Acoustic emission monitoring of uniaxial pressing of ceramic powders

Powder compaction is a critical step in a classical method for the production of zero-defect ceramic products. We have studied the development of this step to determine whether acoustic emission can be used to detect the presence of flaws in a compact. In uniaxial pressing at room temperature, the creation and extension of flaws occur principally during the ejection of the compacts. The type and extent of flaws depend on the mechanical properties of the powder used and on the pressing conditions. Acoustic emission was used to monitor the consolidation by uniaxial pressing of Al₂O₃ powders and a UO₂---PuO₂ powder. It was possible to detect flaws in the compacts, to determine their type for a given powder, and to identify the type of powder used by a direct examination of cumulative counts of acoustic emission events and by a statistical analysis of amplitude distributions. Hence, the introduction of this technique in a fabrication process offers the possibility of detecting the presence of defects in compacts as soon as they are created. This would decrease the difficulties involved in reuse in the process of the powder from defective products, and would limit further flaw development during sintering, which are two major problems in the nuclear industry.