Silica gel is a nanoporous material that can be used as a drying agent, as adsorbent, or as a moistureproof material. It has been widely used in the past for chromatographic applications. In addition to its many applications, silica gel can also be used as a catalyst carrier.
The thermal properties of different binder materials can affect the adsorption performance. For example, PVP 2 wt.% has a higher thermal conductivity than SGP. As a result, the specific heat capacity can be increased. Another way to increase the thermal conductivity of silica gel is to use carbon materials.
The density of silica gel is a measure of its adsorption performance in a non-equilibrium environment. Generally, silica gel adsorbs water vapor at a rate that increases with increasing relative humidity. This is a useful indicator of a desiccant’s moisture adsorption capacity.
Silica gels are usually classified into three types, depending on the density and surface area of their particles. Typical commercial silica gel has a bulk density of 0.7 grams per milliliter and has a surface area of 750 square metres per gram.
Sol-gel materials are formed by hydrolytic condensation of chemical precursors. They produce small silica clusters and larger siloxane rings. During the aging process, siloxane bonds are reformed. When the material is heated, the formation of larger aggregates results.
Silicone gels are also classified according to their surface chemistry. Type A silica gels are more acidic because of their presence of metal contamination.
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