Magnetic particles hematite

As stated above dispersions of hematite particles show some interesting magnetic behaviors. - Chantrell et al. simulated the structure of the agglomerates of magnetic particles, formed in a magnetic fluid in the presence of and in the absence of an external magnetic field, using the Monte Carlo method. 

As is shown in Figure 3, Mossbauer spectra of t)Tpical airborne particles collected in Tokyo (urban area) and at Tokai (remote area) indicate the presence of paramagnetic Fe (iron in common silicate minerals), Fe , and magnetic components (hematite and magnetite)... 

As we are interested to obtain air stable magnetic particle, it is better to transform the hematite into an air stable iron oxide spinels (Fe304/y-Fe203) than the complete reduction to metallic iron. Thus, these nanoparticles have been reduced with hydrogen at 400°C. The formation of the iron oxide spinel was confirmed by XRD. Diffraction patterns do not show the presence of other iron oxide species. 

The ferric oxide, hematite, used in the present work was a high purity powder reagent with a BET surface area of 27 m2/g 30 mg was employed in each run. Some measurements were made on hematite calcined in air to see the effects of sintering the surface on the chemical structure of the adsorbed metal ions. The hematite samples were checked by Mossbauer absorption and powder X-ray diffraction measurements. The Mossbauer absorption spectra consisted of a magnetic sextet with no superparamagnetic component due to fine particles ( ). 

Hematite is paramagnetic above 956 K (Tc). At room temperature it is weakly ferromagnetic and at 260 K (the Morin temperature, Tm), it undergoes a phase transition to an antiferromagnetic state. Particles smaller than about 8 nm display superpara-magnetic relaxation at room temperature. A plot of the dependence of the B f (Hi) of hematite on temperature is shown in Figure 6.7 the plot follows an approximate Brillouin curve. 

Morris et al. (1991) obtained hematite of very small particle size ( 10 nm), termed nanophase by slow thermal decomposition in air of tri-Ee -acetato-hy-droxy-nitrate. XRD shows only two broad lines as in a 2-line ferrihydrite, but the magnetic hyperfine field at 4.2 K of 50.4 T appears to be more in agreement with poorly crystalline hematite. Well-crystalline hematite and Al-hematite were produced by decomposing Ee-Al-oxinates at 700 °C (da Costa et al. 2001). 

The industrial dust deposited in the metropolitan area of Shanghai consisted of high-coercivity (hematite) and low-coercivity (magnetite/maghemite) particles, usually < 10 pm in size. Four different dust sources could be distinguished on the basis of magnetic properties (Shu et al. 2000). Given previously reported links between... 

Dang, M.-Z. Rancourt, D.G. Dutrizac J.E. La-marche, G. Provencher, R. (1998) Interplay of surface conditions, particle size, stoichiometry, cell parameters, and magnetism in synthetic hematite-like materials. Hyperfme Interactions 117 271-319 Daniele, P.G. Rigano, C. Sammartano, S. Zeland,V. (1994) Ionic strength dependence of formation constants - XVIII. The hydrolysis of iron(III) in aqueous KNOj solutions.Ta-lanta41 1577-1582... 

Ozaki, M. Suzuki, H. Takahashi, K. Matijevic, E. (1986) Reversible ordered agglomeration of hematite particles due to weak magnetic interactions. J. Colloid Interface Sci. 

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