After mechanical pulverization, ultrafine silicon carbide powder typically has irregular particle shapes. Due to its small particle size and high surface energy, the powder particles are prone to agglomeration, resulting in poor dispersion. This is detrimental to the subsequent ceramic molding and sintering processes. Therefore, surface modification of the ultrafine silicon carbide powder is required to improve its dispersion and stability, enhancing its molding performance.
There are various methods for surface modification. The most commonly used methods are surface coating modification and surface chemical modification.
Surface Coating Modification
Surface coating modification involves mixing ultrafine powder with modifiers in a specific ratio in water or organic media. This mixture is stirred using a magnetic stirrer or ball mill for a certain amount of time. The modifier adsorbs onto the particle surface through hydrogen bonds, electrostatic forces, or other interactions, forming a monolayer or multilayer coating.
The coating layer increases the electrostatic repulsion or steric hindrance between particles, reducing agglomeration. It also improves the dispersion stability of the ceramic powder in water or organic media.
The key difference between surface coating modification and surface chemical modification is whether the modifier undergoes chemical adsorption or chemical reactions with the powder surface. Surface coating modification is suitable for almost all inorganic powders. Common modifiers used in surface coating include inorganic materials, surfactants, and dispersants.
- Surfactants
Surfactants are amphiphilic substances composed of nonpolar hydrophobic and polar hydrophilic parts. They possess properties such as good surface activity, wettability, and the ability to lower surface tension. These characteristics make surfactants effective dispersants for ultrafine powder particles. - Dispersants
Small molecular electrolytes, such as tetramethylammonium hydroxide (TMAH) and citric acid (CA), are commonly used as dispersants. They mainly stabilize the ceramic powder through electrostatic mechanisms. When adsorbed on the particle surface, these dispersants alter the particle’s isoelectric point and increase its zeta potential, thereby enhancing electrostatic repulsion between particles.
Surface Chemical Modification
Surface chemical modification involves chemical reactions or chemical adsorption between the modifier and the functional groups on the powder surface. This results in the modifier being grafted or coated on the powder surface, improving its surface properties.
Surface chemical modification mainly includes surface graft polymerization and coupling agent modification.
Surface graft polymerization attaches polymers to the surface of inorganic powders. The space hindrance produced by the polymer suppresses agglomeration, improving powder dispersion. The distinctive feature of surface graft polymerization is that the polymer grafted on the powder surface is synthesized during the modification process.
Silane coupling agents are widely used for the surface modification of ceramic powders. They are simple and effective. Silane coupling agents are particularly suitable for modifying ceramic powders with hydroxyl groups, as the hydroxyl groups can react with the hydrolysis products of silane to form covalent bonds. Therefore, silane coupling agents are one of the few modifiers that can chemically react with the surface of silicon carbide powder.
Epic powder
Epic Powder specializes in advanced powder processing and surface modification solutions. Our range of equipment, including the three roller coating machine, pin mill coating machine, and turbo mill coating machine, is designed to meet the precise needs of ultrafine powder modification. These machines efficiently coat and modify powders, enhancing their dispersion and stability for applications in ceramics, electronics, and beyond. Whether you’re working with silicon carbide powder modification or other materials, Epic Powder provides cutting-edge technology to optimize your powder’s performance.
