Getter activation and uses

Abstract

A method of removing a contaminant from an environment is described, the method comprising the steps of: (i) heating a reduced and passivated getter material to a temperature in the range of (T T - X) to (T T + Y) to form an activated getter material having a surface active for removal of the contaminant, the getter material containing crystallites of a metal in elemental form encapsulated by a layer comprising a metal oxide, wherein T T is the Tamann temperature of the metal in elemental form in degrees Celsius, X is 400 and Y is 200; and (ii) exposing the activated getter material to the environment comprising the contaminant.

Description

[0001] This invention relates to a method for activating getters and its use for removing contaminants.

[0002] A getter is an adsorbent composition that functions by adsorption or absorption and is typically used within a container to remove unwanted substances from the atmosphere within that container. The container can be, for example, a housing for an electrical or electronic device. Alternatively, the container can be used to maintain a vacuum, or as part of an insulating unit under vacuum, wherein the getter is used to maintain the vacuum.

[0003] Getter compositions are known. For example, WO2015 / 015221 discloses a getter composition suitable for removing hydrogen and moisture, comprising an alkaline earth metal oxide or a precursor thereof and a transition metal oxide or a precursor thereof, wherein the transition metal is selected from copper, nickel, and cobalt. A class of getters known as non-evaporative getters (NEGs) are primarily porous alloys or powder mixtures of Al, Zr, Ti, V, and Fe. EP0719609 (A2) discloses a method for preparing non-evaporative getter materials by mixing metallic getter elements, one or more getter alloys, and a solid organic compound, wherein all components are in powder form with a specific particle size. These alloys can be thermally activated to create a metallic surface that adsorbs or absorbs contaminant gases such as hydrogen, water, oxygen, and carbon oxides, thus serving as a means of maintaining high vacuum (e.g., in vacuum packaging) or maintaining the primary purity of the gas. However, NEG alloys are limited by very low metallic surface areas, such as those shown in EP0719609 (A2), where the surface area is less than 0.2 m². 2 / g.

[0004] While prior art getter compositions are useful in many applications, they are limited by their inherently low surface area for removing active metals. A method has been discovered that overcomes the limitations of prior art methods and provides a significantly larger active adsorption surface area.

[0005] Therefore, the present invention provides a method for removing contaminants from the environment, the method comprising the steps of: (i) heating a reduced and passivated getter material to (T T -X) to (T) T Temperatures within the range of +Y) are used to form an activated getter material with a surface active for pollutant removal. This getter material contains microcrystals of metal in elemental form encapsulated in a layer comprising metal oxides, wherein T... T (i) The Taman temperature of the metal in elemental form, in degrees Celsius, where X is 400 and Y is 200; and (ii) the activated getter material is exposed to an environment containing the contaminant.

[0006] The Taman temperature is a known property of metals and is the temperature at which atoms or molecules in a solid acquire sufficient energy to make their bulk mobility and reactivity apparent. The Taman temperature is typically half the melting point; for example, copper has a Taman temperature of 405°C, cobalt 604°C, iron 631°C, and nickel 590°C.

[0007] The heating step produces an activated getter material having a surface active for removing contaminants (such as contaminant gases) from the environment. This environment can be an inert gas, such as nitrogen, helium, or argon, or it can be a vacuum or partial vacuum.

[0008] The heating step can be performed on the material before, during, or after the reduced and passivated getter material is transferred to the container in which the material is to be used. Therefore, the method may include the step of mounting a reduced and passivated getter material or an activated getter material in a container in which the material is to be used. In one arrangement, the container may be a flow-through container, i.e., a container (or vessel) through which an inert fluid (such as an inert gas) can pass. In another arrangement, the container is sealed, in which case the method may further include the step of sealing the container under vacuum or an inert gas atmosphere to form a sealed container. The heating step to generate the activated getter can be performed before, during, or after the sealing step.

[0009] This method is suitable for reduced and passivated getter materials containing any metal capable of capturing or removing contaminants. The metal may be present in the reduced and passivated getter material in an amount ranging from 1% to 95% by weight (expressed as metal).

[0010] This method is particularly suitable for getters containing metals selected from copper, cobalt, iron, and nickel. The applicant has found that nickel-containing getters are particularly suitable for activation by the method of the present invention. The reduced and passivated nickel getter activated by the method of the present invention can have a nickel content, expressed as Ni, in the range of 1% to 95% by weight, preferably 10% to 60% by weight, and more preferably 30% to 60% by weight.

[0011] This reduced and passivated getter material contains microcrystals of metal in elemental form encapsulated in a layer comprising a metal oxide. Unlike NEG materials, the microcrystals are dispersed on the surface of a support that physically separates the metal microcrystals, thereby providing a getter with a higher metal surface area achievable in NEG materials. The microcrystals can be formed by precipitating a reducible metal compound and a support compound from solution or by impregnating a reducible metal compound onto a support. The reduced metal surface area of ​​the getter in this invention can reach 5 m². 2 / g to 50m 2 Within the range of / g.

[0012] The term "reduction and passivation" refers to a getter containing a metal that can be reduced to its elemental form. This metal has undergone a previous reduction step to form its elemental form in situ (i.e., outside the container where the metal will be used), and the elemental form of the metal has been passivated by encapsulating it in a layer containing metal oxides using a suitable oxidation treatment to prevent spontaneous and uncontrolled oxidation from atmospheric oxygen. The layer containing metal oxides may consist of metal oxides or may include metal carbonates. The layer containing metal oxides provides a barrier against bulk oxidation of the getter, allowing the getter to be safely handled in air without self-heating. The reduction step can be performed using any known method by applying a reducing agent or reducing gas to the oxidizing material under conditions that convert at least a portion of the metal oxide into its elemental form. For example, it can be performed by heating the corresponding metal oxide to a temperature in the range of 175°C to 600°C in a reducing gas stream containing hydrogen. The reducing gas can be pure hydrogen or a diluted hydrogen stream, such as a mixture of hydrogen and nitrogen. Passivation can be performed using any known method by applying an oxidizing agent to a reducing getter to re-oxidize the surface layer on the elemental metal, thereby encapsulating the metal in elemental form with a layer containing metal oxides. For example, passivation can be performed under controlled conditions using oxygen, air, and / or carbon dioxide (appropriately diluted with an inert gas such as nitrogen or argon). Such methods are known. For example, methods for preparing reduced and passivated compositions of copper, cobalt, and nickel are disclosed in US5928985(A), US2013184360(A1), and GB2118453(A), respectively.

[0013] Reduced and passivated getter materials advantageously possess only sufficient elemental metal passivation to prevent undesirable self-heating and depletion of getter capacity during normal handling and transport. Too little passivation results in an unstable getter; too much passivation leads to excessively long heating steps. Therefore, the preferred degree of oxidation (which can alternatively be expressed as the degree of reduction (DoR) of the passivated getter) is in the range of 10% to 90%. For nickel getters, the DoR can be 10%-90%, but preferably in the range of 20% to 80%, more preferably in the range of 35%-70%. For cobalt getters, the DoR can be 10%-90%, but preferably in the range of 20% to 80%, more preferably in the range of 35%-65%. For copper getters, the DoR can be 10%-90%, but preferably in the range of 15% to 70%, more preferably in the range of 20%-50%. The DoR can be readily determined by known temperature-programmed reduction (TPR) methods. A suitable method involves initially passing a hydrogen gas stream through the sample at ambient temperature. As the gas flows, the sample temperature increases linearly over time, and the consumption of dihydrogen is monitored. The degree of reduction (DoR) can then be calculated as a percentage using the following formula:

[0014]

[0015] Where 'a' is the amount of reduced reducible metal (mol / g) and 'b' is the total amount of reduced reducible metal present in the material (mol / g). The amount of reduced reducible metal can be calculated using the main oxide phase. For nickel monoxide, the dihydrogen consumption ratio is 1:1, therefore,

[0016] a = bc

[0017] Where c represents the total dihydrogen consumption.

[0018] The heating step is performed in the absence of a reducing agent. The heating step can be performed by heating the getter material to a desired temperature. For example, heating may include, but is not limited to, induction heating or filament heating. The heating step heats the reduced and passivated getter material to a temperature at (T... T -X) to (T) T Temperatures within the range of +Y) are used to form a surface on the getter material that is active for pollutant removal, wherein T T The Taman temperature is defined in degrees Celsius as the metal in elemental form, where X is 400 and Y is 200. Not wishing to be bound by theory, the applicant believes that by heating the claimed reduced and passivated getter material, which is reconstructed to provide a portion of the metal in elemental form at the surface of the metal crystallites, an activated getter material is formed having a higher metal surface area than that achievable with currently thermally activated getter materials. The Taman temperature is generally half the melting point of the metal and can be determined by known references, such as “Heterogeneous Catalyst Deactivation and Regeneration”: a review by M.D. Argyle and C. Bartholomew in Catalysts, March 2015, 5(1), pp. 145–269. The lower limit temperature to which the getter can be heated is defined by T. T -X degrees Celsius is given, where X is 400. Therefore, X can range from 1 to 400. For example, X can be 350, 250, 200, 100, or 50 or less. The upper limit of the temperature to which the getter can be heated is given by T. T +Y is given in degrees Celsius, where Y is 200. Therefore, Y can be in the range of 1 to 200. For example, Y can be 150, 125, 100, 75, 50, 25, or less. Above the Taman temperature, sintering of metal microcrystals may occur, leading to a decrease in metal surface area and thus reduced effectiveness. Therefore, Y is preferably 100 or less.

[0019] When the getter contains nickel, the reduced and passivated getter material can be heated to a temperature ranging from 190°C to 790°C, preferably from 300°C to 700°C, more preferably from 400°C to 600°C.

[0020] The reduced and passivated getter material can be heated at a constant or varying heating rate, and can be heated in one, two or more stages and held at one or more intermediate temperatures or at the highest temperature for a period of time, which may be referred to as the "dwell time". The heating step can be performed in the range of 5 minutes to 24 hours, but preferably in the range of 10 minutes to 5 hours (including any dwell time during which the getter is held at a constant elevated temperature).

[0021] To prevent the active surface formed by heating from deactivating due to oxidation, an activating getter is used under vacuum or in an inert gas atmosphere. The vacuum is preferably at least 98.70% (≥1 bar or ≥100.01 kPa negative gauge pressure). The inert gas can be any gas that does not react with the metal, and is suitably selected from nitrogen, helium, and argon. The oxygen (O2) content of the inert gas should be minimized and preferably ≤0.010% by volume, more preferably ≤0.002% by volume.

[0022] The activated getter prepared by the method of the present invention can be used to remove contaminants selected from one or more of hydrogen, water, oxygen, carbon dioxide, carbon monoxide, and hydrocarbons. The getter is particularly effective at removing or capturing hydrogen.

[0023] The getter obtained by this method can be used, for example, to maintain a vacuum in Dewar containers or pipelines used for transporting oil in cold climates. The getter can also be used to remove contaminants from gaseous atmospheres to maintain the environment within a housing, such as protecting electronic components, or to purify gases before use, for example, in semiconductor manufacturing.

[0024] The invention will now be further described with reference to the following embodiments.

[0025] Example 1: Preparation of reduced and passivated getter materials

[0026] Getter 1 is CRG-F is a precipitated nickel material, commercially available from Johnson Matthey PLC. This material contains 61.3% nickel, expressed as Ni.

[0027] This material can be prepared by coprecipitation as described in US4250060.

[0028] The getter material is provided in oxidized form and is therefore first reduced and passivated as follows: 1 g of the material is loaded into a quartz reactor in an Altamira AMI200 dynamic chemisorption apparatus. The material is first dried under argon at 50 cc / min by raising the temperature to 35°C, then increasing it to 100°C at 10°C / min, and holding it at 100°C for 60 minutes. The material is then reduced in 100% hydrogen at a flow rate of 50 cc / min through the sample. During the reduction step, the temperature is raised to 650°C at 10°C / min and held at that temperature for 2 hours. The reduced material is then cooled to a final temperature of 25°C at a flow rate of 30°C / min under a 50:50 mixture of helium and argon at 50 cc / min and held at that temperature for 30 minutes. The reduced material is then passivated by passing a mixture of helium at 48 cc / min and oxygen at 2 cc / min over the reduced material for 60 minutes (held at 25°C). The passivated material was then treated at 25°C with a mixture of 10 cc / min oxygen and 40 cc / min helium for 60 minutes, and then discharged from the reactor.

[0029] The properties of the reduced and passivated getter materials are listed in Table 1:

[0030] Table 1: Getter Characteristics

[0031]

[0032] Ni content was determined using X-ray fluorescence (XRF). DoR was measured as follows: 0.1 g of reduced and passivated getter material was weighed and placed in the quartz reactor of an Altamira AMI200 dynamic chemisorption apparatus. The material was dried, thereby heating it to 140 °C at 10 °C / min under an argon flow of 40 ml / min and holding for 1 hour. The material was then cooled to room temperature (approximately 20 °C). The material was then treated with a mixture of 10% (v / v) hydrogen in argon at 40 ml / min, while simultaneously raising the temperature to 1000 °C at 10 °C / min and holding at that temperature for 15 minutes. Hydrogen consumption was quantified using a thermal conductivity detector. The degree of reduction of the sample was then calculated using the amount of hydrogen consumed, combined with elemental analysis from XRF, according to the following chemical equation: the number of moles of hydrogen consumed equals the number of moles of nickel oxide reduced to nickel metal.

[0033] NiO + H₂ → Ni + H₂O

[0034] Then calculate DoR using the following formula:

[0035]

[0036] Where c is the number of moles of hydrogen consumed during the measurement, and b is the number of moles of nickel in any form present in the original sample being analyzed.

[0037] Example 2: Activation without the application of reducing gas

[0038] The reduced and passivated getter material from Example 1 was placed in a reaction vessel and heated for 2 hours under vacuum or flowing nitrogen, with hydrogen adsorption monitored. Hydrogen adsorption is considered a measure of surface adsorption capacity because it occurs primarily when nickel is in elemental form. Approximately 1 g of the reduced and passivated getter material 1 was weighed into a glass reaction vessel and heated to the desired temperature at a heating rate of 10 °C / min under a nitrogen flow (200 cc / min) or vacuum. The material was held at this temperature for an additional 120 minutes. The material was then cooled to 35 °C under vacuum and held for 60 minutes below 10 μmHg (1.333224 Pa). A leak test was then performed. Hydrogen adsorption was then measured at 35 °C within a pressure range of 100 mmHg–760 mmHg (13332.2 Pa–101325 Pa) to establish an adsorption isotherm. The total adsorption at 760 mmHg is recorded below based on the weight of the oxide material before reduction and passivation.

[0039] For each individual aliquot of the sample, the activation temperature was gradually increased during continuous operation, and the above method was followed each time.

[0040] The Taman temperature of Ni is 590°C, and therefore the temperature range of Ni in this invention is 190°C-790°C.

[0041] Hydrogen adsorption was measured at 35°C. At this temperature, no reduction of the nickel oxide layer occurs, and therefore the adsorption exhibits a getter surface formed by the heating step. The results are listed in Tables 2 and 3 below.

[0042] Table 2: Heating under nitrogen atmosphere

[0043] getter Temperature (°C) <![CDATA[H2 adsorption (cm 3 / g)]]> 1 300 12.1 500 12.3 700 8.9

[0044] Table 3: Heating under vacuum

[0045] getter Temperature (°C) <![CDATA[H2 adsorption (cm 3 / g)]]> 1 120 0.1 300 10.3 500 10.8 700 8.5

[0046] The results show that a getter surface has been formed. Heating at 700°C (110°C higher than the Taman temperature of nickel) appears to reduce H2 adsorption compared to heating at 500°C.

[0047] The hydrogen adsorption isotherm generated after heating getter material 1 under vacuum was also used to calculate the relevant nickel surface area. The results are listed in Table 4.

[0048] Table 4: Heating under vacuum

[0049] getter Temperature (°C) <![CDATA[Metal surface area (m 2 / g)]]> 1 120 <0.1 300 31.4 500 34.2 700 26.8

[0050] At the start of the measurement, the metal surface area was calculated per gram of material. It is clear that a metal surface area exceeding 10 m² can be achieved using this method. 2 / gram of getter.

Claims

1. A method for removing pollutants from the environment, the method comprising the following steps: (i) Heating the reduced and passivated getter material to (T) T -X) to (T) T Temperatures within the range of +Y) are used to form surfaces active for pollutant removal and within 5m 2 / g to 50m 2 An activated getter material with a reduced metal surface area in the range of / g, wherein the reduced and passivated getter material contains microcrystals of said metal, selected from nickel, cobalt, iron, or copper, dispersed on a carrier surface and encapsulated in a layer containing metal oxides, in elemental form, wherein T T The Taman temperature of the elemental metal is in degrees Celsius, where X is 400 and Y is 200; and (ii) exposing the activated getter material to an environment containing the contaminant, wherein the microcrystals of the elemental metal encapsulated in the layer containing the oxide of the metal are formed by precipitation of a reducible metal compound and a carrier compound from a solution or by impregnation of a reducible metal compound on a carrier.

2. The method of claim 1, wherein the heating step is performed on the material before, during, or after the reduced and passivated getter material is transferred to the container to be used.

3. The method of claim 2, further comprising the step of sealing the container under vacuum or inert gas to form a sealed container.

4. The method of claim 1, wherein the metal in the reduced and passivated getter material comprises nickel.

5. The method of claim 4, wherein the nickel content in the reduced and passivated getter material is in the range of 1% by weight to 95% by weight.

6. The method of claim 1, wherein the reduced and passivated getter material has a reduction degree in the range of 10% to 90%.

7. The method of claim 1, wherein the heating step is performed under a vacuum of at least 98.7%.

8. The method according to claim 1, wherein the heating step is performed under an inert gas selected from nitrogen, helium, and argon.

9. The method of claim 1, wherein the metal in the reduced and passivated getter material is nickel, and the reduced and passivated getter material is heated to a temperature in the range of 190°C to 790°C.

10. The method of claim 1, wherein the contaminant is selected from one or more of hydrogen, carbon dioxide, water, oxygen, carbon monoxide and hydrocarbons.

11. The method according to claim 1, wherein the pollutant is hydrogen.

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