GETTER ACTIVATION AND USE

Abstract

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

Claims

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

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

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

4. The method according to claim 1, wherein the metal in the reduced and passivated getter material comprises nickel, cobalt, iron or copper.

5. A The method according to claim 1, wherein the metal in the reduced and passivated getter material comprises nickel.

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

7. The method according to claim 1, wherein the crystallites of the metal in elemental form encapsulated by the layer comprising an oxide of the metal are dispersed over the surface of a support.

8. The method according to claim 1, wherein the crystallites of the metal in elemental form encapsulated by the layer comprising an oxide of the metal are formed by precipitation of reducible metal compounds and support compounds from solution or impregnation of reducible metal compounds on a support.

9. A The method according to claim 1, wherein the reduced metal surface area of the getters is in the range of 5 to 50 m.sup.2/g.

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

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

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

13. The method according to claim 1, wherein the metal in the reduced and passivated getter material is nickel and the temperature to which the reduced and passivated getter material is heated is in the range 190 to 790? C.

14. A The method according to claim 1, wherein the contaminant is selected from one or more of hydrogen, carbon dioxide, water, oxygen, carbon monoxide and a hydrocarbon.

15. The method according to claim 1, wherein the contaminant is hydrogen.

16. The method according to claim 5, wherein the nickel content of the reduced and passivated getter material is in the range 10 to 60% by weight.

17. The method according to claim 1, wherein the heating step is performed under nitrogen containing less than 0.010% by volume of oxygen.

18. The method according to claim 1, wherein the metal in the reduced and passivated getter material is nickel and the temperature to which the reduced and passivated getter material is heated is in the range 300 to 700? C.

19. The method according to claim 1, wherein the metal in the reduced and passivated getter material is nickel and the temperature to which the reduced and passivated getter material is heated is in the range 400 to 600? C.

Description

Example 1: Reduced and Passivated Getter Material Preparation

[0021] Getter 1 was KATALCO? CRG-F, a precipitated nickel material, commercially available from Johnson Matthey PLC. The material contained 61.3% nickel, expressed as Ni.

[0022] The material may be prepared by co-precipitation as described in U.S. Pat. No. 4,250,060.

[0023] The getter material was supplied in oxidic form and so was first reduced and passivated as follows: 1 g of the material was charged into a quartz reactor in an Altamira AMI200 Dynamic Chemisorption device. The material was first dried under 50 cc/min argon by raising the temperature to 35? C. and then increasing the temperature at 10? C./min to 100? C. before holding at 100? C. for 60 minutes. The material was then reduced in 100% vol hydrogen flowing over the sample at 50 cc/min. During the reduction step the temperature was increased at 10? C./min up to 650? C., where it was held for 2 hours. The reduced material was then cooled under a 50 cc/min flow of a 50:50 mixture of helium and argon at a rate of 30? C./min to a final temperature of 25? C., where it was held for 30 minutes. The reduced material was then passivated by flowing a mixture of 48 cc/min helium and 2 cc/min oxygen over the reduced material for 60 minutes, held at 25? C. The passivated material was then treated with a mixture of 10 cc/min oxygen and 40 cc/min helium at 25? C. for 60 minutes before discharge from the reactor.

[0024] The properties of the reduced and passivated getter material are set out in Table 1:

TABLE-US-00001 TABLE 1 Getter properties Ni content (% wt Maximum Reduction Degree of Reduction Getter expressed as Ni) Temperature (? C.) (DoR, %) 1 61.3 460 65
The Ni content was established using X-Ray Fluorescence (XRF). The DoR was measured as follows: 0.1 g of the reduced and passivated getter material was weighed and charged into a quartz reactor in the Altamira AMI200 Dynamic Chemisorption device. The material was subjected to a drying process whereby it was heated under a flow of 40 ml/min argon to 140? C. at 10? C./min and held for 1 hour. The material was then cooled to room temperature (ca 20? C.). The material was then treated with a mixture of 10% vol hydrogen in argon at 40 ml/min while increasing the temperature at 10? C./min up to 1000? C., where it was held for 15 minutes. The hydrogen consumption was quantified using a thermal conductivity detector. The amount of hydrogen consumed was then used, in conjunction with elemental analysis from XRF, to calculate the degree of reduction of the sample as the moles of hydrogen consumed equals the moles of nickel oxide reduced to nickel metal, according to the chemical equation:

[00002]$\mathrm{NiO}+H_2.fwdarw.\mathrm{Ni}+H_{2}O$

[0025] The DoR was then be calculated by the following equation:

[00003]$\mathrm{DoR}=\frac{\left(b-c\right)}{b}?100$

[0026] Where c is the moles of hydrogen consumed during the measurement, and b is the moles of nickel, in any form, present in the original sample analysed.

Example 2: Activation without Applying a Reducing Gas

[0027] The reduced and passivated getter material from Example 1 was placed in a reaction vessel and heated either under vacuum or under flowing nitrogen gas for 2 hours and the hydrogen adsorption monitored. Hydrogen adsorption is considered to be a measure of gettering capacity of the surface as it occurs primarily once the nickel is in elemental form.

[0028] Approximately 1 g of reduced and passivated getter material 1 material was weighed into a glass reaction vessel and heated under nitrogen flow (200 cc/minute) or vacuum using a ramp rate of 10? C./minute to the desired temperature. The material was held at the temperature for a further 120 minutes. The material was then cooled to 35? C. under vacuum then held for 60 minutes below a 10 ?mHg (1.333224 Pa). At this point a leak test was conducted. Hydrogen adsorption was then measured at 35? C. over a pressure range 100-760 mmHg (13332.2-101325 Pa), building an adsorption isotherm. The total adsorption at 760 mmHg based on the weight of the oxidic material before reduction and passivation is reported below.

[0029] Consecutive runs with increasing activation temperature were conducted on single aliquots of sample, following the method above each time.

[0030] The Tammann temperature for Ni is 590? C., and so the temperature range within the invention for Ni is 190-790? C.

[0031] Hydrogen adsorption was measured at 35? C. At this temperature no reduction of the nickel oxide layer occurs, and so adsorption demonstrates that a getter surface has been formed by the heating step. The results are set out in Tables 2 and 3.

TABLE-US-00002 TABLE 2 Heated under nitrogen Temperature H.sub.2 adsorption Getter (? C.) (cm.sup.3/g) 1 300 12.1 500 12.3 700 8.9

TABLE-US-00003 TABLE 3 Heated under vacuum Temperature H.sub.2 adsorption Getter (? C.) (cm.sup.3/g) 1 120 0.1 300 10.3 500 10.8 700 8.5

[0032] The results demonstrate that a getter surface has been generated. Heating at 700? C., 110 degrees above the Tammann temperature for nickel, appears to reduce H2 adsorption compared to the heating at 500? C.

[0033] The hydrogen adsorption isotherms generated after heating getter material 1 under vacuum were also used to calculate associated nickel surface areas. The results are set out in Table 4.

TABLE-US-00004 TABLE 4 Heated under vacuum Temperature Metal surface area Getter (? C.) (m.sup.2/g) 1 120 <0.1 300 31.4 500 34.2 700 26.8

[0034] Metal surface areas are quoted per gram of material at the start of the measurement. It can clearly be seen that metal surface areas achievable by the method are in excess of 10 m.sup.2 per gram of getter.