What impacts will powder agglomeration cause?

Powder agglomeration is a common problem in the ceramic preparation process, which exerts an adverse impact on the performance and quality of ceramic products. The occurrence of agglomeration is mainly caused by the intermolecular forces between particles, such as van der Waals forces, which lead to the aggregation of particles into clusters. The formation of agglomerates reduces the fluidity, dispersibility, and sintering activity of ceramic powders, thereby affecting the sintering performance, mechanical properties, and microstructure of ceramics. The impacts of powder agglomeration on ceramic products are mainly reflected in the following aspects:

1. Morphological Impact: Agglomeration results in a decrease in the packing density and morphological uniformity of ceramic green bodies. This is because the voids between particles inside the agglomerates are relatively large, leading to a reduction in the overall packing density. Meanwhile, the presence of agglomerates also disrupts the morphological uniformity of ceramic products.
2. Performance Impact: Agglomerates introduce a large number of defects and pores, which seriously affect the density, strength, toughness, and reliability of sintered bodies. The bonding force between particles inside agglomerates is weak, which easily causes the sintered body to fracture under stress, thus reducing the mechanical properties of the product. In addition, agglomerates may also affect the thermal, electrical, and optical properties of ceramic products.
3. Sintering Process: Agglomerates accelerate the secondary recrystallization of powder during sintering, leading to the formation of large grains. As a result, ceramic products fail to meet the nanometer size requirements and lose the unique properties of nanoceramics.
4. Shrinkage Rate and Compactness: The size, shape, and distribution of agglomerates significantly reduce the shrinkage rate of sintered bodies, as well as the compactness and morphological uniformity of ceramic components. Firstly, agglomeration prevents the effective arrangement and contact of particles in ceramic powder, which reduces the shrinkage rate of ceramic products during sintering. Sintering is a process in which particles are tightly bonded through mass transfer between them at high temperatures. The presence of agglomerates hinders the direct contact and effective sintering of particles, thereby affecting the shrinkage of sintered bodies. Secondly, the voids between particles inside agglomerates are relatively large, and these voids are difficult to eliminate completely during sintering, leading to a decrease in the compactness of sintered bodies. Compactness is one of the important indicators to measure the performance of ceramic products; insufficient compactness will directly affect the strength, hardness, wear resistance, corrosion resistance, and many other properties of ceramic products.
5. Sintering Temperature: The presence of agglomerates reduces the sintering activity of powder, making it necessary for ceramic products to undergo sintering at a higher temperature to complete the densification process. This is because the bonding force between particles inside agglomerates is weak, and effective mass transfer and particle rearrangement can only occur at higher temperatures to achieve sintering densification. In addition, the voids between particles inside agglomerates are relatively large, and more energy is required to eliminate these voids during sintering, which also necessitates an increase in sintering temperature. Therefore, the presence of agglomerates widens the sintering temperature range of ceramic products and makes the sintering process more difficult. Agglomeration is divided into two types: soft agglomeration and hard agglomeration. Soft agglomeration is caused by electrostatic attraction or van der Waals forces between particles, and such agglomerates can be easily redispersed into individual particles under external forces. In contrast, hard agglomeration is formed by chemical bonding or sintering neck formation between particles, and such agglomerates are relatively stable and difficult to break by simple mechanical means. To prevent and reduce the agglomeration of ceramic powder, a series of measures can be taken. Firstly, during the preparation process, appropriate pH value, temperature, concentration, and other conditions are controlled to keep the particles in a highly dispersed state. Secondly, an appropriate amount of dispersants or electrolytes is added to inhibit agglomeration through adsorption, colloid action, and steric hindrance effect. In addition, special treatment methods, such as freeze-drying, can be adopted during the preparation process to remove impurities on the particle surface and reduce the occurrence of agglomeration. In addition to the control measures during the preparation process, agglomeration can also be eliminated through post-treatment. For example, grinding treatment can break agglomerates into smaller particles through mechanical force; ultrasonic treatment can destroy agglomerates by utilizing the cavitation and mechanical effects generated by sound waves. In addition, high-temperature calcination is also an effective method to eliminate agglomeration, which breaks the chemical bonds or sintering necks in agglomerates at high temperatures, thereby obtaining ceramic powder with good dispersibility. The agglomeration of ceramic powder is a problem that requires attention. Through reasonable preparation processes and control measures, the occurrence of agglomeration can be effectively reduced, and the performance and quality of ceramic products can be improved. Therefore, in order to prepare high-performance ceramic products, it is crucial to prevent the occurrence of powder agglomeration.