1. Free water: It is the water absorbed when the material is in direct contact with water. It exists in the large capillary with a diameter of 10-5 cm. The water is loosely combined with the material, so it is easy to remove. When this part of the water is removed, the material particles move closer to each other and shrink. The size of the shrinkage volume is approximately equal to the volume of the lost free water, so free water is also called shrinkage water.
2. Atmospheric adsorption water: The water that firmly exists in the fine capillaries of the material (less than 10-5 cm in diameter) and on the surface of the finely dispersed material particles is called atmospheric adsorption water. Atmospheric adsorption water is a general term. The amount of atmospheric adsorption water depends on the temperature and humidity of the surrounding medium; the greater the relative humidity in the air, the more adsorption water the material contains.
When the water contained in the material is balanced with the water in the surrounding medium, the water balance water level W, and the balance water belongs to atmospheric adsorption water.
At a certain temperature, the balance between the moisture contained in the material and the moisture contained in the saturated air (Φ=100%) is called atmospheric adsorption water Wabsorption. In fact, this is the highest point of atmospheric adsorption water. Above this point, it is free water.
The material does not shrink when the atmospheric adsorption water is discharged, and no stress is generated in the product. The drying speed can be accelerated as much as possible without producing waste.
3. Chemically bound water: refers to the water contained in the raw material mineral composition (such as kaolin). This water is not discharged during drying and can only be discharged when heated to a dehydration temperature of 400~500℃. Excluding chemically bound water does not cause shrinkage, only reduces the weight of the material, and its porosity increases.
2025-03-28
