A novel operando observation technique for slurry drying behavior using laser microscopy

Abstract

Drying is a critical process involved in ceramic manufacturing because it strongly affects defect formation and the dimensional stability of green bodies. However, direct experimental observation of particle-level behavior during slurry drying remains limited in practical applications. In this technical report, an operando observation technique based on laser microscopy is introduced to analyze slurry drying behavior at the submicron particle scale. An aqueous alumina slurry with a typical composition was prepared, and green bodies simulating sheet forming were dried in air under atmospheric pressure with controlled relative humidities of 35, 50, and 75 % at 20 °C. During drying, local particle motion was continuously observed using laser microscopy, while macroscopic shape deformation and weight change were evaluated under identical environmental conditions. Particle image velocimetry analysis was applied to quantify particle velocity, migration direction, and displacement in the thickness direction. Drying progressed from the outer region toward the center of the green body under all relative humidities. Lower relative humidity (RH) resulted in higher initial drying rates and faster particle motion. At RH 35 %, the maximum particle velocity reached 0.9 µm/s during the initial drying stage. A transient increase in particle flow velocity was observed under all conditions, accompanied by enhanced thickness shrinkage. Although the final thickness reduction was ∼100 µm regardless of humidity, the timing and rate of shrinkage showed clear dependence on humidity. Furthermore, particle motion was accelerated after passing through a macroscopic convex deformation region, while the particle migration velocity did not coincide with the macroscopic deformation rate. These results demonstrate that combined operando observation of microscopic particle behavior and macroscopic deformation provides valuable insight into slurry drying behavior. The proposed technique should serve as a practical tool for evaluating drying processes and supporting slurry design in ceramic processing.