Silica gel creates a porous form of silicon dioxide with nanometer-scale voids. This amorphous material traps water molecules through adsorption rather than absorption, making it an excellent desiccant.
Historical Development
The material emerged in the 1640s as a scientific curiosity. Walter A. Patrick, a chemistry professor at Johns Hopkins University, patented the synthetic production method in 1918. The material proved vital during World War I, protecting soldiers through gas mask filters.
Physical Properties
The gel’s structure contains irregular frameworks of silicon and oxygen atoms. Its high surface area (750-800 m²/g) enables it to adsorb up to 37% of its weight in moisture. The material stays hard even when saturated with water, though softer than pure quartz.
Types and Applications
Type A pellets offer 2.5nm pores for basic moisture control. Type B features larger 4.5-7.0nm pores for liquid absorption. Type C provides micro-pored structures ideal for specialized applications like cat litter.
Practical Uses
Moisture Control
The gel protects electronics, preserves food freshness, and prevents condensation in industrial equipment. Museums use it to maintain precise humidity levels for artifact preservation.
Industrial Applications
The material serves as:
- Chromatography medium
- Chemical synthesis platform
- Water filtration component
- Food additive (FDA approved up to 2%)
Safety Considerations
The basic form remains non-toxic and stable. However, dust can irritate eyes and lungs. Some varieties contain harmful indicators – cobalt chloride (blue to pink) faces EU restrictions due to cancer risks. Methyl violet offers a safer alternative, changing from orange to green with moisture exposure.
Citations:
https://en.wikipedia.org/wiki/Silica_gel
Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other liquids, or may be filled by gas or vacuum. In the last case, the material is properly called silica xerogel.
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| Identifiers | |
|---|---|
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| ChemSpider |
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| ECHA InfoCard | 100.065.880 |
| UNII | |
CompTox Dashboard (EPA) | |
| Properties | |
| SiO2 | |
| Molar mass | 60.08 g/mol |
| Appearance | Transparent beads |
| Odor | Odorless |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Silica xerogel with an average pore size of 2.4 nanometers has a strong affinity for water molecules and is widely used as a desiccant. It is hard and translucent, but considerably softer than massive silica glass or quartz, and remains hard when saturated with water.
Silica xerogel is usually commercialized as coarse granules or beads, a few millimeters in diameter. Some grains may contain small amounts of indicator substance that changes color when they have absorbed some water. Small paper envelopes containing silica xerogel pellets, usually with a "do not eat" warning, are often included in dry food packages to absorb any humidity that might cause spoilage of the food.
'Wet' silica gel, as may be freshly prepared from alkali silicate solutions, may vary in consistency from a soft transparent gel, similar to gelatin or agar, to a hard solid, namely a water-logged xerogel. It is sometimes used in laboratory processes, for example to suppress convection in liquids or prevent settling of suspended particles.