Facts and Information About Indicating Silica Gel
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Transcript of Facts and Information About Indicating Silica Gel
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
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
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 )
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
DescriptionSILICA GEL BLUE
(INDICATING TYPE)Assay (as SiO2) Min 97%pH 4 - 8Bulk Density (g/ml) 0.65 - 0.85Loss on Drying % <6
Adsorption Capacity @ 100% humidity
35-40
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
Description SILICA GEL Orange (INDICATING TYPE)
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
SILICA GEL BLUE & SILICA GEL ORANGEPROPERTIES Silica Gel
BlueSilica Gel Orange
Remarks
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
Orange-Brown-Cyan(Green)
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