Silica gel - safe protection?
In our products, we use health-friendly active natural clay, which has almost the same absorption capacity as silica gel and is from natural sources. Silica gel is a pioneer in the field of protective technology, so we decided to look at it.
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.
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 millimetres in diameter. Some grains may contain small amounts of indicator substance that changes colour 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.
Silica gel was in existence as early as the 1640s as a scientific curiosity. It was used in World War I for the adsorption of vapours and gases in gas mask canisters. The synthetic route for producing silica gel was patented by chemistry professor Walter A. Patrick at Johns Hopkins University in 1918.
In World War II, silica gel was indispensable in the war effort for keeping penicillin dry, protecting military equipment from moisture damage, as a fluid cracking catalyst for the production of high octane gasoline, and as catalyst support for the manufacture of butadiene from ethanol (feedstock for synthetic rubber production).
Silica gel is non-toxic, non-flammable, and non-reactive and stable with ordinary usage. It will react with hydrogen fluoride, fluorine, oxygen difluoride, chlorine trifluoride, strong acids, strong bases, and oxidizers. Silica gel is irritating to the respiratory tract and may cause irritation of the digestive tract, and dust from the beads may cause irritation to the skin and eyes, so precautions should be taken. Crystalline silica dust can cause silicosis, but synthetic amorphous silica gel is indurated so does not cause silicosis. Additional hazards may occur when doped with a humidity indicator.