Moisture content
From Freepedia
Moisture content (MC) is a term used in a wide range of scientific and technical areas to express the quantity of water that a material contains.
For rigid materials such as ceramic materials the moisture content w is expressed as mass moisture/dry volume of the material:
For materials which change volume depending on water content such as wood mass moisture/dry mass of the specimen has to be applied.
Moisture is a mixture of two things: adsorbed moisture at internal surfaces and capillary condensed moisture in small pores. At low relative humidity's moisture consists mainly of adsorbed water. At higher relative humidity liquid moisture becomes more and more important, depending on the pore size. In wooden based materials, however, almost all moisture is adsorbed at humidities below 98 % RH.
In biological applications there can also be a distinction between physisorbed water, and free water, the physisorbed water being that closely associated with and relativley difficult to remove from a biological material. The method used to determine water content may affect if water present in this form is accounted for.
Water molecules may also be present in materials closely associated with individual molecules, as "water of crystallization", or as water molecules which are static components of protein structure.
Detemining moisture content can be achieved in many ways depending on the material using electronic moisture analysers, chemical titrations for example the Karl Fischer titration, by determing mass loss on heating (perhaps in the presence of an inert gas), or following freeze drying.
