Humidity indicators

• US 20040209372A1
• Filed: 05/10/2004
• Published: 10/21/2004
• Est. Priority Date: 04/22/1999
• Status: Active Grant

• Current Assignee: PQ Silicas UK Limited (Ecovyst, Inc.)
• Original Assignee: Ineos Silicas Limited (INEOS Holdings Ltd.)
• Inventors: Earl, Graham James, Moreton, Stephen
• Granted Patent: US 6,927,063 B2
• Time in Patent Office: Days
• US Class Current: 436/39
• CPC Class Codes: G01N 31/222 for investigating moisture content

Abstract

Silica-based carrier impregnated with iron(III) or iron(II) salts functions as a humidity indicator giving a yellow/amber to nearly colourless colour change as the carrier humidifies.

Claims

1. A humidity indicator comprising a silica gel carrier containing an iron(II) and/or iron(III) salt or salts as an active indicator, the iron salt being a salt containing more than one cation of which one is iron(II) or iron(III).

2. An indicator as claimed in claim 1 in which the iron salt is ammonium iron(III) sulphate, ammonium iron(II) sulphate or potassium iron(III) sulphate.

3. An indicator as claimed in claim 1 in which the iron(II) or iron(III) salt is present in an amount in the range 0.01 percent to 2.0 percent by weight expressed as Fe based upon weight of dry carrier.

4. A humidity indicator as claimed in claim 1 in which the silica gel is humidified silica gel.

5. A humidity indicator as claimed in claim 1 in which the silica gel is beaded or granular silica gel.

6. A method of monitoring the humidity level within an atmosphere comprising exposing a dried silica gel carrier containing an iron(II) and/or iron(III) salt or salts to said atmosphere and observing the colour changes therein, the iron salt being a salt containing more than one cation of which one is iron(II) or iron(III).

7. A method as claimed in claim 6 in which the iron salt is ammonium iron(II) sulphate, ammonium iron(II) sulphateee or potassium iron(III) sulphate.

8. A method of producing a humidity indicator comprising soaking silica gel carrier with a solution of an iron(II) and/or iron(III) salt or salts to impregnate the carrier and drying the impregnated carrier, the iron salt being a salt containing more than one cation of which one is iron(II) or iron(III).

9. A humidity indicator in the form of an iron impregnated silica gel carrier produced by the method as claimed in claim 8.

10. A humidity indicator composition comprising a silica gel carrier containing ferric sulphate or ferric nitrate.

16. A composition as claimed in claim 10 in which the iron salt is present in an amount in the range 0.01 percent to 2.0 percent by weight expressed as Fe based upon weight of dry carrier.

11. A method of monitoring the humidity level within an atmosphere comprising exposing a dried silica gel carrier containing ferric sulphate or ferric nitrate to said atmosphere and observing colour changes therein.

12. A method of producing a humidity indicator comprising soaking silica gel carrier with a solution of iron sulphate to secure impregnation of the carrier and drying the impregnated carrier.

13. A method as claimed in claim 12 in which the colour of the indicator is enhanced by pH adjustment to higher values.

14. A method as claimed in claim 12 including incorporating alkali to adjust pH to higher values.

15. A method as claimed in claim 13 in which pH adjustment is effected by sodium hydroxide addition.

17. A humidity indicator compound comprising a silica based carrier containing a simple iron salt as the active indicator and in which the colour of the indicator is enhanced by pH adjustment to higher values.

18. A compound as claimed in claim 17 in which the iron salt comprises ferric sulphate.

19. A compound as claimed in claim 17 in which the carrier comprises silica gel.

20. A compound as claimed in claim 19 in which the silica gel is humidified silica gel.

21. A compound as claimed in claim 19 in which the silica gel is beaded or granular silica gel.

22. A method of monitoring the humidity level within an atmosphere comprising providing a dried silica based carrier which contains a simple iron salt and in which the colour of the indicator is enhanced by pH adjustment to higher values, exposing said carrier to said atmosphere and observing colour changes therein.

23. A method as claimed in claim 22 in which pH adjustment is effected by sodium hydroxide addition.

24. A compound as claimed in claim 22 in which the iron salt comprises ferric sulphate.