The dispersion stability of ceramic slurries is crucial in determining the molding quality and final performance of ceramic products, and its dispersion effect directly impacts the feasibility of subsequent processes. Solvent systems for ceramic slurries are mainly divided into water-based and alcohol/ketone organic solvents. Due to differences in polarity and adjustable pH range, these two types of solvents have varying requirements for dispersant compatibility. As a key additive, dispersants, by regulating the surface charge and steric hindrance effect of particles, break particle agglomeration, prevent flocculation or phase separation, and lay the foundation for the preparation of high-performance ceramics.
Water-based ceramic slurries use water as the dispersion medium, offering advantages such as environmental friendliness and low cost, and are widely used in the production of various low- to mid-range ceramics. Water, as a strongly polar solvent, allows for flexible pH adjustment, providing a suitable environment for ionic dispersants. Ionic dispersants generate charged ions through ionization, which adsorb onto the surface of ceramic particles. Utilizing Coulomb repulsion to bind the molecular chain hydration layer, long-term stability of the slurry is achieved.
Sodium polyacrylate (SPA) is a commonly used ionic dispersant in water-based systems. Its sodium carboxylate groups rapidly ionize in aqueous solutions, releasing negatively charged ions that strongly adsorb onto the positively charged sites of ceramic particles. The flexible molecular chains extend to form a dense hydration layer, effectively inhibiting particle aggregation. The pH value of the water-based system significantly affects the effectiveness of SPA; the optimal dispersion effect is achieved in the weakly alkaline range of 8-10. Excessively high or low pH values lead to dispersion failure and slurry flocculation.
Ultrasonic dispersion is crucial for the efficient function of SPA in water-based slurries. Its mechanical vibration and cavitation effects break up particle agglomerates, accelerate the diffusion and adsorption of SPA, enhance the synergistic effect of charge and steric hindrance, and improve slurry stability.
Alcohol/ketone organic solvent systems use weakly or moderately polar solvents as the medium. They are highly volatile, have good wettability, and are suitable for high-end ceramic molding processes. Due to the weak polarity and narrow adjustable pH range of organic solvents, ionic dispersants are insufficiently ionized, making nonionic dispersants the preferred choice. Their dispersion effect relies on the physical adsorption of molecular chains and steric hindrance effects.
Polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) are commonly used nonionic dispersants. PEG adsorbs onto ceramic particles through hydrogen bonds formed by its hydroxyl groups, creating a steric barrier through molecular chain extension. PVP adsorbs particles through its polar pyrrolidone groups; its rigid molecular structure makes its steric hindrance effect more pronounced, making it suitable for high-solids-content slurries.
Ultrasonic dispersion is equally crucial in organic solvent slurries. It breaks up agglomerates, accelerates dispersant diffusion and adsorption, reduces molecular chain entanglement, improves the compatibility between dispersant and solvent, and prevents flocculation and phase separation.
In actual production, dispersants should be selected rationally based on solvent polarity: sodium polyacrylate is preferred for water-based systems, with pH adjusted to a suitable range; PEG and PVP are preferred for organic solvent systems, with a focus on solvent-dispersant compatibility. Simultaneously, ultrasonic process parameters should be optimized to ensure efficient dispersant adsorption and fully leverage synergistic effects.
As ceramic materials develop towards high-end applications, the synergistic effect of dispersants becomes increasingly important. In the future, optimizing the structure of dispersants and innovating ultrasonic processes to enhance the synergistic effect of charge and steric hindrance will become the development direction of ceramic slurry dispersion technology, supporting the large-scale production of high-performance ceramics.
