Dynamics of water vapor adsorption on humidity-indicating silica gel

Abstract

Well-defined CoCl -containing silica gels were prepared by impregnation of the aqueous solution of the salt to silica 2 hydrogel, drying and aging methods. Silica gels having 392-437 m 2 g y1 surface area and 0.21-0.37 cm 3 g y1 pore volume and having an average particle size of 3 mm were obtained. Aging in CoCl solutions decreased the surface area of silica 2 gels from 540 cm 2 g y1 to 392-430 m 2 g y1 and pore volume from 0.27 to 0.21-0.23 cm 3 g y1 for CoCl concentration 2 smaller than 0.28 mol dm y3 in silica gel. Adsorbed water desorbed from the gels absorbing 1917-2555 J g y1 energy as determined by differential scanning calorimetry. The CoCl -containing gels were successfully used in dynamic column 2 experiments, with linear relation between velocities of inlet air and movement of blue to pink boundary. The colour change also makes the detection of the defects in column filling which causes air channelling. q 1998 Elsevier Science B.V. All rights reserved.

Preparation of an efficient humidity indicating silica gel from rice husk ash

“…One reason of high surface area gel formation may be the use of very low concentration of the cobalt chloride. It has been reported (Balkose et al 1998) that the pores of silica gel may be filled by the CoCl 2 to some extent depending upon its concentration. The filling of pores lowers the adsorption capacity of the gel.…”

“…Therefore, a visible indication is necessary to know when the gel is saturated with moisture. Traditionally this has been achieved by impregnating the gel with cobalt salt, usually chloride (Balkose et al 1998), which imparts a deep blue colour to the dry gel. The colour of the dry gel changes from blue to light pink upon water vapour adsorption.…”

Methods of humidity determination Part I: Hygrometry

“…The relation of conductivity to relative humidity in general is not linear and may be applied only within a restricted measuring range. High sensitivity humidity sensors based on single SnO 2 nanowires have linear response in conductivity to humid air [18]. Cells with manganese oxide-clay solid electrolytes have good linearity and fast response in galvanic potential to changes in humidity [19].…”

“…Such indicators are widely used to control the activity of drying agents and as breakthrough indicators [20]. Test methods of qualitative water indication include redden of blue cobalt(II)chloride [18,21]. Usually blue cobalt-II-chloride is dispersed in silica gel.…”

Use, Preparation, and Characterization of Copper-Containing Silica Gel

“…Humidity-indicating silica gels change their color when their moisture content reaches a certain value. Silica gel with Co­(II) is blue when dry and turns pink upon moisture absorption . Co­(II) compounds are expensive, and it would be more economical to use cheaper Cu­(II) compounds for the same purpose.…”