How it Works?
What is Silica Gel; How does Silica Gel work?
Silica 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) of silica gel. It is this structure that makes silica gel a high capacity desiccant. Water molecules adhere to the silica gel crystal surface because it exhibits a lower vapour pressure than the surrounding air. When equilibrium of equal pressure is reached, no more adsorption by silica gel occurs. Thus the higher the humidity of the surrounding air, the greater the amount of water that is adsorbed by silica gel before equilibrium is reached. It is in these higher humidity conditions (above 50% Relative Humidity) that stored or in-transit items are susceptible to damage.
The beauty of silica gel is the physical adsorption of water vapour into its internal pores. There is no chemical reaction, no by products or side effects. Even when saturated with water vapour, silica gel still has the appearance of a dry product, its shape unchanged.
Silica gel was developed just prior to WWI and was used in Allied gas masks; then, in WWII silica gel was used extensively to keep penicillin dry. Silica gel remains the highest capacity adsorbent available today. Not a "gel" as commonly thought of, and not to be confused with "silicon gel", silica gel is a porous, granular form of silica, synthetically manufactured from sodium silicate.
The internal structure of each small silica gel granule is composed of a vast network of inter-connecting microscopic pores, which attract and hold moisture by a phenomena known as physical adsorption and capillary condensation. (It sounds ridiculous, but a single teaspoon of Hydrosorbent Silica Gel has an internal adsorptive area equivalent to a football field, including the two end zones.) Hydrosorbent Silica Gel is inert, non-toxic and safe to use to protect foods, medicines, sensitive materials, electronics, films, etc. Even when saturated with adsorbed moisture, silica gel looks and feels dry to the touch.
Hydrosorbent Silica Gel can be reactivated indefinitely. Each Hydro sorbent Silica Gel unit has a built-in indicator which turns from blue to pink signaling when the product is saturated with moisture and needs reactivation. Once saturated with moisture, silica gel can be easily reactivated in a conventional oven for lifetime protection. Since World War II, silica gel has been the desiccant
Advantages of silica gel as a desiccant.
- Silica gel has many other properties that recommend it as a desiccant.
- Our silica gel can adsorb up to one third of its own weight in water vapour. This adsorption efficiency of silica gel is approximately 35% greater that typical desiccant clays, utilization of silica gel the preferred choice where weight or efficiency are important factors.
- Silica gel has an almost indefinite shelf life if stored in airtight conditions.
- Silica gel can be regenerated and reused if required. Gently heating silica gel will drive off the adsorbed moisture and leave it ready for reuse.
- Silica gel is a very inert material, it will not normally attack or corrode other materials and with the exception of strong alkalis and hydrofluoric acid is itself resistant to attack.
- Silica gel is non-toxic and non-flammable.
- Silica gel is most frequently and conveniently used packed in a breathable sachet or bag. These are available in a wide range of sizes suitable for use with a wide range of applications.
In general, the water vapor adsorption capacity of Silica gel greatly increases with a rise in relative humidity. Factors such as temperature and flow rate can affect the dynamic capacity of the Silica gel.
Silica Gel will selectively adsorb compounds of differing molecular weights. In the liquid phase, compounds of high polarity at more readily adsorbed.
- Water (most readily adsorbed)
- Paraffins (least readily adsorbed)
Dynamic Adsorption is the process by which the Silica Gel removes an impurity (such as water) from a continuously flowing gas stream. The use of Silica gel in a drying column can produce exit gas with a dew point of 100°F.
How to regenerate (Re-Dry) Silica Gel
There are two methods used for re-drying ( regeneration) of silica gel. One method uses the oven, and the other uses the microwave. Before you use either method please read the all the safety precautions described below.
1. Oven Drying Method :
This drying method of silica gel gives the best results even though it takes longer. Set the oven for 120 0C. Place the silica gel in an appropriate container and dry the silica gel until it turns medium blue. The oven drying method takes approximately 1-1/2 hours per quart of silica gel. One quart of silica gel equals weighs approximately 850 grams.
2. Microwave Drying Method :
In this method place the silica gel in an appropriate container and set the microwave power to the medium to medium high setting. Dry silica gel for approximately 3 to 5 minutes and inspect the color change in silica gel crystals. If the silica gel has not dried, stir it with a spoon and heat it for another 3 to 5 minutes. Stir the silica gel mass each time it is inspected. Approximate drying time is 8 to 12 minutes per half kilogram of silica gel. The actual heating times will vary according to the type of microwave. You may set the power setting on high but please be careful not to overheat the silica gel crystals