Facts and Information About Indicating Silica Gel

Indicating Silica Gel

Transcript of Facts and Information About Indicating Silica Gel

Indicating Silica Gel

What is Absorption ???


What is Adsorption ???

Description of Picture goes here.

Absorption is the passage of one substance into or through the bulk of another medium….

Absorb substance spread to saturate to hole of medium to form a solution & get mixed with other medium is so well that one fail to recognise its existence.

Adsorption is the adhesion or sticking together of molecular of gas, liquid or dissolved soilds to the surface of soild or sometimes a liquid…..the molecules are loosely held by the surface & can be easily removed

Adsorbate : - It is the substance which is adsorbed at the surface of another substance Examples are: gases, dyes, water vapors etc.

Adsorbent :- It is the substance which adsorbs the other substance at its surface. Examples are: Silica gel, Activated Alumina, Molecular Sieves,Activated Carbon & Clay etc

Adsorption process

Chemisorption: Chemisorption is a kind of adsorption which involves a chemical reaction between the surface and the adsorbate. New chemical bonds are generated at the adsorbant surface

Physisorption:It also called physical adsorption

Physical adsorption: Van der Waals attraction between adsorbate and adsorbent. The attraction is not fixed to a specific site and the adsorbate is relatively free to move on the surface. This is relatively weak, reversible, adsorption capable of multilayer adsorption

Adsorption Equilibria / Capillary Condensation:

If the adsorbent and adsorbate are contacted long enough an equilibrium will be established between the amount of adsorbate adsorbed and the amount of adsorbate in solution. The equilibrium relationship is described by isotherms

Types of Adsorbents:-

Silica gel Molecular Sieves Activated Alumina Activated CarbonClay

SILICA GEL(IS 3401:1992)

Silica gel is adsorbents in a granular, porous form of Silicon Dioxide made synthetically from Sodium SilicateSilica gel is an amorphous form of silicon dioxide, which is synthetically produced in the form of hard irregular granules(having the appearance of crystals) or hard irregular beads. A microporous structure of interlocking cavities gives a very high surface area (800 square meters per gram). It has an average pore size of 2.4 nanometers and has a strong affinity for water molecules

Manufacturing Process.Silica is prepared by mixing a sodium silicate solution with sulphuric or hydrochloric acid. The solution is then filled up in the pits for crystallisation. The crystals are then washed with water to remove impurities & then dried. The dried Silica is then sieved as per the required sized.Na2 SiO3+2HC1+nH2O → 2NaC1+SiO2•nH2O+H2O

Types of Silica gel

Non- Indicating Silica Gel (Does not change colour after adsorbing moisture)Indicating Silica Gel ( Changes it colour after adsorbing moisture )

Indicating Silica gel

Silica Gel Blue &

Silica Gel Orange

Silica Gel BlueBlue Silica gel is prepared by impregnating White Silica gel with Cobalt Chloride - an indicator, which provides the Blue colour appearance. When free from moisture it will be blue in colour and after adsorbing moisture the particles turn into pinkIt is the cobalt in the cobalt chloride indicator that is responsible for the toxic labelling and disposal restrictions on this product.It is still though considered as non-hazardous for transportation purposes.

Technical Parameter


(INDICATING TYPE)Assay (as SiO2) Min 97%pH 4 - 8Bulk Density (g/ml) 0.65 - 0.85Loss on Drying % <6

Adsorption Capacity @ 100% humidity


Friability 99.5Chloride (as NaCl) Max 0.4%Cobalt (as CoCl2) 0.5%

Sulfates (as Na2SO4) Max 0.5%

Binder (as CaSO4) NIL

Particle Beads size (mm)1-2 mm, 1-3 mm, 2-4 mm, 2-5 mm, 3-5 mm, 3-6 mm, 4-8 mm

Particle Crystals size (mesh)

1-3 mesh, 3-4 mesh, 5-8 mesh

Silica Gel Orange

It is produced by impregnating white Silica Gel with Phenolphthalein due to which the colour of Silica Gel turns orange. Orange indicating Silica Gel is gradually replacing blue Silica Gel as the blue mixture is presumed to cause cancer. This orange Silica in turn changes to a translucent green after it absorbs moisture.

Technical Parameter


Assay (as SiO2) Min 97%

pH 6-8Bulk Density (g/ml)   0.65 - 0.75Loss on Drying % 2.0

Adsorption Capacity -20% RH, 25 degrees C35% RH, 25 degrees C50% RH, 25 degrees C

 9.0% w/w

12.0% w/w22.0% w/w

Friability  99.5Chloride (as NaCl)  Max 0.4%Phenolphthalein 0.2%Colour RH 20% RH 35% RH 50%

Yellow/ Dark OrangeLight OrangeCyan / Blue dark

Available Particle size 2-5 mm, 3-5 mm, 6-8 mesh


BlueSilica Gel Orange


pH 4-8 6-8 Controlled pH conditions

Loss on Drying% Max 6% Max 2% Better dried product

Adsorption Capacity at 100% humidity

Min 35% Min 38% Better capacity for moisture pick up

Colour Indication Blue-White-Pink


Better & clear indication observations

Cobalt 0.4-0.6% NIL Cobalt is carcigen & it is harmful

Environment Safety Hazarder Non-hazarders E C Directive 67/548/EEC


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