Reaction sintering process in granular composites: Application to a superconductor ferrite system

Granular superconductor-ferrite (SIF) composites have been fabricated using various sintering conditions (volume fraction Phi(0) of ferrite, volume fr action Sigma(0) of superconductor, sintering temperature T-sint, sintering time t(sint) ). The superconducting S phase is the well-known Bi (Pb)-2223 phase (T-c = 110 K). The ferrite (F) is NiFe2O4. The reaction sintering pro cess is experimentally described by determining the volume fractions of res idual S and F phases from X-ray diffraction experiments. Magnetic measureme nts are used to analyze the degradation process in both residual ferrite an d superconducting phases. Nonlinear evolutions of the Sigma and Phi residua l volume fractions as a function of initial compositions are observed. To i nterpret these results, we propose to express the chemical kinetics using t wo elemental reactions such as: F+n. S --> P and S+S --> P'. Using various types of kinetics parameters, the solid state reaction in each composite ca n be modeled as a function of the initial Sigma(0) and Phi(0) volume fracti ons. (C) 1999 Academic Press.