An investigation into the dispersion of ceramic particles for multilayer ceramic capacitor fabrication

• Main Author: Simpson, Alistair Brian George
• Published: Ulster University 2017
• Subjects: 621.31
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709888

The most abundant form of ceramic capacitor is the Multilayer Ceramic Capacitor (MLCC) and the most commonly used dielectric material is barium titanate (BaTiCT). BaTiCL is supplied in the form of dry, agglomerated powder and critical to the manufacturing process of MLCCs is good dispersion of these powders, reducing the number of agglomerates which are potential points of breakdown when MLCCs are placed under increasing voltage loads. The main objective of this study was to employ a process engineering focus to examine and identify critical process parameters within the complete dispersion process by experimentation and statistical consideration. A laboratory-scale replica of the industrial process was developed based around a stirred media mill. Dispersions were characterized primarily by measurement of particle size using laser scattering and suspension stability using multiple light scattering. Statistical consideration of the complete dispersion process by factorial analysis and analysis of variance identified three key stages; wetting, deagglomeration and stabilization. A reduction in the number of agglomerates, identified by improved dispersion stability and a narrowing of particle size distribution, was achieved by an increase in mechanical energy input at the wetting and deagglomeration stages. To avoid damage to primary particles, increased energy input during deagglomeration in the stirred media mill was achieved using grinding media beads with reduced diameter, reducing the stress intensity but increasing the number of collisions (“mild dispersion”). Stability of the deagglomerated particles was achieved by steric stabilization and a minimum concentration of polymeric stabilizer was required to enable monolayer coverage of particle surfaces. Below this monolayer point, dispersion stability was reduced due to reagglomeration. An optimum volume fraction of the feed suspension was identified giving the narrowest particle size distribution, avoiding either over­milling due to excess collisions or under-milling due to media dampening. Recommendations have been made to scale-up the findings of this study into an industrial scale process.