Silica Gel - Types, Grades, Etc

hAzzBEEn · Fri Jun 03, 2005 2:27 am

What is the difference between the different designations of Silica Gel?
Here are some that I've seen (XX means a number):

Silica Gel, XX
Silica Gel, Functionalized
Silica Gel, Grade XX
Silica Gel, Indicating

I've seen these through chemical suppliers, and they are very expensive.
What is the difference in those listed and the cheap kind for drying flowers?
I've also seen the kind called "air drying agent" that is cheap.
Is the cheap stuff good for chemical reactions (n-butylamine condensations)?
Does anyone have any other random information about Silica Gel that may be useful?

bio · Working Bee

Here is some general informatio and specs on a CP grade silica gel. Check the major suppliers techdata furnished in their catalogs for a description and uses of different types. Don't use indicating in liquids unless you want cobalt that is.

Silica Gel (SiO2 * H2O)
Perhaps the most commonly used desiccant, silica gel, is an amorphous form for silica manufactured from sodium silicate and sulfuric acid. Its interconnected pores form a vast surface area that will attract and hold water by adsorption and capillary condensation, allowing silica gel to adsorb about 40% of its weight in water. Silica gel is extremely efficient at temperatures below 77°F (25°C) (see Figures 1 and 2),but will lose its adsorption capacity as temperatures begin to rise, much like clay (Table 2). Much of silica gel's popularity is due to its noncorrosive and non-toxic nature; some grades have received U.S. government approval for use in food and drug packaging.

SPECIFICATIONS#
Absorption efficiency : Above 25% under 50% R.H. and 20C temperature : Above 65% under 100% R.H. and 20C temperature
#
Combined Water : Maximum 6% (Loss on drying at 150C)#
Chloride (as NaCl) : Less than 0.05%#
Sulphate (as Na2 So4) : Less than 0.25%#
Organic Matter (as NH3) : Less than 0.001%#
PH : Between 6 to 8#
Cobalt Chloride : 1 to 1.5% (in Indicating type Blue)#
Friability and dust : Less than 0.05%#
Average purity : 99.8 or more % Silica (SiO2) on dry basis

PHYSICAL CONSTRAINTS#
Pore Volume : 1.2 to 1.3 cc/gm#
Pore Diameter : Average 140 to 150 Angstaom Units.#
Surface Area : 500 to 700 square meters per gm#
Average Porosity : 60 to 65%#
Thermal Conductivity : 1 BTU/sq ft / hr/ F /in#
Sp Heat : 0.2 to 0.22 BTU/lb/ F#
Specific Gravity : 2.1 to 2.3#
Hardness : 5 on Moh's Mineralogical Scale#
Oil absorption : 1.6 g/g#
Percentage of Fe/ other impurities : Nil#
Capacity to absorb : Moisture from air, any condensable vapours, oil. Acetylene and other hydrocarbons from liquid oxygen

epck · Sat Jun 04, 2005 2:22 am

Silica gel has two major uses in chemistry -for use in chromatography and as a dessicant.

The Silica gel, indicating is used as a dessicant, where something (Cobalt chloride, I think) is added to indicate when it has used up most of its water absorbing capibilities.

Silica gel, XX is used in chromatography where the number XX refers to the pore size in the silica particles. The bigger the pore size the faster it elutes, the smaller the pore size it gets better seperation.

Silica gel, functionalized is again used in chromatography where different functional groups are added to the silica to change change how 'sticky' the silica is. This allows the experimenter to fine tune his seperation of compounds.

thenewrunne · Chemically Balanced

What about kitty litter 100% silica gel? Can it be safely used as a dessicant? (it says 100% Wink

)

epck · Sat Jun 04, 2005 4:47 am

Maybe, it'll probably depend on what pore size they use. Probably be worth a try.

thenewrunne · Chemically Balanced

What temperature should it be dried at to get rid of any H2O present? For how long? Any chemicals that I can purchase easily to make it indicating?

bio · Working Bee

Dry to constant weight at about 200deg. Different sources say anywhere from 150-250 but it will scorch a little at 250. Also just before use I nuke it for 60 sec on high.

You shouldn't need any indicator for drying solvents. Just use say 20% over the calculated amount assuming worse case water content and swirl once in a while for a few hours. Wash solvents w/ brine first if water immiscible.

hAzzBEEn · Tue Jun 07, 2005 10:55 pm

thenewrunne: Both the indicating (color changing) and the regular silica gel can be purchased for drying out flowers. SWIM has some regular silica get that looks like like little spheres slightly larger that a BB or pellet for an air rifle. You can search for silica gel and flowers using google and find it for sale. You can also find it for packing and shipping in little packets.

epk, bio: Thanks for the information. That was very helpful. I now understand why there are so many different types of silica gel. I was primarily concerned with silica gel used as a dessicant, and the extremely high prices of silica gel from chem suppliers as compared to the generic stuff sold by hobby shops. I'm sure the cheap stuff will work fine for a dessicant.