US2460065A - Cobalt sulfate relative humidity indicators - Google Patents

Description

Patented Jan. 25, 1 949 UNITED STATES ATENT OFFICE 2,460,065 coe'ALr SULFATE REL 'rrv'E nnmnrr'r INDICATORS I Paul Bell Davis, Baltimore, Md., assignor to The Davison Chemical Corporation, Baltimo'ra Md.

No'DraWing. Application February 7, 1945', Serial No. 576,716.

V 8 Claims. 1 This invention relates to indicators and more particularly has reference to compositions for indicating the presence and quantity of moisture in a gaseous atmosphere.

Many chemical compounds and especially a number of salts exist in the anhydrous and hy- In the manufacture of certain products control of the humidity of the airor other gaseous atmosphere is important. Itsometimes happens that even a fraction of a percent of relative humidity in an atmosphere may be detrimental to the operation of a process or the product resulting thereform.

An object of this invention is to indicate the presence of moisture in 'a gaseous atmosphere at predetermined relative humidities or ranges of relative humidities.

Another object of this invention is to provide a moisture indicator capable of response to the moisture in gaseous atmospheres at predetermined relative humidities.

A further object of this invention is to provide a moisture indicator comprising an adsorbent material having a color changing moisture indicating compound carried thereby.

Still another object of this invention is to provide a moisture indicator comprising an adsorbent material having a color changing moisture indicating compound carried therebyin which the adsorbent characteristics of the carrier, its moisture content, the color-moisture content characteristics of the indicating compound and the concentration thereof are correlated to respond to a predetermined relative humidity of a gaseous atmosphere in contact "therewith.

Yet another object of this invention is to provide a moisture indicator comprising a compound which is color responsive to changes in moisture content, carried by silica gel. 7

It is also an object of this invention to provide a method of' making a moisture indicator by depositing a color changing moisture indicating compound in theporesof a porous adsorbent and correlating the character of the adsorbent, its

moisturebontnt, and the character and quan- 2 tity of th color changing compound to obtain a color response to a predetermined relative humidity of a gaseous atmosphere in contact with the indicator.

With these and other objects in View the present invention resides in the association of a compound, having one color in the anhydrous state and a different color in the hydrated state, with an adsorbent such as silica gel and correlating the character of the adsorbent, its moisture con tent and the character and content of the color changing compound. Thus by employing an adsorbent having determined adsorbent charac-' teristics and a determined moisture content as a carrier for a quantity of a predetermined compound exhibiting predetermined color changes with relation to the quantity of water associated therewith, and by varying the quantity of the compound and the temperature to which the carrier and compound are heated, an indicator can be obtained which will respond, by a change in color, to a predetermined relative humidity or range or relative humidities of a gaseous atmosphere to which the indicator is exposed.

A number of compounds such as cobalt sulphate, cobalt bromide, cobalt phosphate, cobalt chloride, cobalt iodide, cobalt thiocyanate, cop'- per bromide, copper chloride, cobalt fluoro-silicate, and others, change color with changes in the amount of water associated therewith. For example, cobalt chloride in the anhydrous state is of a blue color but when associated with water the color changes. When cobalt chloride has taken up its full water content, it has a pink color.

In accordance with the present invention it has been found that by associating a compound,

which has one color in the anhydrous state anda different color when combined with water, with an adsorbent, the so treated adsorbent may be employed for indicating the relative humidity of an atmosphere to which the same is exposed.

For instance, by impregnating an adsorbent such as silica gel with asolution of cobalt chloride, and drying and activating the so treated silica gel, 2. product is obtained having a blue color. When the blue colored silica gel is exposed to a humid atmosphere, moisture from the atmosphere is adsorbed by the silica gel and as the water content of the gel is increased the color of the gel gradually changes to pink. The change in color is due to water combining with the an= hydrous cobalt chloride in the pores of the gel. It has been discovered according to the resent invention that by using a silica el having ce r= tain adsorptive characteristics, by incorporating a certain amount of cobalt chloride in the gel and by heating the treated gel to a certain temperature, the thus treated gel will change color when exposed to an atmosphere having a relative humidity of a certain minimum value or range of values. -It has also been discovered that by changing'one or more of the factors, characteristics or conditions, the thus treated gel will respond to a different minimum relative humidity value or range of values. Apart from varying the factors, characteristics, conditions, etc., itv

EXAMPLE 1 SPECIMEN I-B Cobalt Sulphate (C0304) is highly useful in practicing the present invention. For instance, standard silica gel made by washing an acid reacting hydrogel with acidic wash water at about 150 F., drying and then activating at about 850 Foand of a size of about 6-16 mesh, has been treated with an aqueous solution of 00804 of sufficient concentration and in a sufficient amount to incorporate in the gel a deposit'of C0504 of about 2% of the total weight of the gel and C0504 on a dry basis. After drying at a temperature of about 300 F. and activating at a temperature of about 475 F., the resulting product had a dark purple color or more specifically a Munsell color value of about 5.0 P 4/12.

Upon exposing this product to an atmosphere havinga relative humidity between about fir- /z the color changed to a dark reddish purple at relative humidity, then to a medium red purple at /g% relative humidity, or more specificaziiy to a color ranging between 7.5 P 4/8 and 5.0 RP 6/10 M. C. V.

- EXAMPLE 2 SPECIMEN II-B By varying the temperatures at which the gel containing about 2% C0804 is dried and activated, a color change orbreak occurred upon exposing the so treated gel to an atmosphere having a difierent relative humidity. For in-. stance, upon drying the gel at about 300 F. and activating it at about 850 F. the color will change from 10.0 PB 3/10 Munsell color value to 10.0 P 5/8 M. C. V. when exposed to an atmosphere having a relative humidity of about 3%. Upon exposure to an atmosphere having a relative humidity of about 5% the color "will change further to 5.0 RP 6/10 M. C. V.

EXAIVIPLE 3 SPECIMEN I1I-B posure to an atmosphere having a relative humidity of about 5%; and upon further exposure to an atmosphere having a relative humidity up to about 10% the color will change to 10.0 RP 6/ 10 M. C. V.

4: SPECIMEN II-A.

By treating the gel mentioned in Example 1 with a cobalt sulphate solution so that the gel will contain about 2% cobalt sulphate, drying said gel at a temperature of about 350 F. and activating the same at a temperature of about 725 able for indicating the moisture content of an atmosphere. having a relative humidity ranging between 1% and 3%. For instance, by exposing such a gel having Munsell color value of about 10.0 PB 4/10 to anatmosphere, the relative humidity of which is about 1%, the color will change to about 10.0 P 6/6 M. C(V. and for a relative humidity of about 3% the color will change to about 7.5 RP 7/6 M. C. V. I

EXAMPLE 5 SPECIMEN LA 7 By treating the gel mentioned in Example 1 with a cobalt sulphate solution in a quantity calculated to produce a colored gel containing about /2% cobalt sulphate, drying the so treated gel at 250 F. and activating the same at about 525 R, an indicator gel will beobtained which has a Munsell color value of about 5.0 P 6/4. Upon exposing this indicator gel to an atmosphere having a relative humidity of about 4% the color value will change to about7.5 RP 7/6 M. C. V. and upon exposing the same to an atmosphere having a relative humidity of about /2% the color will change to about 10.0 RP 7/6 M. C. V.

EXAMPLE 6 SPECIMEN IV--B treating a gel similar to that set forth in Example 1 but which had been washed with Water at a temperature of about R, dried and then activated at about 1200 13. and sized to 6-12 mesh, with a quantity of cobaltsulphate solution calculated to impregnate the gel with about 3% cobalt sulphate. Upon drying the so treated gel at a temperature of about 300 F. and activating the same at a temperature of about 1000 F. a product was produced having a Munsell color value of about 10.0 PBS/10. Upon exposing the so treated gel to an atmosphere having a relative humidity of about 5% the color changed to about 10.0 1 4/3 M. C. V. and upon exposing the gel to an atmosphere having a relative humidity of about 10%, thecoloriurth'er changed to about 5.0 RP 6/10 M. C. V.

SPEcnvni III-A exposing the so treated gel to an atmosphere 1 R; an indicator is obtained which is suitace oee 5.. having a relative humidity on? about the color will change to aboutv 5.0 G 5/8 M; C. Upon exposing the gel to. an atmosphere having a relative humidity of about the color will change to 10.0 G 5/6 M. C. V.

EXAMPLES SPECIMEN VIII-A If a copper. bromide impregnated gel corresponding to that of. Example 7 and having a CuBrz content of. about. 4%. isv dried; at about 250 F. and activated. at a temperature of about 350 F., a product is obtained having a. Munsell color value of about 10.0 YB. 2/2. If this product isexposed to an atmosphere having a relative humidity of about the. colorwill' change to about 2.5 GY 4/4 M. C. V. If the. product is exposed to an atmosphere having a relative humidity of about the color will change to about 2.5 G 6/6 M. c. v.

EXAMPLE 9 SPECIMEN IiV-A Cobalt bromide CoBrz is a suitable compound for association with a silica gel for the production of an indicator. For instance, by treating a silica gel such as described in Example 1 with a solution of cobalt bromide in a quantity and having a concentration suilicient to impregnate the gel to an extent of about A CoBrz, drying the product at a temperature of about 275 F. and activating at 400 F., a product is obtained having a Munsell color value of about 5.0 B 3/6. Upon exposing this product to an atmosphere having a relative humidity of about 5%, the color will change to about 7.5 B 7/2 M. C. V. Upon exposing the indicator to an atmospherehaving a relativehumidity of about 10%, the color will change to 7.5 R 8/4 M'. C. V.

' EXAMPLE 1o SPECIMEN VI-A By impregnating the silica gelof Example 1 with a solution of cobalt bromide of such quantity and concentration as to impregnate. thegel to an extent of about 2% C'oBr2 and drying the same at a temperature of about 200- F., a product is obtained having a Munsell color value of" .about 10.0 GY 3/4. Upon exposing this product EXAMPLE 11.

SPECIMEN VII-B By preparing anv indicator gel from silicagel corresponding to that used in Example 1 andimpregnating the same with a quantity of cobalt. bromide to an extent of about 3%v and drying the same at a temperature ofabout; 200,,F.,. a product is obtained having a Munsell color value of about 2.5 G 3/4. Upon exposing this product to an atmosphere having a relative. humidityof about.

10% thev color changed. to about 10.0:YR 5/8 M. C.

V. Upon exposing the product of this. example, to

an atmosphere having a relative humidity of:

about 20% the color changed to 2.5. YR 5 10.

. 6} EXAMPLE 12 SrEoIMEN IX-B' V A silica gel suchas that described in Example lwas impregnated with cobalt bromide to a content of about 2% COBI'z. Upon drying this product at a temperature of about 250 F;, a product was obtained having a Munsell color value-of about 7.5 YR'3/2. The color of this compound changed to abut 2.5 GY 6/4 M. C. V. upon exposing it toan atmosphere having a relative humidity of about 20%. When the product of this example was exposed to an atmosphere having arelative humidity of about the color changed to about 7.5 G 7/6 M. C. V.

SPECIMEN V-A whereby the product has a C03(PO4)2 content of about /g drying the product at about 250 F. and activating it. at a temperature of about 400 R, an indicator gel was obtained having a Munsell color value of about 7.5 PB 3/10. Upon exposing this product to an atmosphere having a relative humidity of about 10% the color changed to about 5.0 R 8/4 M. C. V. When the product was exposed to an atmosphere having a relative humidity of about 20% the color changed to about 2.5 R 8/4 M. C. V.

EXAMPLE l4 SPEC MEN V-B Cobalt chloride may be used invarious concehtrations for association with silica gel for the production of moisture indicators in accordance with the present invention. By incorporating cobalt chloride with a silica gel such as described inconnection with Example 1 to such an. extent that the product has a COC12 content of about, Ao drying the product at av temperature of about 300 F. and activating it. at 400 F., an into an atmosphere having a relative humidity of about 20%.

' EXAMPLE 15 SPECIMEN VII-A about, 20% the color changed to about 10.0 HP

EXAMPLE 1e I Specimen X-B at; treating a. silica. gel similar as that. a

Example 1 but which had been activated at a temperature of about 1100 F. with cobalt chloride in a quantity sufficient to have a C0012 content, drying the same at a temperature of about 300" F. and activating at a temperature of about 400? R, an indicator gel was obtained havinga Munsellcolor valueof about 7.5 PB 2/6. Upon exposing this product to anatmosphere having a relative humidity of about 40%, the. color changed to 10.0P 4/8 M. C. V. The same indi cater exposed to an atmosphere having arelative humidity of about 60% exhibited a color of about 7.5 RP 5/8 M. C. V.

EXAMPLE 17 SPECIMEN VI-B Copper chloride is another chromatic chemical suitable for use in accordance with the present invention. By impregnating silica gel prepared in accordance with that described in Example 1 with copper chloride to an extent whereby the resulting indicator gel has a CuClz content of about 2%, drying at a temperature of about 300 F. and activating at a temperature of about 600 F., a product was obtained having a Munsell.

color value of about 7.5 GYe/fi. Upon exposing this indicator gel to an atmosphere having a relative humidity of about the color changed to about 10.0 GY 7/8 M. C. V. and upon exposing the product to an'atmosphere having a relative humidity of about the color changed to about 2.5 G 7/ 8 M. c. v.

EXAIVIPLE 18 SPECIMEN .VIII-B GY 5/2 M. C. V. When the same product was exposed to an atmosphere having a relative humidity of about 30%, the color changed to about 10.0 PB '6/2 M. C. V.

EXAMPLE 19 SPECIMEN X- -A By heating a silica gel havinga cobalt iodide content of about 2% to a drying temperature of about 250 F., an indicator gel was obtained having a Munsell color value of about 7.5 GY 2/2. This indicator gel changed its'color upon exposure to an atmosphere, having a relative humidity of about 40%, to about 2.5 Y. 6/6 M. C. V. When this same indicator gel was exposed to an atmosphere having a relative humidity of about the color changed to 2/5 YR 7/4 M. C. V. r v I EXAMPLE 2o SPECIMEN IX-A Bytreating a silica gel such as that described in Example 1 with cobalt thiocyanate to produce an indicator gel having a CO(SCN)2 content of about and drying the same at a tempera-' ture of about 250- F., an indicator gel was obtained having a Munsell color value of about an "atmosphere having a relative humidity of about 20%. Upon exposing the same compound to anatmosphere having a relative humidity of about 40% the color further'changed to about 7.5 RP 6/8 M. C. V.

Many of the indicator gels. prepared according to the present invention have high adsorptive characteristics, especially those which are activated after drying and these may beemployed for the same purposes as ordinary desiccant silica gel as well as for moisture indicators. of course, some of the indicator gels, especially those in which drying without activation is employed to correlate the moisture content with 'the other factors and characteristics, do not have the ad-. sorptive capacity. of desiccantsilica gel. These indicator gels therefore are used principally for moisture indicating purposes. In some instances such indicator gels may be dispersed through masses'of desiccant silica gel having high adsorptive capacities to indicate When the desiccant silica gel has taken up a predetermined quantity of moisture.

In impregnating the silica gel with the solution of chromatic chemical, the gel was first subjected to anatmosphere having a high relative humidity to saturate thegei with moisture to such an extent that upon contacting the same with a liquid the gel would not disintegrate, which happens upon contacting freshly activated gel with a liquid. Also by saturating the gel to approximately 30% total volatile matter, only about 50 ml. of solution isrequired to wet about 1 kilogram of gel. As before indicated, the concentration of the solution of chromatic chemical is such that by wetting the saturated gel with the above mentioned quantity of solution per kilogram of gel, the desired concentration of chemical in the gel is obtained.

By holding the gel at the dryingtemperatures indicated in the preceding examples, efiective drying is accomplished. Also by holdin the gel at the activating temperaturesmentioned activation is effected. In each instance, the indicator gel was held at the drying and/or activating temperatures for about three hours.

- While the indicators have been described as including, carriers of silica gel impregnated with a chromatic chemical, it should be understood that other adsorbent carriersmay be used. For

instance, a porous adsorbent glass which is described in the Hood et a1. Patents Nos. 2,106,744, 2,315,328 and 2,315,329, maybe used as set forth in my copending application Serial No. 576,726, (now abandoned), filed-of even date herewith.

,To demonstrate the utility and practicability of the present invention, a specimen set of indicator gels was made and sealed in small glass ampules. Each specimen consisted of three tubes or ampules, one containinga portion of a certain indicator gelbeiore exposure to an atmosphere, the relative humidity of which was to be determined, the second containing a portion of the same indicator gel after exposure to an atmosphere havin a predetermined relative humidity; and the third containing a portion of the same indicator gel after exposure to an atmosphere having a higher relative humidity. Apart from demonstrating the color changes or breaks, these specimens are useful as standards for comparisonof the colors of indicator gels exposed to atmospheres having unknown relative um ie i. V V

Two 'sets of specimens were arranged. in framesior convenience in handling and the frames were designated by Roman numerals and the specimensin each frame were designated by the letters A andB;

v The following Tablel designates the constitution of the indicator gels of the specimens and Table II designatesthe colors of the indicator gels before and after. exposure to two atmospheres of diiferent relative humidities, the humidities being'those at which the colors distinctly change.

In the preceding examples and in Table II, colors .are described 'for the indicator gels when exposed to two atmospheres of different relative humidities. However, these two specific relative'humidities are to be taken as the upper and lower limits of a range in which a distinctive color break will occur, the color changing from that for the activated indicator gel to a color within the range of colors, the limits of which are indicated.

Data concerning the various specimens of indicator gels prepared in accordance with the present invention are given in the following tables:

air having a certain relative humidity. The indicator gel ready for use is supported in any suitable manner for exposure to an atmosphere such as air having an unknown relative humidity. One valuable use of the indicator gels is in connection with the maintenance of a moisture-free atmosphere or an atmosphere the humidity of which is to be maintained below'a predetermined maximum.

From the foregoing description, it will be appreciated that the present invention provides a moisture indicator, a method of making the same and a method of ascertaining the relative humidity of a gaseous atmosphere. Whil'e'reference has been made to a certain chromatic chemicals in the description of the indicator gels mentioned, these are given primarily by way of example since other chromatic chemicals having colors varying with moisture content may be used.

I claim:

l. A method of preparing a quantitative relative humidity indicator comprising impregnating adsorbent silica selected from the group consisting of silica gel and porous glass with about /2 Table I INDEX T0.SPEOI1VIEN SET OF INDIOATING GELS Color Break (Rela- Indicator Per Cent Activated Flame tive Humidity) on No. Gel 111mm Indicator Dned at at- F. F. I {.A. 214 85956-160 005.04 it B. %%P%- 85956-160 .....d 2 H i {.A. 1 3 85956-160 .-...d0--- 2 B. 85956-160 -.---d0 2 In {11. 85956-160 CuBrz. '4 13. 85956-160 C0804. 2 Iv {A 85956-160 (301311. 54 B. 129756-120 C0504. 3 v {A. 85956-160 (303(104) /a B. 85956-160 C00 56 VI A. 85956-160 CoBrz... 2 B. 85956-160 CuGlz. 2 VII {11. 85956-160 ...-.d0. 2 13. 85956-160 CoBrz. 3. 0 VIII {A. 85956-160 CuBrz 4 B. 85956-160 C012 2 I: {A. 85956-160 Co(S B. 85956-160 CoBrz. 2 X A. 85956-160 C012- 2 B. 11956-160 CoC12......--. 5

Table II APPROXIIMATE MUNSELL'GOLOR VALUEG%SO. V.) OF SPECIMEN SET OF INDICATING Frarn Relative 7 Relative Relative No. Humidity M Humidity Humidity M V I A. Activated... $4 7.5 10.0 RP 7/6. B. Activated.... RP 6/10- A. Activated-.- 1 10.0 3 7.5 RP 7/6.

1 B. Activated... a 10.0 a 5.0 RP 6/10. In {11. Aetivated.... 5 5.0 G 10.0 G 5/6.

B. Activated.... 5 7.5 R 10 10.0 RP 6/10. IV 1. Activated.... 5 7.5 B 10 7.5 R 8/4.

B ti t d 5 10. 10 5.0 6/10- V A. Aetivat xL 10 5.0 2.5 R 8/4. B. Activated. 10 7.5 20 7.5 RP 8/2. VI A. Activated. GY 10 5.0 20 2.5 YR 7/6. {B. Activated- GY 4/ 10 10. 20 2.5 G 7/8. VH A. Activated. PB 10 7.5 20 10.0 RF 6/8. B. Activated.... G 3 10 10. 20 2.5 YR 5/10. VH7 A. Activated... 10.0 YB 20 2.5 2.5 G 6 6.

B. Activated... 7.5 PB 20 7.5 30 10.0 P 6/2. IX {1 1. Activated... 7.5 PB 3/ 20 10. 7.5 RP 6/8.

B. Activated... 7.5 YR 20 2.5 40 7.5 G 7/6. c A. Activated... 7.5 GY 40 2.5 2.5 YR 7/4. B. Activated.-.. 7.5 PB 40 10. 60 7.5 HP 5/8.

In using the moisture indicator of the present invention, a gel impregnated with a determined quantity of a selected chromatic chemical is dried, or dried and activated, at predetermined temperatures to produce an indicator having its characteristics, etc, correlated to change color to 3%, on a dry basis, of cobalt sulphate, said cobalt sulphate having one color in a hydrated state and a different color in a less hydrated state, and heat treating the so impregnated silica at 2501000 F., said indicator changing color when exposed to an atmosphere having a relative huupon exposure to a gaseous atmosphere such as midity of 0-10%.

2. A quantitative relative humidity indicator as prepared by the method of claim 1. r

3. A method of preparing a quantitative relative humidity indicator comprisingimpregnating activated silica gel without about /z%, on a dry basis, of cobalt sulphate, drying the impregnated silica gel at a temperature of about 250 F., and activating the impregnated silica gel at atemperature of about 525 F., said indicator changing color when exposed to an atmosphere having a relative humidity of 4. A quantitative relative humidity indicator consisting essentially of silica gel impregnated with about /2%, on adry basis, of cobalt sulphate, said indicator changing color when exposed to an atmosphere having a relative humidity ranging from zero to ,41% and being prepared by the method of claim 3.

5. A method of preparing a quantitative relative humidity indicator comprising impregnating activated silica gel with about 2%, on a dry basis, of cobalt sulphate, drying the impregnated silica gel at a temperature of about 300 F.,'and activating the impregnated silica gel at a temperature of about 475, said indicator changing color when exposed to an atmosphere having a rela tive humidity of A to /2 6. A quantitative relative humidity indicator consisting essentially of silica gel impregnated with about 2%, on a dry basis, said indicator changing color when exposed to an atmosphere having a relative humidity ranging from to and being prepared by the method of claim 5;

7. A method of preparing a quantitative relative humidity indicator comprising impregnating 1'2 activated silica gel with about 3%, on a dry basis, of cobalt sulphate, drying the impregnated silica gel at a temperature of about 300 F., and activating the impregnated silica gel at a temperature of about:1000 F., said indicator changing color when exposed to an atmosphere having a relative humidity of 5-10%.

8. A quantitative relative humidity indicator consisting essentially of silica gel impregnated with about 8%, on a dry basis, of cobalt sulphate, said indicator changing color when exposed to an atmosphere having a relative'humidity ranging from 5 to 10% and being prepared by the method of claim 7.

. PAUL BELL DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,947,381 Connolly et'al. Feb. 13,1934 1,976,875 Connolly et a1 Oct. 16, 1934 2,210,862 Tronstad Aug. 6, 1940 2,214,354 Snelling Sept. 10, 1940 FOREIGN PATENTS Number Country Date 393,094 Great Britain June 1, 1933 280,934 Great Britain Feb. 18, 1929 OTHER REFERENCES.

The Chemical Trade Journal and Chemical Engineer, July 14, 1939, page 31.

Certificate of Correction Patent No. 2,460,065. January 25, 1949. PAUL BELL DAVIS It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 7, example 16, for Munsell color value of about 7.5 PB 2/6. read Munsell color value of about 7 .5 PB 2/8.; line 10, same example, for changed to 10.0 P 4/8 read changed to 10.0 P 4/6;

and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 31st day of May, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.