Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J7/00—Details not provided for in the preceding groups and common to two or more basic types of discharge tubes or lamps
  • H01J7/14—Means for obtaining or maintaining the desired pressure within the vessel
  • H01J7/18—Means for absorbing or adsorbing gas, e.g. by gettering
  • H01J7/183—Composition or manufacture of getters

Definitions

• the present invention relates to vacuum techniques, specifically to nonevaporable getter and a process for its production.
• the invention may be used as a pump for creating and maintaining high vacuum in electronic vacuum devices, e.g. in a cathode-ray tube, in an optical converter, gyroscope, etc., in elementary particles sources and accelerators, e.g. in a thermonuclear plant of TOKAMAK T-15 type.
• the present invention may be used for creating vacuum in devices reducing heat transfer from environment to thermostated media, e.g. in a vacuum flasks, a liquified gas storage, in pipelines for gas and crude oil transportation from wells, which pipelines are thermally insulated to protect environment in the permafrost zone.
• the present invention may be successfully used for inert gases purification.
• the known getter has three layers, one of which being a supporting layer, is made of a plastic material selected from a group comprising, e.g. Fe, Ni or their alloys, and two other surface getter layers each are made of a zirconium-based material, containing, e.g. 16 % by weight of aluminium, the balance being zirconium, or 30 % by weight of vanadium, 20 % by weight of titanium, the balance being zirconium.
• getter layers are made of a material based on a Zr-Al or Zr-V-Ti alloy comprising large amount of intermetallic compounds characterized by increased hardness and brittleness. Therefore when such getters are used under alternating loads, they fail, most often as a result of crumbling.
• zirconium-based getter containing 16 % by weight of aluminium causes increased power consumption because high temperature (about 900 Celsius degrees) is required to activate such getter.
• the known getter has low sorptive capacity with respect to such gases as H 2 , O 2 , CO 2 , CO , N 2 , etc. because the supporting layer made of, e.g. Fe, Ni and their alloys, is neutral to gas sorption, and because of low porosity of getter layers being about 20%.
• the above process for producing nonevaporable getter is hard to realize because it is difficult to reach an optimal correlation between the thickness of the supporting layer and the total thickness of the getter layer; also said process involves high loss in powder material resulting in increased getter costs.
• the known getter contains from 20 to 35 % by weight of vanadium (V), from 0.1 to 0.5 % by weight of calcium (Ca), and the balance being titanium (Ti).
• Said getter shows increased mechanical strength when used under alternating loads, due to high plasticity of the material being a solid solution of vanadium in titanium.
• the presence of elementary calcium in the getter material contributes to an increased rate of gas sorption because calcium showing high chemical activity to oxygen forms calcium oxide (CaO), and calcium oxide particles being uniformly distributed among metal particles, act as antisintering agent contributing to high porosity of the getter.
• CaO calcium oxide
• the above getter is produced as follows. Metal powder containing from 20 to 35 % by weight of vanadium, from 0.1 to 0.5 % by weight of calcium, the balance being titanium, is fed into a deformation zone, wherein said powder material is formed by rolling to produce a getter blank in the form of a ribbon. When said ribbon is leaving the deformation zone, it is cut into standard sections, said sections being transported into a heating zone.
• a pressure of lower than 1 Pa is created and maintained, and the blank is heated to a temperature lower than 0.6 times the melting point of titanium-vanadium alloy, e.g. to 850 Celsius degrees, with further holding.
• the getter thus produced is a plate having 22% porosity, sorption rate with respect to hydrogen being 1.8 m 3 /m 2 s at room temperature, when the quantity of sorbed hydrogen is 1.3 m 3 Pa/kg. Said getter is activated at 300-350 Celsius degrees.
• a getter having said composition may be referred to the getters with low activation temperature, which fact allows to develop pumping means requiring low power consumption. Nevertheless due to reduced sorption rate such getter has restricted applicability, e.g. it cannot be used as a stage in a multistage pumping device used in semiconductors production.
• the object of the present invention is to develop a nonevaporable getter having sorptive rate with respect to hydrogen of over 2 m 3 /m 2 s at room temperature when the quantity of sorbed hydrogen being 1.3 m 3 Pa/kg, due to a larger surface contacting the gas to be pumped out.
• nonevaporable getter containing from 20 to 35 % by weight of vanadium, from 0.1 to 0.5 % by weight of calcium and the balance being titanium, according to the invention, has porosity from 25 to 65 % by volume.
• Said getter has larger number of pores opening at its surface. As a result larger surface contacts the gas to be pumped out, resulting in increased gas sorption rate, e.g. the sorption rate for hydrogen is dver 2 m 3 /m 2 ⁇ s at room temperature when the quantity of sorbed hydrogen is 1.3 m 3 Pa/kg.
• a getter having the porosity less than 25% shows hydrogen sorption rate less than 2 m 3 /m 2 ⁇ s, due to which fact its applicability is restricted.
• a getter having porosity less than 25% cannot be used, e.g. as a stage in a multistage pumping device used in semiconductors production.
• a getter having porosity over 65% has lower mechanical strength, which may result in its crumbling and failing under alternating loads. Such getter cannot be used e.g. in night-vision devices, gyroscopes, etc.
• the getter according to the present invention has increased sorption rate (1.5-3 times) after activation at 300-350 Celsius degrees, due to greater open porosity accounted for increased total porosity of the getter.
• the object of the invention is to develop a process for producing a nonevaporable getter comprising using powder material with branched particles to form porosity in the range from 25 to 65 % in said material.
• Said object is achieved by that in the process for producing a nonevaporable getter comprising feeding a metal powder containing from 20 to 35 % by weight of vanadium, from 0.1 to 0.5 % by weight of calcium, the balance being titanium, into a deformation zone wherein said powder material is formed by rolling to produce a getter blank in the form of a ribbon, said ribbon, when leaving the deformation zone, being cut into standard sections, said sections being transported into a heating zone, in said heating zone a pressure of lower than 1 Pa being created and maintained, and the blank being heated to a temperature lower than 0.6 times the melting point of titanium-vanadium alloy, with further holding, producing a getter having the porosity from 22% to 65% by volume, according to the invention, said metal powder has bulk density in the range from about 0.7 to about 1.5 g/cm 3 , and has less than 70 % by weight of particles having a particle size of less than 50 ⁇ m.
• Bulk density of a metal powder determines pores quantity and size in formed blank. It is generally known that with less values of bulk density the greater values of porosity of the final product are obtained, and vice versa.
• the metal powder fed into the deformation zone should contain less than 70 % by weight of fraction having particle size of less than 50 ⁇ m. Then the metal powder will have bulk density about 1.5 g/cm 3 . In case above metal powder contains less than 20 % by weight of a fraction having particle size of less than 50 ⁇ m, bulk density of said powder will be about 0.7 g/cm 3 .
• getter blank should be heated within the range from about 750 to about 950 Celsius degrees. Said temperature range is determined by the maximum permissible shrinkage level with which the mechanical strength of resulting getter as well as its porosity (25-65 %) are maintained. In case said blank is heated up to less than 750 Celsius degrees in the heating zone, then weaker bonds are formed among the particles, due to low diffusive mobility of metal atoms, which results in reduced mechanical strength of the getter. In case said blank is heated up to over 950 Celsius degrees, considerable shrinkage occurs which causes reduced porosity of the getter thus resulting in lower sorption rate.
• a standard section of said blank may be coiled.
• a nonevaporable getter according to the invention containing from 20 to 35 % by weight of vanadium, from 0.1 to 0.5 % by weight of calcium, the balance being titanium, has porosity from about 25% to about 65% (by volume).
• the getter according to the invention has hydrogen sorption rate over 2 m 3 /m 2 ⁇ s at room temperature, when the quantity of sorbed hydrogen is 1.3 m 3 Pa/kg, the getter being activated at from 300 to 350 Celsius degrees.
• Said properties allow to use said getter in sorption pumps used in elementary particles sources and accelerators, e.g. in thermonuclear plants wherein high pumping rate is to be provided in restricted spaces.
• Metal powder containing from 20 to 35 % by weight of vanadium, from 0.1 to 0.5 % by weight of calcium, the balance being titanium, and having bulk density within the range from about 0.7 to about 1.5 g/cm 3 is fed into a deformation zone.
• Said metal powder contains less than 70% (by weight) of fraction having particle size of less than 50 ⁇ m.
• a force is exerted, e.g. 1 t/cm 2 , exceeding compression strength of said metal powder, which causes plastic deformation of metal particles.
• Ribbon length is much longer than its width, the ribbon having small ; thickness and strength sufficient to transport said ribbon into a heating zone.
• a ribbon is produced having the width of, e.g. from 15 to 80 mm, and the thickness of, e.g. from 0.4 to 0.8 mm.
• a getter blank When a getter blank is leaving the deformation zone, it is cut into standard sections which sections, e.g. having the length 200, 70 mm, etc., are transported into a heating zone.
• said heating zone the pressure below 1 Pa is created and maintained, under which the partial pressure of chemically active gases (excluding hydrogen) should be below 1.10 -2 Pa in said heating zone, and said getter blank is heated to a temperature lower than 0.6 times the melting point of titanium-vanadium alloy, followed by holding.
• Said heating temperature is maintained in the range from about 750 to about 950 Celsius degrees.
• Said temperature range is determined by maximum permissible shrinkage level at which mechanical strength of resulting getter is maintained, namely, tensile strength reaches, e.g. from 1 to 6 kg/mm 2 , and the desired porosity is from 25 to 65 %.
• a standard section of said getter blank is coiled, provided that getter porosity is below 45%. It is known that a ribbon-type blank shows low mechanical strength, which strength decreases when the porosity increases. Experiments have shown that when a blank having porosity over 45% is coiled, said blank fails.
• metal powder is formed by rolling using rollers having the diameter, e.g. ⁇ 100 mm and rolling speed (V) 1.5 m/min.
• V rolling speed
• a getter blank of uniform density is produced in the form of a ribbon having thickness (h) of 0.5 mm and width of 30 mm, the porosity of said blank being greater than the porosity of the final product.
• said metal powder is continuously formed.
• said ribbon-type getter blank is cut into standard sections having length 200 mm, and then said sections are transported into the heating zone.
• the pressure of 0.025 Pa is created and maintained, and the blank is heated to the temperature (T) of 850 Celsius degrees, followed by holding during 1 hour. After cooling the blank is removed.
• Porosity (P) of the final product is 43%, and its tensile strength is 2.1 kg/mm 2 .
• Resulting getter has sorption rate (S) with respect to hydrogen of 4.0 m 3 /m 2 .s at sorption temperature (t) 20 Celsius degrees when the quantity of sorbed hydrogen (Q) is 1.3 m 3 Pa/kg after getter activation at the temperature (Ta KT ) of 350 Celsius degrees during 15 min.
• Metal powder containing 27.20 % by weight of vanadium, 0.21 % by weight of calcium, 72.61 % by weight of titanium, having bulk density ⁇ 0.98 g/cm 3 is fed into a deformation zone, said metal powder containing 48% (by weight) of fraction (q) having particle size of less than 50 ⁇ m.
• metal powder is formed by rolling using rollers as described in Example 1.
• a getter blank of uniform density is produced in the form of a ribbon having thickness (h) of 0.5 mm and width of 30 mm, the porosity of said blank being greater than the porosity of the final product.
• said ribbon-type getter blank is cut into standard sections.
• Said standard sections of getter blank having the porosity (P) below 45% are then coiled into coils with 80 mm inner diameter.
• the length of said standard section is 2.96 m.
• Coiled getter blank is transported into the heating zone wherein the pressure of 0.025 Pa is created and maintained, and the blank is heated to the temperature (T) of 850 Celsius degrees, followed by holding during 1 hour. After cooling the coiled blank is removed.
• Resulting getter is characterized by large sorptive surface which is larger than that of the getter as per Example 1.
• Porosity (P) of the coiled getter is 38.5%, its sorption rate (S) with respect to hydrogen being 3.3 m 3 /m 2 .s at sorption temperature (t) being 20 Celsius degrees, when the quantity (Q) of sorbed hydrogen is 1.3 m 3 Pa/kg after getter activation at the temperature (Ta KT ) of 350 Celsius degrees during 15 min.
• Getter according to the invention having porosity of 30%, when used as the first stage formed by forty plates having dimensions 180x30x0.8 mm in a multistage magnetic discharge pump mounted in accelerator used in semiconductors production, has pumping rate with respect to hydrogen from 0.3 to 2 m 3 /s.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)
• Compressors, Vaccum Pumps And Other Relevant Systems (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• Gas Separation By Absorption (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)

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• 1994
  • 1994-12-29 RU RU9494045576A patent/RU2073737C1/ru not_active IP Right Cessation
• 1995
  • 1995-12-21 CN CN95191862A patent/CN1068907C/zh not_active Expired - Lifetime
  • 1995-12-21 JP JP52158696A patent/JP3231780B2/ja not_active Expired - Fee Related
  • 1995-12-21 WO PCT/RU1995/000276 patent/WO1996021958A2/ru active IP Right Grant
  • 1995-12-21 EP EP95942805A patent/EP0765012B1/en not_active Expired - Lifetime

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