FR2584063A1 - SUPER PURIFIER FOR ARGON GAS AND PROCESS FOR THE PURIFICATION OF ARGON. - Google Patents

Abstract

THE PRESENT INVENTION RELATES TO A SUPER PURIFIER FOR ARGON GAS AND A METHOD FOR SUPER-PURIFYING ARGON GASEOUS. IN ACCORDANCE WITH THE INVENTION, THE SUPER PURIFIER INCLUDES MEANS FOR CONTACTING A GASEOUS ARGON CONTAINING IMPURITIES WITH A DEGASEOUS MATERIAL WHICH IS AN ALLOY OF ZIRCONIUM, VANADIUM AND IRON. THE DEGASSING MATERIAL OF THE SUPER PURIFIER SELECTIVELY SORTS IMPURITIES OF A GASEOUS ARGON CONTAINING IMPURITIES THUS PRODUCING A PURIFIED ARGON GAS. THE PRESENT INVENTION ALSO CONCERNS A PROCESS FOR THE PURIFICATION OF A GASEOUS ARGON CONTAINING IMPURITIES BY USING THIS SUPER PURIFIER. THE PRESENT INVENTION PROVIDES MEANS FOR OBTAINING A HIGHER PURITY GAS ARGON THAN THAT WHICH COULD BE OBTAINED BY THE PREVIOUS PURIFICATION PROCESSES AND APPARATUS.

Description

i Argon, present in the air and constituting approximately 1% of its volume,

  is separated from nitrogen and oxygen by fractional distillation at low temperature. It is introduced either in liquid form or in gaseous form in bottles and placed on the market. High quality internal gas, argon is widely used to create atmospheres for heat treatment of metals, for the manufacture of semiconductor substrates, etc. When it is to be used in super fine micromachining, it must be further purified to remove impurities to a higher purity immediately before use. For consumption of large volumes in industrial processes, the liquid argon is usually vaporized, and the gas obtained is sent through pipes. The problem here is how to meet the requirement for rapid and positive removal of impurities such as nitrogen, oxygen, hydrogen, carbon dioxide, carbon monoxide, water , metal and

  other hydrocarbons, carbonated argon.

  In order to remove these impurities, it has been proposed to eliminate two operations, namely passing the argon gas through a bed of activated carbon or active alumina or through a molecular sieve of zeolite etc. to remove water, carbon dioxide and hydrocarbons, then to put the gas in contact with a metallic degasser of copper or nickel preheated in a temperature range of 150 to 300 C. The process can also be followed by two operations of an additional operation constituting bringing the gas into contact under pressure with a molecular sieve of type 5-A under a pressure of 5 to x105 Pa for an additional purification by elimination of nitrogen, oxygen, hydrogen and residual carbon monoxide. The specification of the

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  Japanese patent application No. 107910/1984, which describes the proposed process, also clearly establishes that the argon gas containing the impurities listed in the following table Constituent 02 CO H2 N2 H20 Dew point (ppm) 1 100 200 200 60 C a was purified in the following manner up to the above composition: Constituent 02 CO H2 N2 H20 Dew point (ppm) 1 - 1 20 - 72 C The process for purifying argon gas described in the Japanese patent application No 107910/1984 mentioned above is an excellent process for obtaining high purity argon gas. However, recent advances in the semiconductor industry suggest that increasingly precise micro-machining and therefore even higher purity argon will be required.

  for the future production of highly integrated circuits.

  In fact, there is already a high demand for argon gas of high purity for testing purposes. The technical problem which the present invention proposes to solve is to lower the current levels of impurities conforming to the prior technology to much lower rates, by two orders of magnitude in parts per million. The Applicant has carried out extensive studies on the means of purifying argon gas to reduce its concentration of impurities by two orders of magnitude in

  ppm from the usual rates as indicated above.

  As a result of these studies, it discovered a degasser which performs even better than the metallic copper or nickel degasser mentioned above, and it resulted in an apparatus and method capable of efficiently purifying argon gas by using the particular degasser. The present invention has been accomplished on this basis. The apparatus according to the invention is a super purifier for argon gas, characterized in that an external envelope is provided with an inlet port for the argon gas to be purified, with an outlet port for purified argon gas, from at least one degassing chamber filled with a degassing alloy of the zirconium-vanadium-iron system and arranged halfway between the two openings, with a flow passage formed in such a way so that the argon gas which enters the inlet orifice flows towards the degasser chamber and leaves the outlet orifice, and the heater system incorporated in the external envelope to maintain the degassing alloy at the temperature at which it operates, the weight composition of the zirconium-vanadium-iron alloy of the degasser being such that the weight dosages of the three elements, when plotted in a ternary composition diagram, are located in a polygon (fig. 1) having as points the points defined by a. 75% Zr- 20% V-5% Fe b. 45% Zr-20% V-35% Fe, and c. 45% Zr- 50% V-5% Fe The process according to the invention is a process for super-purifying argon gas, characterized by the operations consisting of dehydrating the argon gas appropriately, to be purified up to a moisture content of 1 ppm or less, then removing the impurities by adsorption from the low moisture gas by passing the latter through a degasser bed filled with a zirconium system degassing alloy- vanadium-iron maintained at a temperature of 20 to 4000 ° C., this degassing alloy having a composition by weight 4. such that the weight percentages of the three elements, when plotted in a ternary composition diagram, are located in a polygon (FIG. 1) having as points the points defined by a. 75% Zr-20% V-5% Fe, b. 45% Zr-20% V-35% Fe, and c. 45% Zr-50% V-5% V. The ternary degassing alloy of zirconium, vanadium and iron to be used in the present invention may be one of those described in

U.S.-A-4,312,669.

  The weight composition which gives a degasser having particularly good performance is such that the weight percentages of the three elements, when plotted in a ternary composition diagram (fig.l) are located in a polygon having as points the points defined by at. 75% Zr-20% V-5% Fe, b. 45% Zr-20% V-35% Fe, and

vs. 45% Zr-50% V-5% Fe.

  Such a ternary alloy degasser typically absorbs moisture and water vapor quantitatively at temperatures of 20 to 400 C, preferably in the range of 200 to 350 C, without evolution of hydrogen, and on over a wide range of temperatures, it adsorbs hydrogen, CO, CO2 and other gases. These properties have proved to be advantageously usable in the super purifier

argon gas of the invention.

  The weight ratio of the elements constituting the ternary alloy degasser intended for use in the super-purifier of the invention can be

  changed at will in the interval specified above.

  In any case, it is advisable to choose the best possible composition ratio taking into account the

properties of the degasser.

  The zirconium content of the ternary alloy must not be too high or too low, otherwise the alloy would tend to give off hydrogen while adsorbing moisture and it would also become plastic, which created difficulties for the

transform into powder.

  The vanadium content should not be too low either, as it would render the alloy incapable of exhibiting adsorption performance.

  completely satisfactory.

  Based on the weight of iron, we want the

  weight percentage of vanadium is from 75 to 85%.

  The optimal ternary alloy composition of the degasser for the super-purifier of the invention can be such that the weight percentages of the three elements, when plotted on a ternary composition diagram, lie in a polygon (fig. 1) having as vertex the points defined by d. 70% Zr-25% V-5% Fe, e. 70% Zr-24% V-6% Fe, f. 66% Zr-24% V-10% Fe, g. 47% Zr-43% V-10% Fe, h. 47% Zr-45% V-8% Fe, and

i. 50% Zr-45% V-5% Fe.

  The process for the preparation of these alloys is described in the aforementioned US-A-4,312,369. Products manufactured and sold by SAES Getters S.p.A., Milan,

  Italy can advantageously be used.

  It is desirable that the degassing alloy be used in the form of an inter-metallic compound, which

  is easily sprayed and can be handled easily.

  In addition, the increase in specific surfaces makes the

more active spray material.

  The ternary alloy degasser is packed in at least one degasser chamber provided halfway in a gas flow passage between the inlet port of

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  purified argon gas and the purified gas outlet. The chamber or chambers with packed degasser are associated with a heating means installed as an accessory under an external envelope to maintain the degasser at its working temperature, to constitute a

  super gaseous argon purifier of the invention.

  The gaseous argon to be purified is sent through a purifier where it comes into contact with the purifier, so that it is freed of these impurities by

adsorption.

  The degasser which must be packed in the chamber takes the form of pellets, in preference to fine particles, since the former more easily provide gaps between them for the flow of gas. Similarly, the degasser in the form of pellets of uniform size rather than in small agglomerate of regular size facilitates the maintenance of a constant vacuum ratio in the degasser bed, it also facilitates the design of an apparatus and the reproduction of good performance. Thus, the degasser in the form of fine particles or small agglomerates then does not have any drawbacks, the use of a degasser in pellets, compression molded from the powder

  alloy, is preferred because it better meets -

  design and manufacturing requirements

  production of super argon gas purifier.

  The heater system which must be incorporated into the apparatus of the invention to keep the degasser sufficiently hot for the adsorption reaction can take various forms, as will be explained below with regard to the preferred embodiments of the invention. The heating method can be electric heating or indirect heating by using a heating medium which is circulated through a double wall structure, etc. Likewise, the heating zone can be appropriately chosen, for example, in the preheating region upstream of the degasser bed or chamber, or around or inside the mass of the degasser. Since it is desirable that sufficient heating is carried out to carry out a regular adsorption reaction of the degasser with the gas and to produce a temperature distribution as uniform as possible, the combination of the process and the heating zone can be varied. , as needed, to achieve the goal sought in

the best conditions.

  Although it is possible to provide the degasser chamber of the apparatus of the invention inside the external envelope, for example to place it directly in the latter, a preferred arrangement is such that the degasser bed consists of at least one cartridge filled with the degasser material and which is designed to be fitted in the outer casing so that it can be detached for easy replacement. The constituents of the degasser according to the invention adsorb and remove the impurities from the impure argon gas by a chemical adsorption which involves chemical modifications. They are therefore consumed stoichiometrically and have only a limited lifespan. After a specified period of service, the degasser must be replaced by a fresh degasser; otherwise, the goal of super purification of argon gas can no longer be achieved. For this purpose, the super-purifier comprising the outer casing filled with the degasser can be handled as a single element and replaced as such from time to time. It is also possible to introduce the degasser into a cartridge and to disassemble the cartridge from the outer casing to replace it at appropriate time intervals. The cartridge type is more convenient with a

large equipment.

  The cartridge advantageously uses a perforated metal case so as to facilitate the flow of gas. As the super purifier of the invention is intended to purify argon gas until the concentrations of these ingredients constituting the impurities are lowered to 0.01 ppm or less for each, it is recommended that the part of the wall internal of the apparatus with which the purified gas leaving the degasser chamber comes into contact is made of a metal polished on the surface so as to have sufficiently close grains and to be sufficiently smooth to minimize the adsorption of gas , and

  which does not form powder under the effect of corrosion.

  These metals include, for example, without limitation, stainless steels, and patented alloys such as Hastelloy, Incoloy and Monel. Any other metal satisfying the above requirements can be appropriately selected and used. The chosen metal can be "cooked", or heat treated before use to reduce the volume of gas later

released from the metal itself.

  As noted above, the material of the inner wall of the apparatus which contacts purified argon gas advantageously has a densely and smoothly polished surface to minimize gas adsorption. The desired smoothness of the polished surface is numerically defined to be such that the roughness of the surface of the internal wall coming into contact with argon gas, expressed by the average height of the center line (Ra) Japanese Industrial Standard ( JIS) B 0601- 1970 either 0.5 micron or less, preferably 0.25 micron or less. This numerical interval is not always decisive, but

  it is recommended as a safe interval.

  Although the material of the polished internal wall is advantageously used in said zone where the gas flowing out of said chamber of the cartridge comes into contact, it is obviously possible to also use it in the zone where the gas passing through the cartridge comes in contact. In many cases, it is quite inconvenient to use the polished material only in the area where the gas which has passed the cartridge comes into contact. Polishing and baking the surface will dramatically reduce the time it takes before you start to get highly purified gas at a speed

  constant, even in a new device.

  In the apparatus of the present invention, the means for solving the technical problem can be realized in various ways, as suggested above. Thus, it should be noted that the invention is not limited to the particular embodiments thereof described so far, but that various modifications can be made thereto without departing from

  the spirit and scope of the invention.

  In the process of the invention, dehydration is carried out on the following bases. The moisture content of impure argon gas is usually far higher than the levels of other impurities. When special consideration is given to moisture removal, the life of the degasser and therefore the service life of the super argon gas purifier will be remarkably extended, or, in other words, a striking increase in the volume of purified argon gas will be achieved. Any known dehydration technique can be adopted provided that it does not preclude the practice of the present invention. For example, dehydration can be carried out by adsorption with a molecular sieve of synthetic zeolite or a similar compound, with alumina gel

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  or with phosphorus pintoxide, or by freezing at a cryogenic temperature below - 160 C, or by adsorption with silica gel, activated carbon or a

  other adsorbent at low temperature, below - 40 C.

  Fig. 11 shows the relationships between the moisture content of the gas to be purified and the lifetime of the degasser. When the gas has a high moisture content, it is dehydrated before super purification, preferably

  up to a moisture content of 1 ppm or less.

  To adjust the moisture content in the range of 1 ppm or less, the system is designed to operate as follows. By using a humidity meter capable of continuously measuring the moisture trace content, the rate of humidity in the dehydrated argon gas is automatically monitored. When the moisture content of the argon after dehydration has gradually increased to around 1 ppm, the dehydrator is started before the level of 1 ppm is reached, so that the moisture content of the argon gas before it enters the degasser bed is kept in the range of 1 ppm or less. Analyzers suitable for this continuous, automatic measurement of moisture trace content are for example the humidity measuring devices manufactured by Endress und Hauser GmbH, in the FRG and sold under the trade name "ENDRESS -HAUSER HYGROLOG, WMY 170 "and" WMY 370 ", the products sold under the brands" PANAMETRICS Hygrometer, Model 2100 "," - Model 700 ", and" - System I "by Panametrics Inc. of the United States of America and another American product" Du Pont 510 Moisture Analyzer "of EI Du Pont de Nemours & Co. Other performance analyzers comparable to those above or better can obviously be used at

the place of these.

  Such a humidity measuring device can also be used for measuring and monitoring the moisture content in argon gas after purification. The results of the analysis are used as data indicative of the decrease in adsorption capacity of the degasser, and to decide when the super purifier should be operated to replace the cartridge filled with degasser. For the detection and determination of trace impurities other than humidity in the argon gas, an analyzer can be used for ultra microns quantities of gas (mass spectrometer of the pass filter type for analyzes continuous high sensitivity) manufactured by Nichiden - ANELVA Corporation (in Japan) under the trade name "TE - 360B". The analytical values are used as a measure of the decrease in the performance of the analyzer and for the decision on when to operate the super purifier or replace the

degasser cartridge.

  Regarding the analytical values, it is recommended to set up the purification system in such a way that, whenever limits to the higher rate of individual impurities fixed in advance are reached, a start-up is automatically accomplished as planned. Such a system ensured obtaining a high quality final argon gas. In order for the impurities to be removed from the dehydrated argon gas by passage through and adsorption by the degassing bed of zirconium-vanadium-iron alloy, the reaction temperature is maintained in the range of 20 ° C. to 400 ° C. at a temperature below 20 ° C, the impurities are adsorbed by the surface of the degasser but cannot be expected to diffuse into the bulk of the degasser. Thus, adsorption practically stops when the surface is saturated, without making full use of the capacity of the degasser. In the specified range of 20 to 400 C, the degasser fully performs the adsorption, allowing the impurities to diffuse throughout its mass. The apparent service life

  of the degasser is extended accordingly.

  On the other hand, in the region of temperature above 400 C, the hydrogen, after it has been adsorbed by the degasser, can be desorbed because it has an adsorption fraction at equilibrium greater than that of other impurities. It is therefore not desirable to set a reaction temperature exceeding 400 C. In the specified temperature range from to 400 C, a narrower range from 220 to 380 C. is preferred. A temperature in the latter range is the temperature of the most recommended reaction, in that it ensures a high adsorption rate and a complete diffusion of the impurities in the degasser bed

  without possibility of desorption of hydrogen.

  The super argon gas purifier of the present invention is suitable for super purifying the conventionally purified argon gas to an even higher degree of purity. It can purify argon gas by passing through it by lowering the concentrations in the diet of impurities such as oxygen (02), carbon monoxide (CO), carbon dioxide (C02), l nitrogen (N2), hydrogen (H2), methane (CH4), and water (H2O), at 0.01 ppm or less for each. It thus achieves a super purification of the argon gas up to a degree of purity which has never

  been done by any of the existing purifiers.

  Furthermore, the duration of the purifier used in the super argon gas purifier of the invention can be markedly extended and the purifying volume of the argon gas is greatly increased by first reducing the moisture content in the argon gas impure at 1 ppm or less by appropriate dehydration according to the process of the invention, then passing the dehydrated gas through the super

purifier of the invention.

  Various other features of the invention

  moreover emerge from the detailed description which

  follows. Embodiments of the object of the invention are shown, by way of examples not

restrictive, to the accompanying drawings.

  Fig. 1 is a ternary composition diagram of the degasser alloy intended to be used

in the present invention.

  Figs. 2 to 10 are vertical section views of various embodiments of the apparatus according to the invention. Fig. 11 is a graph giving the relationships between the moisture content in the argon gas and the

lifetime of the degasser.

  Argon gas super purifiers implementing the invention are illustrated in FIGS. 2 to 10. Fig.2 shows a super argon gas purifier comprising: an outer casing 3 made of a stainless steel tube (quality SUS 304 TP, compliant with Japanese industrial standard JIS G 3448), which has a orifice for the argon gas 1 in the vicinity of the top and an outlet for the argon gas 2 in the vicinity of the base, the envelope being covered with a thermal insulator 12 over the entire surface; an upper cover 14 adapted to the top of the outer envelope 3; a heater 6 inserted through the upper cover 14 into the space 25 inside the envelope; a degasser bed 4 placed in the space defined above the heater 6 between the upper and lower stops 16, 15; and a perforated plate 7 held in a support 13, which is fixed in its side to the internal wall of the external envelope and carries the bed as well as the perforated plate. The degasser used is a ternary alloy degasser of zirconium (68-72% by weight), vanadium (24-25% by weight), and iron (5-6% by weight), manufactured and sold by SAES Getters SpA, Type No. "St 707" in the form of pellets in the form of a column having a diameter of 3 mm and a height of 4 mm. The stops indicated in 15, 16 consist of a layer each of small spheres d alumina 4 mm in diameter stacked up to a height of about 5 cm. They correct any irregular flow of gas through the degasser, they prevent fine particles from the degasser from dispersing, and even out the temperature distribution. Although the described embodiment uses small spheres of alumina to form stops, small stainless steel balls or a stack of stainless steel mesh can be used instead. Likewise, the stops are not always used, and an embodiment without stop will be described later. In the upper parts of the stops 15, 16 are included sheaths 20, 19 housing thermometers 18, 17, respectively. Like thermometers,

  Chromel-Alumel thermocouples are used.

  The new argon gas to be purified is introduced into the container at the inlet 1, it is heated by the heater 6, it passes through the upper stop 16, and passes from there, in a uniform current through the bed of degasser 4 o it is rid of its content of gaseous impurities by adsorption. The purified gas is sent through the perforated plate 7 and it leaves the container through the outlet orifice 2. FIG. 3 and the following figures show other embodiments of the invention. In all these figures, identical parts are designated by identical numbers, and

  the description of each is omitted or reduced to

  minimum. Fig. 3 represents a super purifier having the same construction as the embodiment of FIG. 2, except that an electric heater 21 is wound around the external envelope 3 and that a thermocouple 22 is installed to measure the temperature This modification makes it easier to adjust the

temperature of said degasser.

  Although fig. 2 and 3 illustrate embodiments in which the degasser bed 4 is directly packed into the outer casing 3, the degasser bed can also be arranged separately. Fig. 4 shows a cartridge arrangement 5 in which the degasser 4 and the stops 15, 16 are housed in a cylinder fitted at both ends with perforated plates 7. After a determined service life, the cartridge 5 can be removed by removing the top cover 14 and be replaced by a new one. This allows for more efficient operation than with

provisions of fig. 2 and 3.

  Fig. 5 shows another embodiment 11, in which the outer casing 3 is double-walled, and consists of an inner wall 24 and an outer wall 23. The space between the walls constitutes a passage through which a heating medium such that steam flows from a heating inlet 30 to an outlet 31. A cooling liquid can be sent in place of the heating medium, depending on the case. In the space defined by the internal wall is lifted a cartridge 5 containing a degasser 4, with an electric heating coil 6 included in the degasser. The heater 6 is connected to an external current source not shown in conductors 8 (only one of them being shown) and by a system of terminals 10. The cartridge 5 has internal and external porous walls 26 kept concentrically at a distance from each other by a support 13. The internal wall 24 of the external casing abuts at its lower end against a base provided with a flange 27 through which passes a gas inlet pipe 1 and a gas outlet 2. The pipe 2 also serves as a support for the cartridge 5. The gaseous argon 9 to be purified is introduced through the inlet orifice 1 into the external space 25, it is heated there to an appropriate temperature, and from there, it is forced to pass through the porous wall 26 in the degasser layer 4 for purification. The purified gas escapes in

  the internal space 25 ′, and exits through the outlet orifice 2.

  Fig. 6 shows an embodiment of the super-purifier 11. The outer casing 3 is again here with double walls, and a space is formed there to circulate a heating medium introduced by an inlet orifice 30 and evacuated by an orifice of output 31 to adjust the temperature. Inside the internal wall is disposed a cartridge 5 filled with a degasser 4 between perforated plates. On both sides of the cartridge are arranged heaters 6 which are connected to external current sources by conductors 8. Impure argon gas 9 is introduced through the inlet orifice 1, it is preheated by the medium of heating, purified by passage through the degasser mass 4 maintained at a temperature given by the

  heaters 6, and it exits through the outlet 2.

  Another embodiment of the super purifier 11 is shown in FIG. 7. A cylindrical outer casing 3 carries a cartridge 5 by means of upper and lower plates (not shown). The cartridge 5 comprises a built-in electric heater 6 with conductors 8 and a degasser mass 4 introduced into the space between the upper and lower perforated plates or layers of

  stops, in which the heater is included.

  Fig. 8 shows another device 11 implementing the invention. An internal cylinder is provided inside an external envelope 3 which consists of internal and external walls and a heat insulator 12 filling the space between the walls. A degasser 4 is packed towards the space between the internal cylinder and the external envelope, and a heater 6 wound around a ceramic rod 36 is inserted in the central space of the internal cylinder. Argon gas to be purified enters the container at the inlet 1, it passes through the degasser 4, and the purified gas leaves the

  container at outlet 2.

  Fig.9 shows another embodiment, which is a variant of the super purifier illustrated in fig. 4, and which is characterized by

  means for recovering heat from purified argon.

  The argon gas 9 to be purified enters a heat exchanger 28 placed under the body of the purifier, undergoes a heat exchange with the outgoing gas, and the gas thus preheated passes through a pipe 29 surrounded by a thermal insulator 12, and through an upper inlet port 1 in a degasser bed 4. The purified gas is cooled in the heat exchanger and it leaves the

  purifier at outlet 2.

  Fig. 10 shows another embodiment.

  The outer casing 3 is a double-walled cylinder, and a heating medium is introduced into the space between the walls at the inlet port 33 and is evacuated at the inlet port 34. Inside of the envelope

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  external 3, a gas-tight cartridge 35 is arranged.

  The space of the cartridge case is divided horizontally by a set of perforated plates 7, and several degasser beds 4 are formed, each filling the space formed by each pair of perforated plates. An electric heater 6 is included in each of the degasser beds, and supplied with electricity by conductors 37, 38. The argon gas 9 to be purified enters through an inlet orifice 1, and the purified gas leaves

through an outlet 2.

  Examples of the invention which use a particular degasser composition will now be explained. The instruments used for the gas analyzes of the examples were as follows: Instruments for the analysis of gases: Gas chromatograph-mass spectrometer, model TE-360B manufactured by Anelva Corp. Moisture meter: Hygrometer, Model 700 (manufactured by Panametric Co.) Surface roughness meter: Surfcorder, Model SE-3H (manufactured by Kosaka Laboratory Co., Ltd.)

Example 1

  Is introduced into the super purifier with argon gas represented in FIG. 2 a sprayed non-evaporable degassing alloy having the composition by weight% Zr-24.6% V-5.4% Fe, and a particle size between 50 and 250 microns. The stainless steel cylinder (SUS 304) has an external diameter of 21.7 mm and an internal diameter of 17.5 mm, its length being 350 mm.The length of the cylinder occupied by the degasser material, including heights, 5 mm each, upper and lower stops of alumina spheres, (bed height) is 200 mm. Impure argon is introduced into the purifier at a temperature of 25 C and at a pressure of 588 kPa (on a pressure gauge) with a flow rate of 0.6 l / min. Argon flows through the degasser bed non-evaporable maintained at 350 C and exits under a pressure of 392 kPa (on the pressure gauge) through the outlet orifice where its impurity rate is measured for various gases. The level of impurities is

  measured 40 min after the start of the flow of argon.

TABLE 1

  Gas Impurity rate Impurity rate at inlet to outlet (ppm) (ppm)

02 0.4 0.006

N2 0.5 0.011

CH4 0.06 0.007

CO 0.07 0.002

CO2 0.04 0.002

  H20 5.0 no trace The level of impurities in the outlet gas remains

constant for 930 hours.

Example 2

  Tablets are produced having a diameter of 3 mm and a height of 4 mm by compression of a non-evaporable degassing alloy having a composition and a particle size identical to those of the degassing alloy of Example 1. The pellets are introduced into the super purifier shown in fig. 3. The stainless steel cylinder (SUS 304) has an outer diameter of 89.1 mm and an inner diameter of 83.1 mm. The length is 660 mm. The length of the cylinder occupied by the pellets of the degasser material, including the thicknesses of the upper and lower stops (of alumina spheres)

  each having a bed height of 5 mm, is 185 mm.

  Impure argon is introduced into the super-purifier at a temperature of 25 C and under a pressure of 392 kPa (using a pressure gauge) with a flow rate of 12 1 / min. The impure argon flows through the non-evaporable degasser bed maintained at a temperature of 350 C by means of a spiral resistance heater, and it exits under a pressure of 387 kPa (on the pressure gauge) through the orifice. outlet o its impurity rate is measured for various gases. The level of impurities is measured 40 min after the start of the flow of argon. The results

  obtained are given in table 2.

TABLE 2

  Gas Impurity rate Impurity rate at inlet to outlet (ppm) (ppm)

02 6.0 0.01

N2 7.5 0.02

CH4 2.0 * 0.009

CO 9.5 0.003

  Co 2 6.3 0.003 H2O 5.0 no trace * The level of methane impurities is obtained in

  deliberately adding CH4 to the gas at the inlet.

  The rate of impurities in the gas at the outlet

remains constant for 930 hours.

Example 3

  In this example, the procedure of Example 2 is repeated on all points, except that the rate

  water impurities is 1 ppm and not 5 ppm.

  Table III gives the results obtained.

TABLE 3

  Gas Impurity rate Impurity rate at inlet to outlet (ppm) (ppm)

02 6.0 0.01

N2 7.5 0.02

CH4 2.0 * 0.009

CO 9.5 0.003

CO2 6.3 0.003

  H20 1.0 no trace * The rate of methane impurities is obtained in

  deliberately adding CH4 to the entrance.

  The rate of impurities in the outlet gas

  remains constant for 2,670 hours.

Example 4

  Tablets are prepared exactly as in Example 2 and placed in the cartridge shown in fig. 4. The cartridge has an outer diameter of 80mm,

  an internal diameter of 78 mm, and a length of 244 mm.

  The same mass of pellets is used as in Example 2. The cartridge is then placed in a cylinder identical to that of Example 2 (except that its length is 719 mm). Impure argon is passed out at through the super-purifier under the same inlet pressure, at the same temperature, and with the same flow rate as in Example 2. The cartridge is maintained at 350 C. The pressure and the composition of the gas at the outlet prove to be identical to those found in example 2.40 min after the start of the flow of argon. The rate of impurities in the gas at the outlet

  here remains constant for 930 hours.

Example 5

  In this example, the procedure of Example 2 is followed on all points except the roughness of

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  the internal surface of the cylinder which is Ra = 0.5 micron (normally R = 2.5 microns) and that the pipe from the stainless steel outlet (external diameter 9.5 mm) has

  a roughness of the internal surface of Ra = 0.2 microns.

  The results of Table IV were obtained

  min after the start of the flow of argon.

TABLE 4

  Gas Impurity rate Impurity rate at inlet to outlet (ppm) (ppm)

02 6.0 0.003

N2 7.5 0.002

CH4 2.0 0.009

CO 9.5 0.003

C02 6.3 0.003

  H20 5.0 no trace The rate of impurities in the outlet gas

remains constant for 930 hours.

  Example 6 In this example, the procedure of Example 5 is followed on all points, except that the water vapor content of the argon gas to be purified is lowered below 0.6 ppm by doing so. first pass through a desiccant bed consisting of a stainless steel cylinder (SUS 304) having an external diameter of 89.1 mm, an internal diameter of 81.1 mm, and a length of 830 mm, filled up to '' at a bed height of 500 mm with a molecular sieve of type 5-A. The pressure at the outlet of the desiccant bed and therefore the pressure at the inlet into the super purifier is 363 kPa (on the pressure gauge) and the outlet pressure of the super purifier is 363 kPa (on the pressure gauge). The level of impurities is

  measured 40 min after the start of the flow of argon.

  The results are given in table V. Gas

02

N2 CH4 CO CO2

H20

TABLE 5

  Input impurity rate (ppm) 6.0 7.5 2.0 9.5 6.3 0.6 Exit impurity rate (ppm) 0.003 0.002 0.009 0.003 0.003 no trace The rate of '' impurities in the gas at the outlet

  remains constant for 2,670 hours.

  The procedure of Example 6 is repeated, except that the temperature is varied to see the effects of various degasser temperatures. The

  results are given in table VI.

TABLE 6

  Impurity rate Impurity rate at inlet to outlet (ppm) (ppm) at temperature

  C 200 C 350 C 400 C

02 6.0 0.003 0.003 0.003 0.003

N2 7.5 0.002 0.002 0.002 0.002

CH4 2.0 2.0 0.2 0.009 0.006

Co 9.5 0.003 0.003 0.003 0.003

CO2 6.3 0.003 0.003 0.003 0.003

  H20 0.6 step by step from step by step from trace to trace from trace to trace The outlet gas remained constant for 30 h 390 h 2670 h 2900 h Energy consumption O 0.56 kW / H 1.04 kW / h 1 0.2 kW / h The table shows that excellent effects are obtained in the temperature range from 20 to 400 o C, in particular in the range from 200 to 400 o C. Examples 7, 8, 9 and 10 pellets with a diameter of 3 mm and a length of 4 mm are prepared by compression of non-evaporable degasser powders having the weight composition indicated in the following table and having particle sizes of 50 to 250 microns (150 microns on average ). These pellets are introduced into a super purifier constructed in the same manner as that of Example 2. Argon gas containing impurities is introduced into the super purifier at a temperature of 25 ° C. under a pressure at the inlet of

  392 kPa (on the pressure gauge) and with a flow rate of 12 1 / min.

  The argon gas containing impurities is sent through the non-evaporable degasser bed maintained at a temperature of 350 C by means of a spiral resistance heater, and it leaves the outlet orifice under a pressure of 387 kPa ( pressure gauge). The level of impurities is measured 40 minutes after the start of the flow of argon, and the results are obtained.

table VII.

  Comp. of the getter alloy Zr (%) V (%) Fe (%)

TABLE 7

  Ex. 7 Impure Gas. Impurities at the outlet at the inlet (ppm) (ppm)

02 6.0 0.01 0.01 0.02 0.03

N2 7.5 0.02 0.02 0.02 0.02

CH4 2.0 0.006 0.01 0.01 0.01

CO 9.5 0.003 0.003 0.008 0.005

CO2 6.3 0.003 0.003 0.006 0.006

  H20 5.0 step by step by footsteps from trace trace trace trace trace duration during which the impurity at the outlet was constant (h) The impurity levels at the outlet are constant

  for the time indicated in the table.

Ex. Ex.

9 Ex. 10 25840i

Claims (11)

  1 - Super purifier for argon gas, characterized in that an external casing is provided with an inlet port for the argon gas to be purified, with an outlet port for the purified argon gas, at least one degasser chamber filled with a degassing alloy of the zirconiumvanadium-iron system and disposed halfway between the two openings; a flow passage formed in such a way that the argon gas which enters the inlet orifice flows through the degasser chamber and exits through the outlet orifice, and a heating means incorporated in the outer casing to maintain the degasser alloy at the temperature at which it operates, the weight composition of the zirconium-vanadium-iron alloy of the degasser being such that the weight percentages of the three elements, when plotted in a composition diagram ternary, are located in a polygon (fig. 1) having for points vertices defined by: a. 75% Zr-20% V-5% Fe, b. 45% Zr-20% V-35% Fe, and vs. 45% Zr-50% V-5% Fe.   2 - Super purifier according to claim 1, characterized in that this degasser alloy used in this degasser chamber is in the form of pellets produced by compression from a Zr-V-Fe alloy sprayed.   3. Super purifier according to claim 1, characterized in that the weight composition of this getter alloy is such that the weight percentages of the three elements, when plotted in a ternary composition diagram, lie in a polygon having vertices the points defined by d. 70% Zr-25% V-5% Fe e. 70% Zr-24% V-6% Fe f. 66% Zr-24% V-10% Fe, g. 47% Zr-43% V-10% Fe, h. 47% Zr-45% V- 8% Fe, and i. 50% Zr-45% V- 5% Fe.   4 - Super purifier according to claim 1, characterized in that this degasser chamber comprises at least one cartridge filled with this degassing alloy, and in that this cartridge is installed so as to be able to be detached in this external envelope in such a way that she can be   easily replaced with a new cartridge.   5 - Super purifier according to claim 4, characterized in that each cartridge comprises a perforated metal container filled with this alloy degasser.   6 - Super purifier according to claim 1, characterized in that the material of the device with which the argon gas purified by the flow through this degasser chamber comes into contact is such that the surface of the internal wall coming in contact with the gas has been polished to a surface roughness (Ra), expressed by the average height of the center line in accordance with the Japanese Industrial Standard (JIS) B 0601-1970, is 0.5 micron or less.   7 - Process for super-purifying argon gas, characterized by the operations consisting in dehydrating the argon gas to be purified in an appropriate manner to a moisture content of 1 ppm or less, then eliminating the impurities by adsorption from gas with a low moisture content by passing it through a degasser bed filled with a degassing alloy of zirconium-vanadium-iron system maintained at a temperature of 20 to 400 C, this degassing alloy having a weight composition such that the weight percentages of the three elements, when plotted in a ternary composition diagram, lie in a polygon (fig.1l) having as vertices the points defined by a. 75% Zr-20% V-5% Fe, b. 45% Zr-20% V-35% Fe, vs. 45% Zr-50% V- 5% Fe.   8 - Method according to claim 7, characterized in that the argon gas in low moisture content flows through this degassing alloy bed   maintained at a temperature of 220 to 380 C. -   9 - Super purifier for purifying argon gas containing impurities, this super purifier comprising: A. an external envelope having a gas inlet port and a gas outlet port; B. a gas flow passage in the outer casing extending from the gas inlet orifice to the gas outlet orifice and allowing fluid communication between them; C. a degasser chamber provided in the gas flow passage, this degasser chamber being disposed between the gas inlet orifice and the gas outlet orifice; D. a degassing material deposited in the degasser chamber, this degassing material being a zirconium-vanadium-iron alloy having a composition which, when plotted on a ternary composition diagram in weight percentages Zr, V and Fe, are located in a polygon having as vertices the points defined by a. 75% Zr-20% V- 5% Fe, b. 45% Zr-20% V-35% Fe, and c. 45% Zr-50% V- 5% Fe, and E. means for heating the degassing material and maintaining the degassing material at a temperature at which the degassing material selectively sorbs the   impurities of a argon gas containing impurities.   10. The super-purifier of claim 9, in which the degassing material is a zirconium-vanadium-iron alloy having a composition which, when plotted on a ternary composition diagram in percentage by weight of Zr, V and Fe, are located in a polygon having as vertices the points defined by: d. 70% Zr-25% V- 5% Fe, e. 70% Zr-24% V- 6% Fe, f. 66% Zr-24% V-10% Fe, g. 47% Zr-43% V-10% Fe, h. 47% Zr-45% V- 8% Fe, and i. 50% Zr-45% V- 5% Fe.   11 - Process for super-purifying a argon gas containing impurities having a moisture content of 1 ppm or less, this process comprising the operations consisting of: I. producing a super-purifier comprising A. an external envelope having an inlet orifice for the gas and a gas outlet; B. a gas flow passage in the outer casing extending from the gas inlet port to the gas outlet port and providing fluid communication therebetween; C. a degasser chamber provided in the gas flow passage, this degasser chamber being disposed between the gas inlet orifice and the gas outlet orifice; D. a degassing material provided in the degasser chamber, this degassing material being a zirconium-vanadium-iron alloy having a composition which, when plotted on a composition diagram 258406:   ternary in weight percent of Zr, V and Fe, are located in a polygon having as vertices the points defined by: a. 75% Zr-20% V- 5% Fe, b. 45% Zr-20% V-35% Fe, and c. 45% Zr-50% V- 5% Fe, and E. means for heating the degassing material and for maintaining the degassing material at a temperature at which the degassing material selectively sorges impurities from argon gas containing impurities; II. to maintain the degassing material at a temperature of at 3350 C;   III. introducing argon gas containing impurities into the outer shell of the super purifier through the gas inlet; IV. contacting the argon gas containing impurities with the degassing material in the super purifier, thereby sorbing the impurities from the argon gas containing impurities to produce a purified argon gas; and V. collect the purified argon gas which leaves the super   purifier through the gas outlet.