Magnetic properties of bulk nanocrystalline cobalt ferrite obtained by high-pressure field assisted sintering

Abstract

We present here an investigation aimed at exploring the role of the microstructure on the magnetic properties of nanostructured cobalt ferrite. Bulk, almost fully dense, nanograined ferrites have been obtained starting from nanopowders prepared by a simple, inexpensive, water-based, modified Pechini method. This synthesis yielded largely aggregated, pure single-phase cobalt ferrite nanoparticles of ca. 35 nm average size, which have been then densified by high-pressure field-assisted sintering. Different sintering conditions (pressure up to 650 MPa and temperature up to 800 °C) and procedures have been used on both as-prepared and milled nanopowders in order to obtain materials with a spectrum of complex microstructures. In all cases, the sintering process did not produce any change in the phase composition. At the same time, using a high uniaxial pressure in combination with relatively low sintering temperatures and times, allowed for obtaining a high degree of densification while preserving the nanometric size of the crystallites. Moreover, we observed that in the densified materials the best magnetic properties are not necessarily associated with a more uniform microstructure, but rather arise from a delicate balance between moderate aggregation, grain size and high density.

Direct Ink Writing: A 3D Printing Technology for Diverse Materials

“…For instance, field‐assisted sintering is only applicable for structures containing magnetic particles. [ 360 ] Thus, minimizing post‐printing procedures and sintering technologies can be challenging.…”

Densification and Fracture Responses of (Ta1−xWx)C–WC Composites

“…Specifically, very large die sizes relative to sample size and/or ultrahard WC die materials are needed. [ 38–40 ]…”

“…Specifically, very large die sizes relative to sample size and/or ultrahard WC die materials are needed. [38][39][40] To overcome these challenges, the implementation of a sintering aid has been explored for enhancing the densification of ceramics, ideally functional at lower temperatures where rapid grain growth does not occur. [41] Sintering aids that are insoluble in TaC-such as TaB 2 -are excellent options.…”