Method and apparatus for discharging hydrogen from a vacuum vessel

Abstract: A method and apparatus for disharging hydrogen from a vacuum vessel (A) by means of a roughing vacuum pump (C) and a turbo-molecular pump (B). During discharge of hydrogen from the vacuum vessel, a material (D) which has excellent reactivity with hydrogen is introduced into the exhaust system. The material reacts with hydrogen to convert hydrogen into another substance of large molecular weight, whereby the evacuating performance of the vacuum exhaust system is improved with respect to discharging of hydrogen.

Description: The present invention relates generally to evacuation of a vacuum vessel and, more particularly, to a method and apparatus for evacuation for efficiently discharging hydrogen from a vacuum vessel. To evacuate a vacuum vessel to the extent of producing a high or ultra-high vacuum, a turbo-molecular pump has been conventionally used. Such type of pumps, however, have a drawback in that they cannot sufficiently discharge light weight gases such as hydrogen from a vacuum vessel since their ability to evacuate light weight gases having a relatively low molecular weight, such as hydrogen is insufficient. JP-A 60 36 789 describes a method and device for obtaining clean high vacuum wherein a hydrogen occluding material is placed at the side of a back pressure of a turbo particle pump, the hydrogen at the back pressure side is absorbed by the hydrogen occluding material to reduce the partial hydrogen pressure at the back pressure side and the arriving degree of vacuum of the turbo particle pump is increased. An object of the present invention is therefore to obviate the above-mentioned drawback by providing a method and apparatus for discharging hydrogen from a vacuum exhaust system to evacuate the interior of a vacuum vessel to produce a high level of vacuum. Another object of the invention is to provide a method and apparatus which are capable of easily discharging hydrogen under high vacuum range as well as low vacuum range with a simple arrangement while fulfilling the above object. A further object of the invention is to provide a method and apparatus which are applicable to a conventional vacuum exhaust system including a single or plurality of turbo-molecular pumps while fulfilling the above objects. To achieve the above-mentioned object, according to one aspect of the present invention, a method of the present invention comprises a step of discharging hydrogen from a vacuum vessel by means of a roughing vacuum pump and a turbo-molecular pump and is characterized by the inclusion of a step of introducing, while discharging hydrogen from the vacuum vessel, a material which has excellent reactivity with hydrogen into the exhaust system. Also, an apparatus of the present invention comprises a roughing vacuum pump and a turbo-molecular pump for evacuating a vacuum vessel, the apparatus being characterized in that in an exhaust system between the vacuum vessel and the roughing vacuum pump an inlet is provided for the introduction of a material which has excellent reactivity with hydrogen. According to another aspect of the present invention, a method of the present invention comprises a step of discharging hydrogen from a vacuum vessel by means of a roughing pump and a turbo-molecular pump and is characterized by the inclusion of the steps of introducing, during discharge of hydrogen from the vacuum vessel, a material which has excellent reactivity with hydrogen into the exhaust system, while exciting or ionizing such a material to promote reaction with hydrogen. Likewise, an evacuating apparatus according to another aspect of the invention comprises a roughing vacuum pump and a turbo-molecular pump for evacuating a vacuum vessel, and is characterized in that in an exhaust system between the vacuum vessel and the roughing vacuum pump an inlet for the introduction of the material which has excellent reactivity with hydrogen is provided together with means for exciting or ionizing such a material. The means for exciting or ionizing the material of excellent reactivity may comprise at least one of: application of microwaves; application of heat energy; irradiation with ultraviolet or laser radiation; irradiation with a beam of electrons or charged particles; irradiation with an ionizing wave or atomic beam; application of magnetic or electrical field; generation of a plasma; loading of a source of heat rays or heater; imparting an elastic wave; and charging a reaction-promoting material such as a catalyst. The material, which has excellent reactivity with hydrogen may be any material which displays such properties. Such a material, however, should preferably be a gas or a material which can be readily gasified, such as halogens, ozone, etc., since a material is introduced into the exhaust system as a gas. If the material used is a liquid or solid, a gasifying chamber, in which such material is gasified by some means such as pressure reduction or temperature increase, is provided before an inlet point for the material into the vacuum exhaust system. To introduce into the vacuum exhaust system the gasified material for reaction with hydrogen, an inlet may be provided at one or more places on the suction port-side, interior, or exhaust-port-side of the turbo-molecular pump. A single, or a plurality of turbo-molecular pumps may be used. In the latter case, a reaction chamber for exciting or ionizing the material therein may be arranged between the turbo-molecular pumps, and the inlet for the introduction of the material may be provided at one or several points in the turbo-molecular pumps including the reaction chamber. As stated above, in the present invention, means for exciting or ionizing the material, which has excellent reactivity with hydrogen, should preferably be provided before the introduction into the vacuum exhaust system or the introduced gas should preferably be excited or ionized in a reaction chamber which is provided between the turbo-molecular pumps so that the introduced gas can rapidly react with hydrogen. In accordance with the method and apparatus of the present invention, a material which has excellent reactivity with hydrogen is introduced into the path of the vacuum exhaust system where it reacts with hydrogen to convert hydrogen into another substance of larger molecular weight, whereby the evacuating performance of the vacuum exhaust system is improved with respect to the function of discharging hydrogen. For example, halogen gases, such as chlorine or fluorine, have excellent reactivity with hydrogen. Chlorine and hydrogen, when reacted with each other, will form hydrogen chloride HCl whose molecular weight (36.5) is about 18 times as large as hydrogen H₂ (2). In this case, since the compression ratio of the turbo-molecular pump has a value for hydrogen chloride which is about 10⁹ times (calculated value) as large as the value for hydrogen, the hydrogen-discharging function is improved. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative examples. Figs. 1 and 2 are diagrams conceptionally showing preferred embodiments of the evacuating apparatus according to the present invention. Embodiment 1 Fig. 1 is a diagram conceptionally showing an embodiment of the evacuating apparatus according to the present invention. In Fig. 1, a vacuum vessel A is initially evacuated by a roughing vacuum pump C and then it is further evacuated by a turbo-molecular pump B to high vacuum. In accordance with the present invention, a reactant which has excellent reactivity with hydrogen is introduced into the evacuating apparatus during evacuating operation. If the reactant is not a gas, then it is initially gasified in a gasifying chamber D, excited in an exciting section E₁, and is then introduced into the turbo-molecular pump B, and the suction and exhaust ports, G₁ and G₃, respectively, of the turbo-molecular pump. A description is given with respect to an example case where chlorine is used as the reactant. If the exciting chamber E₁ is arranged outside the vacuum exhaust system, then chlorine gas is initially introduced into the exciting chamber E₁. In this case, the gasifying chamber D is unnecessary since chlorine is in gaseous form at ordinary temperatures and at ordinary pressures. In this case, the following reaction: Cl₂ → 2 Cl (1) is caused by introducing a microwave into the exciting chamber E₁ to form a plasma state while maintaining the pressure in the exciting chamber E₁ at about 1 Torr, whereby chlorine radicals are generated. Such chlorine radicals are introduced into the vacuum exhaust system through the inlets for material and, within the vacuum exhaust system, the following reaction will occur: H₂ + 2 Cl → 2 HCl (2) Embodiment 2 Fig. 2 is a diagram conceptionally showing another embodiment of the evacuating apparatus according to the present invention. In Fig. 2, two turbo-molecular pumps B₁ and B₂ are arranged in series, between which a reaction chamber E₂ is provided. A reactant is excited in this reaction chamber. In this reaction chamber E₂, irradiation is effected with ultraviolet rays through a light-transmitting window of quartz, for example. In this apparatus, the reactant is initially gasified in the gasifying chamber D and is then introduced into the suction port G₁ and the interior of the turbo-molecular pump B₁, the reaction chamber E₂ and the exhaust port G₃ of the turbo-molecular pump B₂, where it reacts with hydrogen. In this case, if chlorine is introduced as the reactant and irradiation is effected with ultraviolet radiation in the reaction chamber E₂ through a light-transmitting window, the following reaction will occur: hν + Cl₂ → 2 Cl (3) whereby chlorine radicals are generated. Subsequently, the reaction of formula (2) occurs within the vacuum exhaust system and generates hydrogen chloride. Hydrogen chloride thus formed can be promptly discharged by the turbo-molecular pumps since it has a high molecular weight, i.e. 36.5, as described previously. Thus, with the use of the method and apparatus according to the present invention, it is possible to easily discharge hydrogen under high vacuum, which has been very difficult to perform with conventional turbo-molecular pumps. For example, it allows the pressure to promptly reach a range of values not higher than 10⁻¹⁰ Torr (ultra high vacuum). It also makes it possible to discharge, even under a low vacuum range, a substantial amount of hydrogen which could not be discharged by ordinary turbo-molecular pumps so far.

Claims: A method for discharging hydrogen from a vacuum vessel by means of a roughing vacuum pump and a turbo-molecular pump and by means of a material reacting with hydrogen, characterized by the inclusion of the step of introducing, during discharge of hydrogen from the vacuum vessel, a material which has excellent reactivity with hydrogen into the exhaust system. A method for discharging hydrogen from a vacuum vessel by means of a roughing vacuum pump and a turbo-molecular pump, characterized by the inclusion of the steps of introducing, during discharge of hydrogen from the vacuum vessel, a material which has excellent reactivity with hydrogen into the exhaust system, while exciting or ionizing such material to promote the reaction of such a material with hydrogen. The method for discharging hydrogen from a vacuum vessel as claimed in claim 2, wherein said exciting or ionizing of the material of excellent reactivity is effected by means of at least one of: application of microwave; application of heat energy; irradiation with ultraviolet or laser radiation; irradiation with a beam of electrons or charged particles; irradiation with an ionizing wave or atomic beam; application of a magnetic or electrical field; generation of a plasma; loading of a source of heat rays or heater; imparting an elastic wave; and charging a reaction-promoting material such as a catalyst. The method for discharging hydrogen from a vacuum vessel as claimed in any one of claims 1 to 3, wherein said material is a gas or a material which can be readily gasified like halogens or ozone. The method for discharging hydrogen from a vacuum vessel as claimed in claim 4, wherein said gas is chlorine or fluorine. The method for discharging hydrogen from a vacuum vessel as claimed in claim 2 or 3, wherein said exciting or ionizing of said material is effected before introduction of said material into said exhaust system. The method for discharging hydrogen from a vacuum vessel as claimed in claim 2 or 3, wherein said exciting or ionizing of said material is effected in a reaction chamber provided in said exhaust system. An apparatus for discharging hydrogen from a vacuum vessel comprising a roughing vacuum pump and a turbo-molecular pump connected to a vacuum vessel, the apparatus being characterized in that in an exhaust system between the vacuum vessel and the roughing vacuum pump an inlet is provided for the introduction of a material which has excellent reactivity with hydrogen. An apparatus for discharging hydrogen from a vacuum vessel comprising a roughing vacuum pump and a turbo-molecular pump connected to a vacuum vessel, the apparatus being characterized in that in an exhaust system between the vacuum vessel and the roughing vacuum pump an inlet for the introduction of the material which has excellent reactivity with hydrogen is provided together with means for exciting or ionizing such a material. The apparatus for discharging hydrogen from a vacuum vessel as claimed in claim 9, wherein said means for exciting or ionizing the material of excellent reactivity comprises at least one of: application of microwaves; application of heat energy; irradiation with ultraviolet or laser radiation; irradiation with a beam of electrons or charged particles; irradiation with an ionizing wave or atomic beam; application of a magnetic or electrical field; generation of a plasma; loading of a source of heat rays or heater; imparting an elastic wave; and charging with a reaction-promoting material such as a catalyst. The apparatus for discharging hydrogen from a vacuum vessel as claimed in any one of claims 8 to 10, wherein said inlet is suitable for introducing a gas or a material which can be readily gasified like halogens or ozone. The apparatus for discharging hydrogen from a vacuum vessel as claimed in claim 11, wherein said gas is chlorine or fluorine. The apparatus for discharging hydrogen from a vacuum as claimed in any one of claims 8 to 10, wherein said apparatus includes a gasifying chamber for gasifying said material before introduction of said material into said exhaust system. The apparatus for discharging hydrogen from a vacuum vessel as claimed in any one of claims 8 to 10, wherein said apparatus includes a single turbo-molecular pump and a reaction chamber connected to said turbo-molecular pump for effecting exciting or ionizing of said material therein. The apparatus for discharging hydrogen from a vacuum vessel as claimed in claim 14, wherein said inlet is provided in said turbo-molecular pump, and suction and exhaust ports of said turbo-molecular pump. The apparatus for discharging hydrogen from a vacuum vessel as claimed in any one of claims 8 to 10, wherein said apparatus includes a plurality of turbo-molecular pumps and a reaction chamber connected between said turbo-molecular pumps for effecting exciting or ionizing of said material therein. The apparatus for discharging hydrogen from a vacuum vessel as claimed in claim 16, wherein said inlet is provided in said turbo-molecular pumps, suction and exhaust ports of said turbo-molecular pumps and said reaction chamber.

Inventors: OKANO HARUO, OKUMURA KATSUYA, SIBATA AKIO C O EBARA RESEARCH, TSUJIMURA MANABU C O EBARA COR, OKANO, HARUO, OKUMURA, KATSUYA, SIBATA, AKIO, TSUJIMURA, MANABU, SIBATA, AKIO, C/O EBARA RESEARCH CO., LTD., TSUJIMURA, MANABU, C/O EBARA CORPORATION
Applicants: EBARA CORP, TOSHIBA KK, EBARA CORPORATION, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: B01J3
IPC codes: C01B7, B01J3, B01J19, B01J12, C01B5