Additives for amorphous refractories -- Types and functions of dispersants
January 28, 2021
Dispersant is one of the admixtures commonly used in amorphous refractories, which can be divided into inorganic dispersant and organic dispersant. The inorganic dispersant belongs to ionic dispersant, while the organic dispersant is surfactant. For the ionic dispersant, the positive and negative ions can be ionized after the dispersant dissolves in water. These ions are adsorbed on the surface of colloidal particles with different sign charges, and then form a double electric layer on the surface of ions, which leads to the increase of zeta potential. For the non-ionic dispersant, the dispersant dissolves in water and adsorbs on the surface of colloidal particles to form a steric hindrance, The contact between reagent and reaction center is hindered. Both of these two effects will increase the repulsive force between particles, resulting in the release of free water wrapped in the aggregation structure. Therefore, the dispersant can play the role of dispersing particles and lubricating particles.
Inorganic dispersant
Inorganic dispersants are electrolyte compounds which have conductivity and can electrolyze cation and anion groups when dissolved in water. Inorganic dispersants adsorb on the surface of charged particles by ionized ions, which changes the original electric double layer, and then increases the absolute value of zeta potential, resulting in greater electrostatic repulsion, so the colloid has good stability.
(1) Sodium Tripolyphosphate
The molecular formula of sodium tripolyphosphate is na5p3o10 · 6H2O (molecular weight: 476.02) or na5p3o10 (molecular weight: 367.88), also known as sodium triphosphate, pentasodium phosphate and pentasodium phosphate. Sodium tripolyphosphate is easily soluble in water, and the pH value of its aqueous solution is 8-10.
(2) Sodium Hexametaphosphate:
The hydrolysis process of hexametaphosphate is as follows:
(NaPO3)6+H2O=6NaOH+6HPO3
HPO3+H2O=H3PO4
H3PO4=H++H2PO4-
H2PO4-=H++HPO42-
HPO4=H++PO43-
Sodium hexametaphosphate belongs to polymetaphosphate. Its molecular structure is cyclic, but it has a linear long chain configuration. It is adsorbed to the surface of particles through the end group, and the intermediate chain does not participate in the bonding, which can provide additional electrostatic repulsion. In addition, the ionized Na + ions can increase the thickness of the electric double layer, and sodium hexametaphosphate plays a dispersion effect under these two effects.
Organic dispersant
Organic dispersants (i.e. surfactants) can be divided into ionic surfactants (which can ionize ions) and non-ionic surfactants (which cannot ionize ions).
Organic dispersants can disperse the system through the following two dispersion mechanisms: for ionic dispersants, electrostatic repulsion and steric hindrance play a major role; if the adsorption layer is thick and the solvation layer is also thick, steric hindrance plays a leading role; otherwise, electrostatic repulsion plays a leading role. For nonionic dispersants, steric hindrance is the main mechanism.
The structure formula of Citric Acid is as follows
The molecular formula of citric ACID is C6H8O7, which belongs to organic electrolyte and is an anionic dispersant of small organic molecules. Citric acid is a kind of ternary acid, which can ionize different kinds of ions in different pH ranges.
