Dispersion of lanthanoid-coated barium titanate in a paraffin-based extrusion binder system

For the fabrication of small BaTiO3-based PTCR elements by ceramic powder extrusion, a submicron barium titanate (BaTiO3) powder was coated with either CeO2 or La2O3 and mixed with a paraffin-based thermoplastic binder. XPS analysis revealed that the powder surfaces are significantly hydrated and that processing aids are likely to interact with the physisorbed and chemisorbed water rather than directly with the ceramic powder surfaces. From a series of potential C-18 surfactants for this paraffin-based extrusion system, stearic acid was shown to be the most effective dispersant and was consequently used to prepare extrusion feedstocks. Under equivalent extrusion conditions, 50 vol.% CeO2-coated BaTiO3 feedstocks always exhibited poorer extrudability than their La2O3-coated BaTiO3 counterparts. Furthermore, the La-doped material invariably sintered to a higher final density than the Ce-doped material. These processability differences can largely be explained by a lower affinity of the stearic acid surfactant for the CeO2-coated titanate powder.