ja3064843_si_001.pdf (2.33 MB)
Nonequilibrium Synthesis of Silica-Supported Magnetite Tubes and Mechanical Control of Their Magnetic Properties
journal contribution
posted on 2012-09-19, 00:00 authored by Rabih Makki, Oliver SteinbockMaterials synthesis far from thermodynamic equilibrium
can yield
hierarchical order that spans from molecular to macroscopic length
scales. Here we report the nonequilibrium formation of millimeter-scale
iron oxide–silica tubes in experiments that tightly control
the tube radius and growth speed. The experiments involve the hydrodynamic
injection of an iron (II,III) solution into a large volume of solution
containing sodium silicate and ammonium hydroxide. The forming tubes
are pinned to a motorized glass rod that moves at a predetermined
speed. X-ray diffraction and electron microscopy, as well as Raman
and Mössbauer spectroscopy, reveal magnetite nanoparticles
in the range of 5–15 nm. Optical data suggest that the magnetite
particles follow first-order nucleation–growth kinetics. The
hollow tubes exhibit superparamagnetic behavior at room temperature,
with a transition to a blocked state at TB = 95 K for an applied field of 200 Oe. Heat capacity measurements
yield evidence for the Verwey transition at 20 K. Finally, we show
a remarkable dependence of the tubes’ magnetic properties on
the speed of the pinning rod and the injection rate employed during
synthesis.
History
Usage metrics
Categories
Keywords
electron microscopysodium silicateroom temperaturegrowth speedsolutionexperimentMechanical Controlmacroscopic length scalesVerwey transitionhydrodynamic injectionNonequilibrium Synthesisinjection ratemagnetite particlesOptical dataglass rodHeat capacity measurementsmagnetite nanoparticlesammonium hydroxidetube radius20 KTBMagnetic PropertiesMaterials synthesisII200 Oe95 Knonequilibrium formationtubes exhibit superparamagnetic behavior
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC