Search

Abstract: Fe3O4 nanoparticles were prepared by carbothermal reduction method using glucose as carbon source. Heating temperature and holding time effects on crystalline phase composition and magnetic properties of Fe3O4 nanoparticles were investigated by X-ray diffraction, field-emission scanning electron microscopy and vibrating sample magnetometer. Pure Fe3O4 nanoparticles with an average crystallite size of 48nm was obtained at higher heating temperature of 650°C and shorter holding time of 0.5h, or at lower heating temperature of 450°C and longer holding time of more than 6h. The crystallite size of Fe3O4 nanoparticles increases with heating temperature and holding time. Fe3O4 nanoparticles heated at 650°C for 2h have the highest saturation magnetization (M s =97.99emug−1), higher than Fe3O4 prepared by other techniques due to better microstructure, crystallinity and expanded crystalline cell. [ABSTRACT FROM AUTHOR]

Abstract: When sintered Sm(Co, Fe, Cu, Zr) z permanent magnets are prepared by metal injection molding, some organic binders are added in alloy powder, which leads to much residual carbon in the magnets. The residual carbon decreases magnetic properties and destroys the microstructure of the magnets. In this paper, the behavior of carbon in Sm(Co, Fe, Cu, Zr) z permanent magnets has been studied. The results indicate that Sm(Co, Fe, Cu, Zr) z magnets can keep excellent magnetic properties when the carbon content is below 0.1wt.%: Br≥10kGs, H cj ≥22kOe, BHmax ≥25MGOe. When the carbon content is above 0.1wt.%, Br, H cj and BHmax decrease with increasing carbon content evidently. Carbon consumes Zr content and forms ZrC, which reduces the volume fraction of the lamella and Sm(Co, Cu)5 phases. Thus, the cell size increases and the cellular microstructure deteriorates. When the carbon content reaches 0.43wt.%, there is not enough Sm(Co, Cu)5 phase to form a uniform cellular microstructure. Br, H cj and BHmax are approximate to zero. Since carbon has little influence on the content of Sm2(Co, Fe)17 phase, Ms can keep a high value (≥100emu/g). ZrC has high melting point (3420°C) and acts as dispersion particle in the magnets, which prevents the grains of SEM structure growing and reduces the liquid content of green compacts during sintering. Therefore, the density of the magnets decreases. [Copyright &y& Elsevier]

This paper proposes a new method for producing nano-SrFe12O19 powder by the citrate precursor route using solid waste as a source of iron. This solid iron-containing waste, which exists in the form of an oily sludge, is produced by a cold rolling mill. This sludge was first subjected to a process, including sulfuric acid leaching, oxidation, precipitation, and nitric acid leaching, to obtain an iron nitrate (Fe(NO3)3) solution. Next, the Fe(NO3)3 solution was mixed with a strontium nitrate (Sr(NO3)2) solution obtained by subjecting strontium carbonate to nitric acid leaching. Subsequently, citric acid, as chelating agent, and ammonia water, as precipitating agent, were added to the mixed solution to form a gel. The gel was dried and spontaneously combusted, then annealed at different temperatures for 2 h in flowing air. The effects of the Fe3+/Sr2+ molar ratio and annealing temperature on the formation, morphology, and magnetic properties of SrFe12O19 were investigated. The results showed that single-phase SrFe12O19 powder was obtained by decreasing the Fe3+/Sr2+ molar ratio from the stoichiometric value of 12 to 11.6 and increasing the annealing temperature to 1000 °C for 2 h. Adjustment of the Fe/Sr molar ratio to 12 and the annealing temperature to 900 °C enabled the magnetic properties to be optimized, including saturation magnetization (Ms) 80.2 emu/g, remanence magnetization (Mr) 39.8 emu/g, and coercive force (Hc) 6318 Oe. [ABSTRACT FROM AUTHOR]

Abstract: Using spent alkaline Zn–Mn batteries as raw material, Mn–Zn soft magnetic ferrite nanoparticles are prepared by multi-step processes including acid leaching, chemical treatment of battery iron shells and citrate-nitrate precursor auto-combustion. Acid leaching and chemical treatment mechanisms are investigated. Dried gels thermal decomposition process, auto-combustion, phase composition, morphological and magnetic properties of as-prepared Mn–Zn ferrite nanoparticles are characterized by thermogravimetric and differential thermal analysis, X-ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer. Synthesized Mn–Zn ferrite nanoparticles (Mn0.5Zn0.5Fe2O4) have pure ferrite phase, larger saturation magnetization (M s =60.62emug−1) and lower coercivity (H c =30Oe) compared with the same composition ferrites prepared by other techniques due to better crystallinity. Mn–Zn ferrite nanoparticles synthesis method presents a viable alternative for alkaline Zn–Mn batteries recycling. [Copyright &y& Elsevier]

Abstract: Radially oriented Sm(Co,Fe,Cu,Zr) z ring magnets are prepared by powder metallurgy with appropriate magnetic field molding, sintering process and aging treatment. The results indicate that radially oriented Sm(Co,Fe,Cu,Zr) z ring magnets have obvious anisotropy of thermal expansion and sintering shrinkage, which easily lead to the splits and deformation of the ring magnets. So, slow heating, vacuum pre-sintering in sintering process and various quenching processes at different steps during quenching are adopted. The magnets have excellent magnetic properties: B r =10.8 kGs, Hcj =27.6 kOe, BHmax =28.1 MGOe. Besides, there is a uniform magnetization field on the surface of the ring magnets. The average surface magnetization field () is 1.502 kGs. The deviation from average (α) is only 4.2%. The microstructure of the magnets consists of a mixture of homogeneous cellular and lamella structures. [Copyright &y& Elsevier]

Abstract: The anisotropic hybrid magnets of NdFeB/SmFeN have been prepared through the warm compact process in magnetic field. The thin particles of SmFeN (3–5µm) enter into the gaps among big particles of NdFeB (80–100µm), which has remarkable influence on the magnetic properties of hybrid magnets: (a) increasing the density of the magnets; (b) decreasing the content of organic binder in unit volume magnets so as to enhance the effective magnetic properties of the magnets; and (c) improving the magnetic orientation for the high maximum energy product of the magnets. As a result, the anisotropic hybrid magnets with high properties (Br=9.614KGs, H cj=13.71KOe, (BH)max=20.19MGOe and density=6.23g/cm3) has been obtained. [Copyright &y& Elsevier]