Uniform metal iron ellipsoidal particles of around 200 nm in length were obtained by reduction and passivation of alumina-coated ␣ -Fe 2 O 3 ͑hematite͒ particles under different conditions of temperature and hydrogen flow rate. The monodispersed hematite particles were prepared by the controlled hydrolysis of ferric sulfate and further coated with a homogeneous thin layer of Al 2 O 3 by careful selection of the experimental conditions, mainly pH and aluminum salt concentration. The reduction mechanism of ␣ -Fe 2 O 3 into ␣-Fe was followed by x-ray and electron diffraction, and also by the measurements of the irreversible magnetic susceptibility. The transformation was found to be topotactic with the ͓001͔ direction of hematite particles, which lies along the long axis of the particles, becoming the ͓111͔ direction of magnetite and finally the ͓111͔ direction of metal iron. Temperature and hydrogen flow rate during the reduction have been found to be important parameters, which determine not only the degree of reduction but also the crystallite size of the final particles. Magnetic characterization of the samples shows that the only parameters affected by the crystallite size are the saturation magnetization and magnetic time-dependence effect, i.e., activation volume.
The hydrothermal synthesis of CuAPO-5 molecular sieves
has been investigated by using Cu(II) oxide in the
presence of tetraethylammonium hydroxide as a template. The
CuAPO-5 material was characterized by X-ray
powder diffraction, FT-IR spectroscopy, scanning electron microscopy,
and elemental analysis. Supporting
evidence for the framework location of copper was obtained from
electron spin resonance and electron spin-echo modulation spectroscopy experiments.
Thin films of FeAPO-5 molecular sieves deposited on TiN-coated silicon wafers have been generated using pulsed laser ablation. The FeAPO-5 films were employed as the dielectric phase in a capacitive type chemical sensor. The FeAPO-5-based sensors exhibited significant changes in capacitance upon exposure to moisture. Interestingly, the sensor also responded to moisture from breathing which makes it useful not only as a potential humidity sensor but as a respiration monitoring device.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.