Effect of the CoFe2O4 initial particle size when sintered by microwave on the microstructural, dielectric, and magnetic properties

• Published in: International journal of applied ceramic technology Vol. 16; no. 5; pp. 2073 - 2084
• Main Authors: Fernández Perdomo, Claudia P., Zabotto, Fabio L., Garcia, Ducinei, Kiminami, Ruth H. G. A.
• Format: Journal Article
• Language: English
• Published: Malden Wiley Subscription Services, Inc 01.09.2019
• Subjects: Cobalt ferrites; CoFe2O4; Comminution; Densification; Dielectric loss; Dielectric properties; Electric properties; Frequency ranges; Grain growth; Grain size; Grain size distribution; High‐energy milling; Magnetic properties; Microstructure; Microwave sintering; nanoparticle; Nanoparticles; Particle size; Particle size distribution; Permittivity; Sinterability; Sintering
• ISSN: 1546-542X; 1744-7402
• DOI: 10.1111/ijac.13200

The particle size of CoFe2O4 powders (average particle size of 350 nm) was reduced to 50 nm by high‐energy milling. In this paper, special attention was given for analyzing the densification and grain growth of both particle sizes (350 and 50 nm) subject to ultrafast sintering assays using microwave sintering and their effect on the magnetic and electric properties. The results indicated that the grain growth was 10 times higher for the nanoparticle system, reaching similar sizes of ~1 μm in both cases after sintering. The relative density values were higher (95%) in the nanoparticle system due to the wide distribution of particle sizes generated in the grinding process. Qualitatively inferred microscopy analysis showed high sinterability of fine particles with a narrow distribution of grain size when subjected to ultrafast firing processes. Magnetization measurements at room temperature clearly show the reduction of Hc with increasing grain size. Electric resistivity, dielectric constant (ε′), and dielectric loss tangent (tan δ) were measured as a function of frequency at room temperature. The low values of dielectric constant (ε′) and dielectric loss (tan δ) in the low frequency range, shown for all samples sintered by microwave, prove the excellent uniformity in the microstructure. Evaluation of initial particle size effect on final grain size when submitted to microwave sintering. The microwave sintered ferrite nano showed retention of grain growth, with a high homogeneous grain distribution.