SORPTION PUMP WITH MECHANICAL ACTIVATION OF GETTER MATERIAL AND PROCESS FOR CAPTURING OF ACTIVE GASES

Abstract

A sorption pump working according to the principle of mechanical activation of reactive getter materials at ambient temperature is presented. Pumps of the given type allow maintaining vacuum in different devices and apparatuses by sorption of any active gases with a controllable rate.

Description

I. FIELD OF INVENTION

The present invention relates to the field of vacuum technique, in particular to the field of sorption pumps used for chemical capturing of active gases or vapors and gases of lower activity.

II. BACKGROUND

Sorption pumps are widely used in vacuum technologies for the removal of different gases from the evacuated volume. These pumps are usually subdivided into two types, adsorption pumps and getter pumps.

In the first type, molecular sieves, e.g. porous zeolites with a high surface area, serve as sorbents. Sorbents of the second type are sintered porous materials on the basis of transition metals. These getter materials are also characterized by a high surface area.

As any other type of pumps, sorption pumps have their limitations and disadvantages. Without going deep into the detailed characteristics of adsorption and getter pumps, their common weaknesses can be summarized as follows:

1. The high porosity of their structures with openings for gases and a well developed interior surface makes the conventional gas sorbents, like zeolites and getter materials, rather sensitive to the environment. Even a short exposure of these materials to air deprives them of the sorption ability, which can be restored only by aid of regeneration or reactivation of the corresponding material.

2. At room temperature, the relative sorption capacity of zeolites as well as that of the getter materials produced from transition metals is very low. To increase the sorption capacity of zeolites (physical sorption) it is necessary to cool them down to the temperature of liquid nitrogen, while getter materials (chemisorption) have to be heated to temperatures of 450° C. and higher.

3. A significant disadvantage of the known methods of sorption pumping of residual gases is the lack of control over the sorption process; this is true at least with respect to non-evaporable sorption materials. The gas sorption rate in this kind of pumps slowly but steadily decreases until the saturation state of the gas sorption is approached, and this impedes the stabilization of the pressure in the vacuum chamber at the set level.

Due to the above mentioned disadvantages the design of pumps and of supporting auxiliary devices is more complex, and the operation is more expensive than it could be if suitable changes in methodology are introduced. Besides, the resources of sorption materials are not used in the best way since the materials are not consumed to completion.

Below easy and efficient solutions are described, which allow a significant decrease of production and operational costs for the pumps and also create the conditions for the control and standardization of the processes occurring under vacuum conditions.

III. SUMMARY

The new sorption pumps are based on the method of mechanical activation, consisting of mechanical grinding of the initial getter material directly in the evacuated chambers with their residual gases The mentioned grinding of the solid reagent is performed at room temperature with a rate and in quantities, which are determined by the actual sorption demand at any given moment.

Powders, produced in this manner inside the pump in vacuum, i.e. in situ, can immediately enter into a reaction with the residual gases, i.e. react with them in statu nascendi. These materials differ from all conventional sorption powders in their superb reactivity. This superb reactivity is explained by the fact that apart from the inherent reactivity of powders which is due to the high surface area and various structural defects, the as-ground powders are characterized by a large number of short-lived excitation states (dynamic activation). As a result, even without heating many otherwise endothermic reactions of mechanically activated powders with gases or vapors, e.g. with such low activity gases as nitrogen, methane, heptane, etc. become possible.

The pump according to the present invention with a mechanical activation of the getter material has a simple design. It includes a vacuum tight casing connected to the evacuated chamber and a disintegrator, which brings together initial getter material, a milling tool and an actuator, serving as a source of mechanical energy. The bottom parts of the casing are a reaction zone and a collector of the powder particles, which in some variants of the pumps can be periodically removed.

By such a design, a mutual adjustment of three processes can be achieved: the technique of obtaining the initial getter material in the required shape and structure, the technique of milling this material thereby converting it into the active state, and the sorption process itself, the course of which may be regulated according to the needs of the vacuum chamber using the feedback between the chamber and the actuator.

The initial getter material consists of ingots of a reactive alloy with a high concentration of a reactive metal, preferably of barium or lithium grown in cylindrical crucibles by the method of directional solidification of the melt. The ingots produced in these processes with a high growth rate are characterized by a constant composition along the axis and by a low mechanical strength. Taking into account the geometry of the milling device according to the present invention, this technique provides dimensional uniformity and chemical homogeneity of the powder product throughout the entire process. The geometry of the milling operation is chosen in such a way, that the mechanical tool that cuts and removes the particles of the getter material from the surface is moving in a plane which is perpendicular to the ingot axis. As-prepared microparticles of the reactive alloy, which fall off the treated surface of the ingot, are collected in the reaction zone where they form together with the renewed surface of the ingot a super active getter mass. The amount of the reactive mass depends on the mechanical operation performed by the actuator. Since it is easy to control the work of the actuator, a new operational situation is created, which cannot be attained in conventional sorption pumps with their non-controllable sorption processes. Having subordinated the work of the actuator to the readings of the devices which measure and analyze the state of the gas medium in the evacuated chamber, it becomes possible to change the gettering rate in a wide range for maintaining vacuum at any set level.

Sorption pumps with mechanochemical activation of the getter material described in the present invention have the following advantages over sorption pumps of other types:

1. The controlled pumping speed allowing the regulation of the gas pressure in the vacuum chamber in a programmed way, e.g. changing it according to a certain time law, or keeping it at a set constant value. Moreover, this advantage is achieved without special complications in design and operation and without high costs, but rather in the natural way for the given method of controlling the sorption process by simply changing the rate of milling of the ingot according to measuring devices, which are anyway provided with the vacuum equipment.

2. The easy and inexpensive method of production of reactive ingots with a continuous structure without voids or shrinkage holes. The ingots grown with a high rate in tube crucibles by the method of directional solidification are very convenient for a practical use in sorption pumps: unlike the conventional high porosity getter materials which lose their ability to sorb gases after a brief contact with the air, the monolithic reactive ingots are not susceptible to a short exposure to the air. This facilitates the procedure of recharging the pump with fresh getter material. Besides, the pronounced axis texture of directionally solidified ingots as well as the constant chemical composition along the ingot provide homogeneity to the powder produced from it and the constancy of its sorption properties.

3. Activating the getter material by milling at room temperature makes unnecessary its heating or cooling, which is an important step forward, as there is no need for the corresponding additional equipment, and the process of pumping down residual gases becomes less costly.

4. The mechanochemical activation and the general high reactivity of the employed alloys taken together provide conditions to achieve completeness of the sorption processes at fresh powders of the size from one micron to several hundreds of microns at room temperature. As the reactions between powders and gases in this case take place with a high rate, on the whole the new sorption pumps achieve the highest level of efficiency possible when using getter materials. The selection of the right composition of the reactive alloys further allows to reach an exceptional efficiency. In the present invention the preference is given to eutectics on the basis of lithium or barium, or low-melting intermetallic compounds with a high concentration of the reactive metal. These alloys are easy to mill and are also convenient from the metallurgic point of view due to their low liquidus temperature.

IV. DETAILED DESCRIPTION OF THE INVENTION

Powders, due to their developed surface, are more preferable for sorption processes than other forms of getter bodies, and among different powders those freshly produced mechanically possess the highest reactivity. These as-prepared powders have the highest set of all kinds of structural and electronic defects and are characterized in particular by short-lived excited states. Excessive energy, accumulated by the getter material during its mechanical treatment, is released in the process of gas sorption facilitating a faster and more complete progress of the chemical reactions. The lowering of the activation barriers both for the diffusion of the reagents and for their reactions is the origin of these effects.

The production of super active powders directly in the residual gas environment so that they immediately, in statu nascendi, can enter the reaction with gases, has important consequences. Milling of the ingot in situ provides besides the improvement in the kinetics of the sorption processes also the rare possibility of making the sorption process controllable. The pumping speed R is determined mainly by the value of the sticking coefficient of the sorption surface. This surface consists of two parts, the surface of the powder layer and the surface of the ingot (FIG. 1).

For the value of R the following expression is valid:

R=(α₁A₁+α₂A₂)(kT/2πm)^1/2,

where α₁ is the sticking coefficient of the powder layer, A₁ is the area of the cross section of the inside space of the pump at the level of the reaction zone, α₂ is the sticking coefficient of the ingot surface, A₂ is the area of the ingot surface, k is the Boltzmann constant, T is the absolute temperature, m is the mass of a gas molecule, 0<α₁≦1 and 0<α₂≦1. The values of the coefficients α₁ and α₂ are close to zero in the case of an exhausted powder and of the ingot surface after it reacted with gases. To the contrary, α₁ and α₂ tend to 1 when the material is fresh. The pumping speed R at room temperature depends only on the values of α₁ and α₂, which in their turn depend on the intensity of the mechanical treatment of the ingot. Thus, by controlling the work of the milling tool it is possible to control the value of R, and together with it the pressure of the residual gases in the chamber. According to the way in which the mechanochemical activation is realized in the given invention, there is a wide range of conditions, where the pumping speed R and the rate of milling of the ingot are connected by a linear or close to linear dependence. A very high rate of reaction between gases and barium and lithium alloys, as well as dimensional uniformity and chemical homogeneity of the powder product, are the main factors, which are favorable for establishing this dependence.

A natural sorption limitation for the pumps with mechanical activation of getter material is the incapability of noble gases to form chemical bonds with other substances in normal conditions. While active gases and vapors like O₂, CO, CO₂, H₂, H₂O, H₃N etc. as well as low activity gases like N₂, CH₄, etc. react with barium and lithium especially in their activated state, noble gases are sorbed on the surface only under the influence of physical forces. It could be possible to increase the quantity of the sorbed gas in this case as well, e.g. due to decreasing the size of the powder particles to nanolevel or due to cooling the particles to cryogenic temperatures. However, then the new method would loose its simplicity and attractiveness.

FIG. 2 shows schematically one of the possible variants of carrying out the controlled operation of vacuum pumps. Sorption pumps with getter working material are not applicable for pumping down noble gases, therefore when the technological process requires high vacuum a sorption pump (SP in FIG. 2) should be supported by an additional pump (AP in FIG. 2), capable of removing inert gases from the vacuum chamber. This can be a turbo molecular pump, a diffusion pump, etc. The vacuum chamber can be preliminarily evacuated by any suitable method, also including the third pump, e.g. across the line C (FIG. 2), or using both pumps SP and AP. Then, after the set level is reached, the pressure in the chamber is maintained due to the regulated activity of pumps SP and AP, each of which removes from the vacuum chamber its group of gases by aid of the control system consisting of gas analyzers RGA and two controllers, S and A.

Another possible variant of controlled gas pumping with the help of the sorption pump is shown in FIG. 3. This reflects the case of small vacuum chambers, e.g. used in portable analytical devices. Here noble gases which can get into the vacuum chamber during sampling can be blown out with active or moderately active gases, e.g. nitrogen, carbon dioxide, etc. These gases can enter the chamber from a small bottle through valve 2 and are let out through valve D (FIG. 3). After cleaning the chamber the gas is pumped down by pump SP at closed valve 2 and open valve 1.

In principle the method of mechanochemical activation of monolithic getter bodies by way of their milling is applicable to any metallic materials. However, for a number of reasons ingots of reactive metals are more preferable as initial getter materials. One of the explanations for this preference can be found in FIG. 4, where the dependence q=q(t) is shown for the metals, which are most frequently used in getter technologies. Here t is time, and q is the quantity of a certain gas sorbed at a given temperature by a unit of area of the metal concerned during time t.

FIG. 4 shows kinetic curves q=q(t) at room temperature for the metals concerned, which can be sorted according to their sorption mechanism into three classes [K. Meyer. Physikalisch—chemische Kristallographie, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1968; E. Fromm, E. Gebhardt. Gase und Kohlenstoff in Metallen, Springer—Verlag, Berlin, 1976; A. W. Adamson. Physical Chemistry of Surfaces, John Wiley & Sons, New York, 1982]: into passivating metals (curve 1), the behavior of which is described by the Yelovich equation dq/dt=k₀ exp (−k₁q); metals, which follow the parabolic law q=k₂t^1/2 (curve 2); and finally metals, subordinated to the linear law q=k₃t (curve 3), where k₀, k₁, k₂ and k₃ are proportionality factors. In contrast to the passivating metals, which sorb gases at room temperature only until a surface film saturated with gases is formed (FIG. 4, the point coordinates q₁ and t_p on curve 1), metals of the second and third class sorb gases by a continuous growth of a layer of sorption products on their surface.

Such transition metals as Fe, Mn, Ti, Zr etc. belong to the group of passivating metals. Alkali, alkaline-earth, and many rare-earth metals belong to the class with the surface growth of products (curves 2 and 3, FIG. 4). In the present Description, these two classes are covered by the general term reactive metals.

It is seen from FIG. 4 that starting from a certain time t_r>>t, the relation q<<q₂<q₃ is valid, which is true for powder particles with the typical size of r>>h_p, where r is the mean radius of the getter particle and h_p is the mean thickness of the passivating film. It follows that instead of using nanoparticles of transition metals in gas sorption it is much more advantageous to use microparticles of reactive metals, the production of which is easier, cheaper and can be based on established and widely used methods of mechanical milling of solid bodies.

Therefore, the main argument in favor of reactive alloys is that the maximum of relative sorption activity with powder material of the usual dimensional level from a few microns to some hundreds of microns can be achieved at room temperature. In addition, a number of other advantages of reactive alloys can be identified.

Alloys with a high concentration of the reactive component exhibit moderate melting temperatures, usually about 150° C.-650° C. As a result, instead of complex high-temperature vacuum equipment, which is necessary for the production of materials containing transition metals, in the case of the reactive materials only simple and reliable methods of ampoule techniques for the production of ingots under the conditions of normal atmosphere using laboratory tube furnaces are required.

One more useful feature of the alloys with a high concentration of reactive metal Me used in the present invention is that they can be based on alloys of the eutectic type. (FIG. 5). At least one of the constituent phases, namely, the intermetallic constituent, is characterized by high fragility and low tensile strength, being therefore originally prone to mechanical crashing without special efforts.

The following two factors contribute to a facile milling of the ingot into particles uniform in size: the axis texture, which appears as a result of the solidification of the melt under the conditions of an axis temperature gradient, and the geometry of the cutting forces, according to which the cutting edges of the mechanical tool are always in the plane of rotation, which is perpendicular to the ingot axis. At this, both of the kinematically different variants, the movement of the tool in relation to the motionless ingot as well as the motion of the ingot while the abrasive tool is motionless, are acceptable.

In the present invention the melts of a composition within the concentration interval M_nMe_m-c_e (FIG. 5a) or within the interval with the boundaries M_nMe_m-MMe_r (FIG. 5b), where M is the second metal, c_e is an eutectic composition and n, m and r are stoichiometric indices, are used for growing reactive ingots. During the solidification of these melts in a steady-state regime, ingots with a constant concentration lengthwise and with a monolithic structure without through voids are formed. These features result accordingly in a constancy of composition of the produced powder and in a remarkable stability of the ingot to short exposure to the air.

The thin layer of compounds appearing on the free surface of the ingot upon contact with air abruptly decreases the rate of any further reactions with gases. It can subsequently be removed by the cutting tool after the installation of the ingot inside the pump. The total loss of getter in this procedure is negligibly small, and the replacement of a used getter for a new one becomes much easier.

Sorption vacuum pumps with mechanochemical activation of reactive alloys can be used independently in the following applications:

• • where due to technological or other conditions the main requirement is not the vacuum level, but the inadmissibility of any active gases. Examples for that are processes involving the thermal treatment of metal objects, the conservation of biological or perishable organic products, etc.;
  • in portable analytical devices, where the main requirements for the pump are minimization of weight and a maximum in energy saving, and where the problem of noble gases is to be solved by periodical blowing of the vacuum chamber with compressed active gas.

However, in cases where a high vacuum is required, the new sorption pump should be used only in combination with a pump capable of pumping down noble gases (see FIG. 2).

Below some task-specific variants of sorption pumps with mechanical stimulation of the sorption processes are described. While preserving the general design features as the basis for this type of the pumps, they at the same time feature certain distinctive details allowing a better adaptation to the specific applications.

FIGS. 6 and 7 provide the principle scheme of small sorption pumps intended for portable analytical devices with a vacuum chamber. The case with a rotational motion for the treatment of the getter surface is given in FIG. 6. This solution is convenient when the reactive alloy 1 is contained in a metallic tube crucible 2. Drill 3, the cutting blades of which do not hinder the access of gases to the ingot, is rigidly fixed to the dismountable bottom 5 (FIG. 6 a, c), which is hermetically fixed to the pump casing 6. The bottom itself serves as the place for collecting the cut particles 4 and is the lower part of the reaction zone. The upper part of the reaction zone is the free surface of the ingot 1 (FIG. 6, a, b). The ingot is in crucible 2, which with the help of a “tail fin” 13 (FIG. 6a, b, d) produced by flattening of the crucible tube is attached to shaft 10 of feedthrough 12. Feedthrough 12 transmits the torque from actuator 11 or a human operator to the crucible and also creates an axial pressing force, which is necessary for the constant contact between the blades of the drill 3 and the surface of the ingot 1 during its crushing.

The pump casing 6 is connected to the vacuum chamber 9 of the portable device via port 8, which has a built-in porous filter 7 protecting chamber 9 from particles 4 and also linearizing the gas flow parameters during the measurements.

The procedure of replacing the exhausted getter material for a new one is performed in the atmosphere of the purge gas coming into the pump from chamber 9. After filling the pump with this gas, the bottom 5 is dismounted, released from the used powder (FIG. 6c) and returned into the working position (FIG. 6a). In the same way the upper flange with feedthrough 12 is dismounted, the empty crucible is disconnected from shaft 10, a new crucible with an ingot is placed instead (FIG. 6b), the entire assembly is connected to pump casing 6, and the gas flow is shut off.

Another modification of the mini pump, with a shuttle motion of the cutting tool, e.g. a file, is shown in FIG. 7. This design is intended for the utilization of ingots which are manufactured in crucibles with a low mechanical strength, e.g. in graphite cartridges. Here the reactive alloy 1 is milled with the help of file 3 together with the material of the crucible 2 so that the product of milling 4 represents a mixture of graphite particles and particles of the reactive alloy (FIG. 7).

The replacement of the getter material takes place in the same way as described above with the only difference that the new crucible is introduced into the disintegrator through the appendix 12.

While in the pumps of the first type (FIG. 6) the mechanical tool is motionless and both forces, the one pressing the ingot against the tool and the one rotating the ingot, are transmitted to the crucible via shaft 10, in the pumps of the second type the sources of mechanical force are divided (FIG. 7): one is the actuator or operator, transmitting the axial force via the linear feedthrough 11 to cutter 3, which is fixed on the shaft 10 and makes the movements “to and fro” along the ingot surface; the second one is spring 13, pushing the crucible out of appendix 12 and pressing the treated material against the cutting edges of tool 3.

FIG. 8 shows the design of the pump intended for medium and large vacuum chambers, including high vacuum systems. Pen drill 3 is rigidly fixed on the motionless flange 7, and actuator 11 creates a constant pressing force and also provides rotation of crucible 2 with a rate imposed by the controlling system shown in FIG. 2.

Pumps of this type are safe in operation. When the pump works in a stationary mode, a thin fresh layer on the surface of the powder in column 4 covers the exhausted powder material consisting of particles of the end products of the reactions between gases and reactive metals. Therefore when the air gets into the vacuum chambers upon any breakdowns, the losses of getter material are negligibly small (the high insensitivity of the ingot itself in this kind of situations has been mentioned above).

Regular replacement of the getter material is performed in the following way: the gate valve 9 (FIG. 8) is closed; the pump is filled with a suitable gas from a cylinder at open valve 8 to atmospheric pressure, the particle collector 5 is dismounted, and a new one is put in its place; flange with feedthrough 12 and the empty crucible is disconnected from the pump, a new crucible with an ingot is fixed to shaft 10, feedthrough 12 is returned to the working position, and valve 8 is closed.

The above examples refer to pumps with an outside actuator if the motion is transferred from the actuator to the mechanical tool inside the pump with the aid of a vacuum-tight feedthrough. However, the rotor of the actuator can be situated inside the pump and the energy transfer can be performed with the help of a rotating magnetic field, the source of which is placed outside the pump. At this a rotor made of low-coercivity material and pump walls of diamagnetic or paramagnetic material like those used in magnetic stirrers are applied. Therefore, the sorption pumps with mechanical activation of the getter material are applicable not only to periodically opened vacuum chambers, but also to sealed-off devices like Dewar vessels, X-ray tubes, evacuable tubular solar collectors, etc. For applications of this kind there is no need for a continuous operation of the actuator, and it is enough to produce a certain amount of getter material once a year or half a year.

Thus, sorption pumps with mechanical activation of the getter material by milling are compatible with practically all types of vacuum chambers, big stationary and small portable ones; high vacuum chambers as well as those with low vacuum, where the residual gases are only noble gases; periodically opened chambers working in the regime of continuous pumping down, and sealed-off chambers.

The best getter material for these sorption pumps are reactive ingots, grown by directional solidification of the melt in tube containers of an ampoule type with the composition of the ingots chosen in the concentration field within the boundaries M_nMe_m-c_e (FIG. 5a), or M_n Me_m-MMe_r (FIG. 5b), where Me is a reactive metal, preferably barium or lithium.

The binary systems Me-M used in the model apparatus shown in FIG. 5 have been chosen m only for an illustration and for the better understanding of the principle of selection of the getter material. The number of components in the reactive alloy as well as the nature of metals M is not limited. Only the following aspects are important: the alloy should have a high concentration of the reactive metal (sorption ability), it should approach the characteristics of an eutectic (a condition for high fusibility), and it should contain an intermetallic constituent (facilitating the milling). Addition of small amounts of ternary components is also not excluded.

From the multitude of alloys satisfying these concentration conditions, the following barium alloys were selected as preferred examples for initial getter materials employed in the present invention:

Ba_xAg_1-x, 0.60<x<0.78,
Ba_xMg_1-x, 0.33<x<0.65,
Ba_xZn_1-x, 0.67<x<0.75,
as the most low-melting,
Ba_xGa_1-x, 0.54<x<0.92,
Ba_xGe_1-x, 0.67<x<0.96,
Ba_xSi_1-x, 0.50<x<0.87,
as having the highest concentration of barium;
and also the following lithium alloys:
Li_xMg_1-x, 0.23<x<0.30,
Li_xBa_1-x, 0.80<x<0.90,
Li_xPd_1-x, 0.67<x<0.93,
the second component of the latter supports lithium in hydrogen sorption.

There is one more positive option in the controllability of the pumping speed in sorption pumps of the mechanochemical type. Gas pressure and temperature are external parameters, which to a large extent determine the course of processes in the vacuum chamber. The reproducibility of these processes, and consequently the reproducibility of the obtained end product, depend on the ability of the vacuum equipment to maintain these important parameters within the set frames. However, it is common practice in using vacuum pumps like rotary vane pumps, diaphragm pumps, diffusion pumps, turbo molecular pumps, etc. that all of them work at full capacity and with the top speed of pumping down. Therefore any changes in the treated system, both the accidental and the planned ones, e.g. heating of the material or of the equipment for outgassing, introduction of the new reagents, etc., always lead to an abrupt decrease of vacuum and consequently to a destabilization of the processes. The new sorption pumps are able to overcome these negative effects that occur when the system passes from one stage to another. The pumping speed R developed by the pump with mechanical activation of the getter material reaches the level of average turbo molecular pumps at the value of coefficient α≅0.05 and the level of a diffusion pump at 0.05≦α≦0.25. This means that the new sorption pumps presented in the present invention have unused excess capacity, which allows to increase R by about an order of magnitude by using higher milling rates, and to do this synchronously in time and proportionally to the increase of gas release in the treated system.

V. DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1. A scheme of the mechanical activation of the ingot.

1—a monolithic ingot with an axis texture, 2—a collector of powder particles, 3—falling particles, 4—a milling mechanical tool, P—the pressing force, F—the cutting force, A₁—the surface area of the powder fraction, A₂—the area of the free surface of the ingot open to gases.

Different milling regimes are possible, and different pumping speeds correspond to them. If the force P is small and the rate of the movement of the cutting tool along the ingot surface is also small (or the time intervals between the periods of applying the force F are long) the surface has enough time to get covered with the products of reaction between the metal and the gases, so that the powder from the very beginning consists of exhausted material. This is the regime of the minimum pumping speeds when only the surface A₂ is active.

With the growth of the milling rate the system passes into another regime, the regime of the more intensive pumping, when powder particles start participating in the sorption: in the beginning the first metal particles appear, and then their fraction increases till finally a thin layer of fresh super reactive particles appears on the top of column 2.

In the balanced state the thickness of this reactive layer remains constant although the height of the column 2 continuously grows with time. Stabilization is possible in both regimes and depends on the pressure of the residual gases in the vacuum chamber.

FIG. 2. An example of controlled pumping down of a vacuum chamber via the feedback.

RGA—residual gas analyzer, analyzing the composition of the gas phase in the vacuum chamber, S—a controller in the line of the sorption pump SP, A—a controller switching the additional pump AP on and off for removing noble gases from the chamber, C—a reserve vacuum line, e.g. for creation of preliminary vacuum in the vacuum chamber.

FIG. 3. The variant for blowing a small vacuum chamber with an active gas.

1 and 2 are valves, SP—a sorption pump with mechanical activation of getter material, D—a valve for releasing gas into the atmosphere at the excess of pressure. An alternative to the solution given in FIG. 2 is presented: instead of a pump removing noble gases, a venting active gas is used, which after venting of the vacuum chamber is completely captured by the getter material.

FIG. 4. Sorption curves q=q(t) at room temperature for the metals commonly used in getter technologies.

1—passivating transition metals like Fe, Mn, Ni, Ti, Zr, etc., 2—metals with growth of product on the surface according to a parabolic law, 3—metals with growth of the product on the surface according to a linear law, t—time, q—amount of gas sorbed by a surface unit of the metal by the moment of time t, t_p—time for saturation of the surface of the transition metal by gases, q₁—the sorption capacity of the transition metals achieved by the moment of the formation of a passivated film. The thickness of the passivated film does not exceed a few atomic layers; therefore the particles of the transition metals with the diameter of tens of nanometers already contain in the center a zone of unused material, and the fraction of this zone increases with the increase of the diameter of the particles.

By contrast, metals called here reactive metals, such as alkali, alkaline earth or rare earth metals, also with a growth of products of reaction on the surface (curves 2 and 3), sorb gases continuously with dq/dt>0 at any t.

The key feature can be rationalized as follows: as shown by experience, the particles of reactive metals with a diameter of from ˜1 μm to some hundreds of microns react with active gases to completion at room temperature with an acceptable rate. The preferred dimensional range can be easily realized, because the pressing force P, which determines the milling regime and the particle size in particular, is easy to control.

FIG. 5. Phase diagram of the getter material.

T—temperature, c_Me—concentration of the reactive metal Me, T_e—eutectic temperature, T_f—melting point of Me, c_e—eutectic concentration. The concentration boundaries of the melt c_Me, from which by the method of directional solidification the initial ingots are grown, are either M_nMe_m<c_Me≦c_e, where the eutectic c_e has M_nMe_m and Me (FIG. 5,a) as its phase constituents, or M_nMe_m<c_Me≦MMe_r, where MMe_r is an intermetallic compound in the state of thermodynamic equilibrium with Me (FIG. 5, b).

FIG. 6. A small sorption pump with rotational movement.

1—an ingot, 2—a metallic tube crucible with a tail for fixing to the shaft, 3—a milling tool (a drill, a milling cutter, a metallic brush, etc.) for milling, 4—a layer of powder in the lower reaction zone, 5—a detachable bottom (collector) connected with the casing via a sealing, 6—the pump casing, 7—a porous filter (metallic, ceramic, etc.), 8—a port for connecting to a vacuum chamber, 9—a vacuum chamber, 10—a shaft of the feedthrough, 11—an actuator (electrical, pneumatic, manual, etc.), 12—a feedthrough with a flange, 13—a tail.

a—a general view, b—the upper detachable part of the pump, c—the detachable bottom with the rigidly fixed mechanical tool, d—the metallic tube crucible with a tail for grasping by the shaft.

FIG. 7. A small sorption pump with linear milling movement.

1—an ingot, 2—a graphite crucible, 3—a milling tool (a scraper, a file, a metallic brush, etc.), 4—a powder fraction, 5—a detachable bottom (collector) hermetically connected to the vacuum chamber, 6—the pump casing, 7—a porous filter, 8—a port for connecting to a vacuum chamber, 9—a vacuum chamber, 10—a shaft of a feedthrough, 11—a feedthrough for transferring the reciprocating motion from the actuator, 12—an appendix for the crucible with the ingot, 13—a pressing spring.

FIG. 8. A mechanochemical sorption pump for high vacuum applications.

1—an ingot, 2—a metallic tube crucible, 3—a mechanical milling tool (pen drill), 4—the lower reaction zone with getter powder, 5—a detachable bottom of the pump (collector), 6—the pump casing, 7—a port for fixing and replacing the mechanical tool, 8—a valve in the gas line, 9—a gate valve, 10—a shaft of a feedthrough, 11—an actuator, 12—a rotary or linear feedthrough, 13—a tail of the crucible.

Claims

1. A sorption vacuum pump, comprising:

a gas impermeable casing with a reaction zone;

ports for connecting to the vacuum system;

a disintegrator, the constituents of which are a mechanical milling tool (3, 4);

an ingot of a reactive alloy in a tube container;

an actuator as a source of mechanical energy;

a collector for collecting cut particles of the reactive alloy, preferably connected with the casing; and

a feedthrough transferring the motion from the actuator to the milling tool without breaking the hermiticity of the pump and sorbing at room temperature with a controlled pumping speed all active gases due to mechanochemical activation of the reactive alloy.

2. The sorption vacuum pump according to claim 1, where the ingot is obtained by the method of vertical directional solidification of a melt of a metal alloy in a stationary regime leading to the formation of a monolithic solid product with a constant composition lengthwise.

3. The sorption vacuum pump according to claim 2, where for the production of ingots of the reactive alloy a melt with a high concentration of an alkali or an alkaline-earth metal, with a high concentration of lithium and/or barium, or a melt with a ternary or polynary composition of these metals, is used.

4. The sorption vacuum pump according to claim 2, for which the ingots of the reactive alloy are grown from the melt, the composition of which satisfies one of the following concentration ranges: BaxAg1-x, where 0.60<x<0.78, BaxMg1-x, where 0.33<x<0.65, BaxZn1-x, where 0.67<x<0.75; BaxGa1-x, where 0.54<x<0.92, BaxGe1-x, where e 0.67<x<0.96, BaxSi1-x, where 0.50<x<0.87; LixMg1-x, where 0.23<x<0.30, LixBa1-x, where 0.80<x<0.90, or LixPd1-x, where 0.67<x<0.93.

5. The sorption vacuum pump according to claim 4, where the mechanochemical activation is carried out by cutting or scratching off thin surface layers or particles of the ingot and pushing the formed powder into the reaction zone of the pump.

6. The sorption vacuum pump according to claim 5, where the mechanochemical activation of the reactive alloy takes place under the influence of two forces, viz. the force which presses the cutting edges of the tool to the ingot surface, and the force which causes the motion of the cutting edges of the milling tool perpendicular to the axis of the ingot or alternatively, wherein the ingot is moved over the fixed cutting tool.

7. The sorption vacuum pump according to claim 6, where the size of the powder particles is varied—depending on the milling regime—in the range from approximately 1 μm to several hundreds of microns.

8. The sorption vacuum pump according to claim 7, where the control over the pumping speed is executed by changing the rate of the milling of the ingot.

9. The sorption vacuum pump according to claim 8, where the pumping speed is regulated by aid of a feedback system, including a gas analyzer measuring the parameters of the state of the gas phase in the vacuum chamber, and a controller converting the gas analyzer data into commands controlling the work of the actuator.

10. The sorption vacuum pump according to claim 9, where the sorbed active gases or vapors or gases of lower activity include gases or vapors selected from the group consisting of hydrogen, oxygen, nitrogen, the halogens, hydrogen halides, carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen oxides, water, hydrogen sulfide, ammonia, methane, heptane, and other common gaseous components or mixtures thereof.

11. A process of controlled pumping down of a vessel at room temperature by removing any active gases or vapors and gases of lower activity by a reactive alloy, which is activated by its mechanical milling directly in the medium of the gases to be sorbed, in which process a sorption vacuum pump according to claim 1 is used.

12. The pumping down process according to claim 11, where the control over the speed of pumping the gases is achieved by changing the rate of milling of a monolithic ingot of a reactive alloy.

13. The pumping down process according to claim 12, where the control over the speed of pumping the gases is achieved in a programmed way using feedback tracking of the state of the gas phase in the vacuum chamber and regulating the work of the actuator.

14. The pumping down process according to claim 13 where the sorbed active gases or vapors include gases or vapors selected from the group consisting of hydrogen, oxygen, nitrogen, the halogens, hydrogen halides, carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen oxides, water, hydrogen sulfide, ammonia, methane, heptane, and other common gaseous components or mixtures thereof.