figure 1 shows the vacuum component of the present invention as a tube, other vacuum components of a vacuum apparatus can also be used. For example, an SEM column could be used as vacuum component.

The outer surface 14 of the tube 10 is covered by a layer heating element 20. Therein, the layer heating element may be directly coated onto the outer surface of the tube 10. Therein, the layer heating element may be built according to GB 2569996. As detailed shown in figure 4, the layer heating element 20 may comprise at least one electrical insulator layer 22 directly connected to the wall element 12 of the tube 10. On top of the electrical insulator layer 22, a heating layer 24 is built preferably by coating. The heater layer 24 may be built as conductive heater layer or resistive heater layer. Therein, the electrical insulator layer 22 may comprise a material selective from the group consisting of a ceramic, a polymer or a polymer matrix composite. Therein, the ceramic may be selective from the group consisting silicone carbonite, or a nitrate, alumina, aluminum nitrate, spine!, mullite. Alternatively, the electrical insulator layer 22 may be a polymer selected from the group of liquid crystal polymers, including aromatic polyamides and aromatic polyesters, aromatic polyimides, polyamides, polysulpones, polyethylenimines, and polyether ether ketone (PEEK), or derivatives or copolymers thereof. A preferred polyimide may comprise poly(4,4'-oxydiphenylenepyromellitimide). Alternatively, polyamide nylon resins or polybutylene terephthalate resins may be selected. The polymers may additionally -8 -include one or more from the group consisting antistatics, antioxidants, mould release agents, flameproofing agents, lubricants, colorants, flow enhancers, fillers, including nanofillers, light stabilizers and ultraviolet light absorbers, pigments, and plasticisers. In embodiments, the polymer may be a composite comprising a polymer 30 matrix and a dispersed phase which increases the temperature resistance of the polymer matrix: glass fibre reinforced polymers and carbon fibre reinforced polymers are particularly preferred.

Preferably, the heater layer 24 is metallic or ceramic. Preferably, the heater layer 24 is metallic comprise a material selected from the group consisting of nichrome, titanium alloys, kanthal, cupronickel, platinum, iridium, rhenium, palladium, rhodium, gold, copper, silver, tungsten and alloys thereof. Alternatively, heater layer 24 is ceramic and selected from the group consisting of molybdenum disilicide or a positive temperature coefficient ceramic, such as barium titanate or lead titanate.

Preferably, the insulation layer 22, heater layer 24 and/or any further outer insulation layer (not shown) are deposited using one or more of the techniques selected from the group consisting of high velocity oxygen fuel (HVOF), electrophoretic deposition (EPD), low temperature deposition (LPD), electron beam physical vapour deposition (EBPVD), air plasma spray (APS), electrostatic spray assisted vapour deposition (ESAVD), direct vapour deposition, and combinations thereof.

According to the present invention, an NEG material layer 26 is connected to the inner surface 16 of the wall element. Therein, the NEG material layer 26 may comprise a first layer 28 built as dense NEG material layer acting as a barrier to prevent or minimize outgassing of the wall element 12. Therein, the dense NEG material layer 28 is directly connected onto the inner surface of the wall element. The dense NEG material layer may be built by coating. The NEG material layer 26 may comprise a second NEG material layer built as columnar -9 -NEG material layer 30, wherein by the columnar NEG material layer an increased surface is provided in order to enhance pump performance of the NEG material layer. Although figure 1 shows that the NEG material layer 26 has a first NEG material layer and a second layer, the NEG material layer 26 may only comprise one NEG material layer, either a dense NEG material layer or columnar NEG material layer) or may comprise more than two NEG material layers stacked above each other.

Therein, it is shown that the layer heating element 20 covers almost the complete outer surface of the wall element. In addition, the position of the layer heating element 20 corresponds to the position of the NEG material layer 26 at opposite sides of the wall element. Thus, homogenous heating of the NEG material layer is possible. In addition, the NEG material layer extends over the complete or almost complete inner surface of the pipe 10 in order to efficiently prevent outgassing of the pipe 10 into the vacuum and/or increase pump efficiency of the NEG material layer.

The pipe 10 has a first end 32 and a second end 34, wherein at the first end 32 and the second end 34 flanges 36 are connected to connect the pipe for example to a vessel or a vacuum pump. By the flanges 36 a thermal mass is provided limiting the heat provided by the layer heating element 20. At the same time by the flanges 36 the external surface is increased in order to allow efficient heat dissipation by the flanges 36. Thus, by the flanges 36 a thermal barrier is provided preventing heat from the layer heating element 20 to spread to components attached to the first end 32 or the second end 34 of the tube 10. Thus, the heat of the layer heating element 20 is localized to the pipe 10, thereby providing homogeneous and efficient heating of the NEG material layer 26.

In the following it is referred to the figure 2, wherein same or similar elements are denoted with identical reference signs. In the embodiment of figure 2, the layer heating element 20 is limited by thermal insulators built as thinned wall -10 -sections 38. The thinned wall sections are built as conferential grooves in the wall element 12. Thus, by the thinned wall section 38 heat conductivity across these sections is reduced confining the heat produced by the layer heating element 20. Thus, efficient and homogenous heating of the NEG material layer 26 is provided. Therein, the thickness of the wall in the thinned wall section 38 may have less than 80%, more preferably less than 60% and most preferably less than 50% of the wall thickness of the remaining wall element 12.

Referring to figure 3, wherein same or similar elements are denoted with identical reference signs. In the embodiment of figure 3, the layer heating element 20 is limited by insulators built by an insulation material 40. In particular, the insulation material 40 may be a ceramic such as aluminium oxide but is not limited to this specific choice. In particular, the insulation material 40 is selected to have a reduced heat conductivity compared to the material of the wall element 12. Thus, heat conduction across the insulation material 40 is prevented or reduced. Heat of the layer heating element 20 is confined to the component 10 in order to provide efficient and homogenous heating of the NEG material layer. Therein, it is noted that the inner surface of the insulation material 40 extends to the inner surface of the wall element 12. Thus, part of the inner surface of the component 10 is built by the material of the insulation material 40. In order to prevent outgassing or even leakage via the insulation material, which might be porous ceramic, the insulation material 40 is coated by at least one NEG material layer and preferably by a dense material layer as barrier.

Reference list 12 wall element 14 outer surface 16 inner surface 18 interior volume layer heating element 22 electrical insulator layer 24 heater layer 26 NEG material layer 28 dense NEG material layer columnar NEG material layer 32 first end 34 second end 36 flange 38 thinned wall section insulation material

Claims

-12 -CLAIMS1. Vacuum component for a vacuum apparatus, comprising a wall element having an outer surface outside the vacuum and an inner surface inside the vacuum, a layer heating element connected to the outer surface, and an NEG material layer connected to the inner surface at a position corresponding to position of the heating element.
2. Vacuum component according to claim 1, wherein the layer heating ele-ment is a resistive heater or conductive heater.
3. Vacuum component according to claims 1 or 2, wherein the layer heating element covers the complete outer surface.
4. Vacuum component according to any of claims 1 to 3, wherein the heating element comprises a heating layer coated on the outer surface.
5. Vacuum component according to any of claims 1 to 4, wherein the NEG material layer covers the complete inner surface.
6. Vacuum component according to any of claims 1 to 5, wherein the NEG material layer is between 100nm to 1000nm thick, preferably between 300nm and 1000nm thick and most preferably between 400nm and 600nm thick.
-13 - 7. Vacuum component according to any of claims 1 to 6, wherein the NEG material layer comprises a dense NEG material layer and/or a columnar NEG material layer.
8. Vacuum component according to any of claims 1 to 7, wherein the NEG material layer comprises at least two layers starting from the inner surface, wherein a first layer is a dense NEG material layer and a second layer is a columnar NEG material layer.
9. Vacuum component according to any of claims 1 to 8, wherein NEG material layer and/or the layer heating element are partially and preferably fully surrounded by one or more thermal insulators.
10. Vacuum component according to any of claims 1 to 9, wherein the one or more thermal insulators are a thermal mass, wherein preferably the thermal mass is a flange.
11. Vacuum component according to any of claims 1 to 10, wherein the one or more thermal insulators are a thinned wall section.
12. Vacuum component according to any of claims 1 to 11, wherein the one or more thermal insulator is an insulation material with low heat conductivity compared to the material of the component.
13. Vacuum component according to claim 12, wherein the thermal insulation material is a ceramic material or plastic, wherein preferably the thermal insulation material at the inner surface is covered by the NEG material layer.
14. Vacuum component according to any of claims 1 to 13 built as tube.-14 -
15. Vacuum apparatus comprising at least one vessel and at least one vacuum pump, preferably built as turbomolecular pump, wherein the vacuum apparatus further comprises a vacuum component according to any of claims 1 to 14.