Study Of The Preparation And Properties Of α-FeOOH Nanoparticles And The Colloids

γ-Fe2O3 nanoparticles have been successfully synthesized by a chemically induced transformation ofα-FeOOH precursor, and a new transition process induced chemically for preparing oxide nanoparticle is revealed. Nanopaticles were synthesized by FeCl3-6H2O, NaOH and FeCl2(analytical grade). The crystalline phases of the synthesized particles were identified using a XD-2 X-ray diffractometer (XRD) (Beijing Purkinje General inst.,China) using Cu Ka (γ=0.1541 nm) radiation. The morphologies of the precursor and nanoparticles were observed by a Tecnai 10 transmission electron microscope (TEM) (Philips, Netherlands). A EV11 vibrating sample magnetometer (VSM) (ADE, USA) was used to measure the magnetic properties of the product at room temperature. Prepared theα-FeOOH colloid and researched the magneto-optical effect.Some important results in this thesis are summarized as follows:1.α-FeOOH nanoparticles were synthesized using a chemical precipitation that FeCl3·6H2O and NaOH as starting materials, distilled water as solvent. XRD patterns showing well crystalline, TEM observations showing disperser with uniform diameter of 8.16nm and agglomerate, VSM results exhibited paramagnetic properties.2.γ-Fe2O3 nanoparticles have been successfully synthesized by a chemically induced transformation ofα-FeOOH precursor, and a new transition process induced chemically for preparing oxide nanoparticle is revealed. In this method, the precursor (α-FeOOH) was prepared by chemical precipitation then treated in a mixed FeCl2/NaOH solution to produce the nanoparticles. X-ray diffraction indicated that when the precursor was treated with FeCl2 (0.22M) and NaOH (0.19M), the nanoparticles obtained are pureγ-Fe2O3 with uniform diameter of 12.74nm. However, when the concentration of FeCl2 is less than 0.22M or that of NaOH is less than 0.19M, bothα-FeOOH andγ-Fe2O3 phases co-exist in the nanoparticles. Transmission electron microscopy observations showed that the morphologies of the two phase co-existed particles are not identical and the pureγ-Fe2O3 nanoparticles are polygonal, i.e. not spherical.From magnetization data obtained from a vibrating sample magnetometer, the volume ratio ofα-FeOOH andγ-Fe2O3 has been estimated for the two phase particles.3. Theα-FeOOH nanoparticles treated by boiling Fe(NO3)3 solution,α-FeOOH colloid was synthesized by Massart's method and removed agglomerate by centrifugal.Forα-FeOOH nanoparticles with special properties of bulk material is anti-ferromagnetic materials, present paramagnetic nanoparticles and orthogonal system.The incident light with line polarized light and circularly polarized light, The magneto-dichroism and birefringence effect ofα-FeOOH colloid under uniform magnetic field is produced by a pair of Helmholtz type electro-magnets were discussed. Experiments have shown that, for colloids such asα-FeOOH, the magneto-dichroism would behave in a similar way to that of CoFe2O4 ferrofluids in a magnetic field, but be more significant.The liquid-crystal phase, whose building blocks have anisotropic rather than sharp values of the dielectric constant, is considered theoretically and experimentally. Nanoparticles with both anisotropic dielectric constants and weak intrinsic magnetic moments, can be considered equivalent to magnetic dielectric ellipsoids. For colloids based on such ellipsoids, the dielectric constant is isotropic in zero magnetic field. However, when an external magnetic field is applied, the moments' Brownian rotation, which is connected with the rotation of the ellipsoids themselves, will induce the order in the orientation of the dielectric ellipsoids, so that the dielectric constant of the colloids becomes anisotropic. The colloids, with the orientation of the dielectric ellipsoids ordered by a magnetic field, can be viewed as a liquid-crystalline-like phase having optical anisotropy.This chemically induced transformation could provide an effective route for the synthesis of other metal oxide nanocrystallites. We also put forward a kind of circularly polarized light as the light source of measuringα-FeOOH colloid magnetic (lines) magneto-dichroism and birefringence effect. This method can be developed into the scanner can consecutive measurements will greatly shorten the measurement of time. The measurement method is also applicable to other has magnetic (lines) magneto-dichroism and magnetic birefringence effect of the medium. And make a number of Praetical experiments for future Work..