A method for achieving a breakthrough in the solid loading of alumina ceramic slurry

The semiconductor manufacturing and defense sectors have witnessed a substantial increase in demand for advanced ceramic components with large dimensions and intricate geometries. Among the various stages involved in ceramic fabrication, forming is particularly critical because it directly influences the structural reliability of ceramic components and contributes to reducing production costs. Spontaneous coagulation casting (SCC) is an emerging forming technique. In this method, a copolymer of isobutylene and maleic anhydride (denoted as PIBM; trade name: Isobam) functions simultaneously as a dispersant and a gelling agent, allowing for in situ solidification of ceramic slurries to form green bodies. Based on functional groups and molecular weight, PIBM variants include Isobam 104, Isobam 600AF, and Isobam 04, among others.

Achieving high solids loading and low slurry apparent viscosity is essential for successful in situ solidification. Recently, a team led by Shiwei Wang from Shanghai Institute of Ceramics, Chinese Academy of Sciences has reported the preparation of an alumina slurry with high solid loading (58 vol%) and low apparent viscosity (0.54 Pa·s@100 s⁻¹) for the first time, and the alumina powder had an average particle size of 0.45 μm. The density of the green body and ceramic, the mechanical properties of the ceramic have been improved. The sintering densification temperature of the ceramic was decreased.

The team published their work in Journal of Advanced Ceramics on August 28, 2025.

Researchers explored the use of polyacrylic acid (PA) as a dispersant in combination with Isobam 104 for SCC. PA is a commercially available dispersant with a molecular weight of 3,000, which is lower than that of Isobam 600AF (5,500-5,600). Furthermore, PA was modified through pH adjustment with ammonia (NH₃·H₂O) to form ammonium polyacrylate (denoted as M–PA), and its effectiveness as a dispersant for extending the applicability of the SCC method in combination with Isobam 104 was demonstrated.

“A larger absolute zeta potential enhances interparticle repulsion, facilitating stable dispersion in the slurry. To achieve uniform dispersion of alumina particles, anionic dispersants, such as Isobam 600AF and polyacrylic acid, are employed. These agents adsorb onto alumina particle surfaces and stabilize the slurry through electrostatic repulsion. As the organic additives occupy space within the slurry, minimizing their volume allows for a higher proportion of alumina powder, thereby increasing the density and compactness of the green body. Furthermore, their small dimensions would make them particularly suitable for nano–sized ceramic powders, thereby extending the applicability of SCC to a broader range of powder particle sizes,” said Shiwei Wang, professor at Shanghai Institute of Ceramics.

Researchers employed M–PA as a replacement for Isobam 600AF in combination with Isobam 104 to prepare alumina ceramics. The resulting slurry exhibited high solid loading (56 vol%), low apparent viscosity, and capable of spontaneous gelling process was successfully obtained. The resultant alumina ceramics sintered at 1550 °C achieved a relative density of 98.7%, Vickers hardness of 17.3 GPa, flexural strength of 583 MPa, and fracture toughness of 2.8 MPa·m^1/2, all of which exceeded those obtained from ceramics prepared with Isobam 600AF or PA. Further, varying the ratio of M–PA and Isobam 104, solid loading was increased from 56 vol% to 58 vol%. The green body from 58 vol% solid loading can be sintered at a low temperature (1500 °C) to obtain a higher relative density (98.9%) and higher Vickers hardness (17.8 GPa). These findings indicate that M-PA not only serves as a viable replacement for Isobam 600AF but also enhances the final ceramic properties. The use of M-PA in SCC thus offers enhanced material performance and broadens the applicability of SCC technique. Furthermore, the combination of SCC with lower molecular weight dispersants is expected to facilitate the fabrication of high–performance ceramics under low sintering temperature.

This work was supported by the National Natural Science Foundation of China (Nos. 52130207 and U23A6014).

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2024 IF is 16.6, ranking in Top 1 (1/33, Q1) among all journals in “Materials Science, Ceramics” category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508