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A polyacrylic acid (PAA) binder with both binder and disperser properties was applied to prepare alumina granules with and without a segregated binder layer (SBL) to investigate an SBL's effects on the mechanical properties of dry‐pressed alumina green compacts. The formation of SBLs in granules was based on the production of free, unadsorbed PAA ionic molecules in the liquid phase. The green strength of the alumina compact showed a significant increase as SBLs formed. Adequate forming conditions lead to squeezing out of the binder and redistribution of SBLs to bind granules together, thus enhancing the green strength of the compact and successfully eliminating intergranular pores and granule relics.

A new method for evaluating powder flowability, named vibration shear tube method has been developed. In this measurement system, the powder was discharged through a narrow gap between a vibrating tube edge and a flat bottom surface, where the particles experienced high shear forces to overcome the adhesion and friction forces. The vibration amplitude was increased during the measurement, and the mass of particles discharged was measured at constant time intervals. The amount of powder used for the measurement was about 10-40 g. The measurement time was 100-400 s. A series of experiments was carried out using alumina particles of 2-60 μm in mass median diameters. Flowability profiles, i.e. the relationships between the mass flow rate and the vibration acceleration were obtained experimentally. To characterize powder flowability, critical vibration acceleration and characteristic mass flow rate were proposed. The values of these factors were analyzed in detail and the performance of this measurement system was evaluated.