Magnetite

About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.

Synthesis of magnetite nanoparticles by thermal decomposition of ferrous oxalate dihydrate

Abstract: Two different polymorphs of ferrous oxalate dihydrate were synthesized by precipitation of ferrous ions with oxalic acid: α-Fe(C2O4) · 2H2O with a monoclinic unit cell is obtained after precipitation and ageing at 90 °C, whereas the orthorhombic β-type is formed after precipitation at room temperature. The morphology of the oxalate crystals can be tailored from prismatic crystals of the α-polymorph over star-like aggregates of α/β-mixtures to non-agglomerated crystallites of β-oxalate. Thermal decomposition in air gives hematite at T ≥ 250 °C; if the thermolysis reaction is performed at low oxygen partial pressures (e.g., T = 500 °C and pO2 = 10−25 atm) magnetite is obtained. The synthesized magnetite is stoichiometric as signaled by lattice parameters of a0 = 8.39 A. The thermal decomposition of ferrous oxalate is monitored by thermal analysis, XRD, and IR-spectroscopy. The morphology of the oxalate crystals is preserved during thermal decomposition; the oxalates are transformed into spinel particle aggregates of similar size and shape. The crystallite size of the magnetite particles increases with temperature and is 40 or 55 nm, if synthesized from β-oxalate at 500 °C or 700 °C, respectively. The saturation magnetization of the magnetite particles decreases with decreasing particle size. Since the particles are larger than the critical diameter for superparamagnetic behavior they display hysteresis behavior at room temperature.

Synthesis of nonstoichiometric zinc ferrite nanoparticles with extraordinary room temperature magnetism and their diverse applications

Abstract: A series of nonstoichiometric zinc ferrite (ZndFe3−dO4) nanoparticles with Zn-dopant concentration d ranging from 0 to 0.5 was synthesized via thermal decomposition route employing oleic acid as surfactant. The zinc dopant concentration was controlled by the ratio of Zn/Fe precursors. High room temperature saturation magnetization of 110 emu g−1 was obtained for large Zn ferrite particles (more than 100 nm) with nominal composition of Zn0.468Fe2.532O4. The origin of the extraordinary magnetic property was revealed as the Zn substitution of Fe atoms at the tetrahedral site (A site) in the spinel magnetite phase. It was found that the precursor/surfactant ratio was an important parameter for the control of the shape and size of as-synthesized Zn ferrite particles. The details were investigated through a series of experimental work. Size-dependent applications, such as radar absorption and magnetic fluid hyperthermia, were further studied. Both applications required magnetic particles with high saturation magnetization, hence our samples displayed advantages over Fe3O4 magnetite nanoparticles. Especially for magnetic fluid hyperthermia, 26 nm Zn ferrite nanoparticles coated by P-mPEG polymer showed superior biocompatibility and heating efficiency, implying the potential usefulness to in vivo cancer therapy.

Effect of oxygen fugacity and water on phase equilibria of a hydrous tholeiitic basalt

Abstract: The influence of oxygen fugacity and water on phase equilibria and the link between redox conditions and water activity were investigated experimentally using a primitive tholeiitic basalt composition relevant to the ocean crust. The crystallization experiments were performed in internally heated pressure vessels at 200 MPa in the temperature range 940–1,220°C. The oxygen fugacity was measured using the H2-membrane technique. To study the effect of oxygen fugacity, three sets of experiments with different hydrogen fugacities were performed, showing systematic effects on the phase relations and compositions. In each experimental series, the water content of the system was varied from nominally dry to water-saturated conditions, causing a range of oxygen fugacities varying by ~3 log units per series. The range in oxygen fugacity investigated spans ~7 log units. Systematic effects of oxygen fugacity on the stability and composition of the mafic silicate phases, Cr–spinel and Fe–Ti oxides, under varying water contents were recorded. The Mg# of the melt, and therefore also the Mg# of olivine and clinopyroxene, changed systematically as a function of oxygen fugacity. An example of the link between oxygen fugacity and water activity under hydrogen-buffered conditions is the change in the crystallization sequence (olivine and Cr–spinel) due to a change in the oxygen fugacity caused by an increase in the water activity. The stability of magnetite is restricted to highly oxidizing conditions. The absence of magnetite in most of the experiments allows the determination of differentiation trends as a function of oxygen fugacity and water content, demonstrating that in an oxide-free crystallization sequence, water systematically affects the differentiation trend, while oxygen fugacity seems to have a negligible effect.