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AEROSIL® fumed silica is a largely chemically inert material and will therefore remain chemically stable for many decades under suitable storage conditions. This is subject to it not coming into contact with hydrofluoric acid or any highly alkaline subtances, since these types of material will always react with silicon dioxide.
However, if storage conditions are not ideal, volatile substances can be absorbed into AEROSIL® products due to its high specific surface area. Adsorption is most likely with those chemical compounds, which can interact with the silanol groups, particularly via amino- or hydroxyl groups. In the case of water, any adsorption is reversible. The drying loss of hydrophilic AEROSIL® fumed silica can therefore increase with rising humidity and decrease with falling humidity. The adsorption capacity of hydrophobic AEROSIL® fumed silica is significantly less and its moisture adsorption is therefore much lower. AEROSIL® fumed silica has a tapped density of about 50 g/l . The volume really occupied by the silica particles is only approximately 3 percent. It is possible for slight compaction to occur during longer storage time, particularly in the lower layers of a pallet. This can lead to a minor increase in tapped density and to a change in the structure.
It is advisable to store AEROSIL® products and other fumed oxides in closed containers under dry conditions and to protect them from volatile substances. The product should be used within two years of the date of manufacture. The date of manufacture is included in the control number, which is printed on each bag.
More detailed information on storage is provided in the Technical information 1373 “Storage of AEROSIL®”.