Dispersants are widely used in refractory castables. Generally, the construction modes of refractory castables include vibration molding and gunning molding. By improving the rheological properties of refractory castables, the construction time of refractory castables and the labor intensity of workers can be reduced.
Dispersants are classified in many ways. Among them, based on the type of hydrophilic group, they can be divided into anionic dispersants, cationic dispersants, zwitterionic dispersants, There are five types of non-ionic dispersants and mixed dispersants.
Anionic dispersants mainly rely on the negative charges they carry to provide electrostatic effects. After dissociation, the ion clusters are adsorbed on the surface of the charged particles, changing their original double electron layer structure, increasing the zeta potential value of the colloidal particles, and finally improving the stability of the solution. For example, sodium tripolyphosphate (STPP), citric acid (CA), carboxylates and sodium naphthalene sulfonate formaldehyde condensate (FDN).
aSodium tripolyphosphate:
STPP is an inorganic anionic dispersant with a density of 0.3-0.9g/cm3, a chemical formula of Na5P3O10, and Na2PO4 at both ends. Termination, the structure of the entire dispersant is linear. Its solubility is large, the pH value of the aqueous solution is between 8-10, and it is easily hydrolyzed. The hydrolysis products are sodium pyrophosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate.
bCitric acid:
CA is a tricarboxylic acid compound with the chemical formula H3C6H5O7. It has three H+ that can be ionized and contains one molecule of crystal water. Citric acid is relatively acidic,
cPolycarboxylate: Polycarboxylate is a dispersant with a “comb-type” structure artificially formed through molecular design. On the main chain of the polycarboxylate, there are many branched chains with a certain length and rigidity, as well as some sulfonate groups that can charge the particles. It mainly achieves the dispersion effect of castables by causing steric hindrance between particles. The advantage of using polycarboxylate as a dispersant is that the water-reducing effect is obvious and the water-reducing timeliness is strong.
dNaphthalenesulfonate sodium salt:
The pure product of FDN is a white powder, which is obtained through the sulfonation of naphthalene and the neutralization and salting out of sodium hydroxide. The molecular formula is C10H7SO3Na, and the molecular weight is 230.22.
The opposite of anionic dispersants. After dissociation in water, cationic dispersants can produce highly active positively charged groups. The two groups in the amphoteric dispersant are both hydrophilic groups. One of them is positively charged (amino group) and the other is negatively charged (carboxyl group or sulfonic acid group), because different groups are at different pH levels. They exist in different ionic forms at different values, so this type of active agent has an isoelectric point. Nonionic dispersants do not dissociate in aqueous solutions. The hydrophilic groups are mainly polyethylene glycol groups. The polarity of the active agent is controlled by the number of hydrophilic groups.
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