ABSTRACT
Silica gel is an artificially prepared inert crystalline colourless chemical substance composed of silicon and oxygen. Its most important physical property is its high absorptive capacity for water vapour. It has extensive industrial use as a drying agent, and also has found use in a limited way as an absorbent for airborne pollutants. The use of silica gel for humidity-buffering purposes, as in museum applications, is of recent origin (dating from the 1950s). Only a small part of silica gel production is devoted to such use. The method of preparation of silica gel for humidity-buffering purposes is detailed below. Essentially the dry gel is exposed to a humid atmosphere for a fixed period of time until the crystals have absorbed a known amount of moisture. The moisture content is determined by removing samples, weighing, heating to dryness, re-weighing and then calculating the moisture content (dry basis). By consulting the isotherm curves which relate the moisture content of the silica gel (actually the equilibrium moisture contentEMC) to given ambient RH conditions, one can arrive at the degree of exposure to produce the required conditioned gel. Silica gel prepared in this manner can then be stored in polyethylene bags, or other humidity-tight containers for further use.
