Chengli Yang

Preparation and characterization of superparamagnetic functional polymeric microparticles

Abstract Superparamagnetic poly(styrene-divinylbenzene-glycidyl methacrylate) (Pst-DVB-GMA) microparticles were prepared via a modified suspension polymerization process. A magnetic fluid was first prepared by a chemical co-precipitation method. Then magnetic microparticles were produced by mixing the monomers and the magnetic fluid with water in the presence of a stabilizer poly(vinyl pyrrolidone) (PVP) to form a suspension, and finally benzoyl peroxide was added to initiate the co-polymerization. The morphology and magnetic properties of the microparticles were examined by TEM and VSM. The spherically shaped microparticles, with a size range of 4 to 7 μm, showed distinct superparamagnetic characteristics. XRD was used to investigate the structure of the magnetite particles dispersed in the polymer matrix. The microparticles with epoxy groups on their surface can be applied directly to the separation of biomolecules.

Surface Functionalization and Characterization of Magnetic Polystyrene Microbeads

A new approach to the surface functionalization of magnetic polystyrene microbeads with chloroacetyl chloride in the presence of aluminum chloride was reported. Composite microbeads consisting of polymer-coated iron oxide nanoparticles were prepared by spraying suspension polymerization. Functional chloride groups were introduced onto the surface of magnetic polystyrene microbeads by surface chemical reaction without destroying the magnetite nanoparticles within the microbeads. First, a complex was synthesized by a reaction between aluminum chloride and chloroacetyl chloride. Then, the complex was added dropwise to the solution of magnetic polystyrene microbeads, and a surface acylation reaction between complex and polystyrene microbeads was carried out. Subsequently, the amino groups were coupled to the magnetic microbeads via an ammonolysis reaction between ethylenediamine and chloride groups on the acylated magnetic polystyrene microbeads. The chemical composition, surface functional groups, and magnetism of the magnetic polystyrene microbeads before and after surface functionalization were characterized by Fourier transform infrared spectroscopy and vibrating sample magnetometry. The results showed that the surface functionalization reaction had little impact on the magnetism of the microbeads. The content of surface amino groups on the magnetic polystyrene microbeads was found to be 0.2 mmol/g. An affinity dye, Cibacron Blue F3G-A (CB), was then immobilized to prepare a magnetic affinity adsorbent. It was confirmed from X-ray photoelectron spectroscopy spectra that the CB molecules were covalently coupled on the magnetic microbeads.

Formation, structure and magnetic properties of TbFe12−xNbx compounds

TbFe12-xNbx compounds (x=0.55, 0.6, 0.65, 0.7, 0.75 and 0.8) with the ThMn12-type of structure have successfully been synthesized. The structural and magnetic properties of these compounds have been investigated by means of X-ray diffraction and magnetic measurements. With Nb content increasing from x=0.5 to x=0.85 the lattice parameters monotonously increase and the crystal structure does not change. The saturation magnetization decreases monotonously with increasing Nb content. The easy magnetization direction at room temperature has been found in the plane for all compounds. For all compounds investigated, an anomaly has been observed in the M-T curves measured in a field of 0.05 T, which corresponds to a change of the easy magnetization direction. The Curie temperature T-C is almost independent of the Nb content while the spin reorientation temperature T-sr decreases clearly with increasing Nh content

Hard magnetic properties of Sm3Fe26.7VxN4 and Sm3Fe26.7VxCy

Sm3Fe26.7V2.3N4 nitrides and Sm3Fe26.7V2.3Cy carbides have been synthesized by gas-solid phase reaction. Their hard magnetic properties have been investigated by means of additional ball-milling at room temperature. The saturation magnetization of Sm3Fe26.7V2.3N4 almost decreases linearly with increasing ball-milling time t, but that of Sm3Fe26.7V2.3Cy has no obvious change when the ball-milling time increases from t = 1 to 28 h. As a preliminary result, the maximum remanence B-r of 0.94 and 0.88 T, the coercivity mu(0i)H(C) of 0.75 and 0.25 T, and the maximum energy product (BH) of 108.5 and 39.1 kJ/m(3) for their resin-bonded permanent magnets are achieved, respectively, by ball-milling at 293 K

Structure and magnetic properties of PrFe11.5−xVxTi0.5 compounds and their nitrides

Phase formation and magnetic properties of PrFe11.5-xVxTi0.5 compounds (x = 0.5-1.5) and their nitrides have been investigated by X-ray diffraction, differential thermometric analysis (DTA) and magnetic measurements. It is found that PrFe11.5-xVxTi0.5 compounds with ThMn12-type structure can be formed by annealing the as-cast samples in a fairly wide temperature range. The substitution of V for Fe in the compounds results in a decrease of the saturation magnetization and Curie temperature. Upon nitrogenation, the Curie temperature is increased to around 739-763 K, the saturation magnetization increases by about 10%, and the anisotropy fields are all larger than 80 kOe. The PrFe11.5-xVxTi0.5Ndelta compounds have excellent intrinsic magnetic properties favorable for permanent magnet materials. The hard magnetic properties of PrFe10.5VTi0.5Ndelta magnets prepared by mechanical alloying technique have been assessed