Fabrication of multilayer ring transformer

Residual porosity is one of the most common defects found in multilayer ceramic structures. The pores are created in the binder burnout process when solvents and binders are released from the ceramic green body. Without a well-controlled compaction technique, defects between sheets in the stacked body often exist, leading to delamination problems. Also, it is difficult to fabricate a ring-shaped multilayer structure without cracks, especially near the center hole. Due to the difference in thermal expansion coefficients of the mould and the ceramic green body, large internal stress is often induced in the ceramic green body during hot pressing and cracks are initiated during sintering. In this work, the fabrication process of a lead zirconate titanate (PZT) ring-shaped multilayer to be used as a transformer is described. By a specially designed mould and adjustment of the hot pressing conditions, the internal stress induced during hot pressing has been reduced effectively. In particular, the hot pressing process is divided into two steps in order to reduce the clamping of the inner shaft by the ceramic green body. Therefore, the inner shaft can be released easily and the delamination problem can be improved. Also the binder burnout process has been designed carefully by studying the TGA profile. Scanning electron microscopy is used to study the cross-sectional area of the transformer. It is found that the resulting multilayer transformer did not have cracks, pores and delamination. The performance of the transformer will be measured and reported in later work.