WO2010034634A1

WO2010034634A1 - Refrigeration apparatus

Info

Publication number: WO2010034634A1
Application number: PCT/EP2009/061848
Authority: WO
Inventors: Lothar Siegert; Christine TÄSCHNER
Original assignee: Oerlikon Leybold Vacuum Gmbh; Leibniz-Institut Für Festkörper- Und Werkstoffforschung Dresden E.V.
Priority date: 2008-09-24
Filing date: 2009-09-14
Publication date: 2010-04-01
Also published as: DE102008048789A1

Abstract

The present invention relates to an apparatus for the condensation and/or adsorption of gases, particularly in a high vacuum, characterized in that nano-structured carbon particles obtained in particular by way of a CVD or plasma CVD method are connected in a heat-conducting manner to a refrigeration reservoir, which in particular has a temperature of = 20 K.

Description

A refrigeration system

The present invention relates to a device for the condensation and / or adsorption of gases, a method for producing such a device, and a cryopump comprising such a device.

It has long been known that gases and vapors are bound to cooled surfaces. While this effect has been used practically since its discovery for vacuum improvement (cold traps, Baff I es), vacuum generation using cryogenic surfaces, that is, with cryopumps, has only gained increasing interest since 1957 (K. Jousten: "Wutz Manual Vacuum Technology, Theory and Practice ", Vieweg Verlag 2004).

According to DIN 28400, Part 2, "a cryopump is a gas-binding vacuum pump in which the gases condense on frozen surfaces and / or adsorb to deep-frozen sorbents (solid or condensate). The condensate and / or adsorbate is maintained at a temperature at which the equilibrium vapor pressure is equal to or less than the desired low pressure in the vacuum chamber. The cryopump works in the area of high vacuum and ultrahigh vacuum. " Cryo groups are only those vacuum pumps operating in the range of less than 120 K. The selected temperature depends on the type of gas to be pumped off.

Condensation pumps operating at higher temperatures are referred to simply as steam condensers or as condensers.

The capacity of a cryopump is limited because the pumped gas remains bound to the cold surface. In high and ultra-high vacuum, the current main field of application of the cryopump, this is not a disadvantage because of the small amount of gas produced. Undoubtedly, however, the application of low temperatures for vacuum processes at higher pressures will become increasingly important. For short pumping times, the limited capacity of a cryopump may not be disturbing. However, continuous operation at pressures p <ICT ² Pa is only possible with regular regeneration of the pump, the regeneration period is determined by the gas attack in the pump and is the shorter the more gas the cryopump must bind.

In the binding of gases to cold surfaces, various mechanisms are effective. Besides condensation, cryotrapping and cryosorption occur. In practice, it is often not possible to clearly separate these mechanisms. Cryotrapping is understood to mean the condensation of a lower-boiling, and accordingly less condensable, gas in admixture with another, higher-boiling gas. In cryosorption, the lower-boiling gas is deposited on a condensate layer deposited prior to the start of the pumping process höhersiedeπden gas or bound to a cooled solid adsorbent.

The main problem in the application of solid adsorbents (molecular sieves, activated carbon) to reduce the pressure in the high and ultra high vacuum by cryosorption is the heat transfer from the adsorbent to the Kaitfläche. Since at low pressures the Wärmeleϊtung by the gas to be pumped is negligible, the cooling can be done only by heat conduction in the adsorbent itself. For this purpose, a good heat-conducting contact of the adsorbent with the cold surface is required, which is usually made by gluing. The selection of a suitable adhesive must be ensured. The Adsorptionsmϊttei must be degassed as far as possible by heating before cooling the apparatus. In cryogenic technology, this method of cryosorption is expected to become increasingly important.

As Adsorptionsmittel for vacuum generation, the long-known activated carbon and the molecular sieves 4A, 5A and 13X have proven particularly useful. Activated carbon generally has a higher adsorption capacity, measured in Pa m ³ per kg of adsorbent, than the molecular sieves (RA Haefer: "Cryo-Vacuum Technology, Basics and Applications", Springer Verlag 1981), under normal conditions Preferred molecular sieves.

The gas storage capacity at cryogenic temperatures is greater, the greater the active surface of the activated carbon and the lower the temperature of the carbon particles, usually less than about 50 K. The gas occupancy takes place in monolayers on the carbon.

The production of such cold surfaces is carried out by sticking of activated carbon granules, activated carbon fine chippings and other bonded activated carbon particles, but is associated with a high manual effort. In addition, the usable carbon surface is partially ineffective by the adhesive used. In addition, manufacturing technology is limited to flat or only slightly curved metallic surfaces. The adhesive also has poor thermal conductivity.

In addition to simplifying such a production process or providing a simpler alternative process, it is desirable to further increase the surface area of the adsorbent used in order to be able to adsorb and / or condense correspondingly larger amounts of gas.

It is therefore an object of the present invention to provide a device with such an adsorbent, which has a (substantially) larger surface area, based on the masses of the adsorbent, than is the case with the use of various activated carbon variants of the prior art of the FaM. Moreover, it is an object of the present invention to provide the simplest possible method for producing such a device.

The problem underlying the present invention is achieved in a first embodiment by a device for the condensation and / or adsorption of gases, in particular in a high vacuum, thereby characterized in that nanostructured carbon particles, which are obtained in particular by means of CVD or plasma CVD method, heat-conducting with a cold reservoir, which in particular has a temperature of <20 K, are connected.

The state-of-the-art process technology used in the bonding of activated carbon granulate uses an adhesive with a thermal conductivity of only 1.1 to 1.4 W / m ^* K on copper sheet with about 400 W / m ^* K. This results in a significant loss in the heat transfer from the copper sheet over the glue on the activated carbon.

Direct deposition of nanostructures has the significant advantage of directly depositing on copper sheet (or other specified substrate materials) with high thermal conductivity a layer that has very high thermal conductivity and thus provides direct heat transfer between highly thermally conductive materials ,

Nanostructured particles in the context of the present invention are preferably those which have an average particle diameter of from 1 to 100 nm, more preferably from 1 to 50 nm and an average particle length of from 1 .mu.m to a few 1000 .mu.m, preferably from 10 .mu.m to 1000 .mu.m. These are preferably applied directly to the substrate of the cold reservoir by means of OJD or plasma CVD.

For the purposes of the present invention, a cold reservoir means a sufficiently large supply of a substance which, if released to the nanostructured carbon particles (ie heat absorption by them), its temperature - if at all - only changes by a few degrees, preferably by less than 3 K, more preferably by less than 1 K ₇ . The terms "cooling output" and "heat emission" again refer to the cooling or heat flows occurring during normal operation of the device according to the invention - the cold / heat peaks occurring during their startup (eg when starting up a cryopump) should preferably not be included be.

"Conductive" means, in view of the bond between the nanostructured carbon particles and the cold reservoir, that it allows temperature equilibration between the two at a sufficient rate, the term "compound" encompassing all materials that are nano-structured in a cold / heat conduction Carbon particles are (have to) pass to the cold reservoir.

A temperature compensation with sufficient speed preferably results when the thermal conductivity λ of the compound is> 1 W / (mx K), in particular> 10 W / (mx K), in each case based on the temperature of the cold reservoir. The thermal conductivity is of little significance The nanostructured carbon particles are subjected to very little thermal stress, and where there is no continuous heat flow, no significant temperature difference is created by heat transfer. In addition, the initial cooling mass of the nanostructured carbon particles is greater than the mass of the "cold reservoir".

For the purposes of the present invention, gasses are gaseous substances under normal conditions ( ^20.degree. C., 1013 mbar) understood, ie in particular the components of the air, such as oxygen, nitrogen, carbon dioxide, noble gases, methane, hydrogen.

The nanostructured carbon particles are preferably arranged with respect to the cold reservoir such that condensation and / or adsorption of gases can only occur on the nanostructured carbon particles, i. H. in other words, that access of gases to the cold reservoir is preferably prevented.

The cold reservoir preferably has a temperature of <20 K. As mentioned above in the explanation of the prior art, a decrease in the temperature of the cold surface or the nanostructured carbon particles, on which the condensation and / or adsorption of the gases is to take place, is accompanied by an increase in the suction power. Lower temperatures of the cold reserver are therefore preferred,

Nanostructured carbon particles have a comparably large active surface in comparison to various activated carbon variants, in each case based on their masses. However, due to the structure of the nanostructured carbon particles, which is much finer and more open to the vacuum space than an activated carbon macroparticle, an improved adsorption mechanism results. Thus, nanostructured carbon particles are capable of condensing and / or adsorbing a much larger amount of gas. Known activated carbon surfaces are cumbersome, bulky and usually executable only in one layer within a cryopump or a Vakuumrezϊpienten. With a nanostructured carbon particle coated tape or thin sheet metal can fill the limited volume much better, adhesion of the nanostructured carbon particles is given even with subsequent bending. The nanostructured carbon particles are preferably selected from the group consisting of single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), carbon fibers, carbon layers (comprising nanostructured carbon particles), carbon nanotubes. Slats or fullerenes.

With a device according to the invention, it is now possible to ensure a longer operating time under high vacuum at pressures p <1 (T ² Pa) than is achievable with known pumps In particular, a corresponding device in the range of molecular gas particle flow in a pressure range <iθ ^"5 Pa be used.

In the exact embodiment of the device according to the invention, two variants have been found to be preferred:

In the first variant, the nanostructured carbon particles are applied to a substrate via which the nanostructured carbon particles are heat-conductively connected to the cold reservoir.

The (support) substrate preferably comprises at least 600 ° C. temperature-resistant metallic and / or ceramic materials selected from the group comprising: Molybdenum; Tungsten; Stainless steel alloys; Nickel; Nickel alloys; Iron; Iron alloys; Cobalt; Cobalt alloys; Copper, copper alloys, aluminum, aluminum alloys; Al ₂ O ₃ ; Si ₃ N ₄ ; Carbon fiber composite materials; Glass fiber composite materials; Composite materials of glass, ceramics or metal. The deposition of nanostructured carbon particles by the CVD method is carried out at relatively high temperatures from at least 600 ⁰ C.

Preferably, the substrate is a metal, a metal band, a composite material (for example carbon fiber reinforced materials) or a ceramic. Good thermal conductivity is advantageous because it represents at least part of the above-mentioned connection between nanostructured carbon particles and cold reservoir.

Furthermore, it is preferred that at least one additional wholly or partially covered layer of metal / s, metal nitride (s) and / or metal oxide (s) is present between the substrate and the nanostructured carbon particles. Such an intermediate layer, which essentially has nucleation or adhesion promoter functions, is particularly preferred inasmuch as it is suitable for the formation of (specific) nanostructured carbon particles in the preparation / application or for a firm and stable connection to the nanostructured nanopatterns applied to the substrate Carbon particles ensures. In addition, such intermediate layers may also have anti-corrosion properties for the underlying substrate material.

An embodiment of such an embodiment of the present invention is shown in FIG. As stated above, the nanostructured carbon particles 1 can comprise or even consist entirely of one or more-walled carbon nanotubes, carbon fibers, carbon layers, carbon powders, carbon fins or fullerenes. The optional intermediate layer 2 essentially has nucleation. Adhesion promoter properties and / or used for corrosion protection of the substrate 3. The intermediate layer 2 comprises at least one metal, metal nitride and / or metal oxide. A typical example in this context is a nickel layer for corrosion inhibition of the underlying substrate 3. The substrate 3 must be connected to the cold generator, usually the thermal contact surface of a cold head 5, which in turn good thermally conductive contact layers 4, such as indium, indium or the like good thermally conductive and surface roughening balancing soft material may find application.

A second type of embodiment of the device according to the invention is characterized in that the nanostructured carbon particles are arranged in a container which has a discharge protection preventing the outlet of the nanostructured carbon particles from the container and a gas inlet opening.

In this case, the nanostructured carbon particles are preferably sintered, pressed or compacted while retaining at least 80%, more preferably at least 90%, of their porosity. In this way, can be accommodated in the container amount of nanostructured carbon particles and thus in total the Condensation and / or adsorption significantly increase the available surface area.

Both the outlet protection and the gas inlet opening are preferably formed in a single membrane, such that their pores, although permeable to the gases to be condensed and / or adsorbed, are impermeable to the nanostructured carbon particles.

Corresponding embodiments can be found in FIGS. 2 and 3.

The container 10 in Figure 2 may be configured in any shape (cylindrical, cubic, etc.) with the gas inlet opening 13 connected to the exit guard 11 to prevent the nanostructured carbon particles 12 from escaping from the container. The container is brought into thermal contact on at least one side surface with the quill head contact surface.

In Fig. 3, the container 14 has a gas-permeable membrane 15 for the gases to be bound to the nanostructured carbon particles. In this case, the pore size of the membrane 15 is selected so that, although the gas particles, but not the nanostructured carbon particles can pass. In this way, a gas inlet into the container is made possible, however, the escape of nanostructured carbon particles prevented.

One or more containers can be thermally and mechanically coupled to the cold head, whereby an indirect coupling over a plurality of container levels is also possible. In a further embodiment, the object underlying the invention is achieved by a method for producing such a device, which is characterized in that nanostructured carbon particles are brought into contact with a cold reservoir. The direct application of the carbon particles to the substrate makes it possible to dispense with adhesion promoters, for example adhesives or similar matrices. As a result, an improved compared to the prior art, very good heat transfer between the nanoparticles and the substrate is ensured.

The nanostrukturlerten carbon particles are preferably applied by CVD or plasma CVD method to the optionally at least one additional wholly or partially coated layer of metal / s, metal nitride / s and / or metal oxide / s having substrate.

Furthermore, it is preferred that before or during the application of the nanostructured Kohlenstoffteiichen further doping and / or catalyst compounds applies, in particular Li, Ti, Fe, Cu, Cr, Co and / or Ni compounds, By such compounds or elements is the Training of specific nanostructures favors or causes or increases the speed of education overall.

In a further embodiment, the object underlying the invention is achieved by a cryopump, which comprises a device according to the invention as described above.

Claims

claims

1. Device for condensation and / or adsorption of gases, in particular in a high vacuum, characterized in that nanostructured Kohienstoffteilchen, which are obtained in particular by means of CVD or plasma CVD method, heat-conducting with a Käitereservoir, which in particular has a temperature of <20 K, are connected.

2. Device according to claim 1, characterized in that the carbon particles are selected from the group comprising: single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon fibers, carbon layers, carbon fins or fullerenes.

3. Device according to one of claims 1 to 2, characterized in that it comprises a substrate on which the carbon particles are thermally conductively connected to the cold reservoir.

4. Device according to one of claims 1 to 3, characterized in that the substrate comprises at least 600 ⁰ C temperature-resistant metallic and / or ceramic materials.

5. Device according to claim 4, characterized in that the temperature-resistant materials are selected from the group comprising: Molybdenum; Tungsten; Stainless steel alloys; Nickel; Nickel alloys; Iron; Iron alloys; Cobalt; Cobalt alloys; Copper, copper alloys, aluminum, aluminum alloys; AI ₂ O ₃ ; Si3N4; Carbon fiber composite materials; Glass fiber composite materials; Composite materials of glass, ceramic or metal.

6. Device according to one of claims 1 to 5, characterized in that the substrate is an arbitrarily shapeable metal sheet, metal strip or a fitting.

7. Device according to one of claims 4 to 6, characterized in that the carbon particles are connected to the substrate via at least one additional wholly or partially coated layer of metal / s, metal nitride / s and / or Meta! Lox / s.

The apparatus according to any one of claims 1 to 3, comprising a container of particles of carbon particles, wherein the container has an exit guard preventing the exit of the carbon particles from the container and a gas inlet opening.

9. Apparatus according to claim 8, characterized in that the carbon particles are sintered, pressed or compact while maintaining at least 80% of their porosity.

10. The device according to claim 8, characterized in that the Kohlenstoffteϊlchen while maintaining at least 90%, sintered their porosity, pressed or compacted.

11. Device according to one of claims 8 to 10, characterized in that the outlet protection and the Gaseintrϊtts- opening comprises a membrane whose pores are permeable to the gases to be condensed and / or adsorbent and impermeable to the carbon particles.

12. The method according to any one of claims 1 to 11, characterized in that the carbon particles by means of CVD or plasma CVD method on the optionally at least one additional wholly or partially coated layer of metal / s, metal nitride / s and / or metal oxide / / s applying substrate and brings them thermally conductive with a cold reservoir in contact.

13. The method according to claim 12, characterized in that applying during the application of the carbon particles further doping and / or catalyst compounds, in particular Li, Ti, Fe, Cu, Cr, Co and / or Ni-containing compounds.

14. Use of a device according to one of claims 1 to 10 in the region of the molecular gas particle flow in a high vacuum in the pressure range <10 ^{~ 5} Pa.

15. Cryopump comprising a device according to one of claims 1 to 10,