Moisture Diffusion in Alumina Green Compact Containing Polyvinyl Alcohol Binder

Moisture content is one of the most important factors governing both structure and properties of green powder compacts of ceramics made through a compaction process. To control the moisture content in powder granules, it is necessary to understand kinetic changes of moisture content in granules, and pressed compacts. The apparent diffusion coefficient of moisture was directly measured for powder compacts containing polyvinyl alcohol (PVA) by following the weight change of the specimen. The parameters examined in this paper were size of specimen, forming pressure, average relative humidity and binder content. The observed rate of change was clearly affected by the PVA content in the compact. Examination of the distribution of PVA in the granules and compacts using optical microscopy (using immersion liquid method) was found to be nonuniform. The diffusion path consisted of an alternate sequence of thin layers of PVA-rich regions and thick layers of PVA-poor regions. The PVA-rich layers had a non-homogeneous structure which contained open pores.