Refractory materials have to have a pre-fire dry baking process before sintering, and this process is also called the process of drying moisture. There are 3 types of moisture in refractory materials, they are: structural water, crystalline water, and free water.
Structural water
What is meant by structural water? Structural water in minerals generally refers to the ionic state of H+, OH- or H3O+ (more commonly OH-) added to the mineral crystal structure. These ions occupy a certain position in the mineral lattice, and their content is certain and firmly bonded. Only under the conditions of 600 ℃ ~ 1000 ℃, the structure of the lattice is destroyed, can escape. Such as kaolinite water loss temperature is 580 ℃, talc is 950 ℃, serpentine is 670 ℃, magnesium hydroxide stone is 410 ℃.
Crystalline water
What crystalline water? Water in the form of neutral molecules (H2O) to participate in the transcrystalline structure of minerals, and occupy a fixed position, the number of water molecules and other components of the mineral into a simple integer ratio of water is called crystalline water. Crystalline water in the mineral lattice combined with the firm degree is much worse than the structure of water. Generally, when heated to 200℃~500℃, it will lose water. The water loss temperature of individual minerals is as high as 600℃. Along with the loss of crystalline water, the crystal structure of the original mineral should be destroyed or modified, so that the reconstructed lattice is called another mineral, and causes changes in the physical properties of the mineral.
Free water
What is meant by free water? Free water is water that does not participate in the lattice composition of a mineral, but is present in the mineral in the form of mechanical adsorption, and therefore in variable amounts. Among them, the ordinary water adsorbed in the surface and crevices of minerals due to surface energy, also called adsorbed water. It can be divided into film water, capillary water and colloidal water depending on its state of existence. The content of adsorbed water varies with the temperature. At atmospheric pressure, when heated to 100℃~110℃, it can all escape from the minerals, but the temperature at which colloidal water escapes is higher, about 100℃~250℃.
There are also interlayer water in the form of neutral molecules in some silicate minerals with a layered structure, and zeolite water in the lattice of zeolite group minerals. Their properties are similar, between crystalline water and adsorbed water.
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