Cold sintering to form bulk maghemite for characterization beyond magnetic properties. Issue 3 (12th September 2019) - Spencer, Mychal P.
Abstract: Maghemite nanoparticles have been sought after for electronic, biomedical, and environment applications, for their soft ferrimagnetic properties and large coercivity. While their magnetic properties are well characterized, their nonmagnetic properties are currently not available because maghemite is prepared as nanoparticles and their bulk forms often have contaminants. In this work, thermodynamically unstable maghemite nanoparticles are cold sintered (130‐250°C) to form bulk samples with submicron‐size grains. Electrical and thermal conductivities of maghemite were evaluated for the first time: 3.5 × 10 −7 S/m and 0.86‐1.30 W/(mK). The relative densities of these cold‐sintered samples are low (55.9%‐64.2%) but comparable with or slightly lower than those previously achieved with higher sintering temperature (~55% at 500°C and ~76% at 1250°C). Such porous maghemite samples with large surface areas can potentially be used as an anode of lithium‐ion batteries, while further densification will be pursued in the future by sintering process modification. Abstract : In this work, we cold sintered thermodynamically unstable maghemite nanoparticles to form bulk monolithic samples without phase transformation and characterized their nonmagnetic properties (electrical and thermal conductivities) for the first time. The relative densities of these cold‐sintered samples are low (55.9%‐64.2%) but comparable with or slightly lower than those previously achieved with higher sintering temperature (~55% at 500°C and ~76% at 1250°C). These cold‐sintered porous maghemite samples have large surface areas and can be applied as an anode of lithium‐ion batteries.